Membrane curvature elastic stress triggers recruitment of PML-II onto the inner nuclear membrane.

Promyelocytic leukemia (PML) protein isoform II is a component of PML nuclear bodies (PML NBs) that also forms patches on nuclear lipid droplets (nLDs) and the inner nuclear membrane (INM). Here we tested whether different metabolic treatments that induce membrane curvature elastic stress (CES) in the INM, detected by recruitment of CTP:phosphocholine cytidylyltransferase α (CCTα) and a nuclear diacylglycerol (DAG) biosensor, are a precondition for PML-II membrane association. We found that treatment of U2OS cells with unsaturated 18-carbon fatty acids and DAG acyltransferase inhibitors caused the rapid formation of PML patches on the INM that coincided with DAG enrichment and the recruitment and stabilization of CCTα, all of which were reversed upon removal of the CES stimulus. PML patches were depleted of canonical PML NB-associated proteins, occurred at sites of lamin depletion, were specific for the PML-II isoform, and occurred in cells regardless of their capacity to assemble nLDs. Induction of INM curvature stress by knockout of the terminal enzymes of the CDP-choline pathway or lipid activators of CCTα also promoted PML patches as well as stabilization of CCTα on the INM. We conclude that CES in the INM promotes the reversible assembly of PML-II-dependent membrane-associated patches.