Expression of insulin-like growth factor I receptors and binding proteins by colonic smooth muscle cells.
We recently demonstrated upregulation of insulin-like growth factor I (IGF-I) binding sites in the smooth muscle layer of inflamed rat colon. The increase in binding sites was due to increased expression of IGF binding proteins (IGFBPs), which modulate the effects of IGF. To further study the role of IGF in the colon, we investigated whether cultured colonic smooth muscle cells (SMC) express IGF-I receptors and IGFBPs. SMC were isolated by collagenase digestion from rat colonic smooth muscle and grown in primary culture. Equilibrium binding experiments using (125)I-labeled IGF-I showed the presence of an IGF-I receptor with a dissociation constant of 1.96 nM and a maximal binding constant of 53,000 receptors/cell. Competition binding studies with IGF-II and insulin, together with chemical cross-linking experiments, corroborated this conclusion. Western ligand blotting of conditioned medium and Northern analysis of total RNA demonstrated that the cells expressed and secreted IGFBP-4, -5, and -3 with molecular masses of 25, 31, and 45 kDa, respectively. These results, together with our in vivo studies in the rat, support a role for IGF in tissue fibrosis and stricture formation during chronic intestinal inflammation.
Zeeh
J M
JM
Department of Medicine, Harbor-University of California, Torrance 90502, USA.
Ennes
H S
HS
Hoffmann
P
P
Procaccino
F
F
Eysselein
V E
VE
Snape
W J
WJ
McRoberts
J A
JA
D000818:Animals; D015153:Blotting, Western; D002478:Cells, Cultured; D003106:Colon / Q000166:cytology / Q000378:metabolism*; D003432:Cross-Linking Reagents; D015870:Gene Expression; D018969:Insulin-Like Growth Factor Binding Proteins / Q000378:metabolism*; D008297:Male; D008970:Molecular Weight; D009130:Muscle, Smooth / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics; D011869:Radioligand Assay; D051381:Rats; D017207:Rats, Sprague-Dawley; D017526:Receptor, IGF Type 1 / Q000378:metabolism*
D003432:Cross-Linking Reagents; D018969:Insulin-Like Growth Factor Binding Proteins; D012333:RNA, Messenger; D017526:Receptor, IGF Type 1