title: Transcriptional regulation of Wnt inhibitory factor-1 by Miz-1/c-Myc.
abstract: The Wnt signaling pathway is capable of self-regulation through positive and negative feedback mechanisms. For example, the oncoprotein c-Myc, which is upregulated by Wnt signaling activity, participates in a positive feedback loop of canonical Wnt signaling through repression of Wnt antagonists DKK1 and SFRP1. In this study, we investigated the mechanism of Wnt inhibitory factor-1 (WIF-1) silencing. Mapping of CpG island methylation of the WIF-1 promoter reveals regional methylation (-295 to -95 bp from the transcription start site) that correlates with transcriptional silencing. We identified Miz-1 as a direct activator of WIF-1 transcriptional activity, which is found at WIF-1 promoter. In addition, we show that c-Myc contributes to WIF-1 transcriptional repression in a Miz-1-dependent manner. Although the transient repression mediated by Miz-1/c-Myc is independent of de novo methylation, the stable repression by this complex is associated with CpG island methylation of the critical -295 to -95-bp region of the WIF-1 promoter. Importantly, Miz-1 and c-Myc are found at WIF-1 promoter in WIF-1 non-expressing cell lines DLD-1 and 209myc. Transient knockdown or somatic knockout of c-Myc in DLD-1 failed to restore WIF-1 expression suggesting that c-Myc is involved in initiating rather than maintaining WIF-1 epigenetic silencing. In a genome-wide screen, DNAJA4, TGFβ-induced and TRIM59 were repressed by c-Myc overexpression and DNA promoter hypermethylation. Our data reveal novel insights into c-Myc-mediated DNA methylation-dependent transcriptional silencing, a mechanism that might contribute to the dysregulation of Wnt signaling in cancer.
authors.affiliation: Cancer Biology Program, The Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins, Baltimore, MD 21231, USA. jlicchesi@yahoo.com
authors.forename: J D F
authors.initials: JD
authors.lastname: Licchesi
authors.forename: L
authors.initials: L
authors.lastname: Van Neste
authors.forename: V K
authors.initials: VK
authors.lastname: Tiwari
authors.forename: L
authors.initials: L
authors.lastname: Cope
authors.forename: X
authors.initials: X
authors.lastname: Lin
authors.forename: S B
authors.initials: SB
authors.lastname: Baylin
authors.forename: J G
authors.initials: JG
authors.lastname: Herman
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics*; D045744:Cell Line, Tumor; D047369:Chromatin Immunoprecipitation; D019175:DNA Methylation; D005786:Gene Expression Regulation / Q000502:physiology*; D020868:Gene Silencing; D006801:Humans; D051741:Kruppel-Like Transcription Factors / Q000502:physiology*; D011401:Promoter Regions, Genetic; D016271:Proto-Oncogene Proteins c-myc / Q000502:physiology*; D012097:Repressor Proteins / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014158:Transcription, Genetic / Q000502:physiology*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D051741:Kruppel-Like Transcription Factors; D016271:Proto-Oncogene Proteins c-myc; D012097:Repressor Proteins; C485569:WIF1 protein, human; C107961:ZBTB17 protein, human