title: 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.
authors.affiliation: Laboratory of Molecular Biology, University Hospital, Third Medical Faculty, Charles University Prague, Czech Republic. jivach@upn.anet.cz
authors.forename: Jiri
authors.initials: J
authors.lastname: Vachtenheim
authors.forename: Blanka
authors.initials: B
authors.lastname: Sestáková
authors.forename: Zdena
authors.initials: Z
authors.lastname: Tuhácková
mesh_terms: D017500:Adenovirus E1A Proteins / Q000737:chemistry; D000595:Amino Acid Sequence; D045744:Cell Line, Tumor; D015536:Down-Regulation; D004789:Enzyme Activation; D015971:Gene Expression Regulation, Enzymologic; D015972:Gene Expression Regulation, Neoplastic; D051548:Histone Acetyltransferases / Q000378:metabolism; D006801:Humans; D008545:Melanoma / Q000201:enzymology / Q000235:genetics / Q000473:pathology; D051739:Microphthalmia-Associated Transcription Factor / Q000235:genetics*; D008969:Molecular Sequence Data; D014442:Monophenol Monooxygenase / Q000235:genetics / Q000378:metabolism; D050505:Mutant Proteins / Q000737:chemistry; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D012097:Repressor Proteins / Q000378:metabolism; D015533:Transcriptional Activation; D014410:Tumor Stem Cell Assay; D050880:p300-CBP Transcription Factors / Q000378:metabolism*
chemical_list: D017500:Adenovirus E1A Proteins; D051739:Microphthalmia-Associated Transcription Factor; D050505:Mutant Proteins; D012097:Repressor Proteins; D014442:Monophenol Monooxygenase; D051548:Histone Acetyltransferases; D050880:p300-CBP Transcription Factors