06.10.2013 Views

View PDF Version - RePub - Erasmus Universiteit Rotterdam

View PDF Version - RePub - Erasmus Universiteit Rotterdam

View PDF Version - RePub - Erasmus Universiteit Rotterdam

SHOW MORE
SHOW LESS

Create successful ePaper yourself

Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.

section, the phenotype of several of the NER-deficient mice is described, paying<br />

special attention to the role of endogenous DNA damage in the onset of some of the<br />

pathologic symptoms.<br />

ERCCl, premature aging and the stress response<br />

The ERCCI gene was the first human NER gene to be isolated via an NERdeficient<br />

Chinese hamster cell mutant as recipient for transfection cloning [31]. In<br />

contTast to other human NER genes cloned following the same strategy, subsequent<br />

studies excluded that ERCCI is involved in any known complementation group of<br />

the three human NER syndromes. This suggests that mutations in this gene are<br />

either very rare, lethal or induce an unexpected phenotype. The EReC I protein<br />

complexes with the XPF product and the resulting heterodimer has a stmcturespecific<br />

endonuclease activity incising the 3'-extending single strand at a double<br />

strand to single strand transition in DNA [32]. In the NER reaction mechanism this<br />

corresponds with the 5' incision of the damaged strand. In addition to NER, the<br />

ERCC lIXPF complex has a function in a mitotic recombination process that<br />

presumably is responsible for repair of intrastrand crosslinks. Chinese hamster<br />

ERCCI and ERCC4 (XPF) mutants are uniquely hypersensitive to DNA<br />

crosslinking agents such as mitomycin C (MMC) [33] and ERCCI-deficient mouse<br />

embryonic stern (ES) cells cany a defect in gene targeting by homologous<br />

recombination when the targeting constmct harbors heterologous ends (G. Weed a,<br />

unpublished observation). Similarly, MEFs isolated from ERCCI knockout mice<br />

Table II. Presumed or established involvement of NER proteins in diverse cellular processes<br />

NER compollell!<br />

TFI!I-I, CSB, CSA<br />

eSB, CSA, XPG (TfllH)<br />

[{]lA, PCNA, DNA poJymerases, ligase I<br />

RAD23a!b<br />

ERCCIIXPF<br />

Process<br />

Basal Transcription, Cell Cycle Regulation<br />

l3ase Excision Repair<br />

Replication<br />

Ubiquitination<br />

Cross Link Repair! Mitotic Recombination<br />

displayed besides a complete NER defect also sensitivity to crosslinking agents and<br />

an enhanced spontaneous and induced mutation rate [34]. Weeda et al reported that<br />

ERCCI MEFs display premature cellular senescence, with large polyploid nuclei in<br />

early passages, and many non-cycling cells [8]. Interestingly, neither established<br />

ERCCI-deficient hamster cells, nor ERCCI-/- ES cells (Weeda, unpublished data)<br />

display this phenotype, suggesting a relation between mortallimrnortal status of the<br />

cell. Premature cellular senescence is also not observed in any of the MEFs of the<br />

other NER mouse models analyzed (J. de Wit, unpublished data). Life span of<br />

ERCCI homozygote mouse mutants is strongly reduced. Two independent studies<br />

NER-deficient mouse models 37

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!