AJP - Gastrointestinal and Liver Physiology, Vol 267, Issue 1 105-G114, Copyright © 1994 by American Physiological Society
Characterization of insulin-like growth factor I receptors in human esophageal epithelial cells
R. Vinayek, L. S. Pichney, U. Tantry, S. K. Dutta, J. Resau and S. Vengurlekar
Division of Gastroenterology, University of Maryland School of Medicine, Baltimore.
In the present study we used 125I-labeled insulin-like growth factor I
(125I-IGF-I) to identify and characterize IGF-I receptors in the
well-characterized and propagable human esophageal epithelial (HEE) cell
line and to characterize their role in cell growth. Binding of 125I-IGF-I
was saturable, time and temperature dependent, reversible, and specific for
IGF-I and related peptides. Scatchard analysis of binding data demonstrated
that HEE cells possess two classes of IGF-I receptors: high affinity
[dissociation constant (Kd) = 0.058 nM] and low capacity (13,870
receptors/cell), and low affinity (Kd = 2.2 nM) and high capacity (39,000
receptors/cell). Binding of 125I-IGF-I was inhibited with the following
relative potencies (half-maximal inhibition): IGF-I (3.0 pM) > IGF-II
(1.2 mM) >> insulin (1.0 microM). Affinity cross-linking of cell
membranes using disuccinimidyl suberate as a cross-linking agent under
reducing conditions revealed a single polypeptide band (relative mol wt
133,000) representing the alpha-subunit of the IGF-I receptor. IGF-I
stimulated [3H]thymidine incorporation and cell proliferation in a
dose-dependent manner with detectable effect observed with 0.5 nM IGF-I and
maximal effect at 50 nM IGF-I. IGF-I occupation of low-affinity IGF-I
receptors appears to mediate cell growth. The present results demonstrate
that HEE cells possess two classes of IGF-I receptors: one class has a high
affinity and low capacity and the other has a low affinity and high
capacity for IGF-I. Occupation of low-affinity IGF-I receptors by IGF-I
appears to mediate cell growth.
