title: Insulin-like growth factor binding protein-6 interacts with the thyroid hormone receptor α1 and modulates the thyroid hormone-response in osteoblastic differentiation.
abstract: Insulin-like growth factor binding protein-6 (IGFBP-6) is a member of the insulin-like growth factor binding protein family, which has both Insulin-like growth factor-dependent and independent effects on cell growth. In previous studies, we have shown that recombinant IGFBP-6 could be translocated into the cell nucleus. But the effect in the nucleus of IGFBP-6 is not clear. In the present study, we use multiple methodologies including Glutathione S-transferase pull-down assay, co-immunoprecipitation, fluorescence resonance energy transfer to demonstrate that IGFBP-6 can directly interact with thyroid hormone receptor alpha 1 (TRα1) in vitro and in vivo. We also demonstrate that the DNA-binding domains and Ligand-binding domains of TRα1 and N-terminal domains and C-terminal domains of IGFBP-6 are involved in the interaction. This interaction also can block the formation of TR: retinoid X receptor heterodimers. Furthermore, immunofluorescence co-localization studies show IGFBP-6 and TRα1 could co-localize in the nucleus of the cells. Reporter gene experiment shows that IGFBP-6 negatively regulates the growth hormone promoter activity induced by ligand activated TRα1. Moreover, real-time RT-PCR demonstrates that IGFBP-6 could inhibit the osteocalcin mRNA transcription induced by Triiodothyronine (3,3',5-Triiodo-L-thyronine, T3) in osteoblastic cells. Finally, alkaline phosphatase activity was significantly decreased in osteoblastic cells when the cells were transfected with IGFBP-6 in the presence of T3. In conclusion, these studies provide evidence that overexpression of IGFBP-6 suppresses osteoblastic differentiation regulated by TR in the present of T3.
authors: National Laboratory of Medical Molecular Biology, Department of Biochemistry and Molecular Biology, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing, China.
authors: Jia
authors: J
authors: Qiu
authors: Xiao-Li
authors: XL
authors: Ma
authors: Xin
authors: X
authors: Wang
authors: Hong
authors: H
authors: Chen
authors: Bing-Ren
authors: BR
authors: Huang
mesh_terms: D000469:Alkaline Phosphatase / Q000378:metabolism; D000818:Animals; D002454:Cell Differentiation; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D005786:Gene Expression Regulation; D017930:Genes, Reporter; D006801:Humans; D018976:Insulin-Like Growth Factor Binding Protein 6 / Q000737:chemistry / Q000378:metabolism*; D049410:Luciferases, Renilla / Q000096:biosynthesis / Q000235:genetics; D051379:Mice; D010006:Osteoblasts / Q000378:metabolism / Q000502:physiology*; D015675:Osteocalcin / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding; D054730:Protein Interaction Domains and Motifs; D025941:Protein Interaction Mapping; D055503:Protein Multimerization; D020218:Response Elements; D047488:Retinoid X Receptors / Q000378:metabolism; D037021:Thyroid Hormone Receptors alpha / Q000737:chemistry / Q000378:metabolism*; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D014284:Triiodothyronine / Q000494:pharmacology / Q000502:physiology*
chemical_list: D018976:Insulin-Like Growth Factor Binding Protein 6; D047488:Retinoid X Receptors; D037021:Thyroid Hormone Receptors alpha; D014284:Triiodothyronine; D015675:Osteocalcin; D049410:Luciferases, Renilla; D000469:Alkaline Phosphatase