Abstract |
Recent studies using insulin-like growth factor I ( IGF-I) knockout mice demonstrate that IGF-binding protein (IGFBP)-5, an important bone formation regulator, itself is a growth factor with cellular effects not dependent on IGFs. Because IGFBP-5 contains a nuclear localization sequence that mediates transport of IGFBP-5 into the nucleus, we propose that IGFBP-5 interacts with nuclear proteins to affect transcription of genes involved in bone formation. We therefore undertook studies to identify proteins that bind to IGFBP-5 using IGFBP-5 as bait in a yeast two-hybrid screen of a U2 human osteosarcoma cDNA library. Five related clones that interacted strongly with the bait corresponded to the FHL2 gene, which contains four and a half LIM domains. Co-immunoprecipitation studies with lysates from U2 cells overexpressing FHL2 and IGFBP-5 confirmed that interaction between IGFBP-5 and FHL2 occurs in whole cells. In vitro interaction studies revealed that purified FHL2 interacted with IGFBP-5 but not with IGFBP-3, -4, or -6. Northern blot analysis showed that FHL2 was strongly expressed in human osteoblasts. Nuclear localization of both FHL2 and IGFBP-5 was evident from Western immunoblot analysis and immunofluorescence. The role of FHL2 as an intracellular mediator of the effects of IGFBP-5 and other osteoregulatory agents in osteoblasts will need to be verified in future studies.
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Authors | Yousef G Amaar, Garrett R Thompson, Thomas A Linkhart, Shin-Tai Chen, David J Baylink, Subburaman Mohan |
Journal | The Journal of biological chemistry
(J Biol Chem)
Vol. 277
Issue 14
Pg. 12053-60
(Apr 05 2002)
ISSN: 0021-9258 [Print] United States |
PMID | 11821401
(Publication Type: Journal Article, Research Support, Non-U.S. Gov't, Research Support, U.S. Gov't, Non-P.H.S., Research Support, U.S. Gov't, P.H.S.)
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Chemical References |
- DNA, Complementary
- FHL2 protein, human
- Fhl2 protein, mouse
- Homeodomain Proteins
- Insulin-Like Growth Factor Binding Protein 3
- Insulin-Like Growth Factor Binding Protein 4
- Insulin-Like Growth Factor Binding Protein 5
- Insulin-Like Growth Factor Binding Protein 6
- LIM-Homeodomain Proteins
- Muscle Proteins
- Recombinant Proteins
- Transcription Factors
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Topics |
- Active Transport, Cell Nucleus
- Animals
- Blotting, Northern
- Blotting, Western
- Cell Nucleus
(metabolism)
- Cytoplasm
(metabolism)
- DNA, Complementary
(metabolism)
- Gene Library
- Genetic Vectors
- Homeodomain Proteins
(chemistry, metabolism)
- Humans
- Insulin-Like Growth Factor Binding Protein 3
(metabolism)
- Insulin-Like Growth Factor Binding Protein 4
(metabolism)
- Insulin-Like Growth Factor Binding Protein 5
(chemistry, metabolism)
- Insulin-Like Growth Factor Binding Protein 6
(metabolism)
- LIM-Homeodomain Proteins
- Mice
- Microscopy, Fluorescence
- Muscle Proteins
- Plasmids
(metabolism)
- Precipitin Tests
- Protein Binding
- Protein Structure, Tertiary
- Recombinant Proteins
(metabolism)
- Retroviridae
(genetics)
- Transcription Factors
- Transfection
- Tumor Cells, Cultured
- Two-Hybrid System Techniques
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