PI 3-kinase gamma and protein kinase C-zeta mediate RAS-independent activation of MAP kinase by a Gi protein-coupled receptor.
Receptors coupled to the inhibitory G protein Gi, such as that for lysophosphatidic acid (LPA), have been shown to activate MAP kinase through a RAS-dependent pathway. However, LPA (but not insulin) has now been shown to activate MAP kinase in a RAS-independent manner in CHO cells that overexpress a dominant-negative mutant of the guanine nucleotide exchange protein SOS (CHO-DeltaSOS cells). LPA also induced the activation of MAP kinase kinase (MEK), but not that of RAF1, in CHO-DeltaSOS cells. The RAS-independent activation of MAP kinase by LPA was blocked by inhibitors of phosphatidylinositol 3-kinase (PI3K) or by overexpression of a dominant-negative mutant of the gamma isoform of PI3K. Furthermore, LPA induced the activation of the atypical zeta isoform of protein kinase C (PKC-zeta) in CHO-DeltaSOS cells in a manner that was sensitive to wortmannin or to the dominant-negative mutant of PI3Kgamma, and overexpression of a dominant-negative mutant of PKC-zeta inhibited LPA-induced activation of MAP kinase. These observations indicate that Gi protein-coupled receptors induce activation of MEK and MAP kinase through a RAS-independent pathway that involves PI3Kgamma-dependent activation of atypical PKC-zeta.
Takeda
H
H
Second Department of Internal Medicine, Kobe University School of Medicine, Kusunoki-cho, Chuo-ku, Kobe 650-0017, Japan.
Matozaki
T
T
Takada
T
T
Noguchi
T
T
Yamao
T
T
Tsuda
M
M
Ochi
F
F
Fukunaga
K
K
Inagaki
K
K
Kasuga
M
M
D000818:Animals; D016466:CHO Cells; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D002417:Cattle; D006224:Cricetinae; D004789:Enzyme Activation / Q000187:drug effects; D019204:GTP-Binding Proteins / Q000378:metabolism*; D007328:Insulin / Q000494:pharmacology; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism*; D008246:Lysophospholipids / Q000494:pharmacology; D048369:MAP Kinase Kinase 1; D020929:Mitogen-Activated Protein Kinase Kinases; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics / Q000378:metabolism*; D011493:Protein Kinase C / Q000235:genetics / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D051381:Rats; D011956:Receptors, Cell Surface / Q000378:metabolism*; D014162:Transfection; D018631:ras Proteins / Q000378:metabolism; D000099221:Protein Kinase C zeta
D017871:Calcium-Calmodulin-Dependent Protein Kinases; D019204:GTP-Binding Proteins; D007328:Insulin; D007527:Isoenzymes; D008246:Lysophospholipids; D048369:MAP Kinase Kinase 1; D020929:Mitogen-Activated Protein Kinase Kinases; D019869:Phosphatidylinositol 3-Kinases; D011493:Protein Kinase C; D017346:Protein Serine-Threonine Kinases; D011505:Protein-Tyrosine Kinases; D011956:Receptors, Cell Surface; D018631:ras Proteins; D000099221:Protein Kinase C zeta