The IGFBP-3 mRNA and protein levels are IGF-I-dependent and GH-independent in MG-63 human osteosarcoma cells

Roberto R. Rosato, Katia Gerland, Hélène Jammes, Nelly Bataille-Simoneau, Berta Segovia, Louis Mercier, André Groyer

Research output: Contribution to journalArticle

3 Scopus citations

Abstract

Growth Hormone (GH), Insulin-like Growth Factors (IGFs) and IGF-Binding Proteins which modulate the IGFs' bioavailability (e.g. IGFBP-3, -4, -5), are essential regulators of bone remodeling. In this study, MG-63 human osteosarcoma cells were used as a model system to investigate the mechanism(s) whereby IGF-I and GH control IGFBP-3 gene expression. Physiological concentrations of IGF-I (1-20 nM) induced a dose-dependent increase in the steady-state amount of IGFBP-3 mRNA (maximal stimulation: ∼9-10-fold). This increase was detectable 3 h after the onset of IGF-I treatment, was enhanced over a 24 h period, then plateaued until at least 30 h. Consistently, a dose-dependent increase in IGFBP-3 secretion (∼40-50-fold at IGF-I concentrations≥16 nM) was observed by western ligand- and immuno-blot analysis of MG-63 cells conditioned medium, and its time course was similar to that observed for IGFBP-3 transcripts. IGFBP-3 mRNA stability (t1/2 ∼20 h) was identical in the presence or absence of IGF-I treatment. By contrast, human (h) GH treatment (24-72 h) of MG-63 cells did not increase IGFBP-3 secretion in the conditioned medium. Ectopic expression of recombinant rat GH-R resulted in hGH-enhanced expression of GH-responsive reporter gene constructs, but did not increase endogenous IGFBP-3 gene expression, suggesting that the GH unresponsiveness was not only due to the very low level of GH binding sites at the plasma membrane level. Altogether, these results support the conclusions that in MG-63 cells (i) transcriptional rather post-transcriptional mechanisms are involved in the IGF-I-induced increase of IGFBP-3; (ii) the abundance of GH-R is very low at the plasma membrane level; (iii) the dowstream GH-signaling cascade is fully functional in this human osteosarcoma cell line; and (iv) the endogenous IGFBP-3 gene is not responsive to hGH in human MG-63 osteosarcoma cells.

Original languageEnglish (US)
Pages (from-to)15-27
Number of pages13
JournalMolecular and cellular endocrinology
Volume175
Issue number1-2
DOIs
StatePublished - Apr 25 2001

Keywords

  • Actinomycin-D
  • Gene expresssion
  • Growth hormone
  • Growth hormone receptor
  • IGFBP-3
  • Insulin-like growth factor-I
  • Osteosarcoma cells

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Endocrinology

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