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

Expanding the Disorder-Function Paradigm in the C-Terminal Tails of Erbbs

ErbBs are receptor tyrosine kinases involved not only in development, but also in a wide variety of diseases, particularly cancer. Their extracellular, transmembrane, juxtamembrane, and kinase folded domains were described extensively over the past 20 years, structurally and functionally. However, their whole C-terminal tails (CTs) following the kinase domain were only described at atomic resolution in the last 4 years. They were shown to be intrinsically disordered. The CTs are known to be tyrosine-phosphorylated when the activated homo- or hetero-dimers of ErbBs are formed. Their phosphorylation triggers interaction with phosphotyrosine binding (PTB) or Src Homology 2 (SH2) domains and activates several signaling pathways controling cellular motility, proliferation, adhesion, and apoptosis. Beyond this passive role of phosphorylated domain and site display for partners, recent structural and function studies unveiled active roles in regulation of phosphorylation and interaction: the CT regulates activity of the kinase domain; different phosphorylation states have different compaction levels, potentially modulating the succession of phosphorylation events; and prolines have an important role in structure, dynamics, and possibly regulatory interactions. Here, we review both the canonical role of the disordered CT domains of ErbBs as phosphotyrosine display domains and the recent findings that expand the known range of their regulation functions linked to specific structural and dynamic features.

A Chimeric Egfr Protein Reporter Mouse Reveals Egfr Localization and Trafficking In Vivo

EGF receptor (EGFR) is a critical signaling node throughout life. However, it has not been possible to directly visualize endogenous Egfr in mice. Using CRISPR/Cas9 genome editing, we appended a fluorescent reporter to the C terminus of the Egfr. Homozygous reporter mice appear normal and EGFR signaling is intact in vitro and in vivo. We detect distinct patterns of Egfr expression in progenitor and differentiated compartments in embryonic and adult mice. Systemic delivery of EGF or amphiregulin results in markedly different patterns of Egfr internalization and trafficking in hepatocytes. In the normal intestine, Egfr localizes to the crypt rather than villus compartment, expression is higher in adjacent epithelium than in intestinal tumors, and following colonic injury expression appears in distinct cell populations in the stroma. This reporter, under control of its endogenous regulatory elements, enables in vivo monitoring of the dynamics of Egfr localization and trafficking in normal and disease states.

Submandibular salivary glands: influence on growth rate and life span in mice

Submandibular glands accumulate a variety of growth factors, especially in male mice. Surgical excision of these glands (sialoadenectomy) results in alterations in several organs and systems including the liver, skin and reproductive system. We studied the life-long consequences of sialoadenectomy in male mice. Animals were operated at the age of 10 weeks. Thereafter, body weight and food and water intake were controlled until death. Few weeks after surgery, body weight was lower in sialoadenectomized than in control mice. The difference remained stable until the age of 80 weeks. In spite of the lower body weight, food intake was higher in sialoadenectomized mice than in controls. The first death of sialoadenectomized mice occurred 10 weeks earlier than that of the first control, and the initial death rate in sialoadenectomized mice was almost twice the rate in controls. After 100 weeks of life, the death rate increased in control mice, but suddenly decreased in sialoadenectomized mice. The consequence was that the mean life span of the last 25% surviving animals was 10 weeks longer in sialoadenectomized than in control mice. Autopsy examination suggests that the effect of sialoadenectomy on death rate may be the consequence of a contrasting effect on tumour growth. Our results indicate that submandibular glands, or rather the factors derived from these glands, have contrasting roles in tumour growth. At early ages they may be survival factors and protect tissues, whereas at later ages they may stimulate the growth of transformed cells.

High level of EGF-R expression in carcinomatous skin invasion: Does it reflect the tissue characteristics of the breast carcinoma aggressiveness?

Background: The normal function and distribution of EGF-R and its role in breast cancer aggressiveness, prognosis and prediction, have become extremely important in the light of the recently developed methods of EGF-R targeting. In the aim to investigate the relationship between EGF-R and the aggressive tumor behavior, the EGF-R content was analyzed as related to the presence of inflammatory breast skin involvement. Methods: EGF-R, ER and PR content was determined at diagnosis, using the biochemical methods, in the group of 103 unselected breast cancer patients, either in primary tumors (TU), lymph nodes (LN) or skin tissue samples (65, 27 and 11 cases respectively). In 10 patients with inflammatory breast cancers, TU/LN tissue was sampled from 3, and skin from 7 patients. Results: ER and PR content was significantly higher in tumor and LN tissue, compared to the invaded skin the EGF-R content was, on the contrary, significantly higher in skin than in TU or LN tissue. However, no difference was found between TU and LN in all three receptors' content. When the receptor content was analyzed in 10 patients with inflammatory breast cancer, higher levels of both ER and PR were found in tumor biopsies than in skin biopsies, while for the EGF-R the result was opposite. Significantly lower ER content and a trend towards higher EGF-R content was found in the inflammatory breast cancers in comparison to the non-inflammatory ones. Conclusion: Although we examined a small number of patients, our results suggest that the EGF-R could be a marker of breast cancer aggressiveness. However, the influence of the normal skin cells contaminating the biopsied tumor tissue cannot be ruled out. The predictive role of EGF-R deserves to be further investigated especially in locally advanced inflammatory breast cancer patients.

The effect of epidermal growth factor on prostaglandin synthesis of oestrogenized rat uterus is mediated by nitric oxide

We examined the possible relationship between cytokines, nitric oxide and prostaglandins (PGs) in the estrogenized rat uterus. Results indicate that epidermal growth factor (EGF) enhances the synthesis of prostaglandins in estrogenized rat uteri and induces the augmentation of nitric oxide (NO) production in this tissue by stimulating iNOS. While the effect of EGF is abolished by L-NMMA, an NO antagonist, the NS-398, a cyclooxygenase-II (COX-II) inhibitor, prevents the augmentation of prostanoids induced by EGF. These results suggest that there is an interaction among EGF, NO and PGs and that in this interrelationship are involved COX-II and iNOS. This mechanism might be important during implantation and labor.

Activation and glucagon regulation of mitogen-activated protein kinases (MAPK) by insulin and epidermal growth factor in cultured rat and human hepatocytes

Many hepatocellular activities may be proximally regulated by intracellular signalling proteins including mitogen-activated protein kinases (MAPK). In this study, signalling events from epidermal growth factor (EGF) and insulin were examined in primary cultured human and rat hepatocytes. Using Western immunoblots, rat and human hepatocytes were found to produce a rapid tyrosine phosphorylation of the EGF receptor and MAPK following 0.5-1 min exposure to EGF. Phosphorylation of p42 and p44 MAPK was observed following 2.5 min exposure to EGF. Insulin treatment produced phosphorylation of the insulin receptor beta subunit; she phosphorylation was not observed. MAPK phosphorylation corresponded with a shift in molecular weight and an increase in kinase activity. Insulin-dependent activation of MAPK was unequivocally observed only in human hepatocytes, though a slight activation was detected in rat. Co-treatment with insulin and EGF produced phosphorylation and complete electrophoretic shift in molecular weight of MAPK, with an additive or synergistic increase in enzyme activity in rat but not human hepatocytes; human hepatocyte MAPK was maximally stimulated by EGF alone. Glucagon pretreatment blocked phosphorylation, gel mobility shift and kinase activity of MAPK induced by insulin but only partially blocked EGF-induced MAPK activation in human hepatocytes. Glucagon also reduced the activation of MAPK by EGF in rat hepatocytes. Pre-treatments with forskolin or cyclic AMP analogues diminished in the insulin-, EGF- and insulin plus EGF-dependent activation of MAPK in rat hepatocytes without effecting phosphorylation of receptors or MAPK. These results indicate that although EGF and insulin may both signal through the MAPK/ras/raf/MAPK pathway, the response for MAPK differs between these ligands and between species. Further, in both rat and human, glucagon exerts its effects through a cyclic AMP-dependent mechanism at a level in the insulin and EGF signal transduction pathways downstream of MAPK but promixal to MAPK. The partial inhibition of EGF-induced MAPK phosphorylation by glucagon in human hepatocytes provides further evidence for a raf-1-independent pathway for activation of MAPK.

Perturbation of epidermal growth factor clearance after radioiodination and its implications

The clearance of human epidermal growth factor (hEGF1-53) has been thought to be mediated mainly by a high-capacity receptor system, yet relatively low in vivo clearance rates (<10 mL/min/kg) and long terminal elimination half-lives (>120 min) have been observed in rats receiving the peptide that was iodinated by the oxidative chloramine-T (CT) method. We investigated if a mild, less oxidative iodination by the lactoperoxidase (Enzymobeads, EB) method, which is known to yield an iodinated peptide with receptor-binding equivalence, could produce a labeled peptide that behaves pharmacokinetically similar to the native material. For comparison, a parallel study was also conducted with EB-125I-hEGF1-48, which in its native form has a much reduced receptor binding activity due to the loss of the C-terminal pentapeptide. Plasma radioactivity concentrations were determined by trichloroacetic acid (TCA) precipitation and immunoprecipitation. Rats cleared unlabeled hEGF1-53 and hEGF1-48 markedly faster (CL(tot) > 120 mL/min/kg) than their radiolabeled counterparts. Approximately 96% of the hEGF1-53 dose was cleared during the initial phase (0-4 min), as opposed to only 5-14% for the iodinated peptide. Similar change was also observed for EB-125I-hEGF1-48 and CT-125I-hEGF1-53. The pharmacokinetic behavior of EB-125I-hEGF1-53 was, in fact, comparable to that of CT-125I-hEGF1-53. These observations indicate that receptor-binding equivalence does not have direct relationship with in vivo EGF clearance. Both iodination methods (oxidative CT and less oxidative EB) might have perturbed one or more steps in the cascade of ligand-receptor internalization and intracellular procession, which in turn modified the disposition of the peptides. In addition, the two independent precipitation techniques for the same peptide generated different kinetic outcomes. The overall experimental results suggest that it is unacceptable to use an iodinated form to characterize the disposition of peptides/proteins like EGF with a specific receptor system mediating its clearance.

Methoxychlor mimics the action of 17 beta-estradiol on induction of uterine epidermal growth factor receptors in immature female rats

Epidermal growth factor (EGF) and its receptor (EGF-R) have been implicated as mediators for estrogen induced cellular growth. This study examines whether the action of the estrogenic pesticide methoxychlor (MXC) parallels the action of 17 beta-estradiol (E2) on uterine EGF-R. Administration of 20 micrograms E2/sexually immature female rat increased 125I-EGF binding to membranes extracted from whole uteri 175% over endogenous levels, while 500 mg MXC/kg led to a 156% increase. E2 in both 20 and 40 micrograms/rat doses and 500 mg MXC/kg led to maximal stimulation over endogenous levels, 12-h posttreatment. Rats were treated with E2, MXC, or vehicle plus 100 micrograms actinomycin-D (ACT-D) or 100 micrograms cycloheximide (CYCLO) per rat to determine if mRNA transcription and translation are involved in the increased EGF-R binding following estrogenic treatment. Only ACT-D inhibited the estrogenic stimulation of EGF-R binding, resulting in a 44% decrease when given concurrently with E2 or MXC, suggesting transcription is required. Additionally, ACT-D decreased endogenous receptor levels by 55%. No other differences were detected. When EGF-R binding data were analyzed by the method of Scatchard, both E2 and MXC, at maximal dosages, elevated uterine EGF-R binding sites by over 200% after 12 h as measured by maximal binding (Bmax) with no significant difference in dissociation constant (Kd) values. These results demonstrate that both E2 and MXC can stimulate the number of EGF-R binding sites without significantly altering the receptor binding affinity (Kd). Further, this stimulation is time dependent and is affected by dose.

Transforming growth factor-alpha and other growth factors stimulate cell division in olfactory epithelium in vitro

The rate of cell division in olfactory epithelium (OE) is upregulated by ablation of the olfactory bulb (Carr and Farbman, 1992), or downregulated by occlusion of a naris. We used an organ culture assay of fetal rat olfactory mucosa to study regulation of the mitotic rate. Addition of any one of three members of the epidermal growth factor (EGF) family-EGF, transforming growth factor-alpha (TGF-alpha), or amphiregulin (AR)-to a serum-free culture medium resulted in a two- to threefold increase in the number of dividing OE cells. TGF-alpha elicited a maximal response in a dose of 100-200 pM culture medium and was 2 orders of magnitude more potent than the other EGF family members. Addition of TGF-beta 1, TGF-beta 2, insulinlike growth factor-1 or platelet-derived growth factor to the culture medium had slightly less effect than EGF or AR, in about the same molar dose range; addition of nerve growth factor had virtually no net effect on cell division. Immunohistochemistry on adult rat OE showed that basal cells, supporting cells, and acinar cells of Bowman's glands were immunoreactive with antibody to TGF-alpha but not with antibody to EGF. Most growth factors upregulated division of both olfactory neuron progenitors and supporting cells. The data suggest that several growth factors, most prominently TGF-alpha 1, may participate in the mitotic regulation of OE.

Epidermal growth factor receptor expression by acoustic neuromas

Antibodies directed against epidermal growth factor receptor (EGFr) impede proliferation and induce differentiation of EGFr-positive cancers. To explore the effectiveness of anti-EGFr monoclonal antibodies on acoustic neuromas (ANs), we first sought to evaluate EGFr expression by ANs. The records of all patients with the diagnosis of AN at our institution from January 1989 to July 1994 were reviewed. Immunohistochemical analysis for EGFr was performed on formalin-fixed, paraffin-embedded archival surgical specimens. Skin, liver, and placenta were used as positive tissue controls. Purified rabbit immunoglobulin G replacing the experimental antibody acted as a negative control, and normal eighth cranial nerve was evaluated for background staining. Slides were scored as 0, +, ++, or and for percentage of positive cells by two pathologists, with Antoni A and Antoni B areas scored separately. Results demonstrate that most tumors are revealed to be EGFr positive with a mild degree of staining. Antoni A areas generally have greater staining than Antoni B regions, while normal eighth cranial nerves demonstrate minimal background staining. These results suggest that ANs express low levels of EGFr, with Antoni A areas having the highest levels. While further studies may more accurately quantitate EGFr levels in these tumors, the clinical efficacy of anti-EGFr-based therapies for ANs seems doubtful.

Epidermal growth factor administration decreases liver glycogen and causes mild hyperglycaemia in mice

Several laboratories report different effects of epidermal growth factor (EGF) on glycogen metabolism in hepatocytes. The discrepancies may be attributed to differences in the experimental conditions. It is therefore important to establish the actual effect of EGF in vivo. Because large physiological variations of EGF concentration in plasma occur in mice, we used this species to address this question. In freshly isolated mouse hepatocytes, EGF increased glycogen degradation in a dose-dependent manner. The maximal effect (36% increase over basal glycogenolysis) was smaller than maximal effects of classical glycogenolytic hormones like adrenaline or glucagon (more than 150% increase over basal). This is in keeping with the smaller effect of EGF on phosphorylase a activity. In contrast with these hormones, EGF did not inhibit glycolysis. Thus these effects of EGF in mouse hepatocytes are similar to those recently described by us in rat hepatocytes [Quintana, Grau, Moreno, Soler, Ramirez and Soley (1995) Biochem J 308, 889-894]. When administered to whole animals, EGF increased phosphorylase a activity, decreased the glycogen content in the liver and caused mild hyperglycaemia. Taking together the results obtained for isolated cells and for whole animals, we suggest that the glucosyl residues released from glycogen are used mostly by the liver rather than released to the circulation. This would be different from the action of the classical glycogenolytic hormones, adrenaline and glucagon.

EGF receptor mRNA and protein in rat lacrimal acinar cells: evidence of its EGF-dependent phosphotyrosilation

This study was designed to demonstrate the presence of the epidermal growth factor (EGF) receptor in the rat exorbital lacrimal gland. EGF receptor gene transcription was demonstrated 1) by reverse transcription-polymerase chain reaction analysis of lacrimal gland and acinar cells from RNA with a set of specific primers deduced from the rat EGF receptor sequence and 2) by Northern blot analysis of rat lacrimal gland mRNA. Lacrimal acinar cell preparations contain a low but detectable amount of specific 125I-EGF binding sites and efficiently internalize the ligand on binding at 37 degrees C. A sheep polyclonal antibody, directed against the human EGF receptor, detects a protein of 170 kDa by Western blot analysis of membrane proteins of the whole gland. This protein can be immunoprecipitated by the same antibody from whole gland membrane proteins as well as from solubilized acinar cells. Incubations of acinar cells in the presence of EGF results in an increased content of tyrosine-phosphorylated residues in immunoprecipitated 170-kDa protein. Taken together, these results demonstrate for the first time both EGF receptor gene transcription and protein expression in a lacrimal tissue, i.e., the rat exorbital lacrimal gland. These results also suggest a specific cellular location of the EGF receptor in a cell population contained in acinar cell preparations.

Possible role of variant RNA transcripts in the regulation of epidermal growth factor receptor expression in human placenta

Epidermal growth factor receptor (EGFR) plays an important role in growth and differentiation. The human placenta expresses high levels of the receptor. In the placenta, as in many other human tissues, EGFR is encoded by two RNA transcripts of 5.8 kb and 10.5 kb. The placenta also expresses a putative truncated EGFR transcript of 1.8 kb, which encodes only the ligand binding domain of the receptor. The etiology and role of these variant EGFR transcripts is unknown. Using the human placenta as a model to study this area, we report 1) the relationships among these transcripts suggest that the induction of alternate pathways of EGFR RNA processing is involved in their etiologies; 2) the 10.5 kb transcript may be the principal transcript involved in determining the level of the protein receptor; and 3) the isolation of a soluble protein with characteristics consistent with a translational product corresponding to the 1.8 kb transcript, which may act in regulating the activity of EGFR. Together these results suggest that alternate processing of EGFR RNA into variant transcripts may represent a novel mechanism involved in the regulation of the receptor protein.

Effects of epidermal growth factor (EGF), platelet-derived growth factor (PDGF) and fibroblast growth factor (FGF) on human adipocyte development and function

We investigated the effects of epidermal growth factor (EGF), platelet-derived growth factor (PDGF) and fibroblast growth factor (FGF) on the differentiation of human adipocyte precursor cells and some metabolic aspects of newly formed fat cells kept in primary culture. Exposure of stromal cells from human adipose tissue to EGF (0.01-100 ng mL-1) resulted in a dose- and time-dependent decrease in the number of developing fat cells and the activity of glycerol-3-phosphate dehydrogenase (GPDH), a marker of adipose differentiation. Continuous presence of EGF completely blocked lipid accumulation with a ED50 in the range of 0.2 ng mL-1. This inhibitory action of EGF was associated with a potent stimulation of cell proliferation, up to 8-fold compared with cultures in the absence of EGF. PDGF (0.1-50 ng mL-1) and FGF (0.1-100 ng mL-1) provoked a less marked suppression of GPDH activities which was significant at concentrations of 10 ng mL-1 and higher. A 12 day exposure to EGF of differentiated cells was followed by a suppression of GPDH and, again, a significant increase in cell number. Concomitantly, a distinct loss of cellular lipids was observed in the newly formed adipocytes. This effect could be partly explained by a stimulation of lipolysis, since EGF caused an increase of glycerol in the culture medium. Addition of PDGF or FGF to newly developed fat cells had no effect on lipolysis but, at higher concentrations, also decreased GPDH activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunocytochemical study of epidermal growth factor receptor, transforming growth factor alpha, and "squamous differentiation" in human endometrial carcinoma

The expression of epidermal growth factor receptor (EGFr) and transforming growth factor alpha (TGF-alpha) was compared with the presence of "squamous differentiation" (SD) visualized in various histotypes of endometrial carcinoma by using a panel of monoclonal antibodies. The results of the current study demonstrate that EGFr and TGF-alpha are present in routinely processed endometrial carcinoma. The highest positive EGFr and TGF-alpha expression was seen in the group of adenocarcinomas with SD. The more intense EGFr and TGF-alpha immunoreactivity was observed in "squamous" foci both in adenoacanthomas (AA) and in adenosquamous carcinomas (AS). These EGFr- and TGF-alpha-positive squamous areas prevalently displayed a "stratification-related" cytokeratin (CK) immunoprofile characterized by the expression of CKs 1, 4, 5, 10, 13, 14, and 16. No correlation was found between EGFr- and TGF-alpha-positive status and depth of myometrial invasion or surgical stage. These results clearly demonstrate that EGFr and TGF-alpha expression is related remarkably to endometrial carcinoma with "squamous" areas both morphologically and immunophenotypically. This specific association leads us to suggest that EGFr and TGF-alpha expression in endometrial carcinoma may be prevalently involved in the equilibrium of cell differentiation of the "squamous" foci commonly observed in this group of neoplasias.

Cytokines and growth factors in implantation

A variety of cell types at the blastocyst implantation site produce cytokines and growth factors that could play an important role in the implantation process. Furthermore, receptors for cytokines and growth factors have been detected on embryonic and trophoblastic cells. The purpose of the article is to review the published literature on the effect of cytokines and growth factors on implantation events, and to present recent data from our laboratory on effects of growth factors and cytokines on mouse blastocyst implantation events in vitro.

A recombinant form of Pseudomonas exotoxin A containing transforming growth factor alpha near its carboxyl terminus for the treatment of bladder cancer

The epidermal growth factor receptor (EGFR) is overexpressed on the superficial layers of malignant urothelium and is suspected of playing a role in tumor progression. TP40 is a chimeric protein composed of transforming growth factor-alpha (TGF alpha) fused to a modified form of Pseudomonas exotoxin A (PE) that is selectively cytotoxic to EGFR-bearing cells and is currently undergoing clinical study for the intravesical therapy of bladder cancer. We constructed a recombinant toxin PE35/TGF alpha-KDEL as an improved agent for the local therapy of EGFR-bearing bladder cancer. PE35/TGF alpha-KDEL does not require intracellular proteolysis to generate a carboxyl-terminal fragment capable of reaching the target cell cytosol and contains a modified carboxyl-terminal sequence KDEL, that increases toxin activity. These features make PE35/TGF alpha-KDEL from 10- to 700-fold more potent than TP40 on four human bladder cancer cell lines. PE35/TGF alpha-KDEL may be a useful agent for treatment of EGFR-bearing cancers.

Quantitative determination of EGF-R during epidermal wound healing

Little is known about the intrinsic regulation of growth factors of cytokines during the normal epidermal wound-healing processes in skin. A simplified model of wounding (tape stripping to remove the stratum corneum) was used to study the role of epidermal growth factor receptors (EGF-R) in this process. Although the dynamics of EGF-R in epidermal wound healing have not been determined, the immunoreactive EGF-R that are present presumably play an active role. Prior studies show that 1) EGF-R are present in increased numbers in proliferative skin diseases; 2) a hypertrophic epidermis, closely resembling normal wound healing, is induced in mouse skin by EGF injections; and 3) exogenous topical EGF potentiates wound healing. The number of immunoreactive receptors as measured by an enzyme-linked immunosorbent assay (ELISA) and histologic methods increased prior to an increase in epidermal thickness, total protein, and DNA content. This early increase in the levels of EGF-R was followed by a sharp decline in EGF-R and subsequent decline in epidermal thickness (hypertrophy), total protein, and DNA levels. Alterations in the temporal sequence in these parameters indicate that the EGF-R-mediated signaling systems play an active role in epidermal wound repair.

Existence of two pathways for the endocytosis of epidermal growth factor by rat liver: phenylarsine oxide-sensitive and -insensitive pathways

The effect of phenylarsine oxide (PAO) on the internalization rate of epidermal growth factor (EGF) was investigated using perfused rat liver and isolated rat hepatocytes. In perfused liver, a tracer concentration of 125I-EGF alone or with excess unlabeled EGF (20 nM) was perfused and the internalization rate constants (kint) were measured. In the absence of PAO, kint values did not differ significantly for either dose condition. However, with the addition of PAO to the perfusate, the kint value dropped to 4% of that of the control at the low concentration of EGF, while dropping to only 40% of that of the control at the high concentration of EGF. These results suggest the existence of a PAO-insensitive internalization pathway having a kint value comparable with that of the other pathway. Similar EGF concentration-dependent inhibition of 125I-EGF internalization caused by PAO was ascertained using isolated rat hepatocytes. PAO also decreased the cellular ATP content in isolated hepatocytes. However, when we lowered the cellular ATP content with rotenone, the cell-surface binding and internalization of EGF were comparable with the control levels. We concluded that there exist dual pathways for the internalization of EGF and that excess doses of EGF lead to EGF internalization not only through a PAO-sensitive pathway but also through a PAO-insensitive pathway, whereas at a tracer dose of EGF, the internalization occurs mainly via the PAO-sensitive pathway.

Minoxidil: inhibition of proliferation of keratinocytes in vitro

Previous studies have suggested that minoxidil stimulates growth of keratinocytes, possibly in a manner similar to the action of epidermal growth factor. Using both a short-term assay, thymidine incorporation, and a longer term assay, cell counting, to assess proliferative growth, we tested the activity of minoxidil in human keratinocyte cultures grown in 0.1 mM Ca(++). Minoxidil failed to stimulate growth in these assays. At concentrations of 5-10 micrograms per ml, minoxidil showed half-maximal inhibition of both EGF- and placental extract-stimulated thymidine incorporation. Minoxidil also inhibited proliferative growth in the presence or absence of placental extract. Direct measurement of the ability of minoxidil to compete for binding to the EGF receptor indicated that minoxidil probably does not bind to the EGF receptor. Minoxidil was not toxic, as keratinocytes continued to survive and grow, although at a slower rate, in the presence of minoxidil.

Characterization of epidermal growth factor binding to hepatic plasma membranes of rainbow trout (Oncorhynchus mykiss)

Epidermal growth factor (EGF) is a potent mitogen which exerts its effects through a transmembrane receptor located on target cells. Since little is known about EGF in nonmammalian animals, experiments were conducted to characterize the EGF receptor in rainbow trout hepatic cell membranes. The binding of mouse EGF with rainbow trout receptors was peptide-specific, saturable, reversible, and of high affinity. Optimal binding was observed at pH 7.2. Both monovalent and divalent cations augmented the specific binding of EGF, by a factor of two- to threefold over control values, but were not needed for binding to occur. Scatchard plot of the saturation data was curvilinear. Analysis of the data by kinetic methods indicated the curvilinear nature of the Scatchard plot was due to multiple receptor sites of differing affinity and not to site-to-site interactions. Rate constants for association (K11) were 9.38 X 10(8) M-1 * min-1 and 2.28 X 10(7) M-1 * min-1 for the high and low affinity sites, respectively. Rate constants for dissociation (K-1) were 2.03 X 10(-3) min-1 and 2.07 X 10(-1) min-1 for high and low affinity sites, respectively. The apparent dissociation constants determined from the rate constants for the high affinity (KD = 2.3 X 10(-11) M) and low affinity (KD = 9.1 X 10(-9) M) were in agreement with constants estimated by equilibrium methods. Maximum binding capacities were 13 fmol EGF bound/mg protein of protein and 270 fmol EGF bound/mg of protein for the high and low affinity receptor sites, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterisation and distribution of epidermal growth factor receptors in equine hoof wall laminar tissue: comparison of normal horses and horses affected with chronic laminitis

Epidermal growth factor (EGF) receptors were detected in plasma membrane preparations of equine hoof wall laminar tissue at concentrations comparable to that of equine liver. Scatchard analysis of the equilibrium binding data suggested the presence of two classes of EGF binding sites in most of the controls (plasma membranes from clinically normal horses); a high-affinity class and a more numerous low-affinity class. The dissociation constant of the low-affinity class of EGF-specific receptors (KD = 1 x 10(-9)M) is in reasonable agreement with other values established for the EGF receptor. The variability between individual estimates for the KD of the high-affinity receptor class precluded an accurate estimate for those sites. A possible explanation is discussed. The high-affinity binding sites were uniformly absent in plasma membranes prepared from horses affected by chronic laminitis. Autoradiographic analysis localised the EGF receptors primarily to the secondary epidermal laminae, with an apparent greater density over the proliferative basal keratinocytes. Little label was associated with the dermal or the keratinised primary epidermal laminae. Tissue from horses with chronic laminitis had EGF receptors located uniformly over the hyperplastic epidermal keratinocytes. These data suggest that an EGF-mediated response may be involved in the hyperproliferative response that is characteristic of chronic laminitis.

Kinetic analysis of receptor-mediated endocytosis of epidermal growth factor by isolated rat hepatocytes

The interaction of epidermal growth factor (EGF) with cell surface receptors and their subsequent endocytosis in isolated rat hepatocytes were analyzed by measuring changes in the concentrations of cell surface-bound, internalized, and degraded EGF. The kinetic model proposed by Wiley and Cunningham (Cell 25: 433-440, 1981) and Gex-Fabry and Delisi [Am. J. Physiol. 247 (Regulatory Integrative Comp. Physiol. 16): R768-R779, 1984] was basically utilized for the model analysis. The following kinetic parameters were obtained: association and dissociation rate constants for EGF-receptor interaction, internalization rate constant for EGF-receptor complex (kappa e), internalization rate constant for free receptor (kappa t), sequestration rate constant (kappa s) of the complex from shallow (exchangeable) to deep (nonexchangeable) membraneous compartment, intracellular degradation rate constant and initial cell-surface receptor density. The kappa s value, which was obtained by analyzing the time profiles of EGF association with cells, was approximately 5-10 times larger than the kappa e value determined by directly measuring internalized EGF with the acid-washing technique. This suggests the necessary presence of deep (nonexchanging) compartment of the complex in the plasma membrane. The calculated kappa e value is at least several times larger than the kappa t value, yielding the kinetic basis for the occurrence of receptor downregulation induced by excess EGF. We conclude that, in the overall receptor-mediated processing of EGF after bound to the cell surface receptors, the dissociation process is rapid [half-time (t1/2) less than 1 min], the degradation process is much slower (t1/2 approximately equal to 3 h), and the receptor internalization process is intermediate (t1/2 approximately equal to 6-7 min). In addition, two pools for EGF-receptor complex in the plasma membrane seem to be present, although their identification cannot be made.

Estrone modulates the EGF receptor in the liver of db/db mouse

The genetically diabetic db/db mouse is an excellent model to study the effect of diabetes on hormone receptors. The decrease of EGF binding sites could be detected in the hepatic microsomes of diabetic mice as early as 3 weeks of age. In addition, there was an age-related decrease in the autophosphorylating activity of EGF receptor isolated from the liver of diabetic mice. Estrone feeding (0.005%) partially restored this autophosphorylating activity. Northern blot analysis showed that the hepatic EGF receptor transcripts were dramatically decreased during the progression of diabetes and could be reversed by estrone feeding. Transfection experiments carried out on HepG2 cells using EGF receptor promoter (pERCAT-6) demonstrated that addition of 2 x 10(-8) M estrone stimulated chloramphenicol acetyltransferase activity. Our results suggest that estrone modulates EGF receptor by enhancing EGF receptor transcripts and the promoter activity of this gene.

EGF receptor-binding activity in the urine of normal horses and horses affected by chronic laminitis

A heterologous radioreceptor binding assay (RRA) has been developed capable of detecting nanogram amounts of epidermal growth factor (EGF) receptor-binding activity in equine urine. The binding parameters of [125I]mEGF (murine EGF) to EGF receptors on equine plasma membranes are in good agreement with values from other EGF-RRA systems. The dissociation constant estimated from equilibrium methods (KD = 4 X 10(-10) M) is in reasonable agreement with that determined from the rate constants (KD = 6 X 10(-10) M) and is in good agreement with values determined in other species. The assay is specific for equine EGF (eEGF) receptor-binding activity and capable of detecting less than 0.34 nM eEGF receptor-binding activity in urine. Equine EGF receptor-binding activity in equine urine form adult horses varied widely between samples (8.5 +/- 6.5 nM). This variability was somewhat reduced when values were adjusted for dilutional effects using urine creatinine as an indicator (3.6 +/- 2.0 nanomoles/g creatinine). No significant differences were demonstrated between the means of EGF binding activity concentrations in clinically normal horses and horses affected by chronic laminitis.

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

The binding of human epidermal growth factor (hEGF), beta-urogastrone, to plasma membranes isolated from rat gastric mucosa was studied to characterize gastric EGF receptors. The binding of [125I]hEGF was temperature dependent, reversible, and saturable. A single class of binding sites for EGF with a dissociation constant of 0.42 nM and maximal binding capacity of 42 fmol/mg protein was suggested. There was little change in the binding of [125I]hEGF upon addition of peptide hormones (secretin, insulin), antiulcer drugs (cimetidine), or an ulcer-inducing reagent (aspirin). Cross-linking of [125I]hEGF to gastric plasma membranes with the use of disuccinimidyl suberate resulted in the labeling of a protein of 150 kDa. These results indicate the presence of EGF receptors on plasma membranes of rat gastric mucosa.

Morphologic demonstration of receptor-mediated endocytosis of epidermal growth factor by isolated bile duct epithelial cells

It was recently shown that intrahepatic bile duct epithelial cells in situ or after isolation from rat liver have coated pits and vesicles, suggesting that they participate in receptor-mediated endocytosis. Therefore, using a morphologic approach and epidermal growth factor coupled to horseradish peroxidase or colloidal gold as probes, we studied freshly isolated or short-term cultured intrahepatic bile duct epithelial cells prepared from normal rat liver to determine if they participate in receptor-mediated endocytosis. Immunoelectron microscopy using a monoclonal antibody against the epidermal growth factor receptor was also used to examine for the presence of the growth factor receptor on the cells. Immediately after isolation, the cells did not internalize either epidermal growth factor-horseradish peroxidase or epidermal growth factor-colloidal gold; no growth factor receptor could be shown on these cells by immunocytochemistry, either. In contrast, cells cultured for 24 h bound and internalized both epidermal growth factor-horseradish peroxidase and epidermal growth factor-colloidal gold at 37 degrees C and showed growth factor receptors diffusely distributed on the plasma membrane. When cultured cells exposed to epidermal growth factor-colloidal gold were fixed with glutaraldehyde containing saponin and tannic acid, colloidal gold particles were observed in coated pits and in coated and uncoated vesicles. Preincubation of cultured cells with native epidermal growth factor completely blocked the internalization of both epidermal growth factor-horseradish peroxidase and epidermal growth factor-colloidal gold. When rat liver was stained in situ for epidermal growth factor receptor, reaction product was observed by immunoelectron microscopy exclusively on the basal surface of the plasma membrane of the intrahepatic bile duct epithelial cells. These results indicate that bile duct epithelial cells internalize epidermal growth factor by endocytosis via coated pits containing receptors localized in situ exclusively to the basal domain of their plasma membranes. The data demonstrate for the first time that intrahepatic bile duct epithelial cells participate in receptor-mediated endocytosis and raise the possibility that they are a target for epidermal growth factor.

Effect of salivarectomy on the growth of gastrointestinal mucosa and urinary secretion of epidermal growth factor in rats

The effect of salivary epidermal growth factor (EGF) on the growth and metabolism of gastrointestinal mucosa was examined by comparing DNA synthesis, DNA and RNA content, and weight of mucosa of salivarectomized and sham operated male rats. DNA synthesis of gastric mucosa was suppressed at 2 days after salivarectomy. Both weight and DNA content of oxyntic mucosa in the salivarectomized group were significantly lower than that of the sham operated group. Although salivarectomy suppressed DNA synthesis of jejunal mucosa, the difference was not significant statistically. The effect of salivarectomy on colonic mucosa was least in the gastrointestinal tract. Such a result suggested that the gradient-oriented antitrophic effect was brought about by salivarectomy. Urinary EGF excretion after salivarectomy was examined by radioreceptor assay. Although the antitrophic effect of salivarectomy on oxyntic mucosa was highest on day 2, no significant difference of urinary EGF concentration was detected on day 2. From these results it is suggested that the effect of salivarectomy on the gastrointestinal tract was not due to the change of EGF in systemic circulation but due to the change of luminal EGF.

Epidermal growth factor receptors in rat placenta, amnion and yolk sac: characteristics of specific binding are dependent on gestational age

Studies of [125I]-EGF binding to the rat placenta, amnion and yolk sac were carried out on days 14, 17 and 20 of gestation. In the placenta EGF binding was detectable on all 3 days; in the amnion EGF binding was undetectably low on day 14 but was present on days 17 and 20, while in the yolk sac EGF binding was undetectably low on all 3 days. Although Scatchard analysis of EGF binding to placental tissue raised the possibility of high and low affinity receptors, a statistical analysis of the ligand binding data was consistent with the presence of only one type of EGF receptor. The overall affinity of the receptors did not change with stage of gestation. However, the concentration of EGF receptors was lower in placental tissue on day 17 than on days 14 or 20 of gestation; the receptor concentrations were similar on days 14 and 20. It is suggested that EGF binding to the placenta, amnion, and yolk sac may reflect the levels of cell proliferation in those tissues in the latter part of gestation.

Decrease in the number of receptors for epidermal growth factor in the liver of D-galactosamine-intoxicated rats

Hepatic transport of epidermal growth factor (EGF) was studied in D-galactosamine-intoxicated rats by the multiple-indicator dilution (MID) method. The extraction ratio of 125I-labeled EGF in the intoxicated rats, obtained from a model-independent analysis of the dilution curves, decreased to 45% of the control values. A distributed two-compartment model was fitted to the dilution data by nonlinear least-squares regression, and the kinetic parameters, kon.PT (product of on-rate constant and receptor density), koff (off-rate constant) and ks (sequestration rate constant) were determined. The values of kon.PT and ks in the intoxicated rats decreased to approximately one-half and one-third of those in the control rats respectively. Similar decreases in the kon.PT and ks values in the intoxicated rats were also observed for the transport of 125I-labeled insulin, a positive control, into the liver. The 125I-labeled EGF binding experiment at equilibrium using liver homogenates revealed that the intoxication reduced the receptor density (PT) to one-third of the control values, whereas the equilibrium dissociation constant (kd) did not change significantly. The activities of Na+,K+-ATPase, cytochrome P-450 and glutathione S-transferase decreased in the intoxicated rats to 70-80% of the control values. The number of nuclei per unit area of tissue slices was also reduced to 70% of the control. Thus, the extent to which the enzyme activities and the number of nuclei decreased in the intoxicated liver was smaller than that of the number of EGF receptors. It is concluded that the reduction of EGF receptors cannot be explained by the "intact hepatocyte hypothesis" but rather by the functional change of hepatocytes induced by the administration of D-galactosamine.

Effect of lipoxygenase products on choriogonadotropin secretion by cultured human choriocarcinoma JEG-3 cells pre- and post-stimulation with epidermal growth factor and a phorbol ester

Previous studies using arachidonic acid and preferential inhibitors of the arachidonic acid pathway have implicated the lipoxygenase system in choriogonadotropin (hCG) secretion by JEG-3 cells. Presently, JEG-3 cells are used in order to examine the effect of lipoxygenase products on hCG secretion. Results show that 30 microM 15-hydroxyeicosatetraenoic acid (15-HETE) induces an approximately 3-fold increase in basal hCG secretion, while 5-HETE, 12-HETE, and leukotriene LTA4 have no significant effect. In addition, 15-HETE potentiates the stimulation of hCG secretion induced by 3 nM epidermal growth factor (EGF), but has no significant effect on the stimulation of hCG induced by 22 nM tetradecanoylphorbol acetate (TPA). The present study further implicates the arachidonic acid pathway in the control of hCG secretion and documents that the effect of EGF can be rate-limited by a product of the lipoxygenase system.

Preparation of EGF labeled liposomes and their uptake by hepatocytes

The preparation of epidermal growth factor (EGF) bearing liposomes (EGF-liposomes) and their uptake by rat hepatocytes were described. EGF was bound to the liposomal surface by the disulfide bridge linkage using a heterobifunctional cross-linking reagent, N-hydroxysuccinimidyl-3-(2-pyridyl-dithio) propionate. EGF-liposomes were taken up in a significant amount by rat hepatocytes in an EGF receptor mediated manner, and their uptake was dependent on the amount of labeled EGF coupled to the liposomal surface. These results raise the possibility that the EGF-liposomes may be an effective drug carrier to the cells having EGF-receptors like some cancer cells.

Identification of a phosphotyrosyl-protein phosphatase in mouse epidermis

Binding of epidermal growth factor (EGF) stimulates tyrosyl protein kinase activity of its receptor in the epidermis. This tyrosine residue phosphorylation is thought to be one mechanism by which EGF mediates its effects such as growth stimulation. To modulate a cellular response to EGF, an enzyme which dephosphorylates phosphotyrosyl residues should be present to oppose the effect of the tyrosyl kinase activity of the EGF receptor. We have identified an enzyme in the neonatal mouse epidermis which has the ability to dephosphorylate tyrosyl residues in vitro on EGF receptors. This phosphatase is a soluble protein with a molecular weight greater than 10,000 daltons and shows optimum activity at neutral pH. This epidermal tyrosyl protein phosphatase is not inhibited by tartrate, ATP, and micromolar levels of zinc, but is inhibited by millimolar levels of zinc, magnesium, manganese, and fluoride. Unlike other well-known phosphotyrosyl phosphatases, alkaline phosphatase, and calcineurin, this enzyme is not inhibited by EDTA. Thus, we have identified and partially characterized a possibly unique phosphotyrosyl phosphatase from the epidermis.

Receptor-mediated transport of peptide hormones and its importance in the overall hormone disposition in the body

A remarkable feature of the pharmacokinetics of polypeptide hormones is the contribution of specific binding sites (receptors) to the polypeptide hormone distribution and clearance in the body. The concept of "transport receptor" is now well established, and receptor-mediated endocytosis (RME) is recognized as a general mechanism in the uptake of biologically important peptide hormones. This article focuses on the kinetic analysis of the RME of polypeptides, based mainly upon the observations of the kinetics of epidermal growth factor in the liver. The following points are emphasized: (1) How can we determine the existence and the kinetic constants of polypeptide RME in vivo and in the perfused liver system? A liver perfusion method, the single-pass multiple-indicator dilution technique, has been shown to be suitable for analyzing the dynamics of interaction of peptide hormones with their cell surface receptors. (2) What is the importance of down-regulation of transport receptors to the overall kinetics of polypeptides in vivo? Time profiles of polypeptide plasma concentrations and their surface receptors in the liver after iv administration of epidermal growth factor were simulated with a physiologic pharmacokinetic model that includes kinetic constants representing the interaction of polypeptides and their receptors.

Placental keratinocyte growth factor: partial purification and comparison with epidermal growth factor

A water-soluble extract of term human placenta, which was previously shown to promote proliferative growth of human keratinocytes in defined medium, enhanced both cellular attachment and proliferative growth. We have partially purified the activity which enhanced cell growth and examined its action in keratinocytes. Activity was precipitated from the crude extract by (NH4)2SO4 between 33 and 60% saturation and chromatographed by gel filtration. The activity did not bind to heparin-Sepharose at low ionic strength but was adsorbed to DEAE-cellulose from which it was eluted with NaCl and then passed over phenyl-HPLC to remove bovine serum albumin previously added to protect the activity. The active fraction was applied to gel exclusion HPLC in the presence of 0.02% octyl-beta-D-glucopyranoside, which yielded an apparent Mr 35,000 for the factor. Purification was approximately 200-fold with approximately 4% recovery. The factor appears to be a protein, since activity is destroyed by trypsin. Autoradiography of cultures treated with the placental factor or epidermal growth factor (EGF) revealed that approximately 50% of cells were labeled after treatment with either growth factor compared to 9% in control cultures after a [3H]thymidine pulse. Protein synthesis was increased by about 50% 42 h after treatment with either agent, consistent with a 50% increase in nuclear labeling. Cell number was increased fivefold after 6 days in the presence of the partially purified factor, whereas EGF increased cell number eightfold. Stimulation of [3H]thymidine incorporation by the partially purified factor, in contrast, was about twice that produced by EGF, indicating that thymidine incorporation is preferentially stimulated by the placental factor and does not correlate well with other parameters of proliferative growth. The placental keratinocyte growth factor is a unique factor with a novel effect on incorporation of thymidine into DNA.

Phospholipase C activity in human placental membrane

Receptor-stimulated hydrolysis of polyphosphoinositides by action of phospholipase C appears to be an important mediator of cell activation through the generation of the second messengers, in particular inositol triphosphate (IP3). In order to understand placental function better, activity of IP3 production from membrane in cell-free system was examined. Incubation of membrane preparation from [3H]inositol-labelled human placenta with Ca2+ in the presence of 1 mM ATP and 1 mM GTP resulted in the rapid production of IP3 in a dose dependent manner; half-maximal effect occurred at 10 microM. On the other hand, little effect was observed in the case of membrane prepared from [3H]arachidonic acid-labelled placenta, suggesting higher requirement of Ca2+ for phospholipase A2 activation. These data suggest that placenta contains phospholipase C hydrolyzing polyphosphoinositide at physiological concentration of Ca2. This is the first report to provide direct evidence of transmembrane signalling mechanisms in the human placenta, and may provide a clue to the etiology of placental disorders.

Dynamic determination of kinetic parameters for the interaction between polypeptide hormones and cell-surface receptors in the perfused rat liver by the multiple-indicator dilution method

Hepatic elimination of epidermal growth factor (EGF) via receptor-mediated endocytosis was studied by a multiple-indicator dilution method in the isolated perfused rat liver, in which cell polarity and spatial organization are maintained. In this method EGF was given with inulin, an extracellular reference, as a bolus into the portal vein, and dilution curves of both compounds in the hepatic vein effluent were analyzed. Analysis of the dilution curve for EGF, compared with that for somatostatin, which showed no specific binding to isolated liver plasma membranes, resulted as follows: (i) both extraction ratio and distribution volume of 125I-labeled EGF decreased as the injected amount of unlabeled EGF increased; (ii) the ratio plot [ln (inulin/EGF) versus time] of the dilution curve for EGF exhibited an upward straight line initially for a short period of time (approximately equal to 10 sec), whereas the ratio plot [ln (inulin/somatostatin) versus time] of somatostatin gradually decreased. The multiple-indicator dilution method was used for other peptides also. Insulin and glucagon, known to have hepatocyte receptors, behaved similarly to EGF in shape of their ratio plots. Thus, analysis of dilution curves can reveal whether or not the cell surface has receptors for certain peptides. In addition, the dilution curves for EGF at various doses (tracer approximately equal to 30 micrograms) were analyzed simultaneously based on a kinetic model incorporating the perfusion rate, the association rate constant of EGF to surface receptors (kappa on), the dissociation rate constant of EGF from the EGF-receptor complex (kappa off), and the sequestration rate constant of the complex. The kinetic parameters [the dissociation constant (Kd = kappa off/kappa on) and the number of surface receptors] calculated by this analysis were comparable with reported values obtained by in vitro direct binding measurements at equilibrium using liver homogenates. We conclude that the multiple-indicator dilution method is a good tool for analyzing the dynamics of peptide hormones--cell-surface receptor interaction under a condition in which spatial architecture of the liver is maintained.

Epidermal growth factor receptor numbers in male and female mouse primary hepatocyte cultures

Epidermal growth factor receptors (EGF-R) were measured in adult male and female mouse primary hepatocyte cultures. On culture day 1, female hepatocytes had significantly fewer EGF-R than male hepatocytes (1.3 x 10(4) versus 6.2 x 10(5) per cell). Over the next three days, morphological changes consistent with progressive heptocyte dedifferentiation were observed. During this period, EGF-R numbers progressively increased in female cultures and decreased in male cultures, and by day 4 the sexual difference in EGF-R numbers was obliterated. These results indicate that a relationship exists between the degree of differentiation in hepatocyte cultures and the expression of EGF-R on the cell surface.

Reduction of adipose tissue lipoprotein lipase activity as a result of in vivo administration of 2,3,7,8-tetrachlorodibenzo-p-dioxin to the guinea pig

Within 1 hr of intraperitoneal administration of 1 microgram 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)/kg, lipoprotein lipase (LPL) activity was reduced 38% from initial levels in the adipose tissue of the guinea pig. Maximal depression was observed after 2 days and persisted throughout the 10-day observation period. Oral administration of glucose restored LPL activity in TCDD-treated animals after 1 day but only partially after 2 and 5 days, and had no effect after 10 days of exposure. Although initial (2-day) serum insulin levels were depressed, the inability of glucose to restore LPL activity after prolonged exposure was not due to malabsorption of glucose nor to changes in serum thyroxine or insulin concentration. TCDD also inhibited the lipolytic pathway in the adipocyte, but had no effect on hormone sensitive lipase (HSL). Since HSL and LPL are reciprocally regulated, it was concluded that TCDD acts on the adipocyte to uncouple HSL-LPL reciprocity as well as to reduce LPL production.

Conformational and receptor binding properties of human EGF and TGF-alpha second loop fragments

The solution conformation of the second loop fragment of human EGF, [Ala20] EGF (14-31), was determined using two-dimensional NMR homonuclear Hartmann-Hahn and rotating frame nuclear Overhauser enhancement spectroscopy. The results are compared with the conformation of the second loop fragment of human TGF-alpha, [Ala21] TGF-alpha(16-32), and with that of the second loop of intact EGF. Comparison of the two experimentally determined structures of the second loop fragments shows significant differences in the turn regions of each peptide. For the EGF fragment, hydrophobic side chain groups protrude away from the ring, whereas for the TGF-alpha fragment hydrophilic groups are directed away from the ring. Although these turn regions represent the putative receptor binding sites, neither second loop fragment binds to the EGF receptor. The biological activity is discussed in terms of the conformational differences found for the two second loop fragments.

Epidermal growth factor receptor in human breast cancers: correlation with estrogen and progesterone receptors

Epidermal growth factor receptor (EGFR), determined by the Scatchard curve method, was found in 22 cases of a random series of 100 patients with breast carcinoma. Two groups of patients were identified, one (n = 16) with a low concentration (0-50 fm/mg protein) of EGFR but with a high affinity (Kd = 3.2 nM), and the other (n = 6) with a high concentration (90-210 fm/mg protein) of EGFR but with a lower affinity (Kd = 6.3 nM). A significant inverse relationship was found between the presence of EGFR and receptors for estrogen (p less than 0.001) and progesterone (p = 0.001). EGFR was found in no (0/8) tumors with Grade I histoprognostic grade, 17% (10/58) Grade II, and 38% (11/29) Grade III (p less than 0.05). EGFR is present therefore in poorly differentiated tumors and associated with other factors of poor prognosis. Our in vivo analyses confirm results found in tissue culture derived from human breast carcinoma cells.