Metastases are thought to arise from cancer stem cells and their tumor initiating abilities are required for the establishment of metastases.,Nevertheless, in metastatic melanoma, the nature of cancer stem cells is under debate and their contribution to metastasis formation remains unknown.,Using an experimental metastasis model, we discovered that high levels of the WNT receptor, FZD7, correlated with enhanced metastatic potentials of melanoma cell lines.,Knocking down of FZD7 in a panel of four melanoma cell lines led to a significant reduction in lung metastases in animal models, arguing that FZD7 plays a causal role during metastasis formation.,Notably, limiting dilution analyses revealed that FZD7 is essential for the tumor initiation of melanoma cells and FZD7 knockdown impeded the early expansion of metastatic melanoma cells shortly after seeding, in accordance with the view that tumor initiating ability of cancer cells is required for metastasis formation.,FZD7 activated JNK in melanoma cell lines in vitro and the expression of a dominant negative JNK suppressed metastasis formation in vivo, suggesting that FZD7 may promote metastatic growth of melanoma cells via activation of JNK.,Taken together, our findings uncovered a signaling pathway that regulates the tumor initiation of melanoma cells and contributes to metastasis formation in melanoma.
Cellular plasticity confers cancer cells the ability to adapt to microenvironmental changes, a fundamental requirement for tumour progression and metastasis.,The epithelial to mesenchymal transition (EMT) is a transcriptional programme associated with increased cell motility and stemness.,Besides EMT, the mesenchymal to amoeboid transition (MAT) has been described during tumour progression but to date, little is known about its transcriptional control and involvement in stemness.,The aim of this manuscript is to investigate (i) the transcriptional profile associated with the MAT programme and (ii) to study whether MAT acquisition in melanoma cancer cells correlates with clonogenic potential to promote tumour growth.,By using a multidisciplinary approach, we identified four different treatments able to induce MAT in melanoma cells: EphA2 overexpression, Rac1 functional inhibition using its RacN17 dominant negative mutant, stimulation with Ilomastat or treatment with the RhoA activator Calpeptin.,First, gene expression profiling identified the transcriptional pathways associated with MAT, independently of the stimulus that induces the MAT programme.,Notably, gene sets associated with the repression of mesenchymal traits, decrease in the secretion of extracellular matrix components as well as increase of cellular stemness positively correlate with MAT.,Second, the link between MAT and stemness has been investigated in vitro by analysing stemness markers and clonogenic potential of melanoma cells undergoing MAT.,Finally, the link between MAT inducing treatments and tumour initiating capability has been validated in vivo.,Taken together, our results demonstrate that MAT programme in melanoma is characterised by increased stemness and clonogenic features of cancer cells, thus sustaining tumour progression.,Furthermore, these data suggest that stemness is not an exclusive feature of cells undergoing EMT, but more generally is associated with an increase in cellular plasticity of cancer cells.