Role of BIG2, a Guanine-Nucleotide Exchanging factor for ADP-Ribosylation Factors, in Insulin-Regulated Glucose Transporter Translocation

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We here show that BIG2 plays an important role in a formation of Glut4 vesicles from endosomal compartment in both basal and insulin-stimulated adipocytes. In 3T3-L1 adipocytes, knockdown of BIG2 by RNA interference leaded to insufficient insulin-stimulated Glut4 translocation to the plasma membrane. The basal distribution of Glut4 was analyzed by subcellular fractionation. It was shown that the formation of Glut4-vesicles in the BIG2-knockdown cells was strongly repressed. Here, we used an in vitro reconstitution of Glut4-vesicles in order to demonstrate that these Glut4-vesicles are formed from endosomal membranes in a BIG2-dependent manner. Reducing endogenous BIG2 inhibited in vitro formation of Glut4 vesicles from the endosomal compartment prepared from not only unstimulated but insulin-stimulated adipocytes.