Nocodazole inhibits insulin-stimulated glucose transport in 3T3-L1 adipocytes via a microtubule-independent mechanism

Insulin stimulates glucose transport in adipocytes and muscle cells by trig gering redistribution of the GLUT4 glucose transporter from an intracellula r perinuclear location to the cell surface. Recent reports have shown that the microtubule-depolymerizing agent nocodazole inhibits insulin-stimulated glucose transport, implicating an important role for microtubules in this process. In the present study we show that 2 mum nocodazole completely depo lymerized microtubules in 3T3-L1 adipocytes, as determined morphologically and biochemically, resulting in dispersal of the perinuclear GLUT4 compartm ent and the Golgi apparatus. However, 2 mum nocodazole did not significantl y effect either the kinetics or magnitude of insulin-stimulated glucose tra nsport. Consistent with previous studies, higher concentrations of nocodazo le (10-33 mum) significantly inhibited basal and insulin-stimulated glucose uptake in adi. pocytes. This effect was not likely the result of microtubu le depolymerization because in the presence of taxol, which blocked nocodaz ole-induced depolymerization of microtubules as well as the dispersal of th e perinuclear GLUT4 compartment, the inhibitory effect of 10-33 muM nocodaz ole on insulin-stimulated glucose uptake prevailed. Despite the decrease in insulin-stimulated glucose transport with 33 muM nocodazole we did not obs erve inhibition of insulin-stimulated GLUT4 translocation to the cell surfa ce under these conditions. Consistent with a direct effect of nocodazole on glucose transporter function we observed a rapid inhibitory effect of noco dazole on glucose transport activity when added to either 3T3-L1 adipocytes or to Chinese hamster ovary cells at 4 degreesC. These studies reveal a ne w and unexpected effect of nocodazole in mammalian cells which appears to o ccur independently of its microtubule-depolymerizing effects.