Sphingosine-1-phosphate-induced oxygen free radical generation in smooth muscle cell migration requires Galpha12/13 protein-mediated phospholipase C activation.
BACKGROUND
Sphingosine-1-phosphate (S-1-P) is a bioactive sphingolipid that stimulates the migration of vascular smooth muscle cell (VSMC) through G-protein coupled receptors; it has been shown to activate reduced nicotinamide dinucleotide phosphate hydrogen (NAD[P]H) oxidase. The role of phospholipase C (PLC) in oxygen free radical generation, and the regulation of VSMC migration in response to S-1-P, are poorly understood.


METHODS
Rat arterial VSMC were cultured in vitro. Oxygen free radical generation was measured by fluorescent redox indicator assays in response to S-1-P (0.1microM) in the presence and absence of the active PLC inhibitor (U73122; U7, 10nM) or its inactive analog U73343 (InactiveU7, 10nM). Activation of PLC was assessed by immunoprecipitation and Western blotting for the phosphorylated isozymes (beta and gamma). Small interfering (si) RNA to the G-proteins Galphai, Galphaq, and Galpha12/13 was used to downregulate specific proteins. Statistics were by one-way analysis of variance (n = 6).


RESULTS
S-1-P induced time-dependent activation of PLC-beta and PLC-gamma; PLC-beta but not PLC-gamma activation was blocked by U7 but not by InactiveU7. PLC-beta activation was Galphai-independent (not blocked by pertussis toxin, a Galphai inhibitor, or Galphai2 and Galphai3 siRNA) and Galphaq-independent (not blocked by glycoprotein [GP] 2A, a Galphaq inhibitor, or Galphaq siRNA). PLC-beta activation and cell migration was blocked by siRNA to Galpha12/13. Oxygen free radical generation induced by S-1-P, as measured by dihydroethidium staining, was significantly inhibited by U7 but not by InactiveU7. Inhibition of oxygen free radicals with the inhibitor diphenyleneiodonium resulted in decreased cell migration to S-1-P. VSMC mitogen-activated protein kinase activation and VSMC migration in response to S-1-P was inhibited by PLC- inhibition.


CONCLUSIONS
S-1-P induces oxygen free radical generation through a Galpha12/13, PLC-beta-mediated mechanism that facilitates VSMC migration. To our knowledge, this is the first description of PLC-mediated oxygen free radical generation as a mediator of S-1-P VSMC migration and illustrates the need for the definition of cell signaling to allow targeted strategies in molecular therapeutics for restenosis.
D000818:Animals; D002465:Cell Movement / Q000187:drug effects; D002478:Cells, Cultured; D004789:Enzyme Activation; D004963:Estrenes / Q000494:pharmacology; D044365:GTP-Binding Protein alpha Subunits, G12-G13 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D008246:Lysophospholipids / Q000378:metabolism*; D020935:MAP Kinase Signaling System; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D032389:Myocytes, Smooth Muscle / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D019255:NADPH Oxidases / Q000037:antagonists & inhibitors / Q000378:metabolism; D009861:Onium Compounds / Q000494:pharmacology; D037342:Pertussis Toxin / Q000494:pharmacology; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D054799:Phospholipase C beta / Q000037:antagonists & inhibitors / Q000378:metabolism*; D051966:Phospholipase C gamma / Q000378:metabolism; D010766:Phosphorylation; D011760:Pyrrolidinones / Q000494:pharmacology; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D017382:Reactive Oxygen Species / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D013110:Sphingosine / Q000031:analogs & derivatives* / Q000378:metabolism; D013997:Time Factors; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
D004963:Estrenes; D008246:Lysophospholipids; D009861:Onium Compounds; D010726:Phosphodiesterase Inhibitors; D011760:Pyrrolidinones; D034741:RNA, Small Interfering; D017382:Reactive Oxygen Species; C060229:1-(6-((3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione; C060506:sphingosine 1-phosphate; C007517:diphenyleneiodonium; D019255:NADPH Oxidases; D037342:Pertussis Toxin; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D048051:p38 Mitogen-Activated Protein Kinases; D054799:Phospholipase C beta; D051966:Phospholipase C gamma; D044365:GTP-Binding Protein alpha Subunits, G12-G13; D013110:Sphingosine