title: Drosophila split ends homologue SHARP functions as a positive regulator of Wnt/beta-catenin/T-cell factor signaling in neoplastic transformation.
abstract: Wnt ligands have pleiotropic and context-specific roles in embryogenesis and adult tissues. Among other effects, certain Wnts stabilize the beta-catenin protein, leading to the ability of beta-catenin to activate T-cell factor (TCF)-mediated transcription. Mutations resulting in constitutive beta-catenin stabilization underlie development of several human cancers. Genetic studies in Drosophila highlighted the split ends (spen) gene as a positive regulator of Wnt-dependent signaling. We have assessed the role of SHARP, a human homologue of spen, in Wnt/beta-catenin/TCF function in mammalian cells. We found that SHARP gene and protein expression is elevated in human colon and ovarian endometrioid adenocarcinomas and mouse colon adenomas and carcinomas carrying gene defects leading to beta-catenin dysregulation. When ectopically expressed, the silencing mediator for retinoid and thyroid receptors/histone deacetylase 1-associated repressor protein (SHARP) protein potently enhanced beta-catenin/TCF transcription of a model reporter gene and cellular target genes. Inhibition of endogenous SHARP function via RNA inhibitory (RNAi) approaches antagonized beta-catenin/TCF-mediated activation of target genes. The effect of SHARP on beta-catenin/TCF-regulated genes was mediated via a functional interaction between SHARP and TCF. beta-Catenin-dependent neoplastic transformation of RK3E cells was enhanced by ectopic expression of SHARP, and RNAi-mediated inhibition of endogenous SHARP in colon cancer cells inhibited their transformed growth. In toto, our findings implicate SHARP as an important positive regulator of Wnt signaling in cancers with beta-catenin dysregulation.
authors.affiliation: Department of Internal Medicine, The Cancer Center, University of Michigan, Ann Arbor, Michigan 48109-2200, USA.
authors.forename: Ying
authors.initials: Y
authors.lastname: Feng
authors.forename: Guido T
authors.initials: GT
authors.lastname: Bommer
authors.forename: Yali
authors.initials: Y
authors.lastname: Zhai
authors.forename: Aytekin
authors.initials: A
authors.lastname: Akyol
authors.forename: Takao
authors.initials: T
authors.lastname: Hinoi
authors.forename: Ira
authors.initials: I
authors.lastname: Winer
authors.forename: Hua V
authors.initials: HV
authors.lastname: Lin
authors.forename: Ken M
authors.initials: KM
authors.lastname: Cadigan
authors.forename: Kathleen R
authors.initials: KR
authors.lastname: Cho
authors.forename: Eric R
authors.initials: ER
authors.lastname: Fearon
mesh_terms: D000236:Adenoma / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D000818:Animals; D002471:Cell Transformation, Neoplastic / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D003110:Colonic Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D004268:DNA-Binding Proteins; D045325:HCT116 Cells; D018398:Homeodomain Proteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D006801:Humans; D051379:Mice; D008822:Mice, Transgenic; D009687:Nuclear Proteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D016601:RNA-Binding Proteins; D015398:Signal Transduction; D015533:Transcriptional Activation; D051153:Wnt Proteins / Q000378:metabolism*; D051176:beta Catenin / Q000378:metabolism*
chemical_list: D004268:DNA-Binding Proteins; D018398:Homeodomain Proteins; D009687:Nuclear Proteins; D016601:RNA-Binding Proteins; C476510:SPEN protein, human; D051153:Wnt Proteins; D051176:beta Catenin