Golgi and plasma membrane pools of PI(4)P contribute to plasma membrane PI(4,5)P2 and maintenance of KCNQ2/3 ion channel current

Plasma membrane (PM) phosphatidylinositol 4,5-bisphosphate [PI(4,5)P-2] regulates the activity of many ion channels and other membrane-associated proteins. To determine precursor sources of the PM PI(4,5)P-2 pool in tsA-201 cells, we monitored KCNQ2/3 channel currents and translocation of PHPLC delta 1 domains as real-time indicators of PM PI(4,5)P-2, and translocation of PHOSH2x2, and PHOSH1 domains as indicators of PM and Golgi phosphatidylinositol 4-phosphate [PI(4) P], respectively. We selectively depleted PI(4) P pools at the PM, Golgi, or both using the rapamycin-recruitable lipid 4-phosphatases. Depleting PI(4) P at the PM with a recruitable 4-phosphatase (Sac1) results in a decrease of PI(4,5)P-2 measured by electrical or optical indicators. Depleting PI(4) P at the Golgi with the 4-phosphatase or disrupting membrane-transporting motors induces a decline in PM PI(4,5)P-2. Depleting PI(4) P simultaneously at both the Golgi and the PM induces a larger decrease of PI(4,5)P-2. The decline of PI(4,5)P-2 following 4-phosphatase recruitment takes 1-2 min. Recruiting the endoplasmic reticulum (ER) toward the Golgi membranes mimics the effects of depleting PI(4) P at the Golgi, apparently due to the trans actions of endogenous ER Sac1. Thus, maintenance of the PM pool of PI(4,5)P-2 appears to depend on precursor pools of PI(4) P both in the PM and in the Golgi. The decrease in PM PI(4,5)P-2 when Sac1 is recruited to the Golgi suggests that the Golgi contribution is ongoing and that PI (4,5)P-2 production may be coupled to important cell biological processes such as membrane trafficking or lipid transfer activity.