Abstract
Sterol-regulated ubiquitination is an obligatory step in ER-associated degradation (ERAD) of HMG CoA reductase, a rate-limiting enzyme in cholesterol synthesis. Accelerated degradation of reductase, one of several strategies animal cells use to limit production of cholesterol, requires sterol-induced binding of the enzyme to ER membrane proteins called Insigs. Once formed, the reductase-Insig complex is recognized by a putative membrane-associated ubiquitin ligase (E3) that mediates the reductase ubiquitination reaction. Here, we show that gp78, a membrane bound E3, binds to Insig-1 and is required for sterol-regulated ubiquitination of reductase. In addition, gp78 couples regulated ubiquitination to degradation of reductase by binding to VCP, an ATPase that plays a key role in recognition and degradation of ERAD substrates. The current results identify gp78 as the E3 that initiates sterol-accelerated degradation of reductase, and Insig-1 as a bridge between gp78/VCP and the reductase substrate.
Publication types
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Research Support, N.I.H., Extramural
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Research Support, Non-U.S. Gov't
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Research Support, U.S. Gov't, P.H.S.
MeSH terms
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Adenosine Triphosphatases
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Animals
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Cell Cycle Proteins / genetics
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Cell Cycle Proteins / metabolism
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Cell Line
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Cricetinae
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Humans
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Hydroxymethylglutaryl CoA Reductases / metabolism*
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Intracellular Signaling Peptides and Proteins
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Membrane Proteins / genetics
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Membrane Proteins / metabolism*
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Models, Biological
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Protein Binding
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Protein Structure, Tertiary
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Receptors, Autocrine Motility Factor
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Receptors, Cytokine / genetics
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Receptors, Cytokine / metabolism*
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Sterols / metabolism*
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Ubiquitin / metabolism*
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Ubiquitin-Protein Ligases / genetics
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Ubiquitin-Protein Ligases / metabolism*
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Valosin Containing Protein
Substances
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Cell Cycle Proteins
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INSIG1 protein, human
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Intracellular Signaling Peptides and Proteins
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Membrane Proteins
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Receptors, Cytokine
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Sterols
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Ubiquitin
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Hydroxymethylglutaryl CoA Reductases
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AMFR protein, human
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Receptors, Autocrine Motility Factor
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Ubiquitin-Protein Ligases
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Adenosine Triphosphatases
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VCP protein, human
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Valosin Containing Protein