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Mucosal melanomas of different anatomic sites share a common DNA methylation profile but show different patterns of genetic and epigenetic alterations

ABSTRACT: Cutaneous, ocular and mucosal melanomas are histologically indistinguishable tumors that are driven by different spectrum of genetic alterations. With current methods, identification of the site of origin of a melanoma metastasis is challenging, in particular when the metastasis is the first tumor manifestation. Genome wide DNA methylation profiling has shown promise for the identification of the site of tumor origin in various settings. Here we explore the DNA methylation landscape of melanomas from different sites and analyze if different melanoma origins can be distinguished by their epigenetic profile. We performed DNA methylation analysis, next generation DNA panel sequencing and copy number analysis of 82 non-cutaneous and 25 cutaneous melanoma samples. We further analyzed eight normal melanocyte cell culture preparations by DNA methylation profiling. DNA methylation analysis clearly separated uveal melanomas from melanomas of other primary sites while mucosal, conjunctival and cutaneous melanomas were epigenetically almost identical. Still, we observed DNA methylation differences in cancer-related genes, such as low frequencies of RARB and CDKN2A promoter methylation in mucosal melanomas, while conjunctival melanomas frequently harbored APC promoter methylation. Furthermore, all investigated melanomas of the paranasal sinus showed loss of PTEN expression, mainly caused by promoter methylation. This was less frequently seen in melanomas of other sites. Copy number analysis revealed recurrent amplifications in mucosal melanomas, including chromosome 4q, 5p, 11q and 12q. Most melanomas of the oral cavity showed gains of chromosome 5p with TERT amplification while 11q amplifications were enriched in melanomas of the nasal cavity. Mucosal, conjunctival and cutaneous melanomas show a surprisingly similar DNA methylation profile and identification of the site of origin by DNA methylation testing is likely not feasible. Still, our study shows that there are DNA methylation differences on the gene level in known tumor drivers, related to the anatomical primary site.

ORGANISM(S): Homo sapiens

PROVIDER: GSE178416 | GEO | 2021/09/21

REPOSITORIES: GEO

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Project description:Melanoma genomes are often characterized by large numbers of sunlight-induced mutations. However, epigenetic alterations, in the form of aberrant DNA methylation patterns, are also abundant. Using MIRA-seq, we have carried out a comprehensive characterization of the DNA methylome in a series of metastatic melanoma samples and catalogued the methylation changes relative to normal melanocytes, the presumed cells of origin for these tumors. Individual melanoma tumors contained up to several thousand hypermethylated regions. We discovered 179 tumor-specific methylation peaks that were present in all (27/27) melanomas and may lend themselves as effective disease biomarkers, and 3124 methylation peaks were present in >40% of the tumors. We specifically examined the relationship between presence of the Polycomb mark, H3K27me3 in melanocytes and tumor-specific DNA methylation in melanoma. We found that 150 of the approximately 1,200 tumor-associated methylation peaks near transcription start sites (TSS) were H3K27me3-marked in melanocytes. Notably, DNA methylation in melanoma was specific for distinct H3K27me3 peaks rather than for H3K27me3-enriched regions with broad genomic coverage. Yet, there were also numerous H3K27me3 peak-associated TSS regions that were completely resistant to DNA methylation in tumors. Furthermore, a rather large group of genes became methylated in melanoma but lacked H3K27me3 in melanocytes. There was no relationship between presence of BRAF V600 mutations and the number of methylation peaks in individual tumors. Gene expression analysis showed a strong signature of upregulated immune response genes in melanomas presumably as a result of lymphocyte infiltration. Genes down-regulated in tumors were enriched for melanocyte differentiation and pigmentation factors. Overall, there was limited correlation between tumor-associated DNA methylation changes and changes in gene expression although distinct melanocyte differentiation genes including KIT, PAX3 and SOX10 became methylated and downregulated in melanoma. Using MIRA-Seq, DNA methylation profiles of 27 malignant melanomas and 3 primary cultured melanocyte samples were determined

Project description:Melanoma genomes are often characterized by large numbers of sunlight-induced mutations. However, epigenetic alterations, in the form of aberrant DNA methylation patterns, are also abundant. Using MIRA-seq, we have carried out a comprehensive characterization of the DNA methylome in a series of metastatic melanoma samples and catalogued the methylation changes relative to normal melanocytes, the presumed cells of origin for these tumors. Individual melanoma tumors contained up to several thousand hypermethylated regions. We discovered 179 tumor-specific methylation peaks that were present in all (27/27) melanomas and may lend themselves as effective disease biomarkers, and 3124 methylation peaks were present in >40% of the tumors. We specifically examined the relationship between presence of the Polycomb mark, H3K27me3 in melanocytes and tumor-specific DNA methylation in melanoma. We found that 150 of the approximately 1,200 tumor-associated methylation peaks near transcription start sites (TSS) were H3K27me3-marked in melanocytes. Notably, DNA methylation in melanoma was specific for distinct H3K27me3 peaks rather than for H3K27me3-enriched regions with broad genomic coverage. Yet, there were also numerous H3K27me3 peak-associated TSS regions that were completely resistant to DNA methylation in tumors. Furthermore, a rather large group of genes became methylated in melanoma but lacked H3K27me3 in melanocytes. There was no relationship between presence of BRAF V600 mutations and the number of methylation peaks in individual tumors. Gene expression analysis showed a strong signature of upregulated immune response genes in melanomas presumably as a result of lymphocyte infiltration. Genes down-regulated in tumors were enriched for melanocyte differentiation and pigmentation factors. Overall, there was limited correlation between tumor-associated DNA methylation changes and changes in gene expression although distinct melanocyte differentiation genes including KIT, PAX3 and SOX10 became methylated and downregulated in melanoma. Genome-wide gene expression analysis of 17 melanomas and 3 melanocyte samples

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Mucosal melanomas of different anatomic sites share a common DNA methylation profile but show different patterns of genetic and epigenetic alterations

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