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Insulin-like growth factor-binding proteins in the human fetus: tissue-specific protein secretion, immunologic
E M Pannier1, J C Irwin, L C Giudice
1Department of Gynecology and Obstetrics, Stanford University Medical Center, CA 94305-5317.
Objectives:
The objectives of this study were to investigate the profile of insulin-like growth factor-binding proteins secreted by human fetal tissues and their immunologic identification and tissue-specific gene expression.
Study Design:
Explants of midgestational fetal tissues from seven fetuses were cultured with and without cycloheximide. Conditioned media were examined for insulin-like growth factor-binding proteins by Western ligand blot analysis, and insulin-like growth factor-binding proteins were identified by immunoprecipitation. Gene expression was analyzed by Northern analysis.
Results:
Fetal liver and kidney explants secreted insulin-like growth factor-binding protein-1 to insulin-like growth factor-binding protein-4, with insulin-like growth factor-binding protein-1 being the most prominent in liver. Fetal lung secreted insulin-like growth factor-binding protein-2 and insulin-like growth factor-binding protein-4 and lesser amounts of insulin-like growth factor-binding protein-3, whereas white matter explants secreted exclusively insulin-like growth factor-binding protein-2 and insulin-like growth factor-binding protein-4. Cycloheximide inhibited secretion of binding proteins, suggesting de novo synthesis. Northern blot analyses were consistent with the protein studies.
Conclusion:
These data demonstrate that insulin-like growth factor-binding protein secretion by fetal tissues is tissue specific.