PKA-mediated phosphorylation of the human KATP channel: separate roles of Kir6.2 and SUR1 subunit phosphorylation

Abstract

ATP-sensitive potassium (K(ATP)) channels play important roles in many cellular functions such as hormone secretion and excitability of muscles and neurons. Classical ATP-sensitive potassium (K(ATP)) channels are heteromultimeric membrane proteins comprising the pore-forming Kir6.2 subunits and the sulfonylurea receptor subunits (SUR1 or SUR2). The molecular mechanism by which hormones and neurotransmitters modulate K(ATP) channels via protein kinase A (PKA) is poorly understood. We mutated the PKA consensus sequences of the human SUR1 and Kir6.2 subunits and tested their phosphorylation capacities in Xenopus oocyte homogenates and in intact cells. We identified the sites responsible for PKA phosphorylation in the C-terminus of Kir6.2 (S372) and SUR1 (S1571). Kir6.2 can be phosphorylated at its PKA phosphorylation site in intact cells after G-protein (Gs)-coupled receptor or direct PKA stimulation. While the phosphorylation of Kir6.2 increases channel activity, the phosphorylation of SUR1 contributes to the basal channel properties by decreasing burst duration, interburst interval and open probability, and also increasing the number of functional channels at the cell surface. Moreover, the effect of PKA could be mimicked by introducing negative charges in the PKA phosphorylation sites. These data demonstrate direct phosphorylation by PKA of the K(ATP) channel, and may explain the mechanism by which Gs-coupled receptors stimulate channel activity. Importantly, they also describe a model of heteromultimeric ion channels in which there are functionally distinct roles of the phosphorylation of the different subunits.

Serine-385 phosphorylation of inwardly rectifying K+ channel subunit (Kir6.2) by AMP-dependent protein kinase plays a key role in rosiglitazone-induced closure of the KATP channel and insulin secretion in rats

“…In addition to being regulated by various nucleotides, the activity of the K ATP channel can be further modulated by phosphorylation events induced by activated protein kinase A and protein kinase C [21,22]. These phosphorylation events occur at selective amino acid e Phosphorylation of the FSIS-containing peptide of Kir6.2 in the immunoprecipitated AMPK kinase assay from rat islets in the absence or presence of rosiglitazone (9 µmol/l) and/or compound C (40 µmol/l, pretreatment for 1 h) in rat islets.…”

“…K ATP channels are heterooctamers which are composed of four sulfonylurea receptor (SUR1) subunits and four inwardly rectifying K + channel (Kir6.2) subunits [19], which are regulated by allosteric activation with various nucleotides [20]. K ATP channel activity can also be regulated by phosphorylation events of the constituent proteins, such as phosphorylation of Ser 372 of the Kir6.2 subunit and Ser 1571 of the SUR1 subunit by protein kinase A [21] and phosphorylation of the Thr 180 residue of the Kir6.2 subunit by protein kinase C [22]. In this study, we investigated the function of AMPK in the rosiglitazone-potentiated insulin secretory response, and the potential site of phosphorylation of the Kir6.2 subunit.…”

Mechanisms of action of glucagon-like peptide 1 in the pancreas

“…The mechanism of this glucose dependent action of GLP-1 is now believed to be via phosphorylation of the K ATP channel by PKA. Initial experiments indicated that PKA phosphorylation of K ir6.2 (S 372 ) increased channel activity and that phosphorylation of SUR1 (S 1571 ) decreased burst duration and open probability (Beguin et al, 1999). However point mutation analysis has also targeted 1448 S as a specific residue on SUR1 that is phosphorylated in response to GLP-1 treatment (Light et al, 2002).…”

ATP-sensitive K channel channel/enzyme multimer: Metabolic gating in the heart

“…Lactate modulates the ATP sensitivity of K ATP channels and would accumulate in the vicinity of LDH, and thus of cardiac K ATP channels, under anaerobic conditions [100]. Other examples include direct channel effects of G protein subunits [101,102], changes in the composition of membrane phospholipids that interact with Kir6.2 to modulate pore function [103,104], activation of the protein kinase systems PKC and PKA with channel effects through phosphorylation/dephosphorylation [105][106][107][108], and pH effects through protonation of channel proteins [109].…”