BRD7 is a recently identified bromodomain gene. It exhibits much higher-level of mRNA expression in normal nasopharyngeal epithelia than in NPC biopsies and cell lines [
11,
12]. Over-expression of BRD7 in NPC cells is effective in inhibiting cell growth and cell cycle progression of NPC cells [
13‐
15], but little is known about its down-expression in NPC cells. In this study, we found that BRD7 promoter is hemimethylated in a number of NPC cell lines including HNE1, CNE1, 6–10B and 5–8F cell lines, and that the methylation status of BRD7 promoter is inversely proportional with BRD7 mRNA expression in NPC cells. Thus, pharmacological inhibition of DNA methylation by 5-Aza-CdR enhanced BRD7 mRNA expression in NPC cells. This is in agreement with previous studies that, indeed, hemimethylation is sufficient to inhibit the expression of p16ink4A [
17] and hMLH1 gene [
18] in HCT116 and HT29 cell lines, respectively. Numerous studies have suggested that DNA methylation can suppress gene transcription either by directly inhibiting the interaction of transcription factors with their regulatory sequences or by attracting methylated DNA binding proteins that, in turn, recruit histone deacetylases and histone methyltransferases, resulting in an inactive chromatin structure [
19,
20]. Our study indicates that DNA methylation represses BRD7 gene transcription by directly inhibiting the interaction of transcription factors with their regulatory elements, as judged by the inability of TSA to potentiate 5-Aza-CdR-mediated expression of BRD7 gene. Sp1 is a well-investigated factor that regulates transcription through specific sequences in G/C-rich promoter regions and is often critical for transcription initiation of TATA-less promoters [
21]. We identified several Sp1 binding sites in BRD7 promoter. Sp1 has high affinity to BRD7 promoter [
16]. Sequence analysis of the bisulfite-modified BRD7 promoter demonstrated that cytosine residues flanking functional Sp1 elements at -353/-337 and -330/-317 are methylated. It is known that methylation of specific cytosine residues in or near transcription regulatory motifs can block accessibility of the transcription factor [
22‐
24]. Indeed, we found that methylation of cytosines flanking the -353/-337 and -330/-317 element impaired the ability of nuclear protein to bind the Sp1 binding sites in BRD7 promoter. Moreover, in vitro methylation of BRD7 promoter construct with SssI methylase leads to an almost complete loss of the activity of BRD7 promoter in NPC cell lines. NPC is highly radiosensitive and chemosensitive, but treatment of patients with locoregionally advanced disease remains problematic [
25,
26]. New biomarkers for NPC, including DNA copy number of EBV or methylation of multiple tumour suppressor genes, which can be detected in serum and nasopharyngeal brushings, have been developed for the molecular diagnosis of this tumor. Recent findings suggest that epigenetic inactivation of multiple tumor suppressor genes plays an important role in the tumourigenesis of NPC, such as aberrant methylation of the 5-CpG island of Ras association domain family 1A (RASSF1A), RARβ2, death-associated protein kinase (DAP-kinase), p16 (CDKN2A), p15 (CDKN2B), p14 (ARF) and O6-methylguanine DNA methyltransferase (MGMT), DLC1, TSLC1, TIG1 in NPC [
27‐
33]. In the present study, among the 18 NPC patients, aberrant promoter methylation of BRD7 gene was detected in 100% of tumor biopsies and matched blood samples of NPC patients. In contrast, weak promoter methylation of BRD7 gene was observed in half of the blood samples from normal, healthy, age-matched individuals, indicating that epigenetic inactivation of BRD7 gene plays an important role in the tumorigenesis of NPC. This is a provocative observation, suggesting that the methylation status of BRD7 promoter may serve as a clinical biomarker for early detection and prescreening patients with clinical symptoms or individuals at high risk as well as in monitoring patients for recurrence. Further studies are necessary to confirm this.