on October 16, 2008
Published online before print October 16, 2008, doi: 10.1161/ATVBAHA.108.172700
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Submitted on October 9, 2007
Accepted on October 3, 2008
PIAS1 Mediates TGF
-Induced SM 
-Actin Gene Expression Through Inhibition of KLF4 Function-Expression by Protein Sumoylation
Keiko Kawai-Kowase ;
From the Department of Medicine and Biological Science (K.K.-K., H.M., T.T., T.S., T.I., M.A., M.K.), Gunma University Graduate School of Medicine, Japan; the Laboratory of Pharmaceutical Sciences (T.O.), Tokushima Bunri University, Kagawa School of Pharmaceutical Sciences, Japan; and the Department of Molecular Physiology and Biological Physics (G.K.O.), University of Virginia School of Medicine, Charlottesville.
* To whom correspondence should be addressed. E-mail: mkuraba{at}med.gunma-u.ac.jp.
Objective—TGF
and proliferation/phenotypic switching of smooth muscle cells (SMCs) play a pivotal role in pathogenesis of atherosclerotic and restenotic lesions after angioplasty. We have previously shown that the protein inhibitor of activated STAT (PIAS)1 activates expression of SMC differentiation marker genes including smooth muscle (SM) 
-actin by interacting with serum response factor (SRF) and class I bHLH proteins. Here, we tested the hypothesis that TGF activates SM -actin through PIAS1.
Methods and Results—An siRNA specific for PIAS1 and ubc9, an E2-ligase for sumoylation, inhibited TGF-induced expression of SM -actin in cultured SMCs as determined by real-time RT-PCR. Overexpression of PIAS1 increased SM -actin promoter activity in a TGF control element (TCE)-dependent manner. Because the TCE within the SM -actin promoter could mediate repression through interaction with KLF4, we tested whether PIAS1 regulates the function of KLF4 for SMC gene expression. PIAS1 interacted with KLF4 in mammalian two-hybrid and coimmunoprecipitation assays, and overexpression of PIAS1 inhibited KLF4-repression of SM -actin promoter activity. Moreover, PIAS1 promoted degradation of KLF4 through sumoylation.
Conclusions—These results provide evidence that PIAS1 promotes TGF-induced activation of SM -actin gene expression at least in part by promoting sumoylation and degradation of the TCE repressor protein, KLF4.