Overexpression of meloe gene in melanomas is controlled both by specific transcription factors and hypomethylation

Our plain-English summary of Overexpression of meloe gene in melanomas is controlled both by specific transcription factors and hypomethylation, by M. Bobinet, V. Vignard, L. Florenceau, et al (PloS One, 2013).

The study

• Authors: M. Bobinet, V. Vignard, L. Florenceau, F. Lang, N. Labarriere, A. Moreau-Aubry
• Journal: PloS One
• Published: 2013;8(9):e75421
• Cited by: 7 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

The melanoma antigens MELOE-1 and MELOE-2 are encoded by a messenger, called meloe, overexpressed in melanomas compared with other tumour cell types and healthy tissues. They are both able to elicit melanoma-specific T cell responses in melanoma patients, and MELOE-1-specific CD8 T cells have been involved in melanoma immunosurveillance. With the aim to develop immunotherapies targeting this antigen, we investigated the transcriptional mechanisms leading to the preferential expression of meloe messenger in the melanocytic lineage. We defined the minimal promoter region of meloe gene and identified binding motifs for a set of transcription factors. Using mutagenesis, co-transfection experiments and chromatin immunoprecipitation, we showed that transcription factors involved in meloe promoter activity in melanomas were the melanocytic specific SOX9 and SOX10 proteins together with the activated P-CREB protein. Furthermore, we showed that meloe promoter was hypomethylated in melanomas and melanocytes, and hypermethylated in colon cancer cell lines and mesotheliomas, thus explaining the absence of P-CREB binding in these cell lines. This was a second key to explain the overerexpression of meloe messenger in the melanocytic lineage. To our knowledge, such a dual transcriptional control conferring tissue-specificity has never been described for the expression of tumour antigens.

In plain English

This was a laboratory study of human cell lines, not a study of asbestos exposure. Mesothelioma cell lines appeared only as one comparison group. The authors studied why a gene message called meloe, which codes for the melanoma antigens MELOE-1 and MELOE-2, is made in large amounts in melanoma. They confirmed that meloe was overexpressed in melanoma cell lines and melanocytes (pigment cells) compared with other tumour cell lines, including four mesothelioma lines. Mutating the gene's binding sites for the SOX and CREB proteins caused a drastic loss of the activity of the gene's switch region (its promoter). Adding SOX9 or SOX10 to a colon cancer line and a mesothelioma line (Meso163) restored that activity. In mesothelioma cells, none of the three proteins was bound to the promoter. The promoter region was almost totally unmethylated in melanocytes and melanoma cells. It was hypermethylated in mesothelioma lines (100% in Meso45 and 77% in Meso163) and in colon cancer lines (64% in SW480 and 85% in SW707). The authors concluded that this methylation likely impairs the binding of activated CREB (P-CREB) in non-melanoma cells, contributing to low meloe expression.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Laboratory (in vitro) molecular study of human cell lines: gene expression measurement (qPCR), promoter deletion and mutation with reporter assays, co-transfection, chromatin immunoprecipitation, and DNA methylation analysis
• Who was studied: Human cell samples, not people: eight melanocyte samples and cell lines from twelve melanomas, three colon cancers, four mesotheliomas (Meso45, Meso61, Meso85, Meso163), two lung cancers, one renal carcinoma, one breast cancer and one neuroblastoma; Nantes, France
• Exposure: No asbestos or other fiber exposure was studied. The study examined transcription factors (SOX9, SOX10, P-CREB) and promoter DNA methylation in relation to expression of the meloe gene.
• Main results:
  • meloe was overexpressed in melanoma cell lines and in melanocytes compared with colon, renal, lung, breast, mesothelioma and neuroblastoma cell lines
  • In the M113 melanoma cell line, mutating the SOX and CREB binding sites of the meloe promoter caused a drastic loss of promoter activity (P less than 0.001)
  • SOX10 protein was detected only in melanoma cells; SOX9 was strong in melanoma cells and weak in colon carcinoma and mesothelioma cells; P-CREB was detected in all cell lysates
  • Adding SOX9 or SOX10 to the SW480 colon carcinoma line and the Meso163 mesothelioma line restored meloe promoter activity
  • SOX9, SOX10 and P-CREB were bound to the meloe promoter in M113 melanoma cells; none of them was bound in Meso163 mesothelioma cells
  • The meloe promoter region (26 CpG sites) was almost totally unmethylated in melanocytes and melanoma cells
  • The same region was hypermethylated in mesothelioma cells: 100% in Meso45 and 77% in Meso163
  • The same region was hypermethylated in colon carcinoma cells: 64% in SW480 and 85% in SW707
• The authors' conclusion: The authors concluded that meloe expression in melanomas depends on SOX9, SOX10 and P-CREB, and that hypermethylation of the CREB binding site in non-melanoma cell lines likely impairs P-CREB binding, contributing to low meloe expression in those cells.
• Limitations the authors state:
  • The authors note that, although the putative PAX3 and MITF sites tested were not involved in promoter activity, binding of these factors at more distant sites, and a role for them in meloe regulation, cannot be excluded
  • The authors state that this first study focused only on the SOX and CREB factors

Topics

Medical terms in this study, explained in our Lexicon: Colorectal Cancer, Mesothelioma.

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