Notch signaling activation induces cell death in MAPKi-resistant melanoma cells.

The role of Notch signaling in melanoma drug resistance is not well understood. In this study, we show that although NOTCH proteins are upregulated in metastatic melanoma cell lines, Notch signaling inhibition had no effect on cell survival, growth, migration or the sensitivity of BRAFV600E-melanoma cells to MAPK inhibition (MAPKi). We found that NOTCH1 is downregulated in melanoma cell lines with intrinsic and acquired resistance to MAPKi. Forced expression of NICD1, the active form of Notch1, caused apoptosis of the NOTCHlo , MAPKi-resistant cells, but not the NOTCHhi , MAPKi-sensitive melanoma cell lines. Whole transcriptome-sequencing analyses of NICD1-transduced MAPKi-sensitive and MAPKi-resistant cells revealed differential regulation of endothelin 1 (EDN1) by NICD1, that is, downregulation in MAPKi-resistant cells and upregulation in MAPKi-sensitive cells. Knockdown of EDN1 partially mimicked the effect of NICD1 on the survival of MAPKi-resistant cells. We show that the opposite regulation of EDN1 by Notch signaling is mediated by the differential regulation of c-JUN by NICD1. Our data show that MAPKi-resistant melanoma cells acquire vulnerability to Notch signaling activation and suggest that Notch-c-JUN-EDN1 axis is a potential therapeutic target in MAPKi-resistant melanoma.