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Replication of damaged DNA: molecular defect in xeroderma pigmentosum variant cells
1UPR9003 du CNRS, Cancérogenèse et Mutagenèse Moléculaire et Structurale, ESBS et IRCAD, Strasbourg, France.
Abstract:
Individuals with Xeroderma pigmentosum (XP) syndrome have a genetic predisposition to sunlight-induced skin cancer. Genetically different forms of XP have been identified by cell fusion. Cells of individuals expressing the classical form of XP (complementation groups A through G) are deficient in the nucleotide excision repair (NER) pathway. In contrast, the cells belonging to the variant class of XP (XPV) are NER-proficient and are only slightly more sensitive than normal cells to the killing action of UV light radiation. The XPV fibroblasts replicate damaged DNA generating abnormally short fragments either in vivo [A.R. Lehmann, The relationship between pyramidine dimers and replicating DNA in UV-irradiated human fibroblasts, Nucleic Acids Res. 7 (1979) 1901-1912; S.D. Park, J.E. Cleaver, Postreplication repair: question of its definition and possible alteration in Xeroderma pigmentosum cell strains, Proc. Natl. Acad. Sci. U.S.A. 76 (1979) 3927-3931.] or in vitro [S.M. Cordeiro, L.S. Zaritskaya, L.K. Price, W.K. Kaufmann, Replication fork bypass of a pyramidine dimer blocking leading strand DNA synthesis, J. Biol. Chem. 272 (1997) 13945-13954; D.L. Svoboda, L.P. Briley, J.M. Vos, Defective bypass replication of a leading strand cyclobutane thymine dimer in Xeroderma pigmentosum variant cell extracts, Cancer Res. 58 (1998) 2445-2448; I. Ensch-Simon, P.M. Burgers, J.S. Taylor, Bypass of a site-specific cis-syn thymine dimer in an SV40 vector during in vitro replication by HeLa and XPV cell-free extracts, Biochemistry 37 (1998) 8218-8226.], suggesting that in XPV cells, replication has an increased probability of being blocked at a lesion. Furthermore, extracts from XPV cells were found to be defective in translesion synthesis [A. Cordonnier, A.R. Lehmann, R.P.P. Fuchs, Impaired translesion synthesis in Xeroderma pigmentosum variant extracts, Mol. Cell. Biol. 19 (1999) 2206-2211.]. Recently, Masutani et al. [C. Masutani, M. Araki, A. Yamada, R. Kusomoto, T. Nogimori, T. Maekawa, S. Iwai, F. Hanaoka, Xeroderma pigmentosum variant (XP-V) correcting protein from HeLa cells has a thymine dimer bypass DNA polymerase activity, EMBO J. 18 (1999) 3491-3501.] have shown that the XPV defect can be corrected by a novel human DNA polymerase, homologue to the yeast DNA polymerase eta, which is able to replicate past cyclobutane pyrimidine dimers in DNA templates. This review focuses on our current understanding of translesion synthesis in mammalian cells whose defect, unexpectedly, is responsible for the hypermutability of XPV cells and for the XPV pathology.
Insights
Xeroderma pigmentosum variant (XPV) cells have defective translesion synthesis, leading to DNA replication issues and increased cancer risk. A novel DNA polymerase eta corrects this defect, offering insights into XPV pathology.
Area of Science:
- Molecular Biology
- Genetics
- Dermatology
Background:
- Xeroderma pigmentosum (XP) syndrome confers a genetic predisposition to sunlight-induced skin cancer.
- Classical XP (groups A-G) involves nucleotide excision repair (NER) deficiency.
- Xeroderma pigmentosum variant (XPV) cells are NER-proficient but exhibit unique DNA replication defects.
Purpose of the Study:
- To review the understanding of translesion synthesis (TLS) in mammalian cells.
- To elucidate the role of TLS defects in XPV cell hypermutability and pathology.
- To highlight the function of DNA polymerase eta in correcting XPV defects.
Main Methods:
- Cell fusion studies to identify different XP complementation groups.
- Analysis of DNA replication and repair mechanisms in XPV fibroblasts.
- In vitro replication assays using cell-free extracts.
- Identification and characterization of novel DNA polymerases.
Main Results:
- XPV cells replicate damaged DNA, generating abnormally short fragments.
- XPV cell extracts show defects in translesion synthesis.
- A novel human DNA polymerase eta corrects the XPV defect by bypassing DNA lesions.
Conclusions:
- Defective translesion synthesis is responsible for the hypermutability and pathology of XPV.
- DNA polymerase eta plays a crucial role in bypassing DNA damage during replication.
- Understanding TLS in XPV provides insights into DNA repair and cancer development.