These tools will no longer be maintained as of December 31, 2024. Archived website can be found here. PubMed4Hh GitHub repository can be found here. Contact NLM Customer Service if you have questions.


Pubmed for Handhelds

PUBMED FOR HANDHELDS

Search MEDLINE/PubMed

  • Title: Regulation of insulin-like growth factor-binding protein-4 in human endometrial stromal cell cultures: evidence for ligand-induced proteolysis.
    Author: Irwin JC, Dsupin BA, Giudice LC.
    Journal: J Clin Endocrinol Metab; 1995 Feb; 80(2):619-26. PubMed ID: 7531715.
    Abstract:
    The present study investigates the regulation of IGFBP-4 levels by insulin-like growth factor (IGF) peptides in human endometrial stromal cell cultures. A 24-kilodalton (kDa) IGF-binding protein (IGFBP) secreted by stromal cells was identified as IGFBP-4 by immunoprecipitation and Western ligand blotting. Western ligand blot analysis of conditioned medium showed that treatment of stromal cells with IGF-I or IGF-II induced a dose-dependent reduction of detectable IGFBP-4 levels. Two IGF analogs that bind type I IGF receptors, but have reduced affinity for IGFBPs, increased detectable levels of IGFBP-4, and their ability to reduce IGFBP-4 at high concentrations was positively correlated with their affinity for this binding protein. LR3-IGF-I, which has 1000-fold lower binding affinity than IGF-I, increased detectable IGFBP-4 at all concentrations tested. Des-(1-3)-IGF-I, whose affinity for IGFBP-4 is 30-fold lower than that of IGF-I, increased detectable IGFBP-4 at low concentrations (0.1-10 ng/mL), but reduced its levels at 100 ng/mL, consistent with the significant binding to IGFBP-4 at this concentration. In contrast, IGFBP-4 was undetectable in cultures receiving Leu27-IGF-II, which has reduced affinity for the type IIGF receptor but unaltered affinity for IGFBPs and the type II receptor. High concentrations of insulin (100 ng/mL), which interacts with type I IGF receptors without binding IGFBPs, also increased detectable levels of IGFBP-4 in stromal cultures. The addition of IGF-I or IGF-II to cell-free conditioned medium from stromal cells cultured in the absence of IGFs resulted in the reduction of detectable endogenous IGFBP-4 levels. The effects of IGFs on IGFBP-4 levels in this cell-free system were time, temperature, and pH dependent and were prevented by the serine proteinase inhibitor, aprotinin, by the divalent cation chelator, EDTA, and by the metal ion chelator, 1,10-phenanthroline. Western immunoblotting showed that the IGF-induced reduction of intact 24-kDa IGFBP-4 was accompanied by the generation of an immunoreactive fragment of approximately 16 kDa, which was not detectable by Western ligand blotting. Cell-free conditioned medium from endometrial stromal cultures proteolyzed covalently cross-linked [125I]IGF-II-IGFBP-4 complexes in the absence of added IGFs, generating an 18-kDa radiolabeled fragment, and addition of free IGF peptide did not enhance the degradation of IGF-II-IGFBP-4 complexes.(ABSTRACT TRUNCATED AT 400 WORDS)
    [Abstract] [Full Text] [Related] [New Search]