title: c-Myc represses FOXO3a-mediated transcription of the gene encoding the p27(Kip1) cyclin dependent kinase inhibitor.
abstract: The p27(Kip1) (p27) cyclin-dependent kinase inhibitor and c-Myc oncoprotein play essential roles in control of cell cycle progression and apoptosis. Induction of p27 (CDKN1B) gene transcription by Forkhead box O proteins such as FOXO3a leads to growth arrest and apoptosis. Previously, we observed that B cell receptor (surface IgM) engagement of WEHI 231 immature B lymphoma cells with an anti-IgM antibody results in activation of FOXO3a, growth arrest and apoptosis. As ectopic c-Myc expression in these cells prevented anti-IgM induction of p27 and cell death, we hypothesized that c-Myc represses FOXO3a-mediated transcription. Here we show that c-Myc inhibits FOXO3a-mediated activation of the p27 promoter in multiple cell lines. The mechanism of this repression was explored using a combination of co-immunoprecipitation, oligonucleotide precipitation, and chromatin immunoprecipitation experiments. The studies demonstrate a functional association of FOXO3a and c-Myc on a proximal Forkhead binding element in the p27 promoter. This association involves the Myc box II domain of c-Myc and the N-terminal DNA-binding portion of FOXO3a. Analysis of publicly available microarray datasets showed an inverse pattern of c-MYC and p27 RNA expression in primary acute myeloid leukemia, prostate cancer and tongue squamous cell carcinoma samples. The inhibition of FOXO3a-mediated activation of the p27 gene by the high aberrant expression of c-Myc in many tumor cells likely contributes to their uncontrolled proliferation and invasive phenotype.
authors.affiliation: Department of Biochemistry, Boston University Medical School, 715 Albany Street, Boston, Massachusetts 02118, USA.
authors.forename: Vidyalakshmi
authors.initials: V
authors.lastname: Chandramohan
authors.forename: Nora D
authors.initials: ND
authors.lastname: Mineva
authors.forename: Brian
authors.initials: B
authors.lastname: Burke
authors.forename: Sébastien
authors.initials: S
authors.lastname: Jeay
authors.forename: Min
authors.initials: M
authors.lastname: Wu
authors.forename: Jian
authors.initials: J
authors.lastname: Shen
authors.forename: William
authors.initials: W
authors.lastname: Yang
authors.forename: Stephen R
authors.initials: SR
authors.lastname: Hann
authors.forename: Gail E
authors.initials: GE
authors.lastname: Sonenshein
mesh_terms: D000818:Animals; D017209:Apoptosis; D001665:Binding Sites; D002460:Cell Line; D050760:Cyclin-Dependent Kinase Inhibitor p27 / Q000235:genetics* / Q000378:metabolism; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors / Q000737:chemistry / Q000378:metabolism*; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D051379:Mice; D009369:Neoplasms / Q000201:enzymology / Q000473:pathology; D011401:Promoter Regions, Genetic / Q000235:genetics; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D016271:Proto-Oncogene Proteins c-myc / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012097:Repressor Proteins / Q000378:metabolism*; D014158:Transcription, Genetic
chemical_list: C499517:FOXO3 protein, human; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors; D016271:Proto-Oncogene Proteins c-myc; D012333:RNA, Messenger; D012097:Repressor Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27