Roles of Ras-Erk in apoptosis of PC12 cells induced by trophic factor withdrawal or oxidative stress

To understand the role of Ras-MAPK (mitogen-activated protein kinase) in trophic factor withdrawal- and oxidative stress-induced apoptotic cell death processes, undifferentiated rat pheochromocytoma PC12 cells and a PC12 variant cell line stably expressing the Ras dominant-negative mutant (M-M17-26) were subjected to serum withdrawal in the absence or presence of H₂O ₂ treatment. The extent of cell death was analyzed by lactate dehydrogenase release, internucleosomal DNA fragmentation, and caspase-3 assays. Both serum withdrawal and H₂O₂ treatment induced apoptotic cell death in PC12 cells, and the extent of cell death was greatly enhanced in M-M17-26 cells. DNA fragmentation induced by serum withdrawal or H₂O₂ treatment was blocked completely by a general caspase inhibitor, Z-VAD-FMK. A selective MAPK kinase inhibitor, U0126, blocked the H₂O₂-induced phosphorylation of Erk1/2 (extracellular signal-regulated kinase) in PC12 cells and increased the levels of active caspase-3 in M-M17-26 under serum withdrawal or H₂O₂ treatment. In addition, the short-term H₂O₂ treatment (5-30 min) was sufficient to cause DNA fragmentation in M-M17-26 cells even though H₂O₂ was removed and cells were incubated in regular growth medium with complete serum for 24 h. However, similar, short-term H₂O₂ treatment of PC12 cells did not induce DNA fragmentation 24 h later. These results suggest that the Ras-Erk pathway is critical in mediating protection against apoptotic cell death induced by either trophic factor withdrawal or increased oxidative stress.