Expression cloning of human EGF receptor complementary DNA: gene amplification and three related messenger RNA products in A431 cells

Cancer therapeutics: understanding the mechanism of action

An intended consequence of the significant investment to characterize the mammalian genome, and its alterations in neoplastic diseases, has been the discovery and commercialization of new approaches to anticancer therapy. As a result, the list of available targets, formerly directed against the processes of DNA replication and mitosis, or in hormonal regulation of growth of tissue, has been dramatically extended. Many of the newer targets represent normal or aberrant signaling pathways, and are present within the cancer cell as second messengers, on its surface (as receptors), or in the external milieu (as ligands). These targets are, therefore, important to the cancer cell phenotype, and affect proliferation, differentiation, and death options for the cell. Another group of targets encompass the cancer cell's relationship to the tissue environment (both stroma and nonneoplastic cells). These targets involve interactions with blood supply (angiogenesis), immune function (evasion), and matrix (invasion and metastasis). Thus, most targets are directly or indirectly critical to some aspect of cancer cell physiology, although a few additional targets are being approached as localization signals for the delivery of otherwise less specific chemotherapeutic or radiotherapeutic agents. The development of new therapeutic approaches has expanded the scope of research required to characterize the mechanism of action for anticancer agents in preclinical models and in clinical trials. In preclinical research, mechanism of action studies have supported the selection of therapeutic agents, appropriate models of efficacy, and experimental design, as well as rational characterization and prediction of nontumor (host) effects. In clinical research, mechanism of action studies have supported the identification of surrogate markers of efficacy (critical for determining adequacy of dose and latency of response), and the selection of patient subpopulations and tumor subtypes most likely to exhibit clinical responses. Finally, information on mechanism of action may suggest strategies for combination therapies and predict potential mechanisms of disease resistance to therapy.

Effects of Gefitinib on Serum Epidermal Growth Factor Receptor and HER2 in Patients with Advanced Non-Small Cell Lung Cancer

PURPOSE

The aim of this study was to assess serum extracellular binding domains of epidermal growth factor receptor (EGFR) and HER2 as surrogate markers of Gefitinib (Iressa, ZD1839, AstraZeneca, London, United Kingdom) activity in patients with non-small cell lung cancer.

EXPERIMENTAL DESIGN

Serum EGFR and HER2 levels were monitored in blood samples taken within 1 week of starting Gefitinib at day 28 and at every computed tomography scan evaluation. EGFR and HER-2 were assayed in duplicate using commercial sandwich enzyme-linked immunosorbent assay kits (Oncogene Science Bayer Corporation, Cambridge, UK). A logistic regression analysis was performed to evaluate: (1) the relationship between best overall tumor response and basal EGFR and HER2 levels, and (2) the association between best overall tumor response and the differences of EGFR and HER2 levels obtained at the best overall tumor response and at baseline.

RESULTS

Forty-six pretreated patients were evaluated, including F/M:11/35, Eastern Cooperative Oncology Group performance status 0-1/2:39/7, IIIB/IV:11/35, and adenocarcinoma/nonadenocarcinoma 29/17. Five partial responses (11%) and 14 stable disease responses (30%) were observed. Median pretreatment EGFR and HER2 were 83.3 ng/ml and 13.7 ng/ml. For baseline EGFR and HER2, the odds ratio of progression was 0.95 [95% confidence interval (CI), 0.91-0.98; P=0.01] and 0.87 (95% CI, 0.74-1.03; P=0.11), respectively. The difference between the best overall tumor response and basal EGFR value was predictive for response with a 6% increase in the odds of progression for an increase of 1 ng/ml (odds ratio, 1.06; 95% CI, 1.01-1.11; P=0.009) and for progression-free survival with a hazard ratio of 1.03 (95% CI, 1.01-1.04; P=0.003).

CONCLUSION

Modifications of EGFR serum values during treatment seem to reflect Gefitinib activity.

EPIDERMAL GROWTH FACTOR RECEPTOR ANTAGONISTS: NOVEL THERAPY FOR THE TREATMENT OF HIGH-GRADE GLIOMAS

Overactivation of epidermal growth factor receptor (EGFR) signaling has been recognized as an important step in the pathogenesis and progression of multiple forms of cancer of epithelial origin. This knowledge has led to a surge of interest in novel anticancer therapies targeting key constituents of the EGFR signal transduction pathway. Several molecular strategies have been developed recently to modulate either EGFR or the downstream signal beyond the cell surface receptor. The important role of aberrant EGFR signaling in the progression of malignant gliomas makes EGFR-targeted therapies of particular interest in this form of cancer. The use of anti-EGFR therapies against malignant brain tumors, although in its infancy, promises to yield exciting results as these new drugs probably will enhance the usefulness of existing therapies.

Epidermal growth factor receptor: a promising target in solid tumours

The epidermal growth factor receptor (EGFR) is expressed in a wide variety of solid tumours. It has been demonstrated that the EGFR-associated signaling pathway plays an important role in carcinogenesis and cancer progression. In the new therapeutic paradigm of molecular-targeted cancer therapy, interference with intracellular signaling cascades is an appealing treatment approach. Inhibitory strategies under study include monoclonal antibodies, tyrosine kinase inhibitors, EGFR-ligand conjugates, EGFR immunoconjugates, and antisense oligonucleotides. Many of these strategies have demonstrated efficacy against EGFR-expressing tumour cells in preclinical studies, prompting a large number of clinical trials. In particular, clinical studies using monoclonal antibody blockade and EGFR tyrosine kinase inhibitors have suggested that EGFR blockade is a well-tolerated and effective treatment strategy; however, more trials are needed to precisely define how these agents will fit into modern cancer care.

Targeting the HER-kinase axis in cancer

The human epidermal growth factor receptor (HER) family of receptor tyrosine kinases controls critical pathways involved in the differentiation, growth, division, and motility of normal epithelial cells. Most human solid tumors are of epithelial origin. The process of malignant transformation and progression in many cancers may depend on activation of ligands and receptors that function as part of the HER-kinase pathway. This signaling axis has earned increased attention because of the development of antibodies and small-molecule tyrosine kinase inhibitors that specifically target components of the HER-kinase axis for cancer therapy. This review focuses on the basic biology underlying HER-kinase pathway activation and the current state of development for agents that target this axis. In particular, the importance of pan-HER inhibitors is discussed.

Novel treatments in non–small cell lung cancer

Although it has been exciting for lung cancer doctors to observe objective remissions with gefitinib and erlotinib in heavily pretreated NSCLC patients, all of the reported phase III trials testing noncytotoxic, targeted therapies in NSCLC have been negative. Two basic strategies have been employed in developing and conducting these randomized studies. In the case of gefitinib and the matrix metalloproteinase inhibitors, phase III trials were launched based on preclinical data. The second strategy was based on survival results from phase II trials involving regimens consisting of the targeted agent and chemotherapy. Unfortunately, negative results have been observed with the first phase III study (chemotherapy +/- ISIS 3521), which was based on the results of a phase II trial. The initial negative results with targeted agents suggest that a paradigm shift in cancer drug development is needed. Typically, the development of a cytotoxic agent involves determination of the maximum tolerated dose, followed by an assessment of activity as defined by the objective response rate in specific tumor types. "Active" drugs are then moved into phase III testing to determine the effect on survival. Other than targeting the specific tumor type and defining the usual eligibility parameters, no attempt is made to select patients for treatment with new agents. It seems unlikely that there will be significant progress with the targeted therapies unless there is a paradigm shift from this classic model of cancer drug development to a model in which much greater effort is directed toward identifying the target or targets in preclinical models. Intensive effort should be devoted to the development of reliable, clinically applicable assays for the targets that could identify patients who are most likely to benefit from a specific treatment. Rothenberg et al recently made similar recommendations with respect to improving the drug discovery process for cancer. These investigators have emphasized testing new agents in the most appropriate setting, increasing efforts to understand the role of the target, and collection of tissue in an effort to select appropriate patients. Although results from initial randomized trials of targeted therapies in NSCLC have been relatively disappointing, this is not a time to be discouraged. Rather, it is a time to increase the collaborative efforts between basic scientists and clinical investigators.

Expression of epidermal growth factor receptor in gastric carcinomas

BACKGROUND & AIMS

Epidermal growth factor receptor belongs to the family of type I receptor tyrosine kinases. Overexpression of epidermal growth factor receptor has been observed in a variety of cancers with or without amplification of the gene. Novel chemotherapies targeting receptor tyrosine kinases might be effective for the treatment of cancers in which overexpression of this protein is a feature. The aim of this study was to assess the potential efficacy of epidermal growth factor receptor-targeted therapy in gastric cancer. This was achieved by determining the frequency of increased epidermal growth factor receptor expression in gastric cancers and investigating the relationship between protein overexpression and gene amplification.

METHODS

Immunohistochemical evaluation of 413 gastric cancers was carried out by using a monoclonal antibody to the epidermal growth factor receptor. The intensity of reactivity was scored by using a 4-tier system (negative, 1+, 2+, and 3+). All positive staining (>1+) tumors overexpressing the protein were then analyzed for gene amplification by fluorescence in situ hybridization by using a gene-specific probe.

RESULTS

High levels of overexpression (2+ or 3+ staining) were found in 9 of 413 (2.2%) patients, whereas low levels of overexpression (1+) were found in 34 (8.2%) of the study cohort. Fluorescence in situ hybridization analysis showed that more than 10 copies of the gene were recognized in all 5 cancers with 3+ staining and in 2 of the 4 tumors with 2+ staining.

CONCLUSIONS

Although a high level of overexpression of epidermal growth factor receptor is uncommon in gastric carcinomas, it almost exclusively occurs by gene amplification.

Erlotinib: a new therapeutic approach for non-small cell lung cancer

Although treatment with cytotoxic agents has produced modest survival improvement in patients with stage III and IV non-small cell lung cancer (NSCLC), it appears that a plateau has been reached with currently available chemotherapeutic regimens. Increasing knowledge regarding the properties of malignant neoplasms has identified a number of potential therapeutic targets. The epidermal growth factor receptor (EGFR) is one of these targets. Preclinical models have revealed that tumour growth can be inhibited by monoclonal antibodies directed against EGFR and EGFR-specific tyrosine kinase inhibitors. Erlotinib (Tarceva trade mark; OSI Pharmaceuticals, Genentech and Roche), a quinazoline derivative with good oral absorption, is one of several EGFR tyrosine kinases that has been studied in clinical trials. In a Phase I study, mild diarrhoea and mild rash were the most common toxicities. At a dose of 200 mg/day, diarrhoea was the dose-limiting toxicity. The observation that EGFR overexpression is relatively common in NSCLC led to a Phase II trial of erlotinib at the maximum-tolerated dose (150 mg/day) in previously treated NSCLC patients. Erlotinib produced a 12% response rate and there was no apparent relationship between response and tumour EGFR levels. More recent reports suggest that patients who develop a rash have higher responses. Based on its single agent activity, erlotinib has been evaluated in two Phase III trials which compared erlotinib plus chemotherapy to chemotherapy alone in previously untreated NSCLC patients. Erlotinib has also been compared to placebo in a Phase III trial which was limited to advanced stage NSCLC patients whose disease had progressed after two previous chemotherapy regimens. The optimum use of erlotinib in NSCLC will be determined by the results of the completed and future Phase III trials.

Growth factor receptors in breast cancer: potential for therapeutic intervention

Increased expression and activation of receptor tyrosine kinases occurs frequently in human breast carcinomas. Several therapies targeting these receptors are currently in clinical trials. Therapeutic strategies include blockade of individual receptors with monoclonal antibodies and inhibition of tyrosine kinase function. Trastuzumab is the first of these biologic therapies to be approved for patients with human epidermal growth factor receptor 2 (HER2)-overexpressing metastatic breast cancer. Novel trastuzumab-based combinations are being investigated in patients with advanced breast cancer. Large clinical trials have also been launched in the adjuvant setting. Small molecules that inhibit specific tyrosine kinases (e.g., epidermal growth factor receptor, HER2) are in phase I and phase II clinical trials. Other growth-factor-targeted drugs that have reached clinical development include STI571 and antibodies directed at the insulin-like growth factor pathway. Biologic therapies directed against these important receptors are promising. In this review we discuss challenges and opportunities for the development of growth-factor-targeted approaches for the treatment of breast cancer.

Epidermal growth factor receptor: association of extracellular domain negatively regulates intracellular kinase activation in the absence of ligand

The epidermal growth factor receptor (EGFR) plays an important role in many types of human cancers. Receptor amplification, autocrine activation and/or deletion of exons 2-7 of EGFR gene have all been associated with tumor development. The traditional model of EGFR activation via ligand induced dimerization and consequential kinase activation does not provide full understanding of its tumorigenicity. The main function of the receptor extracellular domain (ECD) has been thought to be ligand recognition and binding. We report that the EGFR ECD, through its association also negatively regulates the activity of the intracellular kinase in the absence of ligand. Even in the absence of its ligands, the EGF receptor forms homodimers, however, the ECD prevents constitutive receptor kinase activation through its intrinsic ligand-independent interaction. The removal of this domain, either partial or total, results in constitutive activation of the receptor kinase as observed by its phosphorylation in intact cells. Furthermore, EGF receptors truncated in the ECD induce phosphorylation of the wild-type full-length receptor, indicating an inter-molecular inhibitory mechanism by the receptor ECD. The tumor associated delta2-7EGFR mutant also dimerizes with and phosphorylates the wild type EGFR in the absence of ligand. Thus, in addition to its role in ligand recognition, EGFR ECD interacts with each other, imposing an inhibitory effect on the activation of the intracellular kinase.

EGFR blockade with ZD1839 ("Iressa") potentiates the antitumor effects of single and multiple fractions of ionizing radiation in human A431 squamous cell carcinoma. Epidermal growth factor receptor

PURPOSE

Signaling pathways initiated by the epidermal growth factor receptor (EGFR) play important roles in the response to ionizing radiation. In this study the consequences of inhibiting the EGFR on the response of A431 cells (human vulvar squamous cell carcinoma cells that overexpress EGFR) to radiation, were investigated in vitro and in vivo, using the selective EGFR-tyrosine kinase inhibitor, ZD1839 ("Iressa").

METHODS AND MATERIALS

The effect of ZD1839 on proliferation, apoptosis, and clonogenic survival after radiation was determined in vitro. For in vivo studies, athymic nude mice with established subcutaneous A431 xenografts (approximately 100 mm(3)) were treated with either a single 10 Gy fraction or 4 daily 2.5 Gy fractions of radiation with or without ZD1839 (75 mg/kg/day intraperitoneally for 10 days) to determine effects on tumor growth delay.

RESULTS

Treatment of A431 cells with ZD1839 in vitro reduced proliferation, increased apoptosis, and reduced clonogenic survival after radiation. Strikingly greater than additive effects of ZD1839 in combination with radiation on tumor growth delay were observed in vivo after either a single 10 Gy fraction (enhancement ratio: 1.5) or multiple 4 x 2.5 Gy fractions (enhancement ratio: 4). ZD1839 reduced tumor vascularity, as well as levels of vascular endothelial growth factor (VEGF) protein and mRNA induced by stimulation with epidermal growth factor (EGF), suggesting a possible role of inhibition of angiogenesis in the effect.

CONCLUSIONS

Inhibiting EGFR-mediated signal transduction cascades with ZD1839 potentiates the antitumor effect of single and multiple fractions of radiation. These data provide preclinical rationale for clinical trials of EGFR inhibitors including ZD1839 in combination with radiation.

A monoclonal antibody recognizing human cancers with amplification/overexpression of the human epidermal growth factor receptor

Epidermal growth factor receptor (EGFR) has attracted considerable attention as a target for cancer therapy. Wild-type (wt)EGFR is amplified/overexpressed in a number of tumor types, and several mutant forms of the coding gene have been found, with DeltaEGFR, a deletion mutation lacking exons 2-7 of the external domain, being the most common and particularly associated with glioblastoma. We generated monoclonal antibodies (mAbs) against NR6(DeltaEGFR) (mouse fibroblast line NR6 transfected with DeltaEGFR). mAb 806 with selective reactivity for NR6(DeltaEGFR) in mixed hemadsorption assays, fluorescence-activated cell sorting, Western blot, and immunohistochemistry was analyzed in detail and compared with mAbs 528 (anti-wtEGFR) and DH8.3 (anti-DeltaEGFR). In xenograft tumors and molecularly pretyped glioblastomas, the reactivity pattern was as follows: 528 reactive with amplified and nonamplified wtEGFR; DH8.3 reactive with DeltaEGFR; and 806 reactive with amplified/overexpressed wtEGFR (with or without DeltaEGFR). In normal tissues, 528 but not DH8.3 or 806 was widely reactive with many organs, e.g., liver expressing high EGFR levels. In glioblastoma and non-CNS tumor panels, 806 was reactive with a high proportion of glioblastomas and a substantial number of epithelial cancers of lung and of head and neck. DH8.3 reactivity was restricted to DeltaEGFR-positive glioblastoma. Thus, 806 represents a category of mAbs that recognizes tumors with EGFR amplification/overexpression but not normal tissues or tumors with normal EGFR levels. Our study also indicates that DeltaEGFR is restricted to glioblastoma, in contrast to other reports that this mutation is found in tumors outside the brain.

EGF/ErbB receptor family in ovarian cancer

In summary, the EGF/ErbB family of receptor tyrosine kinases has been shown to play a key role in normal ovarian follicle development, and cell growth regulation of the ovarian surface epithelium. Disregulation of these normal growth regulatory pathways, including overexpression and/or mutation of EGFR/ErbB receptor family members, as well as elements of their downstream signalling pathways, have been shown to contribute to the etiology and progression of epithelial ovarian cancer. It is, therefore, not surprising that these gene products, and their related soluble receptor isoforms may have clinical utility as tumor and/or serum biomarkers of disease activity. Moreover, since several of these soluble receptor isoforms have potent growth inhibitory activity, and are naturally occurring in the circulation, they are ideal candidates for the development of novel therapeutics for the treatment of ovarian cancer patients.

A specific binding site for a fragment of the B-loop of epidermal growth factor and related peptides

Fragments of the B-loop of the epidermal growth factor family of peptides are reported to have mitogenic and angiogenic properties but appear to fail to compete with radioiodinated EGF in receptor binding. In this study, 11 analogs of a fragment of the B-loop of EGF-related peptides from several species were synthesized to study binding to A431 human epidermoid carcinoma using both 125I-EGF and [3'4'-3H-Tyr(22,29), Abu(20,31)]EGF(20-31)-NH(2). Specific binding sites were found for the human fragment and 8 analogs at a density five times higher than that of the EGF receptors. Analogs did not compete with 125I-EGF for binding to the EGF receptor. The novel binding site may mediate the biological effects of the fragments. The primary rather than secondary structure of the fragments appears to determine affinity.

EGF-R signaling through Fyn kinase disrupts the function of integrin alpha6beta4 at hemidesmosomes: role in epithelial cell migration and carcinoma invasion

We have examined the mechanism and functional significance of hemidesmosome disassembly during normal epithelial cell migration and squamous carcinoma invasion. Our findings indicate that a fraction of EGF receptor (EGF-R) combines with the hemidesmosomal integrin alpha6beta4 in both normal and neoplastic keratinocytes. Activation of the EGF-R causes tyrosine phosphorylation of the beta4 cytoplasmic domain and disruption of hemidesmosomes. The Src family kinase inhibitors PP1 and PP2 prevent tyrosine phosphorylation of beta4 and disassembly of hemidesmosomes without interfering with the activation of EGF-R. Coimmunoprecipitation experiments indicate that Fyn and, to a lesser extent, Yes combine with alpha6beta4. By contrast, Src and Lck do not associate with alpha6beta4 to a significant extent. A dominant negative form of Fyn, but not Src, prevents tyrosine phosphorylation of beta4 and disassembly of hemidesmosomes. These observations suggest that the EGF-R causes disassembly of hemidesmosomes by activating Fyn, which in turn phosphorylates the beta4 cytoplasmic domain. Neoplastic cells expressing dominant negative Fyn display increased hemidesmosomes and migrate poorly in vitro in response to EGF. Furthermore, dominant negative Fyn decreases the ability of squamous carcinoma cells to invade through Matrigel in vitro and to form lung metastases following intravenous injection in nude mice. These results suggest that disruption of hemidesmosomes mediated by Fyn is a prerequisite for normal keratinocyte migration and squamous carcinoma invasion.

Cloning and biological activity of epigen, a novel member of the epidermal growth factor superfamily

High throughput sequencing of a mouse keratinocyte library was used to identify an expressed sequence tag with homology to the epidermal growth factor (EGF) family of growth factors. We have named the protein encoded by this expressed sequence tag Epigen, for epithelial mitogen. Epigen encodes a protein of 152 amino acids that contains features characteristic of the EGF superfamily. Two hydrophobic regions, corresponding to a putative signal sequence and transmembrane domain, flank a core of amino acids encompassing six cysteine residues and two putative N-linked glycosylation sites. Epigen shows 24-37% identity to members of the EGF superfamily including EGF, transforming growth factor alpha, and Epiregulin. Northern blotting of several adult mouse tissues indicated that Epigen was present in testis, heart, and liver. Recombinant Epigen was synthesized in Escherichia coli and refolded, and its biological activity was compared with that of EGF and transforming growth factor alpha in several assays. In epithelial cells, Epigen stimulated the phosphorylation of c-erbB-1 and mitogen-activated protein kinases and also activated a reporter gene containing enhancer sequences present in the c-fos promoter. Epigen also stimulated the proliferation of HaCaT cells, and this proliferation was blocked by an antibody to the extracellular domain of the receptor tyrosine kinase c-erbB-1. Thus, Epigen is the newest member of the EGF superfamily and, with its ability to promote the growth of epithelial cells, may constitute a novel molecular target for wound-healing therapy.

Surrogate endpoint biomarkers and their modulation in cervical chemoprevention trials

BACKGROUND

Surrogate endpoint biomarkers (SEBs) are used as intermediate indicators of a reduction in cancer incidence in chemoprevention studies. SEBs should be expressed differentially in normal and high risk tissue; appear at a well defined stage of carcinogenesis; be studied with reasonable sensitivity, specificity, and accuracy; and be modulated in chemoprevention trials. The concept of SEBs may be useful in the trials of many new therapies.

METHODS

The current review includes a comprehensive review of the literature. Many SEBs have been the subject of intense study and include quantitative histopathology and cytology, proliferation markers, regulation markers, differentiation markers, general genomic instability markers, and tissue maintenance markers. Because of the critical biologic and epidemiologic role of the human papillomavirus (HPV) in cervical carcinogenesis, the relation between these markers and HPV should be considered. In addition, biomarkers of HPV infection and its regression should be sought.

RESULTS

Several chemoprevention trials have been published that have included the use of SEBs. The biomarkers that appear most promising in these clinical trials can be measured quantitatively and reproducibly: quantitative histology and cytology, proliferating cell nuclear antigen (PCNA), MIB-1, MPM-2, HPV viral load, epidermal growth factor receptor, polyamines, and ploidy. The markers that have been demonstrated to be modulated in chemoprevention trials in the literature are quantitative histology and cytology, PCNA, MPM-2, HPV viral load, and polyamines.

CONCLUSIONS

The surrogate endpoint biomarkers of most interest in future research should correlate well with HPV infection, be modulated by several therapeutic agents, and have limited variability and ease in measurement.

Identification of a novel AU-Rich element in the 3' untranslated region of epidermal growth factor receptor mRNA that is the target for regulated RNA-binding proteins

The epidermal growth factor receptor (EGF-R) plays an important role in the growth and progression of estrogen receptor-negative human breast cancers. EGF binds with high affinity to the EGF-R and activates a variety of second messenger pathways that affect cellular proliferation. However, the underlying mechanisms involved in the regulation of EGF-R expression in breast cancer cells are yet to be described. Here we show that the EGF-induced upregulation of EGF-R mRNA in two human breast cancer cell lines that overexpress EGF-R (MDA-MB-468 and BT-20) is accompanied by stabilization (>2-fold) of EGF-R mRNA. Transient transfections using a luciferase reporter identified a novel EGF-regulated approximately 260-nucleotide (nt) cis-acting element in the 3' untranslated region (3'-UTR) of EGF-R mRNA. This cis element contains two distinct AU-rich sequences (~75 nt), EGF-R1A with two AUUUA pentamers and EGF-R2A with two AUUUUUA extended pentamers. Each independently regulated the mRNA stability of the heterologous reporter. Analysis of mutants of the EGF-R2A AU-rich sequence demonstrated a role for the 3' extended pentamer in regulating basal turnover. RNA gel shift analysis identified cytoplasmic proteins (~55 to 80 kDa) from breast cancer cells that bound specifically to the EGF-R1A and EGF-R2A cis-acting elements and whose binding activity was rapidly downregulated by EGF and phorbol esters. RNA gel shift analysis of EGF-R2A mutants identified a role for the 3' extended AU pentamer, but not the 5' extended pentamer, in binding proteins. These EGF-R mRNA-binding proteins were present in multiple human breast and prostate cancer cell lines. In summary, these data demonstrate a central role for mRNA stabilization in the control of EGF-R gene expression in breast cancer cells. EGF-R mRNA contains a novel complex AU-rich 260-nt cis-acting destabilizing element in the 3'-UTR that is bound by specific and EGF-regulated trans-acting factors. Furthermore, the 3' extended AU pentamer of EGF-R2A plays a central role in regulating EGF-R mRNA stability and the binding of specific RNA-binding proteins. These findings suggest that regulated RNA-protein interactions involving this novel cis-acting element will be a major determinant of EGF-R mRNA stability.

Comparative genomic sequence analysis and isolation of human and mouse alternative EGFR transcripts encoding truncated receptor isoforms

This study presents the annotated genomic sequence and exon-intron organization of the human and mouse epidermal growth factor receptor (EGFR) genes located on chromosomes 7p11.2 and 11, respectively. We report that the EGFR gene spans nearly 200 kb and that the full-length 170-kDa EGFR is encoded by 28 exons. In addition, we have identified two human and two mouse alternative EGFR transcripts of 2.4-3.0 kb using both computational and experimental methods. The human 3.0-kb and mouse 2.8-kb EGFR mRNAs are predominantly expressed in placenta and liver, respectively, and both transcripts encode 110-kDa truncated receptor isoforms containing only the extracellular ligand-binding domain. We also have demonstrated that the aberrant 2.8-kb EGFR transcript produced by the human A431 carcinoma cell line is generated by splicing to a recombinant 3'-terminal exon located in EGFR intron 16, which apparently was formed as a result of a chromosomal translocation. Finally, we have shown that the human, mouse, rat, and chicken 1.8- to 3.0-kb alternative EGFR transcripts are generated by distinct splicing mechanisms and that each of these mRNAs contains unique 3' sequences that are not evolutionarily conserved. The presence of truncated receptor isoforms in diverse species suggests that these proteins may have important functional roles in regulating EGFR activity.

The EGF receptor family as targets for cancer therapy

Human carcinomas frequently express high levels of receptors in the EGF receptor family, and overexpression of at least two of these receptors, the EGF receptor (EGFr) and closely related ErbB2, has been associated with a more aggressive clinical behavior. Further, transfection or activation of high levels of these two receptors in nonmalignant cell lines can lead to a transformed phenotype. For these reasons therapies directed at preventing the function of these receptors have the potential to be useful anti-cancer treatments. In the last two decades monoclonal antibodies (MAbs) which block activation of the EGFr and ErbB2 have been developed. These MAbs have shown promising preclinical activity and 'chimeric' and 'humanized' MAbs have been produced in order to obviate the problem of host immune reactions. Clinical activity with these antibodies has been documented: trastuzumab, a humanized anti-ErbB2 MAb, is active and was recently approved in combination with paclitaxel for the therapy of patients with metastatic ErbB2-overexpressing breast cancer; IMC-C225, a chimeric anti-EGFr MAb, has shown impressive activity when combined with radiation therapy and reverses resistance to chemotherapy. In addition to antibodies, compounds that directly inhibit receptor tyrosine kinases have shown preclinical activity and early clinical activity has been reported. A series of phase III studies with these antibodies and direct tyrosine kinase inhibitors are ongoing or planned, and will further address the role of these active anti-receptor agents in the treatment of patients with cancer.

Transmembrane transforming growth factor-alpha tethers to the PDZ domain-containing, Golgi membrane-associated protein p59/GRASP55

Transforming growth factor-alpha (TGF-alpha) and related proteins represent a family of transmembrane growth factors with representatives in flies and worms. Little is known about the transport of TGF-alpha and other transmembrane growth factors to the cell surface and its regulation. p59 was purified as a cytoplasmic protein, which at endogenous levels associates with transmembrane TGF-alpha. cDNA cloning of p59 revealed a 452 amino acid sequence with two PDZ domains. p59 is myristoylated and palmitoylated, and associates with the Golgi system, where it co-localizes with TGF-alpha. Its first PDZ domain interacts with the C-terminus of transmembrane TGF-alpha and select transmembrane proteins. p59 is the human homolog of GRASP55, which is structurally related to GRASP65. GRASP55 and GRASP65 have been shown to play a role in stacking of the Golgi cisternae in vitro. C-terminal mutations of transmembrane TGF-alpha, which decrease or abolish the interaction with p59, also strongly impair cell surface expression of TGF-alpha. Our observations suggest a role for membrane tethering of p59/GRASP55 to select transmembrane proteins, including TGF-alpha, in maturation and transport to the cell surface.

Rhomboid and Star facilitate presentation and processing of the Drosophila TGF-α homolog Spitz

Activation of the Drosophila epidermal growth factor receptor (DER) by the transmembrane ligand, Spitz (Spi), requires two additional transmembrane proteins, Rhomboid and Star. Genetic evidence suggests that Rhomboid and Star facilitate DER signaling by processing membrane-bound Spi (mSpi) to an active, soluble form. To test this model, we use an assay based on Xenopus animal cap explants in which Spi activation of DER is Rhomboid and Star dependent. We show that Spi is on the cell surface but is kept in an inactive state by its cytoplasmic and transmembrane domains; Rhomboid and Star relieve this inhibition, allowing Spi to signal. We show further that Spi is likely to be cleaved within its transmembrane domain. However, a mutant form of mSpi that is not cleaved still signals to DER in a Rhomboid and Star-dependent manner. These results suggest strongly that Rhomboid and Star act primarily to present an active form of Spi to DER, leading secondarily to the processing of Spi into a secreted form.

An alternative HER-2/neu transcript of 8 kb has an extended 3'UTR and displays increased stability in SKOV-3 ovarian carcinoma cells

HER-2/neu is a potent oncogene that predicts poor outcome when overexpressed in ovarian cancer. The SKOV-3 ovarian carcinoma cell line, one of the only models for HER2-driven ovarian cancer, expresses a major uncharacterized 8-kb alternative HER-2 transcript.

OBJECTIVES

The aim of this study was to characterize the structure and determine the origin of the alternative sequence and examine the possible role of the 8-kb alternative transcript in overexpression of the HER-2 gene.

METHODS

The structure of the 8-kb transcript was investigated using polymerase chain reaction (PCR) and nucleotide sequencing of cDNA clones. PCR analysis of genomic DNA was used to assess the origin of the 8-kb transcript. The stability of the 8-kb mRNA was assessed by Northern blot analysis of RNA extracted from cells treated with transcriptional inhibitors.

RESULTS

Similar 5'UTR and coding sequence but an extended 3'UTR were contained in the 8-kb compared to the well-characterized 4.5-kb HER-2 transcript. Genomic DNA had continuity between the novel 3'UTR sequence from the 8-kb transcript and adjacent HER-2 terminal exon sequence. The 8-kb transcript had a half-life of 13 h compared to 5.5 h for the 4.5-kb transcript (P<0.01).

CONCLUSIONS

The 8-kb transcript is generated from alternative polyadenylation site usage rather than gene rearrangement. Since the 8-kb transcript contains alternative sequence found at the 3' end of the normal HER-2 gene, it could be expressed in other cells. Increased stability of the 8-kb transcript may confer a selective advantage for SKOV-3 cells by providing enhanced HER-2 expression.

Regulation of EGF-receptor expression by EGF and TGF alpha in epidermoid cancer cells is cell type-specific

The epidermal growth factor receptor (EGF-R) and its major ligands EGF and transforming growth factor alpha (TGF alpha) play an important role in the development of multiple human tumors. However, little is known of the comparative effects of each ligand on the regulation of EGF-R expression. To investigate this issue we used two similar human epidermoid cancer cell lines that overexpress EGF-Rs (KB and A431). In KB cells, EGF and TGF alpha increased EGF-R mRNA and protein levels by 2-3 fold over 8 h, associated with a greater than 4-fold stabilization of EGF-R mRNA half-life. EGF and TGF alpha also increased transcription of EGF-R mRNA 2-3-fold in KB cells. In contrast, EGF and TGF alpha only minimally increased EGF-R mRNA and protein in A431 cells, without changing EGF-R mRNA half-life. Basal EGF-R mRNA half-life was 2 fold greater in A431 cells than in KB cells (6-7 h versus 2-3 h), whilst the half-life of a mutant 2.6 kb EGF-R mRNA present in A431 cells, which lacks the 3-untranslated region (3'-UTR), was 2 fold greater than the full-length EGF-R mRNA. RNA gel-shift studies demonstrated that KB and A431 cells contain cytoplasmic proteins that bind specifically to an AU-rich sequence from the 3'-UTR of EGF-R mRNA. Taken together, these results demonstrate that in KB cells EGF and TGF alpha upregulate EGF-R expression at both transcriptional and post-transcriptional levels. The identification of AU-rich EGF-R mRNA-specific RNA-binding proteins from epidermoid cancer cells that overexpress EGF-Rs suggests that regulated RNA-protein interactions involving this region may play a central role in modulating EGF-R mRNA stability.

A sandwich type acridinium-linked immunosorbent assay (ALISA) detects soluble ErbB1 (sErbB1) in normal human sera

The epidermal growth factor receptor (ErbB1) is overexpressed in various human tumor-derived cell lines and neoplasms, where it is believed that receptor dysregulation plays a role in oncogenic transformation and tumor progression. In addition to the ErbB1 holoreceptor, numerous studies demonstrate that cells synthesize soluble or secreted forms of ErbB1, i.e., sErbB1. Overexpression of ErbB1 in a variety of tumors has led us to hypothesize that sErbB levels also may be altered during oncogenesis, tumor progression, and/or metastasis; and that these molecules may be useful tumor biomarkers. To address this hypothesis we have developed an acridinium-linked immunosorbent assay (ALISA) specific for the extracellular domain of ErbB1 that can be used to quantify the levels of sErbB1 molecules in body fluids and conditioned culture media. This assay can also detect full-length ErbB1 in cell and tissue extracts. Our ALISA is characterized by high sensitivity (intra-assay LLD < 1 fmol/ml), a broad linear range (approximately 1 to 4000 fmol/ml), and good reproducibility (CVs < 10%). Specificity experiments show that this ALISA detects p170 ErbB1 and soluble forms of ErbB1 that embody extracellular subdomains I through IV, but not forms of sErbB1 lacking subdomain IV. Our ALISA does not detect full-length ErbB2, ErbB3, or ErbB4; or p105 soluble ErbB2. We report that serum sErbB1 levels of healthy women (median = 3716 fmol/ml), ranging in age from 43 to 76 years, differ significantly from those of healthy men (median = 24,512 fmol/ml), ranging in age from 25 to 79 years. Additional analyses do not indicate that serum sErbB1 levels change with age in either healthy men or women. Immunoprecipitation experiments show that monoclonal antibodies specific for extracellular epitopes of ErbB1 completely neutralize the detection of sErbB1 in normal human sera by ALISA. Finally, we show by immunoprecipitation and Western immunoblot analyses with monoclonal antibodies specific for the extracellular domain of ErbB1 that normal human female and male sera contain a approximately 110-kDa protein. We conclude that our ALISA is measuring the relative levels of this p110 sErbB1 analog in normal human sera. Our ALISA, therefore, should be useful for measuring the levels of ErbB1 and sErbB1 molecules in tumor biopsy specimens and body fluids, respectively, and for determining whether sErbB1, like ErbB1, is a useful tumor biomarker.

An antisense EGFR oligodeoxynucleotide enveloped in Lipofectin induces growth inhibition in human malignant gliomas in vitro

Epidermal growth factor receptor (EGFR) plays an important role in the progression of malignancy in gliomas. We studied the growth inhibition of the malignant glioma cell lines using an antisense EGFR oligodeoxynucleotide enveloped with Lipofectin. At a concentration of 5 microM of the antisense EGFR oligodeoxynucleotide enveloped with Lipofectin, the proliferation of three malignant glioma cell lines was significantly inhibited (p < 0.05) compared with that of the cells exposed to 5 microM sense EGFR oligodeoxynucleotide. The activity of the tyrosine kinase and the DNA synthesis was also significantly suppressed (p < 0.05). These findings show that the antisense EGFR oligodeoxynucleotide enveloped with Lipofectin has a possibility to become a useful gene therapy against malignant gliomas.

Levels of TGF-alpha and EGFR protein in head and neck squamous cell carcinoma and patient survival

BACKGROUND

The most accurate predictor of disease recurrence in patients treated for head and neck squamous cell carcinoma is, at present, the extent of regional lymph node metastasis. Since elevated levels of epidermal growth factor receptor (EGFR) and of its ligand, transforming growth factor-alpha (TGF-alpha), have been detected in primary tumors of patients with head and neck squamous cell carcinoma, we determined whether tumor levels of these proteins were of prognostic importance.

METHODS

Monoclonal antibodies specific for EGFR and TGF-alpha were used for immunohistochemical detection of each protein in tissue sections of primary tumors from 91 patients who were treated by surgical resection. Levels of immunoreactive EGFR and TGF-alpha were quantified by use of a computerized image analysis system and were normalized to appropriate standards. The logrank test and proportional hazards regression analysis were used to calculate the probability that EGFR and TGF-alpha levels were associated with disease-free survival (i.e., no recurrence of cancer) and cause-specific survival (i.e., patients do not die of their disease). All P values were two-sided.

RESULTS

When tumor levels of EGFR or TGF-alpha were analyzed as continuous variables, disease-free survival and cause-specific survival were reduced among patients with higher levels of EGFR (both P = .0001) or TGF-alpha (both P = .0001). In a multivariate analysis, tumor site, tumor level of EGFR, and tumor level of TGF-alpha were statistically significant predictors of disease-free survival; in a similar analysis, regional lymph node stage and tumor levels of EGFR and of TGF-alpha were significant predictors of cause-specific survival.

CONCLUSION

Quantitation of EGFR and TGF-alpha protein levels in primary head and neck squamous cell carcinomas may be useful in identifying subgroups of patients at high risk of tumor recurrence and in guiding therapy.

Genetic factors in lung disease. Part II: Lung cancer and angiotensin converting enzyme gene

The recent progress in molecular biology has led to the elucidation of pathogenesis of lung cancer. The development of a lung cancer requires multiple genetic changes, consisting of the activation of oncogenes, including the K-ras and myc genes, and of inactivation of tumour suppressor genes, including the Rb, p53 and CDKN2 genes. Knowing the specific genes undergoing such changes should be useful as biomarkers for the early detection of cells destined to become malignant. Moreover, such genetic changes could be targets of newly designed drugs and gene-based therapy. Although the angiotensin I-converting enzyme was originally discovered in equine plasma, it has been recognized in various organs and cells other than vascular endothelial cells. This enzyme is also known to have wide substrate specificity to many peptides. The definite roles of angiotensin converting enzyme (ACE) in the respiratory system are largely unknown. Recent progress in molecular biology of the ACE, however, gives us a good chance to look over the significance of ACE in respiratory diseases as well as cardiovascular disorders. In this review, we show the recent advances in the basic studies of the ACE and refer to its clinical application.

Expression of the type 1 tyrosine kinase growth factor receptors EGF receptor, c-erbB2 and c-erbB3 in bladder cancer

Expression of the c-erbB3 protein was determined in transitional cell carcinoma of the bladder by immunohistochemistry. Strong membrane staining was observed in 10 per cent of cases (7/70) and cytoplasmic and membrane overexpression in 20 per cent (14/70). Overexpression of the epidermal growth factor (EGF) receptor (36 per cent, 25/70) and c-erbB2 proteins (9 per cent 6/70) was determined in the same series of cases. c-erbB3 overexpression was positively correlated with EGF receptor expression (P < 0.025) but appeared to be inversely associated with c-erbB2 overexpression.

Transformation of NIH 3T3 cells by HER3 or HER4 receptors requires the presence of HER1 or HER2

Members of the epidermal growth factor receptor (EGFR) subfamily of receptor protein tyrosine kinases have been implicated in the pathogenesis of various malignancies. The ability of one EGFR subfamily member to influence, or function synergistically with, another is likely to be a general feature of these receptors. To assess the role of receptor heterodimerization, we analyzed the ability of Neu differentiation factor (NDF) to induce cell growth and transformation of NIH 3T3 cells transfected with different combinations of the EGFR subfamily of receptors. NDF induced mitogenesis, but not transformation, of cells expressing either HER3 or HER4 alone. However, NDF-induced cell transformation was observed when either HER1 or HER2 was coexpressed with HER3 or HER4. In analogous receptor phosphorylation experiments, NDF-induced transphosphorylation appears to be correlated with synergistic transformation of NIH 3T3 cells. Interestingly, transphosphorylation between HER1 and HER4 can be stimulated by either EGF or NDF.

Chemoprevention trials and surrogate end point biomarkers in the cervix

Cervical cancer is the second most common malignancy in women worldwide and remains a significant health problem for women, especially minority and underserved women. Despite an understanding of the epidemiologic risks, the screening Papanicolaou smear, and morbid and costly treatment, overall survival remains 40%. New strategies, based on the clinical and molecular aspects of cervical carcinogenesis, are desperately needed. Chemoprevention refers to the use of chemical agents to prevent or delay the development of cancer in healthy populations. Chemoprevention studies have several unique features that distinguish them from classic chemotherapeutic trials; these features touch on several disciplines and weave knowledge of the biology of carcinogenesis into the trial design. In the design of chemoprevention trials, four factors are important: high risk cohorts must be identified; suitable medications must be selected; study designs should include Phases I, II, and III; and studies should include the use of surrogate end point biomarkers. Surrogate end point biomarkers are sought because the cancer develops over a long period of time, and studies of chemopreventives would require a huge number of subjects followed for many years. Surrogate end point biomarkers serve as alternative end points for examination of the efficacy of chemopreventives in tissue. High risk cohorts include women with cervical intraepithelial neoplasia (CIN) or squamous intraepithelial lesions (SIL). Nutritional studies have helped define micronutrients of interest (folate, carotenoids, vitamin C, vitamin E). Other medications of interest include retinoids (4-hydroxyphenylretinamide [4-HPR], retinyl acetate gel, topical all-trans-retinoic acid), polyamine synthesis inhibitors (alpha-difluoromethylornithine [DFMO]), and nonsteroidal anti-inflammatory drugs (ibuprofen). Phase I chemoprevention studies of the cervix have tested retinyl acetate gel and all-trans-retinoic acid. Phase II trials of all-trans-retinoic acid, beta-carotene, and folic acid have been and are being carried out, whereas Phase III trials of all-trans-retinoic acid have been completed and have shown significant regression of CIN 2 but not CIN 3. Phase I studies of DFMO and Phase II studies of DFMO and 4-HPR are underway. Surrogate end point biomarkers under study include (1) quantitative cytology and histopathology; (2) human papillomavirus type testing; (3) biologic measures of proliferation, regulation, differentiation, and genomic instability; and 4) fluorescence spectroscopic emission. Clinical trials with biologic end points will contribute to our understanding of the neoplastic process and hence aid us in developing new preventive and therapeutic strategies.

EGFR gene amplification--rearrangement in human glioblastomas

Immunostaining using an affinity-purified rabbit polyclonal antibody against the extracellular domain of the epidermal-growth-factor receptor (EGFR) showed over-expression occurring in a fraction of tumor cells in 17 out of 18 human glioblastomas and in a majority of cells in 7 of the 18. Southern-blotting technique using a full-length EGFR cDNA probe showed a variable degree of amplification in 10 of the 17 glioblastomas, which was associated with EGFR over-expression in each case. In 2 of the glioblastomas with EGFR gene amplification, a rearrangement of the gene affecting the extracellular domain of the receptor was identified and DNA sequence analyses revealed an identical deletion-rearrangement of 801 base pairs between exons 2 to 7, resulting in an in-frame fusion of exons 1 and 8.

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.

The role of the epidermal growth factor receptor in human gliomas: II. The control of glial process extension and the expression of glial fibrillary acidic protein

Our earlier investigations of the biology of the epidermal growth factor receptor (EGFR) in human gliomas demonstrated that the level of EGFR expression did not directly predict the glioma growth response to EGF, suggesting that the function of the EGFR in glioblastomas might not be limited to mediating the growth effects of EGF. We conducted the current studies to investigate the function(s) of the EGFR not related to growth control in human gliomas. These investigations show that the EGFR mediates the stimulative effects of EGF on glial process extension and glial fibrillary acidic protein (GFAP) expression. In addition, the level of EGFR expression correlates inversely with glioma cell responsiveness to differentiation promoting agents (for example, nerve growth factor and transforming growth factor-beta) that act through transmembrane tyrosine kinase receptors. Thus, glioma lines with a high level of EGFR expression (for example, T-98G cells) responded to fewer differentiation promoting factors than lines with a low level of EGFR expression (such as U-373MG cells). Our results suggest that the EGFR in gliomas may participate in mediating the process extension and GFAP stimulative effects of both EGF and other differentiation promoting agents. These properties represent components of the differentiated state in glia because their expression is stimulated by dibutyryl cyclic adenosine monophosphate in normal astrocytes. The involvement of the EGFR in the expression of these glial specific properties suggests that the EGFR may play an important role in glial differentiation.

The role of the epidermal growth factor receptor in human gliomas: I. The control of cell growth

The epidermal growth factor receptor (EGFR) gene is amplified in over 40% of primary human glioblastomas and overexpressed in the majority. The authors' investigations demonstrate that the function of the EGFR in glioblastomas is distinct from that in other human cancers because it does not appear to mediate the primary growth-promoting effect of EGF. Findings show that the level of EGFR expression does not directly predict the growth response to EGF, with growth stimulated in some cells but inhibited in others when cells were cultured in plastic dishes. On the other hand, when human glioblastoma cells were placed in soft agar cultures, the cell line expressing the highest levels of the EGFR demonstrated considerable colony formation in response to EGF treatment. In addition, cell lines with the highest EGFR levels were also more resistant to the growth-suppressive effects of retinoic acid when maintained in soft agar. These observations suggest that even though the overexpression of the EGFR did not confer a distinct growth advantage to glioma cells cultured on flat culture dishes, the ability of these cells to maintain anchorage-independent growth in soft agar especially in response to EGF and retinoic acid is facilitated. Because anchorage-independent growth is the best in vitro correlate to tumorigenicity, amplification and overexpression of the EGFR in human glioblastoma cells may be in part responsible for the tumorigenic potential of these cells.

Detection of c-erbB-2/neu and fibroblast growth factor-3/INT-2 but not epidermal growth factor receptor gene amplification in endometrial cancer by differential polymerase chain reaction

BACKGROUND

It currently is well established that the activation of protooncogenes could trigger uncontrolled cell growth and cancer development. Although this correlation already has been evidenced in several human tumors, no conclusive studies have related oncogene activation with the development of endometrial neoplasia. Nevertheless, few reports suggest that c-erbB-2/neu, which is a prognostic marker in breast cancer, epidermal growth factor receptor (EGFR), which is overexpressed in a variety of neoplasms, and fibroblast growth factor-3 (FGF-3/INT-2), which has been found to be amplified in breast and ovarian cancer, could be implicated in the development of endometrial adenocarcinoma.

METHODS

Amplification of c-erbB-2/neu, EGFR, and FGF-3/INT-2 was examined in 50 endometrial carcinomas, 10 adenomatous hyperplasias, and 50 normal endometrial samples, using the genomic differential polymerase chain reaction with the single copy reference gene interferon-gamma. Quantitation of the ratios between the amplified bands was assessed by image analysis.

RESULTS

c-erbB-2 and FGF-3/INT-2 were amplified in a first group of 7 (14%) and a further group of 7 (14%) patients, respectively, of a total of 50 in whom endometrial cancer had been studied. In the latter seven, a strong correlation between this genetic marker and an advanced disease stage (International Federation of Gynecology and Obstetrics Stage III) was found. In two patients, both genes were amplified. No EGFR gene amplification was detected in any case.

CONCLUSION

c-erbB-2/neu but not EGFR gene amplification was detected and FGF-3/INT-2 amplification and advanced disease were correlated in endometrial cancer.

Endocytosis and lysosomal targeting of epidermal growth factor receptors are mediated by distinct sequences independent of the tyrosine kinase domain

Ligand-induced internalization of the epidermal growth factor receptor (EGFR) leads to accelerated receptor degradation. Two models have been proposed to explain this. In the first model, induced internalization expands the intracellular pool of receptors, leading to enhanced lysosomal targeting. The second model proposes that activation of intrinsic receptor kinase activity induces inward vesiculation of endosomes, thus interrupting receptor recycling. To test these models, we created EGFR mutants that lack the conserved tyrosine kinase domain, but retain different parts of the distal carboxyl terminus regulatory region. Mutants lacking all distal regulatory sequences underwent slow internalization (0.02 min-1) and turnover (t1/2 approximately 24 h), similar to unoccupied, holo-EGFR. Mutant receptors that lacked the kinase domain, but retained the entire distal regulatory domain, were constitutively internalized and targeted to lysosomes, even in the absence of EGF. The turnover of these receptors (t1/2 approximately 11 h) was similar to that of occupied, kinase-active holo-EGFR (t1/2 approximately 9.5 h). These results show that receptor tyrosine kinase activity is not required for the targeting of EGFR to lysosomes. Receptor mutants which expressed previously identified endocytic sequences underwent rapid internalization. Unexpectedly, enhanced turnover of EGFR mutants required additional sequences located between residues 945 and 991 in the holo-EGFR. Thus, internalization and lysosomal targeting of EGFR are separate processes mediated by distinct sequences. Our results indicate that induced internalization is necessary, but not sufficient, for enhanced EGFR degradation. Instead, down-regulation requires exposure of previously cryptic internalization and lysosomal targeting sequences. Occupied EGFR thus appear to be handled by the endocytic machinery in the same fashion as other constitutively internalized or lysosomally targeted receptors.

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.

Mutation of proline-1003 to glycine in the epidermal growth factor (EGF) receptor enhances responsiveness to EGF

We have shown previously that the epidermal growth factor (EGF) receptor is phosphorylated at Ser-1002 and that this phosphorylation is associated with desensitization of the EGF receptor. Ser-1002 is followed immediately by Pro-1003, a residue that may promote the adoption of a specific conformation at this site or severe as a recognition element for the interaction of the EGF receptor with other proteins. To examine these possibilities, we have mutated Pro-1003 of the EGF receptor to a Gly residue and have analyzed the effect of this mutation on EGF-stimulated signaling. Cells expressing the P1003G EGF receptors exhibited higher EGF-stimulated autophosphorylation and synthetic peptide phosphorylation compared to cells expressing wild-type EGF receptors. In addition, the ability of EGF to stimulate PI 3-kinase activity and mitogen-activated protein kinase activity was enhanced in cells expressing the P1003G EGF receptor. Cells expressing P1003G receptors also demonstrated an increased ability to form colonies in soft agar in response to EGF. These results indicate that mutation of Pro-1003 leads to a potentiation of the biological effects of EGF. The findings are consistent with the hypothesis that Pro-1003 plays a role in a form of regulation that normally suppresses EGF receptor function.

Expression and localization of mRNA for epidermal growth factor and epidermal growth factor receptor in human cholesteatoma

The roles of epidermal growth factor (EGF) and epidermal growth factor receptor (EGF-R) in the proliferation and progression of the epithelium of middle ear cholesteatoma were studied. An attempt was made to elucidate the site and degree of localization of the EGF mRNA and EGF-R mRNA in the epithelium of the cholesteatoma by means of the non-radioactive in situ hybridization method. Ten cholesteatoma specimens excised during operations and six normal skin specimens (control) collected from the external ear canal were used in this study. The signal of the EGF mRNA was slightly expressed in part of the basal cells in only one of the six control specimens, while the signal was strongly expressed along the basal cells of the cholesteatoma epithelium in five of the ten specimens. The signal of the EGF-R mRNA was observed along the basal cell layer in five of the six control specimens, while the signal was strongly expressed in all layers of the cholesteatoma epithelium in all ten specimens. The expression was especially marked in the basal cell layer. These findings suggest the possibilities that abnormal expression of the EGF-R mRNA in nearly entire epithelial layers of cholesteatoma is due to overexpression of EGF-R gene, and that there is a mechanism of epithelial basal cell proliferation through an autocrine regulatory system via EGF and EGF-R.

The lin-15 locus encodes two negative regulators of Caenorhabditis elegans vulval development

During Caenorhabditis elegans vulval development, an inductive signal from the anchor cell stimulates three of the six vulval precursor cells (VPCs) to adopt vulval rather than nonvulval epidermal fates. Genes necessary for this induction include the lin-3 growth factor, the let-23 receptor tyrosine kinase, and let-60 ras. lin-15 is a negative regulator of this inductive pathway. In lin-15 mutant animals, all six VPCs adopt vulval fates, even in the absence of inductive signal. Previous genetic studies suggested that lin-15 is a complex locus with two independently mutable activities, A and B. We have cloned the lin-15 locus by germline transformation and find that it encodes two nonoverlapping transcripts that are transcribed in the same direction. The downstream transcript encodes the lin-15A function; the upstream transcript encodes the lin-15B function. The predicted lin-15A and lin-15B proteins are novel and hydrophilic. We have identified a molecular null allele of lin-15 and have used it to analyze the role of lin-15 in the signaling pathway. We find that lin-15 acts upstream of let-23 and in parallel to the inductive signal.

Nef induces CD4 endocytosis: requirement for a critical dileucine motif in the membrane-proximal CD4 cytoplasmic domain

CD4 is crucial for antigen-driven helper T cell signaling and is used as receptor by the human immunodeficiency virus (HIV). The HIV early protein Nef causes a loss of CD4 from cell surfaces through a previously undefined posttranscriptional mechanism. Here, we demonstrate that Nef acts by inducing CD4 endocytosis, resulting in its degradation in lysosomes. CD4 down-regulation is strongly enhanced by the association of Nef with cell membranes through myristoylation. The study of chimeric molecules reveals that 20 membrane-proximal residues of the CD4 cytoplasmic domain are sufficient to confer Nef sensitivity. Within this region, a dileucine motif, reminiscent of an endocytosis and lysosomal targeting signal found in the CD3 gamma and delta chains, is crucial for CD4 response to Nef.

Hormone receptors and cathepsin D levels in human breast epithelial cells transformed by chemical carcinogens and c-Ha-ras transfection

The objective of this work was to determine whether transformation of the human breast epithelial cell line MCF-10F by the chemical carcinogens 7, 12-dimethylbenz(a)anthracene (DMBA) or benzo(a)pyrene (BP), or c-Ha-ras oncogene transfection, influence the expression of epidermal growth factor receptor (EGFR), estrogen (ER) or progesterone (PR) receptors, and the content of cathepsin-D (Cath.D). MCF-10F control cells did not express any of the phenotypes of neoplastic transformation, whereas carcinogen-treated cells and clones derived from the latter formed colonies in agar-methocel, and exhibited increased chemotaxis and chemoinvasion. Clone BP-1E was also tumorigenic in SCID mice. The BP1 cell line transfected with mutated c-Ha-ras oncogene, named BP1-Tras, became more aggressive after transfection and decreased the latency time to tumorigenesis. Radioligand binding and immunocytochemical reactions were utilized for determining the receptors and Cath.D content of control and carcinogen-treated cells and their derived clones. MCF-10F cells contained 37 fmol/mg of protein of EGFR, ER and PR were undetectable, and Cath.D content was 70 fmol/mg protein. EGFR content was significantly higher in D3-1 and BP1-E cell lines vs the control MCF-10F and the other DMBA and BP clones, correlating positively with the emergence of the transformation phenotype. Whereas EGFR levels were not significantly different in BP1-Tras cells when compared with BP1-E, the former were more tumorigenic in SCID mice, an observation suggesting an alternative pathway in these cells in the formation of tumors.(ABSTRACT TRUNCATED AT 250 WORDS)