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
J. Hayakawa et al., 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, CANCER RES, 60(21), 2000, pp. 5988-5994
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.