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(Arteriosclerosis, Thrombosis, and Vascular Biology. 2009;29:99.)
© 2009 American Heart Association, Inc.

Cell Biology/Signaling

PIAS1 Mediates TGFβ-Induced SM -Actin Gene Expression Through Inhibition of KLF4 Function-Expression by Protein Sumoylation

Keiko Kawai-Kowase; Takayuki Ohshima; Hiroki Matsui; Toru Tanaka; Takehisa Shimizu; Tatsuya Iso; Masashi Arai; Gary K. Owens; Masahiko Kurabayashi

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.

Correspondence to Masahiko Kurabayashi, Department of Medicine and Biological Science, Gunma University Graduate School of Medicine, 3-39-22 Showa-machi, Maebashi, Gunma, 371-8511, Japan. E-mail mkuraba{at}med.gunma-u.ac.jp

Objective— TGFβ 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 TGFβ activates SM -actin through PIAS1.

Methods and Results— An siRNA specific for PIAS1 and ubc9, an E2-ligase for sumoylation, inhibited TGFβ-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 TGFβ 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 TGFβ-induced activation of SM -actin gene expression at least in part by promoting sumoylation and degradation of the TCE repressor protein, KLF4.

We provide evidence showing that PIAS1 and ubc9, an E2-ligase for sumoylation, contributed to TGFβ-induced activation of SM -actin gene expression through a TGFβ control element which binds KLF4. We also demonstrate that PIAS1 interacted with KLF4, promoted degradation of KLF4 by protein sumoylation, and thereby inhibited KLF4-dependent repression of SM -actin promoter activity.

Key Words: transforming growth factor β • protein inhibitor of activated STAT1 • vascular smooth muscle cells • Krüppel-like factor