Vol. 282, Issue 1, E52-E58, January 2002
IGFBP-3 binding to endothelial cells inhibits plasmin and
thrombin proteolysis
B. A.
Booth,
M.
Boes,
B. L.
Dake,
K. L.
Knudtson, and
R. S.
Bar
Department of Internal Medicine, Diabetes and Endocrinology
Research Center, Veterans Administration Medical Center, The
University of Iowa, Iowa City, Iowa 52246
Insulin-like growth factor-binding protein
(IGFBP)-3 contains a highly basic COOH-terminal heparin-binding region,
the P3 region, which is thought to be important in the binding of
IGFBP-3 to endothelial cells. IGFBP-3 and IGFBP-4, and their chimeras IGFBP-34 and IGFBP-43, were treated with
plasmin and with thrombin, proteases known to cleave IGFBP-3. IGFBP-3
was highly susceptible to plasmin, whereas IGFBP-4 was less so.
Substitution of the P3 region for the P4 region in IGFBP-4
(IGFBP-43) increased the ability of the protease to digest
IGFBP-43; substitution of the P4 region for the P3 region
in IGFBP-3 (IGFBP-34) decreased the digestion of
IGFBP-34. When 125I-labeled IGFBP-3 or
125I-IGFBP-43 was first bound to vascular
endothelial cells, subsequent proteolysis by either plasmin or thrombin
was substantially inhibited. Proteolysis of
125I-IGFBP-34 was not inhibited in the presence
of endothelial cells. The P3 peptide was cleaved by plasmin but not by
thrombin. We conclude that the P3 region is central to proteolysis of
IGFBP-3 by plasmin and thrombin, processes which were inhibited by
association of IGFBP-3 with endothelial cells.
IGFBP proteases
