BREFELDIN-A INHIBITS INSULIN-DEPENDENT RECEPTOR REDISTRIBUTION IN HIRCB CELLS

Brefeldin A (BFA) is a potent inhibitor of intracellular vesicle traff ic. We have investigated the effects of BFA on the traffic of the insu lin receptor in HIRcB cells, a cell line derived from Rat-1 fibroblast s that over-expresses a normal human insulin receptor. We report here that insulin-dependent receptor redistribution is inhibited by BFA and that this drug has no effects on the insulin-independent redistributi on of the receptor. Autophosphorylation of the insulin receptor and th e stimulation of mitogen-activated protein kinase (MAPK) by insulin we re not affected by treatment with the drug. The effects of BFA were fu rther shown to require addition of the drug prior to the addition of i nsulin. BFA added 10 min after stimulation with insulin had no effects on the redistribution of the receptor. Dose-response studies demonstr ated that the effects of BFA were half-maximal at a dose of 1 mu g/ml and maximal at about 10 mu g/ml. These findings suggest that BFA block s an early step in the chain of events that lead to insulin receptor i nternalization without affecting the interactions of the receptor with insulin, the stimulation of the tyrosine kinase activity of the recep tor by the hormone, or other insulin-regulated signalling pathways, su ch as the activation of MAPK.