Phosphatidylinositol 4,5-bisphosphate (PIP 2) controls magnesium gatekeeper TRPM6 activity

Abstract

TRPM6 is crucial for human Mg 2+ homeostasis as patients carrying TRPM6 mutations develop hypomagnesemia and secondary hypocalcemia (HSH). However, the activation mechanism of TRPM6 has remained unknown. Here we demonstrate that phosphatidylinositol-4,5-bisphophate (PIP 2) controls TRPM6 activation and Mg 2+ influx. Stimulation of PLC-coupled M1-receptors to deplete PIP 2 potently inactivates TRPM6. Translocation of over-expressed 5-phosphatase to cell membrane to specifically hydrolyze PIP 2 also completely inhibits TRPM6. Moreover, depolarization-induced-activation of the voltage-sensitive-phosphatase (Ci-VSP) simultaneously depletes PIP 2 and inhibits TRPM6. PLC-activation induced PIP 2-depletion not only inhibits TRPM6, but also abolishes TRPM6-mediated Mg 2+ influx. Furthermore, neutralization of basic residues in the TRP domain leads to nonfunctional or dysfunctional mutants with reduced activity by PIP 2, suggesting that they are likely to participate in interactions with PIP 2. Our data indicate that PIP 2 is required for TRPM6 channel function; hydrolysis of PIP 2 by PLC-coupled hormones/agonists may constitute an important pathway for TRPM6 gating, and perhaps Mg 2+ homeostasis.