CISPLATIN RESISTANCE AND REGULATION OF DNA-REPAIR IN CAMP-DEPENDENT PROTEIN-KINASE MUTANTS

Drug resistance in cancer poses a major problem to the success of chem otherapy. Increased resistance to the DNA-damaging chemotherapeutic dr ug cisplatin may be associated with a variety of factors including dec reased drug accumulation, increased intracellular levels of thiols, an d increased DNA repair, We have found that mutants of the Chinese hams ter ovary (CHO) and the mouse adrenocortical carcinoma Y1 cells harbor ing a defective regulatory subunit (RI) of the cAMP-dependent protein kinase (PKA) exhibited increased resistance to cisplatin, These mutant s are cross-resistant to other DNA-damaging chemotherapeutic agents, i ncluding bleomycin and melphalan, In addition, wild-type CHO cells tra nsfected with and overexpressing the yeast phosphodiesterase gene or a dominant mutant RI alpha subunit gene also displayed similar increase d resistance to cisplatin, However, mutants with altered catalytic (C) subunits showed a sensitivity to cisplatin similar to the wild-type c ells. Further analysis by gel shift assay using cisplatin-damaged DNA as probes and nuclear extracts derived from the RI subunit mutants sho wed increased binding of nuclear factor(s) to the damaged DNA, In addi tion, a host cell reactivation assay of DNA repair, using a cisplatin- damaged reporter plasmid, detected enhanced capacity for repair of DNA lesions in the PKA mutants, These results suggest that DNA repair may be increased in the PKA mutants, We speculate that functional inactiv ation of PKA may result in increased DNA repair and the acquisition of resistance to DNA-damaging anticancer drugs in cancer.