Analysis of CRTC3 genomic occupancy upon forskolin stimulus in B16F1 cells.
Triggering of cAMP and mitogen-activated (MAPK) pathways in response to hormonal and growth factor cues promotes melanocyte pigmentation and survival in part through induction of the master regulator MITF by cAMP-responsive factor CREB. We examined the role of CREB coactivators (CRTC1-3) in transduction of cAMP and MAPK signals in melanocytes. We found that CRTC3 knock-out in mice and B16F1 melanoma cells decreases pigmentation by directly regulating the expression of the melanosomal transporter OCA2. In addition to effects of cAMP, CRTC3 activation was also promoted by ERK1/2-mediated phosphorylation at Ser391; amounts of phosphorylated CRTC3-S391 were constitutively elevated in human melanoma cells expressing mutated BRAF or NF1. Knock-out of CRTC3 in A375 melanoma cells impaired their anchorage-independent growth, migration and invasiveness, whereas CRTC3 over-expression increased survival in response to BRAF inhibition by vemurafenib. Analysis of spontaneous CRTC3 mutations in melanomas reveals that increased activity of this co-activator associates with reduced patient survival. Our results highlight the importance of CRTC3 in pigmentation and melanoma progression. Overall design: Profiles of genomic occupancy of CRTC3 in B16F1 cells treated with vehicle or cAMP agonist forskolin. Controls include CREB, MITF, phospho-PolII and acetylated Histone3 (H3acK27).