Title: the Ring Domain of Piasy Is Involved in the Suppression of Bone Morphogenetic Protein-signaling Pathway Running Title: Regulation of Bmp Signaling by Piasy

Bone morphogenetic proteins (BMPs) play central roles in differentiation, development, and physiologic tissue remodeling. Recently, we have demonstrated that a protein inhibitor of activated STAT, PIASy suppresses TGF-b signaling by interacting with Sma and MADrelated protein 3 (Smad3). In this study, we examined a PIASy dependent inhibitory effect on BMP signaling. PIASy expression was induced by BMP-2 stimulation and suppressed BMP2-dependent Smad activity in hepatoma cells. Furthermore, BMP-2-regulated Smads directly bound to PIASy. We also demonstrated that the RING domain of PIASy played an important role in PIASy-mediated suppression of Smad activity. We here provide evidence that the inhibitory action of PIASy on BMP-regulated Smad activity was due to direct physical interactions between Smads and PIASy through its RING domain.