Epigenetically reprogramming metastatic tumor cells with an embryonic microenvironment

We have previously shown that the microenvironment of human embryonic stem cells (hESCs) is able to change and reprogram aggressive cancer cells to a less aggressive state. Some mechanisms implicated in the phenotypic changes observed after this exposure are mainly associated with the Nodal signaling pathway, which plays a key role in tumor cell plasticity. However, several other molecular mechanisms might be related directly and/or indirectly to these changes, including microRNA (miRNA) regulation and DNA methylation. Aim: To further explore the epigenetic mechanisms potentially underlying the phenotypic changes that occur after exposing metastatic melanoma cells to a hESC microenvironment. Materials & Methods: A total of 365 miRNAs were screened using the TaqMan (R) Low Density Arrays. We also evaluated whether DNA methylation could be one of the factors regulating the expression of the inhibitor of Nodal, Lefty, in hESCs (where it is highly expressed) vs melanoma cells (where it is not expressed). Results: Using these experimental approaches, we identified miRNAs that are up- and down-regulated in melanoma cells exposed to a hESC microenvironment, such as miR-302a and miR-27b, respectively. We also demonstrate that Notch4 is one of the targets of miR-302a, which is upstream of Nodal. Additionally, one of the mechanisms that might explain the absence of the inhibitor of Nodal, Lefty, in cancer cells is silencing by DNA methylation, which provides new insights into the unregulated expression of Nodal in melanoma. Conclusion: These findings suggest that epigenetic changes such as DNA methylation and regulation by microRNAs might play a significant role in tumor cell plasticity and the metastatic phenotype.