Characterization of the Epidermal Growth Factor Receptor in the Gastric Mucosa

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Abstract
The effects of epidermal growth factor (EGF), a potent mitogen involved in mucosal protection, are mediated by specific cellular receptors. Here, we present the characteristics and binding properties of EGF receptors in the gastric mucosa. The studies were conducted using cell membranes isolated by subcellular fractionation of rat stomach mucosal scrapings. Specific binding of [125I]-EGF to the membrane preparations was assessed at room temperature for various periods of time and at different pHs. The results showed that the binding was proportional to the incubation time up to 1 h and was not affected by a pH change between 4.0 and 7.0. Scatchard analysis of the binding data inferre the presence of 2 binding sites, one of high affinity (Kd = 1.34 nM, Bmax = 34 fmol/mg protein) and the other of low affinity (Kd = 484 nM, Bmax = 2.29 pmol/mg protein). Cross-linking experiments using disuccinimidyl suberate to link the [125I]-EGF to gastric membranes followed by polyacrylamide gel electrophoresis and autoradiography revealed that the major receptor for EGF was a protein of 170 kilodaltons. When the solubilized membranes were subjected to wheat germ agglutinin affinity chromatography, the purified material was found to act as substrate for EGF-stimulated phosphorylation. The major component which was labeled by the [γ-32P]-ATP was also found to be a 170-kilodalton protein. The data are the first to provide evidence that the gastric mucosa possesses a functional EGF receptor and describe its binding characteristics.

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