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1. ratio. RLIP76 was induced by oxidative or hyperglycemic stress; the concomitant increase in insulin endocytosis was completely abrogated by inhibiting the transport activity of RLIP76. Hydrocortisone could transiently correct hypoglycemia in RLIP76/animals, despite inhibited activity of key glucocorticoid-regulated hepatic gluconeogenic enzymes, phosphoenolpyruvate carboxykinase, glucose-6-phosphatase, and fructose 1,6-bisphosphatase, in RLIP76/. == CONCLUSIONS == The GS-E conjugate transport activity of RLIP76 mediates insulin resistance by enhancing the rate of clathrin-dependent Rabbit Polyclonal to TUSC3 endocytosis of insulin. Because RLIP76 is induced by oxidative stress, it could play a role in insulin resistance seen in pathological conditions characterized by increased oxidative stress. Oxidative stress is Capsaicin implicated in chronic diseases (14) including insulin resistance that leads to type 2 diabetes (58). Pancreatic -cells are relatively susceptible to the damaging effects of free radicals because of low levels of free radical quenching enzymes including catalase, glutathione peroxidase, and superoxide dismutase (9). Short exposure of -cells to H2O2suppresses insulin mRNA levels and insulin secretion (10). Likewise, exposure of -cells to high glucose concentrations leads to increased intracellular free Capsaicin radical content and inhibited insulin release (11). Reactive oxygen species (ROS) generated during oxidative stress are known to activate signaling proteins including stress kinases (e.g., c-Jun NH2-terminal kinase, p38, inhibitor of B kinase) in addition to the extracellular receptor kinases that can affect the cellular response to insulin. The downregulation of insulin response under oxidant exposure involves activation of tumor necrosis factor-; increased Ser/Thr phosphorylation of insulin receptor and insulin receptor substrate-1 (IRS1) (12,13) Capsaicin reduces Capsaicin the redistribution of IRS1 and phosphatidylinositol 3 kinase from the cytosolic to microsomal fraction, reduces protein kinase-B (Akt) phosphorylation, and results in decreased trafficking of GLUT4 to the plasma membrane. Prolonged exposure to oxidative stress also affects the transcription of GLUT4 (14). In parallel with the protein signaling pathway described above, a chemical signaling pathway is activated by oxidative stress. This pathway begins with ROSs derived from oxidative degradation of polyunsaturated fatty acids, and is linked with multiple protein signaling pathways. Activation of protein kinase C and nuclear factor-B results in increased activity of NADPH oxidase (15), which amplifies oxidative stress by augmenting the recycling of Fe3+to Fe2+(16). The autocatalytic chain reaction of lipid peroxidation, where a single lipid peroxide species can lead to the formation of up to a thousand lipid peroxides, provides a built-in magnification for ROS-mediated signaling. The – and -unsaturated lipid aldehydes generated through -scission of linoleic acid, -linoleic acid, or arachidonic acid hydroperoxides play an important role in this signaling. 4-Hydroxy-t-2-nonenal (4HNE), the most abundant alkenal generated in cells, is a versatile second messenger for signaling that can affect multiple signaling pathways including those for apoptosis, differentiation, proliferation, and receptor tyrosine-kinase (RTK)mediated signaling (17,18). 4HNE controls the expression and activity of many signaling proteins involved in insulin resistance, including stress kinases, nuclear factor-B, and chaperones (19), and affects RTK signaling, thus HNE could modulate insulin signaling and glucose homeostasis. Glutathione transferases (particularly GSTA44) and RLIP76 (a 76-kDa splice variant, encoded by the human geneRALBP1) are the two major determinants of 4HNE levels in cells (20). Although 4HNE is substrate for several enzymes including aldehyde dehydrogenases, aldose reductase, and Cyt-p450, the major pathway for its disposition from cells is through its GST catalyzed conjugation to GSH (20) and subsequent ATP-dependent transport of the conjugate (GS-HNE) catalyzed by RLIP76 (21). The mechanisms for the efflux of glutathione electrophile (GS-E) conjugates are complex, involving other ABC transporters, but knockout mouse studies have shown that RLIP76 plays a dominant.