Dataset Information

An ERAD independent role for rhomboid pseudoprotease Dfm1 in mediating sphingolipid homeostasis

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 clients from the ER membrane to the cytosol in a process known as retrotranslocation. Our recent work demonstrates that rhomboid pseudoprotease, Dfm1, is involved in the retrotranslocation of ubiquitinated integral membrane ERAD substrates. To survey for potential interaction partners of Dfm1, we performed protein-proximity labeling by BioID (proximity-dependent biotin identification) followed by mass spectrometry and identified several interacting proteins known to play a role in the sphingolipid biosynthesis pathway. Specifically, we found that Dfm1 physically interacts with the SPOTS complex, which is composed of serine palmitoyltransferase (SPT) enzymes and accessory components and is critical for catalyzing the first rate-limiting step of the sphingolipid biosynthesis pathway. We demonstrate for the first time that Dfm1 has a role in ER export, a function that is independent of Dfm1s canonical ERAD retrotranslocation function. Specifically, we show that loss of Dfm1 results in the accumulation of phosphorylated Orm2 at the ER, suggesting a novel role for Dfm1 in controlling Orm2 export from the ER and its subsequent degradation by EGAD. Moreover, the recruitment of Cdc48 by Dfm1, which is critical for its role in ERAD retrotranslocation, is dispensable for Dfm1s role in ER export. Given that the accumulation of human Orm2 homologs, ORMDLs, is associated with many maladies, our study serves as a molecular foothold for understanding how dysregulation of sphingolipid metabolism leads to various diseases.

INSTRUMENT(S): Q Exactive

ORGANISM(S): Saccharomyces Cerevisiae (ncbitaxon:4932)

SUBMITTER: Sonya Neal

PROVIDER: MSV000090333 | MassIVE |

REPOSITORIES: MassIVE

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Publications

An ERAD-independent role for rhomboid pseudoprotease Dfm1 in mediating sphingolipid homeostasis.

Bhaduri Satarupa S Aguayo Analine A Ohno Yusuke Y Proietto Marco M Jung Jasmine J Wang Isabel I Kandel Rachel R Singh Narinderbir N Ibrahim Ikran I Fulzele Amit A Bennett Eric J EJ Kihara Akio A Neal Sonya E SE

The EMBO journal 20221109 4

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 retrotransloc ...[more]

PMID: 36350249

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Project description:The ARV1-encoded protein mediates sterol transport from the endoplasmic reticulum (ER) to the plasma membrane. Yeast ARV1 mutants accumulate multiple lipids in the ER and are sensitive to pharmacological modulators of both sterol and sphingolipid metabolism. Using fluorescent and electron microscopy, we demonstrate sterol accumulation, subcellular membrane expansion, elevated lipid droplet formation and vacuolar fragmentation in ARV1 mutants. Motif-based regression analysis of ARV1 deletion transcription profiles indicates activation of Hac1p, an integral component of the UPR. Accordingly, we show constitutive splicing of HAC1 transcripts, induction of a UPR reporter and elevated expression of UPR targets in ARV1 mutants. IRE1, encoding the unfolded protein sensor in the ER lumen, exhibits a lethal genetic interaction with ARV1, indicating a viability requirement for the UPR in cells lacking ARV1. Surprisingly, ARV1 mutants expressing a variant of Ire1p defective in sensing unfolded proteins are viable. Moreover these strains also exhibit constitutive HAC1 splicing that interacts with DTT-mediated perturbation of protein folding. These data suggest a component of UPR induction in arv1? strains is distinct from protein misfolding. Decreased ARV1 expression in murine macrophages also results in UPR induction, particularly up-regulation of activating transcription factor-4, C/EBP homologous protein (CHOP) and apoptosis. Cholesterol loading or inhibition of cholesterol esterification further elevated CHOP expression in ARV1 knockdown cells. Thus, loss or down-regulation of ARV1 disturbs membrane and lipid homeostasis resulting in a disruption of ER integrity, one consequence of which is induction of the UPR. Yeast strains were grown to mid-logarithmic stage (A600=0.5-0.6) for RNA extraction and hybridization on Ye6100 or S98 Affymetrix gene chips. The control array (sample name C) was carried out in duplicate. The ARV1 mutant array (sample name A) was carried out in triplicate. Both ARV1 mutants Ye6100 arrays were compared to the same control Ye6100 array. Strains represent different isolates of the same genotype, mating type and genetic background (w303). Sturley lab collection (SCY) strains include SCY328 and SCY2004 for controls and SCY820 and SCY840 for ARV1 mutants.

Dataset Information

An ERAD independent role for rhomboid pseudoprotease Dfm1 in mediating sphingolipid homeostasis

Publications

An ERAD-independent role for rhomboid pseudoprotease Dfm1 in mediating sphingolipid homeostasis.

Similar Datasets

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