Latent Membrane Protein 1 (LMP1) and LMP2A Collaborate To Promote Epstein-Barr Virus-Induced B Cell Lymphomas in a Cord Blood-Humanized Mouse Model but Are Not Essential

Abstract

Epstein-Barr virus (EBV) infection is associated with B cell lymphomas in humans. The ability of EBV to convert human B cells into long-lived lymphoblastoid cell lines (LCLs) in vitro requires the collaborative effects of EBNA2 (which hijacks Notch signaling), latent membrane protein 1 (LMP1) (which mimics CD40 signaling), and EBV-encoded nuclear antigen 3A (EBNA3A) and EBNA3C (which inhibit oncogene-induced senescence and apoptosis). However, we recently showed that an LMP1-deleted EBV mutant induces B cell lymphomas in a newly developed cord blood-humanized mouse model that allows EBV-infected B cells to interact with CD4 T cells (the major source of CD40 ligand). Here we examined whether the EBV LMP2A protein, which mimics constitutively active B cell receptor signaling, is required for EBV-induced lymphomas in this model. We find that the deletion of LMP2A delays the onset of EBV-induced lymphomas but does not affect the tumor phenotype or the number of tumors. The simultaneous deletion of both LMP1 and LMP2A results in fewer tumors and a further delay in tumor onset. Nevertheless, the LMP1/LMP2A double mutant induces lymphomas in approximately half of the infected animals. These results indicate that neither LMP1 nor LMP2A is absolutely essential for the ability of EBV to induce B cell lymphomas in the cord blood-humanized mouse model, although the simultaneous loss of both LMP1 and LMP2A decreases the proportion of animals developing tumors and increases the time to tumor onset. Thus, the expression of either LMP1 or LMP2A may be sufficient to promote early-onset EBV-induced tumors in this model. IMPORTANCE EBV causes human lymphomas, but few models are available for dissecting how EBV causes lymphomas in vivo in the context of a host immune response. We recently used a newly developed cord blood-humanized mouse model to show that EBV can cooperate with human CD4 T cells to cause B cell lymphomas even when a major viral transforming protein, LMP1, is deleted. Here we examined whether the EBV protein LMP2A, which mimics B cell receptor signaling, is required for EBV-induced lymphomas in this model. We find that the deletion of LMP2A alone has little effect on the ability of EBV to cause lymphomas but delays tumor onset. The deletion of both LMP1 and LMP2A results in a smaller number of lymphomas in infected animals, with an even more delayed time to tumor onset. These results suggest that LMP1 and LMP2A collaborate to promote early-onset lymphomas in this model, but neither protein is absolutely essential.KEYWORDS EBV, Epstein-Barr virus, LMP1, LMP2A, humanized mouse, lymphoma

Epstein-Barr Virus LMP1-Mediated Oncogenicity

“…In the absence of LMP1, low frequency development of EBV ϩ lymphomas was dependent on CD40 signaling induced by T cells, which likely provides similar growth and survival signals as LMP1, albeit at lower levels (71). Simultaneous LMP1 and LMP2A deletion further reduced and delayed the onset of tumors but did not completely eliminate lymphoma development (72).…”

Epstein-Barr Virus Type 2 Infects T Cells and Induces B Cell Lymphomagenesis in Humanized Mice

“…Advancements in engineering greater levels of immunodeficiency in the recipient mice and the use of human CD34 ϩ hematopoietic stem cells (HSCs) to reconstitute the human immune system have led to more robust reconstitution and the development of functional human lymphocytes (reviewed in references 29, 30, and 31). The contribu-tions of different EBV latent and lytic proteins in B cell lymphomagenesis have been studied using these advanced humanized mouse (hu-mouse) models (32)(33)(34)(35)(36)(37). Development of diffuse large B cell lymphomas (DLBCL) and LPD following EBV infection has been reported but with variable frequencies (38,39).…”

Epstein‐Barr virus LMP2A utilizes Syk and PI3K to activate NF‐κB in B‐cell lymphomas to increase MIP‐1α production

“…Once again, the two proteins use distinct mechanisms to increase IL‐10: LMP1 uses p38K in addition to PI3K to increase IL‐10, while LMP2A uses the activation of the PI3K/BTK/STAT3 pathway without the need for p38K activation and data presented here). Future studies need to address whether the activation of NF‐κB is additive when both LMP1 and LMP2A are present, since previous studies indicate that these two proteins can positively affect the signaling of one another . Taken together, the fact that both LMP1 and LMP2A latency proteins expressed in HRS cells of HL have redundant pathways to increase both prosurvival cytokines and chemokines suggest that EBV has evolved to promote both survival of HRS cells and the establishment of the tumor microenvironment.…”