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Sterol-induced degradation of HMG CoA reductase depends on interplay of two Insigs and two ubiquitin ligases, gp78 and Trc8
- Source :
- Proceedings of the National Academy of Sciences. 108:20503-20508
- Publication Year :
- 2011
- Publisher :
- Proceedings of the National Academy of Sciences, 2011.
-
Abstract
- Accumulation of sterols in membranes of the endoplasmic reticulum (ER) leads to the accelerated ubiquitination and proteasomal degradation of 3-hydroxy-3-methylglutaryl coenzyme A reductase, a rate-limiting enzyme in synthesis of cholesterol and nonsterol isoprenoids. This degradation results from sterol-induced binding of reductase to the Insig-1 or Insig-2 proteins of ER membranes. We previously reported that in immortalized human fibroblasts (SV-589 cells) Insig-1, but not Insig-2, recruits gp78, a membrane-bound RING-finger ubiquitin ligase. We now report that both Insig-1 and Insig-2 bind another membrane-bound RING-finger ubiquitin ligase called Trc8. Knockdown of either gp78 or Trc8 in SV-589 cells through RNA interference (RNAi) inhibited sterol-induced ubiquitination of reductase and inhibited sterol-induced degradation by 50–60%. The combined knockdown of gp78 and Trc8 produced a more complete inhibition of degradation (> 90%). Knockdown of gp78 led to a three to fourfold increase in levels of Trc8 and Insig-1 proteins, which opposed the inhibitory action of gp78. In contrast, knockdown of Trc8 had no effect on gp78 or Insig-1. The current results suggest that sterol-induced ubiquitination and proteasomal degradation of reductase is dictated by the complex interplay of at least four proteins: Insig-1, Insig-2, gp78, and Trc8. Variations in the concentrations of any one of these proteins may account for differences in cell- and/or tissue-specific regulation of reductase degradation.
- Subjects :
- 7-Dehydrocholesterol reductase
Ubiquitin-Protein Ligases
Receptors, Cell Surface
CHO Cells
Reductase
Endoplasmic Reticulum
Cricetulus
Ubiquitin
Cricetinae
Animals
Gene knockdown
Multidisciplinary
biology
Intracellular Signaling Peptides and Proteins
Membrane Proteins
Fibroblasts
Biological Sciences
Hydroxymethylglutaryl-CoA reductase
Ubiquitin ligase
Cell biology
Receptors, Autocrine Motility Factor
Sterols
Biochemistry
Membrane protein
HMG-CoA reductase
biology.protein
Hydroxymethylglutaryl CoA Reductases
RNA Interference
Subjects
Details
- ISSN :
- 10916490 and 00278424
- Volume :
- 108
- Database :
- OpenAIRE
- Journal :
- Proceedings of the National Academy of Sciences
- Accession number :
- edsair.doi.dedup.....6b03f284ddcb2f04013fd490d8fffc73