Protein expression and promoter methylation of the candidate biomarker TCF21 in head and neck squamous cell carcinoma

Epigenetic alterations of the transcription factor 21 (TCF21) gene have been associated with head and neck squamous cell carcinoma (HNSCC) and other tumor entities. So far, however, no reports have appeared in the literature on TCF21 protein expression in HNSCC and its relevance as a putative biomarker. TCF21 protein expression was assessed in 74 HNSCCs and 31 benign tonsils by immunohistochemistry. Methylation analyses of the corresponding gene promoter were performed in 45 HNSCCs and 31 benign tonsils. The TCF21 expression levels in the tumors and controls were compared with each other and within each group and, in addition, with the TCF21 promoter methylation status and various clinicopathological characteristics. Overall, both the expression levels and methylation frequencies of TCF21 were significantly higher in the HNSCCs than in the benign controls (p < 0.001 each). Specifically, TCF21 promoter hypermethylation resulted in a reduced protein expression in a subgroup of the HNSCCs (p = 0.038), but not in the tonsils. In the tonsils, TCF21 protein expression positively correlated with that of CD31 (p = 0.039), a marker for blood vessels. Also, in the tonsils the TCF21 protein methylation frequency showed a positive correlation with age (p = 0.008). The HNSCCs of patients with a positive history for alcohol and nicotine abuse showed higher TCF21 protein expression levels than their respective counterparts (p = 0.028 and p = 0.062, respectively). The same was observed in human papilloma virus (HPV)-negative tumors (p = 0.042), tumors located in the oral cavity (p = 0.016) and early-stage tumors (p = 0.025). Interestingly, expression rates in tumors of the oropharynx, where HPV-positive tumors were most frequently found, tended to be lower (p = 0.065). The methylation frequencies of TCF21 were found to be significantly higher in tumors of patients without nicotine abuse (p = 0.030), in HPV-positive tumors (p = 0.014) and in tumors exhibiting over-expression of p16, a protein induced by HPV (p = 0.006). Both over-expression and increased promoter methylation of TCF21 were frequently observed in HNSCCs. TCF21 promoter hypermethylation was found to lead to gene silencing in the HNSCCs, but not in the benign tonsils. These epigenetic, and possibly also genetic, alterations of the TCF21 gene in HNSCCs may be driven by HPV infection, nicotine and alcohol abuse, or both. These findings, together with its stage- and primary site-dependent expression, turn TCF21 into a promising candidate biomarker in HNSCC.