Transcriptional mechanisms regulating cell cycle progression and dna damage response by e2f7 transcription factor

Resumen

E2F transcription factors (E2F1¿E2F8) control diverse biological processes through regulation of target gene expression. The identification of a large set of genes regulated by each individual E2F, including those coding for microRNAs, has led to a better understanding of the functions performed by the different members of the family. Many studies have detailed the role of classical E2Fs (E2F1¿5) in cell cycle control and DNA damage response. By contrast, the contribution of the newest additions to the family, E2F7 and E2F8, to these processes has not been clearly defined. In this work we have investigated the role of E2F7 in the transcriptional regulation of miRNA and protein¿coding gene expression, and the impact of this regulation on cell cycle progression and genomic stability. RNA¿seq analyses show that a large set of genes involved in DNA replication and cell cycle progression (such as various MCMs, Cyclins and B¿MYB) display aberrantly increased levels in cells lacking E2F7. These genes are also the targets of other E2Fs. Importantly, knockdown of E2F7 expression causes cells to undergo accelerated cell cycle progression, arguing that E2F7 is required to restrain cell cycle progression, through the repression of cell cycle genes. Remarkably, E2F7 represses the expression of a set of genes involved in the maintenance of genomic stability, some of which represent novel E2F target genes. We identify E2F7 as a factor that controls cellular recovery during an ongoing DNA damage response in G2 phase of the cell cycle. This role of E2F7 is specific to certain types of DNA damage. Short¿term depletion of E2F7 confers an increased recovery competence upon treatment with interstrand crosslink¿inducing agents but not upon ¿¿irradiation. Furthermore, we present evidence that E2F7 controls the repair of Cisplatin and Mitomycin¿C induced chromosomal aberrations. Small RNA expression profiles in cells lacking E2F7 evidence that this transcription factor is also required for the timely repression of a set of miRNAs throughout the cell cycle, including miR¿25, miR¿26a, miR¿27b, let¿7b and let¿7f. Interestingly, many of the miRNAs exhibiting increased levels upon E2F7 depletion have been reported to modulate proliferation pathways, suggesting that E2F7 controls cellular responses through the regulation of both protein¿coding and non¿coding RNA expression. Chromatin immunoprecipitation analyses have uncovered direct and indirect mechanisms for E2F7¿mediated regulation of these miRNAs. Interestingly, E2F7 appears to control the levels of several miRNAs through the regulation of c¿MYC and LIN28B expression. These data point to a novel interplay between E2F7, c¿MYC and LIN28B, whereby E2F7 may play a critical role modulating c¿MYC and LIN28B levels, which would in turn affect miRNA gene expression. Altogether, results in this work suggest that E2F7 ensures timely induction and repression of protein¿coding and miRNA genes, allowing correct progression throughout the cell cycle.