Epstein-Barr virus (EBV) latent membrane protein 1 (LMP-1

The protein kinase (PK) encoded by the Epstein-Barr Virus (EBV) BGLF4 gene is the only EBV protein kinase. The expression pattern of EBV PK during the reactivation of the viral lytic cycle and the subcellular localization of the protein were analyzed with a polyclonal antiserum raised against a peptide corresponding to the N terminus of EBV PK. Based on previously published data (E. Gershburg and J. S. Pagano, J. Virol. 76:998-1003, 2002) and the expression pattern described here, we conclude that EBV PK is an early protein that requires viral-DNA replication for maximum expression. By biochemical fractionation, the protein could be detected mainly in the nuclear fraction 4 h after viral reactivation in Akata cells. Nuclear localization could be visualized by indirect immunofluorescence in HeLa cells transiently expressing EBV BGLF4 in the absence of other viral products. Transient expression of 3-terminal deletion mutants of EBV BGLF4 resulted in cytoplasmic localization, confirming the presence of a nuclear localization site in the C-terminal region of the protein. In contrast to the wild-type EBV PK, all of the mutants were unable to hyperphosphorylate EA-D during coexpression or to phosphorylate ganciclovir, as measured by an in-cell activity assay. Thus, the results demonstrate that the nuclear localization, as well as the kinase activity, of BGFL4 is dependent on an intact C-terminal region.Many large DNA viruses encode their own protein kinases that manage different aspects of virus replication and virus-cell interactions (21). Phosphorylation of cellular and viral proteins, which has been observed during lytic infection of cells by herpesviruses, seems to be a common phenomenon that involves a number of different protein kinase activities (17). Two groups of viral protein kinases (PKs) have been identified in herpesviruses. Alphaherpesviruses encode members of both groups. The US3 gene of herpes simplex virus type 1 (HSV-1) (28) exemplifies the first group, which was first predicted to encode protein kinases on the basis of strong similarity to the family of eukaryotic serine/threonine protein kinases. Later, a number of targets for this kinase, such as HSV UL34 (35), US9 (14), UL12 (15), and the cellular proapoptotic protein BAD (15), were identified. UL13, the representative of a second group, has been shown to phosphorylate the viral proteins ICP22 (34), gE and gI (30), and ICP0 (31), as well as cellular translation elongation factor 1 delta (20) and p60 (6). Despite the facts that US3 is involved in the inhibition of apoptosis (2, 22) and both US3 and UL13 regulate a number of key factors, both seem to be dispensable for the replication of HSV-1 in vitro (12,16,24).Beta-and gammaherpesviruses encode only protein kinases belonging to the second group, with homology to HSV UL13. This group, identified by sequence homology, includes UL97 of human cytomegalovirus (HCMV), BGLF4 of Epstein-Barr virus (EBV) (36), U69 of human herpesvirus 6 (1), ORF36 of Kaposi's sarcoma-associated herpesvirus (33), and a fe...

The human cytomegalovirus (HCMV) homolog of the Epstein-Barr virus (EBV) protein kinase (PK), UL97, is inhibited by maribavir (1263W94) and selected indolocarbazoles. Here we show that only one of these indolocarbazoles (K252a), but not maribavir, inhibits autophosphorylation of the EBV PK, BGLF4. However, maribavir and another indolocarbazole, NGIC-I, do inhibit EBV DNA synthesis, suggesting that although these last compounds inhibit both HCMV and EBV, they seem to operate through different pathways.

Epstein-Barr virus (EBV) latent membrane protein 1 (LMP-1) is required for EBV immortalization of primary B cells in vitro. Signal transducers and activators of transcription (STATs) play a pivotal role in the initiation and maintenance of certain cancers. STAT proteins, especially STAT-1, -3, and -5, are persistently tyrosine phosphorylated or activated in many cancers. We show here that EBV-infected type III latency cells, in which the EBV oncoprotein, LMP-1 is expressed, express high levels of four STATs (STAT-1, -2, -3, and -5A) and that LMP-1 is responsible for the induction of three (STAT-1, -2, and -3). In addition, the C-terminal activator region 1 (CTAR-1) and CTAR-2 of LMP-1 cooperatively induced the expression of STAT-1. The cooperativity was evident when CTAR-1 and CTAR-2 were present in cis, but not in trans. Furthermore, NF-kappaB is an essential factor involved in the induction of STAT-1. Most of the induced STATs were not phosphorylated at the critical tyrosine residue activated by many cytokines. However, the induced STATs, at least STAT-1, were functional because it could be activated by interferon (IFN) and could upregulate an IFN-inducible gene. Finally, expression of STAT-1, but not STAT-2 and -3, is associated with EBV transformation. The association of the expression of STAT-1, -2, -3, and -5A with EBV type III latency and the expression of STAT-1 in the EBV transformation process may be part of the viral programming that regulates viral latency and cellular transformation.