wow....Im not really sure what to think about this....maybe I should educate everyone in here as to what insulin IS and what it DOES...then take that same information and apply it to what the OP is asking for.
In addition to its role in regulating glucose metabolism, insulin stimulates lipogenesis, diminishes lipolysis, and increases amino acid transport into cells. Insulin also modulates transcription, altering the cell content of numerous mRNAs. It stimulates growth, DNA synthesis, and cell replication, effects that it holds in common with the insulin-like growth factors (IGFs) and relaxin.
Insulin is synthesized as a preprohormone in the β-cells of the islets of Langerhans. Its signal peptide is removed in the cisternae of the endoplasmic reticulum and it is packaged into secretory vesicles in the Golgi, folded to its native structure, and locked in this conformation by the formation of 2 disulfide bonds. Specific protease activity cleaves the center third of the molecule, which dissociates as C peptide, leaving the amino terminal B peptide disulfide bonded to the carboxy terminal A peptide.
Insulin secretion from β-cells is principally regulated by plasma glucose levels. Increased uptake of glucose by pancreatic β-cells leads to a concomitant increase in metabolism. The increase in metabolism leads to an elevation in the ATP/ADP ratio. This in turn leads to the inhibition of an ATP-sensitive potassium channel (KATP channel). The net result is a depolarization of the cell leading to Ca2+ influx and insulin secretion.
The KATP channel is a complex of 8 polypeptides comprising four copies of the protein encoded by the ABCC8 (ATP-binding cassette, sub-family C, member 8) gene and four copies of the protein encoded by the KCNJ11 (potassium inwardly-rectifying channel, subfamily J, member 11) gene. The ABCC8 encoded protein is also known as the sulfonylurea receptor (SUR). The KCNJ11 encoded protein forms the core of the KATP channel and is called Kir6.2. As might be expected, the role of KATP channels in insulin secretion presents a viable therapeutic target for treating hyperglycemia due to insulin insufficiency as is typical in type 2 diabetes.
Insulin, secreted by the β-cells of the pancreas, is directly infused via the portal vein to the liver, where it exerts profound metabolic effects. These effects are the response of the activation of the insulin receptor which belongs to the class of cell surface receptors that exhibit intrinsic tyrosine kinase activity. The insulin receptor is a heterotetramer of 2 extracellular α-subunits disulfide bonded to 2 transmembrane β-subunits. With respect to hepatic glucose homeostasis, the effects of insulin receptor activation are specific phosphorylation events that lead to an increase in the storage of glucose with a concomitant decrease in hepatic glucose release to the circulation as diagrammed below (only those responses at the level of glycogen synthase and glycogen phosphorylase are represented).
Actions of insulin-insulin receptor interactions at the level of insulin receptor substrate-1 (IRS1) and activation of the kinase cascade leading to altered activities of glycogen phosphorylase and glycogen synthase. PI3K = phosphatidylinositol-3-kinase; PIP2 = phosphatidylinositol-4,5-bisphosphate; PIP3 = phosphatidylinositol-3,4,5-bisphosphate; PDK1 = PIP3-dependent protein kinase; Tsc1 and Tsc2 = Tuberous sclerosis tumor suppressors 1 (hamartin) and 2 (tuberin); Rheb = Ras homolog enriched in brain; mTOR = mammalian target of rapamycin. PKB/Akt = protein kinase B/Akt2; GSK3 = glycogen synthase kinase-3; S6K = 70kDa ribosomal protein S6 kinase, also called p70S6K. The insulin-mediated activation of mTOR also leads to changes in protein synthesis.
Insulin-insulin receptor actions on glycogen homeostasis showing the role of protein targeting glycogen (PTG) in complexing many of the enzymes and substrates together. PTG is a subunit of PP1. Also diagrammed is the response to insulin at the level of glucose transport into cells via GLUT4 translocation to the plasma membrane. GS/GP kinase = glycogen synthase: gycogen phosphorylase kinase. PP1 = protein phosphatase-1. Arrows denote either direction of flow or positive effects, T lines represent inhibitory effects.
In most nonhepatic tissues, insulin increases glucose uptake by increasing the number of plasma membrane glucose transporters: GLUTs. Glucose transporters are in a continuous state of turnover. Increases in the plasma membrane content of GLUTs stem from an increase in the rate of recruitment of the transporters into the plasma membrane, deriving from a special pool of preformed transporters localized in the cytoplasm. GLUT1 is present in most tissues, GLUT2 is found primarily in intestine, pancreatic β-cells, kidney and liver, GLUT3 is found primarily in neurons but also found in the intestine, GLUT4 is found in insulin-responsive tissues such as heart, adipose tissue and skeletal muscle and GLUT5 is expressed in intestine, kidney, testes, skeletal muscle, adipose tissue and brain.
In liver glucose uptake is dramatically increased because of increased activity of the enzymes glucokinase, phosphofructokinase-1 (PFK-1), and pyruvate kinase (PK), the key regulatory enzymes of glycolysis. The latter effects are induced by insulin-dependent activation of phosphodiesterase, with decreased PKA activity and diminished phosphorylation of pyruvate kinase and phosphofructokinase-2, PFK-2. Dephosphorylation of pyruvate kinase increases its' activity while dephosphorylation of PFK-2 renders it active as a kinase. The kinase activity of PFK-2 converts fructose-6-phosphate into fructose-2,6-bisphosphate (F2,6BP). F2,6BP is a potent allosteric activator of the rate limiting enzyme of glycolysis, PFK-1, and an inhibitor of the gluconeogenic enzyme, fructose-1,6-bisphosphatase. In addition, phosphatases specific for the phosphorylated forms of the glycolytic enzymes increase in activity under the influence of insulin. All these events lead to conversion of the glycolytic enzymes to their active forms and consequently a significant increase in glycolysis. In addition, glucose-6-phosphatase activity is down-regulated. The net effect is an increase in the content of hepatocyte glucose and its phosphorylated derivatives, with diminished blood glucose.
In addition to the above described events,a diminished cAMP and elevated protein phosphatase activity combine to convert glycogen phosphorylase to its inactive form and glycogen synthase to its active form, with the result that not only is glucose funneled to glycolytic products, but glycogen content is increased as well.
he role of insulin in the stimulation of protein synthesis occurs at the level of translational initiation and elongation and is exerted primarily via a cascade leading to the activation of mammalian target of rapamycin, mTOR, a protein with homology to a family of proteins first identified in yeast that bind to the immunosuppressant drug, rapamycin. Rapamycin gets its name from the fact that the compound was isolated from the bacterium Streptomyces hygroscopicus discovered on Easter Island (Rapa Nui). mTOR is a kinase whose catalytic domain shares significant homology with lipid kinases of the PI3K family.
mTOR is actually a component of two distinct multiprotein complexes termed mTORC1 and mTORC2 (mTOR complex 1 and mTOR complex 2). The activity of mTORC1 is sensitive to inhibition by by rapamycin whereas mTORC2 is not. Within the context of mTOR activity, mTORC1 is the central complex as it is responsible for integrating a diverse series of signal transduction cascades initiated by changes in both intra- and extracellular events. Activation and/or regulation of mTORC1 is involved in the control of cell proliferation, survival, metabolism and stress responses. These events can be triggered by nutrient availability, glucose, oxygen, and numerous different types of cell surface receptor activation, each of which eventually impinge on the activity of mTORC1. The components of mammalian mTORC1 include mTOR, Raptor (regulatory associated protein of TOR), Deptor (DEP domain containing mTOR-interacting protein), mLST8 (mammalian homolog of yeast LST8), and PRAS40 (proline-rich Akt/PKB substrate of 40kDa). Deptor and PRAS40 are inhibitors of mTOR activity within the complex. PRAS40 is a raptor-binding protein that is directly phosphorylated by mTOR, which then prevents PRAS40 inhibition of mTOR.
The components of mammalian mTORC2 include mTOR, Deptor, mLST8, Sin1, Poctor (protein observed with Rictor; also known as PRR5L for proline-rich 5-like protein), and Rictor (rapamycin-insensitive companion of mTOR). mTORC2 is involved in the control of the activity of serum- and glucocorticoid-induced kinase (SGK). Full activation of Akt/PKB requires the involvement of mTORC2.