DNA repair diseases: What do they tell us about cancer and aging?

Carlos FM Menck and Veridiana Munford

Departamento de Microbiologia, Instituto de Ciências Biomédicas, Universidade de São Paulo, São Paulo,

SP, Brazil.

Abstract

The discovery of DNA repair defects in human syndromes, initially in xeroderma pigmentosum (XP) but later in many

others, led to striking observations on the association of molecular defects and patients’ clinical phenotypes. For ex

ample, patients with syndromes resulting from defective nucleotide excision repair (NER) or translesion synthesis

(TLS) present high levels of skin cancer in areas exposed to sunlight. However, some defects in NER also lead to

more severe symptoms, such as developmental and neurological impairment and signs of premature aging. Skin

cancer in XP patients is clearly associated with increased mutagenesis and genomic instability, reflecting the defec

tive repair of DNA lesions. By analogy, more severe symptoms observed in NER-defective patients have also been

associated with defective repair, likely involving cell death after transcription blockage of damaged templates. En

dogenously induced DNA lesions, particularly through oxidative stress, have been identified as responsible for these

severe pathologies. However, this association is not that clear and alternative explanations have been proposed. De

spite high levels of exposure to intense sunlight, patients from tropical countries receive little attention or care, which

likely also reflects the lack of understanding of how DNA damage causes cancer and premature aging.

Keywords: xeroderma pigmentosum, ultraviolet, DNA damage, oxidative stress, DNA repair.

Introduction

During evolution, the stability of genetic material

plays a fundamental role in the maintenance of life. The

equilibrium between the benefits of changes in the blue-

print of life, which facilitates diversity, and the perpetua

tion of genetic information is fundamental for evolution. In

multicellular organisms, this equilibrium faces other prob

lems, such as the transmission of genetic instability to new

generations of cells (gametic cells) and components of the

organism structure (somatic cells). For example, in hu

mans, genetic instability in somatic cells has been directly

associated with the formation of cancer, and cells may die

to avoid these deleterious effects. However, cell death may

trigger processes associated with organism aging.

The long DNA molecules, that compose genetic ma

terial, are not stable. Exogenous factors (such as ultraviolet,

UV, from daylight), chemical products (such as smoke,

pollution, and natural and artificial drugs), endogenous

agents, and normal byproducts of cell metabolism, includ

ing radical oxygen species (ROS) generated during respira

tion, constantly threaten DNA stability (Andressoo and

Hoeijmakers, 2005; Iyama and Wilson 3rd, 2013). These

agents damage the DNA molecule, and cells must attend to

these DNA lesions to properly survive and evolve. To

maintain the equilibrium necessary for survival and diver-

sity, evolution has equipped all living beings with the tools

to either remove or tolerate DNA damage. In general, these

tools, called DNA repair mechanisms or pathways, take

care of the DNA molecule, avoiding the deleterious conse

quences of the different types of DNA lesions. DNA repair

pathways are highly conserved in nature, indicating these

mechanisms are as old as life on Earth.

The importance of DNA repair mechanisms is dra

matically demonstrated in certain human syndromes that

are characterized as being defective in DNA repair pro

cesses, exacerbating the clinical effects of the unrepaired

DNA damage, such as xeroderma pigmentosum (XP).

Most XP patients are defective in nucleotide excision re

pair (NER), which removes DNA lesions induced by the

UV component of sunlight, although some XP patients

have also shown defects in the replication of UV-damaged

DNA. The main clinical symptoms of XP patients include

the high frequency of tumors in the exposed areas of skin,

indicating a clear causative relationship between

unrepaired DNA lesions, genetic instability (XP cells are

highly mutable) and cancer. Some XP patients, however,

present more severe clinical phenotypes, including devel

opmental problems, neurodegeneration and premature ag

ing (Lehmann, 2003; Lehmann et al., 2011; DiGiovanna

Genetics and Molecular Biology, 37, 1 (suppl), 220-233 (2014)

www.sbg.org.br

Send correspondence to Carlos F.M. Menck. Departamento de

Microbiologia, Instituto de Ciências Biomédicas, Universidade de

São Paulo, Av. Prof. Lineu Prestes 1374, 05508-900 São Paulo,

SP, Brazil. E-mail: [email protected].

Review Article

and Kraemer, 2012). These severe symptoms have been

associated with other syndromes, such as Cockayne syn

drome (CS), that have also been shown to be defective in

NER (see below) (Cleaver et al., 2013). The reasons for

these more severe clinical aspects are still not clearly un

derstood, although, in general, these symptoms implicate

unrepaired DNA damage in the process of neurological

degeneration and aging. In this work, we discuss the his

torical data associated with the lack of DNA repair and its

deleterious consequences on the human organism, focus

ing on the scientific contribution of the findings in XP and

NER-related human diseases associated with cancer and

aging. Other human syndromes, such as ataxia telangiec

tasia, Fanconi Anemia, Werner syndrome, among others,

associated with defects in other DNA repair pathways or

DNA damage responses, also show symptoms associated

with cancer, aging and developmental and neurological

problems. These syndromes also support the relevance of

DNA damage in these processes and also indicate that dif

ferent DNA repair pathways correspond to networks that

protect the genome. However, these syndromes will not be

reviewed here, and the reader is invited to search for more

information in other recent reviews (Kim and D’Andrea,

2012; Knoch et al., 2012; Marinoglou, 2012; Moraes et

al., 2012; Shiloh and Ziv, 2013). Moreover, mouse mod-

els with defective DNA repair mimic some human clinical

phenotypes, including many aging symptoms. Indeed, an-

imal models have provided several clues and numerous

data to support this debate, but this information will only

be commented in this work when they are applied directly

to some aspects of DNA repair. For more information con-

cerning animal models, the reader is referred to recent re-

views (Diderich et al., 2011; Goss et al., 2011;

Niedernhofer et al., 2011; Gredilla et al., 2012; Jaarsma et

al., 2013).

Most studies concerning XP patients have been per

formed in developed countries (North America and Eu

rope) at high latitudes, with the exception of African-born

patients studied in Europe. The doses of UV in the sun

shine at high latitudes are low compared with tropical

countries, such as Brazil and other Latin American coun

tries. Thus, although exposed to a more aggressive envi

ronment, the patients in these countries have primarily re

mained unattended, except for a few recent studies. More

than just identifying gene mutations that affect XP pa

tients in tropical countries, these studies have contributed

to the understanding of how DNA repair defects correlate

with genotype-phenotype associations. A prospective ap

proach using next-generation sequencing to diagnose the

mutations of XP and NER-related patients may help these

individuals and their families to address the disease and

may eventually contribute with new data for understand

ing how DNA lesions lead to cancer, neurodegeneration

and/or aging.

XP and the Discovery of Molecular Defects in

DNA Repair

XP is a rare autosomal recessive disease; most pa

tients exhibit high sensitivity to sunlight. The patients pres

ent strong skin freckle-like pigmentation and lesions in

areas exposed to sunlight. These skin-aging symptoms may

also appear as precancerous skin lesions, such as actinic

keratosis, and most XP patients, when unprotected, develop

skin cancer (non melanoma and melanoma) before the age

of 10. Compared with the entire population, XP patients

have a 10,000-fold increase in the incidence of non-mela

noma skin tumors and a 2,000-fold increase in the inci

dence of melanoma before the age of 20 (Kraemer et al.,

1994). Certain exposed areas of the face, such as the eyes

and mouth, may also suffer from the sensitivity to sunlight

and develop lesions, including tumors. Many XP patients

present photophobia. The frequency of internal tumors also

shows a 10-fold increase in XP patients. Interestingly, 20 to

30% of XP patients develop progressive neurological prob

lems (DiGiovanna and Kraemer, 2012; Sepe et al., 2013).

The estimated incidence of XP in the population varies: 1

per 250,000 in USA (Robbins et al., 1974) and 1 per

450,000 in Western Europe (Kleijer et al., 2008). In some

places, such as Japan and North Africa, the incidence of XP

may be higher (1 per 20,000), likely reflecting the high

prevalence of certain mutations due to founder effects

(Hirai et al., 2006; Soufir et al., 2010).

XP was the first syndrome associated with a defect in

the DNA processing pathway. The dermatologists Moritz

Kaposi (Hungarian) and Ferdinand Ritter von Hebra (Aus-

trian) provided the first clinical description of XP patients

(Hebra and Kaposi, 1874). By the nineteenth century, the

syndrome was correctly considered as an inherited disease

and was associated with sunlight exposure. This condition

was referred to as xeroderma pigmentosum (for dry and

pigmented skin, from the Greek words xero and derma; and

Latin word pigmentosum). Subsequently, DeSanctis and

Cacchione (1932) described a more severe form of XP,

DeSanctis-Cacchione syndrome (DSC), which was associ

ated with neurological degeneration.

In 1968, James Cleaver identified the molecular de

fects associated with XP, showing that XP cells were hy

persensitive to UV light and unable to perform unscheduled

DNA synthesis (UDS) after UV irradiation (Cleaver,

1968). As described below, UDS is part of the NER path

way after the removal of DNA damage. This outstanding

discovery provided the first evidence that a cell defect in

DNA metabolism is associated with a clinical phenotype,

explaining, in part, the high photosensitivity of XP skin.

Soon, clever experiments, fusing cells from different

patients, facilitated the identification of complementation

groups (De Weerd-Kastelein et al., 1972). Specifically, if

the fusion of two different cells resulted in the restoration of

UDS, then the cells were deficient in different comple

Menck and Munford 221

mentation groups or genes. If the fusion did not restore

UDS, the cells were deficient in the same gene and be

longed to the same complementation group. These types of

experiments led to the classification of XP in seven differ

ent complementation groups (XP-A to XP-G), correspond

ing to seven genes with mutations that might result in XP.

Years later, the cells of some XP patients, however, were

demonstrated as NER proficient and capable of UDS. The

inability of these cells to replicate DNA after UV irradia

tion (daughter-strand repair) indicated other problems in

terms of dealing with DNA lesions, although these cells

maintained the ability to remove these lesions (Lehmann et

al., 1975). These cells were referred to as XP variants

(XP-V). The subsequent identification of DNA polymerase

activity associated with the XPV protein (DNA polymerase

eta) confirmed that XP-V patients are deficient in trans

lesion synthesis (TLS) (Kannouche and Stary, 2003;

Masutani et al., 2008).

The cells from all XP patients show an increased fre

quency of mutagenesis after exposure to UV light that is

correlated with molecular defects in DNA damage process

ing, leading to mutagenic consequences in the cells and in-

creased tumorigenesis in patients. Thus, these correlations

were the first clear demonstration that DNA damage and

mutations cause cancer (van Steeg and Kraemer, 1999;

Cleaver, 2000).

Other NER-Defective Genetic Disorders

As described above, approximately 20 to 30% of XP

patients also develop progressive neuronal impairment and

premature aging. The symptoms include hearing loss, swal-

lowing difficulties and mental retardation. Neuronal degen-

eration has been identified as the primary cause for these

clinical features; however, in some cases, severe develop

mental problems, such as growth retardation and micro

cephaly, have been observed. These more severe symptoms

are associated with the DSC as well as XP in combination

with Cockayne syndrome (CS), and this combined disorder

is referred to as XP/CS. Indeed, CS is a rare autosomal re

cessive disorder, first described in 1936 (Cockayne, 1936).

CS patients suffer from sun sensitivity and exhibit many

premature aging features, including cachectic dwarfism,

kyphosis, arrested sexual development, thin hair, subcuta

neous fat loss, osteoporosis and a characteristic “bird-like”

face (deep sunken eyes and prominent ears). The neurologi

cal symptoms include microcephaly, progressive hearing

and visual loss, progressive ataxia, delayed psychomotor

development, and mental retardation. These features reflect

dysmyelination and neurodegeneration, and the brain

shows prominent calcification (Iyama and Wilson 3rd,

2013; Jaarsma et al., 2013). Similar to XP cells, initial stud

ies with CS cells revealed hypersensitivity to UV irradia

tion, although normal levels of UDS and daughter strand re

pair were observed (Schmickel et al., 1977; Andrews et al.,

1978a). A few years later, the nature of the molecular repair

defect in CS cells was identified as a failure to recover RNA

synthesis after DNA damage induced through

UV-irradiation (Mayne and Lehmann, 1982), suggesting a

problem with the transcription of a damaged template. Im

portantly, this RNA synthesis impairment was used to iden

tify two different complementation groups for CS cells

(CS-A and CS-B) and an independent complementation

group in XP/CS cells (associated with the XP-B group)

with similar molecular defects (Lehmann, 1982). This im

portant discovery revealed two NER sub-pathways associ

ated with global genome repair (GGR) and RNA transcrip

tion (transcription coupled repair-TCR).

Subsequently, other genetic disorders were described

as the direct results of NER defects. In some cases, the pa

tients present neuronal and/or developmental problems,

such as trichothiodystrophy (TTD), where the patients

show features similar to CS (short stature, skeletal abnor

malities, impaired intelligence, decreased fertility, and

photosensitivity) and fragile and brittle hair due to the sul

fur-deficiency and reduced levels of cysteine-rich matrix

proteins (Stefanini et al., 2010). Cerebro-oculo-facio-ske

letal syndrome (COFS) is considered to be a severe form of

CS, with symptoms appearing at birth (Suzumura and Ari-

saka, 2010), and XPF-ERCC1 progeroid (XFE) syndrome

is associated with renal and liver abnormalities (Nieder-

nhofer et al., 2006). However, UV-sensitive syndrome

(UVSS) has been described as a mild genetic disorder lead-

ing to skin photosensitivity (Spivak, 2005; Oh and Spivak,

2010). Curiously, all these syndromes show skin photo-

sensitivity and defects impairing NER, but among their

clinical features, there has been no report of increased can-

cer frequency.

With the advent of DNA recombinant techniques in

the 1980s, many research groups have attempted to clone

the mutated genes in these NER-related diseases, although

this proved to be a difficult task because DNA transfection

in human cells was not trivial. In the 1990s, however, the

use of mutated rodent cells deficient for different DNA re

pair pathways facilitated the cloning of XP genes, contrib

uting to the understanding of the mechanisms of NER and

TLS, described in more detail below. As human genes

showed cross complementation with rodent cells, these

genes have been, in many cases, referred to as ERCC (for

excision cross-complementing) genes (Boulikas, 1996).

The human genes identified in NER-related diseases and

TLS, with their chromosomal locations and summarized

functions, are shown in Figure 1.

The XP Molecular Defects: Removing DNA

Damage via NER or Replicating Damaged DNA

through TLS

Classical XP (XP-A to XP-G) cells are defective in

the removal of DNA damage through NER, and XP-V cells

tolerate the lesions by replicating damaged templates

222 DNA repair avoids cancer and aging

through TLS. These mechanisms are schematically repre

sented in Figures 2 and 3.

Although NER was first described for the removal of

UV-induced lesions (such as cyclobutane pyrimidine di

mers, CPDs, and 6-4 pyrimidine-pyrimidone, 6-4PPs), this

pathway is recognized as a versatile and flexible mecha

nism. Specifically, NER removes structurally unrelated

bulky lesions, which promote DNA distortions in the dou

ble helix. These lesions include DNA adducts or intra-

strand crosslinks induced by chemical agents (such as

benzo(a)pyrene, a product of tobacco smoke, and cisplatin,

an anticancer chemotherapeutic drug) that react with DNA

or injuries induced by endogenous agents, such as lesions

generated by oxidation through ROS produced in the cells

as a potential byproduct of respiration. There are more than

30 proteins that act in a sequential and concerted manner to

remove DNA damage (Costa et al., 2003). Notably, defec

tive activity in seven of these proteins (from XPA to XPG)

may result in a clinical XP phenotype. Moreover, the defec

tive activity of CSA and CSB may result in severe CS

symptoms (Jaarsma et al., 2013). Other NER proteins have

also been recently described, where mutations cause NER

syndromes: TTDA/p8 (part of TFIIH complex, Giglia-Mari

et al., 2004), causing TTD; ERCC1 (partner of XPF endo

nuclease), causing XFE, CS and COFS (Suzumura and

Arisaka, 2010, Kashiyama et al., 2013); UVSSA causing

UVSS (Schwertman et al., 2012; Zhang et al., 2012).

NER can be summarized as having four sequential

steps, including i) lesion recognition, ii) unwinding the

damaged double helix, iii) cleavage and excision of the

damaged strand and iv) filling the gapped molecule, fol

lowed by DNA synthesis and final ligation (Figure 2). TLS

through XPV also facilitates tolerance of UV-induced

photoproducts, such as CPDs, and other types of DNA

damage induced through other DNA damaging agents (Fi

gure 3).

Two different sub-pathways have been implicated in

the recognition step of NER, depending on the location of

the lesion. The global genome repair (GGR) sub-pathway

involves the recognition of DNA lesions throughout the ge

nome, and it depends on the XPC/HR23B protein complex

as the primary DNA damage detector. For some types of le

Menck and Munford 223

Figure 1 - Human chromosomal location and general description of the genes encoding proteins involved in nucleotide excision repair (NER) and

translesion synthesis (TLS). Mutations in these genes cause human syndromes, listed in the table.

sions, such as CPDs, the damaged DNA binding (DDB)

complex (composed of two proteins, including XPE) is re

quired for improving the efficiency of damage recognition

and removal. The transcription-coupled repair (TCR) sub-

pathway acts on the transcribed strand of actively ex

pressed genes. The existence of this sub-pathway was first

observed when DNA damage was not homogeneously re

moved from the genome of mammalian cells, and the pref

erential repair of CPD lesions was detected in active genes

(Bohr et al., 1985). Subsequently, this preferential repair

system was demonstrated as being selective for the tran

scribed strand, implicating the transcription machinery in

the recognition of DNA damage (Mellon et al., 1987). Sub

sequent studies with CS cells demonstrated that these cells

were deficient in the preferential repair of active genes

(Mullenders et al., 1988; Venema et al., 1990). Indeed, the

CSA and CSB proteins are important players in the recog

nition of DNA lesions in the TCR pathway, triggered by the

blockage of RNA polymerase II during transcription.

The next step, common to both GGR and TCR sub-

pathways, is initiated through the recruitment of the tran

scription factor TFIIH, a multiprotein complex, which

includes XPB and XPD proteins, 3’-5’ and 5’-3’, respec

tively, ATP-dependent DNA helicases. This complex un

winds ~30 bp at the damaged DNA site, which is covered

by a single RPA (from Replication Protein A) complex (a

single-stranded DNA binding complex, composed of three

sub-unities). RPA and XPA proteins are likely involved in

the correct three-dimensional assembly of the NER ma

chinery prior to the endonucleolytic cleavage step. XPG

proteins and the XPF/ERCC1 complex are the main endo

nucleases that nick DNA at both sides, some nucleotides

away from the damage. Although XPG is required for

XPF/ERCC1 activity, this heterodimer makes the initial

5’-incision, followed by the XPG incision at the 3’ side of

the lesion (Fagbemi et al., 2011). The final step of NER is

the gap filling through repair synthesis. Replicative DNA

polymerases (Pol d and Pol e) use the 3’-hydroxyl extrem

ity, generated by the XPF/ERCC1 incision, as a primer to

synthesize DNA at the 30-nucleotide-gap. The resulting

nick at the 5’ end of the gap is sealed through DNA ligase I

224 DNA repair avoids cancer and aging

Figure 2 - Schematic representation of nucleotide excision repair (NER): the proteins associated with human diseases are highlighted. The downstream

NER pathway and each of the sub-pathways (GGR and TCR) for lesion recognition are indicated, showing the different steps for DNA lesion removal in

an error-free manner.

or III (Moser et al., 2007). Thus, normal NER restores the

original DNA molecule in an error-free manner.

The replication machinery may encounter unrepaired

DNA lesions, potentially resulting in a blockage in DNA

synthesis, as replicative DNA polymerases do not have the

capacity to use damaged templates. This important block

age may lead to the collapse of the replication fork, produc

tion of double-strand breaks, and, ultimately, cell death

(Batista et al., 2009). To tolerate DNA damage in replicat

ing templates, nature has evolved several alternative DNA

polymerases that replace the replicating polymerases (also

termed polymerase switching) and replicate the lesions

through TLS (Figure 3). Among the many alternative DNA

polymerases described during the last two decades (Sale et

al., 2012; Sale, 2013), XPV protein, or DNA polymerase

eta (Pol h), deserves special attention. Mutations in this

DNA polymerase have been implicated in the human syn

drome XP. The defective activity of this protein in XP-V

cells results in sensitive to UV-light or cisplatin treatment,

particularly when the cells are transformed with SV40 or

HPV, inhibiting the activity of p53 protein. These cells are

also highly mutable after UV-light, which explains the high

incidence of skin tumors in XP-V patients. Pol h bypasses

certain types of lesions, such as the CPDs induced through

UV-light, although the activity of this polymerase through

6-4PPs is controversial. The lack of Pol h leads to a strong

blockage of the replication forks in XP-V cells, but replica

tion can still recover through the action of other alternative

polymerases (Kannouche and Stary, 2003; Quinet et al.,

2014). Interestingly, Pol h is an error prone DNA polymer

ase, showing reduced replication fidelity. However, this

polymerase seems is capable of bypassing thymidine CPDs

correctly through the insertion of adenosines in the daugh-

ter strand. Thus, the increased mutagenesis observed in

UV-irradiated XP-V cells may reflect the activities of other

polymerases that replicate this lesion in an error prone man-

ner (Kannouche and Stary, 2003; Masutani et al., 2008).

DNA Damage and Repair

vs.

Cancer

Skin photosensitivity is a common clinical feature of

all patients showing defective NER responses. The in-

creased sensitivity to UV-light is also observed in cells

from XP, CS, TTD, or UVSS patients. Thus, the defective

removal of UV photoproducts likely results in this photo

sensitivity (Lehmann, 2003; Oh and Spivak, 2010). How

ever, although these syndromes reflect defects on the same

DNA processing pathway, apart from photosensitivity,

they are clinically highly heterogeneous, including increa

sed carcinogenesis, and more severe clinical features, such

as abnormal development, neurodegeneration and prema

ture aging. This clinical heterogeneity raises several unan

swered questions concerning how unrepaired DNA damage

leads to a plethora of different symptoms.

The highly increased mutagenesis induced by UV ir

radiation in XP cells is well correlated with the high levels

of skin cancer observed in XP patients for all XP comple

mentation groups, including NER-defective, and TLS-

defective (Figure 4). Indeed, UV-induced signature muta

tions were observed in specific tumor suppressor genes

(such as p53 and patched) in skin tumors from XP patients,

demonstrating the causal role of unrepaired lesions and mu

tations in the formation of tumors in these patients (Dumaz

et al., 1993; Bodak et al., 1999; D’Errico et al., 2000;

Giglia-Mari and Sarasin, 2003). Even internal tumors ob

served in XP patients carry mutations provoked by unre

Menck and Munford 225

Figure 3 - Schematic representation of translesion synthesis (TLS) by Pol

h. The replication fork is blocked by DNA damage, and after a series of

events (including the monoubiquitination of PCNA), a polymerase switch

provides DNA polymerase eta (XP-V) with an opportunity to bypass the

lesion. In this figure, only one strand (leading strand) is represented. At the

end of the process the lesion remains in the DNA, but the replication of this

molecule can proceed.

paired lesions, likely originating from oxidative stress

(Giglia et al., 1998).

Thus, there are clear indications that unrepaired DNA

damage induces mutations, and these mutations cause can

cer. Nevertheless, the lack of tumors in CS and TTD pa

tients is puzzling. Although the cells from CS patients are

defective in a sub-pathway of NER (TCR), the cells from

these patients (Parris and Kraemer, 1993) and rodent cells

with mutations in the CSB homolog (Vreeswijk et al.,

1998) show increased mutations after UV irradiation.

Moreover, mouse models defective for CSA and CSB show

skin cancer predisposition after UVB irradiation (van der

Horst et al., 1997, 2002), unlike their human counterparts.

As GGR is more efficient in human cells compared with ro

dent cells (Hanawalt, 2001), this sub-pathway could protect

CS patients from developing skin tumors. Alternatively, it

has been proposed that CS cells have a strong signal for cell

death after DNA damage, likely reflecting higher levels of

transcription blockage (McKay et al., 2001), which may

have a reverse effect on cancer development, as dead cells

cannot induce cancer. However, XP-A cells are also highly

sensitive to DNA lesions, but XP-A patients always de

velop skin tumors. Notably, the lifetime of severely af

fected CS, TTD, COFS and XFE patients is typically short

and may require living indoors (due to severe clinical fea

tures), reducing their exposure to sunlight and the

probability of developing tumors.

Until recently, most mutation studies have investi

gated base substitution and small point mutations, deletions

and insertions, although certainly larger changes in the

DNA sequence, including gross rearrangements, copy

number variations and chromosomal anomalies and other

types of genomic instabilities, are affected by unrepaired

DNA damage, representing known alterations in human

cancer (Amiel et al., 2004). Moreover, even with clear evi

dence of sunlight being responsible for skin cancer, many

questions remain concerning what is the part of the spec

trum acting in tumorigenesis, either in XP patients or the

normal population. Although the results strongly suggest a

role for CPDs, the main lesion induced by UVB (280-320

nm), in skin carcinogenesis, this type of lesion is also gen

erated after UVA (320-400 nm) irradiation, and other le

sions induced by this spectrum of sunlight should also be

considered (Douki et al., 2003; Cadet et al., 2012; Schuch

et al., 2013). Indeed, a recent study implicated an important

role for both CPDs and 6-4PPs in the biological conse

quences of UVA light in XP cells (Cortat et al., 2013). Skin

tumors are the most frequent types of cancer in human pop

ulations, particularly in countries near the tropics; thus, a

detailed understanding of how these cancers are induced

226 DNA repair avoids cancer and aging

Figure 4 - The consequences of DNA damage and how defective NER and TLS may explain certain clinical phenotypes. Different types of DNA damage

can be induced by a variety of endogenous and exogenous agents. NER removes several of these lesions and TLS helps to replicate them, aiming mainte-

nance of the genome stability, and guaranteeing normal cell proliferation, and normal human life (represented in green). When these mechanisms fail,er-

rors in DNA replication increase mutagenesis and genetic instability, resulting in higher photosensitivity (observed in UVSS and XP patients) and risk of

cancer development (observed in XP patients). Defective GGR-NER and TLS better explain these phenotypes (in red, superior part of the figure). Alter-

natively, endogenous DNA damage (including those induced by ROS) may disturb the transcription and/or cause replication blockage, leading to cell

death, thus defective TCR-NER better explain the more severe phenotypes (including premature aging) of XP/CS, CS and other syndromes. Other effects,

such as impaired transcription or damaged mitochondria may also be involved in these phenotypes (in red lower part of the figure).

through exposure to sunlight is highly relevant to the gen

eral public health. Further investigations with XP patients

and XP cells can provide important contribution to this

field.

Unrepaired DNA Damage and the Aging

Process

Concerning other symptoms, such as developmental

problems, neurological abnormalities and premature aging,

observed in more severely affected XP patients and other

NER-related syndromes (such as CS, COFS, TTD and

XFE), the causal effects remain far from being understood.

This puzzling question was first raised in the 1970s, when

the UV-survival of XP cells from several complementation

groups were compared to understand the neurological ab

normalities (Andrews et al., 1976, 1978b; Kraemer et al.,

1976). In general, the cells from patients with more severe

symptoms were more UV sensitive than those with no neu

rological abnormalities. Similar results were soon de

scribed for CS-derived cells, indicating the sensitivity of

these cells to UV damage (Andrews et al., 1978a). Ulti-

mately, it was concluded that extremely inefficient DNA

repair could not protect these neurons (or supporting glial

cells) from DNA damage in some of the patients, and the

neurons would die prematurely.

Interestingly, in the first reports, XP-C patients were

already noticed as less affected by the severe symptoms. In-

deed, XP patients mutated in the XPC, XPE (both partici-

pate in the initial steps of GGR pathway of NER, see

Figure 2) and XPV (TLS, Figure 3) genes present symp-

toms associated with skin lesions, but not affecting the ner-

vous system. This observation indicates that defects in the

GGR sub-pathway of NER and TLS through Pol h could

explain the increased tumorigenesis observed in the skin of

these patients, which prevents mutagenesis, as described

above. Thus, patients with mutations in these genes and

other genes (XPA, XPB, XPD, XPF and XPG) that partici

pate downstream in the GGR sub-pathway may present

only XP phenotypes associated with skin lesions, which

may be avoided by preventing sun exposure.

On the other hand, TCR impairment is clearly associ

ated with more severe symptoms in NER-related syndro

mes (Figure 4). The high levels of cell death of TCR

impaired cells in response to DNA damage, likely triggered

by a blockage in RNA transcription, have been associated

with the severe symptoms in CS patients (McKay et al.,

2001). A similar explanation may also be associated with

XP/CS, COFS, TTD, and XFE syndromes. However, the

nature of the DNA damage resulting in this increased cell

death remains unknown. Endogenously induced lesions

generated by free radicals, including ROS, are the strongest

candidates for these effects. Indeed, CS-B cells have been

demonstrated as deficient in the repair of DNA damage

generated through oxidative stress under many circum

stances. Initially, CSB was shown to be important for the

removal of 8-oxoguanine (8-oxoG), a known lesion pro

duced by oxidative stress, in human cells irradiated with

ionizing radiation (Tuo et al., 2001, 2003). Subsequently,

this effect was also described for CS-A human primary

fibroblasts (D’Errico et al., 2007). Mouse models defective

in CSB protein were shown to accumulate oxidized purine

modifications (8-oxoG and (5’S)-8,5’-cyclo 2’-deoxyade

nosine) in certain tissues with age (Osterod et al., 2002;

Kirkali et al., 2009). More recently, CS-A and CS-B pri

mary human cells and CS-B reprogrammed iPS cells were

shown to have altered metabolic redox balance, with in

creased levels of intracellular ROS and basal (and induced)

levels of DNA damage (Andrade et al., 2012; Pascucci et

al., 2012).

Consistent with this model, CS-A and CS-B cells are

more sensitive to hydrogen peroxide treatment compared

with cells derived from UVSS patients, who present only

photosensitivity symptoms. Host cell reactivation after the

transfection of damaged plasmids in human cells yields

similar results. This approach measures the expression of a

reporter gene, and this expression is impaired after DNA

damage, which is recovered through DNA repair in the

transfected cells. Although both CS-B and UVSS cells are

defective in the recovery of UV-irradiated plasmids, only

CS-B cells recover gene expression through plasmids car-

rying oxidized base damage (Spivak and Hanawalt, 2006).

Moreover, a UVSS patient was demonstrated to have a spe-

cific mutation in the CS-A gene, and cells derived from this

patient were highly sensitive to UV irradiation; however, in

contrast to CS-A cells from CS patients, these UVSS cells

were not sensitive to potassium bromate or other agents that

generate oxidative stress (Nardo et al., 2009). Similar re

sults were obtained in XP patients carrying missense muta

tions in the XPG gene. Specifically, the cells from mildly

affected patients (clinically showing only photosensitivity)

were sensitive to UV-light but not to the treatment of

photoactivated methylene blue (which generates singlet ox

ygen), in contrast to XP-G/CS cells that were sensitive to

this oxidative stress. Host cell reactivation also confirmed

that the XPG alleles containing missense mutations fully

reactivated the expression of reporter genes from plasmids

damaged with photoactivated methylene blue in XP-G/CS

deficient cells, while only partial reactivation was obtained

in UV-irradiated plasmids (Soltys et al., 2013).

Thus, defective transcriptional repair of DNA dam

age generated through oxidative stress is associated with

more severe clinical features, such as developmental and

neuronal abnormalities and premature aging, while the de

fective repair of UV induced DNA damage is associated

with photosensitivity phenotypes (Andressoo and Hoeijm

akers, 2005). However, other published data challenge this

model: XPC protein has also been implicated in the repair

of DNA damage induced through oxidative stress, although

XP-C patients present only clinical features associated with

Menck and Munford 227

skin photosensitivity, with no symptoms involving neuro

logical or developmental problems. Human XP-C primary

keratinocytes and fibroblasts are hypersensitive to treat

ment with oxidizing agents and accumulate oxidized DNA

damage after oxidant exposure (D’Errico et al., 2006). A

similar defect was shown in the host cell reactivation of

photoactivated methylene blue damaged adenovirus vec

tors (Kassam and Rainbow, 2007). The participation of

both XPA and XPC proteins in the repair of photoactivated

methylene blue-induced DNA damage was also investi

gated in cells treated with this agent or in the host cell reac

tivation of damaged plasmids. The results suggest that the

NER pathway directly participates in the repair of DNA le

sions generated through oxidative stress (Berra et al.,

2013). However, live imaging data indicates that proteins

that initiate NER (XPC and CSB) are rapidly recruited to

sites of the cell nuclei containing oxidized base damage,

with the absence of the detectable recruitment of other

downstream NER factors. These results indicate that the

binding of XPC and CSB to the sites of DNA damage is in

dependent on a further NER reaction (Menoni et al., 2012).

Therefore, as the participation of XPC protein in cell

protection from oxidative stress is confirmed, the lack of

oxidative stress-mediated DNA damage repair may be nec-

essary but not sufficient to explain the severe pathology of

neurological and developmental symptoms and the acceler-

ated aging observed in NER-related syndromes. Further de-

fects are needed to construct these severe symptoms, and

many possibilities are being investigated. Thus, two poten-

tial hypotheses emerge that may help to understand and

eventually answer this question: mitochondrial DNA dam-

age and general deficiency in transcription.

Indeed, the participation of NER factors in mitochon

dria is gaining support. CS-B protein was shown to stimu

late the repair of 8-oxoG in the mitochondrial DNA

(Stevnsner et al., 2002, Aamann et al., 2010). Moreover,

CS-B cells are deficient in autophagy, leading to increased

oxidative stress and the accumulation of damaged mito

chondria. Interestingly, these effects could be reversed

through the addition of autophagy stimulators, such as lith

ium chloride and rapamycin, to the cell culture medium

(Scheibye-Knudsen et al., 2012). Moreover, the participa

tion of many of the proteins in TCR in the global transcrip

tion machinery may also be important. A general reduction

in transcription through RNA polymerase II has been ob

served in CSB cells (Balajee et al., 1997). The participation

of CSB in transcription elongation and TFIIH as an initia

tion transcription factor should be considered for these

“transcription syndromes” (Compe and Egly, 2012;

Velez-Cruz and Egly, 2013). The need for the repair of

DNA damage to achieve the effects observed in these pa

thologies has also been questioned, as the defects on tran

scription through RNA polymerases I and II may solely

explain the severe symptoms of CS patients (Brooks,

2013).

Some patient cases still add more confusion to the ge

netic basis of carcinogenesis and neurological abnormali

ties resulting from NER defects. Although CS patients do

not present skin tumors, at least one case of siblings show

ing a severe XP phenotype (diagnosed as the DeSanctis-

Cacchione variant of XP) were identified with a missense

mutation in the CSB gene (Colella et al., 2000). In contrast,

a UVSS patient has been demonstrated as completely null

for this same CSB gene (Horibata et al., 2004). The under

standing of the molecular basis underlying these clinical

phenotypes may help to understand the intricate role of

DNA damage and repair in the human pathology of cancer

and aging.

XP Under the Tropical Sun

Although sunlight is much more intense at low lati

tudes, with higher intensity of UVB light and more severe

DNA lesions (Schuch et al., 2012), most studies with XP

patients has been performed in Europe, USA and Japan, un

der high latitudes. In tropical and poorer countries, these

patients are typically, and unfortunately, unattended. Diffi

culties in diagnosis, including the lack of information from

local medical dermatologists and complications in obtain-

ing appropriate rigorous photoprotection, are just some of

the problems faced by these patients and families.

Most of the reports of gene identification and atten-

tion to XP families in these countries depend on studies per-

formed in USA or Europe. These studies showed interest-

ing data of genetic clusters, such as the one identified in

Guatemala for an isolated community, where 12 children

carried a new mutation in the XPC gene, likely reflecting

consanguineous marriage (Cleaver et al., 2007). Another

genetic cluster was also recently described in patients from

a French Comorian Island near the Indian Ocean in West

Africa. Among the black Mayotte population, more than 32

XP patients carried a mutation in the XPC gene (Cartault et

al., 2011), likely resulting from a founder effect from the

African continent. Although black skin protects these pa

tients, these individuals still suffer from the heavy sunlight

intensity, with the development of skin tumors and early

ocular injuries. Another important finding was the preva

lence of a specific mutation (c.1643_1644delTG,

p.Val548AlafsX25) in the XPC gene in North Africa. This

mutation was observed in 87% of the XP-C patients in this

location, primarily in unrelated families, reflecting a

founder mutation aging 50 generations or 1250 years (Sou

fir et al., 2010). It is curious how this deleterious mutation

can still be observed, despite a strong negative selection,

especially in these sunny environments. Certainly, the mu

tated allele is kept in heterozygote individuals, as they pres

ent normal repair phenotype.

Recently, evidence has been obtained from the direct

assistance of patients in the tropical countries, showing

sporadic cases (Halpern et al., 2008) and more complete

studies in the genetic identification of mutations (mostly

228 DNA repair avoids cancer and aging

novel) in XPC (Leite et al., 2009), XPV (Ortega-Recalde et

al., 2013) and XPG (Soltys et al., 2013) genes. One of the

mutations described for the XPC gene in Brazil (Leite et al.,

2009) is the same as the highly prevalent mutation reported

in North Africa (Soufir et al., 2010), indicating the potential

migration from Africa to Europe and subsequently to Brazil

(likely from Portugal). The two novel XPG missense muta

tions observed in the two siblings in Brazil were shown to

produce proteins with low repair of UV-photoproducts, but

normal repair of lesions generated through oxidative stress,

likely explaining the mild phenotype of these patients (Sol

tys et al., 2013). Moreover, a pioneering effort for the sys

tematic identification of mutations that affect XPC and

XPA genes has recently been underway in Brazilian pa

tients, and these results will contribute to both the assis

tance to these patients and the scientific knowledge on the

distribution of these pathological mutations (K. Santiago

and MI Achatz, unpublished data). Interestingly, among

those XP patients some have a Native American Indian ori

gin, as the XP community described in Guatemala (Cleaver

et al., 2007) and the XP severely affected children belonging

to the Navajo Reservation in Southwest of USA

(http://globalgenes.org/xeroderma-pigmentosum-suddenly-

arises-on-navajo-reservation/). Most likely, these will not be

the only cases for Native Americans, suggesting mutated al

leles of XP genes, causing the disease, have possibly existed

before the human migration to the Americas, from Asia.

Moreover, another genetic cluster has been reported

in the Brazilian state of Goias (a sunny central area of this

country), with more than 20 affected XP patients diagnosed

in an isolated community (Chaibub, 2011). Genetic identi

fication of the mutation is underway, and preliminary data

indicate that the XPV gene is affected in this population

(unpublished results).

Conclusions and Perspectives

The wide spectrum of symptoms and diseases caused

by NER deficiency reflects the relevance of this repair

Menck and Munford 229

Figure 5 - Strategies for molecular diagnosis of XP patients. Identification of XP gene mutation based on a series of biological and biochemical assays us

ing primary cells obtained from patient skin biopsies. Although the information from these cells has always been rich, the direct sequencing of DNA re

pair genes using next generation sequencing techniques may facilitate the molecular diagnosis using blood or saliva samples.

pathway in the maintenance of genome stability in humans.

Since 1968, the molecular defects affecting XP patients and

other syndromes have been described. Studies with cells

from these patients have contributed to our current under

standing of the causes of cancer and the development of

tools to fight tumors (Moraes et al., 2012). We have also

learned a great deal concerning aging, which might im

prove the health and quality of life of the elderly. Thus, the

human society is indebted to NER-defective patients, al

though little can really be done to help them. Gene therapy

for these patients is at its infancy (Magnaldo and Sarasin,

2004; Menck et al., 2007), and not even the simple identifi

cation of the genetic mutation is provided in many coun

tries worldwide, particularly in developing countries. This

identification could, at least, provide some prognosis for

the disease and support for genetic counseling for the af

fected families. Until recently, there was a strong need for

biological essays for the identification of the genetic com

plementation group in XP patients, requiring skin biopsies,

which are painful for the patient, and cell culture, which is

time consuming and requires specific skills. The direct se

quencing of exomes (Ortega-Recalde et al., 2013) or spe-

cific genes using next generation sequencing techniques of

DNA isolated directly from saliva samples provides an ex-

cellent opportunity for the rapid diagnosis of these muta-

tions (Figure 5). Thus, new horizons may bring hope for the

XP patients and their families.

Acknowledgments

This work was financially supported through grants

from the Fundação de Amparo à Pesquisa do Estado de São

Paulo (FAPESP) and Conselho Nacional de Desenvol

vimento Científico e Tecnológico (CNPq).

References

Aamann MD, Sorensen MM, Hvitby C, Berquist BR, Muftuoglu

M, Tian J, de Souza-Pinto NC, Scheibye-Knudsen M, Wil

son 3rd DM, Stevnsner T, et al. (2010) Cockayne syndrome

group B protein promotes mitochondrial DNA stability by

supporting the DNA repair association with the mitochon

drial membrane. FASEB J 24:2334-2346.

Amiel A, Peretz G, Slor H, Weinstein G and Fejgin MD (2004)

Molecular cytogenetic parameters in fibroblasts from pa

tients and carriers of xeroderma pigmentosum. Cancer

Genet Cytogenet 149:154-160.

Andrade LN, Nathanson JL, Yeo GW, Menck CF and Muotri AR

(2012) Evidence for premature aging due to oxidative stress

in iPSCs from Cockayne syndrome. Hum Mol Genet

21:3825-3834.

Andressoo JO and Hoeijmakers JH (2005) Transcription-coupled

repair and premature ageing. Mutat Res 577:179-194.

Andrews AD, Barrett SF and Robbins JH (1976) Relation of DNA

repair processes to pathological ageing of the nervous sys

tem in xeroderma pigmentosum. Lancet 19:1318-1320.

Andrews AD, Barrett SF, Yoder FW and Robbins JH (1978a)

Cockayne’s syndrome fibroblasts have increased sensitivity

to ultraviolet light but normal rates of unscheduled DNA

synthesis. J Invest Dermatol 70:237-239.

Andrews AD, Barrett SF and Robbins JH (1978b) Xeroderma

pigmentosum neurological abnormalities correlate with col

ony-forming ability after ultraviolet radiation. Proc Natl

Acad Sci USA 75:1984-1988.

Balajee AS, May A, Dianov GL, Friedberg EC and Bohr VA

(1997) Reduced RNA polymerase II transcription in intact

and permeabilized Cockayne syndrome group B cells. Proc

Natl Acad Sci USA 94:4306-4311.

Batista LF, Kaina B, Meneghini R and Menck CF (2009) How

DNA lesions are turned into powerful killing structures: In

sights from UV-induced apoptosis. Mutat Res 681:197-208.

Berra CM, Oliveira CS, Garcia CCM, Rocha CRR, Lerner LK,

Andrade LCL, Baptista MS and Menck CFM (2013) Nucle

otide excision repair activity on DNA damage induced by

photoactivated methylene blue. Free Radic Biol Med

61C:343-356.

Bodak N, Queille S, Avril MF, Bouadjar B, Drougard C, Sarasin

A and Daya-Grosjean L (1999) High levels of patched gene

mutations in basal-cell carcinomas from patients with xero

derma pigmentosum. Proc Natl Acad Sci USA 96:5117-

5122.

Bohr VA, Smith CA, Okumoto DS and Hanawalt PC (1985) DNA

repair in an active gene: Removal of pyrimidine dimers from

the DHFR gene of CHO cells is much more efficient than in

the genome overall. Cell 40:359-369.

Boulikas T (1996) Xeroderma pigmentosum and molecular clon-

ing of DNA repair genes. Anticancer Res 16:693-708.

Brooks PJ (2013) Blinded by the UV light: How the focus on tran-

scription-coupled NER has distracted from understanding

the mechanisms of Cockayne syndrome neurologic disease.

DNA Repair 12:656-671.

Cadet J, Mouret S, Ravanat JL and Douki T (2012) Photoinduced

damage to cellular DNA: Direct and photosensitized reac-

tions. Photochem Photobiol 88:1048-1065.

Cartault F, Nava C, Malbrunot AC, Munier P, Hebert JC, N’guyen

P, Djeridi N, Pariaud P, Pariaud J, Dupuy A, et al. (2011) A

new XPC gene splicing mutation has lead to the highest

worldwide prevalence of xeroderma pigmentosum in black

Mahori patients. DNA Repair 10:577-585.

Chaibub SCW (2011) High incidence of xeroderma pigmentosum

in a countryside community in the state of Goiás, Brazil.

Surg Cosmet Dermatol 3:112-115.

Cleaver JE (1968) Defective repair replication of DNA in xero

derma pigmentosum. Nature 218:652-656.

Cleaver JE (2000) Common pathways for ultraviolet skin carcino

genesis in the repair and replication defective groups of

xeroderma pigmentosum. J Dermatol Sci 23:1-11.

Cleaver JE, Feeney L, Tang JY and Tuttle P (2007) Xeroderma

pigmentosum group C in an isolated region of Guatemala. J

Invest Dermatol 127:493-496.

Cleaver JE, Bezrookove V, Revet I and Huang EJ (2013) Concep

tual developments in the causes of Cockayne syndrome.

Mech Ageing 134:284-290.

Cockayne EA (1936) Dwarfism with retinal atrophy and deafness.

Arch Dis Child 11:1-8.

Colella S, Nardo T, Botta E, Lehmann AR and Stefanini M (2000)

Identical mutations in the CSB gene associated with either

Cockayne syndrome or the DeSanctis-cacchione variant of

xeroderma pigmentosum. Hum Mol Genet 9:1171-1175.

230 DNA repair avoids cancer and aging

Compe E and Egly JM (2012) TFIIH: When transcription met

DNA repair. Nat Rev Mol Cell Biol 13:343-354.

Cortat B, Garcia CMC, Quinet A, Schuch AP, de Lima-Bessa KM

and Menck CF (2013) The relative roles of DNA damage in

duced by UVA irradiation in human cells. Photochem

Photobiol Sci 12:1483-1495.

Costa RM, Chiganças V, Galhardo R da S, Carvalho H and Menck

CF (2003) The eukaryotic nucleotide excision repair path

way. Biochimie 85:1083-1099.

De Weerd-Kastelein EA, Keijzer W and Bootsma D (1972) Ge

netic heterogeneity of xeroderma pigmentosum demon

strated by somatic cell hybridization. Nat New Biol 238:80-

83.

D’Errico M, Calcagnile A, Canzona F, Didona B, Posteraro P,

Cavalieri R, Corona R, Vorechovsky I, Nardo T, Stefanini

M, et al. (2000) UV mutation signature in tumor suppressor

genes involved in skin carcinogenesis in xeroderma pig

mentosum patients. Oncogene 19:463-467.

D’Errico M, Parlanti E, Teson M, de Jesus BM, Degan P, Cal

cagnile A, Jaruga P, Bjørås M, Crescenzi M, Pedrini AM, et

al. (2006) New functions of XPC in the protection of human

skin cells from oxidative damage. EMBO J 25:4305-4315.

D’Errico M, Parlanti E, Teson M, Degan P, Lemma T, Calcagnile

A, Iavarone I, Jaruga P, Ropolo M, Pedrini AM, et al. (2007)

The role of CSA in the response to oxidative DNA damage

in human cells. Oncogene 26:4336-4343.

Diderich K, Alanazi M and Hoeijmakers JH (2011) Premature ag-

ing and cancer in nucleotide excision repair-disorders. DNA

Repair 10:772-780.

DiGiovanna JJ and Kraemer KH (2012) Shining a light on xero-

derma pigmentosum. J Invest Dermatol 132:785-796.

Douki T, Reynaud-Angelin A, Cadet J and Sage E (2003) Bipy-

rimidine photoproducts rather than oxidative lesions are the

main type of DNA damage involved in the genotoxic effect

of solar UVA radiation. Biochemistry 42:9221-9226.

DeSanctis C and Cacchione AI (1932) Idiozia xerodermia. Riv

Sper Freniat 56:269-292.

Dumaz N, Drougard C, Sarasin A and Daya-Grosjean L (1993)

Specific UV-induced mutation spectrum in the p53 gene of

skin tumors from DNA-repair-deficient xeroderma pigmen

tosum patients. Proc Natl Acad Sci USA 90:10529-10533.

Fagbemi AF, Orelli B and Schärer OD (2011) Regulation of

endonuclease activity in human nucleotide excision repair.

DNA Repair 10:722-729.

Giglia G, Dumaz N, Drougard C, Avril MF, Daya-Grosjean L and

Sarasin A (1998) p53 mutations in skin and internal tumors

of xeroderma pigmentosum patients belonging to the com

plementation group C. Cancer Res 58:4402-4409.

Giglia-Mari G, Coin F, Ranish JA, Hoogstraten D, Theil A,

Wijgers N, Jaspers NG, Raams A, Argentini M, van der

Spek PJ, et al. (2004) A new, tenth subunit of TFIIH is re

sponsible for the DNA repair syndrome trichothiodystrophy

group A. Nat Genet 36:714-719.

Giglia-Mari G and Sarasin A (2003) TP53 mutations in human

skin cancers. Hum Mutat 21:217-228.

Goss JR, Stolz DB, Robinson AR, Zhang M, Arbujas N, Robbins

PD, Glorioso JC and Niedernhofer LJ (2011) Premature ag

ing-related peripheral neuropathy in a mouse model of pro

geria. Mech Ageing Dev 132:437-442.

Gredilla R, Garm C and Stevnsner T (2012) Nuclear and mito

chondrial DNA repair in selected eukaryotic aging model

systems. Oxid Med Cell Longev 2012:282438.

Halpern J, Hopping B and Brostoff JM (2008) Photosensitivity,

corneal scarring and developmental delay: Xeroderma pig

mentosum in a tropical country. Cases J 1:254.

Hanawalt PC (2001) Revisiting the rodent repairadox. Environ

Mol Mutagen 38:89-96.

Hebra F and Kaposi M (1874) On diseases of the skin including

exanthemata, volume III. The New Sydenham Society

61:252-258.

Hirai Y, Kodama Y, Moriwaki S, Noda A, Cullings HM, Macphee

DG, Kodama K, Mabuchi K, Kraemer KH, Land CE, et al.

(2006) Heterozygous individuals bearing a founder muta

tion in the XPA DNA repair gene comprise nearly 1% of the

Japanese population. Mutat Res 601:171-178.

Horibata K, Iwamoto Y, Kuraoka I, Jaspers NG, Kurimasa A,

Oshimura M, Ichihashi M and Tanaka K (2004) Complete

absence of Cockayne syndrome group B gene product gives

rise to UV-sensitive syndrome but not Cockayne syndrome.

Proc Natl Acad Sci USA 101:15410-15415.

Iyama T and Wilson 3rd DM (2013) DNA repair mechanisms in

dividing and non-dividing cells. DNA Repair 12:620-636.

Jaarsma D, van der Pluijm I, van der Horst GT and Hoeijmakers

JH (2013) Cockayne syndrome pathogenesis: Lessons from

mouse models. Mech Ageing Dev 134:180-195.

Kannouche P and Stary A (2003) Xeroderma pigmentosum vari-

ant and error-prone DNA polymerases. Biochimie

85:1123-1132.

Kassam SN and Rainbow AJ (2007) Deficient base excision re-

pair of oxidative DNA damage induced by methylene blue

plus visible light in xeroderma pigmentosum group C fibro-

blasts. Biochem Biophys Res Commun 359:1004-1009.

Kashiyama K, Nakazawa Y, Pilz DT, Guo C, Shimada M, Sasaki

K, Fawcett H, Wing JF, Lewin SO, Carr L, et al.

(2013) Mal-

function of nuclease ERCC1-XPF results in diverse clinical

manifestations and causes Cockayne syndrome, xeroderma

pigmentosum, and Fanconi anemia. Am J Hum Genet

92:807-819.

Kim H and D’Andrea AD (2012) Regulation of DNA cross-link

repair by the Fanconi anemia /BRCA pathway. Genes Dev

26:1393-1408.

Kleijer WJ, Laugel V, Berneburg M, Nardo T, Fawcett H,

Gratchev A, Jaspers NG, Sarasin A, Stefanini M and

Lehmann AR (2008) Incidence of DNA repair deficiency

disorders in western Europe: Xeroderma pigmentosum,

Cockayne syndrome and trichothiodystrophy. DNA Repair

7:744-750.

Knoch J, Kamenisch Y, Kubisch C and Berneburg M (2012) Rare

hereditary diseases with defects in DNA-repair. Eur J Der

matol 22:443-455.

Kirkali G, de Souza-Pinto NC, Jaruga P, Bohr VA and Dizdaroglu

M (2009) Accumulation of (5’S)-8,5’-cyclo-2’-deoxyade

nosine in organs of Cockayne syndrome complementation

group B gene knockout mice. DNA Repair 8:274-278.

Kraemer KH, Andrews AD, Barrett SF and Robbins JH (1976)

Colony-forming ability of ultraviolet-irradiated xeroderma

pigmentosum fibroblasts from different DNA repair com

plementation groups. Biochim Biophys Acta 442:147-153.

Kraemer KH, Lee MM, Andrews AD and Lambert WC (1994)

The role of sunlight and DNA repair in melanoma and

Menck and Munford 231

nonmelanoma skin cancer. The xeroderma pigmentosum

paradigm. Arch Dermatol 130:1018-1021.

Lehmann AR (1982) Three complementation groups in Cockayne

syndrome. Mutat Res 106:347-356.

Lehmann AR (2003) DNA repair-deficient diseases, xeroderma

pigmentosum, Cockayne syndrome and trichothiodys

trophy. Biochimie 85:1101-1111.

Lehmann AR, Kirk-Bell S, Arlett CF, Paterson MC, Lohman PH,

de Weerd-Kastelein EA and Bootsma D (1975) Xeroderma

pigmentosum cells with normal levels of excision repair

have a defect in DNA synthesis after UV-irradiation. Proc

Natl Acad Sci USA 72:219-223.

Lehmann AR, McGibbon D and Stefanini M (2011) Xeroderma

pigmentosum. Orphanet J Rare Dis 6:70.

Leite RA, Marchetto MC, Muotri AR, Vasconcelos D de M, de

Oliveira ZN, Machado MCR and Menck CF (2009) Identifi

cation of XP complementation groups by recombinant ade

novirus carrying DNA repair genes. J Invest Dermatol

129:502-506.

Magnaldo T and Sarasin A (2004) Xeroderma pigmentosum:

From symptoms and genetics to gene-based skin therapy.

Cells Tissues Organs 177:189-198.

Masutani C, Hanaoka F and Ahmad SI (2008) Xeroderma pig

mentosum variant, XP-V: Its product and biological roles.

Adv Exp Med Biol 637:93-102.

Menck CF, Armelini MG and Lima-Bessa KM (2007) On the

search for skin gene therapy strategies of xeroderma pig-

mentosum disease. Curr Gene Ther 7:163-174.

Marinoglou K (2012) The role of the DNA damage response

kinase ataxia telangiectasia mutated in neuroprotection.

Yale J Biol Med 85:469-480.

Mayne LV and Lehmann AR (1982) Failure of RNA synthesis to

recover after UV irradiation: An early defect in cells from

individuals with Cockayne’s syndrome and xeroderma pig-

mentosum. Cancer Res 42:1473-1478.

McKay BC, Becerril C and Ljungman M (2001) P53 plays a pro

tective role against UV-and cisplatin-induced apoptosis in

transcription-coupled repair proficient fibroblasts. Onco

gene 20:6805-6808.

Mellon I, Spivak G and Hanawalt PC (1987) Selective removal of

transcription-blocking DNA damage from the transcribed

strand of the mammalian DHFR gene. Cell 51:241-249.

Menoni H, Hoeijmakers JH and Vermeulen W (2012) Nucleotide

excision repair-initiating proteins bind to oxidative DNA le

sions in vivo. J Cell Biol 199:1037-1046.

Moraes MC, Neto JB and Menck CF (2012) DNA repair mecha

nisms protect our genome from carcinogenesis. Front Biosci

17:1362-1388.

Moser J, Kool H, Giakzidis I, Caldecott K, Mullenders LH and

Fousteri MI (2007) Sealing of chromosomal DNA nicks

during nucleotide excision repair requires XRCC1 and DNA

ligase III alpha in a cell-cycle-specific manner. Mol Cell

27:311-323.

Mullenders LH, van Kesteren van Leeuwen AC, van Zeeland AA

and Natarajan AT (1988) Nuclear matrix associated DNA is

preferentially repaired in normal human fibroblasts, ex

posed to a low dose of ultraviolet light but not in Cockayne’s

syndrome fibroblasts. Nucleic Acids Res 16:10607-10622.

Nardo T, Oneda R, Spivak G, Vaz B, Mortier L, Thomas P, Orioli

D, Laugel V, Stary A, Hanawalt PC, et al. (2009) A UV-

sensitive syndrome patient with a specific CSA mutation re

veals separable roles for CSA in response to UV and oxida

tive DNA damage. Proc Natl Acad Sci USA 106:6209-6214.

Niedernhofer LJ, Garinis GA, Raams A, Lalai AS, Robinson AR,

Appeldoorn E, Odijk H, Oostendorp R, Ahmad A, van

Leeuwen W, et al. (2006) A new progeroid syndrome re

veals that genotoxic stress suppresses the somatotroph axis.

Nature 444:1038-1043.

Niedernhofer LJ, Bohr VA, Sander M and Kraemer KH (2011)

Xeroderma pigmentosum and other diseases of human pre

mature aging and DNA repair: Molecules to patients. Mech

Ageing Dev 132:340-347.

Oh DH and Spivak G (2010) Hereditary photodermatoses. Adv

Exp Med Biol 685:95-105.

Ortega-Recalde O, Vergara JI, Fonseca DJ, Ríos X, Mosquera H,

Bermúdez OM, Medina CL, Vargas CI, Pallares AE, Res

trepo CM and Laissue P (2013) Whole-exome sequencing

enables rapid determination of xeroderma pigmentosum

molecular etiology. PLoS One 8:e64692.

Osterod M, Larsen E, Le Page F, Hengstler JG, Van Der Horst

GT, Boiteux S, Klungland A and Epe B (2002) A global

DNA repair mechanism involving the Cockayne syndrome

B (CSB) gene product can prevent the in vivo accumulation

of endogenous oxidative DNA base damage. Oncogene

21:8232-8239.

Parris CN and Kraemer KH (1993) Ultraviolet-induced mutations

in Cockayne syndrome cells are primarily caused by cyclo-

butane dimer photoproducts while repair of other photo-

products is normal. Proc Natl Acad Sci USA 90:7260-7264.

Pascucci B, Lemma T, Iorio E, Giovannini S, Vaz B, Iavarone I,

Calcagnile A, Narciso L, Degan P, Podo F, et al. (2012) An

altered redox balance mediates the hypersensitivity of

Cockayne syndrome primary fibroblasts to oxidative stress.

Aging Cell 11:520-529.

Quinet A, Vessoni AT, Rocha CR, Gottifredi V, Biard D, Sarasin

A, Menck CF and Stary A (2014) Gap-filling and bypass at

the replication fork are both active mechanisms for tolerance

of low-dose ultraviolet-induced DNA damage in the human

genome. DNA Repair 14:27-38.

Robbins JH, Kraemer KH, Lutzner MA, Festoff BW and Coon

HG (1974) Xeroderma pigmentosum: An inherited disease

with sun-sensitivity, multiple cutaneous neoplasms, and ab

normal DNA repair. Ann Internal Med 80:221-248.

Sale JE, Lehmann AR and Woodgate R (2012) Y-family DNA

polymerases and their role in tolerance of cellular DNA

damage. Nat Rev Mol Cell Biol 13:141-152.

Sale JE (2013) Translesion DNA synthesis and mutagenesis in

eukaryotes. Cold Spring Harb Perspect Biol 5:a012708.

Scheibye-Knudsen M, Ramamoorthy M, Sykora P, Maynard S,

Lin PC, Minor RK, Wilson 3rd DM, Cooper M, Spencer R,

de Cabo R, et al. (2012) Cockayne syndrome group B pro

tein prevents the accumulation of damaged mitochondria by

promoting mitochondrial autophagy. J Exp Med 209:855-

869.

Schmickel RD, Chu EH, Trosko JE and Chang CC (1977)

Cockayne syndrome: A cellular sensitivity to ultraviolet

light. Pediatrics 60:135-139.

Schuch AP, Yagura T, Makita K, Yamamoto H, Schuch NJ,

Agnez-Lima LF, Macmahon RM and Menck CF (2012)

DNA damage profiles induced by sunlight at different lati

tudes. Environ Mol Mutagen 53:98-206.

232 DNA repair avoids cancer and aging

Schuch AP, Garcia CCM, Makita K and Menck CF (2013) DNA

damage as a biological sensor for environmental sunlight.

Photochem Photobiol Sci 12:1259-1272.

Schwertman P, Lagarou A, Dekkers DH, Raams A, van der Hoek

AC, Laffeber C, Hoeijmakers JH, Demmers JA, Fousteri M,

Vermeulen W, et al. (2012) UV-sensitive syndrome protein

UVSSA recruits USP7 to regulate transcription-coupled re

pair. Nat Genet 44:598-602.

Sepe S, Payan-Gomez C, Milanese C, Hoeijmakers JH and Mas

troberardino PG (2013) Nucleotide excision repair in

chronic neurodegenerative diseases. DNA Repair 12:568-

577.

Shiloh Y and Ziv Y (2013) The ATM protein kinase: Regulating

the cellular response to genotoxic stress, and more. Nat Rev

Mol Cell Biol 14:197-210.

Soltys DT, Rocha CR, Lerner LK, de Souza TA, Munford V,

Cabral F, Nardo T, Stefanini M, Sarasin A, Cabral-Neto JB,

et al. (2013) Novel XPG (ERCC5) mutations affect DNA re

pair and cell survival after ultraviolet but not oxidative

stress. Hum Mutat 34:481-489.

Soufir N, Ged C, Bourillon A, Austerlitz F, Chemin C, Stary A,

Armier J, Pham D, Khadir K, Roume J, et al. (2010) A prev

alent mutation with founder effect in xeroderma pigmen

tosum group C from north Africa. J Invest Dermatol

130:1537-1542.

Spivak G (2005) UV-sensitive syndrome. Mutat Res 577:162-

169.

Spivak G and Hanawalt PC (2006) Host cell reactivation of

plasmids containing oxidative DNA lesions is defective in

Cockayne syndrome but normal in UV-sensitive syndrome

fibroblasts. DNA Repair 5:13-22.

Stefanini M, Botta E, Lanzafame M and Orioli D (2010) Tricho-

thiodystrophy: From basic mechanisms to clinical implica-

tions. DNA Repair 9:2-10.

Stevnsner T, Nyaga S, de Souza-Pinto NC, van der Horst GT,

Gorgels TG, Hogue BA, Thorslund T and Bohr VA (2002)

Mitochondrial repair of 8-oxoguanine is deficient in

Cockayne syndrome group B. Oncogene 21:8675-8682.

Suzumura H and Arisaka O (2010) Cerebro-oculo-facio-skeletal

syndrome. Adv Exp Med Biol 685:210-214.

Tuo J, Müftüoglu M, Chen C, Jaruga P, Selzer RR, Brosh Jr RM,

Rodriguez H, Dizdaroglu M and Bohr VA (2001) The

Cockayne Syndrome group B gene product is involved in

general genome base excision repair of 8-hydroxyguanine in

DNA. J Biol Chem 276:45772-45779.

Tuo J, Jaruga P, Rodriguez H, Bohr VA and Dizdaroglu M (2003)

Primary fibroblasts of Cockayne syndrome patients are de

fective in cellular repair of 8-hydroxyguanine and 8-hydro

xyadenine resulting from oxidative stress. FASEB J

17:668-674.

van der Horst GT, van Steeg H, Berg RJ, van Gool AJ, de Wit J,

Weeda G, Morreau H, Beems RB, van Kreijl CF, de Gruijl

FR, et al. (1997) Defective transcription-coupled repair in

Cockayne syndrome B mice is associated with skin cancer

predisposition. Cell 89:425-435.

van der Horst GT, Meira L, Gorgels TG, de Wit J, Velasco-Miguel

S, Richardson JA, Kamp Y, Vreeswijk MP, Smit B,

Bootsma D, et al. (2002) UVB radiation-induced cancer pre

disposition in Cockayne syndrome group A (CSA) mutant

mice. DNA Repair 1:143-157.

van Steeg H and Kraemer KH (1999) Xeroderma pigmentosum

and the role of UV-induced DNA damage in skin cancer.

Mol Med Today 52:86-94.

Vélez-Cruz R and Egly JM (2013) Cockayne syndrome group B

(CSB) protein: At the crossroads of transcriptional net

works. Mech Ageing Dev 134:234-242.

Venema J, Mullenders LH, Natarajan AT, van Zeeland AA and

Mayne LV (1990) The genetic defect in Cockayne syn-

drome is associated with a defect in repair of UV-induced

DNA damage in transcriptionally active DNA. Proc Natl

Acad Sci USA 87:4707-4711.

Vreeswijk MP, Overkamp MW, Westland BE, van Hees-

Stuivenberg S, Vrieling H, Zdzienicka MZ, van Zeeland AA

and Mullenders LH (1998) Enhanced UV-induced mutagen-

esis in the UV61 cell line, the Chinese hamster homologue

of Cockayne’s syndrome B, is associated with defective

transcription coupled repair of cyclobutane pyrimidine

dimers. Mutat Res 409:49-56.

Zhang X, Horibata K, Saijo M, Ishigami C, Ukai A, Kanno S,

Tahara H, Neilan EG, Honma M, Nohmi T, et al. (2012)

Mutations in UVSSA cause UV-sensitive syndrome and

destabilize ERCC6 in transcription-coupled DNA repair.

Nat Genet 44:593-597.

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