Transforming Growth Factor-β Regulation of the Insulin-Like Growth Factor Binding Protein-4 Protease System in Cultured Human Osteoblasts

Christopher O. Ortiz, Bing K. Chen, Laurie K. Bale, Michael T. Overgaard, Claus Oxvig, Cheryl A Conover

Research output: Contribution to journalArticle

64 Citations (Scopus)

Abstract

IGFBP-4 is an inhibitor of IGF-I in bone. We show that TGF-β regulates IGFBP-4 and enhances IGF-I-stimulated growth of cultured human bone cells through increased expression of an IGFBP-4 protease, PAPP-A. This effect of TGF-β on IGF-I bioavailability may promote local bone formation. Insulin-like growth factor binding protein (IGFBP-4) proteolysis is implicated in the regulation of local insulin-like growth factor (IGF)-I bioavailability during bone remodeling. The IGFBP-4 protease secreted by normal adult human osteoblastic (hOB) cells in culture is a novel metalloproteinase, pregnancy-associated plasma protein-A (PAPP-A). We have recently identified an inhibitor of PAPP-A, the precursor form of major basic protein (proMBP). Very little is known about the molecular regulation of this IGFBP-4 protease system. In the present study, we determined the effect of transforming growth factor (TGF)-β and IGF-II, the two most abundant growth factors in human bone, on PAPP-A and proMBP expression in primary cultures of hOB cells. Treatment with TGF-β resulted in time- and dose-dependent increases in PAPP-A mRNA expression, with a maximal 12-fold increase after 24 h of stimulation with 10 ng/ml TGF-β. Increased PAPP-A levels in hOB cell-conditioned medium paralleled PAPP-A gene expression. In addition, TGF-β completely suppressed proMBP expression. Treatment of hOB cells with IGF-II had no effect on PAPP-A orproMBP gene expression. However, IGFBP-4 proteolysis in cell-free assay was dependent on IGF-II, and there was increased IGF-II-dependent IGFBP-4 protease activity in conditioned medium from hOB cells that were treated with TGF-β. IGF-I stimulation of hOB cell proliferation was markedly enhanced by pretreatment with TGF-β and [Leu27]IGF-II, and this enhancement was prevented with protease-resistant IGFBP-4. In summary, TGF-β regulates IGFBP-4 proteolysis in hOB cells through increased expression of the protease, PAPP-A, and decreased expression of the inhibitor, proMBP. However, functional activation of the IGFBP-4 protease system is dependent on IGF-II, which acts at a post-translational level. These data support a model whereby local TGF-β and IGF-II in the bone microenvironment coordinately amplify IGF-I bioavailability through controlled IGFBP-4 proteolysis, which may be a means to promote bone formation.

Original languageEnglish (US)
Pages (from-to)1066-1072
Number of pages7
JournalJournal of Bone and Mineral Research
Volume18
Issue number6
DOIs
StatePublished - Jun 1 2003

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Pregnancy-Associated Plasma Protein-A
Transforming Growth Factors
Osteoblasts
Insulin-Like Growth Factor Binding Protein 4
Insulin-Like Growth Factor II
Insulin-Like Growth Factor I
Proteolysis
Biological Availability
Bone and Bones
Protein Precursors
Conditioned Culture Medium
Osteogenesis
Proteins
Gene Expression
Bone Remodeling
Metalloproteases

Keywords

  • Human osteoblasts
  • Insulin-like growth factor binding protein-4
  • Insulin-like growth factor-II
  • Pregnancy-associated plasma protein-A
  • Transforming growth factor-β

ASJC Scopus subject areas

  • Surgery

Cite this

Transforming Growth Factor-β Regulation of the Insulin-Like Growth Factor Binding Protein-4 Protease System in Cultured Human Osteoblasts. / Ortiz, Christopher O.; Chen, Bing K.; Bale, Laurie K.; Overgaard, Michael T.; Oxvig, Claus; Conover, Cheryl A.

In: Journal of Bone and Mineral Research, Vol. 18, No. 6, 01.06.2003, p. 1066-1072.

Research output: Contribution to journalArticle

Ortiz, Christopher O. ; Chen, Bing K. ; Bale, Laurie K. ; Overgaard, Michael T. ; Oxvig, Claus ; Conover, Cheryl A. / Transforming Growth Factor-β Regulation of the Insulin-Like Growth Factor Binding Protein-4 Protease System in Cultured Human Osteoblasts. In: Journal of Bone and Mineral Research. 2003 ; Vol. 18, No. 6. pp. 1066-1072.
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AU - Overgaard, Michael T.

AU - Oxvig, Claus

AU - Conover, Cheryl A

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KW - Insulin-like growth factor binding protein-4

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