Author(s): Hoon DS, Spugnardi M, Kuo C, Huang SK, Morton DL,
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Abstract Aberrant methylation of CpG islands in promoter regions of tumor suppressor genes (TSG) has been demonstrated in epithelial origin tumors. However, the methylation profiling of tumor-related gene promoter regions in cutaneous melanoma tumors has not been reported. Seven known or candidate TSGs that are frequently hypermethylated in carcinomas were assessed by methylation-specific polymerase chain reaction (MSP) in 15 melanoma cell lines and 130 cutaneous melanoma tumors. Four TSGs were frequently hypermethylated in 86 metastatic tumor specimens: retinoic acid receptor-beta2 (RAR-beta2) (70\%), RAS association domain family protein 1A (RASSF1A) (57\%), and O6-methylguanine DNA methylatransferase (MGMT) (34\%), and death-associated protein kinase (DAPK) (19\%). Hypermethylation of MGMT, RASSF1A, and DAPK was significantly lower in primary melanomas (n=20) compared to metastatic melanomas. However, hypermethylation of RAR-beta2 was 70\% in both primary and metastatic melanomas. Cell lines had hypermethylation profiles similar to those of metastatic melanomas. The analysis of these four markers of metastatic tumors demonstrated that 97\% had > or =1 gene(s) and 59\% had > or =2 genes hypermethylated. The methylation of genes was verified by bisulfite sequencing. The mRNA transcripts could be re-expressed in melanoma cell lines having hypermethylated genes following treatment with 5'-aza 2'-deoxycytidine (5Aza-dC). Analysis of melanoma patients' plasma (preoperative blood; n=31) demonstrated circulating hypermethylated MGMT, RAR-beta2, and RASSF1A DNA for at least one of the markers in 29\% of the patients. Our findings indicate that the incidence of TSG hypermethylation increases during tumor progression. Methylation of TSG may play a significant role in cutaneous melanoma progression.
This article was published in Oncogene
and referenced in Journal of Molecular Biomarkers & Diagnosis