Lymphoid enhancer factor-1 and beta-catenin inhibit Runx2-dependent transcriptional activation of the osteocalcin promoter.
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.
Kahler
Rachel A
RA
University of Minnesota Cancer Center, Department of Orthopaedic Surgery and Graduate Program in Microbiology, Immunology and Cancer Biology, Minneapolis, Minnesota 55455, USA.
Westendorf
Jennifer J
JJ
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
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