NRG1 and melanoma: FOXD3 mediates adaptive resistance to RAF inhibitors by directly activating the expression of v-erb-b2 erythroblastic leukemia viral oncogene homolog 3 (ERBB3) at the transcriptional level and enhancing the responsiveness of melanoma cells to the ERBB3 ligand, neuregulin-1 (NRG1)13.