WRN, the protein deficient in Werner syndrome, plays a critical structural role in optimizing DNA repair.
Werner syndrome (WS) predisposes patients to cancer and premature aging, owing to mutations in WRN. The WRN protein is a RECQ-like helicase and is thought to participate in DNA double-strand break (DSB) repair by non-homologous end joining (NHEJ) or homologous recombination (HR). It has been previously shown that non-homologous DNA ends develop extensive deletions during repair in WS cells, and that this WS phenotype was complemented by wild-type (wt) WRN. WRN possesses both 3' --> 5' exonuclease and 3' --> 5' helicase activities. To determine the relative contributions of each of these distinct enzymatic activities to DSB repair, we examined NHEJ and HR in WS cells (WRN-/-) complemented with either wtWRN, exonuclease-defective WRN (E-), helicase-defective WRN (H-) or exonuclease/helicase-defective WRN (E-H-). The single E-and H- mutants each partially complemented the NHEJ abnormality of WRN-/- cells. Strikingly, the E-H- double mutant complemented the WS deficiency nearly as efficiently as did wtWRN. Similarly, the double mutant complemented the moderate HR deficiency of WS cells nearly as well as did wtWRN, whereas the E- and H- single mutants increased HR to levels higher than those restored by either E-H- or wtWRN. These results suggest that balanced exonuclease and helicase activities of WRN are required for optimal HR. Moreover, WRN appears to play a structural role, independent of its enzymatic activities, in optimizing HR and efficient NHEJ repair. Another human RECQ helicase, BLM, suppressed HR but had little or no effect on NHEJ, suggesting that mammalian RECQ helicases have distinct functions that can finely regulate recombination events.
Chen
Lishan
L
Department of Pathology, University of Washington, Seattle, WA 98195-7470, USA.
Huang
Shurong
S
Lee
Lin
L
Davalos
Albert
A
Schiestl
Robert H
RH
Campisi
Judith
J
Oshima
Junko
J
D000251:Adenosine Triphosphatases / Q000235:genetics / Q000378:metabolism; D002461:Cell Line, Transformed; D016922:Cellular Senescence / Q000235:genetics*; D004247:DNA / Q000235:genetics / Q000378:metabolism; D004249:DNA Damage / Q000235:genetics; D004265:DNA Helicases / Q000172:deficiency* / Q000235:genetics / Q000378:metabolism; D004260:DNA Repair / Q000235:genetics*; D005090:Exodeoxyribonucleases / Q000235:genetics / Q000378:metabolism; D005347:Fibroblasts / Q000378:metabolism; D006801:Humans; D009154:Mutation / Q000235:genetics; D053484:RecQ Helicases; D011995:Recombination, Genetic / Q000235:genetics; D014898:Werner Syndrome / Q000201:enzymology* / Q000235:genetics* / Q000503:physiopathology; D000071657:Werner Syndrome Helicase
D004247:DNA; D005090:Exodeoxyribonucleases; D000251:Adenosine Triphosphatases; C097151:Bloom syndrome protein; D004265:DNA Helicases; D053484:RecQ Helicases; C098785:WRN protein, human; D000071657:Werner Syndrome Helicase