Investigation of three new mouse mammary tumor cell lines as models for transforming growth factor (TGF)-beta and Neu pathway signaling studies: identification of a novel model for TGF-beta-induced epithelial-to-mesenchymal transition

p130Cas induces bone invasion by oral squamous cell carcinoma by regulating tumor epithelial-mesenchymal transition and cell proliferation

Bone invasion is a critical factor in determining the prognosis of oral squamous cell carcinoma (OSCC) patients. Transforming growth factor β (TGF-β) is abundantly expressed in the bone matrix and is involved in the acquisition of aggressiveness by tumors. TGF-β is also important to cytoskeletal changes during tumor progression. In this study, we examined the relationship between TGF-β signaling and cytoskeletal changes during bone invasion by OSCC. Immunohistochemical staining of OSCC samples from five patients showed the expression of p130Cas (Crk-associated substrate) in the cytoplasm and phosphorylated Smad3 expression in the nucleus in OSCC cells. TGF-β1 induced the phosphorylation of Smad3 and p130Cas, as well as epithelial-mesenchymal transition (EMT) accompanied by the downregulation of the expression of E-cadherin, a marker of epithelial cells, and the upregulation of the expression of N-cadherin, or Snail, a marker of mesenchymal cells, in human HSC-2 cells and mouse squamous cell carcinome VII (SCCVII) cells. SB431542, a specific inhibitor of Smad2/3 signaling, abrogated the TGF-β1-induced phosphorylation of p130Cas and morphological changes. Silencing p130Cas using an short hairpin RNA (shRNA) or small interfering RNA in SCCVII cells suppressed TGF-β1-induced cell migration, invasion, EMT and matrix metalloproteinase-9 (MMP-9) production. Compared with control SCCVII cells, SCCVII cells with silenced p130Cas strongly suppressed zygomatic and mandibular destruction in vivo by reducing the number of osteoclasts, cell proliferation and MMP-9 production. Taken together, these results showed that the expression of TGF-β/p130Cas might be a new target for the treatment of OSCC bone invasion.

Physical and chemical microenvironmental cues orthogonally control the degree and duration of fibrosis-associated epithelial-to-mesenchymal transitions

Increased tissue stiffness and epithelial-to-mesenchymal transitions (EMTs) are two seemingly discrete hallmarks of fibrotic diseases. Despite recent findings highlighting the influence of tissue mechanical properties on cell phenotype, it remains unclear what role increased tissue stiffness has in the regulation of previously reported fibronectin-mediated EMTs associated with pulmonary fibrosis. Nano-indentation testing of lung interstitial spaces showed that in vivo cell-level Young's moduli increase with the onset of fibrosis from ∼2 to ∼17 kPa. In vitro, we found that stiff, but not soft, fibronectin substrates induce EMT, a response dependent on cell contraction-mediated integrin activation of TGFβ. Activation or suppression of cell contractility with exogenous factors was sufficient to overcome the effect of substrate stiffness. Pulse-chase experiments indicate that the effect of cell contractility is dose- and time-dependent. In response to low levels of TGFβ on soft surfaces, either added exogenously or produced through thrombin-induced contraction, cells will initiate the EMT programme, but upon removal revert to an epithelial phenotype. These results identify matrix stiffness and/or cell contractility as critical targets for novel therapeutics for fibrotic diseases.

Transforming growth factor-β transiently induces vimentin expression and invasive capacity in a canine mammary gland tumor cell line

The epithelial-mesenchymal transition (EMT) is a crucial event that occurs during cancer metastasis and can be induced by transforming growth factor-β (TGF-β) in various tumor cells in vitro. However, little is known about the effects of TGF-β in canine mammary gland tumors (CMGTs). Here, we investigated the role of TGF-β in CMGT. We observed that treatment of the CMGT cell line CHMp13a with TGF-β1 leads to transient induction of the mesenchymal marker vimentin. Real-time measurements of cellular electrical impedance also showed that CMGT invasiveness is transiently increased by TGF-β1 treatment, but is reversed after prolonged stimulation. This phenomenon is similar to the mesenchymal-epithelial transition (MET, the reverse phenomenon of EMT), and a process that is implicated in the establishment of secondary metastatic lesions.

A MULTI-STRATEGY APPROACH TO INFORMATIVE GENE IDENTIFICATION FROM GENE EXPRESSION DATA

An unsupervised multi-strategy approach has been developed to identify informative genes from high throughput genomic data. Several statistical methods have been used in the field to identify differentially expressed genes. Since different methods generate different lists of genes, it is very challenging to determine the most reliable gene list and the appropriate method. This paper presents a multi-strategy method, in which a combination of several data analysis techniques are applied to a given dataset and a confidence measure is established to select genes from the gene lists generated by these techniques to form the core of our final selection. The remainder of the genes that form the peripheral region are subject to exclusion or inclusion into the final selection. This paper demonstrates this methodology through its application to an in-house cancer genomics dataset and a public dataset. The results indicate that our method provides more reliable list of genes, which are validated using biological knowledge, biological experiments, and literature search. We further evaluated our multi-strategy method by consolidating two pairs of independent datasets, each pair is for the same disease, but generated by different labs using different platforms. The results showed that our method has produced far better results.

Prevention of mammary carcinogenesis in MMTV-neu mice by cruciferous vegetable constituent benzyl isothiocyanate

Benzyl isothiocyanate (BITC), a constituent of edible cruciferous vegetables, inhibits growth of human breast cancer cells in culture. The present study provides in vivo evidence for efficacy of BITC for prevention of mammary cancer in MMTV-neu mice. Administration of BITC at 1 and 3 mmol/kg diet for 25 weeks markedly suppressed the incidence and/or burden of mammary hyperplasia and carcinoma in female MMTV-neu mice without causing weight loss or affecting neu protein level. For example, cumulative incidence of hyperplasia/carcinoma was significantly lower in mice fed BITC-supplemented diets compared with control mice (P = 0.01 by Fisher's test). The BITC-mediated prevention of mammary carcinogenesis correlated with suppression of cell proliferation and increased apoptosis. The average number of Ki-67-positive cells in the carcinoma lesions of 3 mmol BITC group was lower by approximately 21% (P < 0.05) compared with tumors from control mice. Apoptotic bodies in the mammary tumor were higher by about 2- to 2.5-fold in the 1 and 3 mmol BITC treatment groups (P < 0.05) compared with control group. The BITC administration also resulted in overexpression of E-cadherin and infiltration of CD3(+) T-cells in the tumor. Although BITC treatment increased cytotoxicity of natural killer (NK) cells in vitro, dietary feeding of BITC failed to augment NK cell lytic activity in an ex vivo assay. The present study demonstrating efficacy of BITC against mammary cancer in an animal model provides impetus to determine its activity in a clinical setting.

Transcriptome profiling of a TGF-beta-induced epithelial-to-mesenchymal transition reveals extracellular clusterin as a target for therapeutic antibodies

Transforming growth factor (TGF)-beta plays a dual role in tumorigenesis, switching from acting as a growth inhibitory tumor suppressor early in the process, to a tumor promoter in late-stage disease. Since TGF-beta's prometastatic role may be linked to its ability to induce tumor cell epithelial-to-mesenchymal transition (EMT), we explored TGF-beta's EMT-promoting pathways by analysing the transcriptome changes occurring in BRI-JM01 mammary tumor epithelial cells undergoing a TGF-beta-induced EMT. We found the clusterin gene to be the most highly upregulated throughout most of the TGF-beta time course, and showed that this results in an increase of the secreted form of clusterin. By monitoring several hallmark features of EMT, we demonstrated that antibodies targeting secreted clusterin inhibit the TGF-beta-induced EMT of BRI-JM01 cells, as well as the invasive phenotype of several other breast and prostate tumor cell lines (4T1, NMuMG, MDA-MB231LM2 and PC3), without affecting the proliferation of these cells. These results indicate that secreted clusterin is a functionally important EMT mediator that lies downstream within TGF-beta's EMT-promoting transcriptional cascade, but not within its growth-inhibitory pathways. To further investigate the role played by secreted clusterin in tumor metastasis, we assessed the effect of several anti-clusterin monoclonal antibodies in vivo using a 4T1 syngeneic mouse breast cancer model and found that these antibodies significantly reduce lung metastasis. Taken together, our results reveal a role for secreted clusterin as an important extracellular promoter of EMT, and suggest that antibodies targeting clusterin may inhibit tumor metastasis without reducing the beneficial growth inhibitory effects of TGF-beta.

Glycoproteomic analysis of two mouse mammary cell lines during transforming growth factor (TGF)-beta induced epithelial to mesenchymal transition

BACKGROUND

TGF-beta acts as an antiproliferative factor in normal epithelial cells and at early stages of oncogenesis. However, later in tumor development TGF-beta can become tumor promoting through mechanisms including the induction of epithelial-to-mesenchymal transition (EMT), a process that is thought to contribute to tumor progression, invasion and metastasis. To identify EMT-related breast cancer therapeutic targets and biomarkers, we have used two proteomic approaches to find proteins that change in abundance upon the induction of EMT by TGF-beta in two mouse mammary epithelial cell lines, NMuMG and BRI-JM01.

RESULTS

Preliminary experiments based on two-dimensional electrophoresis of a hydrophobic cell fraction identified only 5 differentially expressed proteins from BRI-JM01 cells. Since 3 of these proteins were glycoproteins, we next used the lectin, wheat germ agglutinin (WGA), to enrich for glycoproteins, followed by relative quantification of tryptic peptides using a label-free LC-MS based method. Using these approaches, we identified several proteins that are modulated during the EMT process, including cell adhesion molecules (several members of the Integrin family, Fibronectin, Activated leukocyte cell adhesion molecule, and Neural cell adhesion molecule 1) and regulators of cellular signaling (Tumor-associated calcium signal transducer 2, Basigin).

CONCLUSION

Interestingly, despite the fact that TGF-beta induces similar EMT phenotypes in NMuMG and BRI-JM01 cells, the proteomic results for the two cell lines showed only minimal overlap. These differences likely result in part from the conservative cut-off values used to define differentially-expressed proteins in these experiments. Alternatively, it is possible that the two cell lines may use different mechanisms to achieve an EMT transition.

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.

Complexity in interpretation of embryonic epithelial-mesenchymal transition in response to transforming growth factor-beta signaling

Epithelial-mesenchymal transition (EMT) is a highly conserved and fundamental process that governs morphogenesis in development and may also contribute to cancer metastasis. Transforming growth factor (TGF-beta) is a potent inducer of EMT in various developmental and tumor systems. The analysis of TGF-beta signal transduction pathways is now considered a critically important area of biology, since many defects occur in these pathways in embryonic development. The complexity of TGF-beta signal transduction networks is overwhelming due to the large numbers of interacting constituents, complicated feedforward, feedback and crosstalk circuitry mechanisms that they involve in addition to the cellular kinetics and enzymatics that contribute to cell signaling. As a result of this complexity, apparently simple but highly important questions remain unanswered, that is, how do epithelial cells respond to such TGF-beta signals? System biology and cellular kinetics play a crucial role in cellular function; omissions of such a critical contributor may lead to inaccurate understanding of embryonic EMT. In this review, we identify and explain why certain conditions need to be considered for a true representation of TGF-beta signaling in vivo to better understand the controlled, yet delicate mechanism of embryonic EMT.

Transforming growth factor-beta1 induces an epithelial-to-mesenchymal transition state in mouse hepatocytes in vitro

Liver fibrosis is a progressive pathologic process that involves deposition of excess extracellular matrix leading to distorted architecture and culminating in cirrhosis. The role of transforming growth factor-beta (TGF-beta) as a key molecule in the development and progression of hepatic fibrosis via the activation of hepatic stellate cells, among other fibroblast populations, is without controversy. We hereby show that TGF-beta1 induces an epithelial-to-mesenchymal transition (EMT) state in mature hepatocytes in vitro. EMT state was marked by significant upregulation of alpha(1)(I) collagen mRNA expression and type I collagen deposition. Similar changes were found in a "normal" mouse hepatocyte cell line (AML12), thus confirming that hepatocytes are capable of EMT changes and type I collagen synthesis. We also show that in hepatocytes in the EMT state, TGF-beta1 induces the snail-1 transcription factor and activates the Smad2/3 pathway. Evidence for a central role of the TGF-beta1/Smad pathway is further supported by the inhibition of EMT by Smad4 silencing using small interference RNA technology. In conclusion, TGF-beta1, a known pro-apoptotic cytokine in mature hepatocytes, is capable of mediating phenotypic changes and plasticity in the form of EMT, resulting in collagen deposition. Our findings support a potentially crucial role for EMT in the development and progression of hepatic fibrogenesis.

TGF-beta 1 could be a missing link in the interplay between ER and HER-2 in breast cancer

Breast cancer is a very heterogeneous disease considering a number of biomarkers which are under investigation. However, most important biomarkers in a clinical setting are ER (estrogen receptors) and HER-2 (human epidermal growth factor receptor 2), but still only as predictive markers for tamoxifen and trastuzumab therapy. Their prognostic role is still subject of investigation. On the other hand, although, TGF-beta1 is known as marker of invasiveness and metastatic capacity of breast cancer cells, this marker has never been considered to be introduced in routine clinical setting. TGF-beta1 is ER regulated biomarker which act synergistically with HER-2. Aim of this study is to show that clinical significance of determination ER and HER-2 status could be improved, when they are related with TGF-beta1 as additional biomarker. It seems that TGF-beta1 could make a difference regarding prognosis and prediction in breast cancer patients. This hypothesis could be easily verified in corresponding clinical research.