Heparin-Binding EGF-Like Growth Factor (HB-EGF) Mediates 5-HT-Induced Insulin Resistance Through Activation of EGF Receptor-ERK1/2-mTOR Pathway

Abstract

Although an inverse correlation between insulin sensitivity and the level of Gq/11-coupled receptor agonists, such as endothelin-1, thrombin, and 5-hydroxytryptamine (5-HT), has been reported, its precise mechanism remains unclear. In this report, we provide evidence that 5-HT induced production of heparin-binding epidermal growth factor-like growth factor (HB-EGF) and caused insulin resistance in 3T3-L1 adipocytes, primary adipocytes, and C2C12 myotubes. In 3T3-L1 adipocytes, 5-HT stimulated HB-EGF production by promoting metalloproteinase-dependent shedding of transmembrane protein pro-HB-EGF. HB-EGF then bound and tyrosine-phosphorylated EGF receptors, which activated the mammalian target of rapamycin pathway through ERK1/2 phosphorylation. Mammalian target of rapamycin activation caused serine phosphorylation of insulin receptor substrate-1, which attenuated insulin-stimulated tyrosine phosphorylation of insulin receptor substrate-1 and glucose uptake. Pharmacological inhibition of either Gq/11-coupled receptors or metalloproteinases, as well as either inhibition or knockdown of HB-EGF or Gαq/11, restored insulin signal transduction impaired by 5-HT. Inhibition of metalloproteinase activity also abolished HB-EGF production and subsequent EGF receptor activation by other Gq/11-coupled receptor agonists known to cause insulin resistance, such as endothelin-1 and thrombin. These results suggest that transactivation of the EGF receptor through HB-EGF processing plays a pivotal role in 5-HT-induced insulin resistance.