p38 MAP kinase mediates apoptosis through phosphorylation of Bim _EL at Ser-65

The stress-activated c-Jun N-terminal protein kinase (JNK) and p38 mitogen-activated protein (MAP) kinase (p38) regulate apoptosis induced by several forms of cellular insults. Potential targets for these kinases include members of the Bcl-2 family proteins, which mediate apoptosis generated through the mitochondria-initiated, intrinsic cell death pathway. Indeed, the activities of several Bcl-2 family proteins, both pro- and antiapoptotic, are controlled by JNK phosphorylation. For example, the pro-apoptotic activity of Bim _EL, a member of the Bcl-2 family, is stimulated by JNK phosphorylation at Ser-65. In contrast, there is no reported evidence that p38-induced apoptosis is due to direct phosphorylation of Bcl-2 family proteins. Here we report evidence that sodium arsenite-induced apoptosis in PC12 cells may be due to direct phosphorylation of Bim_EL at Ser-65 by p38. This conclusion is supported by data showing that ectopic expression of a wild type, but not a non-phosphorylatable S65A mutant of Bim_EL, potentiates sodium arsenite-induced apoptosis and by experiments showing direct phosphorylation of Bim_EL at Ser-65 by p38 in vitro. Furthermore, sodium arsenite induced Bim_EL phosphorylation at Ser-65, which was blocked by p38 inhibition. This study provides the first example whereby p38 induces apoptosis by phosphorylating a member of the Bcl-2 family and illustrates that phosphorylation of Bim_EL on Ser-65 may be a common regulatory point for cell death induced by both JNK and p38 pathways.