The Molecular Basis of Senp2 in Regulating Smad4 Sumoylation and Its Functions in Triple Negative Breast Cancer

Transforming growth factor-beta (TGF-beta) regulates multi-cellular functions, including cell differentiation, proliferation, migration and apoptosis. Among the TGF-beta signaling transducers, Smad4, a common-mediator Smad, plays a central role in forming complexes with receptor-phosphorylated Smads for transducing the signal into the nucleus. In the past decade, several studies indicate that TGF-beta signaling involves in epithelial-to-mesenchymal transition (EMT) and associates with tumor stem-like properties induction. While many cellular factors regulate the cancer stem-like cell progression, very little is known about the mechanism underlying the role of Smads in TGF-beta elicits prooncogenic response. Previously, our studies focused on the regulation and role of post-translational modification Smad4. We found that Sentrin-specific protease 2 (SENP2) interacts with Smad4, deSUMOylates Smad4, and relieves the Daxx mediated TGF-beta transcriptional repression via the specific motif interaction manner. In addition, this regulation increases MMP-9 protein level and further alters the TGF-beta-induced cell migration. Recently, we found that the protein level of SENP2, Smad4 and MMP-9 was increased and the modification of Smad4 was decreased in MDA-MB-231 sphere cells. Our preliminary data led us to hypothesize that SENP2 deSUMOylates Smad4, prevents Smad4 from ubiquitination-dependent degradation, propagates the TGF-beta signaling and promotes the CSCs formation in triple negative breast cancer. In this proposal, we will determine the roles of Smad4 SUMOylation and protease activity of SENP2 in breast cancer stem cell development. In addition, we will investigate the molecular mechanism of the TGF-beta-mediated pathway regulated by SENP2 in breast cancer progression. Furthermore, we will further characterize whether SENP2 regulates TGF-beta-induced tumor formation with xenograft mice model and tissue array. Moreover, the inhibition potential of SENP2 block peptide and inhibitor in regulating TGF-beta induced cancer formation will be evaluated. Altogether, our proposed studies will not only determine how SUMO protease regulates substrate for desumoylation but also elucidate a possible regulatory mechanism of SUMO protease in TGF-beta signaling-induced cancer progression.