TGFB1 and nasopharyngeal carcinoma: A negative feedback loop between EBNA1 and TGF-β was also postulated, in which expression of EBNA1 in a nasopharyngeal adenocarcinoma cell line, AdAH, has been shown to repress TGF-β1-induced transcription by increasing Smad2 protein turnover [95], an effect that may overcome the ability of TGF-β to repress the Q promoter (Qp), which is responsible for EBNA1 expression in NPC [96].