Downregulation of ATOH8 induced by EBV-encoded LMP1 contributes to the malignant phenotype of nasopharyngeal carcinoma

Abstract

Mechanism for the malignant phenotype of nasopharyngeal carcinoma (NPC) remains poorly understood. Epstein-Barr virus (EBV) consistently appears in nearly all malignant NPC patient samples, suggesting the strong etiological link between the malignant phenotype and EBV infection. Here we found that the EBV-encoded latent membrane protein (LMP1) enhanced cell growth, motility, invasion and xenograft tumor growth of NPC. RNA-seq profiling analysis of LMP1-positive NPC patient tissues indicated that widespread gene repression contributed to malignant phenotype of NPC. The transcription factor binding site (TFBS) enrichment analysis indicated a subset of transcription factors including ATOH8, a novel transcript factor which belongs to the basic helix-loop-helix (bHLH) gene family inversely enriched in promoters of up-regulated genes and down-regulated genes. Importantly, the expression of ATOH8 was suppressed in both immortalized normal nasopharyngeal epithelial cells (NPEC) and NPC cells with LMP1 overexpression. The Real-Time PCR and Western Blot assays indicated that ATOH8 decreased expression in NPC cell lines and patient samples. Moreover, by gain- or loss-of-function assays, we demonstrated that ATOH8 inhibition promoted malignant phenotype, whereas ATOH8 restoration reversed malignant phenotype of NPC. Finally, we demonstrated that LMP1 inhibited ATOH8 expression by epigenetically impairing the occupancy of activating H3K4me3 and enhancing the occupancy of repressive H3K27me3 on ATOH8 promoter. Collectively, our study uncovered the occurrence of malignant phenotype of NPC induced by EBV infection and characterized a novel bHLH transcription factor ATOH8 as a new downstream target of LMP1.