Distribution of chimeric IGF binding protein (IGFBP)-3 and IGFBP-4 in the rat heart: importance of C-terminal basic region.
IGF binding proteins-3 and -4, whether given in the perfused rat heart or given iv in the intact animal, cross the microvascular endothelium of the heart and distribute in subendothelial tissues. IGF binding protein-3, like IGF-I/II, localizes in cardiac muscle, with lesser concentrations in CT elements. In contrast, IGFBP-4 preferentially localizes in CT. In this study, chimeric IGF binding proteins were prepared in which a basic 20-amino-acid C-terminal region of IGF binding protein-3 was switched with the homologous region of IGF binding protein-4, and vice-versa, to create IGF binding protein-3(4) and IGF binding protein-4(3). Perfused IGF binding protein-3(4) behaved like IGF binding protein-4, localizing in connective tissue elements, whereas IGF binding protein-4(3) now localized in cardiac muscle at concentrations identical to perfused IGF binding protein-3. To determine whether these small mutations altered the affinity of the chimera for cells, the ability of (125)I-IGF binding protein-3(4) and (125)I-IGF binding protein-4(3) to bind to microvascular endothelial cells was determined and compared with IGF binding protein-3. IGF binding protein-3(4) retained 15% of the binding capacity of IGF binding protein-3, whereas IGF binding protein-4(3) bound to microvessel endothelial cells with higher affinity and greater total binding than that of IGF binding protein-3. We conclude that small changes in the C-terminal basic domain of IGF binding protein-3 and the corresponding region of IGF binding protein-4 can alter their affinity for cultured cells and influence their tissue distribution in the rat heart.
Knudtson
K L
KL
Department of Internal Medicine, Diabetes and Endocrinology Research Center, Veterans Administration Medical Center, The University of Iowa, Iowa City, Iowa 52246, USA.
Boes
M
M
Sandra
A
A
Dake
B L
BL
Booth
B A
BA
Bar
R S
RS
D000595:Amino Acid Sequence / Q000235:genetics; D000818:Animals; D001483:Base Sequence / Q000235:genetics; D002478:Cells, Cultured; D002678:Chimera; D004730:Endothelium, Vascular / Q000166:cytology / Q000378:metabolism; D005109:Extracellular Matrix / Q000378:metabolism; D066298:In Vitro Techniques; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000235:genetics* / Q000378:metabolism*; D018974:Insulin-Like Growth Factor Binding Protein 4 / Q000235:genetics* / Q000378:metabolism*; D008297:Male; D008969:Molecular Sequence Data; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D010477:Perfusion; D051381:Rats; D017207:Rats, Sprague-Dawley; D014018:Tissue Distribution
D018972:Insulin-Like Growth Factor Binding Protein 3; D018974:Insulin-Like Growth Factor Binding Protein 4