Lipid transfer by ORP3 is required for the regulation of PI4P and PI(4,5)P2 at the plasma membrane in mitosis

Lipid transfer proteins are an evolutionary-conserved families of proteins that transfer lipids at sites of contacts between the membrane of distinct organelles and contribute to the regulation of organelle-specific phospholipids, which set the organelle membrane identity and functions. In mitosis, PI(4,5)P2 accumulation at the plasma membrane is essential for the recruitment of the actomyosin cytoskeleton and the anchoring of the mitotic spindle at the plasma membrane. This is largely regulated by the function of kinases and phosphatases that interconvert phosphoinositide species. Here we demonstrate that during mitosis the ORP3 lipid transfer protein, which transfers PI4P from the plasma membrane to the endoplasmic reticulum (ER), indirectly regulates PI(4,5)P2 at the plasma membrane, in concert with the regulation by phosphoinositide kinases and phosphatases. Phosphorylation of a secondary ORP3 binding domain to the VAPA ER membrane protein strongly recruits ORP3 to the ER, where it is primed for PI4P transfer at ER-plasma membrane contact sites. Defects in ORP3 function during mitosis result in abnormal PI(4,5)P2 distribution and actin cytoskeleton, mitotic spindle geometry, abnormal cell division, and various cell division phenotypes, which lead to aneuploidy and eventually to cell death or genomic instability.