Inhibition of MITF transcriptional activity independent of targeting p300/CBP coactivators

Abstract

Microphthalmia-associated transcription factor (MITF) activates the expression of melanocyte-specific markers and promotes the survival of embryonic, adult and malignant melanocytes. Although numerous MITF-dependent downstream genes have been identified, the mechanisms by which the MITF activity is coregulated remain elusive. Here we used a non-melanocytic cell line U2-OS as a model in which MITF evokes transcription of a paradigmatic MITF target tyrosinase and show that the adenoviral E1A protein represses the MITF-driven transcription in these cells. The E1A CR1 domain (which alone is insufficient to bind p300) was sufficient for repression, while the N-terminus, through which E1A binds the p300/CBP proteins and other coactivators, was unable to repress. Correspondingly, CR1 inhibited colony formation of MITF-positive, but not MITF-negative, melanoma cells. The repression by CR1 was largely independent of the PCAF-binding motif, previously recognized to be necessary for suppression of muscle-specific enhancer. Interestingly, CR1 conferred transcriptional competence to the MITF-CR1 chimera in which the MITF portion was rendered transcription-deficient. Moreover, MITF mutants defective in binding to p300/CBP in vivo still activated transcription, further supporting a p300/CBP-independent coactivation of MITF targets. MITF is amplified in a subset of melanomas and is thought to be required for sustained proliferation of malignant melanocytes. Our results suggest that understanding how CR1 represses Mitf activity may reveal a route to melanoma therapy.

Loss of CITED1, an MITF regulator, drives a phenotype switchin vitroand can predict clinical outcome in primary melanoma tumours

“…It is thus tempting to speculate that rather than simply acting to induce MITF and thereby indirectly enhance transcription of its target genes, that CITED1 may also act as co-factor for MITF at various genomic locations differentially modulating the MITF target gene response at individual promoters. One way that this might be achieved is via MITF-CITED1 competition for CBP/P300 binding as CBP/P300 is a known transcriptional coregulator for MITF, although it is not required for transcription of all MITF targets (Vachtenheim, Šestákov á & Tuháčková, 2007; Yan et al, 2013). …”

MiTF Regulates Cellular Response to Reactive Oxygen Species through Transcriptional Regulation of APE-1/Ref-1

“…cAMP response element-binding protein binds p300 or CBP to modify chromatin structure for transcription activation (Rouaux et al ., 2004). MiTF binds DNA through its basic helix-loop-helix domain and activates transcription in both p300-dependent and -independent manners (Sato et al ., 1997; Vachtenheim et al ., 2007). In the current study MiTF was phosphorylated in both melanoma cells and normal melanocytes after elevated ROS treatment (Figures 3a–c), suggesting that MiTF itself is responsive to cellular ROS change.…”

“Transcription physiology” of pigment formation in melanocytes: central role of MITF

“…The phosphorylation at S73 was shown to be necessary for the interaction with the p300 coactivator (43). However, the truncated MITF construct lacking the N‐terminus including S73 or the S73A mutant lost none of the transactivation potential (44), indicating that interaction of MITF with p300 is not a critical event for constitutive activation. More likely, it might play a physiological role in transient signal‐induced changes of MITF activity.…”