Characterization of epidermal growth factor receptors on plasma membranes isolated from rat gastric mucosa

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Time-dependent alteration of epidermal growth factor receptor in rat stomach by ethanol feeding

This study investigated the time-dependent effects of ethanol (EtOH) feeding on epidermal growth factor binding and epidermal growth factor-mediated functions in the stomach. Adult male rats were fed either an isocaloric control or EtOH-containing liquid diet (36% total calories as EtOH) for 2, 4 and 6 weeks. At the end of each feeding period, animals were sacrificed and the stomach was dissected for the sample preparation. EtOH caused a time-dependent alteration (r = 0.89) of the 125I-epidermal growth factor binding to the gastric mucosal membrane (% control: week 2, 114%; week 4, 64%* and week 6, 45%*, n = 5, *P < 0.05). Protein kinase analysis also showed that EtOH caused a time-dependent decrease of epidermal growth factor-stimulated autophosphorylation of epidermal growth factor receptor protein (180 kDa) during three feeding periods. Western blot analysis, using anti-tyrosine phosphorylated epidermal growth factor receptor (active form) antibody, revealed a major immunoreactive protein band (180 kDa) in all samples pre-incubated with 1 microM epidermal growth factor. Consistent with data from kinase analysis, treatment of EtOH decreased the immunoreactivity of the active form of epidermal growth factor receptor (180 kDa) in the stomach. In conclusion, EtOH feeding caused a time-dependent alteration of epidermal growth factor receptor in the stomach, which may be one of the mechanisms underlying the gastric pathology associated with alcohol abuse.

Chronic ethanol feeding alters the structure and function of the epidermal growth factor receptor in rat stomach

We investigated the effect of chronic ethanol feeding on the EGF receptor in rat stomach. Adult male rats were fed either an isocaloric control or ethanol (EtOH)-containing liquid diet (36% total calories as EtOH) for 4 weeks EtOH significantly reduced the specific binding of 125I-EGF to the gastric mucosal membrane (control vs. EtOH, 2.07 +/- 0.2 vs. 0.94 +/- 0.16 fmol/mg protein; p < 0.01). Scatchard analysis suggested that the lower binding might be due to the reduction of EGF receptor number, and/or the affinity of the high-affinity binding site. Western blot analysis, using anti-EGF receptor antibody, revealed four immunoreactive protein bands (180, 150, 60, and 50 kDa) in the lectin-purified gastric membrane prepared from both groups. However, the intensities of these protein bands in the EtOH-fed animals were 90% lower compared to the controls. In the EGF-responsive protein kinase assay, 32P-ATP was incubated with lectin-purified samples in the absence or presence of 1 microM EGF. EGF stimulated autophosphorylation of the EGF receptor (180 kDa) in stomach from the control groups, but not the EtOH-fed animals. This EtOH-related alteration of the gastric EGF receptor may be one of the mechanisms underlying the gastric pathology associated with alcohol abuse.

Effect of epidermal growth factor on Cu, Zn-superoxide dismutase expression in cultured fibroblasts from rat skin

The effects of epidermal growth factor (EGF) on Cu, Zn-superoxide dismutase (SOD) in cultured fibroblasts from rat skin exposed to superoxide anions were studied. Cross-linking of [125I]hEGF using disuccinimidyl suberate and immunoblot analysis using anti-EGF receptor antibody to crude plasma membrane fractions of fibroblasts showed that a 170 kDa EGF receptor protein was present on the membrane, as in A431 cells which over express a specific EGF receptor. The cytosolic SOD enzyme activity in fibroblasts exposed to superoxide anions 24 h after treatment with EGF plus nafamostat (NM), a potent protease inhibitor, was increased 1.6-fold compared to control-treated cells. Treatment with either EGF or NM alone, evoked little increase in SOD enzyme activity. The increase in Cu, Zn-SOD protein levels corresponded to the increase in cytosolic SOD enzyme activity in fibroblasts. The Cu, Zn-SOD mRNA level in fibroblasts treated with EGF plus NM at 3 and 6 h was higher than that of the control. Additionally, levels of [125I]hEGF degradation products released into the medium from fibroblasts exposed to superoxide anions were significantly reduced in the presence of NM. These results suggest that the stabilization of EGF by NM in culture is an important factor in the expression of its effects, and that EGF induces Cu, Zn-SOD expression by accelerating transcription of the Cu, Zn-SOD gene in cells, resulting in their protection from the effects of superoxide anion radicals.

Effect of acute ethanol treatment on epidermal growth factor receptor in the rat stomach

The present study investigated the effect of acute ethanol (ETOH) treatment on the epidermal growth factor (EGF) receptor in rat gastric mucosa using two different experimental models. In the in vitro experiments, gastric mucosal cells were incubated with 0, 0.05, 0.1, 0.25, and 0.5% ethanol in Dulbecco's modified Eagle's medium (DMEM) for 30 min and then used for the membrane preparation. The EGF receptor binding assay indicated that cells incubated in the presence of ethanol displayed a concentration-dependent increase (r = 0.85) in the 125I-EGF binding. The Western blot analysis using anti-EGF-receptor antibody revealed that ethanol in vitro caused reduction in the immunoreactivity of the major 170-kDa protein. There were also alterations in the minor protein bands (140, 120, and 50 kDa). In the in vivo experiments, rats that fasted overnight were given 1.0 ml of saline or ethanol (5, 10, or 15%) by gastric intubation 30 min before sacrifice. In comparison with the saline controls, ethanol treatment caused a decrease of the EGF receptor binding to the gastric mucosal membrane (saline: 5%: 10%; 15% ETOH, 1.46 +/- 0.18: 1.13 +/- 0.17: 1.27 +/- 0.19: 0.84 +/- 0.14, p < 0.02; mean +/- SEM, n = 9). Furthermore, the immunoblot analysis revealed concentration-dependent decrease in the intensity of the major 170-kDa protein with ethanol. The reduction in the EGF receptor binding and the impairment of the receptor protein might be due to the nonspecific damage of the gastric mucosal membrane by ethanol.