Formin homology domain-containing protein 1 regulates smooth muscle cell phenotype.
OBJECTIVE
Our goal was to test whether formin homology protein 1 (FHOD1) plays a significant role in the regulation of smooth muscle cell (SMC) differentiation and, if so, whether Rho kinase (ROCK)-dependent phosphorylation in the diaphanous autoinhibitory domain is an important signaling mechanism that controls FHOD1 activity in SMC.


RESULTS
FHOD1 is highly expressed in aortic SMCs and in tissues with a significant SMC component. Exogenous expression of constitutively active FHOD1, but not wild-type, strongly activated SMC-specific gene expression in 10T1/2 cells. Treatment of SMC with the RhoA activator sphingosine-1-phosphate increased FHOD1 phosphorylation at Thr1141, and this effect was completely prevented by inhibition of ROCK with Y-27632. Phosphomimetic mutations to ROCK target residues enhanced FHOD1 activity, suggesting that phosphorylation interferes with FHOD1 autoinhibition. Importantly, knockdown of FHOD1 in SMC strongly inhibited sphingosine-1-phosphate-dependent increases in SMC differentiation marker gene expression and actin polymerization, suggesting that FHOD1 plays a major role in RhoA-dependent signaling in SMC.


CONCLUSIONS
Our results indicate that FHOD1 is a critical regulator of SMC phenotype and is regulated by ROCK-dependent phosphorylation. Thus, additional studies on the role of FHOD1 during development and the progression of cardiovascular disease will be important.
Department of Pathology and Laboratory Medicine, University of North Carolina, Chapel Hill, NC 27599-7525, USA.
Dean P
DP
Staus
Alicia L
AL
Blaker
Matt D
MD
Medlin
Joan M
JM
Taylor
Christopher P
CP
Mack
D000199:Actins / Q000378:metabolism; D000818:Animals; D002454:Cell Differentiation / Q000187:drug effects*; D002478:Cells, Cultured; D005326:Fetal Proteins / Q000235:genetics / Q000378:metabolism*; D000080865:Formins; D006801:Humans; D051379:Mice; D023421:Models, Animal; D009131:Muscle, Smooth, Vascular / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism*; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D010641:Phenotype; D010766:Phosphorylation / Q000502:physiology; D034741:RNA, Small Interfering / Q000494:pharmacology; D015398:Signal Transduction / Q000502:physiology; D014162:Transfection; D020741:rho GTP-Binding Proteins / Q000378:metabolism; D054460:rho-Associated Kinases / Q000378:metabolism; D020742:rhoA GTP-Binding Protein
D000199:Actins; C120021:FHOD1 protein, human; D005326:Fetal Proteins; D000080865:Formins; D009687:Nuclear Proteins; D034741:RNA, Small Interfering; D054460:rho-Associated Kinases; C526380:RhoA protein, mouse; D020741:rho GTP-Binding Proteins; D020742:rhoA GTP-Binding Protein