PDGF-mediated activation of phosphatidylinositol 3 kinase in human mesangial cells.
Platelet-derived growth factor (PDGF) stimulates mitogenesis and exerts other biologic activities in glomerular mesangial cells. The precise mechanism of PDGF-induced mitogenesis in these cells is not clear. The activation of a signal transducing enzyme, phosphatidylinositol 3 kinase (PI 3 kinase) is associated with mitogenesis. Activation of PI 3 kinase results from stimulation of tyrosine kinase and G-protein-coupled classes of receptors. The synthesis of D3 phosphorylated inositides, the products of this enzymatic reaction, in non-nucleated cells such as blood platelets is dependent upon protein kinase C activation and G-proteins. We studied the activation of PI 3 kinase in response to PDGF in human glomerular mesangial cells. Using a PI 3 kinase 85 kD subunit specific antibody, we detected mesangial cell PI 3 kinase protein as 110 and 85 kD heterodimer. PDGF stimulated PI 3 kinase activity in antiphosphotyrosine immunoprecipitates in a dose-dependent manner showing maximum activation at 12 ng/ml. The antiphosphotyrosine associated PI 3 kinase activity showed biphasic kinetics with a fast peak within two minutes followed by a second peak at 10 minutes. Antiphosphotyrosine and PI 3 kinase immunoprecipitation studies indicated the association of the 85 kD PI 3 kinase subunit with PDGFR. Direct immunoprecipitation with PDGFR beta antibody showed the association of PI 3 kinase activity with the PDGF-receptor. The isoquinoline sulfonyl piperazine compound H7 at concentrations that inhibit PDGF-stimulated PKC activity had no effect on PDGF-stimulated PI 3 kinase activity in antiphospotyrosine immunoprecipitates. These data indicate that PI3 kinase activation is insensitive to PKC. Treatment of mesangial cells with pertussis toxin at concentrations that partially inhibited PDGF-induced DNA synthesis in human mesangial cells did not inhibit PDGF-induced PI 3 kinase activation. These data indicate that PDGF activates PI 3 kinase in mesangial cells and that pertussis toxin-sensitive G-proteins are not involved in PI 3 kinase activation. The data further dissociate activation of PI 3 kinase from mitogenesis in human mesangial cells.
Choudhury
G G
GG
Department of Medicine, University of Texas Health Science Center, San Antonio.
Biswas
P
P
Grandaliano
G
G
Fouqueray
B
B
Harvey
S A
SA
Abboud
H E
HE
D002478:Cells, Cultured; D002851:Chromatography, High Pressure Liquid; D004247:DNA / Q000096:biosynthesis; D004305:Dose-Response Relationship, Drug; D004591:Electrophoresis, Polyacrylamide Gel; D004789:Enzyme Activation / Q000187:drug effects; D019204:GTP-Binding Proteins / Q000378:metabolism; D005920:Glomerular Mesangium / Q000187:drug effects / Q000201:enzymology*; D006801:Humans; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism*; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology*; D011233:Precipitin Tests; D011493:Protein Kinase C / Q000378:metabolism; D017479:Receptors, Platelet-Derived Growth Factor / Q000378:metabolism
D010982:Platelet-Derived Growth Factor; D004247:DNA; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor); D017479:Receptors, Platelet-Derived Growth Factor; D011493:Protein Kinase C; D019204:GTP-Binding Proteins