title: Proteasome inhibitor induces nucleolar translocation of Epstein-Barr virus-encoded EBNA-5.
abstract: We have previously shown that Epstein-Barr virus (EBV)-encoded EBNA-5 is localized to PML bodies (PODs) in EBV-immortalized lymphoblastoid cell lines (LCLs). Here we have extended our study of the subnuclear localization of EBNA-5 and found a strict co-localization with PML in LCLs and in BL lines with an immunoblastic, LCL-like phenotype. Moreover, GFP-EBNA-5 accumulated in PML bodies upon transfection into LCLs. In contrast, transfection of cell lines of non-immunoblastic origin with an EBNA-5 expression construct showed preferential localization of the protein to the nucleoplasm. Since PML is involved in proteasome-dependent protein degradation, we investigated the total levels and sub-cellular localization of EBNA-5 upon inhibition of proteasome activity. We found that a proteasome inhibitor, MG132, induced the translocation of both endogenous and transfected EBNA-5 to the nucleoli in every cell line tested. The total EBNA-5 protein levels were not affected by the proteasomal block. EBNA-5 forms complexes with heat shock protein Hsp70. The proteasome inhibitor induced a rise in total levels of Hsp70 and dramatically changed its homogeneous nuclear and cytoplasmic distribution into nucleolar and cytoplasmic. This effect was EBNA-5-independent. The nucleolar localization of Hsp70 was enhanced by the presence of EBNA-5, however. EBNA-5 also enhanced the nucleolar translocation of a mutant p53 in a colon cancer line, SW480, treated with MG132. The coordinated changes in EBNA-5 and Hsp70 localization and the effect of EBNA-5 on mutant p53 distribution upon MG132 treatment might reflect the involvement of EBNA-5 in the regulation of intracellular protein trafficking associated with the proteasome-mediated degradation.
authors.affiliation: Microbiology and Tumor Biology Center, Karolinska Institute, S-171 77 Stockholm, Sweden1.
authors.forename: Katja
authors.initials: K
authors.lastname: Pokrovskaja
authors.affiliation: Microbiology and Tumor Biology Center, Karolinska Institute, S-171 77 Stockholm, Sweden1.
authors.forename: Karin
authors.initials: K
authors.lastname: Mattsson
authors.affiliation: Microbiology and Tumor Biology Center, Karolinska Institute, S-171 77 Stockholm, Sweden1.
authors.forename: Elena
authors.initials: E
authors.lastname: Kashuba
authors.affiliation: Microbiology and Tumor Biology Center, Karolinska Institute, S-171 77 Stockholm, Sweden1.
authors.forename: George
authors.initials: G
authors.lastname: Klein
authors.affiliation: Microbiology and Tumor Biology Center, Karolinska Institute, S-171 77 Stockholm, Sweden1.
authors.forename: Laszlo
authors.initials: L
authors.lastname: Szekely
mesh_terms: D001402:B-Lymphocytes / Q000187:drug effects / Q000378:metabolism; D002466:Cell Nucleolus / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism*; D003546:Cysteine Endopeptidases / Q000378:metabolism; D003593:Cytoplasm / Q000187:drug effects / Q000378:metabolism; D019309:Epstein-Barr Virus Nuclear Antigens / Q000235:genetics / Q000378:metabolism*; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism; D004854:Herpesvirus 4, Human / Q000502:physiology*; D006801:Humans; D007976:Leupeptins / Q000494:pharmacology*; D009097:Multienzyme Complexes / Q000037:antagonists & inhibitors* / Q000378:metabolism; D009154:Mutation / Q000235:genetics; D009504:Neutrophils / Q000187:drug effects / Q000378:metabolism; D015530:Nuclear Matrix / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex; D011485:Protein Binding; D021381:Protein Transport / Q000187:drug effects; D014162:Transfection; D014407:Tumor Cells, Cultured; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism
chemical_list: C421621:EBNA-5 protein, Epstein-Barr virus; D019309:Epstein-Barr Virus Nuclear Antigens; D018840:HSP70 Heat-Shock Proteins; D007976:Leupeptins; D009097:Multienzyme Complexes; D016159:Tumor Suppressor Protein p53; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde