FAULTY DNA-POLYMERASE DELTA EPSILON-MEDIATED EXCISION-REPAIR IN RESPONSE TO GAMMA-RADIATION OR ULTRAVIOLET-LIGHT IN P53-DEFICIENT FIBROBLAST STRAINS FROM AFFECTED MEMBERS OF A CANCER-PRONE FAMILY WITH LI-FRAUMENI SYNDROME/

Dermal fibroblast strains cultured from affected members of a cancer-p rone family with Li-Fraumeni syndrome (LFS) harbor a point mutation in one allele of the p53 tumor suppressor gene, resulting in loss of nor mal p53 function, In this study we have examined the ability of these p53-deficient strains to carry out the long-patch mode of excision rep air, mediated by DNA polymerases delta and epsilon, after exposure to Co-60 gamma radiation or far ultraviolet (UV) (chiefly 254 mm) light, Repair was monitored by incubation of the irradiated cultures in the p resence of aphidicolin (ape) or 1-beta-D-arabinofuranosylcytosine (ara C), each a specific inhibitor of long-patch repair, followed by measur ement of drug-induced DNA strand breaks (reflecting non-ligated strand incision events) by alkaline sucrose velocity sedimentation, The LFS strains displayed deficient repair capacity in response to both gamma rays and UV light. The repair anomaly in UV-irradiated LFS cultures wa s manifested not only in the overall genome, but also in the transcrip tionally active, preferentially repaired c-myc gene, Using autoradiogr aphy we also assessed unscheduled DNA synthesis (UDS) after UV irradia tion and found this conventional measure of repair replication to be d eficient in LFS strains. Moreover, both ape and araC decreased the lev el of UV-induced UDS by similar to 75% in normal cells, but each had o nly a marginal effect on LFS cells, We further demonstrated that the L FS strains are impaired in the recovery of both RNA and replicative DN A syntheses after UV treatment, two molecular anomalies of the DNA rep air deficiency disorders xeroderma pigmentosum and Cockayne's syndrome , Together these results imply a critical role for wild-type p53 prote in in DNA polymerase delta/epsilon-mediated excision repair, both the mechanism operating on the entire genome and that acting on expressed genes.