[图片]胰岛素信号通路

The full network is complex and can be divided into five levels: 1) activation of the insulin receptor tyrosine kinase and closely linked events; 2) phosphorylation of a family of substrate proteins; 3) interaction of the receptor and its substrates with several intermediate signaling molecules via SH2 (src homology 2) and other recognition domains; 4) activation of serine and lipid kinases, resulting in a broad range of phosphorylation-dephosphorylation events; and 5) regulation of the final biological effectors of insulin action, such as glucose transport, lipid synthesis, gene expression, and mitogenesis. The SH2 proteins link the insulin receptor substrate (IRS) proteins to a series of cascading reactions involving serine/threonine kinases and phosphatases such as the mitogen-activated protein (MAP) kinases, S6 kinases, and protein phosphatase-1A. These serine kinases act on enzymes such as glycogen synthase, transcription factors, and other proteins to produce many of the final biological effects of the hormone. In adipose tissue and muscle, insulin stimulation also increases glucose uptake by promoting translocation of an intracellular pool of glucose transporters to the plasma membrane. Exactly how this action is linked to the phosphorylation cascade is unknown, but several studies suggest that this important action of insulin, as well as most metabolic effects, is downstream of the enzyme phosphatidylinositol 3-kinase (PI 3-kinase). Other effects of insulin, such as stimulation of glycogen and lipid synthesis, occur through additional intracellular effects to stimulate the enzymes involved in these reactions. ATP—adenosine triphosphate; GAP—GTPase-activating protein; GRB2—growth-factor receptor binding protein 2; GTP—guanosine triphosphate; IGF—insulin-like growth factor; MEK—MAP-Erk kinase; SOS—son-of-seven less protein.