Relationship between tamoxifen-induced transforming growth factor beta 1 expression, cytostasis and apoptosis in human breast cancer cells

Levels of transforming growth factor beta and transforming growth factor beta receptors in rat liver during growth, regression by apoptosis and neoplasia

Transforming growth factor beta1 (TGF-beta1) has been implicated as inhibitor of cell proliferation and a potent inducer of apoptosis in vitro and in vivo after the administration of high doses. To assess the role of endogenous TGF-beta1, we quantitated the cytokine and its receptors in rat liver during regenerative and hyperplastic growth, regression by apoptosis, and in hepatocellular carcinoma (HCC). This was accomplished by Northern blot analysis and by RNase protection assay of the messenger RNA (mRNA) of TGF-beta1 and TGF-beta receptors (TbetaR) types I to III and by an activity bioassay of the TGF-beta proteins. Untreated rat livers were found to contain 15.6 +/- 4.8 ng TGF-beta1 protein/g tissue; TGF-beta2 protein was not detected. To induce toxic cell death and subsequent regenerative DNA synthesis in the liver, rats were treated with a necrogenic dose of carbon tetrachloride (CCl4). After 24 and 48 hours, there was an upregulation of TGF-beta1 (mRNA, up to tenfold; protein, about twofold) and of TbetaRs (mRNA: two- to fourfold); that indicates an overall enhanced production of and sensitivity to TGF-beta1, which may serve to confine the regenerative response. Hyperplastic liver growth and regression of the hyperplasia were induced by treatment with cyproterone acetate (CPA) or nafenopin (NAF) followed by withdrawal; neither mRNAs of TGF-beta1 and TbetaR types I to III nor TGF-beta1 protein exhibited significant changes during the growth phase or during regression by apoptosis. We also studied neoplastic growth. HCC, obtained after long-term treatment with NAF, exhibited high rates of cell replication and apoptosis. The majority of lesions contained mRNA and protein of TGF-beta1 and mRNA of TbetaR types I to III at concentrations similar to those of the surrounding tissue. In conclusion, during liver regeneration there is a pronounced upregulation of expression of both TGF-beta1 and TbetaRs I to III, but not during mitogen-induced liver growth or regression. It appears that apoptosis is induced via altered local concentration of TGF-beta1, in a paracrine and/or autocrine way. By this mechanism the lethal effects of TGF-beta1 may be locally confined, and overshoots of apoptosis in the liver may be prevented.

Additive effect of mifepristone and tamoxifen on apoptotic pathways in MCF-7 human breast cancer cells

MCF-7 cells growing in culture were used to study the mechanism of the antiproliferative activity of the antiprogestin mifepristone, as compared with the antiestrogen 4-hydroxytamoxifen or the combination of both. These steroid antagonists induced a significant time- and dose-dependent cell growth inhibition (cytotoxicity). This inhibition of cell survival was associated with a significant increase in DNA fragmentation (apoptosis), downregulation of bcl2, and induction of TGFbeta1 protein. Abrogation of the mifepristone- and/or 4-hydroxytamoxifen-induced cytotoxicity by TGFbeta1 neutralizing antibody confirms the correlation between induction of active TGFbeta1 and subsequent cell death. The effect of a combination of mifepristone and 4-hydroxytamoxifen on cell growth inhibition, on the increase in DNA fragmentation, bcl2 downregulation, and induction of TGFbeta1 protein was additive and significantly different (P < 0.05) from the effect of monotherapy. A translocation of protein kinase C (PKC) activity from the soluble to the particulate and/or nuclear fraction appeared to be also additive in cells treated with a combination of both 4-hydroxytamoxifen and mifepristone. These results suggest that the mechanism of the additive antiproliferative activity of mifepristone and tamoxifen could be explained at least in part by an additive induction of apoptosis in both estrogen and progesterone receptor positive MCF-7 breast cancer cells. A bcl2 downregulation, the PKC transduction pathway, and TGFbeta1 expression seem to be involved in this additive mechanism of action. Our data further suggest that a combination of an antiprogestin with tamoxifen may be more effective than tamoxifen monotherapy in the management of human breast cancer.

p53-independent dephosphorylation and cleavage of retinoblastoma protein during tamoxifen-induced apoptosis in human breast carcinoma cells

We have investigated several molecular events that occur during the process of tamoxifen-induced apoptosis in human breast carcinoma cells. We show that the treatment of either MCF-7 (containing wild-type p53) or MDA-MB-231 cells (containing mutant p53) with tamoxifen resulted in apoptotic nuclear changes and an increase in the pre-G1 apoptotic population. This was accompanied by activation of the caspase enzymes, as evidenced by specific cleavage of poly(ADP-ribose) polymerase and retinoblastoma (RB) protein. The RB protein was cleaved at both an interior and carboxyl terminus cleavage site. In addition, dephosphorylation of RB was found at an early stage of tamoxifen-induced apoptosis in both cell lines. However, neither induction of p53 in MCF-7 cells nor induction of p21 in either cell line was detected, suggesting that tamoxifen-induced RB dephosphorylation and apoptosis are independent of the p53/p21 pathway. We also observed an increase in levels of the pro-apoptotic Bax protein, the inhibitory cytokine TGF-beta1 and the transcription factor c-Myc in tamoxifen-treated MDA-MB-231 cells, suggesting the possible involvement of these proteins during apoptosis in this system.

Prolactin: the forgotten hormone of human breast cancer

Prolactin (PRL) is both a mitogen and a differentiating agent in the mammary gland. It has been shown to be involved in mammary cancer development in rodents, but in human breast cancer, its role has long been overlooked. Three criteria are applied to demonstrate PRL's involvement in this disease: (1) PRL receptors are present in human breast cancer cells, (2) human breast cancer cells in culture respond to PRL as a mitogen, and (3) PRL is synthesized by human breast cancer cells and inhibition of the binding of PRL to its receptors inhibits cell growth.

Apoptosis: clinical relevance and pharmacological manipulation

Apoptosis, often synonymously used with the term 'programmed cell death', is an active, genetically controlled process that removes unwanted or damaged cells. Suppression, overexpression or mutation of a number of genes which orchestrate the apoptotic process are associated with disease. The diseases in which apoptosis has been implicated can be grouped into 2 broad groups: those in which there is increased cell survival (i.e. associated with inhibition of apoptosis) and those in which there is excess cell death (where apoptosis is overactive). Diseases in which there is an excessive accumulation of cells include cancer, autoimmune disorders and viral infections. Deprivation of trophic factors is known to induce apoptosis in cells dependent on them for survival. This fact has been exploited in the use of antiandrogens or antiestrogens in the management of prostate or breast cancer. Haemopoietic growth factors like granulocyte-macrophage colony stimulating factor (GM-CSF) or interleukin-3 prevent apoptosis in target cells and modulation of levels of these factors has been tried in the prevention of chemotherapy-induced myelosuppression. Until recently, it was thought that cytotoxic drugs killed target cells directly by interfering with some life-maintaining function. However, of late, it has been shown that exposure to several cytotoxic drugs with disparate mechanisms of action induces apoptosis in both malignant and normal cells. Physiological regulation of cell death is essential for the removal of potentially autoreactive lymphocytes during development and the removal of excess cells after the completion of an immune response. Recent work has clearly demonstrated that dysregulation of apoptosis may underlie the pathogenesis of autoimmune diseases by allowing abnormal autoreactive lymphocytes to survive. AIDS and neurodegenerative disorders like Alzheimer's or Parkinson's disease represent the most widely studied group of disorders where an excess of apoptosis has been implicated. Amyotrophic lateral sclerosis, retinitis pigmentosa, epilepsy and alcoholic brain damage are other neurological disorders in which apoptosis has been implicated. Apoptosis has been reported to occur in conditions characterised by ischaemia, e.g. myocardial infarction and stroke. The liver is a site where apoptosis occurs normally. This process has also been implicated in a number of liver disorders including obstructive jaundice. Hepatic damage due to toxins and drugs is also associated with apoptosis in hepatocytes. Apoptosis has also been identified as a key phenomenon in some diseases of the kidney, i.e. polycystic kidney, as well as in disorders of the pancreas like alcohol-induced pancreatitis and diabetes.

Iodine-123 labelled radiopharmaceuticals and single-photon emission tomography: a natural liaison

Most nuclear medicine departments possess one or more imaging apparatuses for single-photon emission tomography (SPET). Molecules of biological interest to assess metabolism and receptor function are often labelled with 123I, which allows proper SPET imaging. The various methods for radiolabelling are reviewed. As the biological integrity of these agents has been demonstrated for numerous radiopharmaceuticals, the purpose of this review is to summarize the efficacy in various fields of medicine, including the imaging of tumours, infection, myocardium and cerebrum.

Synergistic antiproliferative activity of tamoxifen and docetaxel on three oestrogen receptor-negative cancer cell lines is mediated by the induction of apoptosis

The taxanes are a promising family of anti-tumour drugs that block cell cycle replication by interfering with the microtubule network. The clinical use of these drugs involves some problems related to their low solubility and occurrence of resistance, which is mainly dependent on the multidrug-resistant (MDR) phenotype. To investigate the possible interaction between docetaxel and tamoxifen (TAM), three oestrogen receptor-negative cancer cell lines, MDR- MDA-MB 231, MDR + CEM-VBLr and MCF-7 ADRr, were used. In all three cell lines, the combination of docetaxel and TAM was more effective in terms of growth inhibition than single drug exposure. Isobolic analysis confirmed the presence of synergism in all cell lines when docetaxel was used at 0.2 microM and TAM at a dose equal to or higher than 1 microM. Flow cytometric DNA analysis performed on the three cell lines showed that TAM was able to increase the G2/M blocking activity of docetaxel. This blocking activity was followed by an increased flow cytometric DNA fragmentation suggestive of the presence of apoptosis, which was confirmed by DNA gel fragmentation and morphological analysis. While an antagonistic effect on P-glycoprotein (P-gp) activity may contribute to the synergistic effect of tamoxifen and docetaxel on CEM-VBLr and MCF-7 ADRr, other mechanisms must be involved, as the synergistic effect is also apparent with a P-gp-negative cell line.

The 12-lipoxygenase gene-transfected MCF-7 human breast cancer cell line exhibits estrogen-independent, but estrogen and omega-6 fatty acid-stimulated proliferation in vitro, and enhanced growth in athymic nude mice

The estrogen-dependent, linoleic acid (LA)-unresponsive, MCF-7 breast cancer cell line was transfected with 12-lipoxygenase (12-LOX) cDNA (MCF-7/12-LOX cells). The transfectant stably expressed high levels of 12-LOX mRNA and protein, and secreted large quantities of 12-hydroxyeicosatetraenoic acid when cultured with arachidonate. The transfectant grew in vitro in the absence of estrogen, and its growth was stimulated by LA. The MCF-7/12-LOX cells formed small solid tumors when injected into the mammary fat pads of ovariectomized nude mice. Despite this estrogen independence, MCF-7/12-LOX cell growth was stimulated further by estradiol both in vitro and in vivo, and to a greater extent than parental MCF-7 cells.

Role of TGF beta in the anti-estrogen response/resistance of human breast cancer

Transforming growth factor beta (TGF beta) has potent inhibitory effects upon epithelial proliferation and malignant progression may be associated with breakdown of the autocrine and paracrine inhibitory loops in which TGF beta participates. The therapeutic effecs of anti-estrogens may be partially attributable to boosting of local endogenous levels of TGF beta. This article reviews the evidence in support of TGF beta being a proximate effector in mediation of the anti-neoplastic effects of anti-estrogens. Both the conventional estrogen receptor (ER) dependent and ER independent mechanisms of action are likely to be involved. Evidence for preferential stromal induction of TGF beta by anti-estrogens is emphasized, together with the therapeutic potential of this strategy for improving outcome in early breast cancer irrespective of ER status.

Calcitriol and lexicalcitol (KH1060) inhibit the growth of human breast adenocarcinoma cells by enhancing transforming growth factor-beta production

The mechanisms involved in the antiproliferative action of calcitriol (1 alpha, 25(OH)2D3) were investigated using human breast carcinoma epithelial cells (the MCF-7 cell line). Calcitriol and KH1060, a synthetic analog, inhibited cell growth in a time-and dose-dependent way. The substances similarly stimulated total TGF-beta secretion after 24 hours, and Northern blot analyses showed that mRNA levels for TGF-beta 1 were increased, as well. When MCF-7 cells were co-incubated with calcitriol and a neutralizing anti TGF-beta 1, beta 2, beta 3 antibody, growth inhibition was completely abrogated. With KH1060, the antibody could only partly block growth inhibition. This study shows that TGF-beta is involved in the growth response to calcitriol and KH1060 in MCF-7 cells.

Estrogen induces apoptosis in a rat prostatic adenocarcinoma: association with an increased expression of TGF-beta 1 and its type-I and type-II receptors

Rats transplanted with the androgen-sensitive Dunning R3327 PAP prostatic adenocarcinoma were castrated and treated with either estrogen or vehicle alone for short periods (4 hr, 12 hr, 24 hr) and for 6 weeks. In these tumors the expression of TGF-beta 1, TGF-beta type-I and type-II receptors (TGF-beta RI, TGF-beta RII) was examined by immunohistochemistry. Apoptotic cells were identified by in situ nick and labelling (TUNEL). Tumor growth was retarded by castration and even more by additive estrogen treatment. The epithelium of the untreated tumors stained weakly for TGF-beta 1 and TGF-beta RI, but TGF-beta RII was not detected. Castration induced moderate TGF-beta 1 immunoreactivity in a major part of the glandular epithelium after 24 hr. After 12 hr already, castration plus estrogen resulted in an intense staining for TGF-beta 1 in the basal epithelial cells, some of which also showed an apoptotic appearance. The percentage of cells having stained positive for TGF-beta 1 was significantly higher in the estrogen-treated groups than in the castrated group after 12 hr, and its elevated TGF-beta 1 level remained at 6 weeks. Notably, the increased immunoexpression of TGF-beta 1 occurred before the onset of induction of apoptosis. In parallel with the upregulation of TGF-beta 1 after castration, the expression of its receptors. TGF-beta RI and RII, was induced and was further enhanced by the additive estrogen treatment. The number of intensely stained TGF-beta 1 tumor cells showed a strong correlation with the number of apoptotic tumor cells identified by TUNEL in the whole material. Furthermore, TGF-beta 1 immunoreactivity co-localized with the presence of apoptotic cells in the estrogen-treated tumors at 6 weeks after castration.

Synthesis and secretion of transforming growth factor beta isoforms by primary cultures of human breast tumour fibroblasts in vitro and their modulation by tamoxifen

Tamoxifen may mediate its effect in early breast cancer in part via an oestrogen receptor (ER)-independent pathway by directly stimulating fibroblasts to produce the negative paracrine growth factor transforming growth factor (TGF)-beta. We have previously shown that secretion of this factor is induced 3-to 30-fold in human fetal fibroblasts in vitro, and by stromal fibroblasts in vivo following tamoxifen treatment of ER-positive and ER-negative breast cancer patients. Primary cultures of breast tumour fibroblasts have been exposed to tamoxifen for 48 h, and rates of secretion of TGF-beta 1 and TGF-beta 2 measured using a quantitative immunoassay. Fibroblast strains derived from malignant and benign tumours produced and secreted similar amounts of TGF-beta 1, but benign breast tumour fibroblasts secreted significantly higher levels of TGF-beta 2 compared with fibroblasts of malignant origin. Tamoxifen did not induce any consistent increase in TGF-beta secretion into the conditioned medium, but immunofluorescence analysis for the intracellular form of TGF-beta 1 revealed evidence of increased immunoreactive protein in tamoxifen-treated fibroblasts, which is localised to the nucleus. Therefore synthesis of TGF-beta 1 appears to be stimulated by tamoxifen, but increased secretion may be abrogated in vitro. Furthermore, using immunocytochemistry and transient transfection with an ER-responsive reporter construct, no ER was demonstrable in these fibroblasts supporting the proposed ER-independent paracrine pathway.