Sterol transfer, PI4P consumption, and control of membrane lipid order by endogenous OSBP

The network of proteins that orchestrate the distribution of cholesterol among cellular organelles is not fully characterized. We previously proposed that oxysterol-binding protein (OSBP) drives cholesterol/PI4P exchange at contact sites between the endoplasmic reticulum (ER) and the trans-Golgi network (TGN). Using the inhibitor OSW-1, we report here that the sole activity of endogenous OSBP makes a major contribution to cholesterol distribution, lipid order, and PI4P turnover in living cells. Blocking OSBP causes accumulation of sterols at ER/lipid droplets at the expense of TGN, thereby reducing the gradient of lipid order along the secretory pathway. OSBP consumes about half of the total cellular pool of PI4P, a consumption that depends on the amount of cholesterol to be transported. Inhibiting the spatially restricted PI4-kinase PI4KIIIPI triggers large periodic traveling waves of PI4P across the TGN. These waves are cadenced by long-range PI4P production by PI4KloE and PI4P consumption by OSBP. Collectively, these data indicate a massive spatiotemporal coupling between cholesterol transport and PI4P turnover via OSBP and PI4-kinases to control the lipid composition of subcellular membranes.