Transforming growth factor alpha production and epidermal growth factor receptor expression in normal and oncogene transformed human mammary epithelial cells

ERBB Receptors and Their Ligands in the Developing Mammary Glands of Different Species: Fifteen Characters in Search of an Author

The ERBB tyrosine kinase receptors and their ligands belong to a complex family that has diverse biological effects and expression profiles in the developing mammary glands, where its members play an essential role in translating hormone signals into local effects. While our understanding of these processes stems mostly from mouse models, there is the potential for differences in how this family functions in the mammary glands of other species, particularly in light of their unique histomorphological features. Herein we review the postnatal distribution and function of ERBB receptors and their ligands in the mammary glands of rodents and humans, as well as for livestock and companion animals. Our analysis highlights the diverse biology for this family and its members across species, the regulation of their expression, and how their roles and functions might be modulated by varying stromal composition and hormone interactions. Given that ERBB receptors and their ligands have the potential to influence processes ranging from normal mammary development to diseased states such as cancer and/or mastitis, both in human and veterinary medicine, a more complete understanding of their biological functions should help to direct future research and the identification of new therapeutic targets.

MicroSPECT/CT imaging of co-expressed HER2 and EGFR on subcutaneous human tumor xenografts in athymic mice using ¹¹¹In-labeled bispecific radioimmunoconjugates

Epidermal growth factor receptors (EGFR) form heterodimers with HER2 in breast cancer, and increased EGFR expression has been found in HER2-positive tumors resistant to trastuzumab (Herceptin). Our objective was to synthesize bispecific radioimmunoconjugates (bsRICs) that recognize HER2 and EGFR and evaluate their ability to image tumors in athymic mice that express one or both receptors by microSPECT/CT. Bispecific radioimmunoconjugates were constructed by conjugating maleimide-derivatized trastuzumab Fab fragments that bind HER2 to a thiolated form of EGF with an intervening 24 mer polyethylene glycol (PEG24) spacer. Bispecific radioimmunoconjugates were derivatized with diethylenetriaminepentaacetic acid for labeling with (111)In. The ability of (111)In-bsRICs to bind HER2 or EGFR was determined in competition assays using cells expressing one or both receptors. Tumor and normal tissue uptake were examined in CD1 athymic mice bearing subcutaneous tumor xenografts that expressed HER2, EGFR, or both receptors, with or without pre-administration of Fab or EGF to determine specificity. HER2 and EGFR binding and displacement of binding by competitors were found for (111)In-bsICs. The highest uptake of (111)In-bsRICs [7.3 ± 3.5 %ID/g] in 231-H2N human breast cancer xenografts (HER2+/EGFR+) occurred at 48 h post-injection. Pre-administration of trastuzumab Fab decreased uptake in SK-OV-3 (HER2+/EGFR-) human ovarian cancer xenografts from 7.1 ± 1.2 to 2.4 ± 1.5 %ID/g. Pre-administration of excess EGF decreased uptake in MDA-MB-231 (HER2-/EGFR+) human breast cancer xenografts from 5.9 ± 0.5 to 2.0 ± 0.1 %ID/g. All tumors were imaged by microSPECT/CT. We conclude that (111)In-bsRICs composed of trastuzumab Fab and EGF exhibited specific binding in vitro to tumor cells displaying HER2 or EGFR, and were taken up specifically in vivo in tumors expressing one or both receptors, permitting tumor visualization by microSPECT/CT. These agents may ultimately be useful for imaging heterodimerized HER2-EGFR complexes since their bivalent properties permit more avid binding to these complexes.

Quantitative assays for the measurement of HER1-HER2 heterodimerization and phosphorylation in cell lines and breast tumors: applications for diagnostics and targeted drug mechanism of action

Introduction

Ligand-bound and phosphorylated ErbB/HER heterodimers are potent signaling forms of this receptor family, and quantitative measurements of these active receptors may be predictive of patient response to targeted therapies. Using VeraTag™ technology, we developed and characterized quantitative assays measuring epidermal growth factor (EGF)-dependent increases in activated HER receptors in tumor cell line lysates and formalin-fixed, paraffin-embedded (FFPE) tumor sections. We demonstrated the ability of the assays to quantitatively measure changes in activated HER1 and HER2 receptor levels in cell lines following treatment with 2C4, erlotinib, and lapatinib. We utilized these assays to determine the prevalence and distribution of activated HER1, HER2, and HER1-HER2 heterodimers in 43 HER2-positive breast tumors.

Methods

Assays for activated HER1 and HER2 receptors in FFPE and cell lysate formats were developed using VeraTag™ technology, which requires the proximity of an antibody pair for light-dependent release of a fluorescently labeled tag, followed by capillary electrophoresis-based quantitation.

Results

Ligand-dependent and independent HER1-HER2 heterodimer levels measured by lysate and FFPE VeraTag™ assays trended with HER1 and HER2 expression levels in tumor cell lines, which was confirmed by co-immunoprecipitation. The formation of EGF-dependent HER1-HER2 heterodimers were inhibited by the HER2-targeted monoclonal antibody 2C4 and stabilized by the HER1 tyrosine kinase inhibitor (TKI) erlotinib. EGF-dependent HER1 and HER2 phosphorylation was inhibited by lapatinib and erlotinib. Further, we observed that dominant receptor signaling patterns may switch between HER1-HER1 and HER1-HER2, depending on drug mechanism of action and relative levels of HER receptors. In FFPE breast tumors that expressed both HER1 and HER2, HER1-HER2 heterodimers were detected in 25 to 50% of tumors, depending on detection method. The levels of activated phospho-HER1-HER2 heterodimers correlated with HER1 or HER2 levels in an analysis of 43 HER2-positive breast tumors.

Conclusions

VeraTag™ lysate assays can be used as a tool for understanding the mechanism of action of targeted HER-family inhibitors in the preclinical setting, while VeraTag™ FFPE assays of activated HER receptors combined with total HER2 measurements (HERmark^®) in tumor samples may provide a more accurate prediction of clinical response to both HER1 and HER2 targeted therapies.

Autocrine and juxtacrine effects of amphiregulin on the proliferative, invasive, and migratory properties of normal and neoplastic human mammary epithelial cells

Amphiregulin (AR) autocrine loops have been associated with several types of cancer. We demonstrate that SUM149 breast cancer cells have a self-sustaining AR autocrine loop. SUM149 cells are epidermal growth factor (EGF)-independent for growth, and they overexpress AR mRNA, AR membrane precursor protein, and secreted AR relative to the EGF-dependent human mammary epithelial cell line MCF10A. MCF10A cells made to overexpress AR (MCF10A AR) are also EGF-independent for growth. Treatment with the pan-ErbB inhibitor CI1033 and the anti-EGF receptor (EGFR) antibody C225 demonstrated that ligand-mediated activation of EGFR is required for SUM149 cell proliferation. AR-neutralizing antibody significantly reduced both SUM149 EGFR activity and cell proliferation, confirming that an AR autocrine loop is required for mitogenesis in SUM149 cells. EGFR tyrosine phosphorylation was dramatically decreased in both SUM149 and MCF10A AR cells after inhibition of AR cleavage with the broad spectrum metalloprotease inhibitor GM6001, indicating that an AR autocrine loop is strictly dependent on AR cleavage in culture. However, a juxtacrine assay where fixed SUM149 cells and MCF10A AR cells were overlaid on top of EGF-deprived MCF10A cells showed that the AR membrane precursor can activate EGFR. SUM149 cells, MCF10A AR cells, and MCF10A cells growing in exogenous AR were all considerably more invasive and motile than MCF10A cells grown in EGF. Moreover, AR up-regulates a number of genes involved in cell motility and invasion in MCF10A cells, suggesting that an AR autocrine loop contributes to the aggressive breast cancer phenotype.

Neuregulin 1-alpha expression in locally advanced breast cancer

The human Neuregulin 1 (NRG1) gene encodes several alternatively spliced ligands that bind to both c-erbB-3 and c-erbB-4, members of the family of type 1 tyrosine kinase growth factor receptors. Antibodies raised to a synthetic peptide recognize selectively the alpha variant of NRG1. The NRG1-alpha isoforms' expression was studied in 115 locally advanced adenocarcinomas of the breast using immunohistochemistry. Absent or low levels of NRG1-alpha were found to be associated with poorer prognosis compared to tumours that had moderate to high levels of the protein.

Telomerase modulates expression of growth-controlling genes and enhances cell proliferation

Most somatic cells do not express sufficient amounts of telomerase to maintain a constant telomere length during cycles of chromosome replication. Consequently, there is a limit to the number of doublings somatic cells can undergo before telomere shortening triggers an irreversible state of cellular senescence. Ectopic expression of telomerase overcomes this limitation, and in conjunction with specific oncogenes can transform cells to a tumorigenic phenotype. However, recent studies have questioned whether the stabilization of chromosome ends entirely explains the ability of telomerase to promote tumorigenesis and have resulted in the hypothesis that telomerase has a second function that also supports cell division. Here we show that ectopic expression of telomerase in human mammary epithelial cells (HMECs) results in a diminished requirement for exogenous mitogens and that this correlates with telomerase-dependent induction of genes that promote cell growth. Furthermore, we show that inhibiting expression of one of these genes, the epidermal growth factor receptor (EGFR), reverses the enhanced proliferation caused by telomerase. We conclude that telomerase may affect proliferation of epithelial cells not only by stabilizing telomeres, but also by affecting the expression of growth-promoting genes.

Matrix-independent survival of human keratinocytes through an EGF receptor/MAPK-kinase-dependent pathway

Normal epithelial cells undergo apoptosis when they are denied contact with the extracellular matrix, in a process termed "anoikis." Conversely, malignant epithelial cells typically acquire anchorage independence, i.e., the capacity to survive and grow in the absence of matrix interaction. Here we asked the question whether anoikis is affected by signaling through the EGF receptor (EGFR). We focused on the EGFR because EGFR signaling is frequently deregulated in malignant epithelial cells. We demonstrate that EGFR activation markedly alleviated the requirement of matrix engagement for survival of primary and immortalized human keratinocytes in suspension culture. Protection of epithelial cells through EGFR activation against anoikis was associated with and required sustained MAPK phosphorylation during the early phase of suspension culture. Interestingly, high levels of MAPK phosphorylation were not only required for EGFR-mediated protection against anoikis but also occurred as a consequence of caspase activation at later stages of suspension culture. These results demonstrate that EGFR activation contributes to anchorage-independent epithelial cell survival and identify MAPK activation as an important mechanism in this process.

The evaluation of human breast lesions with magnetic resonance imaging and proton magnetic resonance spectroscopy

PURPOSE

MR spectroscopy (MRS) assists in lesion characterization and diagnosis when combined with magnetic resonance imaging (MRI). Cancerous lesions demonstrate elevated composite choline levels arising from increased cellular proliferation. Our study investigated if MR spectroscopy of the breast would be useful for characterizing benign and malignant lesions.

MATERIALS AND METHODS

Single voxel proton MR spectroscopy (MRS) was acquired as part of an MR imaging protocol in 38 patients referred upon surgical consultation. The MR spectra were read independently in a blinded fashion without the MR images by three spectroscopists. The MRI exam was interpreted in two settings: (a) as a clinical exam with detailed histories and results from previous imaging studies such as mammography or ultrasound included and (b) as a blinded study without prior histories or imaging results.

RESULTS

Elevated choline levels were demonstrated by MRS in 19 of the 23 confirmed cancer patients. The sensitivity and specificity for determining malignancy from benign breast disease with MRS alone were 83 and 87%, respectively, while a blinded MRI review reported 95 and 86%, respectively.

CONCLUSIONS

Proton MR spectroscopy provides a noninvasive, biochemical measure of metabolism. The technique can be performed in less than 10 min as part of an MRI examination. MRI in combination with MRS may improve the specificity of breast MR and thereby, influence patient treatment options. This may be particularly true with less experienced breast MRI readers. In exams where MRI and MRS agree, the additional confidence measure provided by MRS may influence the course of treatment.

Quantitative analysis of the EGF receptor autocrine system reveals cryptic regulation of cell response by ligand capture

Autocrine signaling is important in normal tissue physiology as well as pathological conditions. It is difficult to analyze these systems, however, because they are both self-contained and recursive. To understand how parameters such as ligand production and receptor expression influence autocrine activity, we investigated a human epidermal growth factor/epidermal growth factor receptor (EGF/EGFR) loop engineered into mouse B82 fibroblasts. We varied the level of ligand production using the tet-off expression system and used metalloprotease inhibitors to modulate ligand release. Receptor expression was varied using antagonistic blocking antibodies. We compared autocrine ligand release with receptor activation using a microphysiometer-based assay and analyzed our data using a quantitative model of ligand release and receptor dynamics. We found that the activity of our autocrine system could be described in terms of a simple ratio between the rate of ligand production (VLT) and the rate of receptor production (VR). At a VLT/VR ratio of <0.3, essentially no ligand was found in the extracellular medium, but a significant number of cell receptors (30-40%) were occupied. As the VLT/VR ratio increased from 0.3 towards unity, receptor occupancy increased and significant amounts of ligand appeared in the medium. Above a VLT/VR ratio of 1.0, receptor occupancy approached saturation and most of the released ligand was lost into the medium. Analysis of human mammary epithelial cells showed that a VLT/VR ratio of <5×10−4was sufficient to evoke >20% of a maximal proliferative response. This demonstrates that natural autocrine systems can be active even when no ligand appears in the extracellular medium.

Growth inhibition and growth stimulation by estradiol of estrogen receptor transfected human breast epithelial cell lines involve different pathways

Epidermal growth factor (EGF) and estradiol (E2) are important mitogens in breast epithelial cells, and expression of epidermal growth factor receptor (EGFR) and estrogen receptor (ER) is often inversely correlated in human breast cancer cells. Stable transfection of ER-negative cells with ER cDNA is not sufficient to restore E2-mediated growth stimulation, on the contrary, E2 often inhibits growth of ER-transfected cell lines. In this study we used the ER-transfected human breast epithelial cell lines HMT-3522F9, growth inhibited by E2 in the presence of EGF, and HMT-3522F9/S3B, growth stimulated by E2 in the absence of EGF. In S3B cells, no active MAP kinase could be detected in response to E2, suggesting that signalling through the MAP kinase is not the major pathway in the E2-mediated growth stimulation. Interestingly, a decreased level of active MAP kinase was observed in HMT-3522F9 cells in response to E2, indicating that in these cells cross-talk between the ER and the MAP kinase signalling pathway could be due to the E2-mediated growth inhibition. Moreover, we found that EGF-induced signalling also could be reduced by E2 in S3B cells, suggesting a general mechanism of action by E2 in cells concomitantly expressing ER and EGFR.

Transforming growth factor-alpha, epidermal growth factor receptor, and PCNA immunoexpression in uterine leiomyosarcomas and leiomyomas in B6C3F1 mice

The role of growth factors in the development of murine uterine mesenchymal tumors is unknown. In this study, immunohistochemical expression of transforming growth factor alpha (TGF-alpha) and its receptor epidermal growth factor (EGF-R) was assessed in spontaneous uterine leiomyomas and leiomyosarcomas in B6C3F1 mice. Cell proliferation, which has been induced by some growth factors, was evaluated by immunohistochemical detection of an endogenous marker of cell proliferation, proliferating cell nuclear antigen (PCNA). PCNA labeling indices were determined and compared to the intensity and distribution of TGF-alpha staining in sequential sections of control myometrium or tumor tissue. Results showed uterine leiomyosarcomas had positive cytoplasmic staining for TGF-alpha; however, all uterine leiomyomas evaluated were negative. Positive EGF-R staining was also observed in the uterine leiomyosarcomas, but not in the leiomyomas. EGF-R immunoexpression was detected primarily within the cytoplasm of the leiomyosarcoma cells, with occasional nuclear immunoreactivity. Immunohistochemical staining for PCNA was more intense and there were increased numbers of positively staining nuclei in the leiomyosarcomas compared to samples of control myometrium or leiomyomas. The mean labeling index for the uterine leiomyosarcomas (7.40%) was significantly (p < 0.01) higher than that of leiomyomas (0.29%) and control uterine myometrium (0.13%). We conclude, that TGF-alpha and its receptor, EGF-R, are expressed more intensely in uterine leiomyosarcomas, compared to leiomyomas in B6C3F1 mice. Immunoexpression of TGF-alpha may be an important biomarker of malignancy in uterine smooth muscle tumors in mice. Futhermore, TGF-alpha may play a critical role in increased proliferation of uterine smooth muscle tumor cells as suggested by increased immunolocalization of PCNA in rodent leiomyosarcomas expressing TGF-alpha, although other factors regulating cell replication can not be ruled out.

Dual regulation of proliferation and apoptosis: c-myc in bitransgenic murine mammary tumor models

Recent progress in the study of c-Myc has convincingly demonstrated that it possesses a dual role in regulating both proliferation and apoptosis; however, the manner in which c-Myc influences these cellular response pathways remains incompletely characterized. Deregulation of c-Myc expression, via many mechanisms, is a common feature of multiple cancers and is an especially prominent feature of many breast cancers. Of significant interest to those who study mammary gland development and neoplasia is the unresolved nature and contribution of apoptosis to breast tumorigenesis. Recently, the use of transgenic mice and gene-knockout mice has allowed investigators to evaluate the pathological mechanisms by which different genes influence tumor development and progression. In this review, we address two distinct c-myc-containing bitransgenic murine mammary tumor models and discuss the contribution and possible future directions for resolution of cancer-relevant molecular pathways influenced by c-Myc.

Transforming growth factor alpha and mouse models of human breast cancer

Transforming growth factor alpha (TGFalpha) is a principal molecule in the normal and neoplastic development of the mammary gland. Binding of TGFalpha to the epidermal growth factor receptor (EGFR), activates the EGFRs' endogenous tyrosine kinase activity and stimulates growth of the epithelium in the virgin and pregnant mouse mammary gland. TGFalpha expression can be detected in breast cancer cells in vivo and in vitro and overexpression can elicit partial transformation or immortalized human and rodent mammary epithelial cells. Despite evidence implicating TGFalpha in the development of mammary neoplasia, the actual mechanism of TGFalpha-induced transformation is unclear. Transgenic mouse models targeting heterologus TGFalpha to the mammary gland have established TGFalpha overexpression can induce hyperproliferation, hyperplasia and occasional carcinoma. These transgenic studies demonstrated a facilitating, proliferative role for TGFalpha in the development of neoplasia and implicated several oncogenes that can cooperate with TGFalpha to transform the mammary epithelium. From studies of EGFR signaling pathways, inhibitory and modulating agents such as anti-EGFR antibodies and specific kinases inhibitors have been used to block the action of this pathway and prevent the development of TGFalpha-induced neoplasia and tumor formation. Studies in Stat5a knockout mice have established that the JAK2/Stat5a pathway can facilitate the survival of the mammary epithelium and can impact the progression of TGFalpha-mandated mammary tumorigenesis. Together these experiments indicate that TGFalpha and the EGFR signaling pathway are potentially amenable to therapies for treatment of human breast disease.

Differential regulation of EGF-like growth factor genes in human keratinocytes

ErbB signaling increases protein levels of multiple EGF-like growth factors in epithelial cells. To better understand this process, we examined the effects of EGF receptor stimulation on the transcription and mRNA stability of TGF-alpha, amphiregulin (AR), and heparin-binding EGF-like growth factor (HB-EGF) in human keratinocytes. EGF stimulation increased transcription of TGF-alpha, AR, and HB-EGF by 3- to 4-fold within 1 to 2 h. However, AR and HB-EGF mRNA levels peaked at 2 h and then rapidly declined, whereas TGF-alpha transcripts remained elevated for at least 6 h. Actinomycin D decay experiments yielded the rank order of transcript stability TGF-alpha > AR > HB-EGF. Interestingly, ligand treatment appeared to stabilize TGF-alpha and AR mRNAs, whereas HB-EGF transcripts were destabilized. These data demonstrate that gene-specific alterations in gene transcription and mRNA stability play important roles in the temporal regulation of EGF-like growth factor gene expression.

Human mammary epithelial cells rapidly exchange empty EGFR between surface and intracellular pools

Binding of ligand to the epidermal growth factor receptor (EGFR) initiates a series of processes including activation of the intrinsic EGFR tyrosine kinase, receptor autophosphorylation, and the assembly of active signaling complexes at the plasma membrane. Concomitantly, receptor trafficking is initiated, and the receptor is ultimately delivered to the lysosome, where it is degraded. Virtually all studies on EGFR trafficking have used fibroblasts and transformed cells. Because EGFR exerts a potent effect on the physiology of epithelial cells, we examined the regulation of EGFR activity and trafficking in nontransformed human mammary epithelial cells (HMEC). We found that HMEC that displayed a luminal phenotype were largely unresponsive to EGF and maintained a majority of their EGFR at the cell surface. In contrast, HMEC with a basal phenotype were highly responsive to EGF and, at steady state in the absence of exogenous ligand, distributed empty EGFR into intracellular pools. Maintenance of the intracellular pools was a direct consequence of specific and rapid endocytosis of the empty EGFR. The trafficking pattern was EGFR specific, used coated pits, and did not require receptor tyrosine kinase activity. Such an mechanism redistributes EGFR signaling potential among different membrane domains and into vesicles with unique biochemical microenviroments. In addition, our data show that EGFR endocytosis can be regulated in the absence of ligand binding and receptor activation in a cell-type-specific manner.

Immunolocalization of transforming growth factor alpha and epidermal growth factor receptor in lungs of patients with cystic fibrosis

Transforming growth factor alpha (TGF-alpha) is expressed in respiratory epithelial cells and alveolar macrophages during development and following lung injury. In the present study, the presence and sites of synthesis of TGF-alpha and its receptor, the epidermal growth factor receptor (EGF-R), were assessed in lung tissue from patients with severe lung disease caused by cystic fibrosis (CF). Lung sections from 24 individuals with CF, obtained at the time of lung transplantation, were compared to lung sections from five lung donors without CF. Cellular sites of TGF-alpha, EGF-R, and cellular sites of proliferation were assessed by immunohistochemistry. All CF lung sections contained multiple cell types with detectable TGF-alpha. Compared to control sections, intensity of TGF-alpha immunostaining in macrophages, airway epithelial cells, and peribronchial submucosal cells was increased. EGF-R was detected in respiratory epithelial and peribronchial stromal cells but not in alveolar macrophages. The intensity of EGF-R staining in CF lung tissue did not differ from that of controls. An increased number of cells expressing Ki-67 nuclear antigen was detected in peribronchial submucosal cells but not bronchiolar epithelial cells in the CF lungs. The increased expression of TGF-alpha in CF lung tissue supports the concept that TGF-alpha plays a role in paracrine/autocrine regulation of lung remodeling associated with injury and repair in the lungs of individuals with cystic fibrosis.

Protection by alpha-tocopherol but not ascorbic acid from hydrogen peroxide induced cell death in normal human breast epithelial cells in culture

Alpha-tocopherol and ascorbic acid have been suggested to play a role in breast cancer prevention due to their antioxidative capacity. Increased exposure to endogenous and exogenous sex steroids is a known risk factor for breast cancer. We have studied the effects of alpha-tocopherol and ascorbic acid on hydrogen peroxide induced cell death in sex hormone treated normal breast epithelial cells in culture. We found that alpha-tocopherol but not ascorbic acid alone protected the cells. The effect of alpha-tocopherol increased when ascorbic acid was added to the cultures. The hydrogen peroxide degradation rate decreased in cultures treated with alpha-tocopherol alone and in combination with ascorbic acid compared to cells grown in medium or with ascorbic acid only. Oestradiol and progesterone treatment did not influence the results. Possible beneficial effects of combining various antioxidants, endogenous as well as exogenous, on human breast tissue need to be investigated further both in vivo and in vitro.

Impact of oestradiol and progesterone on antioxidant activity in normal human breast epithelial cells in culture

The risk of developing breast cancer increases after long term use of oestrogen and progestagen, and carcinogenesis in the breast is partly due to oxidative damage to DNA bases. Therefore, we studied the effects of 17 beta-oestradiol and progesterone on the antioxidative status and the vulnerability to oxidative stress exhibited by normal human breast epithelial cells in culture. After exposure to hydrogen peroxide, cells grown with oestradiol alone or with both oestradiol and progesterone showed significantly decreased viability compared to cells grown in medium without added hormones. There was, however, no difference in hydrogen peroxide degradation rate between controls and hormone treated cultures. When desferrioxamine was added, the viability increased and the hydrogen peroxide degradation rate decreased. The levels of several antioxidants were altered in cells grown in the presence of oestradiol and progesterone: the concentrations of glutathione reductase and catalase decreased significantly while the levels of glutathione peroxidase and reduced glutathione did not change. The alterations in enzyme activity and cell vulnerability were more pronounced in cultures treated with a combination of oestradiol and progesterone. We conclude that the redox balance in the cultured normal human breast epithelial cells was altered by treatment with oestradiol and progesterone, and that this change led to the increased death of cells subsequently exposed to hydrogen peroxide. This effect may have implications for sex hormone dependent diseases of the breast.

Mechanisms of transcriptional regulation of cellular genes by SV40 large T- and small T-antigens

During the past decade a number of virus-encoded transcriptional trans-activators that regulate the expression of viral genes have been reported. These trans-activators may also affect the expression or activity of several cellular genes or gene products to create an optimal cellular environment that favors viral replication. Among the better-studied viral trans-activating proteins are the Simian virus 40 large T- and small t-antigens. During the last few years, mechanisms by which these two viral proteins influence cellular gene expression start to emerge. They are grouped provisionally and reflect the methods used to determine the effects of large T-antigen. Large T-antigen may influence cellular gene expression by: i. altering mRNA levels of cellular transcription factors; ii. interacting with and regulating the DNA-binding or transcriptional activity of specific transcription factors; iii. functionally substitution of eukaryotic transcription factors; iv. direct binding to DNA; or v. regulating components of signaling transduction pathways. Small t-ag seems to exert its effect mainly through inhibiting a cellular phosphatase, protein phosphatase 2A, thereby modulating components of signal transduction pathways and preventing dephosphorylation of several transcription factors. However, small t-ag may also control cellular gene expression by regulating mRNA levels of transcription factors or by interacting with other transcription factors.

EGF-related peptides in the pathophysiology of the mammary gland

Normal mammary gland development is the result of complex interactions between a number of hormones and growth factors. Normal and malignant human mammary epithelial cells are able to synthesize and to respond to various different, locally acting growth factors and growth inhibitors. Among these, the EGF-related peptides play an important role in regulating the proliferation and differentiation of human mammary epithelial cells. EGF4 and TGF4 are able to stimulate the lobulo-alveolar development of the mammary gland in vivo as well they are involved in the pathogenesis of human breast cancer. Experimental evidence suggests that estrogen-induced proliferation of breast carcinoma cells is mediated in part by EGF-related growth factors. It has also been demonstrated that activation of certain cellular protooncogenes such as c-Ha-ras in human mammary epithelial cells results in cellular transformation and in an increased production of several EGF-related growth factors such as TGFalpha and amphiregulin. Coexpression of both EGF-related peptides and their own receptors frequently occurs in human breast carcinomas and in human breast cancer cell lines, suggesting that an autocrine pathway of uncontrolled cell growth sustains neoplastic transformation.

An enhanced and sensitive autocrine stimulation by transforming growth factor-alpha is acquired in the brain metastatic variant of a human non-small-cell lung cancer cell line

Transforming growth factor-alpha (TGF-alpha)-mediated autocrine regulation in human non-small-cell lung cancer (NSCLC) cells NCI-H226 and its brain metastatic variant H226Br were compared. An enhanced TGF-alpha-induced dose-dependent mitogenic responsiveness in H226Br cells was observed. Neutralising antibody that binds TGF-alpha inhibits H226Br cell growth more effectively than NCI-H226 cell growth. Binding assay with 125I-labelled epidermal growth factor (EGF) revealed that H226Br has two types of EGF receptors (EGFRs), whereas the parental cell line, NCI-H226, has only one. H226Br cells contain twice as many EGFRs as H226 cells, as proved by Scatchard analysis and immune kinase assay. Northern analysis indicated that there is more EGFR transcript in H226Br than in NCI-H226, indicating a transcriptional EGFR gene elevation during metastasis progression. The level of accumulated immunoactive TGF-alpha is lower in the conditioned medium of H226Br than in that of NCI-H226. demonstrating down-regulation of TGF-alpha transcript. The accumulated data suggest an elevated and sensitive autocrine modulation by TGF-alpha and EGFR in immortalising the brain metastatic variant cells that were derived from a human NSCLC squamous cell line.

Plasma membrane phosphotyrosine, Her2-NEU, and epidermal growth factor receptor in human breast cancer. A comparative study

Experimental therapeutic regimens for breast cancer include strategies to block the activity of specific oncogenes. Because oncogenesis is a multistep process, specific oncogenes may drive tumor production at one stage yet not function in another. Since the effectiveness of therapy targeted against oncogenes depends on their function in the tumor, correlation of oncogene function to specific stages of tumor development has therapeutic implications. Among the oncogenes known to be important in breast cancer production are two cell surface growth factor receptors, epidermal growth factor receptor (EGFR) and Her2-NEU (NEU). These proteins are receptor tyrosine kinases that autophosphorylate specific tyrosine residues on activation. The oncogenic potential of these receptors depends on this autophosphorylation. We examined 86 primary formalin-fixed, paraffin-embedded breast tumors for overexpression of EGFR and NEU and correlated our findings with the presence of cell surface phosphotyrosine as an indicator of tyrosine kinase activity at the plasma membrane. Our data indicate that only 34% of tumors that overexpress EGFR or NEU show plasma membrane phosphotyrosine, indicating that in the majority of these tumors, the overexpressed oncogene may not be active at this stage.

Transforming growth factor-alpha promotes tumor markers secretion from human ovarian cancers in vitro

BACKGROUND

The regulatory mechanism of tumor markers secretion has not been well clarified.

METHODS

Serum levels of CA 125 and tissue polypeptide antigen (TPA) from 17 patients with Stage III serous cystadenocarcinoma were measured prior to an initial surgical treatment. Epidermal growth factor receptor (EGFR) status was examined by an 125I-EGF binding assay in a human serous cystadenocarcinoma cell (SHIN-3) and in the 17 primary carcinomas. SHIN-3 cell and the EGFR-expressing primary cancer cells (n = 4) were cultured with or without various concentrations of transforming growth factor (TGF-alpha), a ligand for EGFR, and the CA 125 and TPA concentrations in the conditioned media were measured.

RESULTS

EGFR was expressed in 12 primary carcinomas and in the SHIN-3 cell, and it was absent in the remaining 5 carcinomas. Pre-therapeutic serum CA 125 and TPA levels were significantly greater (P < 0.05) in patients with EGFR-expressing carcinomas (n = 5). These data suggest a possible involvement of EGFR in regulating these tumor markers secretion. TGF-alpha increased the CA 125 and TPA secretion from SHIN-3 cell. It also promoted the CA 125 secretion in 2 of 4 EGFR-expressing primary ovarian carcinoma specimens.

CONCLUSIONS

These results suggest that a signal through the EGFR may be involved in regulating the CA 125 and TPA secretion from human ovarian carcinomas.

The epidermal growth factor receptor and its ligands as therapeutic targets in human tumors

The epidermal growth factor receptor (EGFR) is detected on many non-haematopoietic tissues and is frequently overexpressed in human tumors. With its ligand, TGF-alpha, it forms a well-defined autocrine growth loop. Several clinical approaches, using EGFR as a therapeutic target, are being investigated, particularly monoclonal antibodies combined with chemotherapy, and pharmacological inhibition of downstream components of the EGFR signaling pathway.

Growth factor-independent proliferation of rat mammary carcinoma cells by autocrine secretion of neu-differentiation factor/heregulin and transforming growth factor-alpha

Serially transplantable rat mammary tumor (RMT) cells are not dependent on exogenous epidermal growth factor (EGF) and insulin-like growth factor-I for continuous growth in serum-free medium. Previously, we found that conditioned medium obtained from these cells contained EGF-like mitogenic activity and stimulated tyrosine phosphorylation of a 185-kDa protein in EGF-dependent mammary epithelial cells. This protein is distinct from the EGF receptor and resembles a 185-kDa tyrosine-phosphorylated protein present in RMT cells themselves. The results of the studies reported here indicate that the tyrosine-phosphorylated p185 detected in growth factor-independent RMT cells and in human mammary epithelial cells exposed to RMT-conditioned medium was activated erbB-2 protein. Partial purification of the activating factor present in RMT-conditioned medium yielded a heparin-binding growth factor with biochemical properties similar to those of neu differentiation factor/heregulin (NDF/HRG). RNA-polymerase chain reaction analysis demonstrated that RMT cells expressed mRNA for NDF/HRG, and western-blot analysis confirmed the presence of the 45-kDa secreted form of NDF/HRG in conditioned medium from the growth factor-independent RMT cells. The biological activity of partially purified rat NDF/HRG was examined and found to be the same as that of the pure growth factor. In addition, we found that RMT-conditioned medium, fractionated on an anion-exchange column and by reverse-phase high-pressure liquid chromatography, contained a potent EGF-like growth factor that was distinct from NDF/HRG. This factor competes with 125I-EGF for binding to EGF receptors and has an apparent molecular mass of 6600 Da. This factor copurifies by high-pressure liquid chromatography with pure transforming growth factor-alpha (TGF-alpha), and the cells are positive for TGF-alpha mRNA. Thus, growth factor-independent RMT cells also synthesize and secrete TGF-alpha. These results indicate that growth factor-independent cells secrete two growth factors with overlapping biological activities and suggest that autocrine loops mediated by these factors are important in the growth factor-independent proliferation of the RMT cells.

Alterations in transforming growth factor-alpha and epidermal growth factor receptor expression during rat esophageal tumorigenesis

Transforming growth factor-alpha (TGF-alpha) stimulates cell proliferation through interaction with its receptor, the epidermal growth factor receptor (EGFR), by activating its tyrosine kinase activities. The simultaneous overexpression of TGF-alpha and EGFR by tumor cells is thought to trigger the autocrine growth pathway, leading to uncontrolled proliferation. To examine their roles in rat esophageal tumorigenesis induced by the chemical carcinogen N-nitrosomethylbenzylamine (NMBA), TGF-alpha, and EGFR expression was evaluated in normal rat esophageal epithelium, in NMBA-induced preneoplastic lesions, and in papillomas by quantitative reverse transcription-polymerase chain reaction (RT-PCR), in situ hybridization, and immunohistochemical analyses. Compared with the levels in normal epithelium, the TGF-alpha and EGFR mRNA levels in esophageal papillomas were 3.6 and 1.9 times higher, respectively. In the preneoplastic epithelium, although a trend of increased TGF-alpha and EGFR mRNA levels was observed, collectively there were no significant differences between preneoplastic and normal samples by RT-PCR analysis. In situ hybridization and immunohistochemical staining showed increased levels of TGF-alpha and EGFR mRNA and protein products in papillomas and in pronounced hyperplastic and dysplastic lesions. TGF-alpha and EGFR expression correlated with each other and with the expression of proliferating cell nuclear antigen, a marker for cell proliferation. These results suggest that disregulation of TGF-alpha and EGFR expression may contribute to autonomous cell growth and may play an important role in rat esophageal tumorigenesis induced by NMBA.

Role of mesenchymal-epithelial interactions in mammary gland development

The mammary gland is a hormone-target organ derived from epidermis and develops as a result of reciprocal mesenchymal-epithelial interactions. The induction of mammary differentiation from indifferent epidermal cells by mammary mesenchyme implies induction of the complement of hormone receptors characteristic of normal mammary epithelium in cells of the epidermis. Considering the facts that mammary epithelial differentiation is induced by mammary mesenchyme and that certain aspects of hormone response (androgen-induced mammary regression) are inextricably linked to mesenchymal-epithelial interactions, it is evident that the biology of the mammary gland arises from and is maintained via cell-cell interactions. As a corollary, perturbation of stromal-epithelial interactions in adulthood may play a role in mammary carcinogenesis and in turn may provide opportunities for differentiation therapy.

Transforming growth factor-alpha and epidermal growth factor in hamster tissues: biochemical and immunohistochemical studies

In Syrian golden hamster kidneys and submaxillary glands, the levels of EGF, determined by radioimmunoassay, were much lower than in the same organs of two other rodent species, mouse and rat. In submaxillary glands, the EGF/TGF-alpha receptor-binding activities were also much lower in hamster than in mouse and rat. In contrast, the TGF-alpha content of hamster kidneys, determined by radioimmunoassay, was higher than in the kidneys of the other animals, as was the EGF/TGF-alpha receptor-binding activity. Using immunohistochemistry, the TGF-alpha immunoreactivity in hamster kidneys was localized both in proximal and distal tubules with the exception of the macula densa area. The levels of TGF-alpha in the submaxillary glands were very low in all the animals tested. Hamster kidney extracts contained a specific immunoreactive protein with the M(r) and the N-terminal amino acid sequence (VVSHFNECPD) expected for mature hamster TGF-alpha. Western blot analysis of hamster renal solubilized membrane proteins using anti-EGF receptor antibodies revealed three immunoreactive protein bands of which one had the M(r) expected for the EGF/TGF-alpha receptor. The immunohistochemical pattern of this receptor in hamster kidneys proximal tubular cells was very similar to the other tested rodent species.

Changes in oestrogen, progesterone and epidermal growth factor receptor concentrations and affinities during the oestrous cycle in the normal mammary gland and uterus of dogs

Changes in the concentrations and affinities of receptors for oestrogen (ER), progesterone (PR) and epidermal growth factor (EGF-R) were studied in mammary glands of healthy bitches with regard to age, the location in the mammary chain and the stage of the oestrous cycle. Uterus was used as the reference tissue for the evaluation of steroid receptors. Mammary and uterine samples from 7 healthy bitches were taken at five stages of the oestrous cycle in such a way that all the locations in the mammary chain were represented at each stage of the cycle (10 samples/dog). ER, PR and EGF-R were detected by biochemical assays using increasing concentrations of tritiated (steroids) or iodinated (EGF) ligands. A significant direct correlation was found between the ER and PR concentrations for mammary and uterine samples. No significant correlation was found between the steroid receptors and EGF-R concentrations. Mammary ER concentrations were significantly higher in bitches of 5 years of age or older than in younger ones; in posterior glands (4th and 5th pairs) than in anterior glands; and in the mid-luteal phase. Mammary PR did not vary significantly with age or location but was significantly lower in the early luteal phase than in other phases. A similar decrease in PR concentrations was observed in the uterus during the early luteal phase and uterine ER and PR concentrations were very low in the mid-luteal phase. Mammary EGF-R were not significantly higher in the early or mid-luteal phase than in pro-oestrus or anoestrus. The differences observed between the uterine and mammary steroid receptor concentrations during the oestrous cycle could be due to different mechanisms for regulating steroid receptor expression in the two tissues. Mammary EGF-R concentrations may be linked, as in other species, to cellular proliferation and/or to the serum progesterone concentrations.

The role of amphiregulin in breast cancer

Amphiregulin (AR) is an epidermal growth factor (EGF)-related peptide that operates exclusively through the EGF receptor and that can bind to heparin. AR also possesses nuclear localization sequences in the extended NH2-terminal region suggesting an additional intracellular site of action. AR mRNA and protein expression have been detected in primary human mammary epithelial cell strains, nontransformed human mammary epithelial cell lines, several human breast cancer cell lines, and primary human breast carcinomas. The frequency and levels of AR protein expression are generally higher in invasive breast carcinomas than in ductal carcinomas in situ or in normal, noninvolved mammary epithelium. In addition, AR can function as an autocrine and/or juxtacrine growth factor in human mammary epithelial cells that have been transformed by an activated c-Ha-ras proto-oncogene or by overexpression of c-erb B-2. AR expression is also enhanced by mammotrophic hormones such as estrogens and other growth factors such as EGF.

Effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin on growth factor expression in the human breast cancer cell line MCF-7

The aim of this study was to examine whether changes in growth factor or cytokine expression could be responsible for the growth inhibitory effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on the human breast cancer MCF-7 cell line. Treatment of MCF-7 cells with 10 nM TCDD for 7 days reduced the cell growth to 60% of control; this effect was partly abolished by cotreatment of the cells with 100 nM 17 beta-estradiol (E2). The inhibition of cell growth by TCDD was accompanied by an enhanced secretion of transforming growth factor-beta (TGF-beta) and the TGF-beta content in cell culture supernatants was 2-fold higher than in controls. Using reverse transcription polymerase chain reaction (RT-PCR), the effect of TCDD on the expression of TGF-beta isoforms, transforming growth factor-alpha (TGF-alpha), tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 beta (IL-1 beta) was investigated. It was demonstrated that incubation with 1, 10 and 100 nM TCDD for 24 h increased mRNA levels of TGF-alpha, TNF-alpha and IL-1 beta. The strongest effect was found on IL-1 beta, the mRNA level of which was dose-dependently increased. TCDD had a minor effect on TGF-alpha and TNF-alpha mRNA. The mRNA levels were significantly increased after treatment with 10 and 100 nM TCDD. The mRNA expression of TGF-beta 1 and TGF-beta 2 was unchanged, whereas the TGF-beta 3 mRNA level was enhanced 2 to 3-fold after TCDD treatment. From the results, we suggest that TCDD-induced growth inhibition in MCF-7 cells is related to the growth inhibitory action of a set of growth factors and cytokines which have a contextual action on MCF-7 cell proliferation.

Correlation of TGF-beta 1 expression with medroxyprogesterone acetate responsiveness in mouse mammary adenocarcinomas

We investigated the expression of transforming growth factors beta 1 and alpha (TGF-beta 1, TGF-alpha) in hormone-responsive (MPA-R) and unresponsive (MPA-U) tumor lines obtained from medroxyprogesterone acetate (MPA)-induced mammary adenocarcinomas in BALB/c mice. The tumors were transplanted into MPA-treated and untreated mice. TGF-beta 1 gene expression was observed in the MPA-R lines growing in untreated animals, but not in MPA-treated mice. TGF-beta 1 mRNA was not detected in the MPA-U tumor lines growing in either MPA-treated or untreated animals. In MPA-R lines the levels of TGF-beta 1 expression were inversely correlated to growth rate. High-affinity TGF-beta 1 receptors were present in the MPA-R tumors. These results suggest that one of the mechanisms by which MPA exerts its proliferative effect on MPA-R tumor lines is inhibition of the expression of TGF-beta 1. Thus, the lack of expression of TGF-beta 1 in MPA-U tumors may be related to the acquisition of autonomous growth.

Relationship between epidermal growth factor receptor levels, autophosphorylation and mitogenic-responsiveness in normal mouse mammary epithelial cells in vitro

Mammary epithelial cells were isolated from mid-pregnant BALB/c mice, grown within collagen gels and maintained on DME/F12 (1:1) media containing 10% bovine calf serum and 10 micrograms/ml insulin. Initial time-course and dose-response studies showed that epidermal growth factor (EGF)-induced autophosphorylation of the EGF-receptor (EGF-R) in these cells was maximal 5 min after exposure to 75 ng/ml EGF. Mammary epithelial cells displaying little or no growth during their first 2 days in primary culture cells were found to contain low levels of EGF-R. However, EGF-induced autophosphorylation of the EGF-R in these cells was extremely intense. Subsequent studies demonstrated that during the proliferative and plateau phases of growth, EGF-R levels progressively increased, while conversely EGF-induced autophosphorylation of the EGF-R decreased over time in primary culture. These results demonstrate that EGF-R levels and autophosphorylation do not show a direct correlation with mammary epithelial cell mitogen-responsiveness. Intense EGF-R autophosphorylation appears to be required for initiating growth, but sustained mammary epithelial cell proliferation occurs when EGF-R autophosphorylation is low. This inverse relationship between EGF-R levels and autophosphorylation may reflect changes in receptor affinity and function during the various phases of mammary epithelial cell growth in primary culture.

Implantation and growth of epidermal growth factor (EGF) receptor expressing human ovarian cancer xenografts in nude mice is dependent on EGF

BACKGROUND

The importance of epidermal growth factor (EGF) receptor-dependent growth has not been clarified for in vivo growth of primary human ovarian cancers.

METHODS

Seventeen primary human ovarian cancer tissue samples were examined for the presence of EGF receptors by a 125I-EGF-binding study. Three groups of mice were inoculated with EGF receptor expressing and not-expressing cancer tissues. The groups were as follows: control group, Sx group (mice that underwent sialoadenectomy; EGF depleted mice), and Sx+EGF (EGF-replaced) group. The ability of the inoculated tissues to implant and grow then was studied.

RESULTS

Of the 17 primary ovarian cancers, 12 expressed EGF receptors and 5 did not. Eight of 12 EGF-receptor expressing cancer tissues implanted and formed growing tumors in control animals. None implanted in the Sx animals. Epidermal growth factor receptor-expressing cancers implanted in Sx animals that received EGF administration. Two of five EGF receptor-negative ovarian cancers implanted and grew in both control and Sx animals.

CONCLUSION

Growth of EGF receptor-expressing primary human ovarian cancers may be dependent on EGF in vivo.

Receptor blockade with monoclonal antibodies as anti-cancer therapy

Human tumors express high levels of growth factors and their receptors, and many types of malignant cells appear to exhibit autocrine- or paracrine-stimulated growth. Therefore, antireceptor directed therapies have the potential of being useful anti-cancer agents. A series of murine monoclonal antibodies (MAbs) directed against human growth factor receptors and their corresponding growth factors have been produced. MAbs against the receptors for epidermal growth factor, Her2/Neu, transferrin, insulin-like growth factor, interleukin, (IL)-2 and IL-1 are currently being evaluated. MAbs directed against epidermal growth factor, transforming growth factor-alpha, bombesin, IL-2, and IL-6 also are under study. These MAbs have shown promising preclinical activity, and some of them are being tested in clinical trials. So far, anti-tumor responses have been observed with anti-IL-2 receptor, anti-bombesin and anti-IL-6 MAbs. Further research is focusing in the production of "chimeric" and "humanized" MAbs, in order to obviate the problem of host immune reactions.

Role of mesenchymal-epithelial interactions in normal and abnormal development of the mammary gland and prostate

Development of the mammary gland (MG) and prostate occurs via mesenchymal-epithelia interactions. Epithelial MG buds are induced in ventral epidermis by mammary mesenchyme, which ultimately specifies the functional expression of the ability to produce milk. Mammary ductal branching is induced by embryonic mammary mesenchyme and is promoted by the mammary fat pad postnatally. These influences of connective tissue on the differentiation of mammary epithelium (ME) begin prenatally, but in adulthood, the connective tissue environment of adult ME profoundly influences epithelial growth, ductal branching, epithelial differentiation, and the ability of adult ME to produce milk. In a similar fashion, prostatic development occurs via mesenchymal-epithelial interactions in which urogenital sinus mesenchyme (UGM) induces epithelial morphogenesis, regulates epithelial proliferation, and evokes the expression of epithelial androgen receptors and prostate-specific secretory proteins. Although prostatic development is induced by androgens, androgenic effects on epithelial development are elicited via androgen receptors of UGM. As in MG, mesenchymal-epithelial interactions in the prostate begin during fetal periods, but continue into adulthood. The responsiveness of adult epithelial cells from various glands to stroma raises the possibility that carcinomas also may be regulated by connective tissue. Indeed, UGM can induce a rat prostatic carcinoma (Dunning tumor) to undergo striking changes in differentiation, which are accompanied by a reduction in growth rate and an apparent loss of tumorigenesis. Although the mechanism of mesenchymal-epithelial interactions remains unknown, the communication between the epithelium and stroma undoubtedly is multifactorial, involving the extracellular matrix, soluble growth or differentiation, and angiogenesis.

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)

Interaction of transforming growth factor-alpha and epidermal growth factor receptor in breast carcinoma. An immunohistologic study

BACKGROUND

Interaction of transforming growth factor-alpha (TGF-alpha) with its receptor, epidermal growth factor receptor (EGFR), has been implicated as an autoregulatory autocrine mechanism of breast epithelial proliferation.

METHODS

To examine the interrelationship and clinical relevance of TGF-alpha and EGFR in breast carcinoma, methanol-fixed cryostat sections from 73 patients were immunostained with monoclonal antibodies to epidermal growth factor (EGF), EGFR, and TGF-alpha.

RESULTS

Neither EGFR nor TGF-alpha staining was diagnostic or specific for the detection of malignant neoplastic cells. Both exhibited staining along the basal lamina of most benign ducts and lobules. TGF-alpha staining was observed in neoplastic cells in 41% and in non-neoplastic cells (peritumoral stroma and benign duct/lobular epithelium) in 36% of patients. Staining for EGF and TGF-alpha failed to correlate with node status or grade; however, TGF-alpha negative tumors were more frequently positive for estrogen receptor (ER) (70% versus 14%; P = 0.03). The presence of EGFR correlated with positive lymph node status (P = 0.004), poor differentiation (P = 0.001), and negative ER status (P = 0.0001). EGFR staining was more common in neoplasms which recurred, but this approached significance only in the group with node-negative disease (mean follow-up, 52 months; P = 0.06), and neoplastic cell TGF-alpha correlated with disease recurrence in patients with node-positive disease (no recurrence, -13% positive versus recurrence, -52% positive; P = 0.01). Concurrent TGF-alpha/EGFR staining, present in 18% of tumors, also was predictive of disease recurrence (no recurrence, 3% positive for both versus recurrence, 31% positive for both, P = 0.03).

CONCLUSIONS

TGF-alpha is heterogeneously expressed in neoplastic and host-derived components of breast tumors. Concurrent EGFR/TGF-alpha immunostaining may characterize a clinically aggressive subset of breast carcinomas, possibly reflecting autocrine interaction, and conferring growth advantage or metastatic phenotype.

The epidermal growth factor receptor as a target for therapy in breast carcinoma

The epidermal growth factor (EGF) receptor and its ligands have an important regulatory role in breast carcinoma. We have produced a series of monoclonal antibodies (MAbs) directed against the external portion of the EGF receptor. These MAbs prevent the binding of the ligands to the receptor, block ligand-induced activation of the receptor, and can inhibit the growth of breast cancer cells both in tissue culture and in human tumor xenografts in nude mice. We have also shown that anti-EGF receptor antibodies greatly enhance the antitumor effects of chemotherapeutic agents active in breast cancer. Phase I clinical trials with single doses of MAb conducted in patients with tumors over-expressing EGF receptors demonstrated favorable pharmacokinetics, good tumor imaging, and a lack of toxicity. A human:murine chimeric antibody has been produced with comparable affinity and antitumor activity that will enable us to administer repeated doses of MAb either alone or in combination with chemotherapy. Our pre-clinical data support the concept that the EGF receptor may be an optimal target for treatment with receptor blocking antibodies, either alone or in combination with chemotherapy.

Epidermal growth factor-related peptides in the pathogenesis of human breast cancer

A number of different epidermal growth factor (EGF)-related peptides such as EGF, transforming growth factor alpha (TGF alpha), amphiregulin (AR), heregulin (HRG), and cripto-1 (CR-1), are coexpressed to varying degrees in both normal and malignant mammary epithelial cells. However, in general the frequency and level of expression of TGF alpha, AR, and CR-1 are higher in malignant breast epithelial cells than in normal mammary epithelium. In addition, several of these peptides such as TGF alpha and AR can function as autocrine and/or juxtacrine growth factors in mammary epithelial cells, and their expression is stringently regulated by mammotrophic hormones such as estrogens, activated proto-oncogenes that have been implicated in the pathogenesis of breast cancer, and other growth factors. The redundancy of expression that is observed for a number of these structurally related peptides in both normal and malignant mammary epithelial cells suggests that some of these peptides may be involved in regulating other aspects of cellular behavior such as differentiation in addition to proliferation.

Secretion of transforming growth factor alpha and expression of its receptor in human mammary cell lines

The secretion of transforming growth factor alpha (TGF alpha) and the expression of cell-surface receptors for epidermal growth factor (EGF) were measured in a series of human mammary cell lines. The amount of TGF alpha secreted by the cells did not correlate with the phenotype of the cells (epithelial or myoepithelial), the mechanism of immortalization of the cells (SV40 or spontaneous) or the source of the cells (normal mammary gland, benign hyperplastic lesion, malignant tumour). The level of expression of cell-surface receptors for EGF was markedly increased as a consequence of SV40-immortalization of mammary cells, but otherwise did not correlate with the phenotype of the cells or the source of the cells. Much of the increase was accounted for by the appearance of a large number of low-affinity receptors for EGF in the SV40-immortalized cells. It is suggested that one of the mechanisms whereby SV40-immortalization suppresses the senescence of primary cultures of human mammary epithelial cells involves increasing the level of expression of receptors for EGF. In contrast the level of secretion of TGF alpha by cells in culture is probably a consequence of the mechanisms of adaptation of each cell line to culture conditions, and does not reflect the level of secretion of TGF alpha by cells in vivo.