YAP and TAZ are intracellular messengers communicating multiple interacting extracellular biophysical and biochemical cues to the transcription apparatus in the nucleus and back to the cell/tissue microenvironment interface through the regulation of cytoskeletal and extracellular matrix components. Their activity is negatively and positively controlled by multiple phosphorylation events. Phenotypically, they serve an important role in cellular plasticity and lineage determination during development. As they regulate self-renewal, proliferation, migration, invasion and differentiation of stem cells, perturbed expression of YAP/TAZ signaling components play important roles in tumorigenesis and metastasis. Despite their high structural similarity, YAP and TAZ are functionally not identical and may play distinct cell type and differentiation stage-specific roles mediated by a diversity of downstream effectors and upstream regulatory molecules. However, YAP and TAZ are frequently looked at as functionally redundant and are not sufficiently discriminated in the scientific literature. As the extracellular matrix composition and mechanosignaling are of particular relevance in bone formation during embryogenesis, post-natal bone elongation and bone regeneration, YAP/TAZ are believed to have critical functions in these processes. Depending on the differentiation stage of mesenchymal stem cells during endochondral bone development, YAP and TAZ serve distinct roles, which are also reflected in bone tumors arising from the mesenchymal lineage at different developmental stages. Efforts to clinically translate the wealth of available knowledge of the pathway for cancer diagnostic and therapeutic purposes focus mainly on YAP and TAZ expression and their role as transcriptional co-activators of TEAD transcription factors but rarely consider the expression and activity of pathway modulatory components and other transcriptional partners of YAP and TAZ. As there is a growing body of evidence for YAP and TAZ as potential therapeutic targets in several cancers, we here interrogate the applicability of this concept to bone tumors. To this end, this review aims to summarize our current knowledge of YAP and TAZ in cell plasticity, normal bone development and bone cancer.Cells 2020, 9, 972 2 of 34 co-activators Yes-associated protein 1 (YAP-1, YAP) and its paralogue, the transcriptional co-activator with PDZ-binding motif (TAZ, WWTR1), which are typically controlled on the post-translational level by upstream regulatory signaling pathways in organ development and tissue homeostasis [2,3]. YAP and TAZ were reported to affect self-renewal and lineage commitment of stem cells [4][5][6][7], while hyperactivation of YAP and TAZ have been linked to cancer growth and metastasis in various tumors [8][9][10]. TAZ levels are elevated in approximately 20% of cancers and drive invasion and metastasis [11,12], while YAP is frequently overexpressed or amplified in cancer and was shown to promote resistance to chemotherapy in oncogene-addicted tumors up...

Understanding the function of oral mucosal epithelial barriers is essential for a plethora of research fields such as tumor biology, inflammation and infection diseases, microbiomics, pharmacology, drug delivery, dental and biomarker research. The barrier properties are comprised by a physical, a transport and a metabolic barrier, and all these barrier components play pivotal roles in the communication between saliva and blood. The sum of all epithelia of the oral cavity and salivary glands is defined as the blood-saliva barrier. The functionality of the barrier is regulated by its microenvironment and often altered during diseases. A huge array of cell culture models have been developed to mimic specific parts of the blood-saliva barrier, but no ultimate standard in vitro models have been established. This review provides a comprehensive overview about developed in vitro models of oral mucosal barriers, their applications, various cultivation protocols and corresponding barrier properties.

Ewing sarcoma (EwS) is a highly metastatic bone cancer characterized by the ETS fusion oncoprotein EWS-FLI1. EwS cells are phenotypically highly plastic and switch between functionally distinct cell states dependent on EWS-FLI1 fluctuations. Whereas EWS-FLI1high cells proliferate, EWS-FLI1low cells are migratory and invasive. Recently, we reported activation of MRTFB and TEAD, effectors of RhoA and Hippo signalling, upon low EWS-FLI1, orchestrating key steps of the EwS migratory gene expression program. TEAD and its co-activators YAP and TAZ are commonly overexpressed in cancer, providing attractive therapeutic targets. We find TAZ levels to increase in the migratory EWS-FLI1low state and to associate with adverse prognosis in EwS patients. We tested the effects of the potent YAP/TAZ/TEAD complex inhibitor verteporfin on EwS cell migration in vitro and on metastasis in vivo. Verteporfin suppressed expression of EWS-FLI1 regulated cytoskeletal genes involved in actin signalling to the extracellular matrix, effectively blocked F-actin and focal-adhesion assembly and inhibited EwS cell migration at submicromolar concentrations. In a mouse EwS xenograft model, verteporfin treatment reduced relapses at the surgical site and delayed lung metastasis. These data suggest that YAP/TAZ pathway inhibition may prevent EwS cell dissemination and metastasis, justifying further preclinical development of YAP/TAZ inhibitors for EwS treatment.

Abstract. Genomic editing using the CRISPR/Cas9 technology allows selective interference with gene expression. With this method, a multitude of haploid and diploid cells from different organisms have been employed to successfully generate knockouts of genes coding for proteins or small RNAs. Yet, cancer cells exhibiting an aberrant ploidy are considered to be less accessible to CRISPR/Cas9-mediated genomic editing, as amplifications of the targeted gene locus could hamper its effectiveness. Here we examined the suitability of CRISPR/Cas9 to knockout the receptor tyrosine kinase Axl in the human hepatoma cell lines HLF and SNU449. The genomic editing events were validated in two single cell clones each from putative HLF and SNU449 knockout cells (HLF-Axl --1, HLF-Axl --2, SNU449-Axl --1, SNU449-Axl --2). Sequence analysis of respective AXL loci revealed one to six editing events in each individual Axl -clone. The majority of insertions and deletions in the AXL gene at exon 7/8 resulted in a frameshift and thus a premature stop in the coding region.However, one genomic editing event led to an insertion of two amino acids resulting in an altered protein sequence rather than in a frameshift in the AXL locus of the SNU449-Axl --1 cells. Notably, while no Axl protein expression could be detected by immunoblotting in all four cell clones, both expression of total Axl as well as release of soluble Axl into the supernatant was observed by ELISA in incompletely edited SNU449-Axl --1 cells. Importantly, a comparative genomic hybridization array revealed comparable genomic changes in Axl knockout cells as well as in cells expressing Cas9 nickase without guide RNAs in SNU449 and HLF cells, indicating vast alterations in genomic DNA triggered by nickase. Together, these data show that the dynamics of CRISPR/Cas9 may cause incomplete editing events in cancer cell lines, as gene copy numbers vary based on genomic heterogeneity.

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The term epithelial to mesenchymal transition (EMT) and its reverse (MET) describe the dynamic and reversible metamorphosis of cells from a highly organized to a loose migratory phenotype through cytoskeletal reorganization causing cellular plasticity. EMT/MET are inherent to normal embryonal development and wound healing, but cancer cells hijack the underlying mechanisms to enable oscillations between proliferation, invasion and migration that cause metastasis, the major killer of cancer patients. Recently, fluctuations of the oncoprotein EWS-FLI1 were identified to drive EMT/MET in Ewing sarcoma. We previously demonstrated that, in presence of EWS-FLI1, transcriptional co-activators MRTFB and TAZ are largely blocked from associating with TEAD and its target genes keeping tumor cells in a poorly migratory, highly proliferative state. In contrast, under EWS-FLI-low conditions, MRTFB and TAZ associate with YAP/TEAD complexes on chromatin resulting in cytoskeletal target gene activation and phenotypic transition to a highly migratory and low proliferative state. We therefore hypothesized that pharmacologic inhibition of YAP/TAZ/TEAD protein interaction should prevent Ewing sarcoma cells from EMT and consequently interfere with their metastatic potential. Verteporfin is a small molecule safely used in the treatment of age-related macular degeneration. Independent of its photosensitizing activity exploited in ophthalmology, it is a YAP/TAZ pathway -blocking compound. In vitro treatment of EWS-FLI1-low Ewing sarcoma cells with verteporfin resulted in decreased YAP/TAZ/TEAD complex formation in the nanomolar range, reversal of the de-repression of a EWS-FLI1 controlled EMT transcriptional signature, and inhibition of tumor cell migration in a Boyden chamber assay. Upon orthotopic implantation of TC71 Ewing sarcoma cells into the tibial crest of SCID beige mice, intra-peritoneal treatment of mice with 25mg verteporfin/kg/day before and after amputation of the affected limb led to a drastic decrease of lung metastases without affecting primary tumor growth and without obvious general toxicity. Therefore, YAP/TAZ pathway blockade holds promise as a potential metastasis-preventive strategy in the treatment of Ewing sarcoma patients with primary localized disease. Citation Format: Lisa Bierbaumer, Anna M. Katschnig, Branka Radic-Sarikas, Jeffrey R. Petro, Karin Mühlbacher, Dave N. Aryee, Anna R. Pötsch, Sandra Högler, Lukas Kenner, Aykut Uren, Heinrich Kovar. Targeting YAP/TAZ pathway inhibits Ewing sarcoma metastasis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1049.

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Oscillations between proliferative and migratory/invasive cell states are at the core of the metastatic process. Transition between these states involves reversible shifts in transcriptional programs that orchestrate cytoskeletal remodeling. Ewing sarcoma pathogenesis depends on EWS-FLI1, an aberrant ETS transcription factor that drives cellular transformation and proliferation of presumably mesenchymal progenitor cells. Recently, it has been reported that transient modulation of EWS-FLI1 expression results in an epithelial-to-mesenchymal transition-like phenotype of Ewing sarcoma cells and in increased metastasis (Chaturvedi et al., 2014; Franzetti et al., 2016). It has been proposed that EWS-FLI1 low cells exist in small amounts in primary Ewing sarcoma tumors and thus provide a potential source for tumor dissemination, leading to adverse prognosis. In our studies, we investigate the mechanistic basis of EWS-FLI1 dose-dependent Ewing sarcoma plasticity and recently reported on the activation of an MRTFB/TEAD transcriptional module promoting cytoskeletal reprograming in response to low EWS-FLI1 levels (Katschnig et al., 2016). Here, we show that the proliferative state depends on the activity of nuclear beta-catenin complexed to FOXM1. We find that EWS-FLI1 not only drives FOXM1 expression on the RNA level, but also sustains nuclear FOXM1 stability by a mechanism involving FOXM1 protein demethylation by lysine-specific demethylase 1 (LSD1/KDM1A). Experimental evidence suggests that EWS-FLI1 regulates LSD1 protein stability in Ewing sarcoma cells by directly activating a ubiquitin-specific protease. Modulation of EWS-FLI1 led to loss of expression of the deubiquitinting enzyme (DUB), and consequently to rapid depletion of LSD1 and FOXM1 proteins and subcellular redistribution of beta-catenin to the cytoplasm. Genetic (siRNA) and pharmacologic inhibition of the DUB or LSD1 recapitulated the destabilizing effect on FOXM1 in EWS-FLI1-high Ewing sarcoma cells, blocking tumor cell proliferation. In addition, they led to complete loss of beta-catenin expression by a mechanism that is currently under investigation. Therefore, our study identifies targetable enzymatic activities downstream of EWS-FLI1 that are required to sustain Ewing sarcoma proliferation. Citation Format: Jozef Ban, Dave Aryee, Lisa Bierbaumer, Heinrich Kovar. EWS-FLI1 orchestrates Ewing sarcoma plasticity through a post-translational modification cascade regulating FOXM1 stability [abstract]. In: Proceedings of the AACR Special Conference on the Advances in Pediatric Cancer Research; 2019 Sep 17-20; Montreal, QC, Canada. Philadelphia (PA): AACR; Cancer Res 2020;80(14 Suppl):Abstract nr B40.