Epstein–Barr virus latent membrane protein 1 represses p53-mediated DNA repair and transcriptional activity

Abstract

The latent membrane protein 1 (LMP1) of Epstein-Barr virus (EBV), a viral oncogene, is essential for transformation of resting B cells by the virus. We previously demonstrated that LMP1 could repress DNA repair in p53-wild-type and p53-deficient human epithelial cells. In this study, using a host cell reactivation (HCR) assay, we demonstrated that p53-enhanced DNA repair was repressed by LMP1 in p53-deficient cells. Moreover, we found that LMP1 was able to repress p53-dependent transcriptional activity. Regarding the mechanisms of p53 repression by LMP1, we found that LMP1 did not inhibit p53 function through direct interaction, by promoting protein degradation or reducing its DNA-binding ability. Using chimeric proteins in the reporter assay, we demonstrated that LMP1 inhibited p53 transactivation by influencing the N-terminal transactivation domain of p53. Subsequent experiments using various LMP1 deletion mutants indicated that a C-terminus-activating region of LMP1, CTAR1 or CTAR2, is responsible for the repression of p53-mediated DNA repair and p53-dependent transcription, which is correlated with the region responsible for NF-jB activation. Furthermore, blockage of NF-jB signalling by IjB-DN was shown to abolish the repression of p53 by LMP1, suggesting that LMP1 likely repressed p53 function through the NF-jB pathway. Based on these results, we propose that inhibition of p53-dependent transcriptional activity and DNA repair by LMP1 results in the loss of p53 activity for maintaining genomic stability, which may contribute to the oncogenesis of LMP1 in human epithelial cells.

Characterization of the Uracil-DNA Glycosylase Activity of Epstein-Barr Virus BKRF3 and Its Role in Lytic Viral DNA Replication

“…It has been observed that expression of EBV LMP1 protein represses p53-mediated DNA repair and transcriptional activity through the activation of the NF-B pathway. This suggests that the abrogation of DNA repair by LMP1 may induce genomic instability and contribute subsequently to tumorigenesis (37,38). Here we propose that EBV BKRF3 may function in addition to LMP1 to contribute to genome instability, thus favoring AID/UNG-induced c-myc/IgH translocations.…”

Functional interaction of Ugene and EBV infection mediates tumorigenic effects

“…Latent phase genes of EBV including Zta, LMP1, LMP2A, LMP2B. EBNA1, EBNA2, BGLF4, EBNA3C and truncated LMP1 genes (DX, DT, DBX, DS, D189-222, D189-321 and D350-389) were also sub-cloned into pSG5 expression vector (Liebowitz et al, 1992;Liu et al, 2005). The shRNAi sequences were shown as follows: 145-165, 5 0 -CTCCACTCCCTTCTCCAAAAG-3 0 and 1066-1086, 5 0 -CTGCCCAGTGTAGGTGTATTC-3 0 .…”

“…TW01 and HONE1 cells, human NPC cell lines, were maintained in Dulbecco's modified Eagle's medium supplemented with 10% fetal calf serum (Liu et al, 2005;Fang et al, 2009). …”

LMP1 signaling and activation of NF-κB in LMP1 transgenic mice

“…Data in cell culture indicate that LMP1 upregulates A20, which can block p53-mediated apoptosis (Laherty et al, 1992;Fries et al, 1996). Furthermore, LMP1 represses p53-mediated DNA repair and transcriptional activity and this activity is dependent on the NF-kB pathway (Liu et al, 2005). The presence of elevated p53 protein and lack of mutations in LMP1-positive mouse lymphomas suggests that LMP1 also affects p53 expression and function in vivo.…”