Nonalcoholic fatty liver disease (NAFLD) is a risk factor for type 2 diabetes (T2D), but whether NAFLD plays a causal role in the pathogenesis of T2D is uncertain. One proposed mechanism linking NAFLD to hepatic insulin resistance involves diacylglycerol-mediated (DAG-mediated) activation of protein kinase C-ε (PKCε) and the consequent inhibition of insulin receptor (INSR) kinase activity. However, the molecular mechanism underlying PKCε inhibition of INSR kinase activity is unknown. Here, we used mass spectrometry to identify the phosphorylation site Thr1160 as a PKCε substrate in the functionally critical INSR kinase activation loop. We hypothesized that Thr1160 phosphorylation impairs INSR kinase activity by destabilizing the active configuration of the INSR kinase, and our results confirmed this prediction by demonstrating severely impaired INSR kinase activity in phosphomimetic T1160E mutants. Conversely, the INSR T1160A mutant was not inhibited by PKCε in vitro. Furthermore, mice with a threonine-to-alanine mutation at the homologous residue Thr1150 (
Max C. Petersen, Anila K. Madiraju, Brandon M. Gassaway, Michael Marcel, Ali R. Nasiri, Gina Butrico, Melissa J. Marcucci, Dongyan Zhang, Abudukadier Abulizi, Xian-Man Zhang, William Philbrick, Stevan R. Hubbard, Michael J. Jurczak, Varman T. Samuel, Jesse Rinehart, Gerald I. Shulman
PKCε phosphorylates the INSR at Thr1160.