TP53-status dependent oncogenic EZH2 Activity in Pancreatic Cancer

Pancreatic Ductal Adenocarcinoma (PDAC) remains a dismal malignancy with a 5-year sur-vival rate of less than 10%. Predominately, chemoresistance mediated by the dynamic cel-lular plasticity induced through epigenetic alterations accounts for the high mortality rates of PDAC. The histone methyltransferase enhancer of zeste homolog 2 (EZH2), the catalytic component of the polycomb repressive complex 2 (PRC2), is frequently found overex-pressed in PDAC and has crucial functions in the evasion of tumor-suppressive mecha-nisms. However, recent studies suggest a huge context-dependency of oncogenic EZH2 activity. The tumor suppressor p53 is well characterized for its anti-tumorigenic capacities. However, in human PDAC, TP53 mutations occur with a prevalence of 50-80%, potentially resulting in the loss of tumor suppressor function and the gain of oncogenic function suggesting a TP53-status-dependent functional behaviour of a cell. However, whether and to what extent mutations of TP53 indeed functionally or mechanistically influence EZH2-dependent pro-cesses in PDAC remains largely elusive. In this study, the impact of a specific genetic back-ground on the activity of epigenetic processes has been investigated. The major aim was to illuminate TP53-status-dependent oncogenic EZH2 activity in PDAC progression. Functionally, we demonstrate that EZH2-dependent target gene regulation is determined by the TP53-status and that EZH2 depletion correlates with a better prognosis only in TP53wt PDAC. Moreover, we reveal that EZH2 depletion combined with chemotherapy in-creases apoptosis induction restrictively in TP53wt cells. Hence, our study highlights a strong context-dependency of the EZH2 activity specifically regarding the TP53-status. Therefore, our data suggest that in PDAC subtypes with TP53wt-status, EZH2 depletion together with chemotherapy might represent a beneficial strategy to tackle PDAC, whereas in TP53-mutant PDAC, EZH2 depletion is not advantageous. Furthermore, our findings imply that EZH2 influences p53wt expression on a post-transla-tional level and illustrate that EZH2 targets the CDKN2A gene for transcriptional repression, thus abrogating p14ARF/p19Arf-dependent inhibition of Mdm2-mediated p53 degradation. Moreover, we reveal that PDAC formation is promoted despite TP53wt-status and low EZH2 expression, if EZH2-independent CDKN2A repression occurs, thus demonstrating the im-portance of an intact CDKN2A-TP53wt axis for a beneficial outcome of EZH2 inhibition in PDAC. Moreover, we revealed the existence of a previously unknown EZH2-p53-complex in PDAC, suggesting that also non-canonical functions of EZH2 may contribute to PDAC progression. Conclusively, our data underline the significance of patient stratification to predict and im-prove EZH2 inhibition as a potential treatment strategy in PDAC.2023-06-3

Chromatin-Independent Interplay of NFATc1 and EZH2 in Pancreatic Cancer

Background: The Nuclear Factor of Activated T-cells 1 (NFATc1) transcription factor and the methyltransferase Enhancer of Zeste Homolog 2 (EZH2) significantly contribute to the aggressive phenotype of pancreatic ductal adenocarcinoma (PDAC). Herein, we aimed at dissecting the mechanistic background of their interplay in PDAC progression. Methods: NFATc1 and EZH2 mRNA and protein expression and complex formation were determined in transgenic PDAC models and human PDAC specimens. NFATc1 binding on the Ezh2 gene and the consequences of perturbed NFATc1 expression on Ezh2 transcription were explored by Chromatin Immunoprecipitation (ChIP) and upon transgenic or siRNA-mediated interference with NFATc1 expression, respectively. Integrative analyses of RNA- and ChIP-seq data was performed to explore NFATc1-/EZH2-dependent gene signatures. Results: NFATc1 targets the Ezh2 gene for transcriptional activation and biochemically interacts with the methyltransferase in murine and human PDAC. Surprisingly, our genome-wide binding and expression analyses do not link the protein complex to joint gene regulation. In contrast, our findings provide evidence for chromatin-independent functions of the NFATc1:EZH2 complex and reveal posttranslational EZH2 phosphorylation at serine 21 as a prerequisite for robust complex formation. Conclusion: Our findings disclose a previously unknown NFATc1-EZH2 axis operational in the pancreas and provide mechanistic insights into the conditions fostering NFATc1:EZH2 complex formation in PDAC

<i>TP53</i>-Status-Dependent Oncogenic EZH2 Activity in Pancreatic Cancer

Pancreatic Ductal Adenocarcinoma (PDAC) represents a lethal malignancy with a consistently poor outcome. Besides mutations in PDAC driver genes, the aggressive tumor biology of the disease and its remarkable therapy resistance are predominantly installed by potentially reversible epigenetic dysregulation. However, epigenetic regulators act in a context-dependent manner with opposing implication on tumor progression, thus critically determining the therapeutic efficacy of epigenetic targeting. Herein, we aimed at exploring the molecular prerequisites and underlying mechanisms of oncogenic Enhancer of Zeste Homolog 2 (EZH2) activity in PDAC progression. Preclinical studies in EZH2 proficient and deficient transgenic and orthotopic in vivo PDAC models and transcriptome analysis identified the TP53 status as a pivotal context-defining molecular cue determining oncogenic EZH2 activity in PDAC. Importantly, the induction of pro-apoptotic gene signatures and processes as well as a favorable PDAC prognosis upon EZH2 depletion were restricted to p53 wildtype (wt) PDAC subtypes. Mechanistically, we illustrate that EZH2 blockade de-represses CDKN2A transcription for the subsequent posttranslational stabilization of p53wt expression and function. Together, our findings suggest an intact CDKN2A-p53wt axis as a prerequisite for the anti-tumorigenic consequences of EZH2 depletion and emphasize the significance of molecular stratification for the successful implementation of epigenetic targeting in PDAC