title: Regulation of the bone-restricted IFITM-like (Bril) gene transcription by Sp and Gli family members and CpG methylation.
abstract: BACKGROUND
  BRIL is a bone-specific membrane protein that is involved in osteogenesis imperfecta type V.
  
  
  RESULTS
  Bril transcription is activated by Sp1, Sp3, OSX, and GLI2 and by CpG demethylation.
  
  
  CONCLUSIONS
  Regulation of Bril involves trans-acting factors integrating at conserved promoter elements and epigenetic modifications.
  
  
  CONCLUSIONS
  Identification of the mechanisms governing Bril transcription is important to understand its role in skeletal biology. Bril encodes a small membrane protein present in osteoblasts. In humans, a single recurrent mutation in the 5'-UTR of BRIL causes osteogenesis imperfecta type V. The exact function of BRIL and the mechanism by which it contributes to disease are still unknown. The goal of the current study was to characterize the mechanisms governing Bril transcription in humans, rats, and mice. In the three species, as detected by luciferase reporter assays in UMR106 cells, we found that most of the base-line regulatory activity was localized within ∼250 bp upstream of the coding ATG. Co-transfection experiments indicated that Sp1 and Sp3 were potent inducers of the promoter activity, through the binding of several GC-rich boxes. Osterix was a weak activator but acted cooperatively with Sp1 and GLI2 to synergistically induce the BRIL promoter. GLI2, a mediator of hedgehog signaling pathway, was also a potent activator of BRIL through a single GLI binding site. Correspondingly, agonists of the hedgehog pathway (purmorphamine and Indian hedgehog) in MC3T3 osteoblasts led to increased BRIL levels. The BRIL promoter activity was also found to be negatively modulated through two different mechanisms. First, the ZFP354C zinc finger protein repressed basal and Sp1-induced activity. Second, CpG methylation of the promoter region correlated with an inactive state and prevented Sp1 activation. The data provide the very first analyses of the cis- and trans-acting factors regulating Bril transcription. They revealed key roles for the Sp members and GLI2 that possibly cooperate to activate Bril when the promoter becomes demethylated.
authors.affiliation: Shriners Hospital for Children, Montreal, Quebec H3G 1A6, Canada.
authors.forename: Bahar
authors.initials: B
authors.lastname: Kasaai
authors.forename: Marie-Hélène
authors.initials: MH
authors.lastname: Gaumond
authors.forename: Pierre
authors.initials: P
authors.lastname: Moffatt
mesh_terms: D016475:3T3 Cells; D000818:Animals; D001483:Base Sequence; D001842:Bone and Bones / Q000378:metabolism; D002454:Cell Differentiation; D017124:Conserved Sequence; D018899:CpG Islands; D019175:DNA Methylation; D005260:Female; D020868:Gene Silencing; D057809:HEK293 Cells; D053823:Hedgehog Proteins / Q000378:metabolism; D006801:Humans; D051741:Kruppel-Like Transcription Factors / Q000502:physiology; D008565:Membrane Proteins / Q000235:genetics* / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D058977:Molecular Sequence Annotation; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000502:physiology; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D051381:Rats; D012097:Repressor Proteins / Q000378:metabolism; D015398:Signal Transduction; D016329:Sp1 Transcription Factor / Q000502:physiology; D016385:TATA Box; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D000075746:Zinc Finger Protein Gli2
chemical_list: C082593:GLI2 protein, human; D053823:Hedgehog Proteins; C532488:IFITM5 protein, mouse; D051741:Kruppel-Like Transcription Factors; D008565:Membrane Proteins; D009687:Nuclear Proteins; D012097:Repressor Proteins; D016329:Sp1 Transcription Factor; C408086:Zfp354c protein, mouse; D000075746:Zinc Finger Protein Gli2
keywords: Bril; CpG Methylation; Gene Expression; Gli2; Ifitm5; Osteoblasts; Osx; Sp1; Transcription Promoter; Transcription Regulation