The Ca2+-activated cation channel TRPM4 is regulated by phosphatidylinositol 4,5-biphosphate

Abstract

Transient receptor potential (TRP) channel, melastatin subfamily (TRPM)4 is a Ca 2 þ -activated monovalent cation channel that depolarizes the plasma membrane and thereby modulates Ca 2 þ influx through Ca 2 þ -permeable pathways. A typical feature of TRPM4 is its rapid desensitization to intracellular Ca 2 þ ([Ca 2 þ ] i ). Here we show that phosphatidylinositol 4,5-biphosphate (PIP 2 ) counteracts desensitization to [Ca 2 þ ] i in inside-out patches and rundown of TRPM4 currents in whole-cell patch-clamp experiments. PIP 2 shifted the voltage dependence of TRPM4 activation towards negative potentials and increased the channel's Ca 2 þ sensitivity 100-fold. Conversely, activation of the phospholipase C (PLC)-coupled M1 muscarinic receptor or pharmacological depletion of cellular PIP 2 potently inhibited currents through TRPM4. Neutralization of basic residues in a C-terminal pleckstrin homology (PH) domain accelerated TRPM4 current desensitization and strongly attenuated the effect of PIP 2 , whereas mutations to the C-terminal TRP box and TRP domain had no effect on the PIP 2 sensitivity. Our data demonstrate that PIP 2 is a strong positive modulator of TRPM4, and implicate the C-terminal PH domain in PIP 2 action. PLC-mediated PIP 2 breakdown may constitute a physiologically important brake on TRPM4 activity.

Structures of the calcium-activated, non-selective cation channel TRPM4

“…The previously proposed modulation sites for phosphorylation, PtdInsP 2 binding or calmodulin binding at the C-terminal domain do not appear to be accessible based on the structure 14,16 . However, the structural feature of the C-terminal domain would imply that the coiled coil is capable of undergoing an up-and-down sliding motion, which, in turn, can induce lateral movement through the stretcher helices and propagate to the channel transmembrane pore through the middle tier LHD (Fig.…”

“…Upon Ca 2+ activation, TRPM4 is desensitized to a steady state within a minute at both negative and positive membrane potentials. This TRPM4 desensitization was attributed to the loss of phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P 2 ) in the membrane due to Ca 2+ -activated phospholipase C 13,14 . At the Ca 2+ -desensitized steady state, TRPM4 exhibits voltage-dependent gating with higher channel open probability at depolarizing membrane potential 10 .…”

“…At the Ca 2+ -desensitized steady state, TRPM4 exhibits voltage-dependent gating with higher channel open probability at depolarizing membrane potential 10 . While PtdInsP 2 alone cannot activate the channel, its presence with Ca 2+ reverses channel desensitization, potentiates Ca 2+ sensitivity, and mitigates voltage dependence of the channel 13,14 . Cytosolic ATP can modulate TRPM4 activity in a seemingly paradoxical manner – it inhibits TRPM4 current but can also reverse Ca 2+ desensitization 13,15,16 .…”

Increased IgE-dependent mast cell activation and anaphylactic responses in mice lacking the calcium-activated nonselective cation channel TRPM4

“…That is, in contrast to the electrophysiological properties of the overexpressed channel, which include channel activation at positive potentials and channel closure at negative potentials 17 . However, the voltage dependence of TRPM4 relies critically on phosphatidylinositol-4,5-bisphosphate in the plasma membrane 37,38 ; endogenous phosphatidylinositol-4,5-bisphosphate quantities might work more effectively with endogenous amounts of TRPM4 protein in primary mast cells rather than the overexpressed TRPM4 in HEK293 cells. It is notable that mice lacking type I phosphatidylinositol phosphate kinase, the enzyme that synthesizes phosphatidylinositol-4,5-bisphosphate, have greater mast cell degranulation similar to that of Trpm4 -/-mice 39 .…”

The Mg2+ and Mg2+-Nucleotide-Regulated Channel-Kinase TRPM7

“…Clapham and colleagues (2002) suggested that receptormediated PIP 2 is required to maintain TRPM7 activity, and its breakdown by receptormediated stimulation of phospholipase C (PLC) is responsible for the inhibition TRPM7 they observed when stimulating cells with agonists that couple to PLC. Although several ion channels, including members of the TRPM family [TRPM4 (Zhang et al 2005;Nilius et al 2006), TRPM5 (Liu and Liman 2003), and TRPM8 (Liu and Qin 2005;Rohacs et al 2005)] are subject to PIP 2 -mediated regulation, the case for TRPM7 has not been made without ambiguity. Most of the experiments presented in support of PIP 2 regulation were performed in cells that overexpress TRPM7 or with receptor agonists that can couple to PLC (or both).…”