title: Regulation of cyclooxygenase-2 expression by the Wnt and ras pathways.
abstract: Mutations in the adenomatous polyposis coli (APC) gene and K-ras occur in the majority of human colorectal cancers. Loss of functional APC protein activates the Wnt signal transduction pathway, allowing the nuclear accumulation of beta-catenin, which then binds to T-cell factor-4 (Tcf-4), causing increased transcriptional activation of downstream target genes. We investigated the hypothesis that the activation of the WNT pathway regulates cyclooxygenase-2 (COX-2). COX-2 was down-regulated after the induction of full-length APC in the HT29-APC cell line. We identified a Tcf-4-binding element (TBE) in the COX-2 promoter that specifically bound to Tcf-4 in an electrophoretic mobility shift assay. COX-2 promoter luciferase activity is down-regulated by APC in a promoter reporter construct containing the, TBE but not with mutant TBE. Mutant beta-catenin expression up-regulated the COX-2 promoter activity and the endogenous COX-2 mRNA expression in HuH7, hepatocellular carcinoma cell line, which is partially abrogated by cotransfection with a dominant-negative Tcf-4 expression vector. Although beta-catenin alone did not increase COX-2 protein to detectable levels in HuH7 cells, coexpression of both mutant beta-catenin and mutant K-ras increased COX-2 protein expression, which is consistent with the previous reports that K-ras can stabilize COX-2 mRNA. Taken together, our data support the hypothesis that COX-2 is down-regulated by APC and up-regulated by nuclear beta-catenin accumulation, and additionally implicate the Wnt signal transduction pathway in colon and liver carcinogenesis.
authors.affiliation: Laboratory of Human Carcinogenesis, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892, USA.
authors.forename: Yuzuru
authors.initials: Y
authors.lastname: Araki
authors.forename: Shu
authors.initials: S
authors.lastname: Okamura
authors.forename: S Perwez
authors.initials: SP
authors.lastname: Hussain
authors.forename: Makoto
authors.initials: M
authors.lastname: Nagashima
authors.forename: Peijun
authors.initials: P
authors.lastname: He
authors.forename: Masayuki
authors.initials: M
authors.lastname: Shiseki
authors.forename: Koh
authors.initials: K
authors.lastname: Miura
authors.forename: Curtis C
authors.initials: CC
authors.lastname: Harris
mesh_terms: D025601:Adenomatous Polyposis Coli Protein / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology; D051546:Cyclooxygenase 2; D003598:Cytoskeletal Proteins / Q000502:physiology; D004268:DNA-Binding Proteins / Q000378:metabolism; D015536:Down-Regulation; D015972:Gene Expression Regulation, Neoplastic; D019073:HT29 Cells; D006801:Humans; D007527:Isoenzymes / Q000096:biosynthesis* / Q000235:genetics; D008156:Luciferases / Q000235:genetics / Q000378:metabolism; D008565:Membrane Proteins; D011401:Promoter Regions, Genetic; D011451:Prostaglandin-Endoperoxide Synthases / Q000096:biosynthesis* / Q000235:genetics; D011518:Proto-Oncogene Proteins / Q000502:physiology*; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D051820:TCF Transcription Factors; D015534:Trans-Activators / Q000502:physiology; D058118:Transcription Factor 7-Like 2 Protein; D014157:Transcription Factors / Q000378:metabolism; D014158:Transcription, Genetic; D015854:Up-Regulation; D051153:Wnt Proteins; D029961:Zebrafish Proteins; D051176:beta Catenin; D018631:ras Proteins / Q000502:physiology*
chemical_list: D025601:Adenomatous Polyposis Coli Protein; C495270:CTNNB1 protein, human; D003598:Cytoskeletal Proteins; D004268:DNA-Binding Proteins; D007527:Isoenzymes; D008565:Membrane Proteins; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; D011993:Recombinant Fusion Proteins; D051820:TCF Transcription Factors; C544894:TCF7L2 protein, human; D015534:Trans-Activators; D058118:Transcription Factor 7-Like 2 Protein; D014157:Transcription Factors; D051153:Wnt Proteins; D029961:Zebrafish Proteins; D051176:beta Catenin; D008156:Luciferases; D051546:Cyclooxygenase 2; C496540:PTGS2 protein, human; D011451:Prostaglandin-Endoperoxide Synthases; D018631:ras Proteins