p110 CUX1 Cooperates with E2F Transcription Factors in the Transcriptional Activation of Cell Cycle-Regulated Genes

Molecular Oncology Group, McGill University Health Center, Departments of Biochemistry, Medicine and Oncology, McGill University, Montreal, Canada; Institut de Recherches Cliniques de Montréal

^* To whom correspondence should be addressed. Email: alain.nepveu{at}mcgill.ca.

	Abstract

The p110 CUX1 transcription factor was shown to stimulate cell proliferation by accelerating entry into S phase. As p110 CUX1 can function as a transcriptional repressor or activator depending on promoter context, we investigated its mechanism of transcriptional activation using the DNA pol gene promoter as a model system. Linker-scanning analysis revealed that a low-affinity E2F binding site is required for transcriptional activation. Moreover, co-expression with a dominant-negative mutant of DP-1 suggested that endogenous E2F factors, indeed, are needed for p110-mediated activation. Tandem affinity purification, co-immunoprecipitation, chromatin immunoprecipitation and reporter assays indicated that p110 CUX1 can engage in weak protein-protein interactions with E2F1 and E2F2, stimulate their recruitment to the DNA pol gene promoter and cooperate with these factors in transcriptional activation. On the other hand, in vitro assays suggested that the interaction between CUX1 and E2F1 either is not direct or is regulated by post-translational modifications. Genome-wide location analysis revealed that targets common to p110 CUX1 and E2F1 included many genes involved in cell cycle, DNA replication and DNA repair. Comparison of the fold-enrichment for various E2F factors suggested that binding of p110 CUX1 to a promoter will favor the specific recruitment of E2F1, and to a lesser extent E2F2, over E2F3 and E2F4. Reporter assays on a subset of common targets confirmed that p110 CUX1 and E2F1 cooperate in their transcriptional activation. Overall, our results show that p110 CUX1 and E2F1 cooperate in the regulation of many cell cycle genes.