Multiple roles of insulin. When insulin binds to its receptor it triggers receptor autophosphorylation that generates docking sites for insulin receptor substrate proteins (IRS-1–IRS4). IRS proteins in turn trigger the activation of a wide array of signal transducing proteins (highly simplified in this Figure). The end results of insulin receptor activation are varied and in many cases cell-type specific but includes alterations in metabolism, ion fluxes, protein translocation, transcription rates, and growth properties of responsive cells. Arrows represent positive, activating functions. T-lines represent inhibitory functions. Most abbreviations are described within the text below. PDE3B = phosphodiesterase 3B (also called adipocyte cAMP phosphodiesterase), GS = glycogen synthase, HSL = hormone sensitive lipase, ACC = acetyl-CoA carboxylase, ACL = ATP-citrate lyase.
