G(o)-protein alpha-subunits activate mitogen-activated protein kinase via a novel protein kinase C-dependent mechanism.
Mitogen-activated protein kinase (MAPK) is activated in response to both receptor tyrosine kinases and G-protein-coupled receptors. Recently, Gi-coupled receptors, such as the alpha 2A adrenergic receptor, were shown to mediate Ras-dependent MAPK activation via a pathway requiring G-protein beta gamma subunits (G beta gamma) and many of the same intermediates involved in receptor tyrosine kinase signaling. In contrast, Gq-coupled receptors, such as the M1 muscarinic acetylcholine receptor (M1AChR), activate MAPK via a pathway that is Ras-independent but requires the activity of protein kinase C (PKC). Here we show that, in Chinese hamster ovary cells, the M1AChR and platelet-activating factor receptor (PAFR) mediate MAPK activation via the alpha-subunit of the G(o) protein. G(o)-mediated MAPK activation was sensitive to treatment with pertussis toxin but insensitive to inhibition by a G beta gamma-sequestering peptide (beta ARK1ct). M1AChR and PAFR catalyzed G(o) alpha-subunit GTP exchange, and MAPK activation could be partially rescued by a pertussis toxin-insensitive mutant of G(o) alpha but not by similar mutants of Gi. G(o)-mediated MAPK activation was insensitive to inhibition by a dominant negative mutant of Ras (N17Ras) but was completely blocked by cellular depletion of PKC. Thus, M1AChR and PAFR, which have previously been shown to couple to Gq, are also coupled to G(o) to activate a novel PKC-dependent mitogenic signaling pathway.
van Biesen
T
T
Howard Hughes Medical Institute, Department of Medicine, Duke University Medical Center, Durham, North Carolina 27710, USA.
Hawes
B E
BE
Raymond
J R
JR
Luttrell
L M
LM
Koch
W J
WJ
Lefkowitz
R J
RJ
D000818:Animals; D016466:CHO Cells; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D002522:Chlorocebus aethiops; D006224:Cricetinae; D004789:Enzyme Activation; D046911:Macromolecular Substances; D008954:Models, Biological; D016296:Mutagenesis; D037342:Pertussis Toxin; D010980:Platelet Membrane Glycoproteins / Q000502:physiology; D011493:Protein Kinase C / Q000378:metabolism*; D020794:Receptor Protein-Tyrosine Kinases / Q000378:metabolism; D011956:Receptors, Cell Surface; D043562:Receptors, G-Protein-Coupled; D011976:Receptors, Muscarinic / Q000502:physiology; D011994:Recombinant Proteins / Q000378:metabolism; D015398:Signal Transduction; D014162:Transfection; D010566:Virulence Factors, Bordetella / Q000494:pharmacology*; D018631:ras Proteins / Q000378:metabolism
D046911:Macromolecular Substances; D010980:Platelet Membrane Glycoproteins; D011956:Receptors, Cell Surface; D043562:Receptors, G-Protein-Coupled; D011976:Receptors, Muscarinic; D011994:Recombinant Proteins; D010566:Virulence Factors, Bordetella; C039351:platelet activating factor receptor; D037342:Pertussis Toxin; D020794:Receptor Protein-Tyrosine Kinases; D011493:Protein Kinase C; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D018631:ras Proteins