title: Insulin-like growth factor binding protein-3 modulates osteoblast differentiation via interaction with vitamin D receptor.
abstract: Insulin-like growth factor (IGF) binding protein-3 (IGFBP-3) is a secreted glycoprotein that reduces the bioavailability of IGFs. This glycoprotein has both IGF-dependent and -independent effects on cell growth. However, the mechanisms responsible for the IGF-independent actions of IGFBP-3 are not fully understood. In the present study, we used multiple methodologies including glutathione S-transferase pull-down assay and co-immunoprecipitation to demonstrate that IGFBP-3 can directly interact with vitamin D receptor (VDR) in vitro and in vivo. Furthermore, immunofluorescence co-localization studies showed that IGFBP-3 and VDR could co-localize in the cell nucleus. Reporter gene experiment showed that IGFBP-3 negatively regulates the growth hormone promoter activity induced by ligand-activated VDR. Moreover, real-time RT-PCR demonstrated that IGFBP-3 can inhibit the osteocalcin and CYP24a1 mRNA transcription induced by 1,25-(OH)2D3 in osteoblastic cells. Finally, alkaline phosphatase activity significantly decreased in osteoblastic cells when the cells were transfected with IGFBP-3 in the presence of 1,25-(OH)2D3. In conclusion, these studies provide evidence that overexpression of IGFBP-3 suppresses osteoblastic differentiation regulated by VDR in the presence of 1,25-(OH)2D3. These findings reveal a novel mechanism by which IGFBP-3 functions.
authors.affiliation: Department of Traumatology & Orthopedics, Nanfang Hospital, China.
authors.forename: Jianwei
authors.initials: J
authors.lastname: Li
authors.forename: Dan
authors.initials: D
authors.lastname: Jin
authors.forename: Su
authors.initials: S
authors.lastname: Fu
authors.forename: Gang
authors.initials: G
authors.lastname: Mei
authors.forename: Jian
authors.initials: J
authors.lastname: Zhou
authors.forename: Lei
authors.initials: L
authors.lastname: Lei
authors.forename: Bin
authors.initials: B
authors.lastname: Yu
authors.forename: Gang
authors.initials: G
authors.lastname: Wang
mesh_terms: D002117:Calcitriol / Q000494:pharmacology; D002454:Cell Differentiation / Q000502:physiology*; D002460:Cell Line; D006801:Humans; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000378:metabolism / Q000502:physiology*; D010006:Osteoblasts / Q000166:cytology*; D011485:Protein Binding; D060888:Real-Time Polymerase Chain Reaction; D018167:Receptors, Calcitriol / Q000378:metabolism*
chemical_list: D018972:Insulin-Like Growth Factor Binding Protein 3; D018167:Receptors, Calcitriol; D002117:Calcitriol
keywords: 1,25-(OH)(2)D(3); 1,25-dihydroxyvitamin D3; ALP; IGFBP-3; Oste; Osteoblast differentiation; VDR; VDRE; alkaline phosphatase; insulin-like growth factor binding protein-3; osteocalcin; vitamin D response element; vitamin-D receptor