Myocardin is a smooth and cardiac muscle-specific transcriptional coactivator of serum response factor, and plays an important role in the differentiation of smooth muscle cells (SMCs) and cardiac development.The cellular level and activity of myocardin is tightly regulated through a number of factors.However, the molecular mechanism(s) for regulating myocardin stability and turnover remain undefined.In the present study, we investigated the effect of chaperoneassociated ubiquitin ligase C-terminus of Hsc70 interacting protein (CHIP) on myocardin protein degradation and phenotypic modulation of vascular SMCs.In SMCs transfected with CHIP, myocardin degradation increased in a dose dependent manner.Coimmunoprecipitation and GST-pull-down assays identified that myocardin and CHIP associate through the CHIP charged domain and myocardin TAD.