Multiple Gi proteins participate in nerve growth factor-induced activation of c-Jun N-terminal kinases in PC12 cells

Nerve growth factor (NGF)-mediated activation of mitogen-activated protein kinases (MAPK) is critical for differentiation and apoptosis of PC12 cells. Since NGF employs stress-activated c-Jun N-terminal kinase (JNK) to regulate both programmed cell death and neurite outgrowth of PC12 cells, we examined NGF-regulated JNK activity and the role of G(i/o) proteins. Induction of JNK phosphorylation by NGF occurred in a time- and dose-dependent manner and was partially inhibited by pertussis toxin (PTX). To discern the participation of various signaling intermediates, PC12 cells were treated with specific inhibitors prior to NGF challenge. NGF-elevated JNK activity was abolished by inhibitors of JNK, p38 MAPK, Src, JAK3 and MEK1/2. NGF-dependent JNK phosphorylation became insensitive to PTX treatment upon transient expressions of Galpha(z) or the PTX-resistant mutants of Galpha(i1-3) and Galpha(oA). Collectively, these studies indicate that NGF-dependent JNK activity may be mediated via G(i1-3) proteins, JAK3, Src, p38 MAPK and the MEK/ERK cascade.