Role of Derlin-1 protein in proteostasis regulation of ATP-sensitive potassium channels.

ATP-sensitive potassium (K(ATP)) channels composed of sulfonylurea receptor 1 (SUR1) and Kir6.2 regulate insulin secretion by linking glucose metabolism with membrane potential. The number of K(ATP) channels in the plasma membrane affects the sensitivity of β-cells to glucose. Aberrant surface channel expression leads to insulin secretion disease. Previously, we have shown that K(ATP) channel proteins undergo endoplasmic reticulum (ER)-associated degradation (ERAD) via the ubiquitin-proteasome pathway, and inhibition of proteasome function results in an increase in channel surface expression. Here, we investigated whether Derlin-1, a protein involved in retrotranslocation of misfolded or misassembled proteins across the ER membrane for degradation by cytosolic proteasomes, plays a role in ERAD and, in turn, biogenesis efficiency of K(ATP) channels. We show that both SUR1 and Kir6.2 form a complex with Derlin-1 and an associated AAA-ATPase, p97. Overexpression of Derlin-1 led to a decrease in the biogenesis efficiency and surface expression of K(ATP) channels. Conversely, knockdown of Derlin-1 by RNA interference resulted in increased processing of SUR1 and a corresponding increase in surface expression of K(ATP) channels. Importantly, knockdown of Derlin-1 increased the abundance of disease-causing misfolded SUR1 or Kir6.2 proteins and even partially rescued surface expression in a mutant channel. We conclude that Derlin-1, by being involved in ERAD of SUR1 and Kir6.2, has a role in modulating the biogenesis efficiency and surface expression of K(ATP) channels. The results suggest that physiological or pathological changes in Derlin-1 expression levels may affect glucose-stimulated insulin secretion by altering surface expression of K(ATP) channels.