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Metastasising Melanoma

Analysis of human melanoma cell lines: Immunofluorescence for the transcription factors C/EBPα and MITF expression in murine melanoma cells, regulated by the JAK/STAT pathway control melanoma growth and survival. The experiment was performed in collaboration with Mario Mikula from the Medical University Vienna.

We have established four different genetic mouse models to address the role of STAT transcription factors in metastasizing melanoma driven by oncogenic RAS and loss of Ink4a tumor suppressors. We deleted STAT1, STAT3, STAT5a/b or STAT3/5a/5b conditionally as these transcription factors are regarded as key molecules for melanoma progression. The work is still unpublished and was added to the work of the RM group recently, funded by a melanoma donation. We are also in the process to establish BRaf V600E oncogenic mouse models investigating the crucial role of STAT transcription factors.

We generated a new melanoma mouse model that harbors a floxed STAT5 allele and a Cre transgene specifically expressed under the tyrosinase promoter, which is only active in melanocytes of the skin. These mice were crossed to mice lacking the Ink4a gene locus, which is known to lead to a predisposition to melanoma in patients. Additionally, the model harbors a typical early occurring melanoma mutation, the N-RasQ61K mutation, also expressed under the tyrosinase promoter. The N-RasQ61K mutation leads to hyperpigmentation of the skin, as can be seen e.g. in human nevi. Currently ongoing is a STAT5ab/3 triple knockout model to gain insight into potential compensatory effects between these two transcription factors. B) The knockout was confirmed in immune-histochemical STAT5 staining in primary melanomas, comparing Cre positive and Cre negative mice. C) The differences in survival and metastasis formation in these mice are currently under investigation, particularly if metastasis is frequently from cells escaping the STAT deletion. Lung, lymph node and liver metastases are shown as examples.

Role of Stat3 in a metastasizing malignant melanoma model driven by RAS: We successfully isolated oncogenic RAS-driven and Ink4a-deficient melanoma cell lines from mice harboring a deletion of the Stat3 gene and from control mice that still express STAT3. (A) Successful deletion of STAT3 is prominent using immunocytochemistry on cytospin analysis of cell lines. (B) The same cell lines were used for RNA expression microarray studies to identify changes in cell signalling occurring between the groups of the STAT3 knockout cell lines and the STAT3 wild type cell lines. The immunoblot displays down regulation of STAT3 target genes in the STAT3 knockout cell lines. The plot represents four samples per group. Positive values indicated up regulated STAT3 targets in comparison to STAT3 knockout cells.

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