Structural basis of CBP/p300 recruitment by the microphthalmia-associated transcription factor

The microphthalmia-associated transcription factor (MITF) is a master regulator of the melanocyte cell lineage. Aberrant MITF activity can lead to multiple malignancies including skin cancer, where it modulates the progression and invasiveness of melanoma. MITF-regulated gene expression requires recruitment of the transcriptional co-regulator CBP/p300, but details of this process are not fully defined. In this study, we investigate the structural and functional interaction between the MITF N-terminal transactivation domain (MITF_TAD) and CBP/p300. Using pulldown assays and nuclear magnetic resonance spectroscopy we determined that MITF_TAD is intrinsically disordered and binds to the TAZ1 and TAZ2 domains of CBP/p300 with moderate affinity. The solution-state structure of the MITF_TAD:TAZ2 complex reveals that MITF interacts with a hydrophobic surface of TAZ2, while remaining somewhat dynamic. Peptide array and mutagenesis experiments determined that an acidic motif is integral to the MITF_TAD:TAZ2 interaction and is necessary for transcriptional activity of MITF. Peptides that bind to the same surface of TAZ2 as MITF_TAD, such as the adenoviral protein E1A, are capable of displacing MITF from TAZ2 and inhibiting transactivation. These findings provide insight into co-activator recruitment by MITF that are fundamental to our understanding of MITF targeted gene regulation and melanoma biology.