Mechanisms of Spontaneous Melanoma Regression in MeLiM Pigs
Year: 2008
Type: preprint
Abstract: Cutaneous melanoma, the most aggressive form of skin cancer, is a tumor originating from melanocytes with rapidly increasing incidence. Patients with advanced disease have a poor prognosis since melanoma is mostly resistant to current therapies. Therefore, the development of novel strategies for preventing and treating melanoma is important. To explore novel therapies we need to find appropriate targets and for that knowledge about the biology of melanoma is important. One elegant way to do so, is to study the natural but rare phenomenon of spontaneous melanoma regression. Unfortunately, complete spontaneous regression of advanced melanoma is extremely rare, and therefore hard to investigate. The Melanoblastoma-bearing Libechov Minipig (MeLiM) is a great opportunity to study spontaneous tumor regression. MeLiM pigs, suffering from hereditary melanoma, develop tumors naturally and regress them completely without external influence. Mechanisms leading to spontaneous melanoma regression are poorly understood at present. Therefore the overall objective of this PhD was to investigate mechanisms of spontaneous melanoma regression in MeLiM pigs. In an initial study we gained a global overview of differentially expressed genes between a growing and regressing tumor by conducting Subtractive Suppression Hybridization (SSH). We also performed SSH analysis of cell cultures isolated from growing and regressing melanoma to be able to distinguish between expressional changes induced by tumor microenvironment. Only a few genes were in common between these two SSH analyses. Thus we focused on the SSH results obtained from tumor tissue. We were able to identify a gene signature for growing melanoma that demonstrated common genes with human progressive melanoma (TYR, MITF, MLANA, SDCBP, SILV, TYRP and ZFP106). Genes overexpressed at the beginning of regression were mainly involved in functional classes such as differentiation, immune system, cell cycle arrest, and tumor suppression. Two genes, CD9 and RARRES1, showed a strong upregulation during early melanoma regression on the mRNA and protein level whereas CD9 is a motility-related protein and RARRES1 a putative tumor suppressor. Since spontaneous regression is a dynamic process, we performed time dependent gene expression profiling using DNA chips in a second study. We identified significant gene signatures at different stages of regression that were able to explain the corresponding phenotype. Identified gene signatures were mainly involved in the immune response, the cell cycle, and melanocyte differentiation/pigmentation processes. Interestingly, we showed an early downregulation of cell cycle related genes that could play a role in regression. Also, we identified different immune gene signatures, suggesting a major role of the host's immune system in eradicating melanoma cells. By using immunohistology and flow cytometry we characterized tumor infiltrating cells of the innate and adaptive immune system. During regression the infiltration occurred in two phases: an early phase consisting of antigen presenting cells (SWC3+), followed by a later infiltration of mainly cytotoxic T lymphocytes (CD8+). Furthermore the regression process is accompanied by the presence of big highly pigmented cells that we began to characterize. This work allowed us to point out similarities between the pig and human melanoma on the transcriptomic level along with the already observed parallels on the clinical and genetic level. These findings underline the utility for this model to study human melanoma. This work helped also to decipher the process of spontaneous regression on a cellular and molecular level. In this way we observed an early mitotic arrest of tumor cells, linked to regression, that has not been described so far, and an implication of the immune system. If the immune response is the real inducer of regression needs to be verified. Already, this work contributes to human anti-melanoma therapy as it provides potential targets that could be used for developing new strategies.
Author: Florian Rambow
Language: French
Topic: Melanoma and MAPK Pathways
Subfield: Molecular Biology
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W1553564565