Characterization of epidermal growth factor receptor in rat buccal mucosal cells

Upregulation of endothelin-1 binding in tissues of salt-loaded stroke-prone spontaneously hypertensive rats

Upon maintained on a 1% NaCl drinking solution beginning at 7 weeks of age, the stroke-prone spontaneously hypertensive rat (SHRsp) developed severe hypertension and stroke; most died by 16 weeks. The mechanism by which these diseases evolve remains unclear. Endothelin-1 (ET-1) is a potent, peptidic vasoconstrictor and is implicated in the pathogenesis of various cardiovascular, renal, and central nervous system diseases. The purpose of the present study was to compare the binding of [125I]ET-1 to the brain, heart, kidney, liver, and spleen membrane preparations of 16-week-old SHRsp and age-matched normotensive Wistar-Kyoto rats (WKY). The KD values for [125I]ET-1 binding to the corresponding tissues of the two strains were not significantly different, except in the brain (SHRsp: 17 +/- 1 pM; WKY: 24 +/- 1 pM). In contrast, the Bmax values measured in the brain, heart, kidney, and liver of SHRsp were 1.5- to 2.1-fold greater than those of their WKY counterparts. Competition of [125I]ET-1 binding to the membrane preparations by the specific ETA receptor antagonist BQ-123 or the specific ETB receptor agonist sarafotoxin S6c revealed a similar proportion of ETA and ETB receptor subtypes in the corresponding tissues of the two rat strains. These results indicate that ET-1 binding is upregulated in SHRsp and suggest that ET-1 may play a pathophysiological role in this animal model of genetic hypertension.

Effects of in vivo treatments of nicotine and benzo[a]pyrene on the epidermal growth factor receptor in hamster buccal pouch

This study was conducted to investigate the effects of two major ingredients in cigarette smoke, benzo-alpha-pyrene (BP) and nicotine (Nic), on epidermal growth factor (EGF) receptor in hamster buccal pouch. Adult male Syrian hamsters were treated by apically swabbing the buccal pouch with mineral oil (Control), 0.5 microgram/ml of BP, Nic or BP+Nic in mineral oil, twice a day, 5 days a week for 4 weeks. The BP+Nic treatment resulted in a significant reduction of submandibular gland (SG) EGF (Control vs. BP+Nic, 6.93 +/- 1.31 vs. 4.77 +/- 0.26* ng/g wet tissue, mean +/- S.D., n=5,*P < 0.05). Treatment with BP or Nic also caused a reduction, although not statistically significant, of EGF in SG extract. For the receptor study, all treatments significantly increased [125I]EGF binding to membrane preparations of buccal pouch as compared to Control (Control, BP, Nic, BP+Nic; 12.2 +/- 0.9, 20.5 +/- 2.2*, 17.0 +/- 1.3*, 21.2 +/= 1.6* fmol/mg prot. (mean +/- S.E.M.), n=5, P < 0.05). Scatchard analysis revealed that the higher EGF binding to the BP+Nic-treated sample was due to the higher number of receptors, but not higher affinity. Data from protein kinase study indicate that EGF stimulated phosphorylation of 170- and 150-kDa proteins in buccal membrane preparations. Treatment of BP+Nic resulted in reductions in EGF-stimulated phosphorylation of 170- and 150-kDa proteins by 19 and 72%, respectively. The present study has established an animal model which will benefit investigation of the mechanism by which tobacco alters the EGF receptor in oral buccal mucosa.

Biochemical characterization of epidermal growth-factor receptor in Syrian hamster buccal pouch

Binding of [125I]-epidermal growth factor (EGF) to the membrane of the adult hamster buccal pouch was specific and protein concentration dependent, and was significantly higher than that of rat buccal tissue (hamster versus rat; 12.1 +/- 0.9 versus 9.77 +/- 0.22 fmol/mg protein, mean +/- SD, n = 5, p < 0.01). The higher binding was due to a higher receptor number (Bmax). Western blot analysis using anti-EGF receptor antibody revealed four immunoreactive protein bands of 170, 150, 116 and 55 kDa in hamster buccal membrane preparations. In a separate experiment, the EGF concentration in the phosphate-buffered saline extract of the hamster submandibular gland was determined by radioimmunoassay; the level was significantly much lower (p < 0.01) than that of rat or mouse (hamster, rat, mouse; 24.2 +/- 2.6, 123 +/- 17, 5950 +/- 171 ng/g wet tissue; mean +/- SD, n = 3). The findings suggest that hamster buccal pouch is particularly well suited to the study of the biological functions of oral EGF receptor.

Activation of dihydropyridine-sensitive parotid salivary gland calcium channels by epidermal growth factor

The calcium channel complex of the parotid was isolated from solubilized acinar-cell membranes by affinity chromatography on wheatgerm agglutinin. The channel, after labelling the calcium antagonist-receptor site with [3H]-PN200-100, was reconstituted into phosphatidylcholine vesicles that exhibited active 45Ca2+ uptake. This uptake was independent of sodium and potassium gradients, indicating its electroneutrality. The channels responded in a dose-dependent manner to the dihydropyridine calcium antagonist, PN200-110, which at 0.4 microM exerted a maximal inhibitory effect of 75% on 45Ca2+ uptake; a 46% enhancement in 45Ca2+ uptake occurred with a specific calcium-channel activator, BAY K8644. On epidermal growth-factor (EGF) binding in the presence of ATP, there was an increase in tyrosine phosphorylation of 55 and 170 kDa calcium-channel proteins. Such phosphorylated channels, after reconstitution into vesicles, displayed a 61% greater 45Ca2+ uptake, indicating the involvement of tyrosine kinase in EGF-dependent activation of the calcium channel. The results point towards the importance of EGF in the regulation of calcium homeostasis in salivary gland.

Effect of cigarette smoking on salivary epidermal growth factor (EGF) and EGF receptor in human buccal mucosa

The mouth acts as a primary target for cigarette smoke which is associated with several oral diseases and cancer. The present study investigated the effect of cigarette smoking on salivary EGF and the buccal EGF receptor. Samples of whole saliva and buccal biopsy were obtained from 15 healthy volunteers (10 smokers and 5 non-smokers). The smokers smoked 20 or more cigarettes/day for more than 5 years. Salivary cotinine (a major metabolite of nicotine) was determined by radioimmunoassay (RIA). The salivary cotinine level was consistent with the self-reported smoking status (smokers, 106-530 ng/ml saliva; non-smokers, < 2 ng/ml saliva). As compared to the non-smokers, the salivary EGF concentration (determined by RIA) was 32% lower in those smokers whose salivary cotinine level was 250 ng/ml or higher (non-smokers, 2.21 +/- 0.16; smokers, 1.57 +/- 0.09 ng/ml saliva; mean +/- S.E.M., P < 0.01). There was no significant difference in 125I-labeled EGF binding to the buccal receptor between the two groups. However, EGF stimulated the autophosphorylation of a 170-kDa protein band in the sample of non-smokers, but not in the smokers. The immunoblot analysis using anti-EGF receptor antibody indicated that the smoking-related deficiency in EGF receptor autophosphorylation was due to the functional alteration of the receptor proteins. In conclusion, cigarette smoking reduces the salivary EGF level and impairs the function of buccal EGF receptor, which may be associated with the pathology of smoking-related oral disease.

Benzo[a]pyrene and nicotine impair epidermal growth factor mediated cellular functions of buccal mucosa

This study investigated the effect of two major ingredients in cigarette smoke, benzo[a]pyrene (BP) and nicotine, on epidermal growth factor (EGF) receptor binding and EGF-mediated cellular functions in rat buccal mucosa. Rat buccal tissue was incubated in DMEM in the absence (control) and presence of 10 microM BP or nicotine for 2.5 h at 25 degrees C. There were no significant differences in [125I]EGF binding to the buccal mucosal membranes between the control and treatment groups. Protein tyrosine kinase assay showed that EGF stimulated phosphorylation of a 170-kDa protein band in the controls, but not in the BP- and nicotine-treated samples. The basal [3H]thymidine incorporations were not significantly different between the groups. Nevertheless, addition of 5 nM EGF increased [3H]thymidine incorporation by 22% in the control, but not in the BP- or nicotine-treated group. The results demonstrate that BP and nicotine change the buccal mucosal functions associated with alteration of EGF receptor.

Structure-function relationships of endothelins, sarafotoxins, and their receptor subtypes

The endothelins (ETs) and sarafotoxins (SRTXs) are two structurally related families of potent vasoactive peptides. Although their physiological functions have yet to be precisely elucidated, it seems likely that the ETs are involved in pathophysiological conditions such as hypertension and heart failure. In this minireview, recent advances in the biochemical characterization of the ET/SRTX system, with special reference to structure-function relationships and ET/SRTX receptor subtypes, are described, as well as the recent cloning and expression of ET receptors.

Enhancement of gastric mucosal epidermal growth factor and platelet-derived growth factor receptor expression by sucralfate

1. The effect of an anti-ulcer agent, sucralfate, on the expression of gastric mucosal epidermal growth factor (EGF) and platelet derived growth factor (PDGF) receptors was investigated. 2. Gastric mucosal cell membranes, isolated from the stomach of groups of rats, one receiving twice daily for 3 consecutive days a dose of 100 mg/kg sucralfate, and the other only the vehicle, were used as source for EGF and PDGF receptors. 3. Binding assays revealed the presence of both types of receptors, activation of which led to the elevation of tyrosine kinase activity as evidenced by a marked increase in membrane protein tyrosine phosphorylation patterns. 4. The specific receptor binding in the control group was 2.46 fmol/mg protein for EGF and 1.46 fmol/mg protein for PDGF, whereas the respective binding values in the sucralfate treated group increased by 61 and 65%. 5. The results suggest that sucralfate is capable of enhancement of epithelial proliferative activities through the stimulation of gastric mucosal EGF and PDGF receptors.

Kinetic analyses demonstrate that the equilibrium assumption does not apply to [125I]endothelin-1 binding data

The kinetics of [125I]Endothelin-1 ([125I]ET-1) binding were studied using membranes from rat heart, rat lung, rat brain, and porcine vascular smooth muscle at 37 degrees C in 0.05M Tris-HCl buffer (pH = 7.4). The dissociation half-life (t1/2, diss.) for bound [125I]ET-1 was in excess of 30 hours for each tissue studied. Equilibrium-time requirements for proper Scatchard analysis of [125I]ET-1 were also far in excess of 30 hours for each tissue. These data suggest that determination of dissociation constants, Kd, and receptor concentrations, Bmax, by conventional Scatchard analysis is not feasible with [125I]ET-1. Kinetic analyses may provide a more accurate means for determining [125I-ET-1] binding characteristics including Kd and Bmax.

Ethanol-induced structural and functional alterations of epidermal growth factor receptor in buccal mucosa

1. Ethanol treatment caused a 47% decrease in [125I]EGF binding to the membrane preparations of buccal mucosa resulting from the decrease of binding sites rather than the affinity of high affinity receptor. 2. The immunoblot revealed a protein band of 170 kDa in the control sample, while a barely detectable 200 kDa protein was observed in the ethanol-treated sample. 3. Protein kinase assays using [32P]ATP as probe showed an EGF-stimulated phosphorylation band of 170 kDa in the control but not in ethanol-treated sample. 4. Ethanol did not change the basal incorporation of [3H]thymidine and [35S]methionine, but caused a 38% and 57% decrease of EGF-stimulated thymidine and methionine incorporation, respectively. 5. The data suggest that EtOH decreases EGF receptor binding through modification of the receptor molecule, thereby impairing receptor kinase activity and its physiological function.

Identification of epidermal growth factor receptor in human buccal mucosa

EGF receptor was identified and its binding characteristics were determined. Buccal mucosa was obtained from 12 healthy volunteers (6 males and 6 females) and assayed individually for [125I]-EGF binding. The specific binding of [125I]-EGF to the receptor ranged from 2.85 to 6.12 fmol/mg protein. There was no significant difference in binding between male and female (4.31 +/- 0.61 versus 3.94 +/- 0.53 fmol/mg protein; mean +/- SEM). Individual tissue homogenates were pooled for Scatchard analysis and cross-linking experiments. Scatchard analysis produced curvilinear plots with a Kd of 0.71 nM and Bmax of 0.024 pmol/mg protein for the high-affinity binding sites, and Kd of 435 nM and Bmax of 9.92 pmol/mg protein for the low-affinity binding sites. To determine the molecular weight of the EGF receptor, the [125I]-EGF and receptor complex were cross-linked by DSS and subjected to SDS-PAGE. The autoradiogram of the gel revealed one major protein band of 160K and a minor band of 170 K, characteristics shared with the EGF receptors in other tissues. The study is thought to be the first to demonstrate the presence of the EGF receptor in human buccal tissue and to show its biochemical features.