Phosphorylation regulates the sensitivity of voltage‐gated Kv7.2 channels towards phosphatidylinositol‐4,5‐bisphosphate

Abstract

Key points

• Phosphatidylinositol‐4,5‐bisphosphate (PIP ₂) is a key regulator of many membrane proteins, including voltage‐gated Kv7.2 channels.

• In this study, we identified the residues in five phosphorylation sites and their corresponding protein kinases, the former being clustered within one of four putative PIP ₂‐binding domains in Kv7.2.

• Dephosphorylation of these residues reduced the sensitivity of Kv7.2 channels towards PIP ₂.

• Dephosphorylation of Kv7.2 affected channel inhibition via M ₁ muscarinic receptors, but not via bradykinin receptors.

• Our data indicated that phosphorylation of the Kv7.2 channel was necessary to maintain its low affinity for PIP ₂, thereby ensuring the tight regulation of the channel via G protein‐coupled receptors.

Abstract

The function of numerous ion channels is tightly controlled by G protein‐coupled receptors (GPCRs). The underlying signalling mechanisms may involve phosphorylation of channel proteins and participation of phosphatidylinositol‐4,5‐bisphosphate (PIP ₂). Although the roles of both mechanisms have been investigated extensively, thus far only little has been reported on their interaction in channel modulation. GPCRs govern Kv7 channels, the latter playing a major role in the regulation of neuronal excitability by determining the levels of PIP ₂ and through phosphorylation. Using liquid chromatography‐coupled mass spectrometry for Kv7.2 immunoprecipitates of rat brain membranes and transfected cells, we mapped a cluster of five phosphorylation sites in one of the PIP2‐binding domains. To evaluate the effect of phosphorylation on PIP ₂‐mediated Kv7.2 channel regulation, a quintuple alanine mutant of these serines (S427/S436/S438/S446/S455; A ⁵ mutant) was generated to mimic the dephosphorylated state. Currents passing through these mutated channels were less sensitive towards PIP ₂ depletion via the voltage‐sensitive phosphatase Dr‐VSP than were wild‐type channels. In vitro phosphorylation assays with the purified C‐terminus of Kv7.2 revealed that CDK5, p38 MAPK, CaMKIIα and PKA were able to phosphorylate the five serines. Inhibition of these protein kinases reduced the sensitivity of wild‐type but not mutant Kv7.2 channels towards PIP ₂ depletion via Dr‐VSP. In superior cervical ganglion neurons, the protein kinase inhibitors attenuated Kv7 current regulation via M ₁ receptors, but left unaltered the control by B2 receptors. Our results revealed that the phosphorylation status of serines located within a putative PIP ₂‐binding domain determined the phospholipid sensitivity of Kv7.2 channels and supported GPCR‐mediated channel regulation.

Key points

• Phosphatidylinositol‐4,5‐bisphosphate (PIP ₂) is a key regulator of many membrane proteins, including voltage‐gated Kv7.2 channels.

• In this study, we identified the residues in five phosphorylation sites and their corresponding protein kinases, the former being clustered within one of four putative PIP ₂‐binding domains in Kv7.2.

• Dephosphorylation of these residues reduced the sensitivity of Kv7.2 channels towards PIP ₂.

• Dephosphorylation of Kv7.2 affected channel inhibition via M ₁ muscarinic receptors, but not via bradykinin receptors.

• Our data indicated that phosphorylation of the Kv7.2 channel was necessary to maintain its low affinity for PIP ₂, thereby ensuring the tight regulation of the channel via G protein‐coupled receptors.