The Gp78 ubiquitin E3 ligase drives mitophagy by regulating omegasome formation
- 1University of British Columbia
Abstract
Autophagy is initiated at endoplasmic reticulum (ER)-associated omegasomes, yet how the ER contributes to mitochondrial cargo degradation during early autophagosome formation remains unclear. Gp78 is an ER-resident RING E3 ubiquitin ligase involved in ER-associated degradation (ERAD) that also promotes Parkin-independent mitophagy. However, the spatial relationship between Gp78 ubiquitin ligase activity, omegasome formation, and mitochondrial degradation has yet to be defined. Combining targeted mitochondria labeling and super-resolution STED microscopy, we show that the Gp78 ubiquitin ligase is localized to and regulates DFCP1-positive omegasome formation, where it drives mitochondrial protein breakdown. Using fluorescent mitophagy reporters and acute ivermectin-induced mitophagy, generation of mitophagy intermediates lacking mitochondrial outer membrane (TOMM20) was found to be dependent on the Gp78 RING finger as well as the BAG6-UBL4A-USP13 ubiquitin-ligase module, and independent of PINK1 and Parkin. Object-based analysis of 3D STED images further showed that both DFCP1- and LC3-positive structures associate primarily with intact mitochondrial fragments which show progressive degradation of mitochondrial content. Gp78 localizes to and promotes, via BAG6, the formation of DFCP1-positive omegasomes and mitochondrial protein degradation in these early autophagic structures. ER-derived omegasome biogenesis is therefore coupled to Gp78-dependent ubiquitin ligase activity and local degradation of mitochondrial cargo during mitophagy.
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BibTeX
@misc{ortizsilva2026gp78,
title = {{The Gp78 ubiquitin E3 ligase drives mitophagy by regulating omegasome formation}},
author = {M. Ortiz-Silva and B. Joshi and J. Zheng and R. Takimoto and S. Chopra and N. Yachie and G. Hamarneh and I. R. Nabi},
howpublished = {bioRxiv},
year = {2026},
month = sep,
doi = {10.64898/2026.09.04.749530},
url = {https://www.biorxiv.org/content/10.64898/2026.09.04.749530v1},
note = {CC BY},
}
RIS
TY - UNPB
TI - The Gp78 ubiquitin E3 ligase drives mitophagy by regulating omegasome formation
AU - M. Ortiz-Silva
AU - B. Joshi
AU - J. Zheng
AU - R. Takimoto
AU - S. Chopra
AU - N. Yachie
AU - G. Hamarneh
AU - I. R. Nabi
PY - 2026
DA - 2026/09/04
PB - bioRxiv
DO - 10.64898/2026.09.04.749530
UR - https://www.biorxiv.org/content/10.64898/2026.09.04.749530v1
AB - Autophagy is initiated at endoplasmic reticulum (ER)-associated omegasomes, yet how the ER contributes to mitochondrial cargo degradation during early autophagosome formation remains unclear. Gp78 is an ER-resident RING E3 ubiquitin ligase involved in ER-associated degradation (ERAD) that also promotes Parkin-independent mitophagy. However, the spatial relationship between Gp78 ubiquitin ligase activity, omegasome formation, and mitochondrial degradation has yet to be defined. Combining targeted mitochondria labeling and super-resolution STED microscopy, we show that the Gp78 ubiquitin ligase is localized to and regulates DFCP1-positive omegasome formation, where it drives mitochondrial protein breakdown. Using fluorescent mitophagy reporters and acute ivermectin-induced mitophagy, generation of mitophagy intermediates lacking mitochondrial outer membrane (TOMM20) was found to be dependent on the Gp78 RING finger as well as the BAG6-UBL4A-USP13 ubiquitin-ligase module, and independent of PINK1 and Parkin. Object-based analysis of 3D STED images further showed that both DFCP1- and LC3-positive structures associate primarily with intact mitochondrial fragments which show progressive degradation of mitochondrial content. Gp78 localizes to and promotes, via BAG6, the formation of DFCP1-positive omegasomes and mitochondrial protein degradation in these early autophagic structures. ER-derived omegasome biogenesis is therefore coupled to Gp78-dependent ubiquitin ligase activity and local degradation of mitochondrial cargo during mitophagy.
ER -