title: Inhibition of microtubule assembly in osteoblasts stimulates bone morphogenetic protein 2 expression and bone formation through transcription factor Gli2.
abstract: Bone morphogenetic protein 2 (BMP-2) is essential for postnatal bone formation and fracture repair. By screening chemical libraries for BMP-2 mimics using a cell-based assay, we identified inhibitors of microtubule assembly as stimulators of BMP-2 transcription. These microtubule inhibitors increased osteoblast differentiation in vitro, stimulated periosteal bone formation when injected locally over murine calvaria, and enhanced trabecular bone formation when administered systemically in vivo. To explore molecular mechanisms mediating these responses, we examined effects of microtubule inhibitors on the hedgehog (Hh) pathway, since this pathway is known to regulate BMP-2 transcription in osteoblasts and microtubules have been shown to be involved in Hh signaling in Drosophila. Here we show that in osteoblasts, inhibition of microtubule assembly increased cytoplasmic levels and transcriptional activity of Gli2, a transcriptional mediator of Hh signaling that we have previously shown to enhance BMP-2 expression in osteoblasts (M. Zhao et al., Mol. Cell. Biol. 26:6197-6208, 2006). Microtubule inhibition blocked beta-TrCP-mediated proteasomal processing of Gli2 in osteoblasts. In summary, inhibition of microtubule assembly enhances BMP-2 gene transcription and subsequent bone formation, in part, through inhibiting proteasomal processing of Gli2 and increasing intracellular Gli2 concentrations.
authors.affiliation: Department of Medicine/Clinical Pharmacology, Vanderbilt University Medical Center, Nashville, Tennessee 372321, USA. zhaomin@umkc.edu
authors.forename: Ming
authors.initials: M
authors.lastname: Zhao
authors.forename: Seon-Yle
authors.initials: SY
authors.lastname: Ko
authors.forename: Jin-Hua
authors.initials: JH
authors.lastname: Liu
authors.forename: Di
authors.initials: D
authors.lastname: Chen
authors.forename: Jianghong
authors.initials: J
authors.lastname: Zhang
authors.forename: Baolin
authors.initials: B
authors.lastname: Wang
authors.forename: Stephen E
authors.initials: SE
authors.lastname: Harris
authors.forename: Babatunde O
authors.initials: BO
authors.lastname: Oyajobi
authors.forename: Gregory R
authors.initials: GR
authors.lastname: Mundy
mesh_terms: D000818:Animals; D055396:Bone Morphogenetic Protein 2 / Q000235:genetics*; D002454:Cell Differentiation / Q000187:drug effects; D053823:Hedgehog Proteins / Q000378:metabolism; D051741:Kruppel-Like Transcription Factors / Q000502:physiology*; D051379:Mice; D008822:Mice, Transgenic; D008870:Microtubules / Q000187:drug effects / Q000378:metabolism*; D010006:Osteoblasts / Q000166:cytology / Q000378:metabolism*; D010012:Osteogenesis; D054852:Small Molecule Libraries; D015533:Transcriptional Activation / Q000187:drug effects; D050257:Tubulin Modulators / Q000008:administration & dosage / Q000494:pharmacology*; D000075746:Zinc Finger Protein Gli2
chemical_list: D055396:Bone Morphogenetic Protein 2; C000618551:Gli2 protein, mouse; D053823:Hedgehog Proteins; D051741:Kruppel-Like Transcription Factors; D054852:Small Molecule Libraries; D050257:Tubulin Modulators; D000075746:Zinc Finger Protein Gli2