title: JunB mediates basal- and TGFβ1-induced smooth muscle cell contractility.
abstract: Smooth muscle contraction is a dynamic process driven by acto-myosin interactions that are controlled by multiple regulatory proteins. Our studies have shown that members of the AP-1 transcription factor family control discrete behaviors of smooth muscle cells (SMC) such as growth, migration and fibrosis. However, the role of AP-1 in regulation of smooth muscle contractility is incompletely understood. In this study we show that the AP-1 family member JunB regulates contractility in visceral SMC by altering actin polymerization and myosin light chain phosphorylation. JunB levels are robustly upregulated downstream of transforming growth factor beta-1 (TGFβ1), a known inducer of SMC contractility. RNAi-mediated silencing of JunB in primary human bladder SMC (pBSMC) inhibited cell contractility under both basal and TGFβ1-stimulated conditions, as determined using gel contraction and traction force microscopy assays. JunB knockdown did not alter expression of the contractile proteins α-SMA, calponin or SM22α. However, JunB silencing decreased levels of Rho kinase (ROCK) and myosin light chain (MLC20). Moreover, JunB silencing attenuated phosphorylation of the MLC20 regulatory phosphatase subunit MYPT1 and the actin severing protein cofilin. Consistent with these changes, cells in which JunB was knocked down showed a reduction in the F:G actin ratio in response to TGFβ1. Together these findings demonstrate a novel function for JunB in regulating visceral smooth muscle cell contractility through effects on both myosin and the actin cytoskeleton.
authors: Urological Diseases Research Center, Boston Children's Hospital, Boston, Massachusetts, United States of America.
authors: Aruna
authors: A
authors: Ramachandran
authors: Samudra S
authors: SS
authors: Gangopadhyay
authors: Ramaswamy
authors: R
authors: Krishnan
authors: Sandeep A
authors: SA
authors: Ranpura
authors: Kavitha
authors: K
authors: Rajendran
authors: Sumati
authors: S
authors: Ram-Mohan
authors: Michelle
authors: M
authors: Mulone
authors: Edward M
authors: EM
authors: Gong
authors: Rosalyn M
authors: RM
authors: Adam
mesh_terms: D008841:Actin Cytoskeleton / Q000187:drug effects*; D051339:Actin Depolymerizing Factors / Q000235:genetics / Q000378:metabolism; D000199:Actins / Q000235:genetics* / Q000378:metabolism; D000818:Animals; D002135:Calcium-Binding Proteins / Q000235:genetics / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D008840:Microfilament Proteins / Q000235:genetics / Q000378:metabolism; D009119:Muscle Contraction / Q000187:drug effects; D009124:Muscle Proteins / Q000235:genetics / Q000378:metabolism; D032389:Myocytes, Smooth Muscle / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D018994:Myosin Light Chains / Q000235:genetics / Q000378:metabolism; D043263:Myosin-Light-Chain Phosphatase / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D058105:Polymerization / Q000187:drug effects; D061251:Primary Cell Culture; D034741:RNA, Small Interfering / Q000235:genetics; D051381:Rats; D015398:Signal Transduction / Q000187:drug effects; D014157:Transcription Factors / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism; D053773:Transforming Growth Factor beta1 / Q000494:pharmacology*; D001743:Urinary Bladder / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D054460:rho-Associated Kinases / Q000235:genetics / Q000378:metabolism; D000096985:Calponins
chemical_list: D051339:Actin Depolymerizing Factors; D000199:Actins; D002135:Calcium-Binding Proteins; D008840:Microfilament Proteins; D009124:Muscle Proteins; D018994:Myosin Light Chains; D043263:Myosin-Light-Chain Phosphatase; D034741:RNA, Small Interfering; D014157:Transcription Factors; D053773:Transforming Growth Factor beta1; D054460:rho-Associated Kinases; D000096985:Calponins; C541116:ACTA2 protein, human; C581727:JunB protein, human; C051615:transgelin; C490372:PPP1R12A protein, human