Phosphorylation regulates the sensitivity of voltage-gated Kv7.2 channels towards phosphatidylinositol-4,5-bisphosphate.
Phosphatidylinositol-4,5-bisphosphate (PIP2) 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 PIP2-binding domains in Kv7.2. Dephosphorylation of these residues reduced the sensitivity of Kv7.2 channels towards PIP2. Dephosphorylation of Kv7.2 affected channel inhibition via M1muscarinic receptors, but not via bradykinin receptors. Our data indicated that phosphorylation of the Kv7.2 channel was necessary to maintain its low affinity for PIP2, thereby ensuring the tight regulation of the channel via G protein-coupled receptors.



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 (PIP2). 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 PIP2and 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 PIP2-mediated Kv7.2 channel regulation, a quintuple alanine mutant of these serines (S427/S436/S438/S446/S455; A5mutant) was generated to mimic the dephosphorylated state. Currents passing through these mutated channels were less sensitive towards PIP2depletion 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 PIP2depletion via Dr-VSP. In superior cervical ganglion neurons, the protein kinase inhibitors attenuated Kv7 current regulation via M1receptors, but left unaltered the control by B2 receptors. Our results revealed that the phosphorylation status of serines located within a putative PIP2-binding domain determined the phospholipid sensitivity of Kv7.2 channels and supported GPCR-mediated channel regulation.
Department of Neurophysiology and Neuropharmacology, Center for Physiology and Pharmacology, Medical University of Vienna, 1090, Vienna, Austria.
Isabella
I
Salzer
Institute of Pharmacology, Center for Physiology and Pharmacology, Medical University of Vienna, 1090, Vienna, Austria.
Fatma Asli
FA
Erdem
Department of Pediatrics, Medical University of Vienna, 1090, Vienna, Austria.
Wei-Qiang
WQ
Chen
Department of Pediatrics, Medical University of Vienna, 1090, Vienna, Austria.
Seok
S
Heo
Department of Neurophysiology and Neuropharmacology, Center for Physiology and Pharmacology, Medical University of Vienna, 1090, Vienna, Austria.
Xaver
X
Koenig
Department of Neurophysiology and Neuropharmacology, Center for Physiology and Pharmacology, Medical University of Vienna, 1090, Vienna, Austria.
Klaus W
KW
Schicker
Department of Neurophysiology and Neuropharmacology, Center for Physiology and Pharmacology, Medical University of Vienna, 1090, Vienna, Austria.
Helmut
H
Kubista
Department of Pharmaceutical Chemistry, University of Vienna, 1090, Vienna, Austria.
Gert
G
Lubec
Department of Neurophysiology and Neuropharmacology, Center for Physiology and Pharmacology, Medical University of Vienna, 1090, Vienna, Austria.
Stefan
S
Boehm
Institute of Pharmacology, Center for Physiology and Pharmacology, Medical University of Vienna, 1090, Vienna, Austria.
Jae-Won
JW
Yang
D000818:Animals; D000831:Animals, Newborn; D002478:Cells, Cultured; D051658:KCNQ2 Potassium Channel / Q000502:physiology*; D009474:Neurons / Q000502:physiology; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000502:physiology*; D010766:Phosphorylation; D017207:Rats, Sprague-Dawley; D017783:Superior Cervical Ganglion / Q000166:cytology
D051658:KCNQ2 Potassium Channel; D019269:Phosphatidylinositol 4,5-Diphosphate
KCNQ2; PIP2; ion channel; phosphorylation