Histone modifications, largely regulated by
histone acetyltransferases (HAT) and
histone deacetylases, have been recognized as major regulatory mechanisms governing human diseases, including
cancer. Despite significant effort and recent advances, the mechanism by which the HAT and transcriptional coactivator p300 mediates
tumorigenesis remains unclear. Here, we use a genetic and chemical approach to identify the
microphthalmia-associated transcription factor (MITF) as a critical downstream target of p300 driving human
melanoma growth. Direct transcriptional control of MITF by p300-dependent
histone acetylation within proximal gene regulatory regions was coupled to cellular proliferation, suggesting a significant growth regulatory axis. Further analysis revealed forkhead box M1 (FOXM1) as a key effector of the p300-MITF axis driving cell growth that is selectively activated in human
melanomas. Targeted chemical inhibition of
p300 acetyltransferase activity using a potent and selective catalytic p300/CBP inhibitor demonstrated significant growth inhibitory effects in
melanoma cells expressing high levels of MITF. Collectively, these data confirm the critical role of the p300-MITF-FOXM1 axis in
melanoma and support p300 as a promising novel epigenetic therapeutic target in human
melanoma. SIGNIFICANCE: These results show that MITF is a major downstream target of p300 in human
melanoma whose expression is predictive of
melanoma response to small-molecule inhibition of p300 HAT activity.