on May 1, 2008
Published online before print May 1, 2008, doi: 10.1161/ATVBAHA.108.166066
Submitted on March 1, 2008
Accepted on April 17, 2008
Myocardin Is Sufficient for a Smooth Muscle–Like Contractile Phenotype
Xiaochun Long ;
From the Aab Cardiovascular Research Institute (X.L., J.M.M.), and the Center for Neurodegenerative, and Vascular Brain Disorders (R.D.B., B.V.Z.), University of Rochester School of Medicine & Dentistry, NY; and the University of South Alabama College of Medicine (W.T.G.), Mobile.
* To whom correspondence should be addressed. E-mail: j.m.miano{at}rochester.edu.
Background—Myocardin (Myocd) is a strong coactivator that binds the serum response factor (SRF) transcription factor over CArG elements embedded within smooth muscle cell (SMC) and cardiac muscle cyto-contractile genes. Here, we sought to ascertain whether Myocd-mediated gene expression confers a structural and physiological cardiac or SMC phenotype.
Methods and Results—Adenoviral-mediated expression of Myocd in the BC3H1 cell line induces cardiac and SMC genes while suppressing both skeletal muscle markers and cell growth. Immunofluorescence microscopy shows that SRF and a SMC-like cyto-contractile apparatus are elevated with Myocd overexpression. A short hairpin RNA to Srf impairs BC3H1 cyto-architecture; however, cotransduction with Myocd results in complete restoration of the cyto-architecture. Electron microscopic studies demonstrate a SMC ultrastructural phenotype with no evidence for cardiac sarcomerogenesis. Biochemical and time-lapsed videomicroscopy assays reveal clear evidence for Myocd-induced SMC-like contraction.
Conclusion—Myocd is sufficient for the establishment of a SMC-like contractile phenotype.
Key words: smooth muscle • serum response factor • myocardin • contraction • knockdown