SH2B1 regulation of energy balance, body weight, and glucose metabolism

Abstract

The Src homology 2B (SH2B) family members (SH2B1, SH2B2 and SH2B3) are adaptor signaling proteins containing characteristic SH2 and PH domains. SH2B1 (also called SH2-B and PSM) and SH2B2 (also called APS) are able to form homo- or hetero-dimers via their N-terminal dimerization domains. Their C-terminal SH2 domains bind to tyrosyl phosphorylated proteins, including Janus kinase 2 (JAK2), TrkA, insulin receptors, insulin-like growth factor-1 receptors, insulin receptor substrate-1 (IRS1), and IRS2. SH2B1 enhances leptin signaling by both stimulating JAK2 activity and assembling a JAK2/IRS1/2 signaling complex. SH2B1 promotes insulin signaling by both enhancing insulin receptor catalytic activity and protecting against dephosphorylation of IRS proteins. Accordingly, genetic deletion of SH2B1 results in severe leptin resistance, insulin resistance, hyperphagia, obesity, and type 2 diabetes in mice. Neuron-specific overexpression of SH2B1β transgenes protects against diet-induced obesity and insulin resistance. SH2B1 in pancreatic β cells promotes β cell expansion and insulin secretion to counteract insulin resistance in obesity. Moreover, numerous SH2B1 mutations are genetically linked to leptin resistance, insulin resistance, obesity, and type 2 diabetes in humans. Unlike SH2B1, SH2B2 and SH2B3 are not required for the maintenance of normal energy and glucose homeostasis. The metabolic function of the SH2B family is conserved from insects to humans.

Keywords: Obesity, Type 2 diabetes, Leptin resistance, Insulin resistance, Glucose intolerance, Hypothalamus, Energy balance, Food intake, Hyperphagia, Nonalcoholic fatty liver disease

Core tip: The Src homology 2B (SH2B) family members mediate cell signaling in response to a variety of hormones, cytokines, and growth factors. In the brain, SH2B1 enhances leptin signaling and leptin’s anti-obesity action. In peripheral tissues, SH2B1 cell-autonomously enhances insulin signaling. In pancreatic islets, SH2B1 is required for compensatory β cell expansion in response to insulin resistance and β cell stress. SH2B1-deficiency results in severe leptin resistance, energy imbalance, obesity, and type 2 diabetes. SH2B1 mutations are linked to leptin resistance, insulin resistance, obesity, and type 2 diabetes in humans. Thus, SH2B1 is a critical metabolic regulator in mammals.