Mad4 is regulated by a transcriptional repressor complex that contains Miz-1 and c-Myc.
Myc and Mad family proteins are central regulators of cellular proliferation and differentiation. We show that various Mad family genes have distinct patterns of expression during the chemically induced differentiation of mouse erythroleukaemia (MEL) cells, suggesting that they each serve a different function. Mad4 RNA is highly induced and persists in terminally differentiated cells, in agreement with observations in other systems. Using reporter gene assays in stably transfected MEL cells, we show that induction of Mad4 is mediated by a 49 nt core promoter region. We demonstrate that the initiator element is required for Mad4 activation, and show that induction is associated with the loss from the initiator of a complex that contains Miz-1 and c-Myc. Miz-1 activates the Mad4 promoter in transient transfection assays, and this effect is antagonized by c-Myc. We therefore identify Mad4 as a novel target of transcriptional repression by c-Myc. These data suggest that the expression of Mad4 in proliferating undifferentiated cells is suppressed by the binding of a c-Myc-Miz-1 repressor complex at the initiator, and that the activation of Mad4 during differentiation results, at least in part, from a decrease in c-Myc-mediated repression.
Kime
Louise
L
School of Biochemistry and Molecular Biology, University of Leeds, Leeds LS2 9JT, U.K.
Wright
Stephanie C
SC
D000818:Animals; D001483:Base Sequence; D051792:Basic Helix-Loop-Helix Proteins; D002454:Cell Differentiation / Q000235:genetics; D004247:DNA; D004268:DNA-Binding Proteins / Q000378:metabolism*; D006801:Humans; D051741:Kruppel-Like Transcription Factors; D051379:Mice; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D016271:Proto-Oncogene Proteins c-myc / Q000378:metabolism*; D012045:Regulatory Sequences, Nucleic Acid; D012097:Repressor Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism / Q000502:physiology*; D014157:Transcription Factors / Q000378:metabolism*; D014407:Tumor Cells, Cultured
D051792:Basic Helix-Loop-Helix Proteins; D004247:DNA; D004268:DNA-Binding Proteins; D051741:Kruppel-Like Transcription Factors; D016271:Proto-Oncogene Proteins c-myc; D012097:Repressor Proteins; D014157:Transcription Factors; C484347:MXD4 protein, human; C097224:Mad4 protein, mouse; C107961:ZBTB17 protein, human