Regulation and role of TGF beta production in breast cancer

Hormone Receptor Signaling and Breast Cancer Resistance to Anti-Tumor Immunity

Breast cancers regroup many heterogeneous diseases unevenly responding to currently available therapies. Approximately 70-80% of breast cancers express hormone (estrogen or progesterone) receptors. Patients with these hormone-dependent breast malignancies benefit from therapies targeting endocrine pathways. Nevertheless, metastatic disease remains a major challenge despite available treatments, and relapses frequently ensue. By improving patient survival and quality of life, cancer immunotherapies have sparked considerable enthusiasm and hope in the last decade but have led to only limited success in breast cancers. In addition, only patients with hormone-independent breast cancers seem to benefit from these immune-based approaches. The present review examines and discusses the current literature related to the role of hormone receptor signaling (specifically, an estrogen receptor) and the impact of its modulation on the sensitivity of breast cancer cells to the effector mechanisms of anti-tumor immune responses and on the capability of breast cancers to escape from protective anti-cancer immunity. Future research prospects related to the possibility of promoting the efficacy of immune-based interventions using hormone therapy agents are considered.

Cooperative involvement of NFAT and SnoN mediates transforming growth factor-β (TGF-β) induced EMT in metastatic breast cancer (MDA-MB 231) cells

Epithelial to mesenchymal transition (EMT) is a secondary phenomenon concomitantly associated with the tumor progression. The regulatory signals and mechanistic details of EMT are not fully elucidated. Here, we shared a TGF-β mediated mechanism of EMT in breast cancer (MDA-MB 231) cells. Initial exposure of TGF-β for 48 h, enhanced the rate of cell proliferation and associated with EMT of MDA-MB 231 cells. The EMT was characterized by observing the increased N-cadherin, fibronectin, Snail expression and associated with the morphological change with a reduced E-cadherin expression. NFAT, a transcription factor, alters tumor suppressive function of TGF-β towards tumor progression. Up regulation of NFAT, coupled with a foremost translocation of one oncogenic protein SnoN from cytoplasm to nucleus was noticed during this TGF-β mediated EMT. Silencing of NFAT also showed the inhibition of TGF-β mediated EMT characterized by down regulation of N-cadherin and associated with reduced expression of SnoN. In addition, it was also observed that NFAT sequestering the Smad3 prevents the proteasome mediated degradation of SnoN and this SnoN has a role on the regulation of MMP-2, MMP-9 activity. Increased Smad3-SnoN interaction and proteasome mediated degradation of SnoN were detected after silencing of NFAT with a reduced MMP-2, MMP-9 activity. All of these observations provide a fresh mechanism in which by a twofold involvement of NFAT and SnoN plays a crucial role in TGF-β mediated EMT by recruiting the effector molecules N-cadherin and MMP-2, MMP-9.

Mechanisms of resistance to endocrine therapy in breast cancer: focus on signaling pathways, miRNAs and genetically based resistance

Breast cancer is the most frequent malignancy diagnosed in women. Approximately 70% of breast tumors express the estrogen receptor (ER). Tamoxifen and aromatase inhibitors (AIs) are the most common and effective therapies for patients with ERα-positive breast cancer. Alone or combined with chemotherapy, tamoxifen significantly reduces disease progression and is associated with more favorable impact on survival in patients. Unfortunately, endocrine resistance occurs, either de novo or acquired during the course of the treatment. The mechanisms that contribute to hormonal resistance include loss or modification in the ERα expression, regulation of signal transduction pathways, altered expression of specific microRNAs, balance of co-regulatory proteins, and genetic polymorphisms involved in tamoxifen metabolic activity. Because of the clinical consequences of endocrine resistance, new treatment strategies are arising to make the cells sensitive to tamoxifen. Here, we will review the current knowledge on mechanisms of endocrine resistance in breast cancer cells. In addition, we will discuss novel therapeutic strategies to overcome such resistance. Undoubtedly, circumventing endocrine resistance should help to improve therapy for the benefit of breast cancer patients.

Transforming growth factor-beta signaling: emerging stem cell target in metastatic breast cancer?

In most human breast cancers, lowering of TGFbeta receptor- or Smad gene expression combined with increased levels of TGFbetas in the tumor microenvironment is sufficient to abrogate TGFbetas tumor suppressive effects and to induce a mesenchymal, motile and invasive phenotype. In genetic mouse models, TGFbeta signaling suppresses de novo mammary cancer formation but promotes metastasis of tumors that have broken through TGFbeta tumor suppression. In mouse models of "triple-negative" or basal-like breast cancer, treatment with TGFbeta neutralizing antibodies or receptor kinase inhibitors strongly inhibits development of lung- and bone metastases. These TGFbeta antagonists do not significantly affect tumor cell proliferation or apoptosis. Rather, they de-repress anti-tumor immunity, inhibit angiogenesis and reverse the mesenchymal, motile, invasive phenotype characteristic of basal-like and HER2-positive breast cancer cells. Patterns of TGFbeta target genes upregulation in human breast cancers suggest that TGFbeta may drive tumor progression in estrogen-independent cancer, while it mediates a suppressive host cell response in estrogen-dependent luminal cancers. In addition, TGFbeta appears to play a key role in maintaining the mammary epithelial (cancer) stem cell pool, in part by inducing a mesenchymal phenotype, while differentiated, estrogen receptor-positive, luminal cells are unresponsive to TGFbeta because the TGFBR2 receptor gene is transcriptionally silent. These same cells respond to estrogen by downregulating TGFbeta, while antiestrogens act by upregulating TGFbeta. This model predicts that inhibiting TGFbeta signaling should drive the differentiation of mammary stem cells into ductal cells. Consequently, TGFbeta antagonists may convert basal-like or HER2-positive cancers to a more epithelioid, non-proliferating (and, perhaps, non-metastatic) phenotype. Conversely, these agents might antagonize the therapeutic effects of anti-estrogens in estrogen-dependent luminal cancers. These predictions need to be addressed prospectively in clinical trials and should inform the selection of patient populations most likely to benefit from this novel anti-metastatic therapeutic approach.

The functional implications of Akt activity and TGF-beta signaling in tamoxifen-resistant breast cancer

Development of acquired resistance to tamoxifen is a major clinical problem during endocrine treatment in estrogen receptor positive breast cancer. Transforming growth factor-beta1 (TGF-beta) has been implicated in tamoxifen-induced cellular signaling in breast cancer, and increased Akt activation is associated with tamoxifen-resistant cell types. We hypothesized that the relationship between TGF-beta and Akt signaling may be involved in the development and progression of tamoxifen resistance. Tamoxifen-resistant (Tam-R) cells were established from parental MCF-7 cells by continuously exposing them to 4-hydroxytamoxifen (4-OHT). Tam-R cells were associated with a decrease in TGF-beta1 secretion, TGF-beta-mediated transcriptional response, and growth inhibitory effects of 4-OHT. Tam-R cells expressed significantly higher levels of phosphorylated Akt and lower levels of phosphorylated Smad 3 in both the absence and presence of 4-OHT when compared to MCF-7 cells treated with 4-OHT. Ectopic expression of constitutively active Akt (Myc-Akt(Myr)) rendered MCF-7 cells resistant to activation by TGF-beta and the growth inhibitory effects of 4-OHT, while over-expression of kinase-dead Akt (Myc-Akt(K179M)) or LY294002 treatment of Tam-R cells enhanced TGF-beta activation and blocked cell growth. These results suggest that suppression of TGF-beta signaling by activated Akt is correlated with the development of tamoxifen resistance in breast cancer.

TGFbeta2 and TbetaRII are valid molecular biomarkers for the antiproliferative effects of tamoxifen and tamoxifen metabolites in breast cancer cells

Response to treatment with the antiestrogen tamoxifen is variable and at least partially due to its highly complex metabolism. Tamoxifen is transformed by polymorphic and inducible cytochrome P450 enzymes to a large number of metabolites with varying biological activities. The estrogen receptor dependent growth inhibitory effect of antiestrogens is mediated by activation of antiproliferative Transforming Growth Factor beta (TGFbeta) signal transduction pathways. The aim of the present study was to establish if TGFbeta2 or TGFbeta receptor II (TbetaRII), could be used as markers to assess the pharmacological potency of tamoxifen and its metabolites. Consequently, we analyzed the growth inhibitory effect of tamoxifen and its major metabolites and explored whether it correlated with their capacity to induce TGFbeta2 and TbetaRII expression. Human breast cancer cells (MCF-7 and T47D) were treated with tamoxifen and tamoxifen metabolites and mRNA expression of TGFbeta2 and TbetaRII was analyzed by quantitative RT-PCR. Only two metabolites 4-hydroxytamoxifen and N-desmethyl-4-hydroxytamoxifen had significant antiproliferative activity and were able to induce TGFbeta2 and TbetaRII. Plasma concentrations of these metabolites are usually very low in patients. However, even minor growth inhibitory effects at concentrations which are below the limit of quantification in plasma samples resulted in clearly discernible effects on expression of TGFbeta2 and TbetaRII. Taken together, our data demonstrate that TGFbeta2 and TbetaRII are very specific and sensitive biomarkers for the antiestrogenic activity of tamoxifen metabolites in breast cancer.

TGF-Beta Signaling in Breast Cancer

The antiestrogen tamoxifen is one of the most successful drugs in the endocrine treatment of breast cancer and significantly reduces the risk of recurrence and death. Antiestrogens act by inhibiting the production of growth-stimulatory factors as well as by activating peptides with growth-inhibitory effects like transforming growth factor- beta (TGF-beta). In hormone-responsive breast cancer cells treatment with antiestrogens leads to the conversion of TGF-beta1 into a biologically active form. Expression of TGF-beta2 and TGF-beta receptor (TbetaR) II is induced via a transcriptional mechanism involving p38 MAP kinase. Inhibition of p38 abolishes antiestrogen-dependent growth inhibition. However, the role of TGF-beta in breast cancer progression is ambiguous, as it was shown to display both tumor-suppressing and -enhancing effects. A polymorphism in the promoter of TGF-beta2 that enhances expression of the protein was associated with lymph node metastasis in breast cancer patients, pointing to a role of TGF-beta2 in the process of invasion. An immunohistochemical study on TbetaRI and TbetaRII expression in breast cancer tissues indicates that the estrogen receptor (ER) status of a tumor is an important marker and a potential mediator of the transition of TGF-beta from tumor suppressor to tumor promoter. In ER-negative tumors, expression of TbetaRII was associated with a subset of tumors that appeared to be highly aggressive, leading to strongly reduced overall survival times. Further characterization of the influence of ER expression on TGF-beta signal transduction shows that ER-alpha plays a crucial role in TGF-beta signaling.

The tumour microenvironment and implications for cancer immunotherapy

Tumour cells exist in a complex milieu of cellular and non-cellular components comprising fibroblasts, endothelial cells, immune cells and metabolites of cellular respiration. An elaborate interplay between these components and tumour cells exists with implications for immunological recognition of tumour cells. Tumours have been shown to alter their antigen and cytokine profiles, desensitise and impair immune defences, signal fibroblasts to facilitate metastasis, and take advantage of acidic and hypoxic conditions that impede normal cells. This paper aims to review the roles of the stroma, extracellular matrix and chemistry of the microenvironment on tumour growth, with particular emphasis on interactions with the immune system, and to highlight some of the novel therapeutic strategies that target the tumour microenvironment.

Prognostic significance of transforming growth factor beta receptor II in estrogen receptor-negative breast cancer patients

PURPOSE

The role of transforming growth factor beta (TGF-beta) in breast cancer is ambiguous; it can display both tumor suppressing and enhancing effects. Activation of the TGF-beta signal transduction system is subject to hormonal regulation. This study was conducted to further analyze the role of TGF-beta receptors in breast cancer and to evaluate their significance as prognostic markers.

EXPERIMENTAL DESIGN

Expression of TGF-beta receptor I (TbetaRI) and TGFbeta receptor II (TbetaRII) was retrospectively analyzed by immunohistochemistry in 246 breast cancer patients.

RESULTS

Expression of TbetaRI was strongly correlated with tumor size (P < 0.001) and nodal status (P = 0.012) but only weakly with overall survival (P = 0.056). In contrast, TbetaRII was prognostic for overall survival in univariate analysis (P = 0.0370). In estrogen receptor (ER) -negative patients TbetaRII expression was correlated with highly reduced overall survival (P = 0.0083). In multivariate analysis TbetaRII proved to be an independent and highly significant prognostic marker with a hazard ratio of 6.8. Simultaneous loss of both ER and TbetaRII was associated with longer overall survival times comparable with those of ER-positive patients.

CONCLUSIONS

The results of this exploratory study show that TbetaRII is an independent, highly significant prognostic indicator for overall survival in ER-negative patients. In addition our results are supportive of a mechanism of breast cancer progression in which a selective loss of the tumor inhibitory action of TGFbeta takes place, whereas tumor- promoting aspects remain intact.

Effect of aldosterone on renal transforming growth factor-β

Aldosterone participates in the pathophysiology of several models of progressive chronic renal disease. Because of the causal connection between transforming growth factor-β1(TGF-β) and scarring in many such models, we hypothesized that aldosterone could evoke TGF-β in the kidney. Aldosterone infusion for 3 days in otherwise normal rats caused a more than twofold increase in TGF-β excretion without changes in systolic pressure or evidence of kidney damage. Concurrent treatment with amiloride did not alter this effect, indicating that aldosterone's stimulation of TGF-β was independent of its regulation of sodium or potassium transport. However, concurrent treatment with spironolactone did block the increase in TGF-β, indicating that the effect depends on the mineralocorticoid receptor. Renal mRNA for serum glucocorticoid kinase rose, but no change in TGF-β message occurred, suggesting posttranscriptional enhancement of renal TGF-β. In summary, aldosterone provokes renal TGF-β, and this action may contribute to aldosterone's fibrotic propensity.

Antiestrogenic regulation of transforming growth factor beta receptors I and II in human breast cancer cells

To obtain more information about the interactions between antiestrogens and transforming growth factor beta (TGF-beta) signaling, we analyzed the influence of different types of antiestrogens on the expression of TGF-beta receptors I (TbetaRI) and II (TbetaRII). Our results show that antiestrogens selectively induce TbetaRII but not TbetaRI mRNA.

Plasma transforming growth factor beta1 in breast cancer patients treated with CMF chemotherapy

BACKGROUND

In early breast cancer patients the transformed epithelial cells are thought to be sensitive to transforming growth factor beta1 (TGFbeta1)-mediated growth arrest. TGFbeta1 may therefore act as an anti-tumour promoter. However, in advanced breast cancer resistance to such TGFbeta1 action develops. Neoplastic cells produce TGFbeta1, which may enhance tumour invasion and metastasis, mainly by intensifying angiogenesis, which is an immunosuppressive action. In the light of the potential role of TGFbeta1 in breast cancer pathogenesis, an understanding of the effect of applied therapeutic methods on plasma TGFbeta1 concentration is essential.

OBJECTIVE

To investigate the effect of adjuvant chemotherapy on plasma transforming growth factor beta1 (TGFbeta1) concentration in breast cancer patients with metastases to axillary lymph nodes.

METHOD

Fifteen stage II breast cancer patients on adjuvant chemotherapy with cyclophosphamide, methotrexate and 5-fluorouracil (CMF) were studied along with 15 healthy premenopausal women.

RESULTS

Plasma TGFbeta1 concentration (determined by the ELISA method) in the breast cancer patients did not differ significantly from that of the healthy women. Adjuvant CMF chemotherapy significantly decreased plasma TGFbeta1 concentration in those pre-menopausal breast cancer women with metastases to axillary lymph nodes.

CONCLUSION

The possible pathogenic action of this growth factor in stage II breast cancer disease warrants further investigation to elucidate whether the induced decrease of blood TGFbeta1 concentration is essential to successful chemotherapy.

Plasma levels of soluble CD105 correlate with metastasis in patients with breast cancer

CD105 (endoglin), a receptor for transforming growth factor (TGF) beta1 and beta3 in vascular endothelial cells, is highly up-regulated in blood vessels of tissues where neovascularisation occurs. It modulates endothelial-mesenchymal signalling and is essential for angiogenesis. Indeed, CD105 knock-out mice die from malvascularisation by 11.5 day p.c. In the present study CD105, TGFbeta1 and CD105/TGFbeta1 complexes were quantified in plasma samples from 77 healthy individuals and 92 patients with early stage breast cancer prior to any treatment. When compared with normal controls, both CD105 and CD105/TGFbeta1 complex levels were significantly elevated in breast cancer patients, whereas TGFbeta1 levels were lower in cancer patients. The most important finding to emerge was that CD105 levels were significantly increased in patients who developed distant metastasis compared with disease-free patients. While there was no significant difference between CD105 levels in controls compared to disease-free patients, it was significantly higher in patients with metastatic disease. Thus patients who had died following local relapse or distant metastases possessed the highest levels of CD105. Neither CD105/TGFbeta1 complex nor TGFbeta1 levels correlated with tumour progression. Our data indicate that CD105 might be a valuable novel angiogenic marker for identifying breast cancer patients who are at high risk of developing metastasis.

TGF-beta and cancer

The relationships between transforming growth factor-beta (TGF-beta) and cancer are varied and complex. The paradigm that is emerging from the experimental evidence accumulated over the past decade or so is that TGF-beta can play two different and opposite roles with respect to the process of malignant progression. During early stages of carcinogenesis, TGF-beta acts predominantly as a potent tumor suppressor and may mediate the actions of chemopreventive agents such as retinoids and nonsteroidal anti-estrogens. However, at some point during the development and progression of malignant neoplasms, bioactive TGF-betas make their appearance in the tumor microenvironment and the tumor cells escape from TGF-beta-dependent growth arrest. In many cases, this resistance to TGF-beta is the consequence of loss or mutational inactivation of the genes that encode signaling intermediates. These include the types I and II TGF-beta receptors, as well as receptor-associated and common-mediator Smads. The stage of tumor development or progression at which TGF-beta-resistant clones come to dominate the tumor cell population in different types of neoplasm remains to be defined. The phenotypic switch from TGF-beta-sensitivity to TGF-beta-resistance that occurs during carcinogenesis has several important implications for cancer prevention and treatment.

Resveratrol, a natural product derived from grape, exhibits antiestrogenic activity and inhibits the growth of human breast cancer cells

Resveratrol is a natural phytoalexin compound found in grapes and other food products. In this study, the effect of resveratrol on the growth of human breast cancer cells was examined. Results show that resveratrol inhibits the growth of estrogen receptor(ER)-positive MCF-7 cells in a dose-dependent fashion. Detailed studies with MCF-7 cells demonstrate that resveratrol antagonized the growth-promoting effect of 17-beta-estradiol (E2) in a dose-dependent fashion at both the cellular (cell growth) and the molecular (gene activation) levels. At 5 x 10(-6) M, resveratrol abolished the growth-stimulatory effect mediated by concentrations of E2 up to 10(-9) M. The antiestrogenic effect of resveratrol could be observed at a concentration of 10(-6) M and above. The antiestrogenic effect of resveratrol was also demonstrated at the molecular level. Resveratrol in a dose-dependent fashion antagonized the stimulation by E2 of progesterone receptor gene expression in MCF-7 cells. Moreover, expression of transforming growth factor-alpha and insulin-like growth factor I receptor mRNA was inhibited while the expression of transforming growth factor beta2 mRNA was significantly elevated in MCF-7 cells cultivated in the presence of resveratrol (10(-5) M). In summary, our results show that resveratrol, a partial ER agonist itself, acts as an ER antagonist in the presence of estrogen leading to inhibition of human breast cancer cells.

Role of transforming growth factor beta3 in lymphatic metastasis in breast cancer

Transforming growth factor-betas (TGFbetas) play a prominent role in tumour growth and metastasis by enhancing angiogenesis and suppressing immune surveillance. Despite the increased interest in the effect of TGFbetas on tumour progression, little is known about the importance of TGFbeta3 and its receptor CD105 in breast cancer. In the present study, we measured the plasma levels of TGFbeta3, CD105-TGFbeta3 complexes and TGFbeta1 in 80 patients with untreated early-stage breast cancer using an enhanced chemiluminescence ELISA method. Of the 80 patients, 14 were histologically confirmed as having axillary lymph node metastases, while the remainder had no evidence of lymph node involvement. The results showed that levels of both TGFbeta3 and CD105-TGFbeta3 complex were significantly elevated in patients with positive lymph nodes compared to those without node metastasis. Furthermore, the levels of both TGFbeta3 and CD105-TGFbeta3 complex correlated with lymph node status. The only patient who died of the disease had very high plasma levels of TGFbeta3 and CD105-TGFbeta3 complex and positive lymph nodes; this patient developed lung metastases within 2 years of diagnosis. No significant correlation was seen between either TGFbeta3 or CD105-TGFbeta3 complex levels and tumour stage, size or histological grade. Plasma TGFbeta1 levels were not correlated with node metastasis, tumour stage, grade or size. Our data suggest that plasma levels of TGFbeta3 and CD105-TGFbeta3 complex may be of prognostic value in the early detection of metastasis of breast cancer.

Transforming growth factor-beta in breast cancer: a working hypothesis

Transforming Growth Factor-beta (TGF beta) is the most potent known inhibitor of the progression of normal mammary epithelial cells through the cell cycle. During the early stages of breast cancer development, the transformed epithelial cells appear to still be sensitive to TGF beta-mediated growth arrest, and TGF beta can act as an anti-tumor promoter. In contrast, advanced breast cancers are mostly refractory to TGF beta-mediated growth inhibition and produce large amounts of TGF beta, which may enhance tumor cell invasion and metastasis by its effects on extracellular matrix. We postulate that this seemingly paradoxical switch in the responsiveness of tumor cells to TGF beta during progression is the consequence of the activation of the latent TGF beta that is produced and deposited into the tumor microenvironment, thereby driving the clonal expansion of TGF beta-resistant tumor cells. While tumor cells themselves may activate TGF beta, recent observations suggest that environmental tumor promoters or carcinogens, such as ionizing radiation, can cause stromal fibroblasts to activate TGF beta by epigenetic mechanisms. As the biological effects of the anti-estrogen tamoxifen may well be mediated by TGF beta, this model has a number of important implications for the clinical uses of tamoxifen in the prevention and treatment of breast cancer. In addition, it suggests a number of novel approaches to the treatment of advanced breast cancer.