Epidermal growth factor

Molecular cloning of the microfibrillar protein MFAP3 and assignment of the gene to human chromosome 5q32-q33.2

Microfibrils having a diameter of 10-12 nm, found either in association with elastin or independently, are an important component of the extracellular matrix of many tissues, but characterization of these microfibrils is incomplete. To further our understanding of the gene structure of proteins composing the microfibrils and to identify their chromosomal location, we have cloned and characterized another microfibril protein, designated microfibril-associated protein-3 (MFAP3). The human gene encoding MFAP3 has a very simple structure, containing only two translated exons encoding a protein of 362 amino acids. Monospecific antibodies prepared against the recombinantly expressed protein reacted with the microfibrils found in ocular zonules. MFAP3 does not appear to share homology with any other known protein. The gene was found to be located on chromosome 5q32-q33.2, near the locus 5q21-q31 reported for the fibrillin gene, FBN2, which has been linked to congenital contractural arachnodactyly. MFAP3 is a candidate gene for heritable diseases affecting microfibrils.

Stimulation of phospholipase D by epidermal growth factor requires protein kinase C activation in Swiss 3T3 cells

The proposal that epidermal growth factor (EGF) activates phospholipase D (PLD) by a mechanism(s) not involving phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P2) hydrolysis was examined in Swiss 3T3 fibroblasts. EGF, basic fibroblast growth factor (bFGF), bombesin, and platelet-derived growth factor (PDGF) activated PLD as measured by transphosphatidylation of butanol to phosphatidylbutanol. The increase in inositol phosphates induced by bFGF, EGF, or bombesin was significantly enhanced by Ro-31-8220, an inhibitor of protein kinase C (PKC), suggesting that PtdIns(4,5)P2-hydrolyzing phospholipase is coupled to the receptors for these agonists but that the response is down-regulated by PKC. Activation of PLD by EGF was inhibited dose dependently by the PKC inhibitors bis-indolylmaleimide and Ro-31-8220, which also inhibited the effects of bFGF, bombesin, and PDGF. Down-regulation of PKC by prolonged treatment with 4 beta-phorbol 12-myristate 13-acetate also abolished EGF- and PDGF-stimulated phosphatidylbutanol formation. EGF and bombesin induced biphasic translocations of PKC delta and epsilon to the membrane that were detectable at 15 s. In the presence of Ro-31-8220, translocation of PKC alpha became evident, and membrane association of the delta- and epsilon-isozymes was enhanced and/or sustained in response to the two agonists. The inhibitor also enhanced EGF-stimulated [3H]diacylglycerol formation in cells preincubated with [3H]arachidonic acid, which labeled predominantly phosphatidylinositol, but inhibited [3H]diacylglycerol production in cells preincubated with [3H]myristic acid, which labeled mainly phosphatidylcholine. These data support the conclusion that EGF can stimulate diacylglycerol formation from PtdIns(4,5)P2 and that PKC performs the dual role of down-regulating this response as well as mediating phosphatidylcholine hydrolysis. In summary, all of the results of the study indicate that PLD activation by EGF is downstream of PtdIns(4,5)P2-hydrolyzing phospholipase and is dependent upon subsequent PKC activation.

Pharmacologic enhancement of wound healing

The field of pharmacologic modulation of soft tissue repair is in its infancy. Although the soluble, cellular, and insoluble mediators that govern repair have not been elucidated, the application of pharmacologic concentrations of purified polypeptide growth factors, cytokines, and matrix molecules has nonetheless resulted in the acceleration of normal repair and the reversal of deficient repair in a wide variety of dermal wound models in animals. However, early clinical results using these factors have been less than encouraging, and their potential roles in the armamentarium of chronic wound therapies remain to be established.

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)

Role of GTP-binding proteins in the polyunsaturated fatty acid stimulated proliferation of mouse mammary epithelial cells

Polyunsaturated fatty acids enhance the proliferation of mouse mammary epithelial cells stimulated by epidermal growth factor (EGF) by modulating the post-receptor signaling pathways. The growth stimulatory effect of these fatty acids is completely inhibited by pertussis toxin, whereas the inhibition of EGF and insulin stimulated growth is only partial. The treatment of cell cultures with 12-O-tetradecanoyl-phorbol-13 acetate (TPA) reverses the growth inhibitory effect of pertussis toxin and fully restores the growth as was in the control cultures untreated with the toxin suggesting a role for PKC in this reversal. It appears that the functions of Gi-proteins are required in the mediation of fatty acid effect on growth. The predominant types of Gi alpha in mammary epithelial cells are Gi alpha 1, Gi alpha 2, and Gi alpha 3. Among these, the levels of Gi alpha 1 and 2 appears to be regulated by steroid hormones. Linoleic acid raises the level of GTP-bound Ras in the cells above the levels induced by EGF. Pertussis toxin reduces the level of Ras-GTP and inhibits phosphorylation of MAP kinase by EGF. It has been speculated that Gi-proteins interact with the receptor bound nucleotide exchange factor and the membrane anchored Raf kinase and constitute two sites for pertussis toxin action. The phosphorylation by PKC may uncouple Gi-protein interaction with these effectors and enable the agonist-induced signals to bypass the inhibitory action of PT on growth.(ABSTRACT TRUNCATED AT 250 WORDS)

Hydrogen peroxide preferentially enhances the tyrosine phosphorylation of epidermal growth factor receptor

We found that hydrogen peroxide (H2O2) enhances EGF receptor tyrosine phosphorylation in intact cells as well as solubilized membrane of an EGF receptor hyperproducing cell line NA. An antioxidant MnCl2 effectively inhibited this enhancement. Interestingly, overall phosphorylation of the EGF receptor enhanced by H2O2 was half that of the EGF-enhanced phosphorylation when the receptor immunoprecipitated from [32P]orthophosphate-labeled cells was examined. Tryptic phospho-peptide mapping of these receptors revealed that EGF enhanced the phosphorylation on five specific residues including serine 671, 1,046 and 1,047, threonine 669 and tyrosine 1,173, whereas H2O2 enhanced the phosphorylation remarkably on tyrosine 1,173 and three other residues and only moderately on serine 1,046 and 1,047 and threonine 669. Thus, H2O2 preferentially enhances the tyrosine phosphorylation of EGF receptor through oxidant stress.

EGF receptor-mediated signals are differentially modulated by concanavalin A

NIH 3T3 cells expressing high levels of the human epidermal growth factor (EGF) receptor were used to examine the effects of the lectin concanavalin A (Con A) on EGF-mediated signaling events. Proliferation of NIH 3T3 cells expressing high levels of the human EGF receptor was inhibited in a dose-dependent manner by Con A. At the same time, Con A also inhibited both dimerization and tyrosine phosphorylation of the EGF receptor. Tyrosine phosphorylation of the enzyme phospholipase C-gamma, a substrate of the phosphorylated EGF receptor kinase, was also inhibited. In contrast, EGF-stimulated changes in pH, calcium, and levels of inositol phosphates were unaffected by the presence of Con A. These results indicate that certain signals (changes in the levels of intracellular calcium, pH, and inositol phosphates) mediated by EGF binding to its receptor still occur when receptor dimerization and phosphorylation are dramatically decreased, suggesting that multiple independent signals are transmitted by the binding of EGF to its receptor.

Effect of EGF on rat parotid gland secretory function

The present study reports changes in saliva composition from the rat parotid gland in response to single and repeated administration of epidermal growth factor (EGF). Treatment of rats with EGF (10 micrograms/kg, i.p., twice daily for 3 days) caused an increase in amylase activity in saliva collected from cannulated parotid duct, following stimulation of secretion with pilocarpine, with a corresponding decrease in enzyme activity in the gland. Analysis of parotid gland RNA by reverse transcriptase-PCR generated a single predicted amylase-derived cDNA product of 576 bp. The steady-state levels of mRNA for amylase from EGF-treated parotid total RNA showed a 1.8-fold increase compared to untreated controls. A single dose of EGF (15 min following i.p. injection) elicited an activation of both protein kinase A and protein kinase C activities. While the activation of protein kinase A was still maintained under the chronic EGF regimen, the activity levels of protein kinase C showed down-regulation to untreated control values.

Epidermal growth factor rapidly impairs activation of p34cdc2 protein kinase in HeLa cells at the G2-M boundary

Epidermal growth factor (EGF) has been shown rapidly to inhibit the transition from G2 phase to mitosis: beyond this transition point the cells are refractory to EGF (Kinzel et al., 1990, Cancer Res., 50:7932-7936). Using synchronized HeLa cells, EGF has now been shown to induce an overall decrease of the histone H1 kinase activity of p34cdc2 after 20 min of treatment, a time course which correlates with the number of cells in metaphase. The kinase level of actively mitotic cells is not altered by EGF. Neither the amount of p34cdc2 protein present nor that of Cyclin B in influenced by EGF, and the formation of the p34cdc2/Cyclin B complex is also unaffected. The use of antiphosphotyrosine antibodies, however, showed that p34cdc2 from cultures treated with EGF was more intensely stained than that of control cells, indicating that EGF treatment prevents the tyrosine dephosphorylation which is required for expression of the protein kinase activity of the complex. Taken together, the results show that EGF in HeLa cells very rapidly prevents the p34cdc2/Cyclin B complex from expressing kinase activity at the G2-M boundary, which appears to be the cause for the inhibition in G2 phase.

Systemic treatment with recombinant human epidermal growth factor accelerates healing of sclerotherapy-induced esophageal ulcers and prevents esophageal stricture formations in pigs

Human epidermal growth factor (EGF), a small polypeptide (6 kDa) with mitogenic properties, has been implicated in the protection of gastrointestinal mucosal integrity. The efficacy of EGF in the prevention and healing of sclerotherapy-induced esophageal lesions was investigated in 24 minipigs with surgically induced portal hypertension. In addition, the effect of EGF on intragastric acidity and pharmacokinetics was investigated as possible means to explain its protective mechanism of action. The animals underwent three weekly sessions of sclerotherapy with polidocanol 2% and were concomitantly and for an additional three weeks treated with either placebo or EGF administered paravenously in the esophagus and/or subcutaneously. The subcutaneous treatment with EGF significantly (P < 0.05) reduced esophageal stricture and scar formations associated with sclerotherapy. Gastric pH values were significantly (P < 0.01) elevated only in animals receiving subcutaneous injections of EGF. Furthermore, the subcutaneous administration of EGF was associated with unexpected prolonged plasma concentration of the peptide. These results suggest a possible clinical value of EGF as an adjunctive treatment with the sclerotherapy.

Expression of epidermal growth factor family gene members in early mouse development

Transcription of four members of the epidermal growth factor (EGF) family, EGF, TGF-alpha, Amphiregulin, and Cripto, was investigated in the ovulated unfertilized egg and preimplantation embryo using cDNA libraries. EGF was present as a maternal message only, TGF-alpha was present at low levels in each library, Amphiregulin was not detected, and Cripto transcripts were first detected in the blastocyst cDNA library. In situ hybridization studies of the implanting embryo revealed Cripto expression localized to the entire ectoderm and then to the rapidly growing ectoplacental cone. At gastrulation, Cripto was detected in the primitive streak and developing mesoderm. During organogenesis, Cripto localized to the developing heart. Two Cripto transcripts were detected: one is confined to the early embryo and teratocarcinoma cells, and the other, first found in the fetus, is the major form detected in adult organs.

Protein tyrosyl phosphatase-1B is expressed by normal human epidermis, keratinocytes, and A-431 cells and dephosphorylates substrates of the epidermal growth factor receptor

In the epidermis tyrosine kinases such as those found in the epidermal growth factor receptor (EGF-R) phosphorylate regulatory molecules on tyrosine and play an important role in controlling epidermal growth. Phosphotyrosyl phosphatases (PTPase) that dephosphorylate EGF-R and other proteins phosphorylated on tyrosine must also play an important role in controlling epidermal growth. The presence and metabolism of one such PTPase, PTP-1B, was detected and studied in human skin using biochemical, immunochemical, and molecular biologic methods. The message for PTP-1B was expressed in human epidermis, in keratinocytes cultured from human epidermis, and in human keratinocyte cell lines. The 49-kDa but not the 37-kDa form of PTP-1B was identified in membranes prepared from these cells and tissues by immunodetection on Western blots. Nearly all of the labeled proteins identified by gel electrophoresis of an A-431 particulate fraction phosphorylated with [gamma-32P] ATP in the presence of epidermal growth factor are substrates for PTP-1B because their labeling decreased after incubation with a catalytically active and purified PTP-1B fusion protein. Immunohistochemical methods were used to show that PTP-1B was primarily localized to the basal cell layers in normal thick epidermis. The presence of PTP-1B in intact human epidermis suggests that this molecule is not an artifact limited to cultured cells but is an important molecule in the in vivo regulation of epidermal functions.

The endogenous substrate of low molecular weight acid phosphatase in the brain is an epidermal growth factor receptor

We have recently reported that low molecular weight (LMW) acid phosphatase, which is supposed to possess phosphotyrosine protein phosphatase activity, showed a significant decrease of activity in Alzheimer brains compared to control brains [Ann. Neurol., 33 (1993) 616-621]. In the present study, we investigated the endogenous substrate of LMW acid phosphatase in the brain. LMW acid phosphatase was purified from bovine brain, and the enzyme was obtained with both a high specific activity and a good yield. The bovine brain enzyme was a monomer with a molecular mass of 17 kDa. We used a specific monoclonal anti-phosphotyrosine antibody to detect phosphotyrosine protein in rat brain extracts. The LMW acid phosphatase from bovine brain dephosphorylated a M(r) 170 kDa phosphotyrosine protein in rat brain extracts. This M(r) 170 kDa protein was considered to be the epidermal growth factor (EGF) receptor using a specific antibody. These results suggest that LMW acid phosphatase in the brain may regulate EGF receptor-dependent transmembrane signalling by dephosphorylating the phosphorylated receptor.

Kinetics of phosphorylation of the SH2-containing domain of phospholipase C gamma 1 by the epidermal growth factor receptor

The kinetics of the EGF receptor (EGFR) autophosphorylation and of the phosphorylation by EGFR of a fusion protein (Fp(SH2)) derived from PLC-gamma 1 with two SH2 domains were studied employing purified EGFR or membrane-bound preparations of native and truncated EGFR. With varied ATP concentrations both reactions yielded Michaelis-Menten kinetics. KATP for autophosphorylation was 0.35 microM and for Fp(SH2) phosphorylation 1.35 microM. With Fp(SH2) and were followed by drops to zero velocities at about 1.0 microM Fp(SH2). We conclude that (a) our data support the concept that receptor autophosphorylation is a prerequisite for the interactions between EGFR and the substrate's SH2-domains and their eventual phosphorylation by the receptor, and (b) the interactions between EGFR and the physiological substrate seem to involve mechanisms which allow the substrate to act as an on-off switch in the subsequent substrate phosphorylation reaction.

Protein phosphorylation pattern and role of products of c-erbB-1 and c-abl proto-oncogenes in murine preimplantation embryonic development

PROBLEM

To investigate the protein phosphorylation pattern and role of products of c-erbB-1 and c-abl proto-oncogenes with known tyrosine kinase activity in preimplantation embryonic development in mice.

METHOD

The protein phosphorylation pattern was studied by in vitro 32P metabolic labeling of murine ova/embryos as well as by in vitro kinase assay performed directly on various ova/embryos extracts. The role of products of c-erbB-1 (170 kDa, receptor for epidermal growth factor [EGF]) and c-abl proto-oncogenes (150 kDa) was examined by in vitro culturing murine embryos in the presence of monoclonal antibodies to respective protein products and by co-culturing with EGF, the ligand for EGF receptor (EGF-R).

RESULTS

In vitro metabolic labeling of murine ova/embryos showed 32P incorporation into at least two protein bands of murine ova (M(r) 81 and 36 kDa), six protein bands of two-cell (M(r) 81, 36; and 97, 52, 22 and 19 kDa, respectively), six protein bands of morula (M(r) 81, 36; 97, 22, and 19; and 33 kDa, respectively), and eight protein bands of blastocyst (81, 36; 97, 22, 19; and 115, 58, and 15 kDa, respectively), stage embryos; there were some specific bands in each stage. Prolonged labeling from 2 to 4 h not only resulted in a relative increase in 32P incorporation into these proteins but also revealed additional bands in morula (M(r) 133 and 115 kD) and blastocyst (M(r) 49, 33, and 31 kD) stage embryos. In vitro kinase assays performed directly on various ova/embryos extracts revealed at least three phosphoproteins (M(r) 58, 36 and 33, respectively) that were common to ova, two-cell, morula, and early/late blastocyst stage embryos. Additionally, three protein bands each in murine ova and two-cell embryos (M(r) 108, 81, 73 kDa, respectively), and four protein bands of late blastocyst (M(r) 108, 73; 133 and 18 kDa, respectively) stage embryos were also revealed. Culture of two-cell embryos in the presence of EGF, the ligand for EGF-receptor, resulted in a concentration dependent increase (P < .001) in the number of cells per blastocyst. Monoclonal antibody to c-erbB-1 170 kDa protein (receptor for EGF) did not affect development of in vitro cultured murine embryos from two-cell to morula, but significantly (P < .001) inhibited the in vitro development of morula to late blastocyst stage. Monoclonal antibody to c-abl protein inhibited the development of murine embryos from two-cell to morula (P < .017), as well as, from morula to late blastocyst stage (P < .002 to .01).

CONCLUSIONS

These results suggest that the stage-specific protein phosphorylation pattern and specific products of c-erB-1 and c-abl proto-oncogenes may have a role in preimplantation embryonic development in mice.

The extracellular domain of the epidermal growth factor receptor. Studies on the affinity and stoichiometry of binding, receptor dimerization and a binding-domain mutant

The binding of epidermal growth factor (EGF) or an EGF-like growth factor to the EGF receptor is the initial event which leads to receptor activation, and consequently the induction of cell growth. In order to study this binding interaction in detail, we produced the extracellular domain of the EGF receptor (EGFR) using the baculovirus expression system. Affinity-labeling and Western-blot analyses revealed that the baculovirus-infected insect cells secrete active EGFR extracellular domain relatively efficiently, however a significant amount of inactive EGFR extracellular domain is retained within the cells. The apparent dissociation constant (Kd) of the secreted EGFR extracellular domain for EGF and transforming growth factor alpha (TGF-alpha), as determined using an immobilized receptor binding assay, was approximately 200 nM. Interestingly, this Kd value is 30-40-fold lower than that of the full-length EGFR derived from detergent-solubilized A431 cell membranes. The stoichiometry of binding of the EGFR extracellular domain to EGF and TGF-alpha was examined by band-shift analysis on non-denaturing PAGE and was estimated to be 1:1. We have also shown, using sedimentation equilibrium analysis, that ligand binding induces significant dimerization of the EGFR extracellular domain. Finally, we carried out site-specific mutagenesis on the EGFR extracellular domain in order to define the ligand-binding region. We identified amino acid residues which are close to the binding site since they are common to the epitopes of several ligand-competitive monoclonal antibodies. However, these residues do not contribute directly to ligand binding since the affinity of the mutated EGFR extracellular domain for EGF and TGF-alpha was unaffected.

Effect of tyrphostin on cell growth and tyrosine kinase activity of epidermal growth factor receptor in human gliomas

The effects of tyrphostin, a selective protein tyrosine kinase inhibitor, on epidermal growth factor (EGF)-stimulated cell growth and EGF-receptor tyrosine kinase activity were studied in four human glioma cell lines. Stimulation by EGF induced variable enhancements of cell growth as well as tyrosine phosphorylation of EGF receptor and intracellular target proteins in all glioma cell lines. The level of immunoreactive EGF receptor detected with antibodies against extra- and intracellular domains was moderate in all four glioma cell lines, but markedly decreased with the latter antibody in two glioma cell lines. This variation was associated with considerable reduction of the EGF-stimulated tyrosine autophosphorylation level. Tyrphostin inhibited dose-dependently the EGF-stimulated cell growth and tyrosine autophosphorylation in all glioma cell lines, and the optimum time for the maximum inhibitory effect on tyrosine autophosphorylation was 12 to 18 hours after treatment with tyrphostin. The antiproliferative activity of tyrphostin nearly correlated quantitatively with its potency as an inhibitor of the EGF-stimulated EGF receptor tyrosine kinase activity. Tyrphostin had no significant effect on the immunoreactive EGF receptor levels, on the affinity constants and numbers of EGF receptor, or on the down-regulation and specific internalization of EGF receptor in any glioma cell line, suggesting that the effects of tyrphostin are not likely to be the results of reduction in EGF receptor and EGF binding capacity. In addition, the serum-stimulated cell growth was also inhibited dose-dependently by higher concentrations of tyrphostin in all glioma cell lines. It might be suggested, therefore, that tyrphostin inhibits EGF-stimulated cell growth by a specific suppression of EGF receptor tyrosine kinase activity, and at higher concentrations there appears to be some degree of either nonspecific inhibition or inhibition of serum-stimulated protein tyrosine kinase activity to induce the cell growth inhibition of gliomas.

Structural characterization and alternate splicing of the gene encoding the preadipocyte EGF-like protein pref-1

Preadipocyte factor 1 (pref-1), a member of the EGF-like protein family, is a transmembrane protein with six tandem EGF-like repeats in the putative extracellular domain. Expression of pref-1 is abolished during the in vitro differentiation of 3T3-L1 preadipocytes to adipocytes, and constitutive expression of pref-1 in preadipocytes inhibits their differentiation [Smas, C.M., & Sul, H.S. (1993) Cell 73, 725-734]. In the present studies, we have isolated and characterized genomic clones for pref-1 and have identified multiple pref-1 transcripts generated by alternate splicing. The pref-1 gene consists of five exons and four introns spanning approximately 7.3 kb. By primer extension analysis, the transcription start site was determined to be 169 bp upstream from the translation initiation codon. We have identified functional promoter sequences by transient transfection using a 2.1 kb fragment of the pref-1 5' flanking region linked to a luciferase gene; the pref-1-luciferase fusion gene construct gave 20-fold higher promoter activity as compared to the promoterless vector. Analysis of exon-intron junctions reveals that unlike the majority of the mammalian EGF-like genes, EGF-like repeats of pref-1 are not encoded by discrete exons. Through RT-PCR and the isolation and analysis of multiple pref-1 cDNA clones, we have identified, in addition to full-length pref-1, five alternately spliced forms with various in-frame deletions of all or a part of the sixth EGF-like repeat, juxta-membrane, and predicted transmembrane domains.(ABSTRACT TRUNCATED AT 250 WORDS)

The epidermal growth factor mitogenic signal is modulated by protein kinase C in T51B rat liver cells

The regulation of cell proliferation involves a complex interplay between several signal transduction pathways. The effect of EGF on DNA synthesis in serum starved quiescent, synchronized T51B cells was investigated by [3H]thymidine incorporation and flow cytometry. 1 nM EGF or readdition of serum initiated G1 progression and entry into S phase by 18 h and DNA synthesis reached a maximum by 28 h. Low concentrations of EGF markedly stimulated DNA synthesis, but EGF was not as potent as readdition of serum. The effect of EGF on DNA synthesis was only partially blocked by the tyrosine inhibitors genistein and tyrphostin, suggesting that other signalling pathways play a role in EGF-stimulated mitogenesis. 1 nM EGF caused a rapid, transient increase in the activity of membrane-associated protein kinase C (PKC) followed by a longer sustained increase that continued into S phase. TPA (12-O-tetradecanoyl-phorbol-13-acetate) did not mimic EGF, rather it caused a slight stimulation of membrane-associated PKC activity within 1 h followed by a dramatic downregulation of PKC within 4 h. TPA was without effect on DNA synthesis alone, but when added along with EGF or serum TPA caused a significant enhancement of DNA synthesis. Pretreatment of quiescent, serum-deprived T51B cells with TPA reduced the basal level of DNA synthesis; however, under these conditions EGF became as potent a mitogen as serum. We hypothesize that EGF via activation of PKC regulates the activity of its receptor by switching from high affinity to low affinity states. Downregulation of PKC by long term treatment with TPA removes this regulation thus rendering T15B cells more sensitive to exogenous EGF.

Human cytotrophoblast invasion is up-regulated by epidermal growth factor: evidence that paracrine factors modify this process

Formation of the human placenta requires a subset of cytotrophoblast stem cells to acquire an invasive phenotype. We examined the effect on cytotrophoblast invasiveness of growth factors that control the differentiation of other cells. Exogenous TGF-beta 1, PDGF-AA, PDGF-BB, and TNF-alpha affected neither cell morphology nor the rate of cytotrophoblast invasion in vitro. In contrast, addition of EGF to first trimester cytotrophoblast cultures produced dramatic changes in morphology and a severalfold increase in invasive capacity. The effects of EGF on later gestation cytotrophoblasts, whose invasive capacity is diminished, were much less pronounced. Next we investigated whether cytotrophoblasts themselves produce ligands that interact with the EGF receptor. A radioimmunoassay and a radioreceptor assay failed to detect EGF receptor ligands in cytotrophoblast-conditioned medium. Likewise, by RT-PCR cytotrophoblasts expressed neither EGF nor TGF-alpha mRNA. In contrast, EGF receptor mRNA was expressed and its protein levels remained constant during the experiment. Immunolocalization using F(ab') fragments of an anti-human EGF antibody failed to detect this growth factor in the chorionic villus. We conclude that maternal ligands that interact with the EGF receptor could play an important role by up-regulating trophoblast invasion, particularly during the early stages of pregnancy.

Altered expression of epidermal growth factor receptor and estrogen receptor in MCF-7 cells after single and repeated radiation exposures

PURPOSE

Studies on radiation-induced changes in gene expression are likely to be very important in developing a better understanding of cellular responses to ionizing radiation. While there is some information on the activation of cellular signal transduction pathways after radiation, few late reacting target genes have been identified. This study focuses on the characterization of expression modulation of two critical growth regulatory genes, estrogen receptor and epidermal growth factor-receptor in malignant mammary epithelial cells in response to single and repeated ionizing radiation exposures.

METHODS AND MATERIALS

MCF-7 cells were used for single radiation exposure (2-50 Gy) experiments and MCF-IR-3 cells, generated by exposure to cumulative doses of 60 Gy in 2 Gy fractions, respectively, were used to study the effects of repeated exposures. Steady-state messenger ribonucleic acid levels for estrogen receptor, epidermal growth factor-receptor, and transforming growth factor-alpha were determined by ribonucleic acid protection experiments. Estrogen receptor and epidermal growth factor-receptor protein expression was quantitated by competitive binding studies with 3H-estradiol and 125I-EGF.

RESULTS

MCF-IR-3 cells showed a permanent three-fold down-regulation of the estrogen receptor messenger ribonucleic acid and protein, while epidermal growth factor-receptor was upregulated about nine-fold. Epidermal growth factor-receptor was substantially up-regulated in MCF-7 cells, at both the mRNA and protein levels, within 24 h of a single 2 Gy exposures, while there was a two-fold concomitant increase in transforming growth factor-alpha messenger ribonucleic acid expression. A decrease in estrogen receptor messenger ribonucleic acid and protein was suggested only after higher doses of single radiation exposures.

CONCLUSION

Single and repeated radiation exposures modulate the expression of two critical growth promoting genes, estrogen receptor and epidermal growth factor-receptor, in MCF-7 cells. The inverse expression of estrogen receptor and epidermal growth factor-receptor established for estrogen receptor-positive malignant mammary epithelial cells is maintained in MCF-7 cells after single and repeated exposures suggesting that radiation acts through common regulatory circuits and may modulate the cellular phenotype.

Effects of epidermal growth factor on parathyroid hormone-related protein production by mammary epithelial cells

Parathyroid hormone-related protein (PTHrP) plays a prominent role in the pathogenesis of humoral hypercalcemia of malignancy. However, it is also expressed in various nonmalignant tissues, particularly during fetal organogenesis and tissue differentiation. Thus, PTHrP is synthesized in skin, placenta, and mammary gland during lactation. Little is known, however, about the regulation of PTHrP synthesis and release in nontumoral cells. We investigated the regulation of PTHrP production by epidermal growth factor (EGF), a factor of major importance in the development of lactating breast, in primary cultures of rat mammary epithelial cells. EGF stimulated the production of immunoreactive and bioactive PTHrP in a time- and concentration-dependent manner. A 12 h incubation with 10 ng/ml of EGF increased PTHrP production by 36.0 +/- 7.1% (n = 7 experiments, p < 0.01). This was accompanied by an increase in PTHrP mRNA steady-state levels. The production of PTHrP was stimulated by the protein kinase C (PKC) activator phorbol-12-myristate-13-acetate (PMA) by 82.9 +/- 9.7% (n = 4 experiments, p < 0.01). The effects of PMA and EGF were additive. The EGF-induced stimulation appeared to be independent of extracellular calcium concentration, prostaglandin, or cAMP synthesis, but may have involved tyrosine kinase-mediated mechanisms. These results indicate that EGF was capable of increasing the production of PTHrP by cultured mammary epithelial cells. They also suggest that factors activating the PKC pathway are involved in the upregulation of PTHrP expression in mammary epithelial cells.

Molecular cloning and expression of the gene for a major leucine-rich protein from human hepatoblastoma cells (HepG2)

The human hepatoblastoma cell line, HepG2, exhibits an array of stable properties in culture that have made it a popular cell culture model for studies on regulation of liver-specific gene expression and properties of hepatoma cells. In contrast to other hepatoma cell lines, HepG2 cells overexpress a characteristic detergent-extractable, wheat germ lectin-binding protein with apparent molecular mass of 130 kDa. Using an antibody to screen a phage expression library of HepG2 complementary DNA (cDNA), we identified and cloned a 4734 base pair cDNA which codes for a 130-kDa leucine-rich protein (lrp 130) when expressed in transfected cells. The deduced sequence of lrp130 exhibits sequences weakly homologous to the consensus sequence for the ATP binding site in ATP-dependent kinases and the protein kinase C phosphorylation site of the epidermal growth factor receptor. Consistent with the higher levels of expression of lrp130 antigen, Northern hybridization analysis indicated that HepG2 cells express high levels of the major 4.8 kilobase lrp130 mRNA relative to other hepatoma cells. Although currently of unknown function, lrp130 may be of utility as a marker for liver cell lineages represented by the HepG2 cell line.

Loss of cytotoxic effect of epidermal growth factor (EGF) on EGF receptor overexpressing cells is associated with attenuation of EGF receptor tyrosine kinase activity

The biological activity of epidermal growth factor (EGF) is mediated through the intrinsic tyrosine kinase activity of the EGF receptor (EGFR). In numerous cell types, binding of EGF to the EGFR stimulates the tyrosine kinase activity of the receptor eventually leading to cell proliferation. In tumor-derived cell lines, which overexpress the EGFR, however, growth inhibition is often seen in response to EGF. The mechanism for growth inhibition is unclear. To study the relationship between growth inhibition and EGFR kinase activity, we have used a cell line (PC-10) derived from a human squamous cell carcinoma that overexpresses EGFR. When exposed to 25 ng/ml EGF at low cell densities (1,300 cells/cm2), PC-10 cells exhibit cell death. In contrast, if EGF is added to high density cultures, no EGF mediated cell death is seen. When PC-10 cells were maintained at confluency in the presence of 25 ng/ml EGF for a period of 1 month, they were subsequently found competent to proliferate at low density in the presence of EGF. We designate these cells APC-10. The APC-10 cells exhibited a unique response to EGF, and no concentration of EGF tested could produce cell death. By 125I-EGF binding analysis and [35S]methionine labeling of EGFR, it was found that the total number of EGFR on the cell surface of APC-10 was not decreased relative to PC-10. No difference between PC-10 and APC-10 was seen in EGF binding affinity to the EGFR. Significantly, EGF stimulated autophosphorylation of the EGFR of APC-10 was 8-10-fold lower than that of PC-10. This reduced kinase activity was also seen in vitro in membrane preparations for EGFR autophosphorylation as well as phosphorylation of an exogenously added substrate. No difference between PC-10 and APC-10 in the overall pattern of EGFR phosphorylation in the presence or absence of EGF was detectable. However, the serine and threonine phosphorylation of the EGFR of APC-10 cells was consistently 2-3-fold lower than that seen in PC-10 cells. These results suggest a novel mechanism for EGFR overexpressing cells to survive EGF exposure, one that involves an attenuation of the tyrosine kinase activity of the EGFR in the absence of a change in receptor levels or receptor affinity.

An assessment of immunoreactive epidermal growth factor in urine of patients with urological diseases

To examine the excretion of urinary epidermal growth factor (EGF) in urological diseases and the relationship of EGF urine levels with transitional cell carcinoma (TCC), we measured the concentration of EGF by radioimmunoassay. The series comprised patients with active TCC (n = 52), others in tumor-free status (n = 29) and with non-neoplastic inflammatory diseases (n = 43), and normal controls (n = 50). Urinary EGF values were lower in patients with urological diseases of different etiologies than in normal controls (P < 0.005). Mean EGF levels of patients who had previous bladder tumor resection (n = 21) were not statistically different from normal controls (P = 0.2). For patients with active TCC, EGF urine levels showed a significant inverse relationship to increasing tumor grade (P = 0.02). In addition, subjects who had received nephrectomy for pelvic carcinoma (n = 8) showed significantly lower mean EGF values than those with intact kidneys (n = 21), irrespective of sex (P < 0.05). Immunostaining of EGF on non-neoplastic kidney (n = 9) revealed reactivity in the distal convoluted tubules and thick ascending limbs of Henle. Our results suggest that the kidney is the major source of urinary EGF. Its excretion in urine is decreased in both inflammatory and neoplastic diseases of the urinary tract. EGF may play an important part in the biological activity of TCC. Further study is indicated to investigate the monitoring of EGF urine levels as a marker of recurrence for EGF receptor-positive TCC.

Calphostin-C stimulates epidermal growth factor receptor phosphorylation and internalization via light-dependent mechanism

Calphostin-C with perylenequinone structure is known to bind the regulatory domain of protein kinase C (PKC) and to inhibit kinase activity in vitro in a light-dependent fashion. We have found that calphostin-C induces substantial serine and threonine phosphorylation of the epidermal growth factor (EGF) receptor in a light-dependent fashion in the EGF receptor-hyperproducing squamous carcinoma cell line NA. Tryptic phospho-peptide mapping and phospho-amino acid analysis revealed that calphostin-C-enhanced phosphorylation was on threonine 669, serine 671, serine 1046/1047, and serine 1166. However, calphostin-C did not inhibit phosphorylation of the 80 K protein, a cytosolic major substrate of PKC (MARCKS). Staurosporine, a potent PKC inhibitor with affinity for the catalytic domain of PKC, inhibited phosphorylation of the 80 K protein and 12-O-tetradecanoyl-13-phorbol acetate induction of EGF receptor phosphorylation but did not inhibit the calphostin-C induction of the EGF receptor phosphorylation. These results suggest that the target of calphostin-C in vivo is different from that of staurosporine and thus calphostin-C in vivo does not inhibit PKC. Furthermore, calphostin-C enhanced the internalization of phosphorylated EGF receptor. Thus, calphostin-C apparently activates a novel signal transduction pathway which involves phosphorylation and internalization of the EGF receptor via light-dependent mechanism.

Effects of gravity on the cellular response to epidermal growth factor

EGF and related polypeptides are involved in the regulation of cell growth and differentiation of continuously regenerating tissues, in tissue repair processes and in placental and fetal development. Their initial mode of action generally constitutes binding to specific plasma membrane localized receptors, transduction of the signal across the plasma membrane, subsequent activation of signalling pathways in the cell, and the induction of early nuclear gene expression. EGF-induced signal transmission from the plasma membrane to the nucleus has been studied in microgravity in order to gain insight in the molecular mechanisms that constitute the effects of gravity on cell growth. Exposure of human A431 cells to microgravity strongly suppresses EGF- and PMA-induced c-fos and c-jun expression. In contrast, forskolin- and A23187-induced c-fos expression and constitutive beta-2 microglobulin expression remain unaffected. This suggests that microgravity differentially modulates EGF-induced signal transduction pathways. Since both EGF and PMA are known to be activators of PKC, which is not the case for forskolin and A23187, PKC-mediated signal transduction may be a cellular target for microgravity. Inhibition of EGF-induced c-fos expression by microgravity occurs downstream of the initiation of EGF-induced signal transduction, i.e., EGF binding and EGFR redistribution. In addition to PKC signaling, actin microfilament organization appears to be sensitive to microgravity. Therefore, the inhibition of signal transduction by microgravity may be related to alterations in actin microfilament organization. The fact that early gene expression is affected by agents that alter the organization of the actin microfilament system supports this hypothesis. The decrease in c-fos and c-jun expression in microgravity may result in the decreased formation of the FOS and JUN proteins. Consequently, a short-term reduction in gene expression in microgravity may have a more dramatic effect over the long term, since both the JUN and FOS protein families are required for normal cell cycle progression. However, since more than 20 years of manned spaceflight have shown that humans can survive in microgravity for prolonged periods, it appears that cells in the human body can partly or completely overcome gravitational stress. Although some insight in the molecular basis on human cells has been obtained, future studies will be needed for a better understanding of the grounds for alterations in the cellular biochemistry due to altered gravity conditions.(ABSTRACT TRUNCATED AT 400 WORDS)

Growth factor receptors and their ligands

The understanding of the signal transduction cascade involving growth factors and their receptors is one major key for diagnostic and therapeutic improvements in human neoplasms. Using receptor autoradiography, an inverse relationship for the incidence of somatostatin receptors (SSR) and epidermal growth factor receptors (EGFR) was found in gliomas [1]. In the majority of low grade gliomas, SSR were present but EGFR were absent. In contrast, EGFR were present in most glioblastomas, but no SSR were detected. Recently, the amplification of the EGFR gene and its overexpression was demonstrated to be associated with the development of glioblastomas. Several independent reports revealed that 40-50% of tumors show amplified EGFR [2-4]. The frequency of EGFR amplification was directly associated with tumor malignancy. In addition, amplified EGFR levels indicate a bad prognosis and shorter overall survival [5]. Recent analysis of the EGFR gene in tumors has shown that regions of this gene frequently undergo alteration. Hence, not only amplification but also mutation may be the cause of the increased malignancy in EGFR overexpressing cells [6].

The acute actions of growth factors in smooth muscle systems

Work over the past six to eight years has established that mitogenic polypeptides such as epidermal growth factor-urogastrone (EGF-URO) or platelet-derived growth factor (PDGF), commonly referred to as 'growth factors', can have rapid (seconds to minutes) regulatory actions in a variety of smooth muscle systems. With EGF-URO as a prototype example, this article describes three distinct smooth muscle response paradigms, two of which (type A and type B) comprise a rapid (seconds to minutes) increase in muscle tension) and one of which (type C) is characterized by an EGF-URO-mediated reduction in sensitivity to other agonists. The quite distinct signal transduction pathways for the three types of response paradigms are outlined, and the marked tissue and species variation in the types of smooth muscle responses that can be observed, even for a single growth factor agonist, are summarized. The article also illustrates that G-protein-coupled vasoactive agents such as angiotensin-II and vasopressin, which can act as 'growth factors' in cultured cell systems, can also work via tyrosine kinase pathways to cause contraction in some of the same intact smooth muscle preparations that contract in response to growth factors such as EGF-URO. Attention is drawn to the fact that many so-called 'growth factors', quite apart from stimulating cell division and differentiation, may in many instances act as rapid localized paracrine/autocrine regulators of tissues such as smooth muscle. It is also pointed out that some of the tyrosine kinase-modulated signal pathways usually associated with the mitogenic action of 'growth factors' may be involved not only in the rapid effects of agents such as EGF-URO in smooth muscle but also in the contractile actions of G-protein-linked agonists.

Activation of phospholipase D in CHO cells transfected with the human epidermal growth factor (EGF) receptor: differential effects of protein kinase C activation and EGF

Multiple intracellular signal transduction pathways, including phospholipases A2 and D, can be activated by epidermal growth factor (EGF) in both a protein kinase C (PKC)-dependent and -independent manner. We investigated the activation of phospholipase D (PLD) by a PKC activator, phorbol myristate acetate (PMA) and by EGF in CHO cells transfected with the full-length EGF receptor. In cells labelled with arachidonic acid or linoleic acid, PMA activated a PLD, determined by formation of the transphosphatidylation product phosphatidylethanol in the presence of ethanol. A basal PLD activity was seen in linoleic acid-labelled cells but not in cells labelled with arachidonic acid. This basal activity was augmented by the protein phosphotyrosine phosphatase inhibitor vanadate and reduced by tyrosine kinase inhibition and was contributed to by PKC, as activity could not be elicited following prolonged exposure to phorbol ester, known to down-regulate some PKC isoforms. By contrast, EGF failed to stimulate formation of phosphatidylethanol in cells labelled with either fatty acid species. It is proposed that in the basal condition PKC-dependent PLD activation and protein tyrosine kinase phosphorylation are linked (possibly by a phospholipase C (PLC)-mediated formation of diacylglycerol); EGF which activated a phospholipase A2 (PLA2) but which failed to elicit PLC activation in these cells is without further effect on PLD.

K252a potentiates epidermal growth factor-induced differentiation of PC12 cells

Epidermal growth factor (EGF) induced short neurites in two different strains of PC12 cells. The length of the EGF-induced neurites was markedly increased in the presence of the protein kinase inhibitor K252a, which is known to inhibit differentiation induced by nerve growth factor (NGF). EGF-induced differentiation of PC12 required RNA synthesis and activity of the ras proto-oncogene product. EGF increased the levels of three neurofilament proteins and the mRNA level of two late response genes (SCG10 and 63) known to be induced by NGF. Together, EGF and K252a caused a greater increase in these mRNAs than did either agent alone. K252a did not alter the extent of EGF-induced autophosphorylation of the EGF receptor, but it did decrease the extent of receptor phosphorylation in the absence of added EGF. Thus, the ability of the EGF receptor to trigger neuronal differentiation may depend on the state of its phosphorylation at serine and/or threonine residues. Two other strains of PC12 did not extend neurites when exposed to EGF, even when K252a was also present. Thus, the differentiating effect of EGF on PC12 is PC12 strain-specific.

UVB radiation induces phosphorylation of the epidermal growth factor receptor, decreases EGF binding and blocks EGF induction of ornithine decarboxylase gene expression in SV40-transformed human keratinocytes

We previously demonstrated that epidermal growth factor (EGF) induces a several-fold increase in ornithine decarboxylase (ODC) activity and the steady-state level of ODC mRNA in cultured SV40-transformed human keratinocytes (1). Pretreatment of cell cultures with ultraviolet B (UVB) radiation resulted in a reduction of EGF-induced ODC activity. To determine whether UVB inhibits the accumulation of ODC mRNA by EGF, cells were pretreated with 20 mJ/cm2 UVB or sham-irradiated and then incubated with 100 ng/ml EGF. Northern blot analysis revealed that UVB irradiation entirely blocked the EGF induction of ODC mRNA. Since the binding of EGF to its plasma membrane receptor is the first step in initiating a biological response, the effect of UVB on EGF binding was evaluated. UVB treatment of cultured keratinocytes resulted in an immediate and dose-dependent reduction of EGF binding. Scatchard analysis revealed that the reduction of EGF binding was due to a 52% decrease in the number of available receptors, from 6.2 x 10(4)/cell to 3.0 x 10(4)/cell. However, UVB decreased the EGF-binding affinity very little (Kd = 0.60 nM in control and Kd = 0.75 nM in UVB-treated Z114 cells). In addition, UVB did not alter the rate of EGF internalization. These data suggest that UVB blocks the signal transduction pathway of EGF that is involved in regulation of ODC gene expression. Immunoblot analysis of extracts from irradiated cells showed that UVB induced tyrosine phosphorylation of EGFR and that the quantity of EGFR protein was unaffected by UVB treatment. Phosphorylation of EGFR may be responsible for decreased binding of EGF to its receptor.

Inhibition of the epidermal growth factor receptor tyrosine kinase activity by leflunomide

The active metabolite of leflunomide, A77 1726 inhibits the proliferation of a variety of mammalian cell lines in culture. Epidermal growth factor (EGF)-dependent proliferation is inhibited by A77 1726 at an effective dose of 30-40 microM. A77 1726 appears to directly inhibit the EGF receptor tyrosine-specific kinase activity both in intact cells and purified EGF receptors at the same effective dose. These data suggest that leflunomide inhibits cellular proliferation by the inhibition of tyrosine-specific kinase activities.

Serine/threonine protein kinases and calcium-dependent protease in senescent IMR-90 fibroblasts

Three enzymes relevant to signal transduction were compared in replicating, quiescent and senescent human diploid fibroblasts (HDF). These were Ca(2+)-dependent thiol protease (calpain), cAMP-dependent protein kinase (Pk-A), and calcium/phospholipid-dependent protein kinase C (Pk-C). The amounts of these enzymes in quiescent HDF were slightly greater or the same as in replicating HDF. In contrast, senescent HDF exhibited higher Pk-C, Pk-A and proteolytic activities than did either replicating or quiescent cells. While the elevated protein kinase activities could be accounted for by the larger size of senescent cells relative to younger cells, the increased calpain activity exceeded this size differential. Immunoblotting studies with antisera to both Pk-C and calpain demonstrated increased enzyme concentrations in parallel with the increased activities. Photolabeling cell extracts with an analog of cAMP, 8-N3-[32P]cAMP, provides an estimate of Pk-A concentration. By this criterion, senescent HDF have more Pk-A molecules than do young cells that are either replicating or quiescent. Only the type I isozyme of Pk-A (Pk-A-I) was observed in any of these cells. Photolabeling with 8-N3-[32P]cAMP demonstrated more degradative fragments of the Pk-A regulatory subunit (RI) in senescent cells also. This is a logical consequence of the increased calpain activity in senescent cells, since RI is a substrate for calpain. These results imply that senescent cells do not fail to enter S phase owing to inadequate concentrations of Pk-A or Pk-C. Rather, the increased quantities of these enzymes in senescent cells may reflect aberrations elsewhere along signal transduction pathways that coordinate cell size with cell proliferation.