The adaptor protein NumbL is involved in the control of glucolipotoxicity-induced pancreatic beta cell apoptosis

Abstract

Avoiding loss of functional beta cell mass is critical for preventing or treating diabetes. Currently, the molecular mechanisms underlying beta cell death are partially understood, and there is a need to identify new targets for developing novel therapeutics to treat diabetes. Previously, our group established that Mig6, an inhibitor of EGF signaling, mediates beta cell death under diabetogenic conditions. The objective of this study was to clarify the mechanisms linking diabetogenic stimuli to beta cell death by investigating Mig6-interacting proteins. Using co-immunoprecipitation and mass spectrometry, we evaluated the binding partners of Mig6 under both normal glucose (NG) and glucolipotoxic (GLT) conditions in beta cells. We identified that Mig6 interacts dynamically with NumbL; whereas Mig6 associates with NumbL under NG, this interaction is disrupted under GLT conditions. Further, we demonstrate that siRNA-mediated suppression of NumbL expression in beta cells prevented apoptosis under GLT conditions by blocking activation of NF-{kappa}B signaling. Using co-immunoprecipitation experiments we observed that NumbLs interactions with TRAF6, a key component of NF{kappa}B signaling, are increased under GLT conditions. The interactions among Mig6, NumbL, and TRAF6 are dynamic and context-dependent. We propose a model wherein these interactions activate pro-apoptotic NF-{kappa}B signaling while blocking pro-survival EGF signaling under diabetogenic conditions, leading to beta cell apoptosis. These findings indicate that NumbL should be further investigated as a candidate anti-diabetic therapeutic target.