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Immunostaining for DNA Modifications: Computational Analysis of Confocal Images
Published on: September 7, 2017
Promoter methylation controls the expression of MAGE2, 3 and 4 genes in human cutaneous melanoma
Luca Sigalotti1, Sandra Coral, Gianpaolo Nardi
1Cancer Bioimmunotherapy Unit, Centro di Riferimento Oncologico, Istituto di Ricovero e Cura a Carattere Scientifico, Aviano, Italy.
Abstract:
Cancer-testis antigens expressed by different-histotype transformed cells are suitable targets for tumor immunotherapy. However, their heterogeneous expression in neoplastic lesions limits the eligibility of patients for cancer-testis antigen-directed vaccination, and low levels of cancer-testis antigens' expression may impair immune recognition of malignant cells. Because of the primary clinical relevance of cancer-testis antigens' expression in neoplastic tissues, 68 unrelated or sequential metastatic lesions from 56 patients were used to characterize the molecular mechanisms regulating the presence and levels of expression of different cancer-testis antigens of the MAGE family (i.e., MAGE2, 3 and 4) in cutaneous melanoma. Polymerase chain reaction-based methylation analyses showed that methylation status of specific cytosine-guanine dinucleotides in the promoters of investigated cancer-testis antigens correlated with their heterogeneous expression within unrelated metastatic melanoma lesions, and with their homogeneous expression among sequential metastases from three patients with melanoma. Unlike methylated promoters, unmethylated promoters of MAGE2, 3 and 4 genes drove the expression of reporter gene-enhanced green fluorescent protein after transient transfection of cancer-testis antigen-positive Mel 142 melanoma cells. Furthermore, de novo expression of MAGE3 gene induced by the treatment of Mel 195 melanoma cells with the DNA hypomethylating agent 5-aza-2'-deoxycytidine was associated with a 6%-12% demethylation of selected cytosine-guanine dinucleotides in its promoter. Finally, 5-aza-2'-deoxycytidine induced a 16-fold increase of MAGE3 expression in Mel 313 melanoma cells expressing constitutively low levels of the antigen, but did not affect that of Mel 275 melanoma cells expressing high baseline levels of MAGE3. Overall, these findings identify promoter methylation as a shared mechanism directly regulating the expression of therapeutic cancer-testis antigens in metastatic melanomas, and foresee the clinical use of 5-aza-2'-deoxycytidine to design new chemoimmunotherapeutic strategies in patients with melanoma.
Insights
Promoter methylation regulates cancer-testis antigen expression in melanoma metastases. This finding supports using DNA hypomethylating agents like 5-aza-2'-deoxycytidine for novel chemoimmunotherapy strategies in melanoma patients.
Area of Science:
- Oncology
- Immunology
- Molecular Biology
Background:
- Cancer-testis antigens (CTAs) are promising targets for cancer immunotherapy due to their expression in various tumor types.
- Heterogeneous CTA expression in tumors limits patient eligibility for CTA-directed therapies and can impair immune recognition.
- Understanding the regulation of CTA expression is crucial for developing effective cancer immunotherapies.
Purpose of the Study:
- To investigate the molecular mechanisms regulating the expression of MAGE2, MAGE3, and MAGE4 cancer-testis antigens in cutaneous melanoma metastases.
- To determine the role of promoter methylation in the heterogeneous expression of CTAs within and between melanoma lesions.
- To explore the potential of DNA hypomethylating agents for modulating CTA expression for therapeutic benefit.
Main Methods:
- Analysis of 68 metastatic melanoma lesions from 56 patients.
- Polymerase chain reaction-based methylation analysis of MAGE2, MAGE3, and MAGE4 gene promoters.
- Reporter gene assays to assess promoter activity in melanoma cells.
- Treatment of melanoma cells with the DNA hypomethylating agent 5-aza-2 ac-deoxycytidine to evaluate its effect on CTA expression.
Main Results:
- Promoter methylation status significantly correlated with heterogeneous CTA expression in unrelated melanoma metastases and homogeneous expression in sequential metastases.
- Unmethylated MAGE2, MAGE3, and MAGE4 promoters drove reporter gene expression, indicating their transcriptional activity.
- Treatment with 5-aza-2 ac-deoxycytidine induced demethylation and de novo expression of MAGE3 in some melanoma cells.
- 5-aza-2 ac-deoxycytidine significantly increased MAGE3 expression in melanoma cells with low baseline levels but not in those with high baseline levels.
Conclusions:
- Promoter methylation is a key mechanism regulating the expression of MAGE family cancer-testis antigens in metastatic melanoma.
- DNA hypomethylating agents like 5-aza-2 ac-deoxycytidine can modulate CTA expression, offering potential for novel chemoimmunotherapeutic strategies.
- Targeting CTA expression through epigenetic modifications presents a promising avenue for enhancing melanoma treatment outcomes.
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