title: Lymphoid enhancer factor-1 and beta-catenin inhibit Runx2-dependent transcriptional activation of the osteocalcin promoter.
abstract: Functional control of the transcription factor Runx2 is crucial for normal bone formation. Runx2 is detectable throughout osteoblast development and maturation and temporally regulates several bone-specific genes. In this study, we identified a novel post-translational mechanism regulating Runx2-dependent activation of the osteocalcin promoter. A functional binding site for the high mobility group protein lymphoid enhancer-binding factor 1 (LEF1) was found adjacent to the proximal Runx2-binding site in the osteocalcin promoter. In transcription assays, LEF1 repressed Runx2-induced activation of the mouse osteocalcin 2 promoter in several osteoblast lineage cell lines. Mutations in the LEF1-binding site increased the basal activity of the osteocalcin promoter; however, the LEF1 recognition site in the osteocalcin promoter was surprisingly not required for LEF1 repression. A novel interaction between the DNA-binding domains of Runx2 and LEF1 was identified and found crucial for LEF1-mediated repression of Runx2. LEF1 is a nuclear effector of the Wnt/LRP5/beta-catenin signaling pathway, which is also essential for osteoblast proliferation and normal skeletal development. A constitutively active beta-catenin enhanced LEF1-dependent repression of Runx2. These data identify a novel mechanism of regulating Runx2 activity in osteoblasts and link Runx2 transcriptional activity to beta-catenin signaling.
authors.affiliation: University of Minnesota Cancer Center, Department of Orthopaedic Surgery and Graduate Program in Microbiology, Immunology and Cancer Biology, Minneapolis, Minnesota 55455, USA.
authors.forename: Rachel A
authors.initials: RA
authors.lastname: Kahler
authors.forename: Jennifer J
authors.initials: JJ
authors.lastname: Westendorf
mesh_terms: D016475:3T3 Cells; D000818:Animals; D001665:Binding Sites / Q000235:genetics; D002454:Cell Differentiation / Q000502:physiology; D002455:Cell Division / Q000502:physiology; D050659:Core Binding Factor Alpha 1 Subunit; D003598:Cytoskeletal Proteins / Q000235:genetics* / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D006609:High Mobility Group Proteins / Q000378:metabolism; D051821:Lymphoid Enhancer-Binding Factor 1; D051379:Mice; D008809:Mice, Inbred C3H; D009363:Neoplasm Proteins; D010006:Osteoblasts / Q000166:cytology / Q000502:physiology; D015675:Osteocalcin / Q000235:genetics*; D012516:Osteosarcoma; D011401:Promoter Regions, Genetic / Q000502:physiology; D017434:Protein Structure, Tertiary; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism; D051381:Rats; D013234:Stem Cells / Q000166:cytology / Q000502:physiology; D015534:Trans-Activators / Q000235:genetics* / Q000378:metabolism; D014157:Transcription Factors / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D015533:Transcriptional Activation / Q000502:physiology; D014407:Tumor Cells, Cultured; D051153:Wnt Proteins; D029961:Zebrafish Proteins; D051176:beta Catenin
chemical_list: C495267:CTNNB1 protein, mouse; D050659:Core Binding Factor Alpha 1 Subunit; C495268:Ctnnb1 protein, rat; D003598:Cytoskeletal Proteins; D004268:DNA-Binding Proteins; D006609:High Mobility Group Proteins; C497574:Lef1 protein, mouse; C497575:Lef1 protein, rat; D051821:Lymphoid Enhancer-Binding Factor 1; D009363:Neoplasm Proteins; D011518:Proto-Oncogene Proteins; D015534:Trans-Activators; D014157:Transcription Factors; D051153:Wnt Proteins; D029961:Zebrafish Proteins; D051176:beta Catenin; D015675:Osteocalcin