The ubiquitin ligase Smurf2 suppresses TGFβ-induced epithelial-mesenchymal transition in a sumoylation-regulated manner

Epithelial-mesenchymal transition (EMT) is a fundamental cellular process in epithelial tissue development, and can be reactivated in cancer contributing to tumor invasiveness and metastasis. The cytokine transforming growth factor-beta (TGF beta) is a key inducer of EMT, but the mechanisms that regulate TGF beta-induced EMT remain incompletely understood. Here, we report that knockdown of the ubiquitin ligase Smurf2 promotes the ability of TGF beta to induce EMT in a three-dimensional cell culture model of NMuMG mammary epithelial cells. In other studies, we identify Smurf2 as a target of the small ubiquitin like modifier (SUMO) pathway. We find that the SUMO-E2 conjugating enzyme Ubc9 and the SUMO E3 ligase PIAS3 associate with Smurf2 and promote its sumoylation at the distinct sites of Lysines 26 and 369. The sumoylation of Smurf2 enhances its ability to induce the degradation of the TGF beta receptor and thereby suppresses EMT in NMuMG cells. Collectively, our data reveal that Smurf2 acts in a sumoylation-regulated manner to suppress TGF beta-induced EMT. These findings have significant implications for our understanding of epithelial tissue development and cancer.