Endogenous IGFBP-3 is protected from inducible IGFBP-3 protease activity in normal adult serum.
We have recently demonstrated that the presence or absence of IGFBP-3 protease activity in physiological fluids may not be determined simply by the presence or absence of specific enzymes but rather the presence of inhibitors. In addition, it appears that these inhibitors may not only be associated with the protease(s) but with the IGFBP-3 itself, protecting it from proteolytic cleavage. To provide further evidence for this mechanism of regulation we investigated whether IGFBP-3 protease activity could be unveiled in normal adult serum (NS) and whether the endogenous IGFBP-3 was protected from this activity. The addition of a range of concentrations of heparin, induced IGFBP-3 protease activity in NS. This was comparable to that seen in pregnancy serum (PS) by virtue of the fragmentation pattern and inhibitor profile. While the addition of zinc also revealed IGFBP-3 protease activity in NS the pattern of fragments differed to that seen in PS. Under both conditions, however, the endogenous IGFBP-3 was not proteolytically modified. These results demonstrate that IGFBP-3 protease activity is present in NS and can be activated, although the endogenous IGFBP-3 is relatively protected from such activity.
Division of Surgery, University of Bristol, Department of Hospital Medicine, Bristol Royal Infirmary, Bristol, BS2 8HW, UK. Laura_Maile@med.unc.edu
L A
LA
Maile
E J
EJ
Whellams
J M
JM
Holly
D000328:Adult; D000925:Anticoagulants / Q000494:pharmacology; D015153:Blotting, Western; D004305:Dose-Response Relationship, Drug; D004492:Edetic Acid / Q000494:pharmacology; D004591:Electrophoresis, Polyacrylamide Gel; D010450:Endopeptidases / Q000378:metabolism*; D004790:Enzyme Induction; D005260:Female; D005343:Fibrinolytic Agents / Q000494:pharmacology; D006493:Heparin / Q000494:pharmacology; D006801:Humans; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000097:blood*; D007477:Ions; D011247:Pregnancy; D011263:Pregnancy Trimester, Third / Q000097:blood; D011994:Recombinant Proteins / Q000378:metabolism; D013997:Time Factors; D015032:Zinc / Q000494:pharmacology
D000925:Anticoagulants; D005343:Fibrinolytic Agents; D018972:Insulin-Like Growth Factor Binding Protein 3; D007477:Ions; D011994:Recombinant Proteins; D006493:Heparin; D004492:Edetic Acid; D010450:Endopeptidases; C080473:insulin-like growth factor binding protein-3 protease; D015032:Zinc