Reversible nucleolar translocation of Epstein--Barr virus-encoded EBNA-5 and hsp70 proteins after exposure to heat shock or cell density congestion

Abstract

The Epstein-Barr virus (EBV)-encoded, nuclear matrix-associated EBNA-5 protein is preferentially localized within distinct nuclear blobs in EBV-immortalized lymphoblastoid cell lines. We have previously found that the same blobs also contain retinoblastoma (Rb) protein. We now show that they contain hsp70 protein as well. Both EBNA-5 and hsp70 translocate to the nucleolus under cell density congestion or after heat shock. Both proteins relocate to their original position upon the re-establishment of normal physiological conditions. EBNA-5 is tightly bound to the nuclear matrix. The translocated EBNA-5 is also tightly associated with matrix structures, as shown by sequential elution-based cell fractionation. The Rb protein does not translocate to the nucleolus. The virally encoded EBNA-1, -2, -3 and -6, and cellular PCNA, snRNP and cyclin E are not affected either. The translocation of EBNA-5 to the nucleolus is not species- or cell type-specific since stress conditions induced the same phenomenon in EBNA-5-transfected human, mouse and rat cells of different tissue origins.

Epstein–Barr virus encoded nuclear protein EBNA-3 binds XAP-2, a protein associated with Hepatitis B virus X antigen

“…Immunostaining and digital image capturing was carried out as described (Szekely et al, 1996(Szekely et al, , 1997(Szekely et al, , 1998 using the anti-EBNA-3A monoclonal antibody T2.78-19.…”

“…EBNA-6 moreover has papilloma virus E7 like functions. EBNA-5 accumulates in the PML containing oncogenic domains (PODs) where it co-localizes with the retinoblastoma tumor suppressor protein (Szekely et al, 1996).…”

Recombinant PML adenovirus suppresses growth and tumorigenicity of human breast cancer cells by inducing G1 cell cycle arrest and apoptosis

“…Some viral proteins such as ICPO (Maul et al, 1993), the adenoviral protein E1A, E4-ORF3, and E1B (Carvalho et al, 1995;Doucas et al, 1996). Epstein-Barr nuclear protein 5 (Szekely et al, 1996), and a novel ubiquitin-speci®c protease (Everett et al, 1997) are shown to target and reorganize PODs. These studies demonstrated that after virus infection a dramatic structural change in the PODs was found, suggesting that PODs are the target of tumor virus oncoproteins.…”

Epstein-Barr virus-encoded LMP-1 protein upregulates the pNDCF group of nucleoskeleton-cytoskeleton-associated proteins.

“…The in vitro EBV-converted subline BL41\95 that has switched to a more immunoblastic (type III) phenotype (Torsteinsdottir et al, 1989) showed increased expression of the pNDCFs and vimentin. Most of the pNDCFs were associated with cytoplasmic filaments in these cells, as in LCLs and some type III BLs (Szekely et al, 1997).…”

“…They are not expressed in phenotypically representative (type I) BL cells, or are only present at low levels, localized within the nucleus. In EBVimmortalized LCLs and in some of the LCL-like (type III) BL cell lines, the pNDCFs are expressed at a high level, preferentially associated with vimentin filaments in the cytoplasm (Szekely et al, 1997).…”