Differences in signal transduction between platelet-derived growth factor (PDGF) alpha and beta receptors in vascular smooth muscle cells. PDGF-BB is a potent mitogen, but PDGF-AA promotes only protein synthesis without activation of DNA synthesis.
Cultured vascular smooth muscle cells (VSMC) from spontaneously hypertensive rats express both alpha and beta isoforms of the platelet-derived growth factor (PDGF) receptors at high levels (100,000 and 240,000 sites/cell, respectively). In this cell type, PDGF-BB elicited a mitogenic response; however, PDGF-AA increased only protein synthesis without activating DNA synthesis. Protein kinase C (PKC) was activated by PDGF-AA as well as PDGF-BB with concomitant translocation from cytosol to membrane fractions. However, the hypertrophic effect of PDGF-AA was not affected by depletion of cellular PKC, whereas the mitogenic action of PDGF-BB was partially attenuated by the depletion. Following incubation with PDGF-AA or -BB, phospholipase C-gamma 1 (PLC-gamma 1) and phosphatidylinositol 3-kinase were tyrosine phosphorylated; however, the phosphorylation of Ras-GTPase-activating protein was induced only by PDGF-BB. Both PDGF isoforms resulted in a prompt and transient increase in the level of 1,2-diacylglycerol (DAG), presumably through the action of PLC-gamma 1. After returning to basal levels, the rate of DAG synthesis steadily increased for at least 15 min due to activation of phosphatidylcholine-hydrolyzing phospholipase C (PC-PLC). Incubation with PDGF-BB-activated phospholipase D (PLD) in a PKC-dependent manner resulting in the formation of phosphatidic acid (PA). PA was also formed by the sequential reactions of PC-PLC and DAG kinase in the PDGF-BB-stimulated VSMC, and these sequential reactions were not affected by PKC depletion. In contrast, PDGF-AA stimulation did not result in increased PA synthesis as neither PLD nor DAG kinase activities were affected. PA may be a significant second messenger in the activation of DNA synthesis by PDGF-BB. These results indicate that signaling mechanisms of the PDGF-alpha and -beta receptors in VSMC are distinctly different in signal transduction in VSMC and that the alpha receptor promotes cellular hypertrophy (but not hyperplasia), whereas a mitogenic response is mediated only through the beta receptor.
Inui
H
H
Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, Tennessee 37232.
Kitami
Y
Y
Tani
M
M
Kondo
T
T
Inagami
T
T
D000818:Animals; D016718:Arachidonic Acid / Q000378:metabolism; D000077214:Becaplermin; D001667:Binding, Competitive; D002478:Cells, Cultured; D004247:DNA / Q000096:biosynthesis*; D004075:Diglycerides / Q000378:metabolism; D004789:Enzyme Activation; D015870:Gene Expression; D007700:Kinetics; D008934:Mitogens / Q000494:pharmacology*; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism*; D019814:Myristic Acid; D009227:Myristic Acids / Q000378:metabolism; D010982:Platelet-Derived Growth Factor / Q000378:metabolism / Q000494:pharmacology*; D014176:Protein Biosynthesis; D011493:Protein Kinase C / Q000378:metabolism; D020574:Proto-Oncogene Proteins c-sis; D051381:Rats; D011918:Rats, Inbred SHR; D017479:Receptors, Platelet-Derived Growth Factor / Q000096:biosynthesis / Q000187:drug effects / Q000502:physiology*; D015398:Signal Transduction / Q000187:drug effects; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D010738:Type C Phospholipases / Q000378:metabolism
D004075:Diglycerides; D008934:Mitogens; D009227:Myristic Acids; D010982:Platelet-Derived Growth Factor; D020574:Proto-Oncogene Proteins c-sis; C075278:platelet-derived growth factor A; D019814:Myristic Acid; D000077214:Becaplermin; D016718:Arachidonic Acid; D004247:DNA; D017479:Receptors, Platelet-Derived Growth Factor; D011493:Protein Kinase C; D010738:Type C Phospholipases; D013755:Tetradecanoylphorbol Acetate