Ufd1 is a cofactor of gp78 and plays a key role in cholesterol metabolism by regulating the stability of HMG-CoA reductase.
The membrane-anchored ubiquitin ligase gp78 promotes degradation of misfolded endoplasmic reticulum (ER) proteins and sterol-regulated degradation of HMG-CoA reductase. It was known previously that Ufd1 plays a critical role in ER-associated degradation (ERAD) together with Npl4 and VCP. The VCP-Ufd1-Npl4 complex recognizes polyubiquitin chains and transfers the ubiquitinated proteins to the proteasome. Here we show that Ufd1 directly interacts with gp78 and functions as a cofactor. Ufd1 enhances the E3 activity of gp78, accelerates the ubiquitination and degradation of reductase, and eventually promotes receptor-mediated uptake of low-density lipoprotein. Furthermore, we demonstrate that the monoubiquitin-binding site in Ufd1 is required for the enhancement of gp78 activity and that the polyubiquitin-binding site in Ufd1 is critical for a postubiquitination step in ERAD. In summary, our study identifies Ufd1 as a cofactor of gp78, reveals an unappreciated function of Ufd1 in the ubiquitination reaction during ERAD, and illustrates that Ufd1 plays a critical role in cholesterol metabolism.
State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 320 Yue-Yang Road, Shanghai 200031, China.
Jian
J
Cao
Jiang
J
Wang
Wei
W
Qi
Hong-Hua
HH
Miao
Jing
J
Wang
Liang
L
Ge
Russell A
RA
DeBose-Boyd
Jing-Jie
JJ
Tang
Bo-Liang
BL
Li
Bao-Liang
BL
Song
D033942:Adaptor Proteins, Vesicular Transport; D000596:Amino Acids; D000818:Animals; D001665:Binding Sites; D016466:CHO Cells; D002460:Cell Line; D002784:Cholesterol / Q000378:metabolism*; D006224:Cricetinae; D003412:Cricetulus; D004795:Enzyme Stability; D006801:Humans; D006903:Hydroxymethylglutaryl CoA Reductases / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins; D008077:Lipoproteins, LDL / Q000378:metabolism; D008954:Models, Biological; D011485:Protein Binding; D025941:Protein Interaction Mapping; D011499:Protein Processing, Post-Translational; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000378:metabolism*; D060285:Receptors, Autocrine Motility Factor; D018121:Receptors, Cytokine / Q000737:chemistry / Q000378:metabolism*; D025801:Ubiquitin / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases / Q000737:chemistry / Q000378:metabolism*
D033942:Adaptor Proteins, Vesicular Transport; D000596:Amino Acids; D047908:Intracellular Signaling Peptides and Proteins; D008077:Lipoproteins, LDL; D011506:Proteins; D018121:Receptors, Cytokine; C491497:UFD1 protein, human; D025801:Ubiquitin; D002784:Cholesterol; D006903:Hydroxymethylglutaryl CoA Reductases; C555000:AMFR protein, human; D060285:Receptors, Autocrine Motility Factor; D044767:Ubiquitin-Protein Ligases