Epidermal growth factor. Characteristics of specific binding in membranes from liver, placenta, and other target tissues

Human placental calcitonin receptors

Receptors for the hypocalcaemic hormone, calcitonin (CT), have been identified in a membrane fraction prepared from term human placentae. Binding of 125I-labelled salmon CT (125I-sCT) to the membranes was time- and temperature-dependent, saturable (Bmax. 58 +/- 11 fmol/mg of protein), of high affinity (Kd 80 +/- 21 pM) and poorly reversible. Species-specific CTs and CT analogues competed for 125I-sCT binding with potencies proportional to their known biological potencies. Various unrelated peptide hormones did not compete, indicating that receptor binding was specific for CT. Photoaffinity labelling using a derivatized biologically active sCT analogue, [Arg11,18,3-nitrophenylazide-Lys14]sCT, identified a receptor component of Mr approximately 85,000, comparable with findings in osteoclasts and other target cells. The presence of CT receptors in the human placenta supports other evidence that CT may have a role in the regulation of placental function.

Development of insulin and epidermal growth factor receptors during the differentiation of rat preadipocytes in primary culture

An homogeneous cell population isolated from the inguinal tissue of 3-day-old rats is able to proliferate in primary culture. In the presence of a physiological concentration of insulin (1.5 nM) it converts into cells exhibiting the morphology and the biochemical characteristics of adipocytes. Insulin and epidermal growth factor (EGF) receptors were studied during both the exponential growth and the adipose conversion phases of these cells. Binding experiments with 125I-labelled peptides were performed directly in the culture dishes. The number of high affinity insulin binding sites increased, during the entire culture period studied, reaching 18 days after plating the value of 10,600 x 2360. Control cells (cultured in the presence of anti-insulin antibody) exhibited an increase of the concentration of insulin binding sites from no more than 500 sites/cell to 6880 +/- 1710 sites/cell between dat 0 and 9 (corresponding to the exponential growth phase); this increase was followed by a rapid reduction in insulin receptors during the stationary phase. The density of EGF binding sites increased between day 0 and 4 (one cell cycle), whether the cells were maintained or not with insulin, and plateaued thereafter. Mature adipocytes freshly isolated from the inguinal tissue of 3-day-old rats had no detectable EGF binding sites, but their content in high affinity binding sites for insulin was similar to that of cells after complete adipocyte conversion in primary culture.

Influence of age on epidermal growth factor receptor level in the rat brain

The influence of age on 125I-epidermal growth factor (EGF) binding to rat brain plasma membranes was investigated. The specific binding of EGF to membranes decreased gradually with age in both male and female rats. There was no significant difference in the specific binding between males and females. Scatchard analysis of the binding data showed that the decrease in EGF binding with age was due to a decrease in the number of EGF receptors.

Epidermal growth factor (EGF) in seminal plasma and prostatic gland: a radioreceptor assay

The binding ability of five different cells in culture to mouse epidermal growth factor (mEGF) was studied. A simple radioreceptor assay (RRA) using normal rat kidney cell (NRK-52E) as a source of EGF receptor was established. Maximal binding capacity and apparent dissociation constant of NRK-52E cell were 3.36 femtomoles of mEGF bound per 10(6) cells and 2.85 x 10(-11) M, respectively. EGF-like activity (EGF-LA) in seminal plasma and in cytosols of prostatic gland and seminal vesicle was 39.6 +/- 9.9 ng/ml, 0.67 +/- 0.10 ng/mg protein (mean +/- SE) and less than 0.2 ng/mg protein, respectively. The EGF-LA in seminal plasma was considered to be derived mainly from prostatic gland because the EGF-LA in cytosol of prostatic gland was higher than that of seminal vesicle.

Epidermal growth factor counteracts the glycogenic effect of insulin in parenchymal hepatocyte cultures

Rat parenchymal hepatocytes in monolayer culture were used to study the metabolic effects of epidermal growth factor (EGF) and insulin on ketogenesis, gluconeogenesis and glycogen metabolism. EGF, unlike insulin, did not inhibit ketogenesis from palmitate or gluconeogenesis from pyruvate in hepatocyte cultures. It also had no effect on these pathways in the presence of insulin. In contrast, EGF potently counteracted the stimulation of [14C]pyruvate incorporation into glycogen by insulin, and also glycogen deposition from both gluconeogenic precursors and glucose. The EGF concentration causing half-maximal effect was about 0.1 nM. The anti-glycogenic effect of EGF was observed after both long-term (24 h) and short-term (1 h) exposure to EGF, and was more marked in the presence of insulin than in its absence. EGF did not displace bound insulin, suggesting that it neither competes for the insulin receptor nor affects the affinity of the receptor for insulin. EGF did not alter cellular cyclic AMP; and inhibition of cyclic AMP phosphodiesterase activity did not prevent the anti-glycogenic effect of EGF. In liver-derived dividing epithelial cells, Hep-G2 cells and fibroblasts, which have no capacity for gluconeogenesis, EGF did not counteract the stimulatory effect of insulin on [14C]glucose incorporation into glycogen, and in the epithelial cells EGF increased [14C]glucose incorporation into glycogen. The counter-effect of EGF on the glycogenic action of insulin in parenchymal hepatocytes may be due to a direct effect on glycogen metabolism or to an interaction with the post-receptor events in insulin action.

Epidermal growth factor, like glucagon, exerts a short-term stimulation of alanine transport in rat hepatocytes

Epidermal growth factor causes a transient stimulation of alanine transport in hepatocytes. The stimulation is maximal after 30 min, and the rate returns to the control value after 90 min. These characteristics are very similar to the short-term stimulation of alanine transport by glucagon, which has been attributed to cell membrane hyperpolarization.

Competition of a growth stimulating-/cholecystokinin (CCK) releasing-peptide (monitor peptide) with epidermal growth factor for binding to 3T3 fibroblasts

The growth stimulating-/cholecystokinin (CCK) releasing-peptide (monitor peptide) is a peptide purified from rat bile-pancreatic juice on the basis of its stimulatory activity toward pancreatic enzyme secretion. Its multiple functions and peptide sequence suggested that it is distinct from epidermal growth factor (EGF). However, we found that the peptide competes with [125I]-EGF in the binding to Swiss 3T3 fibroblast cells to almost the same extent as unlabeled EGF does. [125I]-EGF binding was inhibited by 50% by the peptide at 82.8 ng/ml and by unlabeled EGF at 71.4 ng/ml. This suggests that the growth stimulating effect of the peptide on 3T3 fibroblasts is mediated via the EGF receptor, and also suggests that the partial homologous sequence between monitor peptide and EGF is required for the receptor binding, or that the EGF receptor has a broad ligand specificity.

Epidermal growth factor (urogastrone)-stimulated gluconeogenesis in isolated mouse hepatocytes

In freshly isolated mouse hepatocytes obtained from fasted animals, we have studied the receptors for epidermal growth factor urogastrone (EGF-URO) in terms of the electrophoretic profile, ligand affinity, and numbers of EGF-URO receptors present on the cells, and also in terms of the ability of EGF-URO to stimulate gluconeogenesis, as reflected by the increased incorporation of [3-14C]pyruvate into glucose. The effects of EGF-URO were compared with those of glucagon. Ligand-binding studies revealed that the mouse hepatocytes possess an unusually high number of EGF-URO receptors (about 3 X 10(6) binding sites/cell), with a ligand dissociation constant of 4.4 nM. The binding of EGF-URO by mouse hepatocytes was more than 10-fold higher than the previously measured binding of EGF-URO by rat hepatocytes. Crosslink-labeling studies, coupled with gel electrophoretic analysis, demonstrated the presence of intact EGF-URO receptors, although some receptor processing had occurred during the isolation procedure. EGF-URO was able to stimulate the incorporation of 3-14C-labeled pyruvate into glucose; glucagon was unable to do so. In contrast, in rat hepatocytes isolated and assayed under identical conditions, glucagon (10 nM) caused a marked (250%) stimulation of the incorporation of pyruvate into glucose. Maximally, EGF-URO caused a 34% increase in the incorporation of [3-14C]pyruvate into glucose; a half-maximal effect was observed at a concentration of 2.5 nM EGF-URO. The stimulatory effect of EGF-URO was not dependent on the concentration of pyruvate, lactate, glucose, or calcium in the incubation medium. Although raising the concentration of pyruvate in the incubation medium increased the incorporation of [3-14C]pyruvate into glycogen, EGF-URO did not cause any change in the incorporation of radioactivity into glycogen. Overall, our data point to marked differences between rat and mouse liver preparations, in terms of the hormonal regulation of glucose metabolism, and our work documents a potential role for the remarkably high number of mouse hepatocyte EGF-URO receptors in terms of the modulation of gluconeogenesis in the mouse.

Kinetics of epidermal growth factor binding and processing in isolated intact rat hepatocytes. Dynamic externalization of receptors during ligand internalization

The kinetics of binding and processing of epidermal growth factor (EGF) was studied in freshly isolated rat hepatocytes. After isolation the hepatocytes had a nonhomogeneous population of surface EGF receptors consisting of approximately 9000 high-affinity sites (Kd 21 pM) and 165,000 low-affinity sites (Kd 0.62 nM). Incubation at 37 degrees C (45 min) increased the number of surface receptors per cell to about 260,000. This increase was selective for the low-affinity receptors and was cycloheximide-sensitive. During 5 h of incubation at 37 degrees C the hepatocytes internalized 6-7-times more EGF molecules than the number of cell surface receptors, based on clearance measurements. The uptake was unaffected by cycloheximide. Concomitant estimation, using acid/salt elution, of surface-bound EGF and internalized EGF showed that the number of internalized EGF molecules exceeded the decrease in surface-binding 6 times. The ratio between internalized EGF and the decrease in surface binding was temperature-dependent, being reduced to a one-to-one stoichiometry at 10 degrees C. After down-regulation (approximately equal to 75%) induced by 5 nM unlabeled EGF the surface EGF receptors did not recover during subsequent incubation (2 h) at 37 degrees C. However, the remaining surface receptors internalized EGF in ninefold excess of their number. The large discrepancy between internalization capacity and cell surface binding capacity was also found in the presence of cycloheximide. The results support the idea that internalized EGF receptors are partly replaced by externalization of preformed intracellular receptors during EGF uptake in isolated hepatocytes, involving recycling of a small population of EGF receptors and/or recruitment of unexposed, pre-existing receptors.

Human corpus luteum: presence of epidermal growth factor receptors and binding characteristics

Epidermal growth factor receptors are present in many reproductive tissues but have not been demonstrated in the human corpus luteum. To determine the presence of epidermal growth factor receptors and its binding characteristics, we carried out studies on the plasma cell membrane fraction of seven human corpora lutea (days 16 to 25) of the menstrual cycle. Specific epidermal growth factor receptors were present in human corpus luteum. Insulin, nerve growth factor, and human chorionic gonadotropin did not competitively displace epidermal growth factor binding. The optimal conditions for corpus luteum-epidermal growth factor receptor binding were found to be incubation for 2 hours at 4 degrees C with 500 micrograms plasma membrane protein and 140 femtomol 125I-epidermal growth factor per incubate. The number (mean +/- SEM) of epidermal growth factor binding sites was 12.34 +/- 2.99 X 10(-19) mol/micrograms protein; the dissociation constant was 2.26 +/- 0.56 X 10(-9) mol/L; the association constant was 0.59 +/- 0.12 X 10(9) L/mol. In two regressing corpora lutea obtained on days 2 and 3 of the menstrual cycle, there was no detectable specific epidermal growth factor receptor binding activity. Similarly no epidermal growth factor receptor binding activity could be detected in ovarian stromal tissue. Our findings demonstrate that specific receptors for epidermal growth factor are present in the human corpus luteum. The physiologic significance of epidermal growth factor receptors in human corpus luteum is unknown, but epidermal growth factor may be involved in intragonadal regulation of luteal function.

Effect of streptozotocin-induced diabetes on epidermal growth factor receptors in rat liver plasma membrane

The effect of streptozotocin-induced diabetes on 125I-labeled epidermal growth factor (EGF) binding was studied in microsomal membranes from rat liver. The binding of EGF in membranes from diabetic animals was significantly low, the value being about 60% of the control level. Scatchard analysis of the binding data clearly showed that the decrease in EGF binding was due to a decrease in the number of receptors. Treatment of diabetic animals with insulin restored EGF receptors to control levels, whereas the treatment with triiodothyronine had no effect. Serum EGF concentrations measured were almost the same among the control, diabetic, and insulin-treated diabetic groups. These results suggest that insulin deficiency in vivo causes a decrease in hepatic EGF receptors.

Onset of endogenous synthesis of epidermal growth factor in neonatal mice

We have analyzed mouse fetuses and neonates for the presence of epidermal growth factor (EGF)-specific mRNA. No detectable EGF-specific mRNA was found in fetuses, fetal membranes, or placentae from Day 9 of gestation through birth or in the early neonatal period. While the kidneys begin to produce EGF specific transcripts by two weeks postpartum, the salivary glands begin to produce detectable levels of EGF mRNA only after weaning and even then at levels far below the adult amount. Reports of EGF and EGF-related material in rodent fetuses failed to determine whether this material was of maternal or fetal origin. We now conclude that authentic EGF in these embryos is probably of maternal origin. We have performed experiments designed to determine whether EGF can be transported into the fetus. A small percentage of 125I-EGF administered to pregnant females either systemically or directly into the uterine arteries reached the fetus itself. The uterus and the placenta attained a high level of labeling, whereas the amniotic fluid and yolk sac were virtually devoid of the tracer. In the neonatal period, milk may be the physiologically relevant source of EGF. We have found that 125I-EGF ingested by neonates was absorbed into the circulation, reached many internal organs, and was eventually excreted in the urine. Previously demonstrated EGF receptors in mouse embryonic cell types may be activated by either alpha type transforming growth factor or maternal EGF transported via the placenta.

Decreased kinase activity of insulin receptors from adipocytes of non-insulin-dependent diabetic subjects

The tyrosine kinase activity of the insulin receptor was examined with partially-purified insulin receptors from adipocytes obtained from 13 lean nondiabetics, 14 obese nondiabetics, and 13 obese subjects with non-insulin-dependent diabetes (NIDDM). Incubation of receptors at 4 degrees C with [gamma-32P]ATP and insulin resulted in a maximal 10-12-fold increase in autophosphorylation of the 92-kDa beta-subunit of the receptor with a half maximal effect at 1-3 ng/ml free insulin. Insulin receptor kinase activity in the three experimental groups was measured by means of both autophosphorylation and phosphorylation of the exogenous substrate Glu4:Tyr1. In the absence of insulin, autophosphorylation and Glu4:Tyr1 phosphorylation activities, measured with equal numbers of insulin receptors, were comparable among the three groups. In contrast, insulin-stimulated kinase activity was comparable in the control and obese subjects, but was reduced by approximately 50% in the NIDDM group. These findings indicate that the decrease in kinase activity in NIDDM resulted from a reduction in coupling efficiency between insulin binding and activation of the receptor kinase. The insulin receptor kinase defects observed in NIDDM could be etiologically related to insulin resistance in NIDDM and the pathogenesis of the diabetic state.

Epidermal growth factor in blood

The presence of receptors for epidermal growth factor (EGF) in a wide variety of human tissues and also some tumours indicates an as yet undefined role for EGF and it is therefore necessary to know precise concentrations in blood and other fluids. We have investigated the occurrence of EGF in the circulation and found that in platelet rich plasma, EGF levels were 51 +/- 5 pmol/l (mean +/- S.E.M., n = 6) while in platelet poor plasma levels were 2.9 +/- 0.9 pmol/1. In contrast, serum EGF was 37 +/- 7 pmol/l if separated at 30 min and rose to 117 +/- 5 pmol/l if separated at 270 min. Gel chromatography showed that all residual EGF immunoreactivity in platelet poor plasma resided in the high molecular weight form thought to be non biologically active. In serum, delay in separation resulted in an increase in the proportion of EGF immunoreactivity co-eluting with EGF standard. These results suggest that EGF in the circulation is associated with platelets and that the process of blood coagulation leads to release of free EGF.

Epidermal growth factor mimics insulin effects in rat hepatocytes

Epidermal growth factor (EGF) mimicked the effect of insulin to activate glycogen synthase and stimulate glycogen synthesis in isolated rat hepatocytes. Both agents required glucose (greater than 5 mM) and had similar time courses of action. The maximum effect of EGF was approx. 70% of that of insulin, and the half-maximally effective concentrations were 9 nM and 4 nM respectively. Combinations of the two agents produced additive responses. EGF also resembled insulin in its ability to inhibit the effects of 0.1-1.0 nM-glucagon on cyclic AMP and glycogen phosphorylase in hepatocytes. The maximum effect of EGF was approx. 70% of that of insulin, and the half-maximally effective concentrations were approx. 5 nM and 0.5 nM respectively. EGF and insulin inhibited phosphorylase activation by exogenous cyclic AMP, and inhibited cyclic AMP accumulation induced by forskolin. They also inhibited phosphorylase activation provoked by phenylephrine, but not by vasopressin. EGF added alone rapidly activated phosphorylase and increased cytosolic [Ca2+], but the effects were no longer apparent at 5 min and were smaller than those of vasopressin. Insulin did not induce these changes. In hepatocytes previously incubated with myo-[3H]inositol, EGF did not significantly increase myo-inositol 1,4,5-trisphosphate. However, its ability to increase cytosolic [Ca2+] was blocked by neomycin, an inhibitor of phosphatidylinositol bisphosphate hydrolysis. It is concluded that some, but not all, of the effects of EGF in liver are strikingly similar to those exerted by insulin, suggesting that these agents may have some similar mechanisms of action in this tissue.

Characterization of the mouse placental epidermal growth factor receptor: changes in receptor number with day of gestation

The epidermal growth factor (EGF) receptor is present in the mouse placenta in both a low- and a high-affinity form having approximate values for Ka of 10(7) M-1 and 10(9) M-1, respectively. No significant difference (P greater than or equal to 0.05) in the number of receptors existed between placental membrane preparations from days 10 and 17, both for the low- and the high-affinity receptor. The number of both high- and low-affinity receptors was significantly lower (P less than 0.05) for day 14 placental membranes than for either day 10 or day 17 placental membranes. Cross-linking of 125I-EGF to placental membranes resulted in the specific labelling of two major receptor forms with approximate molecular weights of 170,000 and 154,000, as determined by sodium dodecyl sulphate-polyacrylamide gel electrophoresis.

The microvascular response to growth factors in the hamster cheek pouch

Implicit in attempts to characterize and purify biologically active factors is the premise that the bioassay system employed will show a progressive increase in the response as the concentration of the responsible factor increases. We employed the hamster cheek pouch to assay the neovascularization potential of growth factors, including endothelial cell growth supplement (ECGS), epidermal growth factor (EGF), fibroblast growth factor (FGF) and platelet-derived growth factor (PDGF). Each growth factor was applied to the system in graded concentration and two approaches used to assess neovascularization: first, direct serial inspection of the cheek pouches at 40 power; second, tritiated thymidine incorporation into endothelial cells, assessed by radioautography. PDGF induced a dose-related increase in neovascularization, with a threshold dose of 17.5 micrograms/ml and a peak, 56% response, at a PDGF concentration of 175 micrograms/ml. Progressive increases in PDGF concentration, thereafter, induced progressive reductions in the neovascularization rate. Under some conditions optimal bioassay requires serial dilutions of the assay material over a wide range.

Interaction of epidermal growth factor with specific binding sites of enterocytes isolated from rat small intestine during development

Isolated enterocytes from rat small intestine were characterized for their specific binding of epidermal growth factor (EGF). Intestinal epithelial cells were isolated at 4 degrees C to minimize the loss of receptor sites during the isolation procedure. 125I-labelled EGF binding to enterocytes from adult rats was found to be specific, saturable, temperature dependent and trypsin sensitive. Binding performed in the presence of a lysosomotropic agent (NH4Cl) increased the time required to reach maximal binding at 25 degrees C. NH4Cl had no significant effect on the time-course of EGF binding at 4 degrees C and 37 degrees C. A Scatchard plot showed a curvilinear relationship indicating that EGF binds to enterocytes with more than one binding site. Developmentally, enterocytes from fetuses and pups showed characteristic temperature dependence and trypsin sensitivity, but with different levels of binding to EGF. Specific EGF binding was demonstrably higher in enterocytes from small intestine of term fetuses. EGF binding to isolated enterocytes declined rapidly after birth, and the level stayed fairly constant thereafter. Pretreatment of enterocytes from fetal intestine with mature rat milk led to a dose-dependent decrease in EGF binding. These results suggest the presence of endogenous milk factors that modify EGF binding and account for, at least partly, the observed rapid decrease of EGF binding after birth.

The receptors of the VIP family peptides (VIP, secretin, GRF, PHI, PHM, GIP, glucagon and oxyntomodulin). Specificities and identity

A model is proposed for the receptors of the VIP family peptides including a ligand and a cellular domain. Specificities of the receptors are due to different ligand binding sites. Three subgroups of the family can be distinguished accordingly: glucagon and oxyntomodulin; GIP; VIP, secretin r and hGRF, PHI and PHM. In the same species, the expression of these different sites is cell-specific resulting in a stoichiometry of the ligand-receptor interaction which is compatible with physiological regulation of cell function. Specificities of the interaction as studied by native and synthetic analogs is supported both by restricted sequences of amino acids (such as that including the N-terminal histidine residue), and membrane-induced configuration of the ligand. Identity of the receptors is related to their interactions with subunits of the adenylate cyclase system. Arguments are put forward indicating that the alpha subunit of the guanyl regulatory protein is a reasonable candidate for directly transducing to the adenylyl cyclase the information contained in the activated ligand-binding site subunits. Evidence of functional and molecular heterogeneity of the recognizing site and of the alpha subunits leads to the supposition that some types of specific complementarity is retained at this level of interaction, further enhancing the possibility of species and cell differences. On the other hand, the identities found in other sequences of the alpha and ras oncogene products extend to the receptor of the VIP family peptides a pattern of organization which is similar to that recently described for the insulin family of receptors. The role of ligand specific receptor mediated regulation in homologous or heterologous desensitization is reviewed in brief for the peptides of the VIP family as well as the appearance of the specific receptor during the ontogenesis or the cell differentiation. The co-distribution of plasma membrane receptors from other families further adds to the cell specificity resulting for each differentiated cell in unique patterns of recognizing site. Some examples of receptor-receptor interaction are given, indicating that the integration of the different signals by cells might occur at an early step through the transmembranair domain of the receptor.

Direct expression of urogastrone gene in Escherichia coli

Human epidermal growth factor (urogastrone; UG) is a 53-amino acid polypeptide hormone. A 192-bp DNA fragment containing the coding sequence for methionyl UG (Met-UG) and the ribosome-binding site (RBS) was chemically synthesized and placed downstream from the promotor for the Escherichia coli outer-membrane lipoprotein gene (lpp) on a plasmid. E. coli cells harboring the plasmid directed the synthesis of Met-UG at 10(2)-10(3) molecules per cell. Next, the coding sequence for Met-UG was inserted in a runaway-replication plasmid and expressed under the control of the lpp promoter and the RBS derived from bacteriophage Mu cII gene. Upon heat induction, the cells harboring the recombinant plasmid synthesized 10(5) molecules of Met-UG per cell.

Epidermal growth factor binding and receptor distribution in term human placenta

Human placenta has a large number of epidermal growth factor (EGF) receptors when measured either by [125I]iodoEGF binding or by protein yield after purification. To localize EGF receptors in situ in normal human term placenta, two different light microscopic methods were used. To detect unoccupied, accessible EGF binding sites on the extracellular surface of placental cells in intact blocks of tissue, samples were incubated with [125I]iodoEGF, sectioned and autoradiography performed. To detect the total pool of intracellular and extracellular EGF receptors, placental tissue was sectioned, treated with detergent, and then anti-EGF receptor antibody was localized by immunohistoperoxidase techniques. Both [125I]iodoEGF and anti-EGF receptor antibody methods showed that EGF receptors were primarily present on syncytiotrophoblast cells of placental villi. Smooth muscle cells of placental blood vessels also contained EGF receptors. Neither connective tissue cells within the core of terminal chorionic villi nor endothelium of fetal blood vessels had detectable [125I]iodoEGF binding or immunoreactive EGF receptors. Since the quantity of placental smooth muscle cells is only a small fraction compared to trophoblast cells, we conclude that syncytiotrophoblast cells are primarily responsible for the high levels of EGF receptors found in extracts prepared from human term placenta.

Differential short-term effects of growth factors on fatty acid synthesis in isolated rat-liver cells

Hepatocytes in suspension, freshly isolated from meal-fed rats, were used to study the acute influence of growth factors on the rate of de novo fatty acid synthesis. Nerve growth factor (2.5 S) and epidermal growth factor caused a substantial increase in the rate of fatty acid synthesis, whereas fibroblast growth factor was inhibitory. Little effect was observed with nerve growth factor (7 S), bombesin or substance P. Transferrin did not affect hepatic fatty acid synthesis. The results are discussed in relation to the effects of insulin and tumor-promoting phorbol esters.

Epidermal growth factor does not cross the blood-brain barrier

To measure the passage of epidermal growth factor (EGF) through the blood-brain barrier (BBB) 125I-labeled EGF was injected intravenously into adult rats. The distribution of 125I-EGF in the blood and cerebrospinal fluid (CSF) was determined over a time period of several hours. Between 2 to 6 h a stable distribution of intact 125I-EGF in CSF was measured to be approximately 1/500 of the blood-borne EGF, an equilibrium value below those obtained by other investigators for BBB-impermeable compounds, such as inulin and bovine serum albumin. Our data indicate that 125I-EGF, although clearly detectable in the CSF, does not cross the BBB at a higher rate or in higher quantities than would be expected from its molecular size.

Detection of endogenous epidermal growth factor-like activity in the developing chick embryo

Epidermal growth factor-like activity has been detected by radioreceptor assay and radioimmunoassay in the developing chick embryo. Very little activity could be detected prior to Day 8 of embryonic life (hatching is at Day 21). A peak of EGF activity was detectable by both assays over Days 10 to 12. The EGF activity then fell to virtually undetectable levels during Days 14 to 17. A later rise in RRA detectable EGF like activity was then observed over Days 18-20. The EGF activity from a Day 11 embryo chromatographed on high-performance liquid chromatography as a single peak, with very high recovery of activity, at a later elution position than mouse EGF or human EGF.

Binding characteristics of epidermal growth factor receptors in male and female rat liver cell membrane preparations

The binding characteristics of epidermal growth factor (EGF) receptors were studied in cell membrane preparations from adult male (n = 14) and female (n = 13) rat livers. Results indicate a significant lower (about 65%) number of EGF receptors in female preparations. The possibility that the decrease in EGF receptors was only a reflection of an excess free EGF in female preparations was ruled out by means of acid extraction, ultrafiltration, and measurement of EGF in the acid extracts. In view of the known role of EGF in cell differentiation, it may be important to recognize that the number of its receptors, at least in liver preparations, is markedly different between sexes.

Purification and characterization of epidermal growth factor (beta-urogastrone) and epidermal growth factor fragments from large volumes of human urine

We purified human epidermal growth factor (hEGF) and hEGF fragments from a benzoic acid precipitate of the materials not adsorbed to silica gel in 330 liters of human urine by a relatively brief, simple, and efficient method employing sequential batch absorption to and stepwise elution from CM-cellulose and DEAE-cellulose, Bio-Gel P-10 chromatography in 50 mM HCl, and three reverse-phase HPLC steps for final resolution and purification of hEGF components. Recovery of hEGF was 29%. Eight apparently homogeneous hEGF components were recovered, each of which had similar activities in a homologous hEGF radioimmunoassay and an EGF radioreceptor assay using human placental membranes. Amino acid composition analysis indicated that there were four pairs of components that represented intact 53-amino acid hEGF, hEGF-(1-52), hEGF-(1-51), and hEGF-(1-50); intact hEGF accounted for one-third of the total materials recovered. Automated Edman degradation of each component for at least 10 cycles revealed a single amino acid sequence identical to that proposed for human beta-urogastrone. Similar immunoreactive hEGF components were observed in similar proportions in freshly voided urine, indicating that they were not artifacts of the purification process. Thus, multiple forms of fully biologically active hEGF (i.e., beta-urogastrone) can be relatively easily and efficiently purified from large volumes of human urine.

Inhibition by estradiol of binding and mitogenic effect of epidermal growth factor in primary cultures of Xenopus hepatocytes

We demonstrate here the presence of two classes of EGF (epidermal growth factor) binding sites in primary cultures of male Xenopus liver parenchymal cells. One of these corresponds to the high-affinity receptor described in other tissues and species, and which exhibits the property of autophosphorylation. The number of EGF receptors decreased sharply in freshly prepared cultures but recovered to maximum levels within 24 h thereafter. Addition of EGF and insulin to the hepatocyte cultures enhanced the rate of DNA synthesis as measured by the incorporation of [3H]thymidine. Estrogen abolished this increase, reducing the incorporation to that seen with hydroxyurea. At the same time, the addition of estradiol reduced the number or activity of EGF receptors in a dose-dependent manner. The latter paralleled the activation of transcription of vitellogenin genes in Xenopus hepatocytes so that a high rate of DNA synthesis is unnecessary for or incompatible with the activation of the steroid hormone-induced vitellogenin genes.

Peptide binding to intestinal epithelium: distinct sites for insulin, EGF and VIP

Several peptides, including insulin, epidermal growth factor and vasoactive intestinal polypeptide bind to intestinal epithelial cells. However, it is unclear whether one binding site binds several peptides or whether separate sites exist for each peptide. These studies were designed to examine the specificity of peptide binding sites on intestinal epithelial cells. Peptide binding was measured directly with [125I]radiolabelled peptides to isolated enterocytes prepared from rabbit ileum. The characteristics of insulin and epidermal growth factor binding were similar. Both insulin and epidermal growth factor specific binding was saturable, directly correlated to cell concentration and temperature and pH dependent. The total number of insulin binding sites per cell was 4500, that for epidermal growth factor was 2280. Scatchard analysis for both peptides produced curvilinear plots. Dissociation of both peptides from the binding site was increased in the presence of their respective unlabelled peptide. However, insulin specific binding was not altered by epidermal growth factor, and epidermal growth factor specific binding was unaffected by insulin. Further, both insulin and epidermal growth factor failed to inhibit the specific binding of vasoactive intestinal polypeptide to ileal enterocytes, and vasoactive intestinal polypeptide did not inhibit insulin or epidermal growth factor specific binding. These studies demonstrate that insulin, epidermal growth factor and vasoactive intestinal polypeptide interact with three distinct membrane binding sites on the enterocyte.

Substrate specificities of insulin and epidermal growth factor receptor kinases

The abilities of insulin and EGF stimulated protein kinases to phosphorylate a series of exogenous substrates were compared using wheat germ lectin purified preparations of solubilized rat liver membranes. Three different kinds of substrates were found: substrates phosphorylated primarily by insulin stimulated kinase, substrates phosphorylated primarily by EGF stimulated kinase and substrates phosphorylated by both kinases to a similar extent. These results indicate that the insulin and the EGF receptor kinase have different, but overlapping, substrate specificities. In vivo, phosphorylation of cellular proteins by various hormone receptor kinases may be part of the signal transmission process for actions of the hormones. Different substrate specificities of kinases of different hormone receptors may therefore represent an important mechanism to preserve the specificity of the hormonal signal at the post receptor level.

Effects of in vivo-administered 2,3,7,8-tetrachlorodibenzo-p-dioxin on receptor binding of epidermal growth factor in the hepatic plasma membrane of rat, guinea pig, mouse, and hamster

The effect of in vivo-administered 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on epidermal growth factor (EGF) receptor activity of the rat hepatic plasma membrane was studied. TCDD causes a significant reduction in EGF binding at an early stage of toxicity (day 2) and at very low doses (1 microgram/kg, single i.p., rat). This reduction appears to be due to a decline in the number of receptors. There is a good correlation between levels of decline in EGF binding and loss of body weight among TCDD-treated rats. The reduction in EGF binding occurs at a relatively low dose in the guinea pig (a very sensitive species) and at high doses in the hamster (a tolerant species). Among three mice strains, TCDD (115 micrograms/kg, single i.p.) caused 98% reduction in EGF binding in the sensitive strains (C57BL/6J and CBA/J) but only a 50% reduction in the tolerant strain (AKR/J). To relate the above biochemical changes to in vivo effects, TCDD was postnatally administered (through mother's milk) to mouse neonates. The most prominent toxic manifestations were early eye opening and incisor eruption, loss in body weight gain, and retardation of hair growth. All of these symptoms have been ascribed to EGF effects. TCDD was also found to stimulate phosphorylation of the EGF receptor in the rat hepatic plasma membrane. This phosphorylation effect was observed at day 1 and persisted until the end of the test (day 10). It has long been recognized that agents causing reduction in number of EGF receptors (e.g., phorbol esters) elicit in vivo cellular responses that are similar to those caused by exposure to excess doses of growth factors. Accordingly, a hypothesis has been proposed to ascribe some of the EGF-like effects of TCDD, such as fatty infiltration of the liver and hyperplastic proliferation of gastric epithelia and epidermal cells to its action on the EGF receptor.

Comparison of epidermal growth factor binding and receptor distribution in normal human epidermis and epidermal appendages

To localize epidermal growth factor (EGF) receptors in normal human epidermis and other skin structures, two different light microscopic methods were used. EGF binding [( 125I]EGF/R) to the extracellular portion of the EGF receptor was studied by incubating intact skin samples with [125I]EGF, sectioning the tissues, and performing autoradiography. Immunoreactive EGF receptor molecules (IR-EGF/R) were localized with a mono-specific anti-EGF receptor antibody using a 2-step indirect immunocytochemical method (horseradish peroxidase) and detergent permeabilized tissues. This latter method measured the total pool of EGF receptors: occupied and/or internalized forms, precursor forms, and partially degraded forms of the EGF receptor that retain immunoreactivity. Both the [125I]EGF/R and IR-EGF/R localization studies indicated that EGF receptors were present in basal epidermal keratinocytes, sebocytes, outer root sheath cells in hair follicles, smooth muscle cells of arrector pili muscles, and dermal arteries. The highest levels of [125I]EGF/R and IR-EGF/R were found in the dermal ducts of eccrine sweat glands. The distribution of both [125I]EGF/R and IR-EGF/R was not consistent with the concept that EGF exclusively is involved in cellular division and proliferation in normal human epidermis and its appendages, i.e., EGF receptors were also found in tissues that do not undergo rapid proliferation. The present study indicates that EGF may have a more complex regulatory role in the skin than was previously thought.

Transport of epidermal growth factor by rat liver: evidence for a nonlysosomal pathway

Epidermal growth factor (EGF), circulating in the blood, is taken up by rat liver hepatocytes by means of specific and saturable receptor-mediated endocytosis. These experiments were undertaken to determine (a) the transport pathway(s) of EGF taken up by rat liver and (b) the effects of lysosomal inhibition on its transport. 125I-EGF was injected into rat portal veins, and bile samples were collected and analyzed for both total and immunoprecipitable radioactivity. In addition, the livers were examined by electron microscopic autoradiography. Some animals received injections of chloroquine before surgery, to disrupt lysosomal function. The results indicate that most of the EGF taken up by the hepatocytes is transported to lysosomes and degraded. However, a small but significant percentage of endocytosed EGF is transported by a pathway independent of the lysosomal system, resulting in secretion of intact EGF: (a) Both degraded and immunoprecipitable EGF are secreted into bile. (b) Immunoprecipitable radioactivity peaks at 20 min after EGF injection, whereas degradation-associated radioactivity does not peak until 40 min postinjection. (c) EGF isolated from bile is specifically taken up by isolated hepatocytes in monolayer culture, indicating that it is still recognizable by the EGF receptor. (d) When the lysosomal system is inhibited with chloroquine, secretion of degraded EGF is significantly inhibited, whereas the amount of intact EGF secreted into bile is unchanged. The utilization by liver of a dual transport process for EGF represents an unusual system of intracellular ligand processing, whose physiological significance has yet to be determined.

Epidermal growth factor receptors in human breast cancer

The capacity for specific binding of 125I-epidermal growth factor (EGF) was studied in crude membrane fractions from 95 human breast carcinomas. About 42% of the samples showed saturable, high affinity, specific binding of EGF. In 21% of the tumors we were able to demonstrate high (above 10 fmoles/mg protein) binding capacity. Moreover, high EGF receptor values were associated with a low content of estradiol receptor. These studies are related to the definition of new biochemical markers in human breast cancer.

Mechanism of the inhibitory effect of EGF on cAMP-stimulated amino acid transport

EGF inhibits the cAMP stimulation of amino acid transport in primary cultures of rat hepatocytes. This effect is not observed in freshly isolated cells incubated in suspension but only in cells that have been allowed to attach to culture dishes. Sequential addition of cAMP and EGF to monolayer cultures of hepatocytes revealed that EGF does not affect the half-life of the carrier proteins induced by cAMP but rather prevents the induction of new amino acid transport proteins. The EGF effect is inhibited by drugs interfering with protein synthesis. These results indicate that EGF promotes the synthesis of specific proteins that are able to prevent the cAMP induction of amino acid carriers.

[Epidermal growth factor: structure, location, phosphorylation and regulation of its receptor]

Epidermal growth factor (EGF) is a Mr 6045 polypeptide first characterized for its ability to stimulate mitogenesis in epidermal and epithelial cells. The first step in the action of the growth factor is its binding to specific, high affinity membrane receptors. These receptors have been studied in a number of tissues and cell culture lines. The level of EGF receptors is modulated by many agents. EGF down-regulates its receptor. In addition, the number of EGF receptors is decreased by other growth factors (platelet-derived growth factor; transforming growth factor), by many tumor promoters and by viral transformation. Several hormones also can regulate EGF binding in its target tissues.

Receptor modulating properties of an antibody directed against the epidermal growth factor receptor

A murine antiserum with specificity for the human epidermal growth factor (EGF) receptor was used to investigate EGF receptor function. The IgG fraction of this antiserum displayed no EGF-like mitogenic activity, even when cross-linking was ensured by sequential treatment with rabbit anti-(mouse IgG). The interaction of antibody with solubilized purified EGF receptor was characterized in detail. The binding of 125I-antibody to the receptor was not blocked by EGF, but the binding of 125I-EGF to the receptor was blocked by the immune IgG. Scatchard analysis of this reaction revealed a reduction in maximal EGF binding but an enhanced EGF binding affinity. In addition, at low concentrations, the immune IgG was found to enhance receptor kinase activity in the absence of EGF. The enhancement of kinase activity, as measured by receptor phosphorylation, was due to a decreased Km for ATP, and an increased V. These results suggest that the antibody is capable of altering conformations at receptor active sites by binding to non-active species-specific epitopes.

Insulin inhibits the glucocorticoid-mediated increase in hepatocyte EGF binding

Hydrocortisone and dexamethasone produced a time-dependent increase [125I]epidermal growth factor [( 125I]EGF) binding in primary cultures of isolated rat hepatocytes. Maximally effective doses of glucocorticoids resulted in a 70-100% increase in binding. The effect was similar when hepatocytes were maintained on collagen-coated plates or directly on culture dishes. The glucocorticoid-mediated increase in [125I]EGF binding could be detected after 4 h exposure to glucocorticoid and was substantial by 8 h. The major effect of glucocorticoid appeared to be to increase the number of EGF receptors. While insulin (100 nM) had no effect on basal [125I]EGF binding, it significantly inhibited the increase produced by the glucocorticoid. Since the inhibitory effect of insulin was only observed when insulin was added with the inducing glucocorticoid, insulin appears to inhibit an early hydrocortisone-mediated event.

Close similarity of epidermal growth factor receptor and v-erb-B oncogene protein sequences

Each of six peptides derived from the human epidermal growth factor (EGF) receptor very closely matches a part of the deduced sequence of the v-erb-B transforming protein of avian erythroblastosis virus (AEV). In all, the peptides contain 83 amino acid residues, 74 of which are shared with v-erb-B. The AEV progenitor may have acquired the cellular gene sequences of a truncated EGF receptor (or closely related protein) lacking the external EGF-binding domain but retaining the transmembrane domain and a domain involved in stimulating cell proliferation. Transformation of cells by AEV may result, in part, from the inappropriate acquisition of a truncated EGF receptor from the c-erb-B gene.

Visualization of epidermal growth factor receptors in human epidermis

The localization of epidermal growth factor (EGF) receptors in normal human epidermis was examined with two independent experimental methods. The distribution of EGF receptor sites was studied using light microscopic autoradiography with [125I]EGF and direct immunocytochemical techniques with EGF receptor antibodies and protein A-colloidal gold complexes. Direct visualization by autoradiography indicated that the concentration of EGF receptors was greatest in the lower epidermal layers. Ultrastructural morphometric analysis of protein A-gold complexes showed that EGF receptors were primarily associated with the plasma membranes although intranuclear and cytoplasmic localization was also evident. This postembedment immunolocalization method also confirmed the relative differences in the number of EGF receptors found in individual epidermal layers (basalis greater than spinosum greater than granulosum greater than corneum layers). This inverse relationship between numbers of EGF receptors and the degree of epidermal differentiation and/or keratinization may suggest a physiologic role for EGF in these processes in human epidermis.

Ontogenesis and characteristics of epidermal growth factor receptors in human placenta

Epidermal growth factor promotes growth in many cell types. The role of epidermal growth factor during gestation and fetal development is unknown. This study investigates the presence and binding characteristics of epidermal growth factor receptors in placentas throughout gestation. Cell membrane preparations were obtained from first-, second-, and third-trimester placentas and hydatidiform moles. Specific epidermal growth factor receptors were observed as early as 6 weeks of gestation. Throughout gestation, Scatchard analysis of epidermal growth factor binding was curvilinear, and dissociation studies were consistent with site-to-site interaction with negative cooperativity. Affinity constants at high (Ke = 9.9 +/- 0.79 X 10(9) L/mol) and low (Kf = 3.0 +/- 0.25 X 10(9) L/mol) receptor occupancy were unchanged throughout normal gestation. However, the number of receptors per milligram of protein significantly increased with advancing normal gestation (correlation coefficient, r = 0.81). In hydatidiform moles, the number of receptors was reduced when compared to that of normal tissue of similar gestational age. Our study provides a quantitative basis for further evaluation of epidermal growth factor as a possible factor in embryogenesis and fetal development.