Academic Appointments

Professional Education

  • PhD, University of Munich, Molecular Biology (2010)
  • MSc, University of Warsaw, Molecular Biology (2005)
  • BSc, University of Warsaw, Molecular Biology (2003)


All Publications

  • Coordination of stress signals by the lysine methyltransferase SMYD2 promotes pancreatic cancer. Genes & development Reynoird, N., Mazur, P. K., Stellfeld, T., Flores, N. M., Lofgren, S. M., Carlson, S. M., Brambilla, E., Hainaut, P., Kaznowska, E. B., Arrowsmith, C. H., Khatri, P., Stresemann, C., Gozani, O., Sage, J. 2016; 30 (7): 772-785


    Pancreatic ductal adenocarcinoma (PDAC) is a lethal form of cancer with few therapeutic options. We found that levels of the lysine methyltransferase SMYD2 (SET and MYND domain 2) are elevated in PDAC and that genetic and pharmacological inhibition of SMYD2 restricts PDAC growth. We further identified the stress response kinase MAPKAPK3 (MK3) as a new physiologic substrate of SMYD2 in PDAC cells. Inhibition of MAPKAPK3 impedes PDAC growth, identifying a potential new kinase target in PDAC. Finally, we show that inhibition of SMYD2 cooperates with standard chemotherapy to treat PDAC cells and tumors. These findings uncover a pivotal role for SMYD2 in promoting pancreatic cancer.

    View details for DOI 10.1101/gad.275529.115

    View details for PubMedID 26988419

  • Combined inhibition of BET family proteins and histone deacetylases as a potential epigenetics-based therapy for pancreatic ductal adenocarcinoma. Nature medicine Mazur, P. K., Herner, A., Mello, S. S., Wirth, M., Hausmann, S., Sánchez-Rivera, F. J., Lofgren, S. M., Kuschma, T., Hahn, S. A., Vangala, D., Trajkovic-Arsic, M., Gupta, A., Heid, I., Noël, P. B., Braren, R., Erkan, M., Kleeff, J., Sipos, B., Sayles, L. C., Heikenwalder, M., Heßmann, E., Ellenrieder, V., Esposito, I., Jacks, T., Bradner, J. E., Khatri, P., Sweet-Cordero, E. A., Attardi, L. D., Schmid, R. M., Schneider, G., Sage, J., Siveke, J. T. 2015; 21 (10): 1163-1171


    Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal human cancers and shows resistance to any therapeutic strategy used. Here we tested small-molecule inhibitors targeting chromatin regulators as possible therapeutic agents in PDAC. We show that JQ1, an inhibitor of the bromodomain and extraterminal (BET) family of proteins, suppresses PDAC development in mice by inhibiting both MYC activity and inflammatory signals. The histone deacetylase (HDAC) inhibitor SAHA synergizes with JQ1 to augment cell death and more potently suppress advanced PDAC. Finally, using a CRISPR-Cas9-based method for gene editing directly in the mouse adult pancreas, we show that de-repression of p57 (also known as KIP2 or CDKN1C) upon combined BET and HDAC inhibition is required for the induction of combination therapy-induced cell death in PDAC. SAHA is approved for human use, and molecules similar to JQ1 are being tested in clinical trials. Thus, these studies identify a promising epigenetic-based therapeutic strategy that may be rapidly implemented in fatal human tumors.

    View details for DOI 10.1038/nm.3952

    View details for PubMedID 26390243

  • Opposing role of Notch1 and Notch2 in a Kras(G12D)-driven murine non-small cell lung cancer model ONCOGENE Baumgart, A., Mazur, P. K., Anton, M., Rudelius, M., Schwamborn, K., Feuchtinger, A., Behnke, K., Walch, A., Braren, R., Peschel, C., Duyster, J., Siveke, J. T., Dechow, T. 2015; 34 (5): 578-588


    Lung cancer is the leading cause of cancer-related deaths worldwide. Recently, we have shown that Notch1 inhibition resulted in substantial cell death of non-small cell lung cancer (NSCLC) cells in vitro. New compounds targeting Notch signal transduction have been developed and are now being tested in clinical trials. However, the tumorigenic role of individual Notch receptors in vivo remains largely unclear. Using a Kras(G12D)-driven endogenous NSCLC mouse model, we analyzed the effect of conditional Notch1 and Notch2 receptor deletion on NSCLC tumorigenesis. Notch1 deficiency led to a reduced early tumor formation and lower activity of MAPK compared with the controls. Unexpectedly, Notch2 deletion resulted in a dramatically increased carcinogenesis and increased MAPK activity. These mice died significantly earlier due to rapidly growing tumor burden. We found that Notch1 regulates Ras/MAPK pathway via HES1-induced repression of the DUSP1 promoter encoding a phosphatase specifically suppressing pERK1/2. Interestingly, Notch1 but not Notch2 ablation leads to decreased HES1 and DUSP1 expression. However, Notch2-depleted tumors showed an appreciable increase in ?-catenin expression, a known activator of HES1 and important lung cancer oncogene. Characteristically for ?-catenin upregulation, we found that the majority of Notch2-deficient tumors revealed an undifferentiated phenotype as determined by their morphology, E-Cadherin and TTF1 expression levels. In addition, these carcinomas showed aggressive growth patterns with bronchus invasion and obstruction. Together, we show that Notch2 mediates differentiation and has tumor suppressor functions during lung carcinogenesis, whereas Notch1 promotes tumor initiation and progression. These data are further supported by immunohistochemical analysis of human NSCLC samples showing loss or downregulation of Notch2 compared with normal lung tissue. In conclusion, this is the first study characterizing the in vivo functions of Notch1 and Notch2 in Kras(G12D)-driven NSCLC tumorigenesis. These data highlight the clinical importance of a thorough understanding of Notch signaling especially with regard to Notch-targeted therapies.

    View details for DOI 10.1038/onc.2013.592

    View details for Web of Science ID 000348853500005

    View details for PubMedID 24509876

  • SMYD3 links lysine methylation of MAP3K2 to Ras-driven cancer NATURE Mazur, P. K., Reynoird, N., Khatri, P., Jansen, P. W., Wilkinson, A. W., Liu, S., Barbash, O., Van Aller, G. S., Huddleston, M., Dhanak, D., Tummino, P. J., Kruger, R. G., Garcia, B. A., Butte, A. J., Vermeulen, M., Sage, J., Gozani, O. 2014; 510 (7504): 283-?
  • IQGAP1 scaffold-kinase interaction blockade selectively targets RAS-MAP kinase-driven tumors NATURE MEDICINE Jameson, K. L., Mazur, P. K., Zehnder, A. M., Zhang, J., Zarnegar, B., Sage, J., Khavari, P. A. 2013; 19 (5): 626-630


    Upregulation of the ERK1 and ERK2 (ERK1/2) MAP kinase (MAPK) cascade occurs in >30% of cancers, often through mutational activation of receptor tyrosine kinases or other upstream genes, including KRAS and BRAF. Efforts to target endogenous MAPKs are challenged by the fact that these kinases are required for viability in mammals. Additionally, the effectiveness of new inhibitors of mutant BRAF has been diminished by acquired tumor resistance through selection for BRAF-independent mechanisms of ERK1/2 induction. Furthermore, recently identified ERK1/2-inducing mutations in MEK1 and MEK2 (MEK1/2) MAPK genes in melanoma confer resistance to emerging therapeutic MEK inhibitors, underscoring the challenges facing direct kinase inhibition in cancer. MAPK scaffolds, such as IQ motif-containing GTPase activating protein 1 (IQGAP1), assemble pathway kinases to affect signal transmission, and disrupting scaffold function therefore offers an orthogonal approach to MAPK cascade inhibition. Consistent with this, we found a requirement for IQGAP1 in RAS-driven tumorigenesis in mouse and human tissue. In addition, the ERK1/2-binding IQGAP1 WW domain peptide disrupted IQGAP1-ERK1/2 interactions, inhibited RAS- and RAF-driven tumorigenesis, bypassed acquired resistance to the BRAF inhibitor vemurafenib (PLX-4032) and acted as a systemically deliverable therapeutic to significantly increase the lifespan of tumor-bearing mice. Scaffold-kinase interaction blockade acts by a mechanism distinct from direct kinase inhibition and may be a strategy to target overactive oncogenic kinase cascades in cancer.

    View details for DOI 10.1038/nm.3165

    View details for Web of Science ID 000318583000036

  • Coordination of stress signals by the lysine methyltransferase SMYD2 promotes pancreatic cancer GENES & DEVELOPMENT Reynoird, N., Mazur, P. K., Stellfeld, T., Flores, N. M., Lofgren, S. M., Carlson, S. M., Brambilla, E., Hainaut, P., Kaznowska, E. B., Arrowsmith, C. H., Khatri, P., Stresemann, C., Gozani, O., Sage, J. 2016; 30 (7): 772-785
  • Current methods in mouse models of pancreatic cancer. Methods in molecular biology (Clifton, N.J.) Mazur, P. K., Herner, A., Neff, F., Siveke, J. T. 2015; 1267: 185-215


    Pancreatic ductal adenocarcinoma (PDAC) is the fourth leading cause of cancer death in the Western world. The disease has the worst prognosis in the gastrointestinal malignancies with an overall 5-year survival rate of less than 5 %. Therefore, in the search for novel therapeutic targets, biomarkers for early detection and particularly adequate methods to develop and validate therapeutic strategies for this disease are still in urgent demand. Although significant progress has been achieved in understanding the genetic and molecular mechanisms, most approaches have not yet translated sufficiently for better outcome of the patients. In part, this situation is due to inappropriate or insufficient methods in modeling PDAC in laboratory settings. In the past several years, there has been an explosion of genetically engineered mouse models (GEMM) and patient-derived xenografts (PDX) that recapitulate both genetic and morphological alterations that lead to the development of PDAC. Both models are increasingly used for characterization and validation of diagnostic and therapeutic strategies. In this chapter we will discuss state-of-the-art models to consider when selecting an appropriate in vivo system to study disease etiology, cell signaling, and drug development.

    View details for DOI 10.1007/978-1-4939-2297-0_9

    View details for PubMedID 25636470

  • A Meta-analysis of Lung Cancer Gene Expression Identifies PTK7 as a Survival Gene in Lung Adenocarcinoma CANCER RESEARCH Chen, R., Khatri, P., Mazur, P. K., Polin, M., Zheng, Y., Vaka, D., Hoang, C. D., Shrager, J., Xu, Y., Vicent, S., Butte, A. J., Sweet-Cordero, E. A. 2014; 74 (10): 2892-2902


    Lung cancer remains the most common cause of cancer-related death worldwide and it continues to lack effective treatment. The increasingly large and diverse public databases of lung cancer gene expression constitute a rich source of candidate oncogenic drivers and therapeutic targets. To define novel targets for lung adenocarcinoma, we conducted a large-scale meta-analysis of genes specifically overexpressed in adenocarcinoma. We identified an 11-gene signature that was overexpressed consistently in adenocarcinoma specimens relative to normal lung tissue. Six genes in this signature were specifically overexpressed in adenocarcinoma relative to other subtypes of non-small cell lung cancer (NSCLC). Among these genes was the little studied protein tyrosine kinase PTK7. Immunohistochemical analysis confirmed that PTK7 is highly expressed in primary adenocarcinoma patient samples. RNA interference-mediated attenuation of PTK7 decreased cell viability and increased apoptosis in a subset of adenocarcinoma cell lines. Further, loss of PTK7 activated the MKK7-JNK stress response pathway and impaired tumor growth in xenotransplantation assays. Our work defines PTK7 as a highly and specifically expressed gene in adenocarcinoma and a potential therapeutic target in this subset of NSCLC. Cancer Res; 74(10); 2892-902. ©2014 AACR.

    View details for DOI 10.1158/0008-5472.CAN-13-2775

    View details for Web of Science ID 000336720700024

    View details for PubMedID 24654231

  • Current methods in the molecular typing of Mycobacterium tuberculosis and other mycobacteria. BioMed research international Jagielski, T., Van Ingen, J., Rastogi, N., Dziadek, J., Mazur, P. K., Bielecki, J. 2014; 2014: 645802-?


    In the epidemiology of tuberculosis (TB) and nontuberculous mycobacterial (NTM) diseases, as in all infectious diseases, the key issue is to define the source of infection and to disclose its routes of transmission and dissemination in the environment. For this to be accomplished, the ability of discerning and tracking individual Mycobacterium strains is of critical importance. Molecular typing methods have greatly improved our understanding of the biology of mycobacteria and provide powerful tools to combat the diseases caused by these pathogens. The utility of various typing methods depends on the Mycobacterium species under investigation as well as on the research question. For tuberculosis, different methods have different roles in phylogenetic analyses and person-to-person transmission studies. In NTM diseases, most investigations involve the search for environmental sources or phylogenetic relationships. Here, too, the type of setting determines which methodology is most suitable. Within this review, we summarize currently available molecular methods for strain typing of M. tuberculosis and some NTM species, most commonly associated with human disease. For the various methods, technical practicalities as well as discriminatory power and accomplishments are reviewed.

    View details for DOI 10.1155/2014/645802

    View details for PubMedID 24527454

  • A Drug Repositioning Approach Identifies Tricyclic Antidepressants as Inhibitors of Small Cell Lung Cancer and Other Neuroendocrine Tumors CANCER DISCOVERY Jahchan, N. S., Dudley, J. T., Mazur, P. K., Flores, N., Yang, D., Palmerton, A., Zmoos, A., Vaka, D., Tran, K. Q., Zhou, M., Krasinska, K., Riess, J. W., Neal, J. W., Khatri, P., Park, K. S., Butte, A. J., Sage, J. 2013; 3 (12): 1364-1377


    Small cell lung cancer (SCLC) is an aggressive neuroendocrine subtype of lung cancer with high mortality. We used a systematic drug repositioning bioinformatics approach querying a large compendium of gene expression profiles to identify candidate U.S. Food and Drug Administration (FDA)-approved drugs to treat SCLC. We found that tricyclic antidepressants and related molecules potently induce apoptosis in both chemonaďve and chemoresistant SCLC cells in culture, in mouse and human SCLC tumors transplanted into immunocompromised mice, and in endogenous tumors from a mouse model for human SCLC. The candidate drugs activate stress pathways and induce cell death in SCLC cells, at least in part by disrupting autocrine survival signals involving neurotransmitters and their G protein-coupled receptors. The candidate drugs inhibit the growth of other neuroendocrine tumors, including pancreatic neuroendocrine tumors and Merkel cell carcinoma. These experiments identify novel targeted strategies that can be rapidly evaluated in patients with neuroendocrine tumors through the repurposing of approved drugs.Our work shows the power of bioinformatics-based drug approaches to rapidly repurpose FDA-approved drugs and identifies a novel class of molecules to treat patients with SCLC, a cancer for which no effective novel systemic treatments have been identified in several decades. In addition, our experiments highlight the importance of novel autocrine mechanisms in promoting the growth of neuroendocrine tumor cells.

    View details for DOI 10.1158/2159-8290.CD-13-0183

    View details for Web of Science ID 000328257500023

    View details for PubMedID 24078773

  • Genetically engineered mouse models of pancreatic cancer: unravelling tumour biology and progressing translational oncology GUT Mazur, P. K., Siveke, J. T. 2012; 61 (10): 1488-1500


    Pancreatic ductal adenocarcinoma (PDAC) remains a devastating disease despite tremendous scientific efforts. Numerous trials have failed to improve the outcome on this deadliest of all major cancers. Potential causes include a still insufficient understanding of key features of this cancer and imperfect preclinical models for identification of active agents and mechanisms of therapeutic responses and resistance. Modern genetically engineered mouse models of PDAC faithfully recapitulate the genetic and biological evolution of human PDAC, thereby providing a potentially powerful tool for addressing tumour biological issues as well as strategies for early detection and assessment of responses to therapeutic interventions. Here, the authors will discuss opportunities and challenges in the application of genetically engineered mouse models for translational approaches in pancreatic cancer and provide a non-exhaustive list of examples with already existing or future clinical relevance.

    View details for DOI 10.1136/gutjnl-2011-300756

    View details for Web of Science ID 000308707300016

    View details for PubMedID 21873467

  • EGF Receptor Is Required for KRAS-Induced Pancreatic Tumorigenesis CANCER CELL Ardito, C. M., Gruener, B. M., Takeuchi, K. K., Lubeseder-Martellato, C., Teichmann, N., Mazur, P. K., DelGiorno, K. E., Carpenter, E. S., Halbrook, C. J., Hall, J. C., Pal, D., Briel, T., Herner, A., Trajkovic-Arsic, M., Sipos, B., Liou, G., Storz, P., Murray, N. R., Threadgill, D. W., Sibilia, M., Washington, M. K., Wilson, C. L., Schmid, R. M., Raines, E. W., Crawford, H. C., Siveke, J. T. 2012; 22 (3): 304-317


    Initiation of pancreatic ductal adenocarcinoma (PDA) is definitively linked to activating mutations in the KRAS oncogene. However, PDA mouse models show that mutant Kras expression early in development gives rise to a normal pancreas, with tumors forming only after a long latency or pancreatitis induction. Here, we show that oncogenic KRAS upregulates endogenous EGFR expression and activation, the latter being dependent on the EGFR ligand sheddase, ADAM17. Genetic ablation or pharmacological inhibition of EGFR or ADAM17 effectively eliminates KRAS-driven tumorigenesis in vivo. Without EGFR activity, active RAS levels are not sufficient to induce robust MEK/ERK activity, a requirement for epithelial transformation.

    View details for DOI 10.1016/j.ccr.2012.07.024

    View details for Web of Science ID 000308735400007

  • MALDI Imaging Mass Spectrometry for In Situ Proteomic Analysis of Preneoplastic Lesions in Pancreatic Cancer PLOS ONE Gruener, B. M., Hahne, H., Mazur, P. K., Trajkovic-Arsic, M., Maier, S., Esposito, I., Kalideris, E., Michalski, C. W., Kleeff, J., Rauser, S., Schmid, R. M., Kuester, B., Walch, A., Siveke, J. T. 2012; 7 (6)
  • Origin of pancreatic ductal adenocarcinoma from atypical flat lesions: a comparative study in transgenic mice and human tissues JOURNAL OF PATHOLOGY Aichler, M., Seiler, C., Tost, M., Siveke, J., Mazur, P. K., Da Silva-Buttkus, P., Bartsch, D. K., Langer, P., Chiblak, S., Duerr, A., Hoefler, H., Kloeppel, G., Mueller-Decker, K., Brielmeier, M., Esposito, I. 2012; 226 (5): 723-734


    Pancreatic ductal adenocarcinoma (PDAC) and its precursor lesions, pancreatic intraepithelial neoplasia (PanIN), display a ductal phenotype. However, there is evidence in genetically defined mouse models for PDAC harbouring a mutated kras under the control of a pancreas-specific promoter that ductal cancer might arise in the centroacinar-acinar region, possibly through a process of acinar-ductal metaplasia (ADM). In order to further elucidate this model of PDAC development, an extensive expression analysis and molecular characterization of the putative and already established (PanIN) precursor lesions were performed in the Kras(G12D/+) ; Ptf1a-Cre(ex1/+) mouse model and in human tissues, focusing on lineage markers, developmental pathways, cell cycle regulators, apomucins, and stromal activation markers. The results of this study show that areas of ADM are very frequent in the murine and human pancreas and represent regions of increased proliferation of cells with precursor potential. Moreover, atypical flat lesions originating in areas of ADM are the most probable precursors of PDAC in the Kras(G12D/+); Ptf1a-Cre(ex1/+) mice and similar lesions were also found in the pancreas of three patients with a strong family history of PDAC. In conclusion, PDAC development in Kras(G12D/+); Ptf1a-Cre(ex1/+) mice starts from ADM and a similar process might also take place in patients with a strong family history of PDAC.

    View details for DOI 10.1002/path.3017

    View details for Web of Science ID 000301178600005

    View details for PubMedID 21984419

  • Expression and Clinicopathological Significance of Notch Signaling and Cell-Fate Genes in Biliary Tract Cancer AMERICAN JOURNAL OF GASTROENTEROLOGY Mazur, P. K., Riener, M., Jochum, W., Kristiansen, G., Weber, A., Schmid, R. M., Siveke, J. T. 2012; 107 (1): 126-132


    Biliary tract cancer (BTC) is a fatal cancer originating from epithelial cells of the intra- and extra-hepatic biliary duct system and the gallbladder. Genes and pathways regulating stem and progenitor cells as well as cell-fate decisions are increasingly recognized in tumorigenesis. We evaluated the expression of Notch1, Notch2, and HES1 (hairy and enhancer of split 1), as well as the biliary cell-fate regulators SOX9 (SRY (sex determining region Y)-box 9) and HNF1? (hepatocyte nuclear factor 1?), in BTC for correlation with clinicopathological parameters.Tissue microarrays including normal bile ducts and 111 BTCs consisting of 17 intrahepatic cholangiocarcinomas, 58 extrahepatic cholangiocarcinomas, and 36 gallbladder carcinomas were analyzed using immunohistochemistry.Lack of cytoplasmic SOX9 expression was associated with a higher tumor grade (P=0.010) and a significantly reduced overall survival (P=0.002; median 6 months vs. 24 months) in univariate survival analysis, whereas lack of nuclear SOX9 expression was associated with a higher tumor stage (P=0.003). Notch pathway members showed high expression in BTC. However, no correlation was found between cytoplasmic or nuclear Notch1, Notch2, and HES1, as well as HNF1? expression, and any of the clinicopathological parameters. In multivariate analysis, cytoplasmic SOX9 expression was an independent prognostic factor for overall survival (P=0.031, relative risk=0.571).We show strong Notch pathway activation and identify SOX9 as a prognostic marker in BTC. These results substantiate diagnostic and therapeutic approaches targeting developmentally active genes and pathways.

    View details for DOI 10.1038/ajg.2011.305

    View details for Web of Science ID 000300573000020

    View details for PubMedID 21931375

  • MALDI imaging mass spectrometry for in situ proteomic analysis of preneoplastic lesions in pancreatic cancer. PloS one Grüner, B. M., Hahne, H., Mazur, P. K., Trajkovic-Arsic, M., Maier, S., Esposito, I., Kalideris, E., Michalski, C. W., Kleeff, J., Rauser, S., Schmid, R. M., Küster, B., Walch, A., Siveke, J. T. 2012; 7 (6)


    The identification of new biomarkers for preneoplastic pancreatic lesions (PanINs, IPMNs) and early pancreatic ductal adenocarcinoma (PDAC) is crucial due to the diseases high mortality rate upon late detection. To address this task we used the novel technique of matrix-assisted laser desorption/ionization (MALDI) imaging mass spectrometry (IMS) on genetically engineered mouse models (GEM) of pancreatic cancer. Various GEM were analyzed with MALDI IMS to investigate the peptide/protein-expression pattern of precursor lesions in comparison to normal pancreas and PDAC with cellular resolution. Statistical analysis revealed several discriminative m/z-species between normal and diseased tissue. Intraepithelial neoplasia (PanIN) and intraductal papillary mucinous neoplasm (IPMN) could be distinguished from normal pancreatic tissue and PDAC by 26 significant m/z-species. Among these m/z-species, we identified Albumin and Thymosin-beta 4 by liquid chromatography and tandem mass spectrometry (LC-MS/MS), which were further validated by immunohistochemistry, western blot, quantitative RT-PCR and ELISA in both murine and human tissue. Thymosin-beta 4 was found significantly increased in sera of mice with PanIN lesions. Upregulated PanIN expression of Albumin was accompanied by increased expression of liver-restricted genes suggesting a hepatic transdifferentiation program of preneoplastic cells. In conclusion we show that GEM of endogenous PDAC are a suitable model system for MALDI-IMS and subsequent LC-MS/MS analysis, allowing in situ analysis of small precursor lesions and identification of differentially expressed peptides and proteins.

    View details for DOI 10.1371/journal.pone.0039424

    View details for PubMedID 22761793

  • Notch signaling inhibits hepatocellular carcinoma following inactivation of the RB pathway JOURNAL OF EXPERIMENTAL MEDICINE Viatour, P., Ehmer, U., Saddic, L. A., Dorrell, C., Andersen, J. B., Lin, C., Zmoos, A., Mazur, P. K., Schaffer, B. E., Ostermeier, A., Vogel, H., Sylvester, K. G., Thorgeirsson, S. S., Grompe, M., Sage, J. 2011; 208 (10): 1963-1976


    Hepatocellular carcinoma (HCC) is the third cancer killer worldwide with >600,000 deaths every year. Although the major risk factors are known, therapeutic options in patients remain limited in part because of our incomplete understanding of the cellular and molecular mechanisms influencing HCC development. Evidence indicates that the retinoblastoma (RB) pathway is functionally inactivated in most cases of HCC by genetic, epigenetic, and/or viral mechanisms. To investigate the functional relevance of this observation, we inactivated the RB pathway in the liver of adult mice by deleting the three members of the Rb (Rb1) gene family: Rb, p107, and p130. Rb family triple knockout mice develop liver tumors with histopathological features and gene expression profiles similar to human HCC. In this mouse model, cancer initiation is associated with the specific expansion of populations of liver stem/progenitor cells, indicating that the RB pathway may prevent HCC development by maintaining the quiescence of adult liver progenitor cells. In addition, we show that during tumor progression, activation of the Notch pathway via E2F transcription factors serves as a negative feedback mechanism to slow HCC growth. The level of Notch activity is also able to predict survival of HCC patients, suggesting novel means to diagnose and treat HCC.

    View details for DOI 10.1084/jem.20110198

    View details for Web of Science ID 000295318900005

    View details for PubMedID 21875955

  • Early Requirement of Rac1 in a Mouse Model of Pancreatic Cancer GASTROENTEROLOGY Heid, I., Lubeseder-Martellato, C., Sipos, B., Mazur, P. K., Lesina, M., Schmid, R. M., Siveke, J. T. 2011; 141 (2): 719-U436


    Pancreatic ductal adenocarcinoma (PDAC) is a fatal disease without effective chemopreventive or therapeutic approaches. Although the role of oncogenic Kras in initiating development of PDAC is well established, downstream targets of aberrant Ras signaling are poorly understood. Acinar-ductal metaplasia (ADM) appears to be an important prerequisite for development of pancreatic intraepithelial neoplasia (PanIN), a common precursor to PDAC. RAS-related C3 botulinum substrate 1 (Rac1), which controls actin reorganization, can be activated by Ras, is up-regulated in several human cancers, and is required for cerulein-induced morphologic changes in acini. We investigated effects of loss of Rac1 in Kras-induced pancreatic carcinogenesis in mice.Using a Cre/lox approach, we deleted Rac1 from pancreatic progenitor cells in different mouse models of PDAC and in mice with cerulein-induced acute pancreatitis. Acinar epithelial explants of mutant mice were used to investigate the role of Rac1 in vitro.Rac1 expression increased in mouse and human pancreatic tumors, particularly in the stroma. Deletion of Rac1 in Kras(G12D)-induced PDAC in mice reduced formation of ADM, PanIN, and tumors and significantly prolonged survival. Pancreatic epithelial metaplasia was accompanied by apical-basolateral redistribution of F-actin, along with basal expression of Rac1. Acinar epithelial explants that lacked Rac1 or that were incubated with inhibitors of actin polymerization had a reduced ability to undergo ADM in 3-dimensional cultures.In mice, Rac1 is required for early metaplastic changes and neoplasia-associated actin rearrangements in development of pancreatic cancer. Rac1 might be developed as a diagnostic marker or therapeutic target for PDAC.

    View details for DOI 10.1053/j.gastro.2011.04.043

    View details for Web of Science ID 000293523300050

    View details for PubMedID 21684285

  • Identification of Epidermal Pdx1 Expression Discloses Different Roles of Notch1 and Notch2 in Murine Kras(G12D)-Induced Skin Carcinogenesis In Vivo PLOS ONE Mazur, P. K., Gruener, B. M., Nakhai, H., Sipos, B., Zimber-Strobl, U., Strobl, L. J., Radtke, F., Schmid, R. M., Siveke, J. T. 2010; 5 (10)


    The Ras and Notch signaling pathways are frequently activated during development to control many diverse cellular processes and are often dysregulated during tumorigenesis. To study the role of Notch and oncogenic Kras signaling in a progenitor cell population, Pdx1-Cre mice were utilized to generate conditional oncogenic Kras(G12D) mice with ablation of Notch1 and/or Notch2.Surprisingly, mice with activated Kras(G12D) and Notch1 but not Notch2 ablation developed skin papillomas progressing to squamous cell carcinoma providing evidence for Pdx1 expression in the skin. Immunostaining and lineage tracing experiments indicate that PDX1 is present predominantly in the suprabasal layers of the epidermis and rarely in the basal layer. Further analysis of keratinocytes in vitro revealed differentiation-dependent expression of PDX1 in terminally differentiated keratinocytes. PDX1 expression was also increased during wound healing. Further analysis revealed that loss of Notch1 but not Notch2 is critical for skin tumor development. Reasons for this include distinct Notch expression with Notch1 in all layers and Notch2 in the suprabasal layer as well as distinctive p21 and ?-catenin signaling inhibition capabilities.Our results provide strong evidence for epidermal expression of Pdx1 as of yet not identified function. In addition, this finding may be relevant for research using Pdx1-Cre transgenic strains. Additionally, our study confirms distinctive expression and functions of Notch1 and Notch2 in the skin supporting the importance of careful dissection of the contribution of individual Notch receptors.

    View details for DOI 10.1371/journal.pone.0013578

    View details for Web of Science ID 000283419100017

    View details for PubMedID 21042537

  • Notch2 is required for progression of pancreatic intraepithelial neoplasia and development of pancreatic ductal adenocarcinoma PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Mazur, P. K., Einwaechter, H., Lee, M., Sipos, B., Nakhai, H., Rad, R., Zimber-Strobl, U., Strobl, L. J., Radtke, F., Kloeppel, G., Schmid, R. M., Siveke, J. T. 2010; 107 (30): 13438-13443


    Pancreatic cancer is one of the most fatal malignancies lacking effective therapies. Notch signaling is a key regulator of cell fate specification and pancreatic cancer development; however, the role of individual Notch receptors and downstream signaling is largely unknown. Here, we show that Notch2 is predominantly expressed in ductal cells and pancreatic intraepithelial neoplasia (PanIN) lesions. Using genetically engineered mice, we demonstrate the effect of conditional Notch receptor ablation in KrasG12D-driven pancreatic carcinogenesis. Deficiency of Notch2 but not Notch1 stops PanIN progression, prolongs survival, and leads to a phenotypical switch toward anaplastic pancreatic cancer with epithelial-mesenchymal transition. By expression profiling, we identified increased Myc signaling regulated by Notch2 during tumor development, placing Notch2 as a central regulator of PanIN progression and malignant transformation. Our study supports the concept of distinctive roles of individual Notch receptors in cancer development.

    View details for DOI 10.1073/pnas.1002423107

    View details for Web of Science ID 000280602800046

    View details for PubMedID 20624967

  • Conditional ablation of Notch signaling in pancreatic development DEVELOPMENT Nakhai, H., Siveke, J. T., Klein, B., Mendoza-Torres, L., Mazur, P. K., Alguel, H., Radtke, F., Strobl, L., Zimber-Strobl, U., Schmid, R. M. 2008; 135 (16): 2757-2765


    The role of the Notch signaling members Notch1, Notch2 and Rbpj in exocrine pancreatic development is not well defined. We therefore analyzed conditional pancreas-specific Rbpj and combined Notch1/Notch2 knockout mice using Ptf1a(+/Cre(ex1)) mice crossed with floxed Rbpj or Notch1/Notch2 mice. Mice were analyzed at different embryonic stages for pancreatic exocrine and endocrine development. The absence of Rbpj in pancreatic progenitor cells impaired exocrine pancreas development up to embryonic day 18.5 and led to premature differentiation of pancreatic progenitors into endocrine cells. In Rbpj-deficient pancreata, amylase-expressing acini and islets formed during late embryonic and postnatal development, suggesting an essential role of Rbpj in early but not late development. Contrary to this severe phenotype, the concomitant inactivation of Notch1 and Notch2 only moderately disturbed the proliferation of pancreatic epithelial cells during early embryonic development, and did not inhibit pancreatic development. Our results show that, in contrast to Rbpj, Notch1 and Notch2 are not essential for pancreatogenesis. These data favor a Notch-independent role of Rbpj in the development of the exocrine pancreas. Furthermore, our findings suggest that in late stages of pancreatic development exocrine cell differentiation and maintenance are independent of Rbpj.

    View details for DOI 10.1242/dev.013722

    View details for Web of Science ID 000257922600009

    View details for PubMedID 18635610

  • Liver-specific inactivation of Notch2, but not Notch1, compromises intrahepatic bile duct development in mice HEPATOLOGY Geisler, F., Nagl, F., Mazur, P. K., Lee, M., Zimber-Strobl, U., Strobl, L. J., Radtke, F., Schmid, R. M., Siveke, J. T. 2008; 48 (2): 607-616


    The Notch pathway is an evolutionary conserved, intercellular signaling pathway that plays an important role in cell fate specification and the embryonic development of many organs, including the liver. In humans, mutations in the Notch receptor ligand Jagged1 gene result in defective intrahepatic bile duct (IHBD) development in Alagille syndrome. Developmental abnormalities of IHBD in mice doubly heterozygous for Jagged1 and Notch2 mutations propose that interactions of Jagged1 and its receptor Notch2 are crucial for normal IHBD development. Because different cell types in the liver are involved in IHBD development and morphogenesis, the cell-specific role of Notch signaling is not entirely understood. We investigated the effect of combined or single targeted disruption of Notch1 and Notch2 specifically in hepatoblasts and hepatoblast-derived lineage cells on liver development using AlbCre transgenic mice. Hepatocyte differentiation and homeostasis were not impaired in mice after combined deletion of Notch1 and Notch2 (N1N2(F/F)AlbCre). However, we detected irregular ductal plate structures in N1N2(F/F)AlbCre newborns, and further postnatal development of IHBD was severely impaired characterized by disorganized ductular structures accompanied by portal inflammation, portal fibrosis, and foci of hepatocyte feathery degeneration in adulthood. Further characterization of mutant mice with single deletion of Notch1 (N1(F/F)AlbCre) or Notch2 (N2(F/F)AlbCre) showed that Notch2 but not Notch1 is indispensable for normal perinatal and postnatal IHBD development. Further reduction of Notch2 gene dosage in Notch2 conditional/mutant (N2(F/LacZ)AlbCre) animals further enhanced IHBD abnormalities and concomitant liver pathology.Notch2 is required for proper IHBD development and morphogenesis.

    View details for DOI 10.1002/hep.22381

    View details for Web of Science ID 000258247400027

    View details for PubMedID 18666240

  • Notch signaling is required for exocrine regeneration after acute pancreatitis GASTROENTEROLOGY Sivere, J. T., Lubeseder-Martellato, C., Lee, M., Mazur, P. K., Nakhai, H., Radtke, F., Schmid, R. M. 2008; 134 (2): 544-555


    The mechanisms for tissue regeneration and renewal after acute pancreatitis are not well understood but may involve activation of Notch signaling. To study the effect of Notch signaling ablation during acute experimental pancreatitis, we used a chemical and genetic approach to ablate Notch signaling in cerulein-induced pancreatitis in mice.Acute pancreatitis was induced by cerulein treatment in mice treated with the gamma-secretase inhibitor dibenzazepine or in conditional Notch1 knockout mice. Mice were characterized using immunohistologic, biochemical, and molecular methods. To investigate Notch and beta-catenin interaction, acinar 266-6 cells were analyzed using transfection and biochemical assays.Loss of Notch signaling results in impaired regeneration after acute pancreatitis with fewer mature acinar cells in dibenzazepine-treated and Notch1-deficient mice in the regenerative phase 3 days after induction. beta-catenin expression was increased and prolonged during exocrine regeneration. Crosstalk between Notch and beta-catenin-mediated signaling was identified, with Notch1-IC inhibiting beta-catenin-mediated transcriptional activity. This inhibition was dependent on a functional RAM domain.Inhibition of Notch signaling in vivo leads to impaired regeneration of the exocrine pancreas after acute pancreatitis. Our results suggest an interaction of Notch and Wnt signaling in pancreatic acinar cells, providing evidence for a role of these pathways in the regulation of the maturation process of acinar cells.

    View details for DOI 10.1053/j.gastro.2007.11.003

    View details for Web of Science ID 000253032900024

    View details for PubMedID 18242220

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