Early dissemination, metastasis and therapy resistance are central hallmarks of aggressive cancer types and the leading cause of cancer-associated deaths. The EMT-inducing transcriptional repressor ...ZEB1 is a crucial stimulator of these processes, particularly by coupling the activation of cellular motility with stemness and survival properties. ZEB1 expression is associated with aggressive behaviour in many tumour types, but the potent effects cannot be solely explained by its proven function as a transcriptional repressor of epithelial genes. Here we describe a direct interaction of ZEB1 with the Hippo pathway effector YAP, but notably not with its paralogue TAZ. In consequence, ZEB1 switches its function to a transcriptional co-activator of a 'common ZEB1/YAP target gene set', thereby linking two pathways with similar cancer promoting effects. This gene set is a predictor of poor survival, therapy resistance and increased metastatic risk in breast cancer, indicating the clinical relevance of our findings.
The ZEB1 transcription factor is best known as an inducer of epithelial-mesenchymal transitions (EMT) in cancer metastasis, acting through transcriptional repression of CDH1 (encoding E-cadherin) and ...the EMT-suppressing microRNA-200s (miR-200s). Here we analyze roles of the ZEB1 zebrafish orthologs, Zeb1a and Zeb1b, and of miR-200s in control of cell adhesion and morphogenesis during gastrulation and segmentation stages. Loss and gain of function analyses revealed that Zeb1 represses cdh1 expression to fine-tune adhesiveness of migrating deep blastodermal cells. Furthermore, Zeb1 acts as a repressor of epcam in the deep cells of the blastoderm and may contribute to control of epithelial integrity of enveloping layer cells, the outermost cells of the blastoderm. We found a similar ZEB1-dependent repression of EPCAM expression in human pancreatic and breast cancer cell lines, mediated through direct binding of ZEB1 to the EPCAM promoter. Thus, Zeb1 proteins employ several evolutionary conserved mechanisms to regulate cell-cell adhesion during development and cancer.
Background: Regulation of cell adhesion is important for embryonic development and to prevent cancer metastasis.
Results: Zeb1 controls cell adhesion in zebrafish embryos and human cancer cell lines through transcriptional repression of E-cadherin, Epcam, and miR-200s.
Conclusion: Zeb1 fine-tunes E-cadherin- and Epcam-mediated cell adhesion to control cell behavior during gastrulation.
Significance: Conserved cell adhesion regulation mechanisms are crucial for understanding development and cancer invasion.
Invasion and metastasis of carcinomas are often activated by induction of aberrant epithelial–mesenchymal transition (EMT). This is mainly driven by the transcription factor ZEB1, promoting ...tumor‐initiating capacity correlated with increased expression of the putative stem cell marker CD44. However, the direct link between ZEB1, CD44 and tumourigenesis is still enigmatic. Remarkably, EMT‐induced repression of ESRP1 controls alternative splicing of CD44, causing a shift in the expression from the variant CD44v to the standard CD44s isoform. We analyzed whether CD44 and ZEB1 regulate each other and show that ZEB1 controls CD44s splicing by repression of ESRP1 in breast and pancreatic cancer. Intriguingly, CD44s itself activates the expression of ZEB1, resulting in a self‐sustaining ZEB1 and CD44s expression. Activation of this novel CD44s‐ZEB1 regulatory loop has functional impact on tumor cells, as evident by increased tumor‐sphere initiation capacity, drug‐resistance and tumor recurrence. In summary, we identified a self‐enforcing feedback loop that employs CD44s to activate ZEB1 expression. This renders tumor cell stemness independent of external stimuli, as ZEB1 downregulates ESRP1, further promoting CD44s isoform synthesis.
What's new?
The acquisition of an aggressive phenotype in tumors is associated with the epithelial–mesenchymal transition (EMT) program and expression of EMT activators, particularly ZEB1. ZEB1 expression is correlated with expression of CD44, a cancer stem cell marker. The authors of this study have uncovered a self‐sustaining regulatory feedback loop between ZEB1 and CD44. Initial EMT‐inducing activity promotes signaling via the mesenchymal CD44 isoform (CD44s), which regulates ZEB1 expression. ZEB1, in turn, represses the epithelial splicing regulator ESRP1, thereby enforcing CD44s splicing and allowing cancer cells to become independent of external EMT stimuli to provide stemness and metastasis.
Tumor cell invasion, dissemination and metastasis is triggered by an aberrant activation of epithelial-to-mesenchymal transition (EMT), often mediated by the transcription factor ZEB1. Disseminating ...tumor cells must acquire specific features that allow them to colonize at different organ sites. Here we identify a set of genes that is highly expressed in breast cancer bone metastasis and activated by ZEB1. This gene set includes various secreted factors, e.g. the BMP-inhibitor FST, that are described to reorganize the bone microenvironment. By inactivating BMP-signaling, BMP-inhibitors are well-known to induce osteolysis in development and disease. We here demonstrate that the expression of ZEB1 and BMP-inhibitors is correlated with bone metastasis, but not with brain or lung metastasis of breast cancer patients. In addition, we show that this correlated expression pattern is causally linked, as ZEB1 induces the expression of the BMP-inhibitors NOG, FST and CHRDL1 both by directly increasing their gene transcription, as well as by indirectly suppressing their reduction via miR-200 family members. Consequently, ZEB1 stimulates BMP-inhibitor mediated osteoclast differentiation. These findings suggest that ZEB1 is not only driving EMT, but also contributes to the formation of osteolytic bone metastases in breast cancer.
Therapy resistance is a major clinical problem in cancer medicine and crucial for disease relapse and progression. Therefore, the clinical need to overcome it, particularly for aggressive tumors such ...as pancreatic cancer, is very high. Aberrant activation of an epithelial–mesenchymal transition (EMT) and an associated cancer stem cell phenotype are considered a major cause of therapy resistance. Particularly, the EMT‐activator ZEB1 was shown to confer stemness and resistance. We applied a systematic, stepwise strategy to interfere with ZEB1 function, aiming to overcome drug resistance. This led to the identification of both its target gene miR‐203 as a major drug sensitizer and subsequently the class I HDAC inhibitor mocetinostat as epigenetic drug to interfere with ZEB1 function, restore miR‐203 expression, repress stemness properties, and induce sensitivity against chemotherapy. Thereby, mocetinostat turned out to be more effective than other HDAC inhibitors, such as SAHA, indicating the relevance of the screening strategy. Our data encourage the application of mechanism‐based combinations of selected epigenetic drugs with standard chemotherapy for the rational treatment of aggressive solid tumors, such as pancreatic cancer.
Synopsis
Therapy resistance is a major problem in cancer medicine. Based on the identification of novel mediators of ZEB1‐associated therapy resistance, the HDAC inhibitor mocetinostat is found to efficiently restore drug sensitivity in aggressive cancer cells.
Strategy to counteract the well‐known cancer‐promoting functions of the EMT inducer ZEB1.
Identification of the stemness‐inhibiting microRNA miR‐203 as major ZEB1 target inducing drug sensitivity.
Identification of the class I HDAC inhibitor mocetinostat as drug to interfere with ZEB1 function and overcome ZEB1‐associated drug resistance.
Mocetinostat has better effects in combination with chemotherapeutics compared to other HDACis, such as SAHA.
Blueprint for further drug screens with reduction in ZEB1 function as major readout.
Therapy resistance is a major problem in cancer medicine. Based on the identification of novel mediators of ZEB1‐associated therapy resistance, the HDAC inhibitor mocetinostat is found to efficiently restore drug sensitivity in aggressive cancer cells.
Cancer metastasis is the main reason for poor patient survival. Tumor cells delaminate from the primary tumor by induction of epithelial-mesenchymal transition (EMT). EMT is mediated by key ...transcription factors, including ZEB1, activated by tumor cell interactions with stromal cells and the extracellular matrix (ECM). ZEB1-mediated EMT and motility is accompanied by substantial cell reprogramming and the acquisition of a stemness phenotype. However, understanding of the underlying mechanism is still incomplete. We identified hyaluronic acid (HA), one major ECM proteoglycan and enriched in mammary tumors, to support EMT and enhance ZEB1 expression in cooperation with CD44s. In breast cancer cell lines HA is synthesized mainly by HAS2, which was already shown to be implicated in cancer progression. ZEB1 and HAS2 expression strongly correlates in various cancer entities and high HAS2 levels associate with an early relapse. We identified HAS2, tumor cell-derived HA and ZEB1 to form a positive feedback loop as ZEB1, elevated by HA, directly activates HAS2 expression. In an in vitro differentiation model HA-conditioned medium of breast cancer cells is enhancing osteoclast formation, an indicator of tumor cell-induced osteolysis that facilitates formation of bone metastasis. In combination with the previously identified ZEB1/ESRP1/CD44s feedback loop, we found a novel autocrine mechanism how ZEB1 is accelerating EMT.
Invasion and metastasis of carcinomas are often activated by induction of aberrant epithelial–mesenchymal transition (EMT). This is mainly driven by the transcription factor ZEB1, promoting ...tumor‐initiating capacity correlated with increased expression of the putative stem cell marker CD44. However, the direct link between ZEB1, CD44 and tumourigenesis is still enigmatic. Remarkably, EMT‐induced repression of
ESRP1
controls alternative splicing of
CD44
, causing a shift in the expression from the variant CD44v to the standard CD44s isoform. We analyzed whether CD44 and ZEB1 regulate each other and show that ZEB1 controls
CD44s
splicing by repression of
ESRP1
in breast and pancreatic cancer. Intriguingly, CD44s itself activates the expression of
ZEB1
, resulting in a self‐sustaining
ZEB1
and
CD44s
expression. Activation of this novel CD44s‐ZEB1 regulatory loop has functional impact on tumor cells, as evident by increased tumor‐sphere initiation capacity, drug‐resistance and tumor recurrence. In summary, we identified a self‐enforcing feedback loop that employs CD44s to activate
ZEB1
expression. This renders tumor cell stemness independent of external stimuli, as ZEB1 downregulates
ESRP1
, further promoting CD44s isoform synthesis.
What's new?
The acquisition of an aggressive phenotype in tumors is associated with the epithelial–mesenchymal transition (EMT) program and expression of EMT activators, particularly ZEB1. ZEB1 expression is correlated with expression of CD44, a cancer stem cell marker. The authors of this study have uncovered a self‐sustaining regulatory feedback loop between ZEB1 and CD44. Initial EMT‐inducing activity promotes signaling
via
the mesenchymal CD44 isoform (CD44s), which regulates ZEB1 expression. ZEB1, in turn, represses the epithelial splicing regulator ESRP1, thereby enforcing CD44s splicing and allowing cancer cells to become independent of external EMT stimuli to provide stemness and metastasis.
Therapy resistance is a major clinical problem in cancer medicine and crucial for disease relapse and progression. Therefore, the clinical need to overcome it, particularly for aggressive tumors such ...as pancreatic cancer, is very high. Aberrant activation of an epithelial–mesenchymal transition (EMT) and an associated cancer stem cell phenotype are considered a major cause of therapy resistance. Particularly, the EMT‐activator ZEB1 was shown to confer stemness and resistance. We applied a systematic, stepwise strategy to interfere with ZEB1 function, aiming to overcome drug resistance. This led to the identification of both its target gene miR‐203 as a major drug sensitizer and subsequently the class I HDAC inhibitor mocetinostat as epigenetic drug to interfere with ZEB1 function, restore miR‐203 expression, repress stemness properties, and induce sensitivity against chemotherapy. Thereby, mocetinostat turned out to be more effective than other HDAC inhibitors, such as SAHA, indicating the relevance of the screening strategy. Our data encourage the application of mechanism‐based combinations of selected epigenetic drugs with standard chemotherapy for the rational treatment of aggressive solid tumors, such as pancreatic cancer.
The Southern Ocean is characterized by longitudinal water circulations crossed by strong latitudinal gradients. How this oceanographic background shapes planktonic populations is largely unknown, ...despite the significance of this region for global biogeochemical cycles. Here, we show, based on genomic, morphometric, ecophysiological and mating compatibility data, an example of ecotypic differentiation and speciation within an endemic pelagic inhabitant, the diatom Fragilariopsis kerguelensis. We discovered three genotypic variants, one present throughout the latitudinal transect sampled, the others restricted to the north and south, respectively. The latter two showed reciprocal monophyly across all three genomes and significant ecophysiological differences consistent with local adaptation, but produced viable offspring in laboratory crosses. The third group was also reproductively isolated from the latter two. We hypothesize that this pattern originated by an adaptive expansion accompanied by ecotypic divergence, followed by sympatric speciation.
see also the Perspective by Jean‐David Grattepanche
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