ZEB1 expression in type I vs type II endometrial cancers: a marker of aggressive disease

ZEB1 in Pancreatic Cancer

Pancreatic cancer is one of the most malignant human neoplasias. On the molecular level, epithelial-mesenchymal transition (EMT) has been demonstrated to contribute to the malignant phenotype of pancreatic cancer cells. ZEB1 is a transcriptional repressor that has been identified as an inducer of EMT. A negative feedback loop between ZEB1 and microRNA-200c has been shown to regulate this EMT induction in various models. With respect to pancreatic cancer, primary effects of EMT comprise increased local and distant tumor cell dissemination. Another recently described feature of the EMT is the acquisition of cancer stem cell traits. For pancreatic cancer cells, antagonism between ZEB1 and stemness-inhibiting micro-RNAs has been demonstrated to contribute to this process, providing experimental support for the migrating cancer stem cell (MCSC) hypothesis. ZEB1 has also been shown to be associated with drug resistance of pancreatic cancer cells. This article reviews the biological functions of ZEB1 with a focus on pancreatic cancer.

The ZEB/miR-200 feedback loop--a motor of cellular plasticity in development and cancer?

Epithelial-to-mesenchymal transition (EMT) is a fundamental process in development and disease. Zinc-finger enhancer binding (ZEB) transcription factors (ZEB1 and ZEB2) are crucial EMT activators, whereas members of the miR-200 family induce epithelial differentiation. They are reciprocally linked in a feedback loop, each strictly controlling the expression of the other. Now data show that EMT not only confers cellular motility, but also induces stem-cell properties and prevents apoptosis and senescence. Thus the balanced expression of ZEB factors and miR-200 controls all these processes. We therefore propose that the ZEB/miR-200 feedback loop is the molecular motor of cellular plasticity in development and disease, and in particular is a driving force for cancer progression towards metastasis by controlling the state of cancer stem cells.

Mechanisms of the epithelial-mesenchymal transition by TGF-beta

The formation of epithelial cell barriers results from the defined spatiotemporal differentiation of stem cells into a specialized and polarized epithelium, a process termed mesenchymal-epithelial transition. The reverse process, epithelial-mesenchymal transition (EMT), is a metastable process that enables polarized epithelial cells to acquire a motile fibroblastoid phenotype. Physiological EMT also plays an essential role in promoting tissue healing, remodeling or repair in response to a variety of pathological insults. On the other hand, pathophysiological EMT is a critical step in mediating the acquisition of metastatic phenotypes by localized carcinomas. Although metastasis clearly is the most lethal aspect of cancer, our knowledge of the molecular events that govern its development, including those underlying EMT, remain relatively undefined. Transforming growth factor-beta (TGF-beta) is a multifunctional cytokine that oversees and directs all aspects of cell development, differentiation and homeostasis, as well as suppresses their uncontrolled proliferation and transformation. Quite dichotomously, tumorigenesis subverts the tumor suppressing function of TGF-beta, and in doing so, converts TGF-beta to a tumor promoter that stimulates pathophysiological EMT and metastasis. It therefore stands to reason that determining how TGF-beta induces EMT in developing neoplasms will enable science and medicine to produce novel pharmacological agents capable of preventing its ability to do so, thereby improving the clinical course of cancer patients. Here we review the cellular, molecular and microenvironmental mechanisms used by TGF-beta to mediate its stimulation of EMT in normal and malignant cells.

Loss of miR-200c: A Marker of Aggressiveness and Chemoresistance in Female Reproductive Cancers

We focus on unique roles of miR-200c in breast, ovarian, and endometrial cancers. Members of the miR-200 family target ZEB1, a transcription factor which represses E-cadherin and other genes involved in polarity. We demonstrate that the double negative feedback loop between miR-200c and ZEB1 is functional in some, but not all cell lines. Restoration of miR-200c to aggressive cancer cells causes a decrease in migration and invasion. These effects are independent of E-cadherin status. Additionally, we observe that restoration of miR-200c to ovarian cancer cells causes a decrease in adhesion to laminin. We have previously reported that reintroduction of miR-200c to aggressive cells that lack miR-200c expression restores sensitivity to paclitaxel. We now prove that this ability is a result of direct targeting of class III beta-tubulin (TUBB3). Introduction of a TUBB3 expression construct lacking the miR-200c target site into cells transfected with miR-200c mimic results in no change in sensitivity to paclitaxel. Lastly, we observe a decrease in proliferation in cells transfected with miR-200c mimic, and cells where ZEB1 is knocked down stably, demonstrating that the ability of miR-200c to enhance sensitivity to paclitaxel is not due to an increased proliferation rate.

Reciprocal regulation of ZEB1 and AR in triple negative breast cancer cells

Zinc-finger enhancer binding protein (ZEB1) is a transcription factor involved in the progression of cancer primarily through promoting epithelial to mesenchymal transition (EMT). ZEB1 represses the expression of E-cadherin by binding to E-box sequences in the promoter, thus decreasing epithelial differentiation. We show that ZEB1 and androgen receptor (AR) cross-talk in triple negative breast cancer cell lines. Chromatin immunoprecipitation analysis demonstrates that ZEB1 binds directly to the E-box located in the AR promoter. ZEB1 suppression by stably transfecting shRNA in a triple negative breast cancer cell line resulted in a decrease of AR mRNA, protein, and AR downstream targets. ZEB1 knockdown in triple negative breast cancer cells sensitized the cells to bicalutamide by reducing migration compared to the control cells. Conversely, blockade of AR signaling with bicalutamide resulted in a suppression of ZEB1 protein expression in two triple negative breast cancer cell lines. Furthermore, using a breast cancer tissue microarray, a majority of triple negative breast cancers exhibit positive staining for both ZEB1 and AR. Taken together, these results indicate that ZEB1 and AR regulate each other to promote cell migration in triple negative breast cancer cells.

E-cadherin, beta-catenin, and ZEB1 in malignant progression of cancer

The embryonic program 'epithelial-mesenchymal transition' (EMT) is activated during tumor invasion in disseminating cancer cells. Characteristic to these cells is a loss of E-cadherin expression, which can be mediated by EMT-inducing transcriptional repressors, e.g. ZEB1. Consequences of a loss of E-cadherin are an impairment of cell-cell adhesion, which allows detachment of cells, and nuclear localization of beta-catenin. In addition to an accumulation of cancer stem cells, nuclear beta-catenin induces a gene expression pattern favoring tumor invasion, and mounting evidence indicates multiple reciprocal interactions of E-cadherin and beta-catenin with EMT-inducing transcriptional repressors to stabilize an invasive mesenchymal phenotype of epithelial tumor cells.

MicroRNA-200c mitigates invasiveness and restores sensitivity to microtubule-targeting chemotherapeutic agents

The transcription factor ZEB1 is normally not expressed in epithelial cells. When inappropriately expressed in carcinomas, ZEB1 initiates epithelial to mesenchymal transition due to its ability to repress E-cadherin and other genes involved in polarity. Recently, ZEB1 and ZEB2 have been identified as direct targets of the microRNA-200c family. We find that miR-200c levels are high in well-differentiated endometrial, breast, and ovarian cancer cell lines, but extremely low in poorly differentiated cancer cells. Low or absent miR-200c results in aberrant expression of ZEB1 and consequent repression of E-cadherin. Reinstatement of miR-200c to such cells restores E-cadherin and dramatically reduces migration and invasion. Microarray profiling reveals that in addition to ZEB1 and ZEB2, other mesenchymal genes (such as FN1, NTRK2, and QKI), which are also predicted direct targets of miR-200c, are indeed inhibited by addition of exogenous miR-200c. One such gene, class III β-tubulin (TUBB3), which encodes a tubulin isotype normally found only in neuronal cells, is a direct target of miR-200c. This finding is of particular significance because we show that restoration of miR-200c increases sensitivity to microtubule-targeting agents by 85%. Because expression of TUBB3 is a common mechanism of resistance to microtubule-binding chemotherapeutic agents in many types of solid tumors, the ability of miR-200c to restore chemosensitivity to such agents may be explained by its ability to reduce TUBB3. Because miR-200c is crucial for maintenance of epithelial identity, behavior, and sensitivity to chemotherapy, we propose that it warrants further investigation as a therapeutic strategy for aggressive, drug-resistant cancers.