title: AP4 encodes a c-MYC-inducible repressor of p21.
abstract: In the majority of human tumors, expression of the c-MYC oncogene becomes constitutive. Here, we report that c-MYC directly regulates the expression of AP4 via CACGTG motifs in the first intron of the AP4 gene. Induction of AP4 was required for c-MYC-mediated cell cycle reentry of anti-estrogen arrested breast cancer cells and mitogen-mediated repression of the CDK inhibitor p21. AP4 directly repressed p21 by occupying four CAGCTG motifs in the p21 promoter via its basic region. AP4 levels declined after DNA damage, and ectopic AP4 interfered with p53-mediated cell cycle arrest and sensitized cells to apoptosis induced by DNA damaging agents. AP4 expression blocked induction of p21 by TGF-beta in human keratinocytes and interfered with up-regulation of p21 and cell cycle arrest during monoblast differentiation. Notably, AP4 is specifically expressed in colonic progenitor and colorectal carcinoma cells. In conclusion, our results indicate that c-MYC employs AP4 to maintain cells in a proliferative, progenitor-like state.
authors.affiliation: Molecular Tumorpathology, Institute of Pathology, Ruhr University Bochum, D-44789 Bochum, Germany.
authors.forename: Peter
authors.initials: P
authors.lastname: Jung
authors.forename: Antje
authors.initials: A
authors.lastname: Menssen
authors.forename: Doris
authors.initials: D
authors.lastname: Mayr
authors.forename: Heiko
authors.initials: H
authors.lastname: Hermeking
mesh_terms: D001483:Base Sequence; D045744:Cell Line, Tumor; D003110:Colonic Neoplasms / Q000235:genetics / Q000378:metabolism; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000235:genetics*; D004249:DNA Damage / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D015603:Keratinocytes / Q000378:metabolism; D014411:Neoplastic Stem Cells / Q000378:metabolism; D020411:Oligonucleotide Array Sequence Analysis; D011401:Promoter Regions, Genetic; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics / Q000378:metabolism*; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D016212:Transforming Growth Factor beta / Q000494:pharmacology
chemical_list: C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D004268:DNA-Binding Proteins; C489427:MYC protein, human; D016271:Proto-Oncogene Proteins c-myc; D012097:Repressor Proteins; D014157:Transcription Factors; D016212:Transforming Growth Factor beta; C055473:enhancer-binding protein AP-4