RASSF10 Promoter Hypermethylation Is Frequent in Malignant Melanoma of the Skin but Uncommon in Nevus Cell Nevi

The Ras association domain family (RASSF) consists of several tumor suppressor genes, which are frequently silenced in human cancers. We analyzed the epigenetic inactivation of RASSF2 and RASSF10 in malignant melanoma (MM) of the skin, including 5 MM cell lines, 28 primary MM, 33 metastases of MM, 47 nevus cell nevi (NCN), and 22 control tissues. The RASSF2 promoter was epigenetically downregulated in two MM cell lines only, but not in any of the investigated tumor samples. In contrast, hypermethylation of the RASSF10 promoter was found in all investigated cell lines, 19/28 (68%) of the primary MM and 30/33 (91%) of the MM metastases, 2/18 (11%) of the dysplastic NCN, and 0/29 (0%) of the non-dysplastic NCN (difference between MM and all nevi, P<0.001). RASSF10 promoter hypermethylation correlated with a reduced RASSF10 mRNA expression in 3/4 MM cell lines, and treatment with a DNA methylation inhibitor reactivated RASSF10 transcription. Furthermore, immunohistological RASSF10 expression corresponds negatively to its promoter methylation state. In summary, RASSF10 proved to be a characteristically epigenetically silenced tumor suppressor in melanomagenesis, and analysis of RASSF10 methylation status represents a new candidate tool to assist in discrimination between MM and NCN

Claudin11 Promoter Hypermethylation Is Frequent in Malignant Melanoma of the Skin, but Uncommon in Nevus Cell Nevi

Epigenetic inactivation of tumor-related genes is an important characteristic in the pathology of human cancers, including melanomagenesis. We analyzed the epigenetic inactivation of Claudin 11 (CLDN11) in malignant melanoma (MM) of the skin, including six melanoma cell lines, 39 primary melanoma, 41 metastases of MM and 52 nevus cell nevi (NCN). CLDN11 promoter hypermethylation was found in 19 out of 39 (49%) of the primary MM and in 21 out of 41 (51%) of the MM metastases, but only in eight out of 52 (15%) of NCN (p = 0.001 and p = 0.0003, respectively). Moreover, a significant increase in the methylation level of CLDN11 from primary melanomas to MM metastases was revealed (p = 0.003). Methylation of CLDN11 was significantly more frequent in skin metastases (79%) compared to brain metastases (31%; p = 0.007). CLDN11 methylation was also found in five out of six MM cell lines (83%) and its promoter hypermethylation correlated with a reduced expression. Treatment of MM cell lines with a DNA methylation inhibitor reactivated CLDN11 transcription by its promoter demethylation. In summary, CLDN11 proved to be an epigenetically inactivated tumor related gene in melanomagenesis, and analysis of CLDN11 methylation level represents a potential tool for assisting in the discrimination between malignant melanoma and nevus cell nevi

Aberrant Promoter Hypermethylation of RASSF Family Members in Merkel Cell Carcinoma

Merkel cell carcinoma (MCC) is one of the most aggressive cancers of the skin. RASSFs are a family of tumor suppressors that are frequently inactivated by promoter hypermethylation in various cancers. We studied CpG island promoter hypermethylation in MCC of RASSF2, RASSF5A, RASSF5C and RASSF10 by combined bisulfite restriction analysis (COBRA) in MCC samples and control tissue. We found RASSF2 to be methylated in three out of 43 (7%), RASSF5A in 17 out of 39 (44%, but also 43% in normal tissue), RASSF5C in two out of 26 (8%) and RASSF10 in 19 out of 84 (23%) of the cancer samples. No correlation between the methylation status of the analyzed RASSFs or between RASSF methylation and MCC characteristics (primary versus metastatic, Merkel cell polyoma virus infection, age, sex) was found. Our results show that RASSF2, RASSF5C and RASSF10 are aberrantly hypermethylated in MCC to a varying degree and this might contribute to Merkel cell carcinogenesis