Role of apoptosis signal-regulating kinase in regulation of the c-Jun N-terminal kinase pathway and apoptosis in sympathetic neurons

We have previously shown that nerve growth factor (NGF) withdrawal-induced death requires the activity of the small GTP-binding protein Cdc42 and that overexpression of an active form of Cdc42 is sufficient to mediate neurona l apoptosis via activation of the c-Jun pathway. Recently, a new mitogen-ac tivated protein (MAP) kinase kinase kinase, apoptosis signal-regulating kin ase 1 (ASK1) which activates both the c-Jun N-terminal kinase (JNK) and p38 MAP kinase pathways and plays pivotal roles in tumor necrosis factor- and Fas-induced apoptosis, has been identified. Therefore, we investigated the role of ASK1 in neuronal apoptosis by using rat pheochromocytoma (PC12) neu ronal cells and primary rat sympathetic neurons (SCGs). Overexpression of A SK1-Delta N, a constitutively active mutant of ASK1, activated JNK and indu ced apoptosis in differentiated PC12 cells and SCG neurons. Moreover, in di fferentiated PC12 cells, NGF withdrawal induced a four- to fivefold increas e in the activity of endogenous ASK1, Finally, expression of a kinase-inact ive ASK1 significantly blocked both NGF withdrawal- and Cdc42-induced death and activation of c-jun. Taken together, these results demonstrate that AS K1 is a crucial element of NGF withdrawal-induced activation of the Cdc42-c -Jun pathway and neuronal apoptosis.