Epstein-Barr virus (EBV) nuclear antigen leader protein (EBNA-LP

Translation elongation factor 1δ (EF-1δ) is hyperphosphorylated in various mammalianThese results indicate that purified BGLF4 possesses protein kinase activity and mediates EF-1δ hyperphosphorylation. These data also support the hypothesis that the protein kinases that are conserved by herpesviruses universally mediate EF-1δ modification in mammalian cells.

Epstein-Barr virus (EBV) nuclear antigen leader protein (EBNA-LP) consists of W1W2 repeats and a unique C-terminal Y1Y2 domain and plays a critical role in EBV-induced transformation. To identify the cellular proteins associating with EBNA-LP, we performed a yeast two-hybrid screen using EBNA-LP cDNA containing a single W1W2 domain as bait and an EBV-transformed human peripheral blood lymphocyte cDNA library as the source of cellular genes. Our results were as follows. (i) A cDNA in the positive yeast colony was found to encode a cellular protein, human oestrogen-related receptor 1 (hERR1), which is a constitutive transcriptional activator of the various types of oestrogen response elements. (ii) A purified chimeric protein consisting of glutathione S-transferase (GST) fused to hERR1 specifically formed complexes with EBNA-LPs containing one (EBNA-LPR1), two (EBNA-LPR2) or four W1W2 repeats (EBNA-LPR4) transiently expressed in COS-7 cells. Reciprocally, GST fused to EBNA-LPR1 or EBNA-LPR2 pulled down hERR1 transiently expressed in COS-7 cells. (iii) Mutational analyses of EBNA-LP revealed that the Y2 domain of EBNA-LP is responsible for the interaction with hERR1 and two leucines in the Y2 domain , which are conserved among a subset of primate gammaherpesviruses, are interactive sites for hERR1. So far, it has been reported that the only domain of EBNA-LP critical for EBV-induced transformation is the Y1Y2 domain. Potential roles of hERR1 in EBV-induced transformation are discussed. INTRODUCTIONEpstein-Barr virus (EBV) is a human gammaherpesvirus that is closely associated with infectious mononucleosis and a wide variety of human malignancies such as endemic Burkitt's lymphoma, nasopharyngeal carcinoma, Hodgkin's disease, gastric carcinoma and various lymphomas (reviewed in . In vitro, EBV can readily infect resting human B-cells and efficiently immortalize them. The resultant lymphoblastoid cell lines (LCLs) express only a subset of viral genes including six viral nuclear antigens (EBNA-1, -2, -3A, -3B, -3C and LP), three integral latent membrane proteins (LMP-1, -2A and -2B) and two small RNAs (EBERs), possibly for effective stimulation of cell growth and maintenance of the viral episome in proliferating cells (reviewed in ). Among these latency-associated EBV proteins, EBNA-1, EBNA-2, EBNA-3A, EBNA-3C, EBNA-LP and LMP-1 are critical for EBV-induced B-cell immortalization, whereas EBNA-3B, LMP2A, LMP2B and EBERs are not (reviewed by ).The first gene products expressed immediately after the infection by EBV of B-cells are EBNA-LP and EBNA-2 (Alfieri et al., 1991). These genes are transcribed from the BamHI W promoter (Wp), and from the BamHI C promoter (Cp) followed by the gradual waning of Wp activity (Fig. 1A) (Woisetschlaeger et al., 1990(Woisetschlaeger et al., , 1991 promoters of the latency-associated viral genes in LCLs as well as cellular gene expression including c-myc, c-fgr, CD21 and CD23 (reviewed in Kieff, 1996). The other protein, EBNA-LP, a subject of this report, contains multiple copies of a 6...

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