Silencing of tissue factor pathway inhibitor-2 gene in malignant melanomas

Abstract

To identify tumor-suppressor genes inactivated by aberrant methylation of promoter CpG islands (CGIs) in human malignant melanomas, genes unregulated by treatment of cells with a demethylating agent, 5-aza-2′-deoxycytidine (5-aza-dC), were searched for using oligonucleotide microarrays in melanoma cell lines, HMV-I, MeWo and WM-115. Seventy-nine known genes with CGIs were identified as being upregulated (≥16-fold), and 18 of them had methylation of their putative promoter CGIs in 1 or more of 8 melanoma cell lines. Among the 18 genes, TFPI-2, which is involved in repression of the invasive potential of malignant melanomas, was further analyzed. Its expression was repressed in a melanoma cell line with its complete methylation, and was restored by 5-aza-dC treatment. It was unmethylated in cultured neonatal normal epidermal melanocyte, and was induced by ultraviolet B. In surgical melanoma specimens, TFPI-2 methylation was detected in 5 of 17 metastatic site specimens (29%), while it was not detected in 20 primary site specimens (0%) (p = 0.009). By immunohistochemistry, the 5 specimens with promoter methylation lacked immunoreactivity for TFPI-2. The results showed that TFPI-2 is silenced in human malignant melanomas by methylation of its promoter CGI and suggested that its silencing is involved in melanoma metastasis. © 2007 Wiley-Liss, Inc.