Epstein-Barr virus latent membrane protein 2A enhances MYC-driven cell cycle progression in a mouse model of B lymphoma

Elevated expression of MYC is a shared property ofmany human cancers. Epstein-Barr virus (EBV) has been associated with lymphoid malignancies, yet collaborative roles between MYC and EBV in lymphomagenesis are unclear. EBV latent membrane protein 2A (LMP2A) functions as a B-cell receptor (BCR) mimic known to provide survival signals to infected B cells. Co-expression of human MYC and LMP2A in mice (LMP2A/ λ-MYC) accelerates B lymphoma onset compared with mice expressing human MYC alone (λ-MYC mice). Here we show a novel role of LMP2A in potentiating MYC to promote G₁-S transition and hyperproliferation by downregulating cyclin-dependent kinase inhibitor p27^kip1 in a proteasome-dependent manner. Expressing a gain-offunction S10A mutant of p27^kip1 has minor effect on tumor latency. However, pretumor B cells from λ-MYC mice expressing homozygous S10A mutant show a significant decrease in the percentage of S-phase cells. Interestingly, LMP2A is able to counteract the antiproliferative effect of the S10A mutant to promote S-phase entry. Finally, we show that LMP2A expression correlates with higher levels of MYC expression and suppression of p27 ^kip1 before lymphoma onset. Our study demonstrates a novel function of EBV LMP2A in maximizing MYC expression, resulting in hyperproliferation and cellular transformation into cancer cells in vivo.