Inhibition of BAD phosphorylation either at serine 112 via extracellullar signal-regulated protein kinase cascade or at serine 136 via Akt cascade sensitizes human ovarian cancer cells to cisplatin

We studied the roles of the phosphatidylinositol 3-kinase (PI-3K)-protein k inase B/Akt-BAD cascade in both cisplatin-resistant Caov-3 and -sensitive A 2780 human ovarian cancer cell lines. Treatment of both Caov-3 and A2780 ce lls with cisplatin but not with the trans-diaminodichloroplatinum (transpla tin) isomer stimulated the activation of Akt, and the PI-3K inhibitor wortm annin blocked the cisplatin-induced activation of Akt. Treatment of both Ca ov-3 and A2780 cells with cisplatin but not with the trans-diaminodichlorop latinum isomer also stimulated the phosphorylation of BAD at both the Ser-1 12 and Ser-136 sites. Whereas the phosphorylation of BAD at Ser-136 was blo cked by treatment with wortmannin, ifs phosphorylation at Ser-112, was bloc ked by a MAP/ERK kinase inhibitor, PD98059. Exogenous expression of a domin ant-negative Akt in both Caov-3 and A2780 cells decreased the cell viabilit y after treatment with cisplatin, In contrast, no sensitization to cisplati n was observed in cells expressing wild-type Akt, We further examined the r ole of BAD in the viability after cisplatin treatment using BAD mutants. Ex ogenous expression of each of the singly substituted BADS112A or BADS136A i n both Caov-3 and A2780 cells decreased the viability after treatment with cisplatin to a degree intermediate between that caused by exogenous express ion of wild-type BAD and doubly substituted BAD2SA. Cisplatin did not stimu late the phosphorylation of BAD Ser-136, but did stimulate the phosphorylat ion of BAD Ser-112 in cells expressing a dominant-negative Akt, suggesting that BAD Ser-136 but not Ser-112 was phosphorylated by Akt, Our findings su ggest that cisplatin-induced DNA damage causes the phosphorylation of both BAD Ser-112 via an extracellular signal-regulated protein kinase (ERK) casc ade and BAD Ser-136 via a PI-3K-protein kinase B/Akt cascade and that inhib ition of either of these cascades sensitizes ovarian cancer cells to cispla tin.