Lipid-associated PML domains regulate CCTα, Lipin1 and lipid homeostasis

Nuclear LDs (nLDs) originate at the inner nuclear membrane by a mechanism that involves the promyelocytic leukemia (PML) protein. Here we demonstrate that nLDs in oleate-treated U2OS cells are associated with Lipid-Associated PML (LAP) domains that differ from canonical PML nuclear bodies by the relative absence of SUMO1, SP100 and DAXX. nLDs were also enriched in CTP:phosphocholine cytidylyltransferase α (CCTα), the phosphatidic acid phosphatase Lipin1 and diacylglycerol (DAG). High resolution imaging revealed that LAP domains and CCTα occupy distinct polarized regions on nLDs, and that loss of LAP domains in PML knockout U2OS cells reduced the recruitment of CCTα onto nLDs by its amphipathic α-helical M-domain. The association of Lipin1 and DAG with nLDs was also LAP domain-dependent. The disruption of CCTα and Lipin1 localization on nLDs in PML knockout cells resulted in the inhibition of phosphatidylcholine and triacylglycerol synthesis indicating that LAP domains are a unique PML subdomain involved in nLD assembly and regulation of lipid metabolism.