Requirement for ERK activation in cisplatin-induced apoptosis

Cisplatin activates multiple signal transduction pathways involved in coord inating cellular responses to stress, Here we demonstrate a requirement for extracellular signal-regulated protein kinase (ERK), a member of the mitog en-activated protein kinase family in mediating cisplatin-induced apoptosis of human cervical carcinoma HeLa cells. Cisplatin treatment resulted in do se- and time- dependent activation of ERK, That elevated ERK activity contr ibuted to cell death by cisplatin was supported by several observations: 1) PD98059 and U0126, chemical inhibitors of the MEK/ERK signaling pathway, p revented apoptosis; 2) pretreatment of cells with TPA, an activator of the ERK pathway, enhanced their sensitivity to cisplatin; 3) suramin, a growth factor receptor antagonist that greatly suppressed ERK activation, likewise inhibited cisplatin-induced apoptosis; and, finally, 4) HeLa cell variants selected for cisplatin resistance showed reduced activation of ERK followi ng cisplatin treatment. Cisplatin-induced apoptosis was associated with cyt ochrome c release and subsequent caspase-3 activation, both of which could be prevented by treatment with the MEK inhibitors. However, the caspase inh ibitor benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone protected HeLa cell s against apoptosis without affecting ERK activation. Taken together, our f indings suggest that ERK activation plays an active role in mediating cispl atin-induced apoptosis of HeLa cells and functions upstream of caspase acti vation to initiate the apoptotic signal.