Roles of Phospholipase A/Acyltransferase Enzymes in Membrane Remodelling and Organelle Degradation

Biological processes involving changes in membrane structure and properties require cells to adjust their membrane lipid composition accordingly. One of the ways cells can rapidly generate a diverse repertoire of membrane lipids is through remodelling the fatty acid tails of phospholipids. This process is coordinated by phospholipase A (PLA) and acyltransferases (AT). PLA/AT are a family of 5 enzymes evolutionarily conserved in vertebrates. Recently, they have been implicated in processes from organelle degradation during lens differentiation to host immune responses against Toxoplasma infection. However, their lipid-modifying activities in cellular contexts are poorly understood. Here, we reveal PLAAT4 as a novel broad-spectrum phospholipase A through a multi-system approach combining yeast genetics, mammalian cell models, and lipidomics. In wild-type (wt) yeast, human PLAAT4 activity increased the size of lipid droplets, suggestive of fatty acid accumulation. The activity of PLAAT4 also resulted in ER morphological defects and growth inhibition. In a yeast mutant unable to produce storage lipids, consequently fails to resume growth after starvation, has ER morphological defect and autophagic defect, PLAAT4 activity corrected these phenotypes. Lipid analysis of this mutant expressing PLAAT4 revealed fatty acids release at the expense of phospholipids. In HeLa cells, PLAAT4 localises to the ER and was closely associated to recycling endosomes. When challenged with long chain unsaturated fatty acids, HeLa cells overexpressing catalytic-active PLAAT4 were less efficient in converting free fatty acids into storage lipids. Lipidomics analysis of these cells showed a significant increase in all major lyso-PC and lyso-PE species. In OE33, a human oesophageal adenocarcinoma cell line expressing high levels of PLAAT4 endogenously, PLAAT4 KO had no effect on their proliferation. However, a significant proliferation delay was observed upon the double knockout of PLAAT3 and 4, revealing functional redundancy and a possible role of PLAAT enzymes in cancer lipid metabolism. Taken together, our observations suggest that PLAAT4 functions as a broad-spectrum phospholipase A involved in membrane remodelling and lipid homeostasis in yeast and mammalian cell models, making it an exciting target for future investigations.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2025

Author dc:creator

• Guo, Shiyu

Advisor dc:contributor.advisor

• Siniossoglou, Symeon

• lipid
• membrane remodelling
• phospholipase
• Phospholipid metabolism

Licence

• https://www.repository.cam.ac.uk/bitstreams/552efed5-ebd3-4669-8c9d-42c2e4a9c420/download
• http://purl.org/NET/rdflicense/allrightsreserved

Language dc:language

eng

DOI dc:identifier.doi

https://doi.org/10.17863/CAM.125290

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/395954