Direct transdifferentiation of tumorigenic melanoma cells to non-tumorigenic neuron-like cells

Melanoma is an aggressive skin cancer and is highly lethal at advanced stages despite the availability of a variety of established therapeutic options due to the high tumorigenicity and metastatic capacity of melanoma cells. However, there is evidence that changing the lineage of cancer cells leads to a drastic reduction of their tumorigenic potential. Different approaches have been developed to change the phenotype of a cell from one lineage to another, a process called transdifferentiation. In this study, we investigated whether melanoma cells can be transdifferentiated into neurons and how that affects their properties and characteristics. For this reason, we ectopically overexpressed the neuron-specific transcription factors Ascl1, Brn2, Myt1L and NeuroD1 in melanoma cells. We could show that melanoma cells could be transdifferentiated into neuron-like cells that expressed neuronal markers and showed a neuron-like morphology. RNA sequencing and DNA methylation assay were used to further reveal the underlying mechanism. Moreover, the transdifferentiated cells had a significantly reduced tumorigenic and metastatic potential and were more sensitive to radiotherapy compared with their parental counterparts. We conclude that transdifferentiation of cancer cells into terminally differentiated cells could represent a new therapeutic alternative for the treatment of malignant melanoma. Overall design: All melanoma cell lines were transduced with pLU-EF1aL-rtTA3-iCherry. The cells were then selected for mCherry fluorescence using cell sorter BD FACSAria from the Flow Cytometry Core Facility of the DKFZ. Successfully transduced cells were hereafter termed Melanoma-M2. Then the cells were sequentially transduced with the expression constructs for the factors Brn2, Myt1L and NeuroD1 and afterwards treated with 3 different antibiotics (blasticidin, hygromycin and G418) in order to select for cells transduced with the respective constructs. The selected cells were infected with Ascl1 and after induction with doxycycline (1 µg/ml) subjected to selection with puromycin. Melanoma-M2 Cells infected with and selected for all four transcriptional factors were named Melanoma-4F.