Elliott Kieff

Induction of bcl-2 expression by epstein-barr virus latent membrane protein 1 protects infected B cells from programmed cell death

Epstein-Barr virus (EBV) not only induces growth transformation in human B lymphocytes, but has more recently been shown to enhance B cell survival under suboptimal conditions where growth is inhibited; both effects are mediated through the coordinate action of eight virus-coded latent proteins. The effect upon cell survival is best recognized in EBV-positive Burkitts lymphoma cell lines where activation of full virus latent gene expression protects the cells from programmed cell death (apoptosis). Here we show by DNA transfection into human B cells that protection from apoptosis is conferred through expression of a single EBV latent protein, the latent membrane protein LMP 1. Furthermore, we demonstrate that LMP 1 mediates this effect by up-regulating expression of the cellular oncogene bcl-2. The interplay between EBV infection and expression of this cellular oncogene has important implications for virus persistence and for the pathogenesis of virus-associated malignant disease.

An EBV membrane protein expressed in immortalized lymphocytes transforms established rodent cells

Epstein-Barr virus expresses a cytoplasmic and plasma membrane protein (LMP) in latently infected growth transformed lymphocytes. The gene specifying LMP has now been expressed in NIH3T3 and Rat-1 cells. Expression of the gene in these cells resulted in altered cell morphology and some resistance to the growth inhibiting effect of medium containing low serum. In Rat-1 cells, LMP expression often led to loss of contact inhibition and anchorage-independent growth in soft agar. Rat-1 cells expressing LMP were uniformly tumorigenic in nude mice. Thus, LMP is a transforming gene which is likely to account for many aspects of EBV induced cell transformations. This is the first demonstration of a transforming gene in Epstein-Barr virus, a ubiquitous human pathogen associated with neoplasia.

Expression of Epstein–Barr Virus Transformation–Associated Genes in Tissues of Patients with EBV Lymphoproliferative Disease

Epstein-Barr virus (EBV) has been associated with serious or fatal lymphoproliferative disease in immunocompromised patients. EBV nuclear protein 2 and latent membrane protein are characteristically expressed in B lymphocytes proliferating in vitro in response to growth transformation by EBV. These two proteins are thought to be effectors of lymphocyte growth since they increase the expression of B-lymphocyte activation (CD23) and cell-adhesion (LFA 3 and ICAM 1) molecules in vitro. Using monoclonal antibody-immune microscopy, we have demonstrated that these two EBV proteins and their associated B-lymphocyte activation or adhesion molecules are expressed in the infiltrating B lymphocytes in immunocompromised patients with EBV lymphoproliferative disease. These monoclonal antibodies should be useful in the early diagnosis of EBV lymphoproliferative disease and in distinguishing it from other B-lymphocyte cancers associated with EBV, such as Burkitts lymphoma. The finding of EBV nuclear protein 2 and latent membrane protein and their associated activation or adhesion molecules provides a further pathophysiologic link between EBV and the proliferation of B lymphocytes in immunocompromised patients.

Characterization of herpes simplex virus strains differing in their effects on social behaviour of infected cells.

Summary Established (laboratory) strains and fresh isolates of herpes simplex virus from patients with skin and genital lesions were classified into four groups depending on their effects on the social interaction among infected hep-2 cells. The groups comprised strains causing (1) rounding of cells but no adhesion or fusion, (2) loose aggregation of rounded cells, (3) tight adhesion of rounded cells, and (4) fusion of cells into polykaryocytes. Protype strains from each group were found to differ with respect to immunologic specificity, buoyant density in CsCl solutions and stability at 40°.

Nitric Oxide Produced by Human B Lymphocytes Inhibits Apoptosis and Epstein-Barr Virus Reactivation

Nitric oxide (NO) produced by murine macrophages is important in murine resistance to ectromelia virus, herpes simplex virus, and vaccinia virus infection. In contrast, NO production by human mononuclear cells has been difficult to demonstrate, and a role for NO in human responses to infection is uncertain. We report constitutive, low level, macrophage-type NO synthase (iNOS) expression in Epstein-Barr virus (EBV)-transformed human B lymphocytes and Burkitts lymphoma cell lines. Immune NOS activity is involved in maintaining EBV latency through down-regulation of the expression of the immediate-early EBV transactivator Zta. NO also inhibits apoptosis in B lymphocyte cell lines. The effects of NO are largely independent of cGMP and influential on signaling pathways regulated by (sulfhydryl) redox status. These results suggest that NO plays a physiological role in human B cell biology by inhibiting programmed cell death and maintaining viral latency.

Association of TRAF1, TRAF2, and TRAF3 with an Epstein-Barr virus LMP1 domain important for B-lymphocyte transformation: role in NF-kappaB activation.

The Epstein-Barr virus (EBV) transforming protein LMP1 appears to be a constitutively activated tumor necrosis factor receptor (TNFR) on the basis of an intrinsic ability to aggregate in the plasma membrane and an association of its cytoplasmic carboxyl terminus (CT) with TNFR-associated factors (TRAFs). We now show that in EBV-transformed B lymphocytes most of TRAF1 or TRAF3 and 5% of TRAF2 are associated with LMP1 and that most of LMP1 is associated with TRAF1 or TRAF3. TRAF1, TRAF2, and TRAF3 bind to a single site in the LMP1 CT corresponding to amino acids (aa) 199 to 214, within a domain which is important for B-lymphocyte growth transformation (aa 187 to 231). Further deletional and alanine mutagenesis analyses and comparison with TRAF binding sequences in CD40, in CD30, and in the LMP1 of other lymphycryptoviruses provide the first evidence that PXQXT/S is a core TRAF binding motif. The negative effects of point mutations in the LMP1(1-231) core TRAF binding motif on TRAF binding and NF-kappaB activation genetically link the TRAFs to LMP1(1-231)-mediated NF-kappaB activation. NF-kappaB activation by LMP1(1-231) is likely to be mediated by TRAF1/TRAF2 heteroaggregates since TRAF1 is unique among the TRAFs in coactivating NF-kappaB with LMP1(1-231), a TRAF2 dominant-negative mutant can block LMP1(1-231)-mediated NF-kappaB activation as well as TRAF1 coactivation, and 30% of TRAF2 is associated with TRAF1 in EBV-transformed B cells. TRAF3 is a negative modulator of LMP1(1-231)-mediated NF-kappaB activation. Surprisingly, TRAF1, -2, or -3 does not interact with the terminal LMP1 CT aa 333 to 386 which can independently mediate NF-kappaB activation. The constitutive association of TRAFs with LMP1 through the aa 187 to 231 domain which is important in NF-kappaB activation and primary B-lymphocyte growth transformation implicates TRAF aggregation in LMP1 signaling.

Epstein-Barr virus-induced posttransplant lymphoproliferative disorders

Epstein-Barr virus-induced posttransplant lymphoproliferative disease (EBV-PTLD) continues to be a major complication after solid organ transplantation in high-risk patients. Despite the identification of risk factors that predispose patients to develop EBV-PTLD, limitations in our knowledge of its pathogenesis, variable criteria for establishing the diagnosis, and lack of randomized studies addressing the prevention and treatment of EBV-PTLD hamper the optimal management of this transplant complication. This review summarizes the current knowledge of EBV-PTLD and, as a result of two separate international meetings on this topic, and provides recommendations for future areas of study.

Identification of TRAF6, a Novel Tumor Necrosis Factor Receptor-associated Factor Protein That Mediates Signaling from an Amino-terminal Domain of the CD40 Cytoplasmic Region

CD40 signalings play crucial roles in B-cell function. To identify molecules which transduce CD40 signalings, we have utilized the yeast two-hybrid system to clone cDNAs encoding proteins that bind the cytoplasmic tail of CD40. A cDNA encoding a putative signal transducer, designated TRAF6, has been molecularly cloned. TRAF6 has a tumor necrosis factor receptor (TNFR)-associated factor (TRAF) domain in its carboxyl terminus and has a RING finger domain, a cluster of zinc fingers and a coiled-coil domain, which are also present in other TRAF family proteins. TRAF6 does not associate with the cytoplasmic tails of TNFR2, CD30, lymphotoxin-β receptor, and LMP1 of Epstein-Barr virus. Deletion analysis showed that residues 246-269 of CD40 which are required for its association with TRAF2, TRAF3, and TRAF5 are dispensable for its interaction with TRAF6, whereas residues 230-245 were required. Overexpression of TRAF6 activates transcription factor NFκB, and its TRAF-C domain suppresses NFκB activation triggered by CD40 lacking residues 246-277. These results suggest that TRAF6 could mediate the CD40 signal that is transduced by the amino-terminal domain (230-245) of the CD40 cytoplasmic region and appears to be independent of other known TRAF family proteins.

Epstein-Barr Virus gp350/220 Binding to the B Lymphocyte C3d Receptor Mediates Adsorption, Capping, and Endocytosis

The type 2 complement receptor, CR2, a B lymphocyte surface glycoprotein, is known to be a component of the EBV receptor. We now demonstrate that the major EBV outer membrane glycoprotein, gp350/220, is a highly specific ligand for CR2. EBV or beads coated with purified recombinant gp350/220 adsorb to normal B lymphocytes, cap with CR2, become endocytosed into vesicles, and are released into the cytoplasm. This is the first demonstration of herpesvirus glycoprotein-cell glycoprotein receptor interaction in viral adsorption and penetration. The capping of CR2 in response to virus, gp350/220-coated beads, or anti-CR2 monoclonal antibodies is associated with cocapping of surface immunoglobulin. Interaction between CR2 and surface immunoglobulin may be important in modulating the B cell activation that normally follows EBV infection or exposure to antigen.

Epstein–Barr virus and virus human protein interaction maps

A comprehensive mapping of interactions among Epstein–Barr virus (EBV) proteins and interactions of EBV proteins with human proteins should provide specific hypotheses and a broad perspective on EBV strategies for replication and persistence. Interactions of EBV proteins with each other and with human proteins were assessed by using a stringent high-throughput yeast two-hybrid system. Overall, 43 interactions between EBV proteins and 173 interactions between EBV and human proteins were identified. EBV–EBV and EBV–human protein interaction, or “interactome” maps provided a framework for hypotheses of protein function. For example, LF2, an EBV protein of unknown function interacted with the EBV immediate early R transactivator (Rta) and was found to inhibit Rta transactivation. From a broader perspective, EBV genes can be divided into two evolutionary classes, “core” genes, which are conserved across all herpesviruses and subfamily specific, or “noncore” genes. Our EBV–EBV interactome map is enriched for interactions among proteins in the same evolutionary class. Furthermore, human proteins targeted by EBV proteins were enriched for highly connected or “hub” proteins and for proteins with relatively short paths to all other proteins in the human interactome network. Targeting of hubs might be an efficient mechanism for EBV reorganization of cellular processes.