High Doses Of Epidermal Growth Factor Research Articles

Modulation of hepatitis B virus infection by epidermal growth factor secreted from liver sinusoidal endothelial cells

Hepatocytes derived from human iPSCs are useful to study hepatitis B virus (HBV) infection, however infection efficiency is rather poor. In order to improve the efficiency of HBV infection to iPSC-derived hepatocytes, we set a co-culture of hepatocytes with liver non-parenchymal cells and found that liver sinusoidal endothelial cells (LSECs) enhanced HBV infection by secreting epidermal growth factor (EGF). While EGF receptor (EGFR) is known as a co-receptor for HBV, we found that EGF enhanced HBV infection at a low dose of EGF, whereas EGF at a high dose suppressed HBV infection. EGFR is internalized by clathrin-mediated endocytosis (CME) and clathrin-independent endocytosis (CIE) pathways depending on the dose of EGF. At a high dose of EGF, the endocytosed EGFR via CIE is degraded in the lysosome. This study is the first to provide evidence that HBV is endocytosed via CME and CIE pathways at a low and high dose of EGF, respectively. In conclusion, we developed an in vitro system of HBV infection using iPSC-derived liver cells, and show that EGF secreted from LSECs modulates HBV infection in a dose dependent manner.

P38 MAP kinase enhances EGF-induced apoptosis in A431 carcinoma cells by promoting tyrosine phosphorylation of STAT1

While epidermal growth factor (EGF) is a well known mitogen, high doses of EGF result in a paradoxical apoptotic response in the cells that overexpress EGF receptor such as A431 epidermoid carcinoma cells. EGF-induced apoptosis in A431 cells is dependent upon activation of transcription factor STAT1. In this study, we demonstrate that p38 MAP kinase is another important mediator of EGF-dependent pro-apoptotic response in A431 cells. By utilizing p38 MAP kinase inhibitors, SB203580 and BIRB0796, we significantly reduced the integral growth-inhibiting as well as pro-apoptotic effects of EGF. Moreover, we observed that inhibition of p38 MAP kinase markedly decreased phosphorylation of tyrosine 701 in STAT1, while neither EGF-induced accumulation nor serine phosphorylation of STAT1 was decreased. We propose that p38 MAP kinase mediates STAT1 tyrosine phosphorylation, thereby enforcing EGF-induced apoptosis.

Compartmentalization of epidermal growth factor receptor in liver plasma membrane

We have investigated epidermal growth factor (EGF)-induced compartmentalization and activation of the EGF receptor (EGFR) in rat liver plasma membrane (PM) raft subfractions prepared by three different biochemical methods previously developed to characterize the composition of membrane rafts. Only detergent-resistant membranes (DRMs) possessed the basic characteristics attributed to membrane rafts. Following the administration of a low dose of EGF (1 microg/100 g BW) the content of EGFR in PM-DRMs did not change significantly; whereas after a higher dose of EGF (5 microg/100 g BW) we observed a rapid and marked disappearance of EGFR (around 80%) from both PM and DRM fractions. Interestingly, following the administration of either a low or high dose of EGF, the pool of EGFR in the PM-DRM fraction became highly Tyr-phosphorylated. In accordance with the higher level of EGFR Tyr-Phosphorylation, EGF induced an augmented recruitment of Grb2 and Shc proteins to PM-DRMs compared with whole PM. Furthermore neither high nor low doses of EGF affected the caveolin content in DRMs and PM. These observations suggest that EGFR located in DRMs are competent for signaling, and non-caveolae PM rafts are involved in the compartmentalization and internalization of the EGFR.

Effect and mechanism of epidermal growth factor on proliferation of GL15 gliomas cell line

The effects of epidermal growth factor (EGF) on proliferation of G15 glioma cells and the possible mechanisms were investigated. GFAP and EGFR expression was detected by immunohistochemical method. After the cells were treated with EGF at different concentrations, cell count method was used to determine the proliferation of glioma cells, cell cycle and apoptosis were analyzed by flow cytometry (FCM), and laser scan confocal microscope (LSCM) was used to measure the cytoplasmic free calcium. The results showed that GFAP was diffusedly expressed in GL15 cells and EGFR was over-expressed. EGF at doses of < or =1 ng/mL could significantly stimulate cell proliferation, cells in phase G0/G1 decreased, and those in phase S increased. EGF at doses of 10 and 100 ng/ml could inhibit the cell proliferation significantly, and the apoptosis ratio in high dose of EGF group was higher than in control group. EGF could significantly induce a quick rise of intracellular free calcium, but the peak value of intracellular free calcium activated by high dose of EGF was higher than by low dose of EGF. It was suggested that EGF had a dual effect on gliomas: low dose of EGF could stimulate the cell proliferation of gliomas, but high dose of EGF could induce the cell apoptosis and inhibit the proliferation of gliomas, which might be contributed to the difference of intracellular free calcium.

Keratinocyte Growth Inhibition by High-Dose Epidermal Growth Factor Is Mediated by Transforming Growth Factor β Autoinduction: A Negative Feedback Mechanism for Keratinocyte Growth

The epidermal growth factor receptor and its ligands initiate a major signaling pathway that regulates keratinocyte growth in an autocrine manner. It is well known that high doses of epidermal growth factor receptor ligands inhibit keratinocyte growth. Recently, signal transducers and activators of transcription 1-dependent p21Waf1/Cip1 induction were reported to be involved in high-dose epidermal growth factor-dependent cell growth arrest in the A431 squamous cell carcinoma cell line; however, transfection of dominant-negative signal transducers and activators of transcription 1 adenovirus vector did not block epidermal growth factor-induced growth inhibition in normal human keratinocytes. As transforming growth factor beta is a potent inhibitor of keratinocyte proliferation, we hypothesized that transforming growth factor beta contributes to epidermal growth factor-mediated keratinocyte growth inhibition. Epidermal growth factor concentrations of 10 ng per ml enhanced transforming growth factor beta1 mRNA expression from 3 to 6 h poststimulation. Enzyme-linked immunosorbent assay analysis detected 150 pg per ml of transforming growth factor beta1 in the culture medium of keratinocytes incubated with 10 and 100 ng per ml epidermal growth factor, whereas 0.1 and 1.0 ng per ml epidermal growth factor slightly enhance transforming growth factor beta1 production. Epidermal growth factor (100 ng per ml) upregulated luciferase activity of p3TP-lux, which contains three tandem transforming growth factor beta-Smad signaling responsive elements, 6-fold compared with unstimulated cells. The epidermal growth factor-dependent induction of p3TP-lux luciferase activity was disrupted by transfection of the dominant negative form of transforming growth factor beta type I receptor adenovirus vector (AxdnALK5), which suggests that epidermal growth factor-induced transforming growth factor beta acts in an autocrine manner in keratinocytes. Moreover, transfection of AxdnALK5 completely blocked the growth inhibition induced by 100 ng per ml of epidermal growth factor in normal keratinocytes. These data demonstrate that an autocrine transforming growth factor beta1-ALK5 pathway is a negative feedback mechanism for epidermal growth factor-induced normal human keratinocyte growth.

The beta 1 isoform of protein kinase C mediates the protective effects of epidermal growth factor on the dynamic assembly of F-actin cytoskeleton and normalization of calcium homeostasis in human colonic cells.

Using intestinal monolayers, we showed that F-actin cytoskeletal stabilization and Ca(2+) normalization contribute to epidermal growth factor (EGF)-mediated protection against oxidant injury. However, the intracellular mediator responsible for these protective effects remains unknown. Since the protein kinase C-beta1 (PKC-beta1) isoform is abundant in our naive (N) cells, we hypothesized that PKC-beta1 is essential to EGF protection. Monolayers of N Caco-2 cells were exposed to H(2)O(2) +/- EGF, PKC, or Ca(2+) modulators. Other cells were transfected to over-express PKC-beta1 or to inhibit its expression and then pretreated with low or high doses of EGF or a PKC activator, OAG (1-oleoyl-2-acetyl-sn-glycerol), before H(2)O(2). In N monolayers exposed to oxidant, pretreatment with EGF or PKC activators activated PKC-beta1, enhanced (45)Ca(2+) efflux, normalized Ca(2+), decreased monomeric G-actin, increased stable F-actin, and protected the cytoarchitecture of the actin. PKC inhibitors prevented these protective effects. Transfected cells stably over-expressing PKC-beta1 (+3.1-fold) but not N cell monolayers were protected from injury by even lower doses of EGF or OAG. EGF or OAG rapidly activated the over-expressed PKC-beta1. Antisense inhibition of PKC-beta1 expression (-90%) prevented all measures of EGF protection. Inhibitors of Ca(2+)-ATPase prevented EGF protection in N cells as well as protective synergism in transfected cells. EGF protects the assembly of the F-actin cytoskeleton in intestinal monolayers against oxidants in large part through the activation of PKC-beta1. EGF normalizes Ca(2+) by enhancing Ca(2+) efflux through PKC-beta1. We have identified novel biologic functions, protection of actin and Ca(2+) homeostasis, among the classical isoforms of PKC.

PKC-zeta is required in EGF protection of microtubules and intestinal barrier integrity against oxidant injury.

Using monolayers of human intestinal (Caco-2) cells, we showed that epidermal growth factor (EGF) protects intestinal barrier integrity against oxidant injury by protecting the microtubules and that protein kinase C (PKC) is required. Because atypical PKC-zeta isoform is abundant in wild-type (WT) Caco-2 cells, we hypothesized that PKC-zeta mediates, at least in part, EGF protection. Intestinal cells (Caco-2 or HT-29) were transfected to stably over- or underexpress PKC-zeta. These clones were preincubated with low or high doses of EGF or a PKC activator [1-oleoyl-2-acetyl-sn-glycerol (OAG)] before oxidant (0.5 mM H(2)O(2)). Relative to WT cells exposed to oxidant, only monolayers of transfected cells overexpressing PKC-zeta (2.9-fold) were protected against oxidant injury as indicated by increases in polymerized tubulin and decreases in monomeric tubulin, enhancement of architectural stability of the microtubule cytoskeleton, and increases in monolayer barrier integrity toward control levels (62% less leakiness). Overexpression-induced protection was OAG independent and even EGF independent, but EGF significantly potentiated PKC-zeta protection. Most overexpressed PKC-zeta (92%) resided in membrane and cytoskeletal fractions, indicating constitutive activation of PKC-zeta. Stably inhibiting PKC-zeta expression (95%) with antisense transfection substantially attenuated EGF protection as demonstrated by reduced tubulin assembly and increased microtubule disassembly, disruption of the microtubule cytoskeleton, and loss of monolayer barrier integrity. We conclude that 1) activation of PKC-zeta is necessary for EGF-induced protection, 2) PKC-zeta appears to be an endogenous stabilizer of the microtubule cytoskeleton and of intestinal barrier function against oxidative injury, and 3) we have identified a novel biological function (protection) among the atypical isoforms of PKC.

PKC-beta1 mediates EGF protection of microtubules and barrier of intestinal monolayers against oxidants.

Using monolayers of human intestinal (Caco-2) cells, we found that oxidants and ethanol damage the cytoskeleton and disrupt barrier integrity; epidermal growth factor (EGF) prevents damage by enhancement of protein kinase C (PKC) activity and translocation of the PKC-beta1 isoform. To see if PKC-beta1 mediates EGF protection, cells were transfected to stably over- or underexpress PKC-beta1. Transfected monolayers were preincubated with low or high doses of EGF (1 or 10 ng/ml) or 1-oleoyl-2-acetyl-sn-glycerol [OAG; a PKC activator (0.01 or 50 microM)] before treatment with oxidant (0.5 mM H(2)O(2)). Only in monolayers overexpressing PKC-beta1 (3.1-fold) did low doses of EGF or OAG initiate protection, increase tubulin polymerization (assessed by quantitative immunoblotting) and microtubule architectural integrity (laser scanning confocal microscopy), maintain normal barrier permeability (fluorescein sulfonic acid clearance), and cause redistribution of PKC-beta1 from cytosolic pools into membrane and/or cytoskeletal fractions (assessed by immunoblotting), thus indicating PKC-beta1 activation. Antisense inhibition of PKC-beta1 expression (-90%) prevented these changes and abolished EGF protection. We conclude that EGF protection against oxidants requires PKC-beta1 isoform activation. This mechanism may be useful for development of novel therapies for the treatment of inflammatory gastrointestinal disorders including inflammatory bowel disease.

Effect of topical administration of epidermal growth factor on healing of corneal epithelial defects in horses

OBJECTIVE-To characterize healing of corneal epithelial defects in horses and to evaluate the ability of epidermal growth factor (EGF) to modulate rate of corneal epithelial healing in horses. 20 eyes in 12 adult horses. Corneal epithelial wounds were created by mechanically debriding the limbus. Corneal healing was recorded for 3 treatment groups: 50 microg of EGF/ml (n = 5 eyes), 5 microg of EGF/ml (7), and PBS solution (8). Corneal healing was recorded once daily after instillation of fluorescein stain by use of photography and calculating the area of the wound, using imaging software. After corneal debridement, re-epithelialization was rapid and progressed in a linear fashion for the first 5 to 7 days after surgery in all groups. After that period, rates of healing decreased. A profound increase in the degree of inflammation, neovascularization, melanosis, and scarring was observed in eyes treated with the high dose of EGF (50 microg/ml), but there was not a statistical difference in mean healing time or in mean decrease in radius during the linear phase between the control and either EGF treatment groups. However, for all 8 horses in which both eyes were debrided, the first eye healed significantly faster than the second eye, regardless of treatment. Beneficial effects of topical administration of a high dose of EGF for acceleration of healing of corneal defects in eyes of horses are outweighed by the intensity of the associated inflammatory response.

Epidermal growth factor secreted from submandibular salivary glands interferes with the lipolytic effect of adrenaline in mice.

We had described that epidermal growth factor (EGF) interfered with the lipolytic effect of catecholamines in isolated adipocytes. Since catecholamines stimulate the release of EGF from submandibular salivary glands to blood plasma in male mice, we studied whether EGF affected also the lipolytic response to adrenaline in whole animals. We studied the effect of adrenaline in sialoadenectomized and sham-operated mice receiving or not a high dose of EGF following adrenaline injection. There was no difference in plasma EGF concentration between sham-operated and sialoadenectomized animals receiving saline. After adrenaline administration plasma EGF increased by 20-fold in sham-operated but did not increase in sialoadenectomized mice. Indeed, the increase was much higher (more than 100-fold) in mice receiving exogenous EGF. The effect of adrenaline on plasma concentration of both glycerol and nonesterified fatty acids was higher as lower was plasma EGF concentration. Isolated adipocytes obtained from sham-operated or sialoadenectomized mice had identical lipolytic response to adrenaline. The lipolytic response of adipocytes to isoproterenol was decreased by addition of EGF. To study whether the interference with the in vivo lipolytic effect of adrenaline had further metabolic consequences, we measured plasma beta-hydroxybutyrate concentration in plasma. There was no difference in the response to adrenaline between sham-operated and sialoadenectomized mice in spite of the difference in plasma nonsterified fatty acid concentration. Studies in isolated hepatocytes indicated that ketogenesis run at near maximal rate in this range of substrate concentration. These results suggest that EGF in the physiological range decreases the lipolytic effect of adrenaline but does not compromise further metabolic events like the enhancement of ketogenesis.

Epidermal Growth Factor Secreted from Submandibular Salivary Glands Interferes with the Lipolytic Effect of Adrenaline in Mice

We had described that epidermal growth factor (EGF) interfered with the lipolytic effect of catecholamines in isolated adipocytes. Since catecholamines stimulate the release of EGF from submandibular salivary glands to blood plasma in male mice, we studied whether EGF affected also the lipolytic response to adrenaline in whole animals. We studied the effect of adrenaline in sialoadenectomized and sham-operated mice receiving or not a high dose of EGF following adrenaline injection. There was no difference in plasma EGF concentration between sham-operated and sialoadenectomized animals receiving saline. After adrenaline administration plasma EGF increased by 20-fold in sham-operated but did not increase in sialoadenectomized mice. Indeed, the increase was much higher (more than 100-fold) in mice receiving exogenous EGF. The effect of adrenaline on plasma concentration of both glycerol and nonesterified fatty acids was higher as lower was plasma EGF concentration. Isolated adipocytes obtained from sham-operated or sialoadenectomized mice had identical lipolytic response to adrenaline. The lipolytic response of adipocytes to isoproterenol was decreased by addition of EGF. To study whether the interference with the in vivo lipolytic effect of adrenaline had further metabolic consequences, we measured plasma β-hydroxybutyrate concentration in plasma. There was no difference in the response to adrenaline between sham-operated and sialoadenectomized mice in spite of the difference in plasma nonsterified fatty acid concentration. Studies in isolated hepatocytes indicated that ketogenesis run at near maximal rate in this range of substrate concentration. These results suggest that EGF in the physiological range decreases the lipolytic effect of adrenaline but does not compromise further metabolic events like the enhancement of ketogenesis.

Up-regulation of alpha 2 beta 1 integrin cell-surface expression protects A431 cells from epidermal growth factor-induced apoptosis.

High epidermal growth factor (EGF) concentration (10(-8) M) induces inhibition of A431 cell proliferation, resulting in part from an apoptotic process. For some cells escaping this process, proliferation was associated with a decrease in apoptosis. Moreover, these surviving cells displayed marked morphological changes consisting of filopodia formation and cell aggregation. Disrupting cell-cell contacts by lowering extracellular calcium concentration reversed the resistance process, suggesting that apoptosis protection by aggregation may involve intercellular adhesion and cell-cell survival signals probably mediated by calcium-requiring molecules such as integrins. From a panel of integrins tested, only alpha 2 beta 1 integrin cell-surface expression was up-regulated after high apoptotic EGF treatment, and this up-regulation was not observed under a growth-stimulatory EGF concentration (10(-11) M). Double-labeling analysis (alpha 2 beta 1/DNA) implicated alpha 2 beta 1 integrin in the resistance process since 99% of cells that up-regulated alpha 2 beta 1 integrin survived a high dose of EGF. Moreover, the involvement of alpha 2 beta 1 integrin up-regulation in the survival of A431 cells that escape EGF-induced apoptosis was verified using the blocking anti-alpha 2 beta 1 integrin antibody, which was shown to decrease the survival of EGF-stimulated cells. Furthermore, under our culture conditions, alpha 2 beta 1 integrin-dependent cell-cell adhesion can be inhibited without affecting other cell-adhesive interactions, suggesting that alpha 2 beta 1 integrin is involved more directly in cell-cell interaction than in cell-substrate adhesion. Our results provide evidence that EGF-induced up-regulation of alpha 2 beta 1 integrin contributes to the enhancement of cell-cell adhesion, leading to cell aggregate formation, which permits the escape of A431 cells to EGF-induced death by alpha 2 beta 1 integrin signaling.

The Effect of Different Doses of Epidermal Growth Factor on Liver Ornithine Decarboxylase and Na-K ATPase Activities in Newborn Rats

1. Ornithine decarboxylase and Na-K ATPase activities were studied in rat livers that were treated with different doses of epidermal growth factor (EGF). 2. The ornithine decarboxylase activities were studied with spectrophotometry, and results were expressed as micromoles of putrescine per hour per milligram of protein. Na-K ATPase activities were studied on the basis of the principle of measuring the amount of inorganic phosphates released by the hydrolysis of ATP, and the results were expressed as micromoles of inorganic phosphate per hour per milligram of protein. 3. When compared with the controls, although the Na-K ATPase activities were decreased at low doses of EGF, their activities were found to be increased at high doses of EGF. On the other hand, there was a positive correlation between ornithine decarboxylase activities and EGF doses. 4. The results of this study suggest that, whereas the decrease in Na-K ATPase activities at low doses of EGF can be due to the utilization of the enzyme, the increase in Na-K ATPase activities at high doses of EGF can be attributed to its enhanced synthesis.

Cellular Hyperplasia in Rats Following Continuous Intravenous Infusion of Recombinant Human Epidermal Growth Factor

In this study, we determined in vivo morphologic effects of continuous intravenous infusion of recombinant human epidermal growth factor (EGF) in adult Wistar rats. The EGF used consisted of the amino acid residues 1-48 of the human 53-amino-acid EGF molecule, purified from transfected Escherichia coli. Doses of 25, 100, or 250 micrograms/kg body weight were administered using Harvard digital syringe infusion pumps for 4 weeks. At necropsy, the submandibular salivary glands, Harderian glands, liver, kidneys (females only), and ovaries were enlarged and urinary bladders were thickened in 100- and 250-micrograms/kg rats. Numerous tissues of the 100- and 250-micrograms/kg rats contained hyperplastic epithelial cells, and selected organs also had mesenchymal cell proliferation. Epithelial proliferation was most pronounced in the trachea, nasal cavity, nasolacrimal duct, tongue, stomach, small intestine, large intestine, urinary tract, salivary gland ducts, and Harderian gland. Periportal hepatocytes were hypertrophic, correlating with increased liver weight. In addition, mesenchymal cell proliferation was evident in the gastric mucosa lamina propria and in heart valves in 100- and 250-micrograms/kg rats. Increased ovarian weight correlated with increased number and size of corpora lutea and an increased incidence of luteal cysts. Continuous systemic exposure of adult Wistar rats to high doses of EGF resulted in generalized epithelial hyperplasia and tissue-selective mesenchymal proliferation.

EGF causes hyperproliferation and apoptosis in T51B cells: Involvement of high and low affinity EGFR binding sites

We have recently described an in vitro model for liver homeostasis which involves growing T51B rat liver epithelial cells with 1 nM epidermal growth factor (EGF). There is an initial period of hyperplasia, lasting about 3 days, which is followed by an increase in apoptosis. The cell density returns to around the confluent control level 5 days after EGF addition. The dose response of T51B cells to EGF shows three distinct growth patterns. We have carried out EGF binding studies that suggest that the occupancy of the low affinity binding site of the EGF receptor, is responsible for the hyperproliferation seen when the cells are grown with high doses of EGF. These studies also suggest that the apoptosis could be triggered by down-regulation of the receptor, in a manner analogous to the removal of a trophic hormone in other systems.

Fluid balance, electrolyte profiles and plasma parathyroid hormone concentrations in ewes treated with epidermal growth factor

The infusion of low doses of epidermal growth factor (EGF) into lactating ewes stimulates water intake and urine volume. The plasma concentrations and daily output of various electrolytes in milk and urine are also affected. We have investigated this further by recording the effects of EGF infusion on fluid balance, electrolyte profiles and plasma concentrations of glucose and parathyroid hormone (PTH) in non-pregnant, non-lactating ewes. Twenty-four animals (n = 8 per group) received infusions of 100 ml saline/day into the jugular vein for 10 days (days 1-10) followed by EGF at a dose rate of either 1 (low dose), 5 (medium dose) or 10 (high dose) micrograms/kg liveweight per day in 100 ml saline for 5 days (days 11-15). All ewes then received an infusion of 100 ml saline/day for 10 days (days 16-25). Most plasma and urine samples had undetectable concentrations of EGF-immunoreactive material during the periods of saline infusion. During EGF infusion, the highest amounts of EGF infusate excreted in urine were 1.6, 5.9 and 5.6% for ewes in low, medium and high dose groups respectively. Water intake increased by 17% (0.5 kg), 88% (2.5 kg) and 89% (2.3 kg) and urine volume increased by 29% (0.5 kg), 108% (2.2 kg) and 134% (2.1 kg) for the three groups respectively. Fluid balance and feed intake were not affected by EGF infusion, but the output of faecal dry matter was reduced in ewes receiving the two higher doses of EGF. All levels of EGF resulted in hypocalcaemia, increased plasma PTH concentrations and hypermagnesaemia. There was no effect of EGF on plasma concentrations of K+ and glucose or on daily urinary excretion of K+ and Mg2+. The only response to the low dose was a reduced plasma concentration of Na+ and an increased daily urinary urate excretion. The two higher doses increased the daily urinary excretion of Na+, PO4(3-) and urate, but had no effect on the respective concentrations in plasma. Urinary Ca2+ excretion was reduced only during infusion of the medium dose of EGF. The responses of most variables were similar during infusion of the medium and high doses of EGF. All three doses of EGF induced polydipsic and diuretic responses in ewes, and infusions of 5-10 micrograms EGF/kg liveweight per day affected renal excretion of Ca2+, Na+ and PO4(3-). We interpret the responses of the kidney and plasma PTH concentrations as a means of maintaining the homeostasis of plasma profiles of electrolytes.

The effects of intracolonic EGF on mucosal growth and experimental carcinogenesis

Although intra-luminal epidermal growth factor (EGF) may stimulate cell proliferation in the upper gastrointestinal tract, its role in the large bowel has not been established. We have therefore studied the effect of intra-rectal EGF administration on both normal growth and carcinogenesis in the rat colon. Colonic cancer was induced in rats with azoxymethane (10 mg kg-1 week-1 for 12 weeks s.c.) and controls dosed with saline. In each group, animals were randomised to receive EGF (12 nM, 0.8 nM or saline control) in 0.5 ml saline via a rectal tube daily for 24 weeks. At this time, crypt cell production rates (CCPRs) were determined at two sites in the colon: one of maximal and another of minimal exposure to EGF (5 cm and 10 cm from the anal margin respectively). No effects of EGF were seen at 10 cm. The lower dose of EGF gave CCPRs that mirrored the control values. The higher dose of EGF in the animals not treated with azoxymethane stimulated mucosal growth. Azoxymethane increased in CCPR, but this was suppressed by the high dose of EGF. These results suggest that (1) luminal EGF and azoxymethane independently increase the colonic CCPR and their combined effect is not synergistic but antagonistic; (2) EGF may have a role in normal epithelial growth, but does not potentiate colonic carcinogenesis in this model.

Epidermal Growth Factor (EGF) Receptors in Human Chorionic Gonadotropin-Producing Tumor: Transplantation in Nude Mice and the Effect of EGF on Tumor Growth

We examined the presence and characteristics of epidermal growth factor (EGF) receptors in hCG producing tumors (CC-2-JCK) transplanted in female nude mice. We also examined the in vivo effects of EGF on tumor growth. Specific receptors with apparent dissociation constants of 3.89 x 10(-10) and 1.0 x 10(-9) M and binding capacities of 5.96 x 10(-10) and 1.52 x 10(-9) M/mg protein for EGF have been identified in the hCG-producing tumor. [125I]EGF binding to the tumor tissues was time, temperature, and tissue weight dependent and specific. EGF and transforming growth factor-alpha (TGF alpha) competed for [125I]EGF binding, with 50% of the bound [125I]EGF displaced by approximately 0.52 nM EGF and 3.10 nM TGF alpha. TGF beta competed for [125I]EGF binding slightly. Five micrograms of EGF caused an increase in the rate of tumor growth, while 50 micrograms EGF strongly inhibited tumor growth. The concentration of [125I]EGF binding in the tumor treated with low doses of EGF was high, and that in the tumor treated with high doses of EGF was low. These changes in EGF binding were attributable to the changes in the number of high affinity EGF receptors with no significant alteration in binding affinity. In conclusion, the existence of high concentrations of EGF receptors with high affinity and specificity to EGF was demonstrated in an hCG-producing tumor transplanted in nude mice and appeared to be correlated with tumor growth.

Epidermal growth factor: a critical factor in fetal maturation?

Epidermal growth factor (EGF) infused over 3-14 days into fetal sheep of 110-125 days gestation resulted in a number of morphological and endocrine changes. Striking hypertrophy of the skin, wool follicles and their accessory structures was seen, together with a reduction in the ratio of secondary to primary follicles and degenerative changes in wool fibres associated with shedding of fibres. Adrenal, thyroid, liver and kidney weights were increased while thymus weight was decreased. The increase in adrenal size resulted from cortical hypertrophy and was associated with increased cortisol secretion. Thyroid hypertrophy was accompanied by an increase in colloid stores, decreased plasma thyroxine and reverse triiodothyronine (T3) concentrations, unchanged plasma T3 and thyroid-binding globulin and raised thyrotropin (TSH) levels. Thyrotropin receptor affinity and content per gram of tissue were unchanged. Fetal and maternal plasma prolactin and growth hormone levels, and fetal plasma placental lactogen levels, were unchanged, although there was a significant rise in maternal plasma placental lactogen concentrations with high doses of EGF. Other maturational parameters such as switching from fetal to adult haemoglobin and liver glycogen content were unaffected.