Background: Cytoplasmic and nuclear accumulation of beta-catenin in mucoepidermoid carcinoma (MEC) is frequently noted, but the mechanism is unknown.
Methods: The methylation status of adenomatous polyposis coli (APC) and secreted frizzled-related proteins (SFRPs) was examined by methylation-specific polymerase chain reaction (MSP) assay. The association of SFRP1, beta-catenin, and cyclin D1 expression in MEC was evaluated by immunohistochemical staining.
Results: A high percentage of methylation in APC and the SFRP genes was found in MEC compared with adjacent normal tissues, in which SFRP1 (58.6%) was the most frequent methylated gene. Moreover, abundant expression of SFRP1 was noted in normal tissues, whereas reduced SFRP1 expression was detected in 71.7% (33/46) of MECs. There was significant association between methylation and reduced expression of SFRP1. Cytoplasmic/nuclear (C/N) beta-catenin and high cyclin D1 expression were found in 13/55 (23.6%) and 36/55 (65.5%) of cases, respectively. There was significant correlation between C/N beta-catenin expression and reduced SFRP1 expression (P = 0.009). In addition, SFRP1 and beta-catenin expression correlated with tumor malignancy index such as tumor grade and stage. Overall patient survival was significantly worse in patients with reduced SFRP1 and C/N beta-catenin expression (P = 0.009 and P = 0.002, respectively).
Conclusions: Methylation of the SFRP1 gene was the major cause of reduced SFRP1 expression. Reduced SFRP1 led to C/N accumulation of beta-catenin and was associated with tumor malignancy. Therefore, examination of SFRP1 expression and beta-catenin location could be useful predictors of tumor progression and prognosis in patients with MEC.