Syntaxin 1A regulates surface expression of β-cell ATP-sensitive potassium channels

The pancreatic ATP-sensitive potassium (K_ATP) channel consisting of four inwardly rectifying potassium channel 6.2 (Kir6.2) and four sulfonylurea receptor SUR1 subunits plays a key role in insulin secretion by linking glucose metabolism to membrane excitability. Syntaxin 1A (Syn-1A) is a plasma membrane protein important for membrane fusion during exocytosis of insulin granules. Here, we show that Syn-1A and K_ATP channels endogenously expressed in the insulin-secreting cell INS-1 interact. Upregulation of Syn-1A by overexpression in INS-1 leads to a decrease, whereas downregulation of Syn-1A by small interfering RNA (siRNA) leads to an increase, in surface expression of K_ATP channels. Using COSm6 cells as a heterologous expression system for mechanistic investigation, we found that Syn-1A interacts with SUR1 but not Kir6.2. Furthermore, Syn-1A decreases surface expression of K_ATP channels via two mechanisms. One mechanism involves accelerated endocytosis of surface channels. The other involves decreased biogenesis and processing of channels in the early secretory pathway. This regulation is K_ATP channel specific as Syn-1A has no effect on another inward rectifier potassium channel Kir3.1/3.4. Our results demonstrate that in addition to a previously documented role in modulating K_ATP channel gating, Syn-1A also regulates K_ATP channel expression in β-cells. We propose that physiological or pathological changes in Syn-1A expression may modulate insulin secretion by altering glucose-secretion coupling via changes in K_ATP channel expression.