Sphingosine 1-phosphate receptor 2 signals through leukemia-associated RhoGEF (LARG), to promote smooth muscle cell differentiation.
OBJECTIVE
The goals of this study were to identify the signaling pathway by which sphingosine 1-phosphate (S1P) activates RhoA in smooth muscle cells (SMC) and to evaluate the contribution of this pathway to the regulation of SMC phenotype.


RESULTS
Using a combination of receptor-specific agonists and antagonists we identified S1P receptor 2 (S1PR2) as the major S1P receptor subtype that regulates SMC differentiation marker gene expression. Based on the known coupling properties of S1PR2 and our demonstration that overexpression of Galpha(12) or Galpha(13) increased SMC-specific promoter activity, we next tested whether the effects of S1P in SMC were mediated by the regulator of G protein-signaling-Rho guanine exchange factors (RGS-RhoGEFs) (leukemia-associated RhoGEF [LARG], PDZ-RhoGEF [PRG], RhoGEF [p115]). Although each of the RGS-RhoGEFs enhanced actin polymerization, myocardin-related transcription factor-A nuclear localization, and SMC-specific promoter activity when overexpressed in 10T1/2 cells, LARG exhibited the most robust effect and was the only RGS-RhoGEF activated by S1P in SMC. Importantly, siRNA-mediated depletion of LARG significantly inhibited the activation of RhoA and SMC differentiation marker gene expression by S1P. Knockdown of LARG had no effect on SMC proliferation but promoted SMC migration as measured by scratch wound and transwell assays.


CONCLUSIONS
These data indicate that S1PR2-dependent activation of RhoA in SMC is mediated by LARG and that this signaling mechanism promotes the differentiated SMC phenotype.
Medlin
Matt D
MD
Department of Pathology, University of North Carolina, Chapel Hill, NC, USA.
Staus
Dean P
DP
Dubash
Adi D
AD
Taylor
Joan M
JM
Mack
Christopher P
CP
D000818:Animals; D002454:Cell Differentiation / Q000187:drug effects / Q000235:genetics; D002460:Cell Line; D002465:Cell Movement; D004789:Enzyme Activation; D044365:GTP-Binding Protein alpha Subunits, G12-G13 / Q000235:genetics / Q000378:metabolism; D020662:Guanine Nucleotide Exchange Factors / Q000235:genetics / Q000378:metabolism*; D008246:Lysophospholipids / Q000378:metabolism*; D051379:Mice; D032389:Myocytes, Smooth Muscle / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D010641:Phenotype; D034622:RNA Interference; D012333:RNA, Messenger / Q000378:metabolism; D049349:Receptors, Lysosphingolipid / Q000187:drug effects / Q000378:metabolism*; D064067:Rho Guanine Nucleotide Exchange Factors; D015398:Signal Transduction / Q000187:drug effects; D013110:Sphingosine / Q000031:analogs & derivatives* / Q000378:metabolism; D000081025:Sphingosine-1-Phosphate Receptors; D013997:Time Factors; D014158:Transcription, Genetic; D014162:Transfection; D020741:rho GTP-Binding Proteins / Q000378:metabolism*; D020742:rhoA GTP-Binding Protein
C577223:Arhgef12 protein, mouse; D020662:Guanine Nucleotide Exchange Factors; D008246:Lysophospholipids; D012333:RNA, Messenger; D049349:Receptors, Lysosphingolipid; D064067:Rho Guanine Nucleotide Exchange Factors; D000081025:Sphingosine-1-Phosphate Receptors; C533955:sphingosine-1-phosphate receptor-2, mouse; C060506:sphingosine 1-phosphate; D044365:GTP-Binding Protein alpha Subunits, G12-G13; C526380:RhoA protein, mouse; D020741:rho GTP-Binding Proteins; D020742:rhoA GTP-Binding Protein; D013110:Sphingosine