Transcriptional reprogramming of proliferative melanoma cells into a phenotypically distinct invasive cell subpopulation is a critical event at the origin of metastatic spreading.,Here we generate transcriptome, open chromatin and histone modification maps of melanoma cultures; and integrate this data with existing transcriptome and DNA methylation profiles from tumour biopsies to gain insight into the mechanisms underlying this key reprogramming event.,This shows thousands of genomic regulatory regions underlying the proliferative and invasive states, identifying SOX10/MITF and AP-1/TEAD as regulators, respectively.,Knockdown of TEADs shows a previously unrecognized role in the invasive gene network and establishes a causative link between these transcription factors, cell invasion and sensitivity to MAPK inhibitors.,Using regulatory landscapes and in silico analysis, we show that transcriptional reprogramming underlies the distinct cellular states present in melanoma.,Furthermore, it reveals an essential role for the TEADs, linking it to clinically relevant mechanisms such as invasion and resistance.,The key regulators that allow transition from proliferative to invasive phenotype in melanoma cells have not been identified yet.,The authors perform chromatin and transcriptome profiling followed by comprehensive bioinformatics analysis identifying new candidate regulators for two distinct cell states of melanoma.
Melanoma is an aggressive tumor with increasing incidence.,To develop accurate prognostic markers and targeted therapies, changes leading to malignant transformation of melanocytes need to be understood.,In the Xiphophorus melanoma model system, a mutated version of the EGF receptor Xmrk (Xiphophorus melanoma receptor kinase) triggers melanomagenesis.,Cellular events downstream of Xmrk, such as the activation of Akt, Ras, B-Raf or Stat5, were also shown to play a role in human melanomagenesis.,This makes the elucidation of Xmrk downstream targets a useful method for identifying processes involved in melanoma formation.,Here, we analyzed Xmrk-induced gene expression using a microarray approach.,Several highly expressed genes were confirmed by realtime PCR, and pathways responsible for their induction were revealed using small molecule inhibitors.,The expression of these genes was also monitored in human melanoma cell lines, and the target gene FOSL1 was knocked down by siRNA.,Proliferation and migration of siRNA-treated melanoma cell lines were then investigated.,Genes with the strongest upregulation after receptor activation were FOS-like antigen 1 (Fosl1), early growth response 1 (Egr1), osteopontin (Opn), insulin-like growth factor binding protein 3 (Igfbp3), dual-specificity phosphatase 4 (Dusp4), and tumor-associated antigen L6 (Taal6).,Interestingly, most genes were blocked in presence of a SRC kinase inhibitor.,Importantly, we found that FOSL1, OPN, IGFBP3, DUSP4, and TAAL6 also exhibited increased expression levels in human melanoma cell lines compared to human melanocytes.,Knockdown of FOSL1 in human melanoma cell lines reduced their proliferation and migration.,Altogether, the data show that the receptor tyrosine kinase Xmrk is a useful tool in the identification of target genes that are commonly expressed in Xmrk-transgenic melanocytes and melanoma cell lines.,The identified molecules constitute new possible molecular players in melanoma development.,Specifically, a role of FOSL1 in melanomagenic processes is demonstrated.,These data are the basis for future detailed analyses of the investigated target genes.