Cultured fibroblast monolayers secrete a protein that alters the cellular binding of somatomedin-C/insulinlike growth factor I.
We studied somatomedin-C/insulinlike growth factor (Sm-C/IGF-I) binding to human fibroblasts in both adherent monolayers and in suspension cultures. The addition of Sm-C/IGF-I in concentrations between 0.5 and 10 ng/ml to monolayers cultures resulted in a paradoxical increase in 125I-Sm-C/IGF-I binding and concentrations between 25 and 300 ng/ml were required to displace the labeled peptide. The addition of unlabeled insulin resulted in no displacement of labeled Sm-C/IGF-I from the adherent cells. When fibroblast suspensions were used Sm-C/IGF-I concentrations between 1 and 10 ng/ml caused displacement, the paradoxical increase in 125I-Sm-C/IGF-I binding was not detected, and insulin displaced 60% of the labeled peptide. Affinity cross-linking to fibroblast monolayers revealed a 43,000-mol wt 125I-Sm-C-binding-protein complex that was not detected after cross-linking to suspended cells. The 43,000-mol wt complex was not detected after cross-linking to smooth muscle cell monolayers, and binding studies showed that 125I-Sm-C/IGF-I was displaced greater than 90% by Sm-C/IGF-I using concentrations between 0.5 and 10 ng/ml. Because fibroblast-conditioned medium contains the 43,000-mol wt complex, smooth muscle cells were incubated with conditioned medium for 24 h prior to initiation of the binding studies. 125I-Sm-C/IGF-I-binding increased 1.6-fold compared to control cultures and after cross-linking the 43,000-mol wt complex could be detected on the smooth muscle cell surface. Human fibroblast monolayers secrete a protein that binds 125I-Sm-C/IGF-I which can be transferred to the smooth muscle cell surface and alters 125I-Sm-C/IGF-I binding.
Clemmons
D R
DR
Elgin
R G
RG
Han
V K
VK
Casella
S J
SJ
D'Ercole
A J
AJ
Van Wyk
J J
JJ
D002352:Carrier Proteins / Q000378:metabolism*; D002450:Cell Communication; D002478:Cells, Cultured; D005347:Fibroblasts / Q000378:metabolism; D006801:Humans; D007328:Insulin / Q000378:metabolism; D018969:Insulin-Like Growth Factor Binding Proteins; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D007457:Iodine Radioisotopes; D008970:Molecular Weight; D009131:Muscle, Smooth, Vascular / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000378:metabolism; D017451:Receptors, Somatomedin; D013002:Somatomedins / Q000378:metabolism*
D002352:Carrier Proteins; D007328:Insulin; D018969:Insulin-Like Growth Factor Binding Proteins; D007457:Iodine Radioisotopes; D011956:Receptors, Cell Surface; D017451:Receptors, Somatomedin; D013002:Somatomedins; D007334:Insulin-Like Growth Factor I