Epstein-Barr virus EBNA3 proteins bind to the C8/alpha7 subunit of the 20S proteasome and are degraded by 20S proteasomes in vitro, but are very stable in latently infected B cells.
A yeast two-hybrid screen using EBNA3C as bait revealed an interaction between this Epstein-Barr virus (EBV)-encoded nuclear protein and the C8 (alpha7) subunit of the human 20S proteasome. The interaction was confirmed by glutathione S-transferase (GST) pull-down experiments and these also revealed that the related proteins EBNA3A and EBNA3B can bind similarly to C8/alpha7. The interaction between these viral proteins and GST-C8/alpha7 was shown to be significantly more robust than the previously reported interaction between C8/alpha7 and the cyclin-dependent kinase inhibitor p21(WAF1/CIP1). Co-immunoprecipitation of the EBNA3 proteins with C8/alpha7 was also demonstrated after transfection of expression vectors into B cells. Consistent with this ability to bind directly to an alpha-subunit of the 20S proteasome, EBNAs 3A, 3B and 3C were all degraded in vitro by purified 20S proteasomes. However, surprisingly, no sign of proteasome-mediated turnover of these latent viral proteins in EBV-immortalized B cells could be detected, even in the presence of gamma interferon. In actively proliferating lymphoblastoid cell lines, EBNAs 3A, 3B and 3C appear to be remarkably stable, with no evidence of either de novo synthesis or proteasome-mediated degradation.
Touitou
Robert
R
Department of Virology and Ludwig Institute for Cancer Research, Wright-Fleming Institute, Faculty of Medicine, Imperial College London, Norfolk Place, London W2 1PG, UK.
O'Nions
Jenny
J
Department of Virology and Ludwig Institute for Cancer Research, Wright-Fleming Institute, Faculty of Medicine, Imperial College London, Norfolk Place, London W2 1PG, UK.
Heaney
Judith
J
Department of Virology and Ludwig Institute for Cancer Research, Wright-Fleming Institute, Faculty of Medicine, Imperial College London, Norfolk Place, London W2 1PG, UK.
Allday
Martin J
MJ
Department of Virology and Ludwig Institute for Cancer Research, Wright-Fleming Institute, Faculty of Medicine, Imperial College London, Norfolk Place, London W2 1PG, UK.
D000956:Antigens, Viral / Q000378:metabolism*; D001402:B-Lymphocytes / Q000821:virology*; D018797:Cell Cycle Proteins / Q000378:metabolism; D050759:Cyclin-Dependent Kinase Inhibitor p21; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D019309:Epstein-Barr Virus Nuclear Antigens; D004854:Herpesvirus 4, Human / Q000502:physiology*; D006801:Humans; D047468:Immunoprecipitation; D046988:Proteasome Endopeptidase Complex / Q000502:physiology; D011485:Protein Binding; D020798:Two-Hybrid System Techniques
D000956:Antigens, Viral; C493956:CDKN1A protein, human; D018797:Cell Cycle Proteins; D050759:Cyclin-Dependent Kinase Inhibitor p21; C498774:EBNA-3C, epstein-barr virus; D019309:Epstein-Barr Virus Nuclear Antigens; C411723:lymphocryptovirus nuclear antigen 3A; C411724:lymphocryptovirus nuclear antigen 3B; D003546:Cysteine Endopeptidases; C488662:PSMA7 protein, human; D046988:Proteasome Endopeptidase Complex