Functionally significant mutations in the Epstein-Barr virus LMP1 gene and their role in activation of cell signaling pathways

Protein Kinase CK2 and Epstein-Barr Virus

Protein kinase CK2 is a pleiotropic protein kinase, which phosphorylates a number of cellular and viral proteins. Thereby, this kinase is implicated in the regulation of cellular signaling, controlling of cell proliferation, apoptosis, angiogenesis, immune response, migration and invasion. In general, viruses use host signaling mechanisms for the replication of their genome as well as for cell transformation leading to cancer. Therefore, it is not surprising that CK2 also plays a role in controlling viral infection and the generation of cancer cells. Epstein-Barr virus (EBV) lytically infects epithelial cells of the oropharynx and B cells. These latently infected B cells subsequently become resting memory B cells when passing the germinal center. Importantly, EBV is responsible for the generation of tumors such as Burkitt's lymphoma. EBV was one of the first human viruses, which was connected to CK2 in the early nineties of the last century. The present review shows that protein kinase CK2 phosphorylates EBV encoded proteins as well as cellular proteins, which are implicated in the lytic and persistent infection and in EBV-induced neoplastic transformation. EBV-encoded and CK2-phosphorylated proteins together with CK2-phosphorylated cellular signaling proteins have the potential to provide efficient virus replication and cell transformation. Since there are powerful inhibitors known for CK2 kinase activity, CK2 might become an attractive target for the inhibition of EBV replication and cell transformation.

Epstein-Barr Virus Strain Variation

What is wild-type Epstein-Barr virus and are there genetic differences in EBV strains that contribute to some of the EBV-associated diseases? Recent progress in DNA sequencing has resulted in many new Epstein-Barr virus (EBV) genome sequences becoming available. EBV isolates worldwide can be grouped into type 1 and type 2, a classification based on the EBNA2 gene sequence. Type 1 transforms human B cells into lymphoblastoid cell lines much more efficiently than type 2 EBV and molecular mechanisms that may account for this difference in cell transformation are now becoming understood. Study of geographic variation of EBV strains independent of the type 1/type 2 classification and systematic investigation of the relationship between viral strains, infection and disease are now becoming possible. So we should consider more directly whether viral sequence variation might play a role in the incidence of some EBV-associated diseases.

Roles of the PI3K/Akt pathway in Epstein-Barr virus-induced cancers and therapeutic implications

Viruses have been shown to be responsible for 10%-15% of cancer cases. Epstein-Barr virus (EBV) is the first virus to be associated with human malignancies. EBV can cause many cancers, including Burkett's lymphoma, Hodgkin's lymphoma, post-transplant lymphoproliferative disorders, nasopharyngeal carcinoma and gastric cancer. Evidence shows that phosphoinositide 3-kinase/protein kinase B (PI3K/Akt) plays a key role in EBV-induced malignancies. The main EBV oncoproteins latent membrane proteins (LMP) 1 and LMP2A can activate the PI3K/Akt pathway, which, in turn, affects cell survival, apoptosis, proliferation and genomic instability via its downstream target proteins to cause cancer. It has also been demonstrated that the activation of the PI3K/Akt pathway can result in drug resistance to chemotherapy. Thus, the inhibition of this pathway can increase the therapeutic efficacy of EBV-associated cancers. For example, PI3K inhibitor Ly294002 has been shown to increase the effect of 5-fluorouracil in an EBV-associated gastric cancer cell line. At present, dual inhibitors of PI3K and its downstream target mammalian target of rapamycin have been used in clinical trials and may be included in treatment regimens for EBV-associated cancers.

Combinatorial antibody library from multiple sclerosis patients reveals antibodies that cross-react with myelin basic protein and EBV antigen

Multiple sclerosis (MS) is a widespread neurodegenerative autoimmune disease with unknown etiology. It is increasingly evident that, together with pathogenic T cells, autoreactive B cells are among the major players in MS development. The analysis of myelin neuroantigen-specific antibody repertoires and their possible cross-reactivity against environmental antigens, including viral proteins, could shed light on the mechanism of MS induction and progression. A phage display library of single-chain variable fragments (scFvs) was constructed from blood lymphocytes of patients with MS as a potential source of representative MS autoantibodies. Structural alignment of 13 clones selected toward myelin basic protein (MBP), one of the major myelin antigens, showed high homology within variable regions with cerebrospinal fluid MS-associated antibodies as well as with antibodies toward Epstein-Barr latent membrane protein 1 (LMP1). Three scFv clones showed pronounced specificity to MBP fragments 65-92 and 130-156, similar to the serum MS antibodies. One of these clones, designated E2, in both scFv and full-size human antibody constructs, was shown to react with both MBP and LMP1 proteins in vitro, suggesting natural cross-reactivity. Thus, antibodies induced against LMP1 during Epstein-Barr virus infection might act as inflammatory trigger by reacting with MBP, suggesting molecular mimicry in the mechanism of MS pathogenesis.

Functional analysis of epstein-barr virus latent membrane proteins (LMP1) in patients with limphoproliferative disorders

Latent membrane protein1 (LMP1) encoded by the LMP1 gene of the Epstein-Barr virus (EBV) is a transmembrane protein, which can activate a number of cellular signal cascades and transcriptional factors leading to cell transformation. In the present study the sequencing of full-length LMP1 variants isolated from Russian patients with Hodgkin's lymphoma (HL), non-Hodgkin's lymphomaе (NHL) and infectious mononucleosis (IM) has been carried out. The phylogenetic analysis of obtained sequences revealed dominance of the LMP1 variants belonging to proteins of low-divergent group LMP1-B95.8b characterized by minimal set of mutations. Investigation of biological properties in the Russian representatives of this group revealed that expression of studied LMP1 variants in embryonic kidney 293 cells was accompanied by insignificant increase in transcriptional factor NF-κB activation and had minor influence on activation of transcriptional factor AP-1. It was also detected that all investigated low-divergent LMP1 variants expressed in Rat-1 cells induced activation of inducible NO-synthase (iNOS) and intracellular production of nitric oxide (NO). At the same time the level of NO accumulation was lower than that induced by the low-transforming prototype variant LMP1-B95.8. The data obtained indicate that the LMP1 variants, which are the most common among Russian patients with EBV-associated lymphoproliferative diseases, are characterized by minimum number of mutations and rather low ability to activate basic cellular signaling pathways regardless the nature of pathological process, benign (IM) or malignant (HL, NHL). It is suggested that in addition to the modest activation of NF-κB and iNOS induction by LMP1 other factors are involved in the cell transformation process.