Abstract
To identify tumor‐suppressor genes inactivated by aberrant methylation of promoter CpG islands (CGIs) in human malignant melanomas, genes upregulated 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.