title: Binding of FoxM1 to G2/M gene promoters is dependent upon B-Myb.
abstract: The promoters of genes which regulate entry into and progress through mitosis are typically induced maximally in G2 by transcription factors that include B-Myb and FoxM1. As FoxM1 gene transcription is a target of B-Myb, we investigated in this study how these transcription factors functionally interact to regulate these G2/M genes. Using a 3T3 cell line containing floxed B-myb alleles (B-myb(F/F)) that could be conditionally deleted by Cre recombinase, we confirmed that B-myb knockout caused both decreased mRNA expression of several G2/M genes, including FoxM1, and delayed entry into mitosis. Although FoxM1 protein expression was actually unaffected by B-myb knockout when quiescent B-myb(F/F) 3T3 cells re-entered the cell cycle upon serum-stimulation, chromatin immunoprecipitation revealed that FoxM1 binding to G2/M promoters was substantially reduced. FoxM1 transcriptional activity requires sequential phosphorylation by Cyclin-dependent kinases and Plk1, which are B-Myb target genes, and we found that phosphorylation at Plk1-specific sites was somewhat reduced upon B-myb knockout. Neither this effect nor nuclear accumulation of FoxM1, which was unaffected by B-myb knockout, was sufficient to account for the dependence on B-Myb for FoxM1 promoter binding, however. More significantly, assays using paired Birc5 (survivin) promoter-luciferase reporters with either wild-type or mutated Myb binding sites showed that FoxM1 was unable to bind and activate the promoter in the absence of B-Myb binding. Our data suggest that B-Myb is required as a pioneer factor to enable FoxM1 binding to G2/M gene promoters and explains how these transcription factors may collaborate to induce mitosis.
authors.affiliation: Department of Medicine, Imperial College, London, UK.
authors.forename: Christin F
authors.initials: CF
authors.lastname: Down
authors.forename: Julie
authors.initials: J
authors.lastname: Millour
authors.forename: Eric W-F
authors.initials: EW
authors.lastname: Lam
authors.forename: Roger J
authors.initials: RJ
authors.lastname: Watson
mesh_terms: D016475:3T3 Cells; D000818:Animals; D001665:Binding Sites; D018797:Cell Cycle Proteins / Q000235:genetics* / Q000378:metabolism; D018844:Cyclin-Dependent Kinases / Q000235:genetics / Q000378:metabolism; D000072278:Forkhead Box Protein M1; D051858:Forkhead Transcription Factors / Q000235:genetics* / Q000378:metabolism; D059565:G2 Phase Cell Cycle Checkpoints / Q000235:genetics*; D005786:Gene Expression Regulation; D051379:Mice; D018345:Mice, Knockout; D008938:Mitosis / Q000235:genetics*; D010766:Phosphorylation; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism; D015534:Trans-Activators / Q000235:genetics* / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D015533:Transcriptional Activation; D000097869:Polo-Like Kinase 1
chemical_list: D018797:Cell Cycle Proteins; D018844:Cyclin-Dependent Kinases; D000072278:Forkhead Box Protein M1; D051858:Forkhead Transcription Factors; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D015534:Trans-Activators; D014157:Transcription Factors; D000097869:Polo-Like Kinase 1; C491524:Foxm1 protein, mouse; C499306:Mybl2 protein, mouse