GABA regulates electrical activity and tumor initiation in melanoma

Oncogenes can only initiate tumors in certain cellular contexts, which is referred to as oncogenic competence. In melanoma, whether cells in the microenvironment can endow such competence remains unclear. Using a combination of zebrafish transgenesis coupled with human tissues, we demonstrate that GABAergic signaling between keratinocytes and melanocytes promotes melanoma initiation by BRAFV600E. GABA is synthesized in melanoma cells, which then acts on GABA-A receptors on keratinocytes. Electron microscopy demonstrates specialized cell-cell junctions between keratinocytes and melanoma cells, and multi-electrode array analysis shows that GABA acts to inhibit electrical activity in melanoma/keratinocyte co-cultures. Genetic and pharmacologic perturbation of GABA synthesis abrogates melanoma initiation in vivo. These data suggest that GABAergic signaling across the skin microenvironment regulates the ability of oncogenes to initiate melanoma. Overall design: To identify differentially expressed genes between monocultured, co-cultured and switched keratinocytes, we performed RNA-sequencing of the parental keratinocyte populations in monoculture and co-culture and the co-cultured keratinocyte populations that had undergone Cre mediated switching. Each condition was analyzed using three biological replicates for each of the three conditions (9 samples total).