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Evidence for a novel insulin-like growth factor (IGF)-dependent protease regulating IGF-binding protein-4 in dermal fibroblasts.

Publication ,  Journal Article
Fowlkes, J; Freemark, M
Published in: Endocrinology
November 1992

The mechanisms by which insulin-like growth factors (IGFs) reduce IGF-binding protein-4 (IGFBP-4) levels in cellular conditioned media are poorly understood. The effect of IGFs on IGFBP-4 levels in fibroblast conditioned media is not mediated via the type 1 or type 2 cellular IGF receptors, and the IGFs exert little or no effects on IGFBP-4 messenger RNA levels in human adult fibroblasts or in rat neuroblastoma cells. To determine whether the effects of IGFs on IGFBP-4 might be exerted through alterations in IGFBP-4 degradation, we incubated cell-free, fibroblast-conditioned media from either sheep or human dermal fibroblasts with or without IGF-I, IGF-II (each 1 microgram/ml), or insulin (10 micrograms/ml) for 72 h at 37 C. Samples were then analyzed by Western ligand blot using radiolabeled IGFs and by immunoblotting using a polyclonal antisera to human IGFBP-4. In the absence of IGFs, no apparent changes in the basal concentrations of the various IGFBPs were observed. In contrast, incubation of media with IGFs caused a 70-80% reduction in levels of both sheep and human IGFBP-4, whereas incubation with insulin was without effect. Similarly, incubation of cell-free conditioned media containing recombinant human IGFBP-4 with IGF-I caused a reduction in detectable levels of the 28K protein. The decrease in IGFBP-4 levels was accompanied by the appearance of an immunoreactive approximate 17-20K fragment that did not bind radiolabeled IGFs by ligand blot. The IGF-dependent decrease in IGFBP-4 was prevented by coincubation of the media with serine protease inhibitors, EDTA, or 1,10-phenanthrolene, suggesting that IGFs may activate an IGFBP-4 specific metallo-serine protease present in fibroblast conditioned media. Alternatively, binding of IGF-I or -II to IGFBP-4 may enhance the susceptibility of IGFBP-4 to proteolytic degradation. The demonstration that IGF-I and IGF-II can promote directly the proteolytic degradation of IGFBP-4 into fragments that do not bind IGFs provides a novel mechanism by which the IGFs may increase their own availability and/or activity in biological fluids.

Duke Scholars

Published In

Endocrinology

DOI

ISSN

0013-7227

Publication Date

November 1992

Volume

131

Issue

5

Start / End Page

2071 / 2076

Location

United States

Related Subject Headings

  • Somatomedins
  • Skin
  • Sheep
  • Recombinant Proteins
  • RNA, Messenger
  • Phenanthrolines
  • Insulin-Like Growth Factor II
  • Insulin-Like Growth Factor I
  • Insulin-Like Growth Factor Binding Protein 4
  • Insulin
 

Citation

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Fowlkes, J., & Freemark, M. (1992). Evidence for a novel insulin-like growth factor (IGF)-dependent protease regulating IGF-binding protein-4 in dermal fibroblasts. Endocrinology, 131(5), 2071–2076. https://doi.org/10.1210/endo.131.5.1385096
Fowlkes, J., and M. Freemark. “Evidence for a novel insulin-like growth factor (IGF)-dependent protease regulating IGF-binding protein-4 in dermal fibroblasts.Endocrinology 131, no. 5 (November 1992): 2071–76. https://doi.org/10.1210/endo.131.5.1385096.
Fowlkes, J., and M. Freemark. “Evidence for a novel insulin-like growth factor (IGF)-dependent protease regulating IGF-binding protein-4 in dermal fibroblasts.Endocrinology, vol. 131, no. 5, Nov. 1992, pp. 2071–76. Pubmed, doi:10.1210/endo.131.5.1385096.
Journal cover image

Published In

Endocrinology

DOI

ISSN

0013-7227

Publication Date

November 1992

Volume

131

Issue

5

Start / End Page

2071 / 2076

Location

United States

Related Subject Headings

  • Somatomedins
  • Skin
  • Sheep
  • Recombinant Proteins
  • RNA, Messenger
  • Phenanthrolines
  • Insulin-Like Growth Factor II
  • Insulin-Like Growth Factor I
  • Insulin-Like Growth Factor Binding Protein 4
  • Insulin