BCL-2-RELATED PROTEIN EXPRESSION IN APOPTOSIS - OXIDATIVE STRESS VERSUS SERUM DEPRIVATION IN PC12 CELLS

Expression of the BCL-2 protein family members, BAX, BAK, BAD, BCL-xL, BCL-xS, and BCL-2, was measured (by western blotting using specific a ntibodies) in PC12 cells before and during apoptosis induced by - eith er H2O2 treatment or by serum deprivation and during rescue from apopt osis by nerve growth factor (NGF). H2O2-induced apoptosis, as measured by DNA fragmentation, caused: (a) a dose-dependent increase in BAX, ( b) a dose-independent increase in BAK, and (c) a dose-dependent inhibi tion of BAD expression.;By comparison, apoptosis induced by serum depr ivation resulted in a time-dependent decrease in both BAX and BAK, alo ng with a dramatic and sudden decrease in BAD expression. However, whe n PC12 cells were incubated in an apoptosis-sparing medium (i.e., NGF- supplemented serum-free medium), both BAX and BAK were increased signi ficantly, whereas BAD expression remained inhibited. BCL-xL expression was increased by H2O2 but unaffected by serum deprivation or long-ter m NGF treatment. Neither BCL-2 nor BCL-xS expression could be detected in PC12 cells under the experimental conditions tested. Our results s how that the expression of BAX, BAK, BAD, and BCL-xL is altered in a s timulus-dependent manner but cannot be used to define whether a cell w ill undergo or survive apoptosis. The similarity between changes in ex pression of BCL-2-related proteins induced by H2O2 exposure and NGF re scue could reflect activation in part of a common antioxidant pathway.