Deciphering the molecular mechanisms of phosphatidylinositol distribution – PIPELINE

Phosphatidylinositol (PI) is a unique lipid as it is the precursor of phosphoinositides, like PI4P and PI(4,5)P2, which have key roles in the eukaryotic cells. However, little is known about how PI is exported from the endoplasmic reticulum (ER) where it is synthesized, to the Golgi apparatus and the plasma membrane to be converted into phosphoinositides. Different proteins, with the ability to transfer PIs between membranes, could perform this task, but this remains poorly understood. With the PIPELINE project, we aim first to demonstrate that some of these proteins, coupled to PI4P metabolism and other lipid exchange processes, transfer PI from the ER to the Golgi apparatus. Secondly, we will examine whether and how Nir2 protein can mediate rapid and sustained exchanges of PI and phosphatidic acid between the ER and the plasma membrane during the PI cycle, a metabolic process by which PI(4,5)P2 is regenerated to maintain the signaling competence of human cells. Finally, we will define if Sfh3 acts as a sterol/PI exchanger and what is its function in yeast, and likely reveal unexpected links between PI and sterol metabolism.

In pilot experiments, our team (Drin, IPMC) have reconstituted in vitro an ER/Golgi interface, using synthetic membranes and a set of different recombinant proteins, and successfully measured the coupling between the activity of a PI-transfer protein, PI4P metabolism and a sterol/PI4P exchange process. By developing this innovative and unique system as well as click-chemistry approaches with lipids synthesized by JM Brunel's team (MCT), we will determine precisely how PI-transfer proteins can function at the interface between the ER and other organelles. With A. Copic’s team (CRBM), we will also study the functioning of these proteins in human and yeast cells, with recent tools to detect PI and other lipids in organelles. We will thus provide unprecedented insights into the molecular bases of PI distribution in eukaryotic cells.