Statistical comparisons among groups were performed by One-Way ANOVA using SigmaPlot 11.0 (Systat Software inc. expression in severe insulin resistance was associated with decreased ubiquitin-conjugating enzyme 9 (UBC9) expression while expression of GLUT1, TBC1D1 and AS160 was not significantly different among type 2 diabetic patients and matched controls. == Conclusions == Type 2 diabetic patients with severe insulin resistance NU7026 have reduced expression of GLUT4 in skeletal muscle compared to patients treated with oral antidiabetic drugs alone. GLUT4 protein levels may therefore play NU7026 a role in the pathology behind type 2 diabetes mellitus among subgroups of patients, and this may Rabbit Polyclonal to NCOA7 explain the heterogeneous response to insulin treatment. This new obtaining contributes to the understanding of the underlying mechanisms for the development of extreme insulin resistance. == Introduction == Type 2 diabetic patients with extreme insulin resistance represent a major therapeutic challenge in terms of achieving glycaemic goals. Many patients require several hundred models of insulin daily, but despite large amounts of daily insulin, glycemic control remains poor, and it may be difficult to decide whether to increase insulin dosages further or regard patients as being noncompliant. It is unknown whether such patients have defects in the mechanisms that control insulin stimulated glucose uptake. Skeletal muscle is the predominant tissue for insulin stimulated glucose disposal in humans[1]. Glucose enters the muscle cell primarily by facilitated diffusion, utilizing glucose transporter carrier proteins[2]. GLUT4 is the predominantly expressed glucose transporter isoform in muscle, whereas the GLUT1 isoform is usually expressed at much lower abundance[2]. In healthy subjects, whole body glucose disposal and GLUT4 expression correlate[1]. Glucose uptake through GLUT4 is usually regulated by insulin[2]. After binding to its receptor, insulin stimulates an intracellular signaling cascade that ultimately results in the phosphorylation of the Rab-GTPase-activating proteins AS160 (TBC1D4) and TBC1D1[3]. When AS160 and TBC1D1 are phosphorylated on key residues, GLUT4 is usually released and translocates to the cell surface where it docks and fuses with the membrane[3]. After translocation to the cell surface, GLUT4 can either be recycled back to intracellular vesicles or be targeted for lysosomal degradation[4]. This process is regulated by ubiquitin-conjugating enzyme 9 (UBC9) which controls attachment of Small Ubiquitin-like Modifier (SUMO) proteins and thereby regulates degradation of GLUT4 in L6 muscle cells[5]. Similar observations have been made in 3T3-L1 adipocytes where overexpression of UBC9 promotes accumulation of GLUT4, whereas RNAi-mediated depletion of UBC9 causes a selective loss of GLUT4[6]. Resistance to insulin in skeletal muscle and impaired insulin stimulated glucose uptake is a prominent feature of type 2 diabetes mellitus. This is associated with reduced insulin stimulated GLUT4 translocation demonstrated by labeling of GLUT4 around the cell surface[7], most likely caused by a reduced insulin signaling from the insulin receptor[8]. In adipose tissue, type 2 diabetes is usually associated with NU7026 reduced GLUT4 expression[2], but in patients that maintain euglycemia on diet and treatment with oral antidiabetic drugs, the impaired translocation is not due to reduced expression of GLUT4 in skeletal muscle[2],[9][11]. However, type 2 diabetic patients who daily require high doses of insulin may have additional pathological defects in their muscles, and understanding these mechanisms is important for optimizing treatment. We therefore examined expression of GLUT4 and associated proteins in skeletal muscle from type 2 diabetic patients characterized by severe insulin resistance. == Methods == The studies were conducted in accordance with the Helsinki Declaration and the study protocols were approved by the.