The Werner syndrome protein contributes to induction of p53 by DNA damage.

Mutations in the p53 tumor-suppressor gene promote increased genomic instability and cancer. Mutations in the WRN gene, encoding a DNA helicase, underlie the segmental progeroid Werner syndrome (WS). WS is also associated with increased genomic instability and elevated cancer risk. The p53 and WRN proteins can engage in direct protein-protein interactions. We report that excess WRN elicits increased cellular p53 levels and potentiates p53-mediated apoptosis. Importantly, cells derived from WS patients exhibit an attenuated and delayed induction of p53 by UV or by the topoisomerase I inhibitor camptothecin. These results suggest that WRN may participate in the activation of p53 in response to certain types of DNA damage. Furthermore, the failure to induce p53 effectively may contribute to enhanced genomic instability and elevated cancer risk in WS patients.

Physical and functional interaction between p53 and the Werner's syndrome protein.

Werner's syndrome is a human autosomal recessive disorder leading to premature aging. The mutations responsible for this disorder have recently been localized to a gene (WRN) encoding a protein that possesses DNA helicase and exonuclease activities. Patients carrying WRN gene mutations exhibit an elevated rate of cancer, accompanied by increased genomic instability. The latter features are also characteristic of the loss of function of p53, a tumor suppressor that is very frequently inactivated in human cancer. Moreover, changes in the activity of p53 have been implicated in the onset of cellular replicative senescence. We report here that the WRN protein can form a specific physical interaction with p53. This interaction involves the carboxyl-terminal part of WRN and the extreme carboxyl terminus of p53, a region that plays an important role in regulating the functional state of p53. A small fraction of WRN can be found in complex with endogenous p53 in nontransfected cells. Overexpression of WRN leads to augmented p53-dependent transcriptional activity and induction of p21(Waf1) protein expression. These findings support the existence of a cross-talk between WRN and p53, which may be important for maintaining genomic integrity and for preventing the accumulation of aberrations that can give rise to premature senescence and cancer.