Differential reliance of CTD-nuclear envelope phosphatase 1 on its regulatory subunit in ER lipid synthesis and storage

• Published in: Molecular biology of the cell 2024-07, Vol.35 (7), p.mbcE23090382
• Main Authors: Rodríguez, Jake W Carrasquillo, Uche, Onyedikachi, Gao, Shujuan, Lee, Shoken, Airola, Michael V, Bahmanyar, Shirin
• Format: Article
• Language: English
• Subjects: Special Issue on Protein Quality Control
• ISSN: 1059-1524; 1939-4586; 1939-4586
• DOI: 10.1091/mbc.E23-09-0382

Lipin 1 is an ER enzyme that produces diacylglycerol, the lipid intermediate that feeds into the synthesis of glycerophospholipids for membrane expansion or triacylglycerol for storage into lipid droplets. CTD-Nuclear Envelope Phosphatase 1 (CTDNEP1) regulates lipin 1 to restrict ER membrane synthesis, but a role for CTDNEP1 in lipid storage in mammalian cells is not known. Here, we show that CTDNEP1 is reliant on its binding partner NEP1R1 for its stability and function in limiting ER expansion. CTDNEP1 contains an amphipathic helix at its N-terminus that targets to the ER, nuclear envelope and lipid droplets. We identify key residues at the binding interface of CTDNEP1 and NEP1R1 and show that they facilitate complex formation and . We demonstrate that NEP1R1 binding to CTDNEP1 shields CTDNEP1 from proteasomal degradation to regulate lipin 1 and restrict ER size. Unexpectedly, we found that NEP1R1 is not required for CTDNEP1's role in restricting lipid droplet biogenesis. Thus, the reliance of CTDNEP1 function on NEP1R1 depends on cellular demands for membrane production versus lipid storage. Together, our work provides a framework into understanding how the ER regulates lipid synthesis under different metabolic conditions.