Sphingosine-1-phosphate signalling activates E-Syt1 to facilitate HDL-derived cholesterol transport

Cholesterol derived from high-density lipoprotein (HDL) is rapidly redistributed to intracellular compartments in steroidogenic and bile-producing cells, but the molecular mechanisms governing this essential transport process remain poorly understood. Here we uncover a signalling cascade coordinating HDL-derived cholesterol transport through membrane contact sites between the endoplasmic reticulum (ER) and plasma membrane (PM). We find that HDL-resident sphingosine-1-phosphate (S1P) activates S1P receptor 3 and its associated G protein αq, leading to phospholipase-C-β3-mediated hydrolysis of phosphatidylinositol 4,5-bisphosphate and an elevation in cytosolic calcium. This calcium signal triggers the rapid recruitment of Extended-Synaptotagmin 1 to ER–PM membrane contact sites. Genetic or pharmacological disruption of this pathway impairs the non-vesicular transfer of HDL-derived cholesterol to intracellular compartments. Our findings reveal how HDL binding to the cell surface alters ER–PM membrane contact site dynamics through S1P signalling. This ensures efficient offloading and redistribution of HDL cholesterol to support steroid and bile acid synthesis.