WNK1 Promotes PIP2 Synthesis to Coordinate Growth Factor and GPCR-Gq Signaling

Background: PLC-beta signaling is generally thought to be mediated by allosteric activation by G proteins and Ca2+. Although availability of the phosphatidylinositol-4,5-biphosphate (PIP2) substrate is limiting in some cases, its production has not been shown to be independently regulated as a signaling mechanism. WNK1 protein kinase is known to regulate ion homeostasis and cause hypertension when expression is increased by gene mutations. However, its signaling functions remain largely elusive. Results: Using diacylglycerol-stimulated TRPC6 and inositol trisphosphate-mediated Ca2+ transients as cellular biosensors, we show that WNK1 stimulates PLC-beta signaling in cells by promoting the synthesis of PIP2 via stimulation of phosphatidylinositol 4-kinase III alpha. WNK1 kinase activity is not required. Stimulation of PLC-beta by WNK1 and by G alpha(q) are synergistic; WNK1 activity is essential for regulation of PLC-beta signaling by G(q)-coupled receptors, and basal input from G(q) is necessary for WNK1 signaling via PLC-beta. WNK1 further amplifies PLC-beta signaling when it is phosphorylated by Akt kinase in response to insulin-like growth factor. Conclusions: WNK1 is a novel regulator of PLC-beta that acts by controlling substrate availability. WNK1 thereby coordinates signaling between G protein and Akt kinase pathways. Because PIP2 is itself a signaling molecule, regulation of PIP2 synthesis by WNK1 also allows the cell to initiate PLC signaling while independently controlling the effects of PIP2 on other targets. These findings describe a new signaling pathway for Akt-activating growth factors, a mechanism for G protein-growth factor crosstalk, and a means to independently control PLC signaling and PIP2 availability.