ORP3 protein identified as key mediator of lysosomal membrane repair through lipid transfer
Researchers have identified the lipid transfer protein ORP3 as a critical component of late-stage lysosomal membrane repair, acting through a signaling cascade involving ubiquitin, TAK1, p38 MAPK, and LC3B. Lysosomal membrane damage, which can be triggered by certain drugs or cellular stress, must be repaired to maintain cellular homeostasis, and failure to do so is linked to cell death and disease. Understanding this repair mechanism could have implications for conditions involving lysosomal dysfunction, including neurodegenerative diseases and cancer.
A preprint study posted to bioRxiv describes how ORP3, an oxysterol-binding protein-related lipid transfer protein, is recruited to damaged lysosomes during a late-stage repair response. When lysosomal membranes are damaged—modeled experimentally using L-leucine-leucine methyl ester (LLOME) or cationic amphiphilic drugs—ORP3 becomes phosphorylated and is directed to contact sites between the endoplasmic reticulum and damaged lysosomes. This recruitment depends on a signaling chain involving lysosomal membrane ubiquitination, the kinase TAK1, and p38 MAPK, with p38-driven phosphorylation enabling ORP3 to bind the autophagy protein LC3B. The functional role of ORP3 appears to be the physical transfer of phosphatidylcholine from the ER to the damaged lysosome, as a lipid transfer-deficient mutant of ORP3 failed to restore lysosomal function even when properly recruited. Depletion of ORP3 led to impaired lysosomal recovery, increased lipid peroxidation within lysosomes, and reduced cell survival, underscoring its importance. The repair process is terminated when the protein VCP/p97 mediates deubiquitination of the lysosome, switching off ORP3 activity. The findings position ORP3 as a MAPK-regulated lipid transfer protein operating during the autophagic phase of the endolysosomal damage response.
What's missing
As a preprint, this study has not yet undergone formal peer review, so its findings should be considered preliminary. The study relies primarily on in vitro and cell-based models using pharmacological damage agents (LLOME and CADs); whether ORP3 plays the same role in physiologically relevant or in vivo contexts remains to be established. The authors do not address whether ORP3 dysfunction is directly linked to any specific human disease, nor do they explore potential therapeutic targeting of this pathway.
What different sources said
- bioRxivCenter
Lipid transfer protein ORP3 mediates lysosomal repair via LC3B and ubiquitin-TAK1-p38
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