Down-modulation of EGF receptors in cells transformed by the src oncogene

The effects of src oncogene expression on epidermal growth factor (EGF) receptors have been investigated in mouse 3T3 and rat-1 fibroblasts. Transformation of both cell types with src resulted in marked reductions in cellular EGF receptor levels, as assayed by either 125I-EGF binding or immunoprecipitation of receptor protein from radiolabeled cell lysates. In contrast to cells transformed by other types of retroviral oncogenes, the loss of EGF receptors in the src-transformed cells did not appear to be due to secreted transforming growth factor-alpha (TGF-alpha), since such factors were undetectable in culture fluids from the src-transformed cells. By several criteria of transformation, an EGF-receptorless cell line infected with src was shown to be transformed, suggesting that EGF receptors themselves are not obligatory to the src transformation process. We suggest that pp60src down-modulates EGF receptors by an intracellular mechanism and that the loss of the receptors is symptomatic of more general effects of pp60src on the machinery of growth regulation.     

Cyclooxygenase-2 transactivates the epidermal growth factor receptor through specific E-prostanoid receptors and tumor necrosis factor-alpha converting enzyme

Cyclooxygenase-2 is often highly expressed in epithelial malignancies and likely has an active role in tumor development. But how it promotes tumorigenesis is not clearly defined. Recent evidence suggests that this may involve transactivation of the epidermal growth factor receptor through E-prostanoid receptors, but reports differ about the mechanism by which this occurs. We found that E-prostanoid receptors 2-4, but not 1, transactivated the epidermal growth factor receptor. This required metalloproteinase activity, leading to release of growth factors from the cell surface. Both transforming growth factor-alpha and amphiregulin were released in response to over-expression of cyclooxygenase-2, but betacellulin and heparin-binding EGF-like growth factor were not. The metalloproteinase tumor necrosis factor-alpha converting enzyme was required for proteolytic release of transforming growth factor-alpha. We also found that addition of epidermal growth factor receptor ligands to HEK293 cells induced cyclooxygenase-2 expression, suggesting that by activating epidermal growth factor receptor signaling, cyclooxygenase-2 potentially creates a self-perpetuating cycle of cell growth. Consistent with this, inhibition of cyclooxygenase-2 reduced growth of epidermal growth factor receptor over-expressing MCF-10A breast epithelial cells in three-dimensional culture.     

Identification and characterization of polypeptide growth factors secreted by murine embryonal carcinoma cells

Undifferentiated P19 and PC13 murine embryonal carcinoma (EC) cells have been analyzed for their ability to secrete polypeptide growth factors. This has been carried out by a combination of specific bioassays and the use of biochemical and immunological detection methods. Both P19 and PC13 EC cells secrete a platelet-derived growth factor (PDGF)-like growth factor, a type beta transforming growth factor, and insulin-like growth factors. In addition, PC13 EC cells secrete a heparin-binding growth factor functionally related to fibroblast growth factor, while P19 EC cells secrete transforming growth factor-alpha. This is the first demonstration for secretion of transforming growth factor-alpha by an equivalent of early embryonic cells. The possible paracrine growth stimulating effects of these growth factors have been tested on differentiated derivatives of P19 EC cells, corresponding to all three germ layers. The differences in growth factor production by various embryonal carcinoma cells are discussed in relation to the developmental origin of these cell lines.     

Granulocyte-macrophage colony-stimulating factor (GM-CSF) production by glioblastoma cells. Despite the presence of inducing signals GM-CSF is not expressed in vivo.

One of the morphologic hallmarks of human gliomas are inflammatory infiltrates with accumulation of macrophages in the tumor site. The signals leading to the macrophage response are only at the beginning of being understood. Novel chemotactic factors that have recently been characterized as secretory products of glioblastoma cells may attract mononuclear cells from the blood. Within the tumor tissue blood-derived monocytes and macrophages of the brain tissue, the microglial cells, may increase in cell numbers due to tumor-derived growth factors. Both astrocytoma cell lines and cultured astrocytes have been shown recently to produce granulocyte-macrophage (GM)-CSF. We show that in vitro not only astrocytoma but also glioblastoma cell lines secrete GM-CSF when stimulated with TNF-alpha or IL-1. However, there is no evidence for GM-CSF production by glioblastoma cells in vivo: fresh tumor samples lack the mRNA for GM-CSF and the protein is not detectable in the tumor cyst fluids or the cerebrospinal fluids of glioblastoma patients. This contrasts IL-1 and IL-6 that are detectable in the tumor cyst fluids and IL-6 also in the cerebrospinal fluids of the patients. Unlike GM-CSF, transforming growth factor-beta 2 mRNA is expressed in ex vivo tested glioblastoma tissues. Absence of GM-CSF in vivo may be explained by the presence of tumor-derived inhibitory factors, such as transforming growth factor-beta 2 and PGE which suppress GM-CSF production by glioblastoma cells in vitro. The accumulation of macrophages at the tumor site may be due to local elaboration of chemoattractants and/or not yet defined growth factors rather than due to GM-CSF production.     

Heparin-binding growth factor/prostatropin attenuates inhibition of rat prostate tumor epithelial cell growth by transforming growth factor type beta

Summary Normal rat prostate epithelial cell growth requires both epidermal growth factor and heparin-binding growth factor/prostatropin. In contrast, epithelial cells derived from the transplantable Dunning R3327H rat tumor require either epidermal growth factor or heparin-binding growth factor/prostatropin. Transforming growth factor type beta inhibited normal epithelial cell growth. Transforming growth factor beta inhibited epidermal growth factor-dependent growth of tumor epithelial cells, independent of epidermal growth factor concentrations. Transforming growth factor beta increased the effective dose of heparin-binding growth factor type 1 required to support tumor epithelial cell growth by 10-fold but saturating levels of heparin-binding growth factor type 1 (290 pM) completely attenuated the inhibitory effect of transforming growth factor beta. These results suggest that prostate tumor epithelial cells may escape the inhibitory effect of transforming growth factor beta as a consequence of alteration of the concurrent requirement for both epidermal growth factor (or homologues) and heparin-binding growth factors. This work was supported by NCI Grant CA37589. Editor’s Statement The observation that heparin-binding growth factor/prostatropin can counteract the inhibitory effect of transforming growth factor beta in prostate epithelial cells may help explain how some cancers avoid the action of growth inhibitors and provides a model for studying how inhibitory peptides overcome the stimulatory signals generated by growth factors.     

EGF and TGF-alpha stimulate retinal neuroepithelial cell proliferation in vitro.

Peptide growth factors have been shown to have diverse effects on cells of the CNS, such as promoting neuronal survival, neurite outgrowth, and several other aspects of neuronal differentiation. In addition, some of these factors have been shown to be mitogenic for particular classes of glial cells within the brain and optic nerve, and recently two peptide growth factors, fibroblast growth factor and nerve growth factor, have been shown to have mitogenic activity on the CNS neuronal progenitors. We now report that two members of another peptide growth factor, epidermal growth factor and transforming growth factor-alpha, are mitogenic for retinal neuroepithelial cells in primary cultures and provide evidence for the presence of both of these factors in normal developing rat retina.     

Transforming growth factor-alpha in the adult bovine ovary: identification in growing ovarian follicles

The pituitary gonadotropins and gonadal steroids are required for normal follicular growth and development but neither has been shown to act directly as a granulosa cell mitogen in vitro. A number of polypeptide growth factors, however, are known to have pronounced mitogenic effects on the cells of the follicle. We have localized transforming growth factor-alpha (TGF-alpha), a potent mitogen, in bovine thecal cells via immunoperoxidase staining using a monoclonal antibody for TGF-alpha that does not cross-react with epidermal growth factor. TGF-alpha staining is most intense in the theca of follicles at the discrete physiological stages known to show rapid granulosa cell growth (small follicles of 0.7-2.0 mm diameter). Staining intensity for TGF-alpha declines in large preovulatory follicles, coincident with the known decline in granulosa cell mitosis. These studies provide further evidence for paracrine interactions in the ovary and show that TGF-alpha may play an important role in the regulation of follicular development in the adult bovine ovary.     

Production of immortal human endothelial cell lines by strontium phosphate transfection and electroporation of SV40 sequences

Summary Eleven human endothelial cell lines have been produced by introducing sequences from the DNA tumor virus SV40 into human umbilical vein endothelial cells either by strontium phosphate coprecipitation or electroporation. The resultant lines were confirmed as being endothelial in origin by their production of endothelial-specific von Willebrand factor. The growth characteristics of the different lines in normal and reduced levels of serum was determined, as was their cellular response to endothelial cell growth supplement in combination with heparin, basic fibroblast growth factor, transforming growth factor-alpha, and epidermal growth factor.     

Differential effects of epidermal growth factor, transforming growth factor-alpha, and vaccinia virus growth factor in the positive regulation of IFN-gamma production

We have recently shown that epidermal growth factor (EGF) is capable of positive regulation of IFN-gamma production, thus establishing a functional relationship between nonhemopoietic growth factors and the immune system. In order to study this relationship further, EGF and the EGF-related growth factors transforming growth factor-alpha (TGF-alpha) and vaccinia virus growth factor (VGF), which stimulate cellular proliferation via binding to the EGF receptor, were studied for their functional and physicochemical effects on IFN-gamma production. In contrast to the positive signal of purified murine EGF and recombinant human EGF (both at 1 nM), neither synthetic TGF alpha nor recombinant VGF were capable of restoring competence for IFN-gamma production by Th cell-depleted spleen cell cultures. TGF-alpha and VGF, in molar excess, also failed to block the helper signal of EGF for IFN-gamma production. Thus TGF-alpha and VGF failed to functionally compete for the EGF receptor in the murine spleen cell system. Both TGF-alpha and VGF stimulated murine 3T3 cell proliferation at concentrations similar to those of EGF, and thus their failure to provide help for IFN-gamma production was not due to a general lack of biologic activity. Binding studies with 125I-EGF suggest that the EGF receptor on murine lymphocytes is not constitutively expressed, but inducible by the T cell mitogen staphylococcal enterotoxin A. TGF-alpha did not compete with 125I-EGF for the induced receptor. The data suggest that lymphocytes express a novel inducible EGF receptor that differs from that expressed on cells such as 3T3 fibroblasts.     

Characterization of the oligosaccharides associated with the human ovarian tumor marker CA125

CA125 is a mucin commonly employed as a diagnostic marker for epithelial ovarian cancer. Induction of humoral responses to CA125 leads to increased survival times in patients with this form of cancer, suggesting a potential role for this mucin in tumor progression. In this study, oligosaccharides linked to CA125 derived from the human ovarian tumor cell line OVCAR-3 were subjected to rigorous biophysical analysis. Sequencing of the O-glycans indicates the presence of both core type 1 and type 2 glycans. An unusual feature is the expression of branched core 1 antennae in the core type 2 glycans. CA125 is also N-glycosylated, expressing primarily high mannose and complex bisecting type N-linked glycans. High mannose type glycans include Man5-Man9GlcNAc2. The predominant N-glycans are the biantennary, triantennary, and tetraantennary bisecting type oligosaccharides. Remarkably, the N-glycosylation profiles of CA125 and the envelope glycoprotein gp120 (derived from H9 lymphoblastoid cells chronically infected with HIV-1) are very similar. The CA125-associated N-glycans have also recently been implicated in crucial recognition events involved in both the innate and adaptive arms of the cell-mediated immune response. CA125 may therefore induce specific immunomodulatory effects by employing its carbohydrate sequences as functional groups, thereby promoting tumor progression. Immunotherapy directed against CA125 may attenuate these immunosuppressive effects, leading to the prolonged survival of patients with this extremely serious form of cancer.     

Differential regulation of phospholipase A2 by cytokines inhibiting bone formation and mineralization.

Treatment of fetal rat calvarial cells with interleukin-1 alpha, tumor necrosis factor-alpha, transforming growth factor-beta 1, or group II phospholipase A2 inhibits the number of bone nodules formed in long-term cultures. These same mediators also inhibit the mineralization of fully developed bone nodules in a time and dose-dependent fashion. The pro-inflammatory cytokines interleukin-1 alpha and tumor necrosis factor-alpha cause a dose-dependent induction of rat calvarial cell phospholipase A2-II mRNA levels, suggesting that their effects on bone formation may be mediated indirectly by activation of this enzyme. In contrast, transforming growth factor-beta 1, which has more potent effects on bone formation than interleukin-1 alpha or tumor necrosis factor-alpha, suppresses basal levels of phospholipase A2-II mRNA, indicating a different mechanism of action for this cytokine.     

EGF receptor signaling in prostate morphogenesis and tumorigenesis.

The growth and differentiation of the prostate gland are largely dependent on extracellular signaling factors. In addition to androgens, many polypeptide growth factors function through autocrine or paracrine networks. The paracrine interaction between stromal and epithelial cells is critical for androgen regulation, morphogenesis, epithelial cell proliferation, and secretory differentiation. Efforts to identify the essential growth factors and studies on their effects have been prompted by the fact that prostate cells in culture need substances other than androgens for proliferation. In this context, transforming growth factor-alpha and epidermal growth factor, among others, have been studied extensively. Recent advances have suggested that these EGF receptor (EGFR) ligands play roles not only during glandular development but also during neoplastic transformation and tumor progression. The cell responses most relevant to the role of this receptor signaling are both mitogenesis and cell motility. The aim of the review is to provide an overview of current knowledge about EGFR and its ligands in the organogenesis and tumorigenesis of the prostate gland.     

Growth regulation of A431 cells. Modulation of expression of transforming growth factor-alpha mRNA and 2',5'-oligoadenylate synthetase activity

To explore bidirectional regulatory interactions between interferons and autocrine polypeptide factors, we examined the modulation of expression of transforming growth factor-alpha and 2',5'-oligoadenylate synthetase activity in A431 epidermoid carcinoma cells after treatment with interferon-gamma and transforming growth factor-alpha. Treatment of A431 cells with interferon-gamma increased steady state levels of transforming growth factor-alpha mRNA by 4-fold and increased the levels of transforming growth factor-alpha in the culture medium. There were additive growth inhibitory effects upon coaddition of exogenous transforming growth factor-alpha and interferon-gamma to the cultures. Addition of transforming growth factor-alpha to A431 cell cultures in the absence of interferon could stimulate the induction of 2',5'-oligoadenylate synthetase activity by more than 2-fold. These findings demonstrate that the induction of transforming growth factor-alpha in interferon-gamma-treated A431 cells could act to regulate interferon-induced gene(s), e.g. 2',5'-oligoadenylate synthetase, suggesting interactions between a potential autocrine growth factor and the interferon system in the growth regulation of A431 cells.     

The effects of various growth factors on endothelial cell survival in vitro

The effects of various growth factors on endothelial cell survival in vitro were studied. Using rat heart endothelial cells, the cell survival curves were obtained; the cells were cultured until confluent, the medium was changed to serum-free medium with or without growth factors, and the cells were counted after 3, 6, 9, and 12 days. Transforming growth factor-beta, which is known as a potent growth inhibitor for vascular endothelial cells, shortened the rat heart endothelial cell's survival period, while epidermal growth factor or transforming growth factor-alpha prolonged survival. Insulin did not affect the rat heart endothelial cell's survival. Our data indicate that growth factors play a role not only in cell proliferation but also in cell survival in vitro. In addition, elevated levels of growth inhibitors such as transforming growth factor-beta may cause tissue damage in vivo by affecting cell survival.     

Basic fibroblast growth factor and transforming growth factor-alpha are hepatotrophic mitogens in vitro

Basic fibroblast growth factor (bFGF) and transforming growth factor-alpha (TGF alpha) have been identified as potent hepatotrophic mitogens. bFGF and TGF alpha induce DNA synthesis in fetal and adult rat hepatocytes in primary culture and support fetal rat hepatocyte multiplication in chemically defined medium. No additional exogenous growth or progression factors are required by the cells for traversing the cell cycle or for cell division. These mitogenic polypeptides, previously identified in various cell types including liver and endothelial cells, platelets, and macrophages may act locally in a paracrine mode in controlling hepatocyte multiplication in the liver during development and regeneration.     

Natural killer-sensitive targets stimulate production of TNF-alpha but not TNF-beta (lymphotoxin) by highly purified human peripheral blood large granular lymphocytes

Highly purified populations of large granular lymphocytes (LGL) have been shown to mediate natural killer (NK) cell activity. The mechanism of target cell killing by NK cells is as yet undefined; however, it has been postulated that such killing may involve soluble cytotoxic factors produced and secreted by NK cells. The data presented show that NK-sensitive, but not NK-resistant, tumor cell lines induce highly purified populations of human LGL to produce factors with cytotoxic and/or cytostatic activities. We have identified one of these factors as tumor necrosis factor-alpha (TNF-alpha), and have shown that production of this factor is enhanced by recombinant human interferon-gamma (rHuIFN-gamma). We have also examined the role of TNF-alpha in the cytotoxic function of NK cells. The data show that although highly purified LGL populations produce low levels of TNF-alpha, the cytotoxic/cytostatic activity of this lymphokine on tumor target cells does not correlate with the cytotoxic activity of highly purified populations of LGL on tumor target cells. Furthermore, NK cell-mediated cytotoxicity is not reliably inhibited by antibodies directed against various epitopes of recombinant human TNF-alpha and/or recombinant TNF-beta (lymphotoxin) or rHuIFN-gamma. These data show that although TNF-alpha is produced by highly purified NK-containing LGL cell populations, this factor does not appear to be responsible for NK cell cytotoxicity against classical NK target cells such as Molt-4 or K562. We suggest that NK function can be attributed to a combination of factors rather than to a single factor alone, and that at least two major phenomena are involved in LGL function: the rapid cytotoxic events which lead to the cell lysis measured in classical in vitro NK assays such as against K562; and the release of factors such as TNF-alpha with cytotoxic/cytostatic activities which would inhibit the growth of invading tumor cells in vivo.     

CA 125 production and release by ovarian cancer cells in vitro

The antigenic determinant CA 125 is a high molecular weight glycoprotein which is elevated in more than 80% of patients with epithelial ovarian cancer. Despite its good performance as a human tumor marker, only little is known about its physiological function. According to recent publications, CA 125 production and release appear to be related to cellular growth. In order to investigate this putative relationship more closely, we analyzed the pattern of CA 125 production and release by ovarian cancer cells during exponential cell growth, during cell cycle arrest by colchicine and during inhibition of cellular protein synthesis by cycloheximide. The results were correlated with the cell cycle distribution. According to our results, the main determinant of CA 125 release into the culture supernatant is the total cell count. Although cell cycle arrest in the G2 + M phase by means of colchicine treatment resulted in the death of most cells, which was reflected by an increased release of CA 125, no differences in the intracellular production rate between colchicine treated and untreated cells were seen. In contrast, treatment of cells with cycloheximide not only resulted in decreasing cell numbers but also in a complete inhibition of CA 125 production by surviving cells.     

Free CA125 promotes ovarian cancer cell migration and tumor metastasis by binding Mesothelin to reduce DKK1 expression and activate the SGK3/FOXO3 pathway

Objective: CA125/MUC16 is an O-glycosylated protein that is expressed on the surfaces of ovarian epithelial cells. This molecule is a widely used tumor-associated marker for diagnosis of ovarian cancer. Recently, CA125 was shown to be involved in ovarian cancer metastasis. The purpose of this study was to investigate the mechanism of CA125 during ovarian cancer metastasis.Methods: We analyzed the Oncomine and CSIOVDB databases to determine the expression levels of DKK1 in ovarian cancer. DKK1 expression levels were upregulated or downregulated and applied with CA125 to Transwell and Western blot assays to ascertain the underlying mechanism by which CA125 stimulates cell migration via the SGK3/FOXO3 pathway. Anti-mesothelin antibodies (anti-MSLN) were used to block CA125 stimulation. Then the expression levels of DKK1were tested by enzyme-linked immunosorbent assay (ELISA) to eliminate the blocking effect of anti-MSLN to CA125 stimulation. Xenograft mouse models were used to detect the effects of CA125 and anti-MSLN on ovarian cancer metastasis in vivo.Results: DKK1 levels were downregulated in ovarian tumor tissues according to the analyses of two databases and significantly correlated with FIGO stage, grade and disease-free survival in ovarian cancer patients. DKK1 levels were downregulated by CA125 stimulation in vitro. Overexpression of DKK1 reversed the ability of exogenous CA125 to mediate cell migration by activating the SGK3/FOXO3 signaling pathway. Anti-MSLN abrogated the DKK1 reduction and increased the apoptosis of ovarian cancer cells. The use of anti-MSLN in xenograft mouse models significantly reduced tumor growth and metastasis accelerated by CA125.Conclusions: These experiments revealed that the SGK3/FOXO3 pathway was activated, wherein decreased expression of DKK1 was caused by CA125, which fuels ovarian cancer cell migration. Mesothelin is a potential therapeutic target for the treatment of ovarian cancer metastasis.