Journal Article

A novel factor distinct from E2F mediates <i>C-MYC</i> promoter activation through its E2F element during exit from quiescence

Josué Álvaro-Blanco, Lorena Martínez-Gac, Esther Calonge, María Rodríguez-Martínez, Irene Molina-Privado, Juan M. Redondo, José Alcamí, Erik K. Flemington and Miguel R. Campanero

in Carcinogenesis

Volume 30, issue 3, pages 440-448
Published in print March 2009 | ISSN: 0143-3334
Published online January 2009 | e-ISSN: 1460-2180 | DOI: http://dx.doi.org/10.1093/carcin/bgp002
A novel factor distinct from E2F mediates C-MYC promoter activation through its E2F element during exit from quiescence

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Although C-MYC is overexpressed in a number of tumors, the mechanisms governing its expression in normal or tumor cells are not completely understood. Recruitment of the Retinoblastoma protein family members to gene promoters by E2F factors has a dominant negative effect on their activity during the G0 and G1 phases of the cell cycle. Despite the presence of an E2F-binding site on the C-MYC promoter, it escapes the repressive effect of E2F–Retinoblastoma complexes through unknown mechanisms during exit from quiescence. We hypothesized that occupancy of E2F elements by factors distinct from E2F might account for this escape. To test this hypothesis, we investigated whether the E2F element in the C-MYC promoter is regulated differently than E2F elements in promoters that are activated at the G1–S transition. Employing gel shift analysis, the E2F element from the C-MYC promoter was found to form a unique non-E2F complex, referred to as E2F C-MYC Specific (EMYCS), which is not observed with E2F elements from several other promoters. The DNA contact residues for EMYCS are distinct but overlapping with residues required for binding of E2F proteins. Finally, the approximate estimated molecular weight of the DNA-binding component of EMCYS is 105 kDa. Functional studies indicate that EMYCS has transcriptional transactivation capacity and suggest that it is required to activate the C-MYC promoter during exit from quiescence.

Journal Article.  6598 words.  Illustrated.

Subjects: Clinical Cytogenetics and Molecular Genetics

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