title: Cyclophilin C Participates in the US2-Mediated Degradation of Major Histocompatibility Complex Class I Molecules.
abstract: Human cytomegalovirus uses a variety of mechanisms to evade immune recognition through major histocompatibility complex class I molecules. One mechanism mediated by the immunoevasin protein US2 causes rapid disposal of newly synthesized class I molecules by the endoplasmic reticulum-associated degradation pathway. Although several components of this degradation pathway have been identified, there are still questions concerning how US2 targets class I molecules for degradation. In this study we identify cyclophilin C, a peptidyl prolyl isomerase of the endoplasmic reticulum, as a component of US2-mediated immune evasion. Cyclophilin C could be co-isolated with US2 and with the class I molecule HLA-A2. Furthermore, it was required at a particular expression level since depletion or overexpression of cyclophilin C impaired the degradation of class I molecules. To better characterize the involvement of cyclophilin C in class I degradation, we used LC-MS/MS to detect US2-interacting proteins that were influenced by cyclophilin C expression levels. We identified malectin, PDIA6, and TMEM33 as proteins that increased in association with US2 upon cyclophilin C knockdown. In subsequent validation all were shown to play a functional role in US2 degradation of class I molecules. This was specific to US2 rather than general ER-associated degradation since depletion of these proteins did not impede the degradation of a misfolded substrate, the null Hong Kong variant of α1-antitrypsin.
authors.affiliation: Department of Immunology, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Daniel C
authors.initials: DC
authors.lastname: Chapman
authors.affiliation: Department of Biochemistry, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Pawel
authors.initials: P
authors.lastname: Stocki
authors.affiliation: Department of Immunology, University of Toronto, Toronto, Ontario, Canada.|Department of Biochemistry, University of Toronto, Toronto, Ontario, Canada.
authors.forename: David B
authors.initials: DB
authors.lastname: Williams
mesh_terms: D002460:Cell Line; D000072622:Cyclophilin C; D021983:Cyclophilins / Q000235:genetics / Q000378:metabolism*; D003587:Cytomegalovirus / Q000472:pathogenicity; D060746:Endoplasmic Reticulum-Associated Degradation; D015789:HLA-A2 Antigen / Q000378:metabolism; D015395:Histocompatibility Antigens Class I / Q000378:metabolism*; D054884:Host-Pathogen Interactions; D006801:Humans; D037102:Lectins / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D019704:Protein Disulfide-Isomerases / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D053719:Tandem Mass Spectrometry; D014759:Viral Envelope Proteins / Q000235:genetics / Q000378:metabolism*; D014764:Viral Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D015789:HLA-A2 Antigen; D015395:Histocompatibility Antigens Class I; D037102:Lectins; C554484:MLEC protein, human; D008565:Membrane Proteins; D016601:RNA-Binding Proteins; C074546:US11 protein, herpesvirus; C118670:US2 protein, Varicellovirus; D014759:Viral Envelope Proteins; D014764:Viral Proteins; C000602045:transmembrane protein 33, human; C081786:cyclophilin B; D021983:Cyclophilins; D000072622:Cyclophilin C; C496931:PDIA6 protein, human; D019704:Protein Disulfide-Isomerases