Rab8a is involved in membrane trafficking of Kir6.2 in the MIN6 insulinoma cell line

Although ATP-sensitive K+ (K-ATP) channels play an important role in the secretion of insulin by pancreatic beta cells, the mechanisms that regulate the intracellular transport of K-ATP channel subunit proteins (i.e., Kir6.2 and sulfonylurea receptor 1 (SUR1)) to the plasma membrane remain uncharacterized. We investigated the possibility that an interaction between K-ATP channel subunit proteins and Rab8a protein, a member of the RAS superfamily, may be involved in the membrane trafficking of K-ATP channels. Co-immunoprecipitation and immunostaining experiments using co-expression systems with fluorescent protein-tagged Kir6.2 were carried out to identify the coupling of K-ATP channels and Rab8a proteins in the insulin-secreting cell line, MIN6. Rab8a protein co-localized with Kir6.2 protein, a channel pore subunit (in a granular pattern), and with insulin. Knockdown of the Rab8a gene with RNA interference using small interfering RNA systems caused reductions in the amount of total K-ATP and plasma membrane surface K-ATP channels without decreasing the messenger RNA transcription of the K-ATP channel subunits. Rab8a gene knockdown also enhanced glucose-induced insulin secretion. These results suggest that Rab8a may be involved in membrane trafficking of K-ATP channels and the maintenance of normal insulin secretion in the MIN6 pancreatic beta cell line.