BONE SIALOPROTEIN: EXPRESSION & ROLE IN MINERALIZATION

Summary

Principal Investigator: RENNY THEODORE FRANCESCHI
Abstract: Bone sialoprotein (BSP) is a noncollagenous extracellular matrix component of the bone that is intimately associated with initial matrix mineralization and bone remodeling. The Bsp gene has been an important tool used by the project laboratory to understand mechanisms of tissue-specific gene expression in bone. BSP has also been useful for understanding mechanisms of biomineralization. During the previous funding period, we isolated a 2.5 kb murine Bsp gene promoter containing sufficient information to direct osteoblast-selective expression both in cell culture and transgenic mice. Within this promoter, we identified a homeodomain protein-binding site that is required for the osteoblast-selective expression of Bsp in cell culture. The role of this and related sites in the in vivo expression of Bsp is not known. The transcriptional activity of this element can be stimulated by homeodomain proteins associated with bone such as Dlx-5, but we do not know the identity of the protein/s regulating with this site in vivo. Considerable in vitro evidence supports the hypothesis that BSP is a nucleator of hydroxyapatite crystals. We showed that it can also stimulate mineralization when overexpressed in non-mineralizing preosteoblast cell lines. Matrix Gla protein (MGP), in contrast, is a potent inhibitor of mineralization. PTH and PTHrP, both potent inhibitors of osteoblast-mediated biomineralization, inhibit BSP synthesis while rapidly inducing MGP, suggesting that these molecules have opposing actions and are reciprocally regulated. Building on these important findings, this competitive renewal will achieve the following specific aims: Aim 1. Define the in vivo significance of a homeodomain protein-binding site in the murine BSP promoter. Aim 2. Identify the nuclear protein(s) that interact with and regulate the proximal homeodomain site in osteoblast. Aim 3. Define the molecular basis for the regulation of MGP by PTH and PTHrP; assess the ability of BSP and MGP to antagonize each other in cell culture and in vivo. Studies supported by this project will describe a novel mechanism for controlling gene expression in bone and explain important actions of PTH/PTHrP on the regulation of mineralization. Such knowledge is essential for designing new strategies for bone regeneration to treat trauma and pathological conditions such as osteoporosis and periodontal disease.
Funding Period: 1997-05-01 - 2005-11-30
more information: NIH RePORT

Top Publications

  1. pmc Sp proteins and Runx2 mediate regulation of matrix gla protein (MGP) expression by parathyroid hormone
    Supaporn Suttamanatwong
    Department of Diagnostic and Biological Sciences, University of Minnesota School of Dentistry, Minneapolis, 55455, USA
    J Cell Biochem 107:284-92. 2009
  2. pmc Analysis of transcription factor interactions in osteoblasts using competitive chromatin immunoprecipitation
    Hernan Roca
    Department of Periodontics and Oral Medicine, University of Michigan School of Dentistry, Ann Arbor, MI, USA
    Nucleic Acids Res 36:1723-30. 2008
  3. pmc Physical and functional interactions between Runx2 and HIF-1α induce vascular endothelial growth factor gene expression
    Tae Geon Kwon
    Department of Periodontics and Oral Medicine and Biological Chemistry, University of Michigan, Ann Arbor, Michigan 48109 1078, USA
    J Cell Biochem 112:3582-93. 2011
  4. pmc Differentiation-dependent association of phosphorylated extracellular signal-regulated kinase with the chromatin of osteoblast-related genes
    Yan Li
    Department of Periodontics and Oral Medicine, University of Michigan School of Dentistry, Ann Arbor, MI 48109, USA
    J Bone Miner Res 25:154-63. 2010
  5. pmc Identification and functional characterization of ERK/MAPK phosphorylation sites in the Runx2 transcription factor
    Chunxi Ge
    Department of Periodontics and Oral Medicine, School of Dentistry, University of Michigan, Ann Arbor, Michigan 48109 1078, USA
    J Biol Chem 284:32533-43. 2009
  6. pmc Parathyroid hormone increases activating transcription factor 4 expression and activity in osteoblasts: requirement for osteocalcin gene expression
    Shibing Yu
    Division of Hematology Oncology, Department of Medicine, University of Pittsburgh, Pittsburgh, PA 15240, USA
    Endocrinology 149:1960-8. 2008
  7. pmc Critical role of the extracellular signal-regulated kinase-MAPK pathway in osteoblast differentiation and skeletal development
    Chunxi Ge
    Department of Periodontics and Oral Medicine, University of Michigan School of Dentistry, Ann Arbor, MI 48109, USA
    J Cell Biol 176:709-18. 2007
  8. ncbi Role of matrix Gla protein in parathyroid hormone inhibition of osteoblast mineralization
    Rajaram Gopalakrishnan
    Department of Diagnostic and Biological Sciences, University of Minnesota School of Dentistry, Minneapolis, Minn 55455, USA
    Cells Tissues Organs 181:166-75. 2005
  9. ncbi Biological approaches to bone regeneration by gene therapy
    R T Franceschi
    University of Michigan School of Dentistry, 1011 N University Ave, Ann Arbor, MI 48109 1078, USA
    J Dent Res 84:1093-103. 2005
  10. ncbi Cooperative interactions between activating transcription factor 4 and Runx2/Cbfa1 stimulate osteoblast-specific osteocalcin gene expression
    Guozhi Xiao
    Department of Periodontics, Prevention, and Geriatrics, School of Dentistry, University of Michigan, Ann Arbor, Michigan 48109 1078, USA
    J Biol Chem 280:30689-96. 2005

Scientific Experts

  • RENNY THEODORE FRANCESCHI
  • Guozhi Xiao
  • Rajaram Gopalakrishnan
  • Chunxi Ge
  • Hernan Roca
  • Yan Li
  • Di Jiang
  • Tae Geon Kwon
  • Qian Yang
  • Supaporn Suttamanatwong
  • Shibing Yu
  • Ming Zhao
  • Xiang Zhao
  • Guisheng Zhao
  • Nan E Hatch
  • Kim C Mansky
  • Ann E Carlson
  • Jody Schilling
  • Eric D Jensen
  • Jian Zhang
  • Yu Jiang
  • Yumei Lai
  • Xiaoyan Zhang
  • Min Luo
  • Mattabhorn Phimphilai
  • Jeong Tae Koh
  • Zhuoran Zhao
  • Taocong Jin

Detail Information

Publications12

  1. pmc Sp proteins and Runx2 mediate regulation of matrix gla protein (MGP) expression by parathyroid hormone
    Supaporn Suttamanatwong
    Department of Diagnostic and Biological Sciences, University of Minnesota School of Dentistry, Minneapolis, 55455, USA
    J Cell Biochem 107:284-92. 2009
    ..Collectively, these data show that PTH regulates MGP gene transcription in osteoblasts through altered activities of Sp and Runx2 transcription factors...
  2. pmc Analysis of transcription factor interactions in osteoblasts using competitive chromatin immunoprecipitation
    Hernan Roca
    Department of Periodontics and Oral Medicine, University of Michigan School of Dentistry, Ann Arbor, MI, USA
    Nucleic Acids Res 36:1723-30. 2008
    ....
  3. pmc Physical and functional interactions between Runx2 and HIF-1α induce vascular endothelial growth factor gene expression
    Tae Geon Kwon
    Department of Periodontics and Oral Medicine and Biological Chemistry, University of Michigan, Ann Arbor, Michigan 48109 1078, USA
    J Cell Biochem 112:3582-93. 2011
    ..These studies indicate that Runx2 functions together with HIF-1α to stimulate angiogenic gene expression in bone cells and may in part explain the known requirement for Runx2 in bone vascularization...
  4. pmc Differentiation-dependent association of phosphorylated extracellular signal-regulated kinase with the chromatin of osteoblast-related genes
    Yan Li
    Department of Periodontics and Oral Medicine, University of Michigan School of Dentistry, Ann Arbor, MI 48109, USA
    J Bone Miner Res 25:154-63. 2010
    ....
  5. pmc Identification and functional characterization of ERK/MAPK phosphorylation sites in the Runx2 transcription factor
    Chunxi Ge
    Department of Periodontics and Oral Medicine, School of Dentistry, University of Michigan, Ann Arbor, Michigan 48109 1078, USA
    J Biol Chem 284:32533-43. 2009
    ....
  6. pmc Parathyroid hormone increases activating transcription factor 4 expression and activity in osteoblasts: requirement for osteocalcin gene expression
    Shibing Yu
    Division of Hematology Oncology, Department of Medicine, University of Pittsburgh, Pittsburgh, PA 15240, USA
    Endocrinology 149:1960-8. 2008
    ..Collectively, these studies for the first time demonstrate that PTH increases ATF4 expression and activity and that ATF4 is required for PTH induction of Ocn expression in osteoblasts...
  7. pmc Critical role of the extracellular signal-regulated kinase-MAPK pathway in osteoblast differentiation and skeletal development
    Chunxi Ge
    Department of Periodontics and Oral Medicine, University of Michigan School of Dentistry, Ann Arbor, MI 48109, USA
    J Cell Biol 176:709-18. 2007
    ..This work establishes an important in vivo function for the ERK-MAPK pathway in bone that involves stimulation of RUNX2 phosphorylation and transcriptional activity...
  8. ncbi Role of matrix Gla protein in parathyroid hormone inhibition of osteoblast mineralization
    Rajaram Gopalakrishnan
    Department of Diagnostic and Biological Sciences, University of Minnesota School of Dentistry, Minneapolis, Minn 55455, USA
    Cells Tissues Organs 181:166-75. 2005
    ..In addition to MGP, the regulation and possible role of osteopontin, another known regulator of osteoblast mineralization, in PTH-mediated regulation of bone and vascular mineralization is discussed...
  9. ncbi Biological approaches to bone regeneration by gene therapy
    R T Franceschi
    University of Michigan School of Dentistry, 1011 N University Ave, Ann Arbor, MI 48109 1078, USA
    J Dent Res 84:1093-103. 2005
    ....
  10. ncbi Cooperative interactions between activating transcription factor 4 and Runx2/Cbfa1 stimulate osteoblast-specific osteocalcin gene expression
    Guozhi Xiao
    Department of Periodontics, Prevention, and Geriatrics, School of Dentistry, University of Michigan, Ann Arbor, Michigan 48109 1078, USA
    J Biol Chem 280:30689-96. 2005
    ....
  11. ncbi Cooperative interactions between RUNX2 and homeodomain protein-binding sites are critical for the osteoblast-specific expression of the bone sialoprotein gene
    Hernan Roca
    Department of Periodontics, Prevention, and Geriatrics and Center for Craniofacial Regeneration, School of Dentistry, University of Michigan, Ann Arbor 48109 1078, USA
    J Biol Chem 280:30845-55. 2005
    ..Taken together, our data show that RUNX2 is a direct regulator of Bsp in osteoblasts and that it functions in cooperation with DLX5 or a related factor to activate osteoblast-specific gene expression...
  12. ncbi Combinatorial gene therapy for bone regeneration: cooperative interactions between adenovirus vectors expressing bone morphogenetic proteins 2, 4, and 7
    Ming Zhao
    Department of Periodontics, Prevention, and Geriatrics, School of Dentistry and Center for Craniofacial Regeneration, University of Michigan, Ann Arbor, Michigan 48109 1078, USA
    J Cell Biochem 95:1-16. 2005
    ..These studies show that dramatic enhancement of osteogenesis can be achieved using gene therapy to express specific combinations of interacting regenerative molecules...