• Rosenfeld, Ronald (Ron) (PI)

Project: Research project

Project Details


The mitogenic and anabolic actions of the insulin-like growth factors
(IGFs) are modulated by a minimum of six serum binding proteins (BPs) .
The major carrier of IGF peptides in plasma is IGFBP-3, which normally
complexes with IGF-I (or -II) and an acid-labile subunit, to form a 150K
complex. We have recently shown, by western ligand blotting techniques,
that there is a dramatic reduction of intact IGFBP-3 in the sera of
pregnant women, mice and rats, and that this decrease can be attributed
to the presence of a pregnancy-associated protease (P-A-P) which cleaves
IGFBP-3 into smaller fragments. We have demonstrated a similar mechanism
in seminal plasma, and in several malignancy-related proteases. We propose that proteolysis of IGFBP-3 is a regulatory process, whereby
alterations in the affinity of IGFBP-3 for IGF peptides modulates access
of these IGFs to cell membrane receptors. We plan to identify and
characterize IGFBP-3 proteases, with special attention to the P-A-P and
the protease activity of seminal plasma, which we have tentatively
ldentified as prostate-specific antigen (PSA). P-A-P will be purified
and its cDNA cloned. Employing an IGFBP protease assay developed in our,
laboratories, together with PSA and purified P-A-P, we will perform
enzyme kinetic studies, identify specific protease inhibitors, determine
cleavage site specificity, and quantitate protease activity. The source
of P-A-P will be determined by decidual, trophoblast and hepatic explant
and cell cultures, and hormonal regulation of protease activity will be
studied. Immunohistochemical, in situ hybridization, and Northern blot
studies will be performed to identify cells which produce IGFBP-3 and/or
IGFBP-3 proteases. Finally, the IGFBP-3 fragments will be characterized
in terms of: 1) their size; 2) their affinity for IGF-I and -II; 3) their
ability to complex with the acid-labile subunit to form the normal
ternary complex; and 4) their effect upon the ability of IGF-I and -II to
bind to membrane receptors and exert biological action.
Effective start/end date8/1/927/31/97


  • National Institutes of Health


  • Medicine(all)


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