Expression of epidermal growth factor, transforming growth factor-alpha and their receptor genes in human gastric carcinomas; implication for autocrine growth

The expressions of mRNA for epidermal growth factor (EGF), transforming growth factor-alpha (TGF-alpha) and EGF receptor (EGFR) genes were examined in 7 human gastric carcinoma cell lines and 15 gastric carcinoma tissues and the corresponding normal mucosas. All of the gastric carcinoma cell lines expressed mRNA for EGFR and TGF-alpha genes. TMK-1 and MKN-28 cells also expressed EGF mRNA. Production of EGF, TGF-alpha and EGFR protein by gastric carcinoma cell lines was also confirmed by EGF and TGF-alpha specific monoclonal antibody binding. As for surgical specimens, EGFR and TGF-alpha mRNA were detected at high levels in all the tumor tissues. Interestingly, EGF mRNA was detected in 5 (33.3%) of the 15 gastric carcinomas but it was not detected in normal tissues. Moreover, anti-EGF and anti-TGF-alpha monoclonal antibodies inhibited the spontaneous 3H-TdR uptake by gastric carcinoma cells. These results suggest that EGF and/or TGF-alpha produced by tumor cells act as autocrine growth factors for gastric carcinomas.     

The autocrine loop of epidermal growth factor receptor-epidermal growth factor / transforming growth factor-alpha in malignant rhabdoid tumor cell lines: heterogeneity of autocrine mechanism in TTC549.

To investigate the effects of the autocrine loop of epidermal growth factor receptor (EGFR)-epidermal growth factor (EGF) / transforming growth factor-alpha (TGF-alpha) on the proliferation and differentiation of malignant rhabdoid tumor (MRT), we used five MRT cell lines, TM87-16, STM91-01, TTC549, TTC642, and YAM-RTK1. RT-PCR analyses revealed expression of EGFR mRNA in all MRT cell lines. In contrast, the expression of either EGF or TGF-alpha mRNA was detected in all MRT cell lines. Expression of EGF, TGF-alpha, and EGFR as determined by immunocytochemical staining and in situ hybridization, correlated with the results of RT-PCR. Upon differentiation-induction with 12-O-tetradecanoylphorbol-13-acetate (TPA), in TTC549, showing an expression of TGF-alpha but not EGF initially, de novo expression of EGF mRNA appeared abruptly on day 2 of TPA treatment. To confirm the EGFR-EGF / TGF-alpha autocrine loop, we used TGF-alpha, EGF, and their antibodies in the cultures. Monoclonal antibody (mAb) to EGFR alone significantly inhibited the growth of cell line TTC549. However, mAb to EGF or TGF-alpha could inhibit proliferation of this cell line only when administrated together. Our findings would suggest that growth of the TTC549 cell line is constitutionally regulated by TGF-alpha / EGFR, but that inhibition of this autocrine mechanism results in transient activation of an autocrine loop involving EGF / EGFR. Our results may indicate the presence of two different autocrine loops of EGFR-EGF and / or EGFR-TGF-alpha in MRT cell lines. The heterogeneity of autocrine mechanisms found in MRT cell lines would be consistent with the multiphenotypic diversity and aggressive characteristics of this enigmatic tumor.     

EGF and TGF-alpha, the ligands of hyperproduced EGFR in human esophageal carcinoma cells, act as autocrine growth factors

In order to ascertain autocrine growth factors in esophageal carcinomas, we analysed expression of mRNAs and proteins for epidermal growth factor (EGF), transforming growth factor-alpha (TGF-alpha) and epidermal growth factor receptor (EGFR) in 6 esophageal carcinoma cell lines. Gene alterations were also examined. All of the esophageal carcinoma cell lines expressed mRNA for EGFR and TGF-alpha genes. Interestingly, EGF mRNA of about 5.0 kb was also detected in TE-1, TE-2, and TE-8 cells. Production of protein was also confirmed by binding assay and ELISA on 3 of the 6 cell lines. The cells had a relatively high number of EGFRs and produced TGF-alpha and EGF protein at the same time. Furthermore, anti-EGF (KEM-10) and anti-TGF-alpha (WA-3) monoclonal antibodies (MAbs) inhibited spontaneous uptake of tritiated thymidine (3H-TdR) by TE-1 cells which expressed EGF, TGF-alpha and EGFR mRNA and protein. These results strongly suggest that EGF and/or TGF-alpha produced by carcinoma cells function as autocrine growth factors for human esophageal carcinomas.     

Epidermal growth factor and transforming growth factor alpha characteristics of human oral carcinoma cell lines.

This study examined the expression of epidermal growth factor (EGF) cell-surface receptors, the response to exogenous ligand and the autocrine production of transforming growth factor alpha (TGF-alpha) in normal and carcinoma-derived human oral keratinocytes. One of eight malignant cell lines overexpressed EGF receptors, while the remainder expressed receptor numbers similar to normal cells. Exogenous EGF stimulated incorporation of tritiated thymidine in a dose-dependent manner. In keratinocytes expressing normal numbers of EGF receptors, the cellular response to exogenous EGF correlated positively with total EGF receptor number. SCC-derived keratinocytes produced more TGF-alpha than normal cells. There was no statistical correlation between the autocrine production of TGF-alpha, EGF cell-surface receptor expression and cellular response to exogenous EGF. While the growth-stimulatory effects of exogenous TGF-alpha were inhibited by the addition of a neutralising antibody, the presence of this antibody in conditioned medium failed to produce a similar decrease in growth. The results indicate that overexpression of EGF receptors is not an invariable characteristic of human oral squamous carcinoma-derived cell lines. Further, the contribution of TGF-alpha to the growth of normal and carcinoma-derived human oral keratinocytes in vitro may be less significant than previously documented.     

Hematopoietic growth factors secreted by seven human pleural mesothelioma cell lines: interleukin-6 production as a common feature.

Seven mesothelioma cell lines, established from patients with pleural mesothelioma, exhibited substantial heterogeneity regarding in vitro morphology and growth characteristics. Media conditioned by these cell lines and by MeT5A normal mesothelial cells were examined for (i) colony formation on human bone-marrow cells, (ii) hematopoietic growth-factor content and (iii) mitogenic activity on mesothelioma cells. Colony-stimulating activity was produced only by the ZL34 cell line. Analysis of conditioned media by ELISA revealed that all mesothelioma cell lines constitutively produced IL-6, while the MeT5A normal mesothelial cells did not; in addition, GM-CSF and G-CSF were detected in the supernatant of the ZL34 cell line. Using a 3H-thymidine incorporation assay, we showed that all mesothelioma cell lines produced mitogenic activity in the culture supernatant, in contrast to the MeT5A normal mesothelial cells. The mitogenic effect of the hematopoietic growth factors detected in mesothelioma culture supernatants was tested on mesothelioma cells and on MeT5A normal mesothelial cells: IL-6, GM-CSF and G-CSF did not stimulate any DNA synthesis. Our results suggest that these hematopoietic growth factors do not act as autocrine growth factors. A common feature of this panel of mesothelioma cell lines is the production of IL-6; although the biological significance of the aberrant production of cytokines by mesotheliomas remains unclear, IL-6 might be involved in paraneoplastic syndromes such as thrombocytosis.     

Autonomous growth of androgen-independent human prostatic carcinoma cells: role of transforming growth factor alpha

The androgen-independent prostatic carcinoma cell line PC3 is known to exhibit autonomous growth in vitro and in vivo. The purpose of the present study was to investigate the role of transforming growth factor alpha (TGF-alpha) and its receptor, the epidermal growth factor (EGF) receptor, in the regulation of PC3 cell proliferation. Results showed that PC3 cells secrete factors into conditioned medium that are mitogenic for the less aggressive prostatic carcinoma lines DU145 and LNCaP. Gel filtration chromatography of PC3-conditioned medium revealed a major peak of mitogenic activity at a molecular weight of 5,000 to 10,000 which was inhibited by the addition of antibody to TGF-alpha. The synthesis and secretion of TGF-alpha by PC3 cells were further demonstrated by immunoblotting and radioimmunoassay. Radioreceptor analysis showed a single class (Kd 5.3 nM) of EGF receptors on PC3 cells. The presence of Mr 170,000 EGF receptors on PC3 cells was further demonstrated by immunoprecipitation of metabolically labeled proteins. TGF-alpha was effective in stimulating the growth of low-density, but not high-density, PC3 cultures. In addition, the proliferation of PC3 cells under serum-free defined conditions was inhibited by antibodies to TGF-alpha and/or the EGF receptor. These data indicate that TGF-alpha/EGF receptor interactions are partially responsible for autonomous growth of the PC3 cell line and may explain one mechanism of escape from androgen-dependent growth in human prostatic carcinoma.     

Induction of growth factor-receptor and metalloproteinase genes by epidermal growth factor and/or transforming growth factor-alpha in human gastric carcinoma cell line MKN-28

We examined the effects of epidermal growth factor (EGF) and transforming growth factor-alpha (TGF-alpha) on EGF receptor (EGFR) phosphorylation and the expression of mRNAs for oncogenes, growth factors, their receptors and metalloproteinase genes by MKN-28 gastric carcinoma cells which express EGF, TGF-alpha and EGFR genes. Both EGF and TGF-alpha stimulated EGFR phosphorylation, EGF and TGF-alpha induced FOS, MYC and ERBB-2 oncogene expression. Interestingly, EGF increased the expression of mRNAs for TGF-alpha and EGFR. On the other hand, TGF-alpha increased TGF-alpha mRNA but decreased the expression of mRNAs for EGFR and TGF-beta. Furthermore, mRNAs for interstitial collagenase, stromelysin and procollagen type I genes were also enhanced after treatment with EGF and TGF-alpha. These results indicate that EGF and TGF-alpha successively evoke cascade phenomena which favor tumor progression, invasion and extracellular matrix formation, acting as autocrine growth regulators for gastric carcinomas.     

An autocrine mitogenic activity produced by a pleural human mesothelioma cell line.

The pleural human mesothelioma cell line ZL5 established in our laboratory exhibits an unusual phenotype with adherent and floating cells. ZL5 cells grow in a chemically defined medium (ACL3*) and can be maintained over 3 weeks in protein-free basal medium alone (RPMI). Basal medium conditioned by ZL5 cells possesses a mitogenic activity with an autocrine effect, as measured by cell counting and by a 3H-thymidine incorporation assay. Moreover, the conditioned medium affects the DNA synthesis of a variety of other lung-derived cells. The active principle of medium conditioned by ZL5 cells is not identical to the defined growth-factors EGF, PDGF, and TGF-beta, known to stimulate the growth of normal human mesothelial cells: treatment with these factors does not mimic the effect of conditioned medium on ZL5 cells. Our observations suggest that the mesothelioma cell line ZL5 produces an unknown autocrine mitogen.     

Autocrine growth stimulation by transforming growth factor-alpha in human non-small cell lung cancer.

We studied the biological response to and production of transforming growth factor-alpha (TGF-alpha) by the non-small cell lung carcinoma (NSCLC) clonal cell lines H226b, H322a, H460a, H596b. Each of these cell lines expressed epidermal growth factor receptor (EGFR) as determined by [125I]EGF competitive binding and Scatchard analysis and by phosphorylation. The receptors were functionally active as determined in immune complex kinase assays. H322a, H226b, H460a, and H596b cells showed stimulated [3H]thymidine (Thd) uptake in response to TGF-alpha. Exogenously added TGF-alpha increased colony formation in soft agar for three of the cell lines in media containing serum. All cell lines expressed TGF-alpha detected by immunohistochemistry and TGF-alpha mRNA, although to differing degrees. Cell lysates and spent media competed for EGFR binding with EGF, thus demonstrating production of TGF-alpha-like activity. The anti-TGF-alpha monoclonal antibody AB-3 inhibited the uptake of [3H]Thd by proliferating H322a and H226b cells but not H460a and H596b cells. No inhibition occurred with MOPC21 antibody and inhibition was completely reversed by addition of TGF-alpha to the culture. Suramin inhibited cell proliferation and [3H]Thd uptake by all cell lines. Inhibition of H460a and H596b cells was reversed with exogenous TGF-alpha but not PDGF. Our data suggests that TGF-alpha is a mediator of autocrine growth stimulation for NSCLC cells, and that for some NSCLC cells cytoplasmic binding of receptor and ligand is the primary mechanism for autocrine growth stimulation.     

Inhibition of proliferation, migration, and matrix metalloprotease production in malignant mesothelioma cells by tyrosine kinase inhibitors

The epidermal growth factor receptor (EGFR) is expressed in a variety of human solid tumors, including malignant mesothelioma. EGFR has been implicated in regulation of cell proliferation, survival, angiogenesis, and metastasis, making it an ideal target for drug development. ZD1839 (gefitinib) and OSI-774 (erlotinib) are new, low-molecular-weight, EGFR-selective tyrosine kinase (TK) inhibitors, whereas CI-1033 is a pan-EGFR family TK inhibitor. In the present study, we used ZD1839, OSI-774, and CI-1033 and investigated the effect of these drugs on proliferation, migration, and matrix metalloprotease (MMP) production in three malignant mesothelioma cell lines (M14K, ZL34, and SPC212). Using [3H]thymidine incorporation, DNA synthesis assay, we found that all three drugs inhibited transforming growth factor-alpha (TGF-alpha)-induced cellular proliferation in a dose-dependent manner. In addition, all three drugs induced apoptosis in ZL34 cells as determined by flow cytometry using annexin-V staining. Furthermore, all three drugs inhibited TGF-alpha-induced cell migration (chemotaxis) in a dose-dependent manner as determined by Boyden chamber assay. TGF-alpha-induced MMP-9 production was also inhibited in a dose-dependent manner as determined by gelatin zymography in three cell lines tested. In conclusion, our study demonstrates inhibitory effectiveness of EGFR-TK inhibitors in malignant mesothelioma cells and suggests that these drugs may be an effective treatment strategy for malignant mesothelioma.     

Transforming growth factor-alpha: an oncodevelopmental growth factor

Transforming growth factor-alpha (TGF-alpha) is a 50-amino-acid mitogenic peptide that is structurally and, in some cases, functionally related to members of the epidermal growth factor (EGF) family of peptides. TGF-alpha is initially synthesized as a high-molecular-weight, glycosylated, membrane-associated precursor of approximately 160 amino acids. The low-molecular-weight TGF-alpha peptide as well as the precursor are biologically active in a number of systems and can function as transforming proteins when overexpressed. TGF-alpha binds to and activates the EGF receptor, and TGF-alpha and the EGF receptor are coexpressed in a number of human and rodent tumors and tumor cell lines--which suggests that TGF-alpha can function as an autocrine or paracrine growth factor. TGF-alpha is transiently expressed in some fetal and adjacent maternal tissues during development and is also expressed in a number of adult tissues; this pattern of expression suggests that the growth factor is involved in several distinct physiological functions.     

Expressions of epidermal growth factor family and its receptor in hepatocellular carcinoma cell lines: relationship to cell proliferation

In 6 HCC cell lines, clear expressions of EGFR and TGF-alpha were found in flow cytometry, while expressions of EGF, HB-EGF and AR were quite low. TGF-alpha secretion into culture supernatants became measurable when TPA 0.5 microM was added. TPA accelerated the proliferation of KYN-3 cells, and anti-TGF-alpha neutralizing antibody suppressed this proliferation in a dose-dependent manner. Addition of exogenous TGF-alpha, EGF, AR, or HB-EGF with heparin accelerated cell proliferation. In non-stimulated cultures, cell proliferation was suppressed by anti-EGFR neutralizing antibody, but not by the antibodies for EGF, TGF-alpha, AR and HB-EGF. HCC may possess a paracrine system regulated by these 4 ligands, and an autocrine system, under a certain condition, via TGF-alpha and EGFR.     

Epidermal growth factor ligand/receptor loop and downstream signaling activation pattern in completely resected nonsmall cell lung cancer

BACKGROUND: In recent years, molecular insights shed light on the role of the epidermal growth factor receptor (EGFR) in nonsmall cell lung cancer (NSCLC), and new therapeutic agents, such as the EGFR tyrosine kinase inhibitors, were tested successfully, with responsiveness to those agents more likely in those patients with specific EGFR gene alterations. The objective of the current study was to investigate the protein profiles of EGFR, c-erb-B2, transforming growth factor alpha (TGF-alpha) (one of the EGFR ligands commonly expressed in NSCLC), and some downstream molecules, potentially to detect a subset of tumors with an activated autocrine loop that is responsible for higher intracellular signaling. METHODS: One hundred twelve consecutive patients with resected NSCLC were analyzed by immunohistochemistry for EGFR, the c-erb-B2 receptor, TGF-alpha, and pivotal molecules downstream from EGFR activation. Statistical correlations between the investigated molecular expression profiles and clinicopathologic data were performed. RESULTS: EGFR, c-erb-B2, TGF-alpha and downstream molecule expression, per se, was not correlated significantly with any clinicopathologic variables, with the exception of a significant correlation between squamous histology and EGFR and between adenocarcinoma and TGF-alpha. However, nearly 30% of NSCLCs demonstrated coexpression of both TGF-alpha and EGFR, and this molecular status was associated positively with a statistically significant expression of phosphatidylinositol 3 kinase and an inversely with mitogen-activated protein kinase expression. CONCLUSIONS: The presence of a subgroup of NSCLCs with an activated autocrine loop may help to explain the mechanisms that lead to the relative ineffectiveness of the EGFR tyrosine kinase inhibitor and may support new clinical trials to define whether the subgroup of patients with these tumors reasonably may benefit from higher doses of such inhibitors or from the simultaneous inhibition of EGFR downstream signaling targets.     

Overexpression of epidermal growth factor and insulin-like growth factor-I receptors and autocrine stimulation in human esophageal carcinoma cells

The growth-stimulatory effects of epidermal growth factor (EGF), transforming growth factor alpha (TGF-alpha), and insulin-like growth factor-I (IGF-I) on the human esophageal carcinoma cell line CE48T/VGH were evaluated. Under serum-free conditions, EGF, TGF-alpha, and IGF-I promoted 3.6- to 4.1-fold increased cell proliferation. Scatchard analyses and Northern blot hybridization revealed that both the EGF/TGF-alpha receptor and the IGF-I receptor were overexpressed in CE48T/VGH cells. Furthermore, ligand-dependent autophosphorylation of the EGF receptor and the IGF-I receptor was clearly detected using antireceptor and antiphosphotyrosine antibodies. Autocrine regulation was strongly indicated by the following evidence: (a) CE48T/VGH cells were found to express TGF-alpha and IGF-I genes, (b) serum-free conditioned medium promoted the growth of CE48T/VGH cells and stimulated the autophosphorylation of the EGF/TGF-alpha receptor and the IGF-I receptor, and (c) the addition of IGF-I receptor antibodies significantly suppressed CE48T/VGH cell growth under serum-free conditions. Our studies suggest that the overexpression of EGF and IGF-I receptors and autocrine growth regulation may concertedly control the proliferation of esophageal carcinoma cells.     

Absence of constitutive EGF receptor activation in ovarian cancer cell lines.

Previous investigators have noted that certain ovarian cancer cell lines secrete and respond to transforming growth factor-alpha (TGF-alpha), suggesting that endogenous activation of the epidermal growth factor (EGF) receptor through autocrine or paracrine mechanisms might contribute to the proliferative response. In order to determine whether autocrine stimulation was partly responsible for the proliferative response in ovarian cancer, we investigated whether the EGF receptor expressed by ovarian cancer cell lines was constitutively activated as assessed by the presence of tyrosine phosphorylation. A specific anti-phosphotyrosine antibody was used in conjunction with an immunoblotting technique in order to detect EGF receptor phosphorylation in ovarian cancer cell lines in the absence and presence of exogenous EGF. The effects of neutralising anti-EGF receptor antibody on the proliferation of ovarian cancer cell lines was also examined. We found no evidence for constitutive tyrosine phosphorylation of the p170 EGF receptor in eight epithelial ovarian cancer cell lines tested, although each line demonstrated inducible phosphorylation in response to exogenous EGF. The absence of constitutive EGF receptor activation was also noted when cells were grown under high density conditions, thus excluding a role for membrane-bound EGF or TGF-alpha in this process. Media conditioned by five ovarian cancer cell lines, as well as malignant ascites obtained from 12 different ovarian cancer patients, were not capable of stimulating EGF receptor phosphorylation. Finally, the proliferation of ovarian cancer cell lines was not significantly inhibited in the presence of neutralising anti-EGF receptor antibody. These data suggest that EGF receptor activation through autocrine pathways is not a major mechanism for the growth of many ovarian cancer cell lines. Other pathways of signal transduction which bypass the requirement for EGF receptor activation may be important in the proliferation for ovarian cancer cells. Such EGF receptor-independent pathways may limit the effectiveness of strategies designed to inhibit ovarian cancer cell growth through disruption of EGF receptor function.     

Growth control by epidermal growth factor and transforming growth factor-alpha in human lung squamous carcinoma cells.

Although EGF receptor expression is generally elevated in human lung squamous carcinoma, the biological significance of this phenomenon and the role of EGF and TGF-alpha in this disease are poorly understood. We have investigated three human lung squamous carcinoma cell lines (NX002, CX140 and CX143) and have shown, using an antibody (EGFR1) directed against the EGF receptor, that the majority of cells in all three lines express the EGF receptor. Using a ligand binding assay, Scatchard analysis indicated high concentrations (1,300-2,700 fmol mg-1 protein) of a single low affinity binding site (Kd = 3-5 nM) within these lines. Addition of EGF or TGF-alpha at concentrations greater than 0.1 nM resulted in growth inhibition of all three lines and this was associated with an accumulation of cells in the G2/M phase of the cell cycle. Growth inhibitory effects were not explained by an enhancement of cellular differentiation as monitored by involucrin expression and the ability to form cornified envelopes. While the presence of EGF could not be detected in medium conditioned by the NX002 cell line, mRNA for TGF-alpha was detected in all three lines suggesting the possibility of an autocrine loop. These results together with reports of growth inhibition by EGF and TGF-alpha in other systems suggest that EGF and similar molecules might have a growth regulatory role in lung cancer cells and modulation of such may have therapeutic potential.