The role of a novel p97/valosin-containing protein-interacting motif of gp78 in endoplasmic reticulum-associated degradation.
Improperly folded proteins in the endoplasmic reticulum (ER) are eliminated via ER-associated degradation, a process that dislocates misfolded proteins from the ER membrane into the cytosol, where they undergo proteasomal degradation. Dislocation requires a subclass of ubiquitin ligases that includes gp78 in addition to the AAA ATPase p97/VCP and its cofactor, the Ufd1-Npl4 dimer. We have previously reported that gp78 interacts directly with p97/VCP. Here, we identify a novel p97/VCP-interacting motif (VIM) within gp78 that mediates this interaction. We demonstrate that the VIM of gp78 recruits p97/VCP to the ER, but has no effect on Ufd1 localization. We also show that gp78 VIM interacts with the ND1 domain of p97/VCP that was shown previously to be the binding site for Ufd1. To evaluate the role of Ufd1 in gp78-p97/VCP-mediated degradation of CD3delta, a known substrate of gp78, RNA interference was used to silence the expression of Ufd1 and p97/VCP. Inhibition of p97/VCP, but not Ufd1, stabilized CD3delta in cells that overexpress gp78. However, both p97/VCP and Ufd1 appear to be required for CD3delta degradation in cells expressing physiological levels of gp78. These results raise the possibility that Ufd1 and gp78 may bind p97/VCP in a mutually exclusive manner and suggest that gp78 might act in a Ufd1-independent degradation pathway for misfolded ER proteins, which operates in parallel with the previously established p97/VCP-Ufd1-Npl4-mediated mechanism.
Ballar
Petek
P
Medical Biotechnology Center, University of Maryland Biotechnology Institute, Baltimore, Maryland 21201, USA.
Shen
Yuxian
Y
Yang
Hui
H
Fang
Shengyun
S
D000251:Adenosine Triphosphatases; D020816:Amino Acid Motifs; D000818:Animals; D017252:CD3 Complex / Q000378:metabolism; D018797:Cell Cycle Proteins / Q000378:metabolism*; D002460:Cell Line; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins; D047908:Intracellular Signaling Peptides and Proteins; D051379:Mice; D011485:Protein Binding; D011499:Protein Processing, Post-Translational; D011506:Proteins / Q000378:metabolism; D034622:RNA Interference; D060285:Receptors, Autocrine Motility Factor; D018121:Receptors, Cytokine / Q000737:chemistry* / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases / Q000737:chemistry* / Q000378:metabolism*; D000074405:Valosin Containing Protein
D017252:CD3 Complex; C472562:CD3delta antigen; D018797:Cell Cycle Proteins; D036341:Intercellular Signaling Peptides and Proteins; D047908:Intracellular Signaling Peptides and Proteins; D011506:Proteins; D018121:Receptors, Cytokine; C107396:Ufd1 protein, mouse; C555000:AMFR protein, human; C555002:Amfr protein, mouse; D060285:Receptors, Autocrine Motility Factor; D044767:Ubiquitin-Protein Ligases; D000251:Adenosine Triphosphatases; C000614178:VCP protein, human; D000074405:Valosin Containing Protein; C000614179:Vcp protein, mouse