Contact by melanoma cells causes malignant transformation of human epithelial-like stem cells via alpha V integrin activation of transforming growth factor β1 signaling.

The embryonic microenvironment is known to suppress the tumorigenic phenotype of aggressive cancer cells; however, the effects of tumorigenic microenvironments on stem cells have not been sufficiently explored due to the lack of suitable model systems. In order to study the tumorigenic microenviornment, we developed a novel in vitro model system for induction of malignant transformation of human epithelial-like stem cells (hEpSCs), involving co-cultivation and close contact of hEpSCs with the A375 melanoma cell line, together with mutagen treatment of hEpSCs with dimethylbenzanthracene (DMBA). Both factors (close contact and mutagen treatment) were required to transform hEpSCs in vitro and cause phenotypic changes characteristic of epithelial to mesenchymal transition (EMT), including colony formation, decreased E-cadherin and increased N-cadherin and vimentin expression. Direct contact between tumor cells and hEpSCs treated with DMBA increased integrin alpha V (ITGAV gene) expression and caused local activation of the transforming growth factor (TGF)-β1/Smad signaling pathways in hEpSCs. The novel model system described here is being used to elucidate the microenvironmental factors and biological mechanisms involved in the induction of neoplastic progression in hEpSCs in vitro by A375 melanoma cells. A better understanding of the molecular mechanisms by which melanoma cells exert these effects on hEpSCs may open up new avenues for therapeutic and preventive cancer interventions.