Reduced ribosomal RNA expression and unchanged ribosomal DNA promoter methylation in oral squamous cell carcinoma.

Background Ribosomal RNA (rRNA) consists of four non-coding RNAs, the 28S, 5.8S, 18S, and 5S rRNA. Abnormal expression of rRNA has been found in multiple tumors, and the methylation of rDNA promoter may affect rRNA expression as an epigenetic regulatory mechanism. Oral squamous cell carcinoma (OSCC) is a kind of aggressive tumors which occurs in multiple sites in oral cavity. rRNA expression and the methylation of rDNA promoter in modulating rRNA expression in OSCC maintain unclear. This study aims to investigate the rRNA expression, the methylation status within rDNA promoter, and the underlying mechanism of methylation in regulating rRNA expression in OSCC. Methods Twelve primary OSCC and matched normal tissue samples were collected from patients with OSCC. Quantitative real-time PCR was used to evaluate the rRNA level. HpaII/MspI digestion and bisulfite sequencing were used to investigate the methylation status of rDNA promoter. Results Ribosomal RNA levels were suppressed in OSCC as compared with matched normal tissues. HpaII/MspI digestion and bisulfite sequencing showed no significant differences for the methylation of rDNA promoter between the tumor and matched normal tissues. Conclusion The methylation in rDNA promoter could not explain for the suppressed rRNA expression in OSCC tissues.