title: Functional crosstalk between Wnt signaling and Cdx-related transcriptional activation in the regulation of the claudin-2 promoter activity.
abstract: Assembly of tight junctions at the most apical part of the lateral cell membrane is a key event in the differentiation of polarized epithelial cells. Claudin-2, a transmembrane protein involved in tight junction strand formation, has turned out to play a crucial role for the paracellular barrier function by opening pores for small cations. Physiological and pathological variations of epithelial barrier function are accompanied by differential expression of tight junction proteins. Therefore, we characterized molecular mechanisms regulating claudin-2 gene expression. Genomic DNA containing the transcription start point of human claudin-2 was isolated and functionally characterized by reporter gene assays. Activity of the claudin-2 promoter was elevated in mouse mammary epithelial C57 cells expressing Wnt-1. LEF-1, a nuclear effector of the Wnt signaling pathway which is involved in the regulation of cell differentiation and polarization, was found to bind directly to the claudin-2 promoter as revealed by electrophoretic mobility shift assays. Expression of LEF-1 and beta-catenin both enhanced claudin-2 promoter activity. This increase was reduced after mutation of LEF-1 binding sites within the claudin-2 promoter. Furthermore, claudin-2 promoter activity was found to be enhanced by the TCF-4/beta-catenin transcription complex. Therefore, we conclude that gene expression mediated by the promoter of the human tight junction protein claudin-2 is regulated by factors involved in Wnt signaling. Moreover, a functional crosstalk between Wnt signaling and transcriptional activation related to caudal-related homeobox (Cdx) proteins could be demonstrated in the regulation of claudin-2 promoter-mediated gene expression.
authors.affiliation: Department of Gastroenterology, Infectiology and Rheumatology, Charité-Universitätsmedizin Berlin, Campus Benjamin Franklin, Hindenburgdamm 30, 12200, Berlin, Germany. joachim.mankertz@medizin.fu-berlin.de
authors.forename: Joachim
authors.initials: J
authors.lastname: Mankertz
authors.forename: Bernd
authors.initials: B
authors.lastname: Hillenbrand
authors.forename: Shida
authors.initials: S
authors.lastname: Tavalali
authors.forename: Otmar
authors.initials: O
authors.lastname: Huber
authors.forename: Michael
authors.initials: M
authors.lastname: Fromm
authors.forename: Jörg Dieter
authors.initials: JD
authors.lastname: Schulzke
mesh_terms: D001483:Base Sequence; D002460:Cell Line; D057167:Claudins; D004247:DNA; D024202:Electrophoretic Mobility Shift Assay; D005786:Gene Expression Regulation / Q000502:physiology*; D018398:Homeodomain Proteins / Q000502:physiology*; D006801:Humans; D008565:Membrane Proteins / Q000235:genetics*; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D011401:Promoter Regions, Genetic; D011518:Proto-Oncogene Proteins / Q000378:metabolism* / Q000502:physiology; D015398:Signal Transduction; D015533:Transcriptional Activation / Q000502:physiology*; D051153:Wnt Proteins; D051155:Wnt1 Protein; D029961:Zebrafish Proteins
chemical_list: C491273:CDX1 protein, human; C491875:CLDN2 protein, human; C491272:Cdx1 protein, mouse; D057167:Claudins; D018398:Homeodomain Proteins; D008565:Membrane Proteins; D011518:Proto-Oncogene Proteins; C495247:WNT1 protein, human; D051153:Wnt Proteins; D051155:Wnt1 Protein; D029961:Zebrafish Proteins; D004247:DNA