Schwannoma-Derived Growth Factor Interacts with the Epidermal Growth Factor Receptor

Abstract: Schwannoma-derived growth factor (SDGF) is a potent mitogen and neuronal differentiation factor. Because of its relationship to epidermal growth factor (EGF) and the heregulins, it was asked if SDGF interacts with the EGF receptor or HER2/neu. SDGF binds to and causes the phosphorylation on tyrosine of the EGF receptor but not HER2/neu.     

Nanoscale Imaging of Epidermal Growth Factor Receptor Clustering: EFFECTS OF INHIBITORS*

The development of some solid tumors is associated with overexpression of the epidermal growth factor receptor (EGFR) and often correlates with poor prognosis. Near field scanning optical microscopy, a technique with subdiffraction-limited optical resolution, was used to examine the influence of two inhibitors (the chimeric 225 antibody and tyrosine phosphorylation inhibitor AG1478) on the nanoscale clustering of EGFR in HeLa cells. The EGFR is organized in small clusters, average diameter of 150 nm, on the plasma membrane for both control and EGF-treated cells. The numbers of receptors in individual clusters vary from as few as one or two proteins to greater than 100. Both inhibitors yield an increased cluster density and an increase in the fraction of clusters with smaller diameters and fewer receptors. Exposure to AG1478 also decreases the fraction of EGFR that colocalizes with both rafts and caveolae. EGF stimulation results in a significant loss of the full-length EGFR from the plasma membrane with the concomitant appearance of low molecular mass proteolytic products. By contrast, AG1478 reduces the level of EGFR degradation. Changes in receptor clustering provide one mechanism for regulating EGFR signaling and are relevant to the design of strategies for therapeutic interventions based on modulating EGFR signaling.     

Acute Regulation of the Epidermal Growth Factor Receptor in Response to Nerve Growth Factor

PC12 cells possess specific receptors for both nerve growth factor and epidermal growth factor, and by an unknown mechanism, nerve growth factor is able to attenuate the propagation of a mitogenic response to epidermal growth factor. The differentiation response of PC12 cells to nerve growth factor, therefore, predominates over the proliferative response to epidermal growth factor. We have observed that the addition of nerve growth factor to PC12 cells rapidly produces a decrease in surface 125I-epidermal growth factor binding capacity. Unlike previously described nerve growth factor effects on 125I-epidermal growth factor binding capacity, which required several days of nerve growth factor exposure, the decreases we report occur within minutes of nerve growth factor addition: A 50% decrease in 125I-epidermal growth factor binding capacity is evident at 10 min. This rapid nerve growth factor response is concentration dependent; inhibition of 125I-epidermal growth factor binding is detectable at nerve growth factor levels as low as 0.2 ng/ml and is maximal at approximately 50 ng/ml, consistent with known ranges of biological activity. No demonstrable differences in the rate of epidermal growth factor receptor synthesis or degradation were observed in cells acutely exposed to nerve growth factor. Scatchard analysis revealed that acute nerve growth factor treatment decreased the number of both high- and low-affinity 125I-epidermal growth factor binding sites, while the receptor affinity remained unchanged. We have also investigated the involvement of various potential intracellular mediators of nerve growth factor action and of known intracellular modulatory systems of the epidermal growth factor receptor for their capacity to participate in this nerve growth factor activity.     

表皮生长因子及受体在甲状腺肿瘤中的表达

目的:研究表皮生长因子(Epidermal Growth Factor,EGF)及受体(Epidermal Growth Factor Receptor,EGFR)及在甲状腺肿瘤中的表达。方法:应用免疫组织化学法检测91例甲状腺病变组织中EGFR和EGF的表达情况。结果:结节性甲状腺肿、甲状腺腺瘤、分化型甲状腺癌标本中EGFR表达的阳性率分别为15%、25%、68.62%,EGF表达的阳性率分别为10%、15%、68.62%,其中EGFR、EGF在分化型甲状腺癌与其余两组间差异均有统计学意义(P<0.05)。EGFR和EGF在甲状腺乳头状癌中的表达与性别、年龄、肿瘤大小、淋巴结转移、临床分期等临床因素无明显相关。结论:EGF和EGFR的表达可作为鉴别甲状腺肿瘤良恶性的一个指标。     

Intracellular Transactivation of the Insulin-like Growth Factor I Receptor by an Epidermal Growth Factor Receptor

Growth factor receptors may be transactivated not only by homologous receptors, but also by heterologous receptors. We have investigated this possibility, using for this purpose R⁻/EGFR cells, which are mouse embryo cells devoid of IGF-I receptors, but overexpressing the EGF receptor. At variance with mouse embryo cells with a wild-type number of IGF-I receptors and overexpressing the EGF receptor, R⁻/EGFR cells cannot grow in EGF only, nor can they form colonies in soft agar. However, if a wild type human IGF-I receptor is stably transfected into R⁻/EGFR cells, growth in EGF and colony formation in soft agar are restored. To determine a possible interaction between the two receptors, we transfected into R⁻/EGFR cells a number of IGF-I receptor mutants with different impaired functions. The only IGF-I receptor that cannot reverse the growth phenotype of R⁻/EGFR cells is a receptor with a point mutation at the ATP-binding site. All other mutant receptors, even when incapable of responding to IGF-I with a mitogenic signal, made R⁻/EGFR cells fully capable of responding with growth to EGF stimulation. IGF-I receptor mutants that are mitogenic but not transforming made R⁻/EGFR cells grow in EGF only, but were incapable of inducing the transformed phenotype. The mutant IGF-I receptors are activated (tyrosyl phosphorylation of IRS-1) in response to EGF. These experiments indicate that certain IGF-I receptor mutants with loss of function can be reactivated intracellularly by an overexpressed EGF receptor and confirm that the C-terminus of the IGF-IR is required for its transforming activity.     

Biomarkers to Predict Response to Epidermal Growth Factor Receptor Inhibitors

Epidermal growth factor receptors (EGFRs) are amplified and overexpressed in many different human cancers, a phenomenon generally associated with poor prognosis. Inhibitors of the tyrosine kinase activity associated with this receptor have been approved for the treatment of chemotherapy-refractory non-small cell lung cancer, and are in clinical trials for additional tumor types. While these inhibitors, gefitinib and erlotinib, display limited response rates when assessed in a cohort that includes all patients, there are subgroups, defined by patient and tumor characteristics, that preferentially respond to these agents. We recently performed an analysis of tumors obtained form a Phase I trial of erlotinib in patients with glioblastoma multiforme (GBM), the most common malignant brain tumor in adults. We showed that patients whose tumors exhibited overexpression and amplification of EGFR responded better than patients who had normal levels of this gene and protein. We also demonstrated that the phosphorylation state of PKB/Akt was an important determinant for response, with low phospho-PKB/Akt levels predicting good response to erlotinib. We discuss these findings in the context of recent molecular analyses of the placebo-controlled Phase III trials that led to approval of EGFR inhibitors. These data underscore the importance of placebo-controlled trials to distinguish between prognostic indicators of disease progression more generally and predictive markers of response to therapy. Ultimately the goal of these studies is to allow selection of patients who will preferentially respond to EGFR inhibitors.     

Ligand-Induced Translocation of Epidermal Growth Factor Receptor to the Nucleus of NR6/HER Fibroblasts Is Serum Dependent

Ligand-induced translocation of epidermal growth factor receptors (EGF-R) to the nucleus of NR6/HER fibroblasts has been studied by immunoelectron microscopy. Following treatment of NR6/HER cells with epidermal growth factor (EGF) for 1 h, there was a decrease in EGF-R labeling at the plasma membrane and a corresponding increase in EGF-R in the nucleus. This was preceded by a rapid and sustained increase in nuclear phosphotyrosine content, detectable within 2 min of EGF treatment. EGF-R translocation into the nucleus was completely prevented by 18 h serum starvation prior to treatment with EGF. These results indicate that translocation of EGF-R to the nucleus is a controlled process and they suggest theft EGF-R may directly influence nuclear function.     

Conformational Analysis of the Phosphorylated Epidermal Growth Factor Receptor

Phosphorylation-induced conformational changes have been well documented with different receptor tyrosine kinases. However, the susceptible epitopes and the tyrosine residue(s) involved in particular structural alteration mostly remain to be determined. Using a conformation-specific anti-peptide antibody, we have not only identified one such domain in the C-terminal tail of the EGF receptor but also identified the phosphate acceptor sites that are involved in the conformational change.     

人EGFR显性负性突变体负调控内源性EGFR功能的机制分析

通过定向克隆法构建真核表达载体pEGFPN1-DNEGFR,脂质体介导下转染体外培养的SGC-7901细胞,应用Western blotting检测DNEGFR-EGFP蛋白的表达,激光共聚焦显微镜对DNEGFR-EGFP亚细胞结构定位检测;并经RT-PCR、Western blotting检测DNEGFR-EGFP对内源性EGFRmRNA水平、蛋白及磷酸化水平的影响.成功检测到DNEGFR-EGFP蛋白的表达,DNEGFR-EGFP蛋白主要定位于细胞膜,DNEGFR-EGFP能降低内源性EGFR蛋白磷酸化水平,而对内源性EGFRmRNA水平及蛋白水平无影响.研究证明DNEGFR通过降低内源性EGFR蛋白磷酸化水平负调控EGFR功能,为靶向EGFR显性负性策略在肿瘤生物治疗中的进一步研究打下基础.     

The Constitutive Activity of Epidermal Growth Factor Receptor vIII Leads to Activation and Differential Trafficking of Wild-type Epidermal Growth Factor Receptor and erbB2

A constitutively active epidermal growth factor receptor (EGFR) mutant, EGFR variant III (EGFRvIII), has been detected at high frequencies in certain human cancers. This study evaluated transactivation and trafficking of erbB family members as a result of constitutive EGFR activity in a cancer cell line. Expression of EGFRvIII modulated erbB family members through different mechanisms; the erbB3 mRNA level was reduced, whereas wild-type EGFR (wtEGFR) and erbB2 protein levels were diminished, with no change in their mRNA levels, and there was no change in the erbB4 expression level. Both EGFR and erbB2 were internalized as a result of EGFRvIII''s activity and redistributed to the cell surface upon addition of AG1478, an inhibitor of wtEGFR/EGFRvIII catalytic activity. Acute activation of EGFRvIII by removing AG1478 from cells increased phosphorylation of both wtEGFR and erbB2 and caused differential trafficking of EGFRvIII''s activation partners; wtEGFR was directed primarily to lysosomal compartments and partially to recycling compartments, whereas erbB2 was directed primarily to recycling compartments and partially to lysosomal compartments. Our data demonstrate that the constitutive activity of EGFRvIII is sufficient to trigger endocytosis and trafficking of wtEGFR and erbB2, which may play a role in activating signaling pathways that are triggered during receptor endocytosis. (J Histochem Cytochem 58:529–541, 2010)     

Comprehensive Mapping of the Human Kinome to Epidermal Growth Factor Receptor Signaling

Disregulation of epidermal growth factor receptor (EGFR) signaling directly promotes bypass of proliferation and survival restraints in a high frequency of epithelia-derived cancer. As such, much effort is currently focused on decoding the molecular architecture supporting EGFR activation and function. Here, we have leveraged high throughput reverse phase protein lysate arrays, with a sensitive fluorescent nanocrystal-based phosphoprotein detection assay, together with large scale siRNA-mediated loss of function to execute a quantitative interrogation of all elements of the human kinome supporting EGF-dependent signaling. This screening platform has captured multiple novel contributions of diverse protein kinases to modulation of EGFR signal generation, signal amplitude, and signal duration. As examples, the prometastatic SNF1/AMPK-related kinase hormonally upregulated Neu kinase was found to support EGFR activation in response to ligand binding, whereas the enigmatic kinase MGC16169 selectively supports coupling of active EGFR to ERK1/2 regulation. Of note, the receptor tyrosine kinase MERTK and the pyrimidine kinase UCK1 were both found to be required for surface accumulation of EGFR and subsequent pathway activation in multiple cancer cell backgrounds and may represent new targets for therapeutic intervention.     

Mechanisms for Kinase-mediated Dimerization of the Epidermal Growth Factor Receptor

We study a mechanism by which dimerization of the EGF receptor (EGFR) cytoplasmic domain is transmitted to the ectodomain. Therapeutic and other small molecule antagonists to the kinase domain that stabilize its active conformation, but not those that stabilize an inactive conformation, stabilize ectodomain dimerization. Inhibitor-induced dimerization requires an asymmetric kinase domain interface associated with activation. EGF and kinase inhibitors stimulate formation of identical dimer interfaces in the EGFR transmembrane domain, as shown by disulfide cross-linking. Disulfide cross-linking at an interface in domain IV in the ectodomain was also stimulated similarly; however, EGF but not inhibitors stimulated cross-linking in domain II. Inhibitors similarly induced noncovalent dimerization in nearly full-length, detergent-solubilized EGFR as shown by gel filtration. EGFR ectodomain deletion resulted in spontaneous dimerization, whereas deletion of exons 2–7, in which extracellular domains III and IV are retained, did not. In EM, kinase inhibitor-induced dimers lacked any well defined orientation between the ectodomain monomers. Fab of the therapeutic antibody cetuximab to domain III confirmed a variable position and orientation of this domain in inhibitor-induced dimers but suggested that the C termini of domain IV of the two monomers were in close proximity, consistent with dimerization in the transmembrane domains. The results provide insights into the relative energetics of intracellular and extracellular dimerization in EGFR and have significance for physiologic dimerization through the asymmetric kinase interface, bidirectional signal transmission in EGFR, and mechanism of action of therapeutics.     

Role for the Epidermal Growth Factor Receptor in Chemotherapy-Induced Alopecia

Treatment of cancer patients with chemotherapeutics like cyclophosphamide often causes alopecia as a result of premature and aberrant catagen. Because the epidermal growth factor receptor (EGFR) signals anagen hair follicles to enter catagen, we hypothesized that EGFR signaling may be involved in cyclophosphamide-induced alopecia. To test this hypothesis, skin-targeted Egfr mutant mice were generated by crossing floxed Egfr and Keratin 14 promoter-driven Cre recombinase mice. Cyclophosphamide treatment of control mice resulted in alopecia while Egfr mutant skin was resistant to cyclophosphamide-induced alopecia. Egfr mutant skin entered catagen normally, as indicated by dermal papilla condensation and decreased follicular proliferation, but did not progress to telogen as did Egfr wild type follicles. Egfr mutant follicles responded with less proliferation, apoptosis, and fewer p53-positive cells after cyclophosphamide. Treatment of control mice with the EGFR inhibitors erlotinib or gefitinib similarly suppressed alopecia and catagen progression by cyclophosphamide. Secondary analysis of clinical trials utilizing EGFR-targeted therapies and alopecia-inducing chemotherapy also revealed evidence for involvement of EGFR in chemotherapy-induced alopecia. Taken together, our results demonstrated the involvement of EGFR signaling in chemotherapy-induced alopecia, which will help in the design of novel therapeutic regimens to minimize chemotherapy-induced alopecia.     

Epidermal Growth Factor Receptor in Prostate Cancer Derived Exosomes

Exosomes proteins and microRNAs have gained much attention as diagnostic tools and biomarker potential in various malignancies including prostate cancer (PCa). However, the role of exosomes and membrane-associated receptors, particularly epidermal growth factor receptor (EGFR) as mediators of cell proliferation and invasion in PCa progression remains unexplored. EGFR is frequently overexpressed and has been associated with aggressive forms of PCa. While PCa cells and tissues express EGFR, it is unknown whether exosomes derived from PCa cells or PCa patient serum contains EGFR. The aim of this study was to detect and characterize EGFR in exosomes derived from PCa cells, LNCaP xenograft and PCa patient serum. Exosomes were isolated from conditioned media of different PCa cell lines; LNCaP xenograft serum as well as patient plasma/serum by differential centrifugation and ultracentrifugation on a sucrose density gradient. Exosomes were confirmed by electron microscopy, expression of exosomal markers and NanoSight^™ analysis. EGFR expression was determined by western blot analysis and ELISA. This study demonstrates that exosomes may easily be derived from PCa cell lines, serum obtained from PCa xenograft bearing mice and clinical samples derived from PCa patients. Presence of exosomal EGFR in PCa patient exosomes may present a novel approach for measuring of the disease state. Our work will allow to build on this finding for future understanding of PCa exosomes and their potential role in PCa progression and as minimal invasive biomarkers for PCa.     

Plakophilin-2 Promotes Activation of Epidermal Growth Factor Receptor

While growth factor-driven dimerization of receptor tyrosine kinases (RTKs) is a simple and intuitive mechanism of activating RTKs, K.-I. Arimoto et al. (Mol. Cell. Biol. 34:3843–3854, 2014, doi:10.1128/MCB.00758-14) describe a novel means of promoting the activity of RTKs. Namely, plakophilin-2 (PKP2) associates with the epidermal growth factor receptor (EGFR) and enhances its ligand-dependent and ligand-independent activity. This discovery suggests that antagonizing PKP2 may be a new therapeutic opportunity to combat tumors in which activation of EGFR contributes to pathogenesis.     

Epidermal Growth Factor Induces Internalization But Not Degradation of the Epidermal Growth Factor Receptor in a Human Breast Cancer Cell Line

Abstract

Metabolism of the epidermal growth factor (EGF) receptor was studied in the MDA-MB-231 human breast cancer cell line. As in normal fibroblasts the EGF receptor from MDA-MB-231 cells was synthesized from a M_r =160,000 precursor and tunicamycin treatment of cells resulted in accumulation of a M_r =130,000 polypeptide. Unlike normal fibroblasts in which a M_r =170,000 mature form of the EGF receptor was found, MDA-MB-231 cells contained a M_r =172,000 mature form. Addition of EGF to MDA-MB-231 cells led to rapid internalization of EGF receptors, however, internalization did not affect receptor half-life and receptors did not recycle to the cell surface. EGF receptors could be visualized by immunofluorescence and remained sequestered in intracellular membranous structures following internalization. EGF was degraded slowly by MDA-MB-231 cells relative to degradation of EGF by normal cells. A high endogenous level of in vivo phosphorylation of threonine 654 of the EGF receptor was found in MDA-MB-231 cells and treatment of cells with 12-0-tetradecanoyl-phorbol-13-acetate (TPA) further stimulated phosphorylation of this residue. EGF induced receptor internalization resulted in dephosphorylation of threonine 654. The significance of these unusual properties of EGF receptor metabolism in MDA-MB-231 cells is discussed.     

Aging Affects Epidermal Growth Factor Receptor Phosphorylation and Traffic Kinetics

With increasing donor age, cultured human fibroblasts express fewer epidermal growth factor receptors and display decreased mitogenic responsiveness to epidermal growth factor. To determine age-associated differences in epidermal growth factor receptor phosphorylation and traffic kinetics, we studied in fibroblasts derived from donors of different ages autophosphorylation of the receptor after ligand binding and trafficking of the receptor–ligand complexes. We now report an age-associated delay in the rate of receptor phosphorylation after epidermal growth factor stimulation. Furthermore, receptor/ligand trafficking is affected by aging. There is an age-associated decrease and delay in the number of occupied receptors that are transported intracellularly and in their rate of clearance from the plasma membrane. Our data show that aging affects receptor/ligand activation and processing and suggest that the decreased cellular mitogenic response with aging may be, at least in part, the result of decrements in receptor activation and processing.     

Glucocorticoid-Induced Apoptosis: Revisited: A Novel Role for Glucocorticoid Receptor Translocation to the Mitochondria

Recent data cast new light on the mechanisms by which glucocorticoids (GCs)elicit apoptosis of thymocytes and leukemia cells. Here we attempt to integrate recentstudies by others and us, which provide a novel insight to this apoptotic process. In thelast few years it was made clear that there is a tight cooperation between genomic andnon-genomic effects exerted by GC receptors (GRs). GC invokes major alterations in thegene expression profile through GR-mediated transactivation and transrepression, whichultimately tip the balance between pro-survival and pro-apoptotic proteins. Althoughessential in shaping the cell’s proteome, these genomic effects are insufficient to elicitapoptotic death and additional signals are required for activating the pro-apoptoticproteins. Several non-genomic effects have been described that occur immediatelyfollowing exposure to GC, which are imperative for the induction of apoptosis. We haverecently observed that GC induces instant GR translocation to the mitochondria in GCsensitive,but not in GC-resistant, T lymphoid cells. This response contrasts the nucleartranslocation of GR occurring in both cell types. We propose that the sustained elevationof GR in the mitochondria following GC exposure is crucial for triggering apoptosis.