Lipid saturation induces degradation of squalene epoxidase for sterol homeostasis and cell survival

Abstract

A fluid membrane containing a mix of unsaturated and saturated lipids is essential for life. However, it is unclear how lipid saturation might affect lipid homeostasis, membrane-associated proteins, and membrane organelles. Here, we generate temperature-sensitive mutants of the sole fatty acid desaturase geneOLE1in the budding yeastSaccharomyces cerevisiae. Using these mutants, we show that lipid saturation triggers the endoplasmic reticulum–associated degradation (ERAD) of squalene epoxidase Erg1, a rate-limiting enzyme in sterol biosynthesis, via the E3 ligase Doa10-Ubc7 complex. We identify the P469L mutation that abolishes the lipid saturation–induced ERAD of Erg1. Overexpressed WT or stable Erg1 mutants all mislocalize into foci in theole1mutant, whereas the stable Erg1 causes aberrant ER and severely compromises the growth ofole1, which are recapitulated bydoa10deletion. The toxicity of the stable Erg1 anddoa10deletion is due to the accumulation of lanosterol and misfolded proteins inole1. Our study identifies Erg1 as a novel lipid saturation–regulated ERAD target, manifesting a close link between lipid homeostasis and proteostasis that maintains sterol homeostasis under the lipid saturation condition for cell survival.

The constitutively active form of a key cholesterol synthesis enzyme is lipid droplet-localized and upregulated in endometrial cancer tissues

“…TrunSM closely resembles the yeast SM homolog Erg1p, which lacks an N-terminal regulatory domain ( 7 ), is peripherally associated with the ER membrane ( 37 , 38 ) and partitions to LDs ( 39 ). The partitioning of Erg1p depends on two hydrophobic helices at its C terminus ( 40 ), which are also found in human SM (residues ∼516–567) and retained upon its truncation ( 9 , 41 ).…”

Characterization of endoplasmic reticulum-associated degradation in the human fungal pathogen Candida albicans

“…In S. cerevisiae and humans, ERAD machinery controls sterol abundance to meet cellular demands via feedback-regulated degradation of sterol biosynthetic enzymes ( Foresti et al, 2013 ; Garza, Tran & Hampton, 2009 ; Hampton, Gardner & Rine, 1996 ; Huang & Chen, 2023 ; Jo et al, 2011 ; Stevenson, Huang & Olzmann, 2016 ). We observed enrichment of proteins with roles in sterol synthesis in C. albicans ERAD mutants, including CaErg3, the homolog of a bona fide S. cerevisiae ERAD substrate ( Jaenicke et al, 2011 ).…”

“…In addition to their well-characterized roles in protein quality control, ScHrd1 and ScDoa10 also contribute to regulated turnover of otherwise normal proteins. For example, S. cerevisiae and mammalian homologs of Hrd1 and Doa10 promote regulated turnover of sterol biosynthetic enzymes ( Foresti et al, 2013 ; Garza, Tran & Hampton, 2009 ; Hampton, Gardner & Rine, 1996 ; Huang & Chen, 2023 ; Jo et al, 2011 ; Stevenson, Huang & Olzmann, 2016 ).…”

Lipid Biosynthesis Perturbation Impairs Endoplasmic Reticulum-Associated Degradation

“…Additionally, degradation of the misfolded ER luminal yeast protein CPY* is sensitive to CHO2 deletion (THIBAULT et al 2012) and, more modestly, to mutations that impair lipid droplet formation (YAP et al 2020). Yeast and mammalian homologs of Hrd1 and Doa10 promote feedback-regulated degradation of sterol-biosynthetic enzymes as well as turnover of proteins implicated in triacylglycerol and low-density-lipoprotein synthesis (HAMPTON et al 1996;GARZA et al 2009;JO et al 2011;FORESTI et al 2013;STEVENSON et al 2016;HUANG AND CHEN 2023). Moreover, the ER-resident rhomboid pseudoprotease Dfm1 was recently shown to regulate the ER export and Golgi-associated degradation of Orm2, an inhibitor of sphingolipid biosynthesis (BHADURI et al 2022).…”

“…2013; S tevenson et al . 2016; H uang and C hen 2023). Moreover, the ER-resident rhomboid pseudoprotease Dfm1 was recently shown to regulate the ER export and Golgi-associated degradation of Orm2, an inhibitor of sphingolipid biosynthesis (B haduri et al .…”