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Abstract Nearly one‐third of nascent proteins are initially targeted to the endoplasmic reticulum (ER), where they are correctly folded and assembled before being delivered to their final cellular destinations. To prevent the accumulation of misfolded membrane proteins, ER‐associated degradation (ERAD) removes these client proteins from the ER membrane to the cytosol in a process known as retrotranslocation. Our previous work demonstrated that rhomboid pseudoprotease Dfm1 is involved in the retrotranslocation of ubiquitinated membrane integral ERAD substrates. Herein, we found that Dfm1 associates with the SPOTS complex, which is composed of serine palmitoyltransferase (SPT) enzymes and accessory components that are critical for catalyzing the first rate‐limiting step of the sphingolipid biosynthesis pathway. Furthermore, Dfm1 employs an ERAD‐independent role for facilitating the ER export and endosome‐ and Golgi‐associated degradation (EGAD) of Orm2, which is a major antagonist of SPT activity. Given that the accumulation of human Orm2 homologs, ORMDLs, is associated with various pathologies, our study serves as a molecular foothold for understanding how dysregulation of sphingolipid metabolism leads to various diseases.
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This content will become publicly available on March 3, 2027
Derlin-mediated ERAD of lipid regulator ORMDL3 safeguards mitochondrial function
Abstract Mammalian Derlin proteins (Derlin-1, Derlin-2, and Derlin-3) are conserved components of the endoplasmic reticulum–associated degradation (ERAD) machinery that mediate the retrotranslocation and proteasomal degradation of misfolded ER-resident proteins. However, their paralog-specific contributions to cellular homeostasis remain poorly understood. Here, we show that Derlin deficiency disrupts mitochondrial architecture and results in mitochondrial fragmentation and tightening of ER-mitochondria contact sites (MERCs) in HEK293 cells. Mechanistically, we identify ORMDL proteins, evolutionarily conserved negative regulators of sphingolipid biosynthesis, as substrates of Derlin-2- and Derlin-3-dependent ERAD. Derlin deficiency leads to selective accumulation of ORMDL3 and its dose-dependent enrichment at MERCs, where it drives mitochondrial dysfunction in respiration and calcium handling. Reducing ORMDL3 levels restores mitochondrial function, establishing ORMDL3 as a key effector downstream of Derlin loss. Our work establishes ERAD as a critical mechanism of protein quantity control that safeguards organelle homeostasis by preventing aberrant accumulation and mislocalization of ER clients at inter-organelle contact sites. Given that ORMDL family members are central regulators of sphingolipid metabolism and are genetically linked to inflammation, cancer, asthma, inflammatory bowel disease, type 1 and type 2 diabetes, multiple sclerosis, obesity, and nonalcoholic fatty liver disease, these findings connect ERAD-dependent spatial control to sphingolipid homeostasis and a broad spectrum of human pathologies.
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- Award ID(s):
- 2047391
- PAR ID:
- 10697770
- Publisher / Repository:
- bioRxiv
- Date Published:
- Format(s):
- Medium: X
- Institution:
- bioRxiv
- Sponsoring Org:
- National Science Foundation
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