Regulation of DNA Damage Signaling and Cell Death Responses by Epstein-Barr Virus Latent Membrane Protein 1 (LMP1) and LMP2A in Nasopharyngeal Carcinoma Cells

Abstract

Nasopharyngeal carcinoma (NPC) is closely associated with latent Epstein-Barr virus (EBV) infection. Although EBV infection of preneoplastic epithelial cells is not immortalizing, EBVcan modulate oncogenic and cell death mechanisms. The viral latent membrane proteins 1 (LMP1) and LMP2A are consistently expressed in NPC and can cooperate in bitransgenic mice expressed from the keratin-14 promoter to enhance carcinoma development in an epithelial chemical carcinogenesis model. In this study, LMP1 and LMP2A were coexpressed in the EBV-negative NPC cell line HK1 and examined for combined effects in response to genotoxic treatments. In response to DNA damage activation, LMP1 and LMP2A coexpression reduced ␥H2AX (S139) phosphorylation and caspase cleavage induced by a lower dose (5 M) of the topoisomerase II inhibitor etoposide. Regulation of ␥H2AX occurred before the onset of caspase activation without modulation of other DNA damage signaling mediators, including ATM, Chk1, or Chk2, and additionally was suppressed by inducers of DNA single-strand breaks (SSBs) and replication stress. Despite reduced DNA damage repair signaling, LMP1-2A coexpressing cells recovered from cytotoxic doses of etoposide; however, LMP1 expression was sufficient for this effect. LMP1 and LMP2A coexpression did not enhance cell growth, with a moderate increase of cell motility to fibronectin. This study supports that LMP1 and LMP2A jointly regulate DNA repair signaling and cell death activation with no further enhancement in the growth properties of neoplastic cells. E pstein-Barr virus (EBV) is a human gammaherpesvirus that establishes lifelong latency in memory B cells, with sporadic reactivation and transmission from oral epithelia (1). More than 90% of the adult population is latently infected, and a subset can develop EBV-associated malignancies, including nasopharyngeal carcinoma (NPC), gastric cancer, Burkitt lymphoma, Hodgkin lymphoma, and lymphomas in the immunocompromised, including AIDS-associated lymphoma and posttransplant lymphoproliferative disease (2, 3). Epithelial cell infection in vitro frequently results in productive replication, and latently infected oral epithelial cells are rare in persistently infected healthy individuals (4, 5). However, epithelial tumors such as NPC consistently express a type II latency program, which includes latent membrane protein 1 (LMP1), LMP2A, and LMP2B (1, 5). Additionally, monoclonal EBV episomes are detected in NPC, suggesting that NPC tumors are the clonal outgrowth of an initially infected cell likely predisposed to oncogenic transformation from additional genetic and environmental cofactors, such as the loss of p16 and exposure to dietary nitrosamines (2, 3). In contrast to the immortalizing properties of EBV to primary B cells, the contribution of EBV infection to epithelial cell oncogenesis is less understood, as infection alone is insufficient to immortalize or induce oncogenic potential in preneoplastic cell lines from the nasopharynx (5, 6).LMP1 and LMP2A transcripts are ...

CD63 Regulates Epstein-Barr Virus LMP1 Exosomal Packaging, Enhancement of Vesicle Production, and Noncanonical NF-κB Signaling

“…LMP1 expression was detectable but notably lower than in the transfected or inducible models. Previous reports have shown that this level of LMP1 expression is comparable to those found in EBV-infected cell lines (39). Again, nanoparticle tracking analysis revealed an increase in vesicle secretion compared to that with control (empty pBabe vector) cells (P ϭ 0.026) (Fig.…”

Establishment of a nasopharyngeal carcinoma cell line capable of undergoing lytic Epstein–Barr virus reactivation

“…Increased expression of other EBV lytic transcripts, BRLF1, BMRF1, and BLLF1, were also detected following expression of BZLF1. The BRLF1 is an immediate early transactivator activated by BZLF1, which plays an important role in lytic reactivation of EBV in infected epithelial cells [24]. The BMRF1 is an early EBV gene that encodes the polymerase accessory protein (EA-D), which is essential for lytic replication of EBV DNA.…”

EBV infection is associated with histone bivalent switch modifications in squamous epithelial cells

“…A previous study has demonstrated a role for LMP1 in DNA repair suppression through the PI3K/AKT pathway and inactivation of FOXO3a and DDB1 (55). Coexpression of LMP1 and LMP2A in EBV-negative NPC cells is accompanied by a reduction in γH2AX phosphorylation in response to treatment with genotoxins, which can promote DNA replication stress or single-strand breaks (56). Furthermore, in EBV-infected B cells, EBNA3C was reported to suppress DNA damage repair responses (57,58).…”