HRD1 and UBE2J1 target misfolded MHC class I heavy chains for endoplasmic reticulum-associated degradation.
The assembly of MHC class I molecules is governed by stringent endoplasmic reticulum (ER) quality control mechanisms. MHC class I heavy chains that fail to achieve their native conformation in complex with β2-microglobulin (β2m) and peptide are targeted for ER-associated degradation. This requires ubiquitination of the MHC class I heavy chain and its dislocation from the ER to the cytosol for proteasome-mediated degradation, although the cellular machinery involved in this process is unknown. Using an siRNA functional screen in β2m-depleted cells, we identify an essential role for the E3 ligase HRD1 (Synoviolin) together with the E2 ubiquitin-conjugating enzyme UBE2J1 in the ubiquitination and dislocation of misfolded MHC class I heavy chains. HRD1 is also required for the ubiquitination and degradation of the naturally occurring hemochromatosis-associated HFE-C282Y mutant, which is unable to bind β2m. In the absence of HRD1, misfolded HLA-B27 accumulated in cells with a normal MHC class I assembly pathway, and HRD1 depletion prevented the appearance of low levels of cytosolic unfolded MHC I heavy chains. HRD1 and UBE2J1 associate in a complex together with non-β2m bound MHC class I heavy chains, Derlin 1, and p97 and discriminate misfolded MHC class I from conformational MHC I-β2m-peptide heterotrimers. Together these data support a physiological role for HRD1 and UBE2J1 in the homeostatic regulation of MHC class I assembly and expression.
Cambridge Institute for Medical Research, University of Cambridge, Cambridge CB2 0XY, United Kingdom.
Marian L
ML
Burr
Florencia
F
Cano
Stanislava
S
Svobodova
Louise H
LH
Boyle
Jessica M
JM
Boname
Paul J
PJ
Lehner
D004721:Endoplasmic Reticulum / Q000378:metabolism*; D006367:HeLa Cells; D015395:Histocompatibility Antigens Class I / Q000378:metabolism*; D006801:Humans; D006868:Hydrolysis; D017510:Protein Folding; D034741:RNA, Small Interfering / Q000235:genetics; D044763:Ubiquitin-Conjugating Enzymes / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism*; D054875:Ubiquitination
D015395:Histocompatibility Antigens Class I; D034741:RNA, Small Interfering; C489967:UBE2J1 protein, human; D044763:Ubiquitin-Conjugating Enzymes; C482345:SYVN1 protein, human; D044767:Ubiquitin-Protein Ligases
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