The voltage-dependent potassium channel subunit Kv2.1 regulates insulin secretion from rodent and human islets independently of its electrical function

Abstract

Aims/hypothesis It is thought that the voltage-dependent potassium channel subunit Kv2.1 (Kv2.1) regulates insulin secretion by controlling beta cell electrical excitability. However, this role of Kv2.1 in human insulin secretion has been questioned. Interestingly, Kv2.1 can also regulate exocytosis through direct interaction of its C-terminus with the soluble NSF attachment receptor (SNARE) protein, syntaxin 1A. We hypothesised that this interaction mediates insulin secretion independently of Kv2.1 electrical function. Methods Wild-type Kv2.1 or mutants lacking electrical function and syntaxin 1A binding were studied in rodent and human beta cells, and in INS-1 cells. Small intracellular fragments of the channel were used to disrupt native Kv2.1-syntaxin 1A complexes. Single-cell exocytosis and ion channel currents were monitored by patch-clamp electrophysiology. Interaction between Kv2.1, syntaxin 1A and other SNARE proteins was probed by immunoprecipitation. Whole-islet Ca 2+ -responses were monitored by ratiometric Fura red fluorescence and insulin secretion was measured.

The Arabidopsis R-SNARE VAMP721 Interacts with KAT1 and KC1 K+ Channels to Moderate K+ Current at the Plasma Membrane

“…Furthermore, Kv2.1 binding to VAMP2 is lost on assembly of the SNARE core complex in vitro (Tsuk et al, 2008), suggesting that the channel also binds with the SNARE motif of VAMP2. Therefore, only by postulating an elaborate exchange of partners have these observations be integrated with the physiology of neurotransmission (Dai et al, 2012). An added concern is that the SNARE motif of Qa-SNAREs, and most likely of other SNAREs, is notoriously promiscuous in protein binding in vitro (Fletcher et al, 2003).…”

DeSUMOylation Controls Insulin Exocytosis in Response to Metabolic Signals

“…Indeed, both cloned Kv2.1 and the native channel in rodents and humans is inhibited by SUMOylation [24] of a C-terminal lysine (K470) [25]. While inhibition of Kv2.1 currents in itself cannot account for the ability of SUMO1 to block exocytosis, since our exocytosis measurements (such as those in Figure 3, Figure 4, Figure 5) are carried out under conditions where the cell membrane potential is ‘clamped’, it is interesting to note that the Kv2.1 channel can regulate β-cell exocytosis independent of its electrical function, through a direct interaction with the exocytotic protein syntaxin 1A [45,46]. It will thus be interesting to determine whether SUMOylation of Kv2.1 alters its role in β-cell exocytosis and its interaction with syntaxin 1A, which we have also recently identified to itself be SUMOylated in pancreatic islets (unpublished).…”

Cooperative endocytosis of the endosomal SNARE protein syntaxin-8 and the potassium channel TASK-1

“…In addition, the neuronal SNARE proteins stx1A and VAMP2 were reported to interact with K + channels present in neurons, insulin-secreting cells, and cardiomyocytes (Chao et al. , 2011a, b; Dai et al. , 2012) and to modulate their open probability.…”