Cisplatin sensitivity in cAMP-dependent protein kinase mutants of Saccharomyces cerevisiae

The emergence of cisplatin resistance poses a significant problem to the tr eatment of a variety of human malignancies. Therefore, understanding the mo lecular basis of cisplatin resistance could improve the clinical effectiven ess of this anticancer agent. Recently, our laboratory has demonstrated tha t cAMP-dependent protein kinase (PKA) mutants of the Chinese hamster ovary (CHO) and the mouse adrenocortical carcinoma YI cells exhibited increased r esistance to cisplatin as well as other DNA-damaging drugs. Further studies showed that either the functional inactivation of Pk;4 or the mutation in the regulatory subunit gene may cause increased recognition of cisplatin-da maged DNA and enhanced DNA repair capacity. In this study, we evaluated the role of PKA in modulating cellular sensitivity to cisplatin in a series of PKA mutants of Saccharomyces cerevisiae. Mutants with decreased kinase act ivity resulting from a srv2 mutation showed no alterations in cisplatin sen sitivity. Complementation of TPK1 in a yeast strain containing mutant tpk1 and also tpk2 and tpk3 deletions did not significantly alter its sensitivit y to this DNA-damaging agent. Yeast transformants containing increased kina se activity resulting from overexpression of RAS2(Val19) gy TPK1 and yeast strains having increased kinase activities due to mutations in the BCY1 gen e also did not show alterations in their sensitivity to cisplatin. Therefor e, results from these studies unambiguously demonstrate that changes in PKA activity have no effect on cisplatin sensitivity in Saccharomyces cerevisi ae.