MUC1-C auto-regulatory complex with EBNA1 is responsible for latent Epstein-Barr virus-associated gastric cancer progression

Latent Epstein-Barr Virus (EBV) infection promotes cancers derived from B-lymphocytes and epithelial cells by mechanisms that largely remain unclear. EBV-encoded nuclear antigen 1 (EBNA1) is uniformly expressed in EBV-associated cancers; however, how EBNA1 contributes to cancer progression is not known. The MUC1 gene evolved in mammals to protect barrier tissues from viral infections. We report that MUC1 is upregulated in EBV-associated gastric cancers (EBVaGCs). Our results demonstrate that EBNA1 and the oncogenic MUC1-C subunit form an auto-regulatory complex that controls expression of EBNA1, MUC1-C and host cellular genes. EBNA1 appropriates MUC1-C to (i) induce DNA methyltransferase (DNMT) expression and DNA methylation, (ii) suppress CDKN1A encoding p21 to promote proliferation, and (iii) upregulate survivin to confer survival. MUC1-C is also co-opted for localization of EBNA1 in chromatin, expression of EBV latency genes and suppression of lytic genes. Targeting MUC1-C thereby induces the switch of EBV latency to activation of the lytic phase. We further demonstrate that MUC1-C is necessary for EBVaGC stem cell (CSC) state as evidenced by regulation of NOTCH stemness genes and self-renewal capacity. These findings and the demonstration that EBV positivity has no significant effect on survival of patients with GCs indicate that EBNA1 exploits MUC1-C to maintain EBV latency and that prolonged activation of MUC1-C in response to chronic EBV infection promotes EBVaGC malignant progression.