HMG-CoA reductase (HMGR) is the rate-limiting enzyme of sterol synthesis. HMGR is an integral membrane protein that undergoes regulated degradation by ER-associated degradation, or ERAD, in response to changing cellular demand for sterols. We originally showed that the yeast HMGR isozyme Hmg2p is regulated in a manner similar to the mammalian enzyme, allowing us to exploit unique study opportunities available in yeast. Hmg2p undergoes degradation by the HRD pathway, through the action of the Hrdlp E3 ubiquitin ligase, and the sterol pathway molecule FPP regulates HRD-dependent Hmg2p degradation. The HRD pathway also functions in ER quality control, programming the destruction of many misfolded ER proteins. Accordingly, we have proposed the structural transition hypothesis for regulation: that an FPP-derived signal causes Hmg2p to undergo transition to a structure with features of a HRD quality control substrate. We have been testing this model and at the same time increasing our understanding of the HRD pathway, developing several new biochemical assays to directly address these issues. In the current work we will 1) Continue our analysis of the HRD ubiquitin ligase complex, 2) Analyze the features of the Hmg2p protein that allow its regulation by sterol pathway signals, 3) Delineate the identity and action of the lipid signals that control Hmg2p entry into the HRD pathway. 4) Study the mechanism of retrotranslocation of HRD pathway substrates required for ERAD of Hmg2p. Hmg2p degradation lies at the interface of sterol regulation and protein quality control. Thus, our work is relevant both to understanding the cellular control of sterol synthesis, and the destruction of misfolded proteins;two areas of broad and current medical import.

Agency
National Institute of Health (NIH)
Institute
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Type
Research Project (R01)
Project #
5R01DK051996-15
Application #
8022817
Study Section
Membrane Biology and Protein Processing (MBPP)
Program Officer
Haft, Carol R
Project Start
1997-01-01
Project End
2012-01-31
Budget Start
2011-02-01
Budget End
2012-01-31
Support Year
15
Fiscal Year
2011
Total Cost
$295,580
Indirect Cost
Name
University of California San Diego
Department
Biology
Type
Schools of Arts and Sciences
DUNS #
804355790
City
La Jolla
State
CA
Country
United States
Zip Code
92093
Theesfeld, Chandra L; Hampton, Randolph Y (2013) Insulin-induced gene protein (INSIG)-dependent sterol regulation of Hmg2 endoplasmic reticulum-associated degradation (ERAD) in yeast. J Biol Chem 288:8519-30
Hampton, Randolph Y; Sommer, Thomas (2012) Finding the will and the way of ERAD substrate retrotranslocation. Curr Opin Cell Biol 24:460-6
Theesfeld, Chandra L; Pourmand, Deeba; Davis, Talib et al. (2011) The sterol-sensing domain (SSD) directly mediates signal-regulated endoplasmic reticulum-associated degradation (ERAD) of 3-hydroxy-3-methylglutaryl (HMG)-CoA reductase isozyme Hmg2. J Biol Chem 286:26298-307
Heck, Jarrod W; Cheung, Samantha K; Hampton, Randolph Y (2010) Cytoplasmic protein quality control degradation mediated by parallel actions of the E3 ubiquitin ligases Ubr1 and San1. Proc Natl Acad Sci U S A 107:1106-11
Sato, Brian K; Schulz, Daniel; Do, Phong H et al. (2009) Misfolded membrane proteins are specifically recognized by the transmembrane domain of the Hrd1p ubiquitin ligase. Mol Cell 34:212-22
Garza, Renee M; Tran, Peter N; Hampton, Randolph Y (2009) Geranylgeranyl pyrophosphate is a potent regulator of HRD-dependent 3-Hydroxy-3-methylglutaryl-CoA reductase degradation in yeast. J Biol Chem 284:35368-80
Garza, Renee M; Sato, Brian K; Hampton, Randolph Y (2009) In vitro analysis of Hrd1p-mediated retrotranslocation of its multispanning membrane substrate 3-hydroxy-3-methylglutaryl (HMG)-CoA reductase. J Biol Chem 284:14710-22
Hampton, Randolph Y; Garza, Renee M (2009) Protein quality control as a strategy for cellular regulation: lessons from ubiquitin-mediated regulation of the sterol pathway. Chem Rev 109:1561-74
Federovitch, Christine M; Jones, Ying Z; Tong, Amy H et al. (2008) Genetic and structural analysis of Hmg2p-induced endoplasmic reticulum remodeling in Saccharomyces cerevisiae. Mol Biol Cell 19:4506-20
Hampton, Randolph Y (2002) Proteolysis and sterol regulation. Annu Rev Cell Dev Biol 18:345-78

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