title: The RhoA/Rho kinase pathway regulates nuclear localization of serum response factor.
abstract: RhoA and its downstream target Rho kinase regulate serum response factor (SRF)-dependent skeletal and smooth muscle gene expression. We previously reported that long-term serum deprivation reduces transcription of smooth muscle contractile apparatus encoding genes, by redistributing SRF out of the nucleus. Because serum components stimulate RhoA activity, these observations suggest the hypothesis that the RhoA/Rho kinase pathway regulates SRF-dependent smooth muscle gene transcription in part by controlling SRF subcellular localization. Our present results support this hypothesis: cotransfection of cultured airway myocytes with a plasmid expressing constitutively active RhoAV14 selectively enhanced transcription from the SM22 and smooth muscle myosin heavy chain promoters and from a purely SRF-dependent promoter, but had no effect on transcription from the MSV-LTR promoter or from an AP2-dependent promoter. Conversely, inhibition of the RhoA/Rho kinase pathway by cotransfection with a plasmid expressing dominant negative RhoAN19, by cotransfection with a plasmid expressing Clostridial C3 toxin, or by incubation with the Rho kinase inhibitor, Y-27632, all selectively reduced SRF-dependent smooth muscle promoter activity. Furthermore, treatment with Y-27632 selectively reduced binding of SRF from nuclear extracts to its consensus DNA target, selectively reduced nuclear SRF protein content, and partially redistributed SRF from nucleus to cytoplasm, as revealed by quantitative immunocytochemistry. Treatment of cultured airway myocytes with latrunculin B, which reduces actin polymerization, also caused partial redistribution of SRF into the cytoplasm. Together, these results demonstrate for the first time that the RhoA/Rho kinase pathway controls smooth muscle gene transcription in differentiated smooth muscle cells, in part by regulating the subcellular localization of SRF. It is conceivable that the RhoA/Rho kinase pathway influences SRF localization through its effect on actin polymerization dynamics.
authors.affiliation: Departments of Medicine and Pediatrics, University of Chicago, Chicago, IL 60637, USA.
authors.forename: Hong Wei
authors.initials: HW
authors.lastname: Liu
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Halayko
authors.forename: Darren J
authors.initials: DJ
authors.lastname: Fernandes
authors.forename: Gregory S
authors.initials: GS
authors.lastname: Harmon
authors.forename: Joel A
authors.initials: JA
authors.lastname: McCauley
authors.forename: Pawel
authors.initials: P
authors.lastname: Kocieniewski
authors.forename: John
authors.initials: J
authors.lastname: McConville
authors.forename: Yiping
authors.initials: Y
authors.lastname: Fu
authors.forename: Sean M
authors.initials: SM
authors.lastname: Forsythe
authors.forename: Paul
authors.initials: P
authors.lastname: Kogut
authors.forename: Shashi
authors.initials: S
authors.lastname: Bellam
authors.forename: Maria
authors.initials: M
authors.lastname: Dowell
authors.forename: Jason
authors.initials: J
authors.lastname: Churchill
authors.forename: Heinte
authors.initials: H
authors.lastname: Lesso
authors.forename: Kamrouz
authors.initials: K
authors.lastname: Kassiri
authors.forename: Richard W
authors.initials: RW
authors.lastname: Mitchell
authors.forename: Marc B
authors.initials: MB
authors.lastname: Hershenson
authors.forename: Blanca
authors.initials: B
authors.lastname: Camoretti-Mercado
authors.forename: Julian
authors.initials: J
authors.lastname: Solway
mesh_terms: D021581:Active Transport, Cell Nucleus / Q000502:physiology; D000577:Amides / Q000494:pharmacology; D000818:Animals; D001427:Bacterial Toxins / Q000235:genetics; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000494:pharmacology; D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism*; D002478:Cells, Cultured; D004285:Dogs; D004791:Enzyme Inhibitors / Q000494:pharmacology; D047908:Intracellular Signaling Peptides and Proteins; D032342:Muscle Cells / Q000166:cytology / Q000378:metabolism; D009130:Muscle, Smooth / Q000502:physiology; D018995:Myosin Heavy Chains / Q000235:genetics; D011401:Promoter Regions, Genetic; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D011725:Pyridines / Q000494:pharmacology; D026362:Serum Response Factor / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D013844:Thiazoles / Q000494:pharmacology; D053778:Thiazolidines; D014132:Trachea / Q000166:cytology; D014158:Transcription, Genetic; D054460:rho-Associated Kinases; D020742:rhoA GTP-Binding Protein / Q000235:genetics / Q000378:metabolism*
chemical_list: D000577:Amides; D001427:Bacterial Toxins; D019086:Bridged Bicyclo Compounds, Heterocyclic; D004791:Enzyme Inhibitors; D047908:Intracellular Signaling Peptides and Proteins; D011725:Pyridines; D026362:Serum Response Factor; D013844:Thiazoles; D053778:Thiazolidines; C108830:Y 27632; D017346:Protein Serine-Threonine Kinases; D054460:rho-Associated Kinases; D018995:Myosin Heavy Chains; D020742:rhoA GTP-Binding Protein; C037068:latrunculin B