The Actions of a Novel Potent Islet β-Cell–Specific ATP-Sensitive K+ Channel Opener Can Be Modulated by Syntaxin-1A Acting on Sulfonylurea Receptor 1

Abstract

Islet ␤-cell-specific ATP-sensitive K ؉ (K ATP ) channel openers thiadiazine dioxides induce islet rest to improve insulin secretion, but their molecular basis of action remains unclear. We reported that syntaxin-1A binds nucleotide binding folds of sulfonylurea receptor 1 (SUR1) in ␤-cells to inhibit K ATP channels. As a strategy to elucidate the molecular mechanism of action of these K ATP channel openers, we explored the possibility that 6-chloro-3-(1-methylcyclobutyl)amino-4H-thieno[3,2-e]-1,2,4-thiadiazine 1,1-dioxide (NNC55-0462) might influence syntaxin-1A-SUR1 interactions or vice versa. Whole-cell and inside-out patch-clamp electrophysiology was used to examine the effects of glutathione S-transferase (GST)-syntaxin-1A dialysis or green fluorescence protein/syntaxin-1A cotransfection on NNC55-0462 actions. In vitro pull-down binding studies were used to examine NNC55-0462 influence on syntaxin-1A-SUR1 interactions. Dialysis of GST-syntaxin-1A into the cell cytoplasm reduced both potency and efficacy of extracellularly perfused NNC55-0462 in a HEK cell line stably expressing Kir6.2/SUR1 (BA8 cells) and in rat islet ␤-cells. Moreover, inside-out membrane patches excised from BA8 cells showed that both GST-syntaxin-1A and its H3 domain inhibited K ATP channels previously activated by NNC55-0462. This action on K ATP channels is isoform-specific to syntaxin-1A because syntaxin-2 was without effect. Furthermore, the parent compound diazoxide showed similar sensitivity to GST-syntaxin-1A inhibition. NNC55-0462, however, did not influence syntaxin-1A-SUR1 binding interaction. Our results demonstrated that syntaxin-1A interactions with SUR1 at its cytoplasmic domains can modulate the actions of the K ATP channel openers NNC55-0462 and diazoxide on K ATP channels. The reduced levels of islet syntaxin-1A in diabetes would thus be expected to exert a positive influence on the therapeutic effects of this class of K ATP channel openers. Diabetes

α-Synuclein binds the KATP channel at insulin-secretory granules and inhibits insulin secretion

“…Further experiments will be required to specify the steps of the insulin-secretory pathway, trafficking to release sites, priming, docking, and exocytic fusion of the insulin granules to determine where ␣-synuclein exerts its inhibitory effects. The results support models in which ␣-synuclein interacts with secretory vesicles to retard their progression or priming through the secretory pathway to exocytic sites for release, including interactions with the actin cytoskeleton and SNARE proteins (9,15,29,38,44,58,63).…”

Pancreatic β-Cell Electrical Activity and Insulin Secretion: Of Mice and Men

“…In both mouse and man, the Kir6.2 and SUR1 genes are expressed side-by-side on chromosomes 7 and 11, respectively. Numerous proteins have been suggested to interact with the K ATP channel, including 14-3-3 proteins (280), syntaxin (474), EPAC2 (616), actin (85) and many others (344), but in most cases the physiological importance of these interactions remains unclear. It is notable that Abcc8/ABCC8 is expressed at 5-20 fold higher levels than Kcnj11/KCNJ11 (see Appendix Figure 6).…”

Neuroprotective role of ATP-sensitive potassium channels in cerebral ischemia

“…Syntaxin 1A decreases the activity [76] and the membrane expression level of K ATP channels [77] . Syntaxin 1A binding to the SUR1 subunit also attenuates the effect of K + channel openers, such as diazoxide, NNC55-0462, P1075, and cromakalim [78,79] .…”