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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. Graphical Abstract 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.

The mechanisms that initiate heterochromatin formation and maintain its distinction from euchromatin have remained elusive. However, a new study reveals a pathway in which transcriptional repression of pericentric repeats by sequence-specific transcription factors is essential for the integrity of heterochromatin, thereby considerably expanding the role of transcription factors beyond euchromatic gene regulation. Heterochromatin is important for genome integrity and stabilization of gene-expression programs. We have identified the transcription factors Pax3 and Pax9 as redundant regulators of mouse heterochromatin, as they repress RNA output from major satellite repeats by associating with DNA within pericentric heterochromatin. Simultaneous depletion of Pax3 and Pax9 resulted in dramatic derepression of major satellite transcripts, persistent impairment of heterochromatic marks and defects in chromosome segregation. Genome-wide analyses of methylated histone H3 at Lys9 showed enrichment at intergenic major satellite repeats only when these sequences retained intact binding sites for Pax and other transcription factors. Additionally, bioinformatic interrogation of all histone methyltransferase Suv39h–dependent heterochromatic repeat regions in the mouse genome revealed a high concordance with the presence of transcription factor binding sites. These data define a general model in which reiterated arrangement of transcription factor binding sites within repeat sequences is an intrinsic mechanism of the formation of heterochromatin.

Notch signalling is important for development and tissue homeostasis and activated in many human cancers. Nevertheless, mutations in Notch pathway components are rare in solid tumours. ZEB1 is an activator of an epithelial–mesenchymal transition (EMT) and has crucial roles in tumour progression towards metastasis. ZEB1 and miR‐200 family members repress expression of each other in a reciprocal feedback loop. Since miR‐200 members target stem cell factors, ZEB1 indirectly induces stemness maintenance and associated drug resistance. Here, we link ZEB1 and its cancer promoting properties to Notch activation. We show that miR‐200 members target Notch pathway components, such as Jagged1 (Jag1) and the mastermind‐like coactivators Maml2 and Maml3, thereby mediating enhanced Notch activation by ZEB1. We further detected a coordinated upregulation of Jag1 and ZEB1, associated with reduced miR‐200 expression in two aggressive types of human cancer, pancreatic adenocarcinoma and basal type of breast cancer. These findings explain increased Notch signalling in some types of cancers, where mutations in Notch pathway genes are rare. Moreover, they indicate an additional way how ZEB1 exerts its tumour progressing functions. The ZEB1 transcription factor and miRNA‐200 repress each others’ expression, with important consequences for tumour metastasis. Here, Notch pathway components are found as miR‐200 targets, identifying a pathway whereby ZEB1 promotes Notch signalling in cancer cells. See also Vallejo et al in this issue.

Nat. Struct. Mol. Biol. 19, 1023–1030 (2012); published online 16 September 2012; corrected after print 27 December 2012 In the version of this article initially published, Simone Meidhof's affiliations should have included Spemann Graduate School of Biology and Medicine (SGBM), Albert Ludwigs University Freiburg, Freiburg, Germany and the Faculty of Biology, Albert Ludwigs University Freiburg, Freiburg, Germany.

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.