Inactivation of MSH3 by promoter methylation correlates with primary tumor stage in nasopharyngeal carcinoma

The aim of this study was to investigate the inactivation of the MutS homolog human 3 (MSH3) gene by promoter methylation in nasopharyngeal carcinoma (NPC). Methylation-specific PCR, semi-quantitative reverse transcription PCR and immunohistochemical analysis were used to detect methylation and the mRNA and protein expression levels of MSH3 in 54 cases of NPC tissues and 16 cases of normal nasopharyngeal epithelial (NNE) tissues. The association between promoter methylation and mRNA expression, and the mRNA and protein expression of the gene and clinical factors was analyzed. The promoter methylation of MSH3 was detected in 50% (27/54) of the primary tumors, but not in the 16 NNE tissues. The mRNA and protein expression levels were significantly decreased in the 54 cases of human NPC as compared to the 16 NNE tissues (P<0.05). The MSH3-methylated cases exhibited significantly lower mRNA and protein expression levels than the unmethylated cases (P<0.05). The MSH3 mRNA and protein expression levels were significantly associated with the variable T stage (P<0.05); however, they did not correlate with the age and sex of the patients, or with the N stage, TNM classification or histopathological subtype (P>0.05). On the whole, MSH3 was frequently inactivated by promoter methylation and its mRNA and protein expression correlated with the primary tumor stage in NPC.