USP7 and nasopharyngeal carcinoma: Instead, we assessed the effect of USP7 on the initial association of EBNA1 with oriP by treating EBV-negative nasopharyngeal carcinoma cells (CNE2Z) with siRNA against USP7 or GFP (negative control) and then transfecting these cells with an oriP plasmid expressing EBNA1 or an EBNA1 mutant (Δ395–450; see Figure 1A) that we previously showed was specifically defective in binding USP7 [14] and a plasmid lacking EBNA1 binding sites (pLacZ) as control for nonspecific DNA binding.