PI(4,5)P(2) controls plasma membrane PI4P and PS levels via ORP5/8 recruitment to ER–PM contact sites

Phosphatidylinositol 4,5-bisphosphate (PI(4,5)P(2)) is a critically important regulatory lipid of the plasma membrane (PM); however, little is known about how cells regulate PM PI(4,5)P(2) levels. Here, we show that the phosphatidylinositol 4-phosphate (PI4P)/phosphatidylserine (PS) transfer activity of the endoplasmic reticulum (ER)–resident ORP5 and ORP8 is regulated by both PM PI4P and PI(4,5)P(2). Dynamic control of ORP5/8 recruitment to the PM occurs through interactions with the N-terminal Pleckstrin homology domains and adjacent basic residues of ORP5/8 with both PI4P and PI(4,5)P(2). Although ORP5 activity requires normal levels of these inositides, ORP8 is called on only when PI(4,5)P(2) levels are increased. Regulation of the ORP5/8 attachment to the PM by both phosphoinositides provides a powerful means to determine the relative flux of PI4P toward the ER for PS transport and Sac1-mediated dephosphorylation and PIP 5-kinase–mediated conversion to PI(4,5)P(2). Using this rheostat, cells can maintain PI(4,5)P(2) levels by adjusting the availability of PI4P in the PM.