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

Role of TGF-β signaling in the mechanisms of tamoxifen resistance

The transforming growth factor beta (TGF-β) signaling pathway plays complex role in the regulation of cell proliferation, apoptosis and differentiation in breast cancer. TGF-β activation can lead to multiple cellular responses mediating the drug resistance evolution, including the resistance to antiestrogens. Tamoxifen is the most commonly prescribed antiestrogen that functionally involved in regulation of TGF-β activity. In this review, we focus on the role of TGF-β signaling in the mechanisms of tamoxifen resistance, including its interaction with estrogen receptors alfa (ERα) pathway and breast cancer stem cells (BCSCs). We summarize the current reported data regarding TGF-β signaling components as markers of tamoxifen resistance and review current approaches to overcoming tamoxifen resistance based on studies of TGF-β signaling.

Transforming growth factor-β, insulin-like growth factor I/insulin-like growth factor I receptor and vascular endothelial growth factor-A: prognostic and predictive markers in triple-negative and non-triple-negative breast cancer

In the current study, the prognostic and predictive values of serum transforming growth factor-β1 (TGF-β1), insulin-like growth factor I (IGF-I)/IGF-I receptor (IGF-IR) and vascular endothelial growth factor-A (VEGF-A) were evaluated in triple-negative and non-triple-negative breast cancer (TNBC and non-TNBC). The aim was to identify a group of serological biomarkers and to identify possible candidates for targeted therapy in patients with TNBC and non-TNBC. Protein levels of TGF-β1, IGF-I/IGF-IR and VEGF-A in the serum were measured in 43 TNBC, 53 non-TNBC and 20 normal control participants using quantitative ELISA assays. Results were correlated against standard prognostic factors, response to treatment and survival. TNBC was identified to be associated with poor prognosis and serum levels of VEGF-A and IGF/IGF-IR were significantly higher in the TNBC group compared with the non-TNBC group. IGF-IR and VEGF-A overexpression was observed to be correlated with TGF-β1 expression and all of the markers investigated were associated with metastasis and disease progression. In the multivariate analysis, VEGF-A, IGF-I and IGF-IR were observed to be independent predictors for overall survival, whereas TGF-β1 and lymph node status were identified as independent predictors for disease-free survival. The overall response rate was significantly lower in patients with TNBC and those with high levels of TGF-β1, IGF-I/IGF-IR and VEGF-A. In view of the present results, it was concluded that TGF-β1, IGF-I/IGF-IR and VEGF-A overexpression is associated with the presence of aggressive tumors, which exhibit an increased probability of metastasis, a poor response to treatment and reduced survival rate. This indicates that VEGF-A, IGF-IR and IGF-I have the potential to be used as surrogate biomarkers and are promising candidates for targeted therapy, particularly in patients with TNBC.

A functional polymorphism of TGFBR2 is associated with risk of breast cancer with ER(+), PR(+), ER(+)PR(+) and HER2(-) expression in women

Little is known about the correlation between TGFBR2 G-875A and breast cancer risk. Moreover, the associations of the expression of estrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor-2 (HER2) in breast cancer tissues with the TGFB1 C-509T, T+29C and TGFBR2 G-875A polymorphisms remain to be determined. In this study, we genotyped for TGFB1 C-509T, T+29C and TGFBR2 G-875A in fresh surgically resected tissues (n=82) and archived paraffin-embedded specimens (n=88) from 170 patients with breast cancer, as well as peripheral blood samples from 178 cancer-free female individuals. Evaluation of ER, PR and HER2 expression was performed using immunohistochemical staining. Logistic regression analysis was carried out to determine the risk of breast cancer by calculating the odds ratios (ORs) and their 95% confidence intervals (CIs). As a result, no difference was observed in the TGFB1 C-509T, T+29C genotype and allele frequencies between patients and controls. However, the frequency of the TGFBR2 -875A allele was marginally higher in cancer-free female individuals than that of women with breast cancer (24.2 vs. 17.9%, P=0.05). Notably, when stratification was performed by ER, PR and HER2 expression, the TGFBR2 -875A allele was found to correlate significantly to a decreased risk of breast cancer with ER(+) (OR=0.57, 95% CI 0.35-0.92), PR(+) (OR=0.54, 95% CI 0.34-0.88), ER(+)PR(+) (OR=0.55, 95% CI 0.33-0.92) and HER2(-) (OR=0.55, 95% CI 0.34-0.88) under a dominant genetic model. In conclusion, this is the first study to suggest that the TGFBR2 -875A allele modifies predisposition to breast cancer with an expression of ER(+), PR(+), ER(+)PR(+) and HER2(-).

Estrogen receptor alpha attenuates transforming growth factor-beta signaling in breast cancer cells independent from agonistic and antagonistic ligands

To investigate a presumed crosstalk between estrogen receptor alpha (ERalpha) and the TGF-beta signaling pathway in breast cancer, we analyzed the TGF-beta-induced expression of the plasminogen activator inhibitor 1 (PAI-1) gene in ER-positive MCF-7 cells. After siRNA-mediated knock-down of endogenous ERalpha, the transcription level of PAI-1 was upregulated, pointing to an attenuation of TGF-beta signaling by the presence of ERalpha. We verified these findings by a vice versa approach using a primary ER-negative cell model transiently overexpressing either ERalpha or ERbeta. We found that ERalpha, but not ERbeta, led to a strong inhibition of the TGF-beta1 signal, monitored by TGF-beta reporter assays. This attenuation was completely independent of receptor stimulation by beta-estradiol (E2) or inhibition by the pure antagonist ICI 182.780 (ICI). Our results indicate a permanent repression of PAI-1 by ERalpha and suggest a ligand-independent crosstalk between ERalpha and TGF-beta signaling in breast cancer cells.

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.

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.

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.