GTPase-deficient G alpha 16 and G alpha q induce PC12 cell differentiation and persistent activation of cJun NH2-terminal kinases.
Persistent stimulation of specific protein kinase pathways has been proposed as a key feature of receptor tyrosine kinases and intracellular oncoproteins that signal neuronal differentiation of rat pheochromocytoma (PC12) cells. Among the protein serine/threonine kinases identified to date, the p42/44 mitogen-activated protein (MAP) kinases have been highlighted for their potential role in signalling PC12 cell differentiation. We report here that retrovirus-mediated expression of GTPase-deficient, constitutively active forms of the heterotrimeric Gq family members, G alpha qQ209L and G alpha 16Q212L, in PC12 cells induces neuronal differentiation as indicated by neurite outgrowth and the increased expression of voltage-dependent sodium channels. Differentiation was not observed after cellular expression of GTPase-deficient forms of alpha i2 or alpha 0, indicating selectivity for the Gq family of G proteins. As predicted, overexpression of alpha qQ209L and alpha 16Q212L constitutively elevated basal phospholipase C activity approximately 10-fold in PC12 cells. Significantly, little or no p42/44 MAP kinase activity was detected in PC12 cells differentiated with alpha 16Q212L or alpha qQ209L, although these proteins were strongly activated following expression of constitutively active cRaf-1. Rather, a persistent threefold activation of the cJun NH2-terminal kinases (JNKs) was observed in PC12 cells expressing alpha qQ209L and alpha 16Q212L. This level of JNK activation was similar to that achieved with nerve growth factor, a strong inducer of PC12 cell differentiation. Supportive of a role for JNK activation in PC12 cell differentiation, retrovirus-mediated overexpression of cJun, a JNK target, in PC12 cells induced neurite outgrowth. The results define a p42/44 MAP kinase-independent mechanism for differentiation of PC12 cells and suggest that persistent activation of the JNK members of the proline-directed protein kinase family by GTPase-deficient G alpha q and G alpha 16 subunits is sufficient to induce differentiation of PC12 cells.
Heasley
L E
LE
Department of Medicine, University of Colorado Health Sciences Center, Denver 80262, USA.
Storey
B
B
Fanger
G R
GR
Butterfield
L
L
Zamarripa
J
J
Blumberg
D
D
Maue
R A
RA
D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D002454:Cell Differentiation; D004789:Enzyme Activation; D020558:GTP Phosphohydrolases / Q000172:deficiency*; D019204:GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D048031:JNK Mitogen-Activated Protein Kinases; D020928:Mitogen-Activated Protein Kinases; D016501:Neurites; D009474:Neurons / Q000166:cytology*; D016716:PC12 Cells; D016755:Proto-Oncogene Proteins c-jun / Q000096:biosynthesis / Q000235:genetics; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D011994:Recombinant Proteins / Q000378:metabolism; D012190:Retroviridae / Q000235:genetics; D015398:Signal Transduction; D015222:Sodium Channels / Q000096:biosynthesis / Q000235:genetics; D010738:Type C Phospholipases / Q000096:biosynthesis
D016755:Proto-Oncogene Proteins c-jun; D012333:RNA, Messenger; D011994:Recombinant Proteins; D015222:Sodium Channels; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D048031:JNK Mitogen-Activated Protein Kinases; D020928:Mitogen-Activated Protein Kinases; D010738:Type C Phospholipases; D020558:GTP Phosphohydrolases; D019204:GTP-Binding Proteins