Human Adenovirus Type 36 Enhances Glucose Uptake in Diabetic and Nondiabetic Human Skeletal Muscle Cells Independent of Insulin Signaling

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Abstract
OBJECTIVE—Human adenovirus type 36 (Ad-36) increases adiposity but improves insulin sensitivity in experimentally infected animals. We determined the ability of Ad-36 to increase glucose uptake by human primary skeletal muscle (HSKM) cells. RESEARCH DESIGN AND METHODS—The effect of Ad-36 on glucose uptake and cell signaling was determined in HSKM cells obtained from type 2 diabetic and healthy lean subjects. Ad-2, another human adenovirus, was used as a negative control. Gene expression and proteins of GLUT1 and GLUT4 were measured by real-time PCR and Western blotting. Role of insulin and Ras signaling pathways was determined in Ad-36–infected HSKM cells. RESULTS—Ad-36 and Ad-2 infections were confirmed by the presence of respective viral mRNA and protein expressions. In a dose-dependent manner, Ad-36 significantly increased glucose uptake in diabetic and nondiabetic HSKM cells. Ad-36 increased gene expression and protein abundance of GLUT1 and GLUT4, GLUT4 translocation to plasma membrane, and phosphatidylinositol 3-kinase (PI 3-kinase) activity in an insulin-independent manner. In fact, Ad-36 decreased insulin receptor substrate-1 (IRS-1) tyrosine phosphorylation and IRS-1–and IRS-2–associated PI 3-kinase activities. On the other hand, Ad-36 increased Ras gene expression and protein abundance, and Ras siRNA abrogated Ad-36–induced PI 3-kinase activation, GLUT4 protein abundance, and glucose uptake. These effects were not observed with Ad-2 infection. CONCLUSIONS—Ad-36 infection increases glucose uptake in HSKM cells via Ras-activated PI 3-kinase pathway in an insulin-independent manner. These findings may provide impetus to exploit the role of Ad-36 proteins as novel therapeutic targets for improving glucose handling.