SUMO modification reverses inhibitory effects of smad nuclear interacting protein-1 in tgf-β responses

Abstract Smad nuclear interacting protein-1 (SNIP1) is a transcription repressor for the TGF-β and NF-κB signaling pathways through disrupting the recruitment of coactivator p300. However, it is unclear how the functions of SNIP1 in the TGF-β signaling pathway are controlled. Our present studies show that SNIP1 is covalently modified by SUMO in vitro and in vivo at three lysine sites: Lys5, Lys30 and Lys108, with Lys30 being the major SUMO modification site. SUMOylation of SNIP1 is enhanced by SUMO E3 ligases PIAS proteins and inhibited by SUMO proteases SENP1/2. Furthermore, we find that SUMOylation of SNIP1 attenuates its inhibitory effect in TGF-β signaling as SUMO-conjugated form of SNIP1 exhibits impaired ability to disrupt the formation of Smad complex and the interaction between p300 and Smads. Subsequently, SUMOylation of SNIP1 leads to the loss of SNIP1-mediated inhibition on expression of the TGF-β target genes PAI-1 and MMP2, and eventually enhances TGF-β-regulated cell migration and invasion.