Downregulation of sFRP-2 by epigenetic silencing activates the β-catenin/Wnt signaling pathway in esophageal basaloid squamous cell carcinoma

Basaloid squamous cell carcinoma (BSCC) of the esophagus is a rare variant of typical squamous cell carcinoma (SCC) associated with poor survival. A characteristic feature is nuclear accumulation of β-catenin, without a mutation of the gene. We studied the methylation status of Wnt antagonist genes, such as secreted frizzled-related protein (sFRP) gene family members, Wnt inhibitory factor-1 (WIF-1), Dickkopf-1 (Dkk-1), and human Dapper protein-1 (HDPR-1), and alterations of the APC, Axin1, and Axin2 genes in 30 cases of esophageal BSCC. β-catenin and sFRP (sFRP-1, sFRP-2, sFRP-4, sFRP-5) protein expression was examined by immunohistochemistry. APC, Axin1, and Axin2 gene mutations were detected in 3, 2, and 2 cases, respectively, and 6 cases (20 %) harbored at least 1 alteration in these genes. Methylation of the sFRP-2 promoter region was observed in all cases, and methylation was frequent in sFRP-1 and sFRP-5, but infrequent in Dkk-1, WIF-1, sFRP-4, and HDPR-1. sFRP-2 expression was almost completely absent in 25 cases (83 %), consistent with the methylation status. Nuclear accumulation of β-catenin was observed in all cases. sFRP-5 expression was associated with a low nuclear β-catenin labeling index. These results show that sFRP-2 is a target gene of hypermethylation in esophageal BSCC and suggest that sFRP-2 might contribute to BSCC tumorigenesis through the Wnt/β-catenin signaling pathway.