Elucidating the Molecular Mechanisms of Mig6-Induced Apoptosis during Glucolipotoxicity

Presentation Number: LB MON 75
Date of Presentation: April 3rd, 2017

Halesha D Basavarajappa*1, Caree Carson1, Yi-Chun Chen2 and Patrick T Fueger1
1City of Hope BRI, Duarte, CA, 2University of British Columbia

Abstract

Functional beta cell mass is controlled by bidirectional changes in the size, number, and functional capacity of beta cells. In type 2 diabetes (T2D), whereas insulin resistance can be viewed as a triggering event, a loss of functional beta cell mass is required for the full development of this devastating disease. Therefore, preventing a loss of functional beta cell mass is essential for preventing T2D. We have focused our efforts on EGF receptor (EGFR) signaling because it can control cellular proliferation, survival, and repair mechanisms – all features relevant to maintaining beta cell mass – and is dampened during glucolipotoxic conditions similar to those in T2D. Interestingly, we identified that Mig6, an endogenous feedback inhibitor of EGFR (a.k.a. errfi1), is induced in both rodent islets cultured under glucolipotoxic conditions and human T2D islets. In addition, Mig6 overexpression, like GLT, promotes apoptosis in both rodent beta cell lines and islets. Thus, we hypothesized that induction of Mig6 in glucolipotoxicity (GLT) triggers apoptosis and decreases functional beta cell mass. Because Mig6 is an adapter protein and may function as a molecular scaffold, we aimed to further understand the molecular mechanisms of Mig6 by identifying post-translational modifications to and interacting partners of Mig6. We performed mass spectrometry analysis using low-level, flag-tagged Mig6 overexpression with immunoprecipitation from 832/13 beta cells cultured in normal and glucolipotoxic conditions. We detected 18 and 15 phosphorylation events under GLT and normal glucose conditions, respectively, with the predominant being on serine/threonine residues. The notable difference between GLT and normal conditions is that Y304 residue is phosphorylated under GLT. We also identified 90 unique proteins bound to Mig6 during GLT (e.g., BASP1, GPR1N1, GPR1N3, SPTBN1, and LMO7) and 21 unique proteins only bound to Mig6 during normal but not GLT conditions (e.g., NUMBL and NUMB). We speculate that Mig6 controls beta cell survival by its dynamic interaction with pro-apoptotic protein NUMB. In normal conditions, Mig6 sequesters NUMB in the cytosol, and during GLT, this interaction is disrupted, leading to redistribution of NUMB protein from cytosol to nucleus. In the nucleus, NUMB binds to and stabilizes p53, leading to beta cell apoptosis in GLT. In summary, differential interactions of Mig6 and NUMB may determine the fate of pancreatic beta cells under the stressed conditions in diabetes, and this interaction should be explored to understand beta cell death/survival.

 

Nothing to Disclose: HDB, CC, YCC, PTF