EBV latent membrane proteins promote hybrid epithelial-mesenchymal and extreme mesenchymal states of nasopharyngeal carcinoma cells for tumorigenicity

EBV-encoded LMPs are consistently detected in nasopharyngeal carcinoma (NPC). Recent evidence suggests potential roles of LMP1 and LMP2A in Epithelial-to-mesenchymal transition (EMT) process in NPC. EMT engages in the generation and maintenance of cancer stem cells (CSCs) and confers on cancer cells increased tumor-initiating and metastatic potential, and higher resistance to anticancer therapies. However, how LMP1 and LMP2A regulate the EMT process to generate cells with different EMT states and its implications for tumor progression remain unclear. Here we report that LMP1 and LMP2A promote EMT that drives NPC cells from the epithelial-like state (E) (CD104(+), CD44(low)) to epithelial-mesenchymal hybrid (E/M) state (CD104(+), CD44(high)). Furthermore, LMP2A possesses an additional function in stabilizing LMP1 and increasing the level of LMP1 in NPC cells. The elevated LMP1 further forces the EMT to generate extreme-mesenchymal (xM) state cells (CD104(-), CD44(high)). To define the tumorigenic features of cancer stem cells at different states in the EMT spectrum, E, E/M and xM subpopulations were isolated and tested for tumorigenic capability in a tumor xenograft animal model. We found that the cells with E/M phenotypes possess the highest tumor initiating capacity. However, the xM subpopulation exhibits increased vasculogenic mimicry, a hallmark of metastatic cancers. Taken together, coordinated action of LMP1 and LMP2A generates an array of intermediate subpopulations in the EMT spectrum that are responsible for distinct tumorigenic features of NPC such as tumor-initiation, vasculogenesis, and metastasis.