Steven D Leach

Memorial Sloan-Kettering Cancer Center, New York, New York, United States

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Publications (142)996.12 Total impact

  • Developmental Biology 08/2011; 356(1):224-224. DOI:10.1016/j.ydbio.2011.05.368 · 3.64 Impact Factor
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    ABSTRACT: The intracellular protein p120ctn controls cell–cell adhesion by regulation of E-cadherin stability. p120ctn binds to the juxtamembrane region of E-cadherin and regulates its retention at the cell–cell surface. Mice null for p120ctn are not viable. Using Pdx1:Cre and a conditional allele of p120ctn, we deleted p120ctn in all epithelial lineages of the developing mouse pancreas: islet, acinar, and ductal. Loss of p120ctn in the developing pancreas results in expansion of ductal epithelia and loss of acinar cells. Defects in branching morphogenesis are evident at E12.5. During development the phenotype becomes more severe, ultimately resulting in a pancreas comprised primarily of abnormal ductal tissue. Pdx1:Cre; p120ctn fl/fl animals are born dead. Loss of p120ctn results in mislocalization of E-cadherin and loss of b-catenin. Additionally, at E17.5 we observed broad expression of Sox9 and Pdx in Pdx1:Cre; p120ctn fl/fl animals. This suggests inappropriate persistence of progenitor cells at late developmental timepoints. Taken together, our data demonstrates an essential role for p120ctn in pancreatic acinar cell development and differentiation.
    Developmental Biology - DEVELOP BIOL, Chicago, Illinois; 08/2011
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    Bidyut Ghosh, Steven D Leach
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    ABSTRACT: Comment on: Andreia V. Pinho, et al. Cell Cycle 2011; 10: In press.
    Cell cycle (Georgetown, Tex.) 06/2011; 10(11):1717. DOI:10.4161/cc.10.11.15686 · 5.01 Impact Factor
  • Shu Liu, Steven D Leach
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    ABSTRACT: First established as a valuable vertebrate model system for studying development, zebrafish have emerged as an attractive animal system for modeling human cancers. Major technical advances have been essential for the generation of zebrafish cancer models relevant to human diseases. These models develop tumors in various organ sites that bear striking resemblance to human malignances, both histologically and genetically. Thus, the focus of cancer research in zebrafish has transcended the need to validate zebrafish as a viable model organism to study cancer biology. With the significant advantages of in vivo imaging, the power of forward genetics, well-established high efficiency for transgenesis, and ease of transplantation, further exploration of the zebrafish cancer models not only will generate unique insights into underlying mechanisms of cancer but will also provide platforms useful for drug discovery.
    Annual Review of Pathology Mechanisms of Disease 02/2011; 6:71-93. DOI:10.1146/annurev-pathol-011110-130330 · 22.13 Impact Factor
  • Shu Liu, Steven D Leach
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    ABSTRACT: Pancreatic cancer is a genetic disease in which somatic mutations in the KRAS proto-oncogene are detected in a majority of tumors. KRAS mutations represent an early event during pancreatic tumorigenesis, crucial for cancer initiation and progression. Recent studies, including comprehensive sequencing of the pancreatic cancer exome, have implicated the involvement of a number of additional core signaling pathways during pancreatic tumorigenesis. Improving our understanding of genetic interactions between KRAS and these additional pathways represents a critical challenge, as these interactions may provide novel opportunities for diagnosis and treatment. However, studying these interactions requires the expression of multiple transgenes in relevant cell types, an effort that has proven very difficult to achieve using gene targeted mice and is also technically challenging in zebrafish. Based on the ability of the Gal4 transcriptional activator to drive the expression of multiple transgenes under regulation of UAS (upstream activator sequence) regulatory elements, the Gal4/UAS system represents an attractive strategy for the study of genetic interactions. In this chapter, we review our experience using the Gal4/UAS system to model KRAS-initiated pancreatic cancer in zebrafish, as well as our early efforts using this system to study the influence of other cooperating oncogenes. We also describe techniques used to identify and characterize pancreatic tumors in adult transgenic fish.
    Methods in cell biology 01/2011; 105:367-81. DOI:10.1016/B978-0-12-381320-6.00015-1 · 1.44 Impact Factor
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    ABSTRACT: Although activating mutations in RAS oncogenes are known to result in aberrant signaling through multiple pathways, the role of microRNAs (miRNAs) in the Ras oncogenic program remains poorly characterized. Here we demonstrate that Ras activation leads to repression of the miR-143/145 cluster in cells of human, murine, and zebrafish origin. Loss of miR-143/145 expression is observed frequently in KRAS mutant pancreatic cancers, and restoration of these miRNAs abrogates tumorigenesis. miR-143/145 down-regulation requires the Ras-responsive element-binding protein (RREB1), which represses the miR-143/145 promoter. Additionally, KRAS and RREB1 are targets of miR-143/miR-145, revealing a feed-forward mechanism that potentiates Ras signaling.
    Genes & development 12/2010; 24(24):2754-9. DOI:10.1101/gad.1950610 · 12.64 Impact Factor
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    ABSTRACT: The strength of functional imaging lies in its ability to detect malignant disease irrespective of lesion morphology. In this setting, 18FDG-PET can complement management by providing a more accurate diagnosis. When combined as an adjunct to CT, 18FDG-PET can increase the sensitivity, specificity, and accuracy for detecting a pancreatic malignancy, especially in patients in whom CT alone fails to identify a discrete mass or in whom biopsy results are indeterminate. This capability is accentuated with small lesions of the pancreas. 18FDG-PET is significantly more sensitive in detecting metastatic disease than conventional CT imaging. Moreover, 18FDG-PET is able to differentiate tumor response to therapy in the postoperative setting, and could potentially serve to monitor recurrence patterns in the setting of neoadjuvant or adjuvant chemoradiotherapy. Finally, as 18FDG-PET/CT fusion modalities become more widespread and technical advances in image acquisition progress, 18FDG-PET will continue to have an increasing role in the diagnosis, staging, and surveillance of pancreatic cancer, integrating anatomic information with functional imaging.
    Advances in Surgery 09/2010; 44:313-25. DOI:10.1016/j.yasu.2010.05.007
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    ABSTRACT: The question of whether dedicated progenitor cells exist in adult vertebrate pancreas remains controversial. Centroacinar cells and terminal duct (CA/TD) cells lie at the junction between peripheral acinar cells and the adjacent ductal epithelium, and are frequently included among cell types proposed as candidate pancreatic progenitors. However these cells have not previously been isolated in a manner that allows formal assessment of their progenitor capacities. We have found that a subset of adult CA/TD cells are characterized by high levels of ALDH1 enzymatic activity, related to high-level expression of both Aldh1a1 and Aldh1a7. This allows their isolation by FACS using a fluorogenic ALDH1 substrate. FACS-isolated CA/TD cells are relatively depleted of transcripts associated with differentiated pancreatic cell types. In contrast, they are markedly enriched for transcripts encoding Sca1, Sdf1, c-Met, Nestin, and Sox9, markers previously associated with progenitor populations in embryonic pancreas and other tissues. FACS-sorted CA/TD cells are uniquely able to form self-renewing "pancreatospheres" in suspension culture, even when plated at clonal density. These spheres display a capacity for spontaneous endocrine and exocrine differentiation, as well as glucose-responsive insulin secretion. In addition, when injected into cultured embryonic dorsal pancreatic buds, these adult cells display a unique capacity to contribute to both the embryonic endocrine and exocrine lineages. Finally, these cells demonstrate dramatic expansion in the setting of chronic epithelial injury. These findings suggest that CA/TD cells are indeed capable of progenitor function and may contribute to the maintenance of tissue homeostasis in adult mouse pancreas.
    Proceedings of the National Academy of Sciences 12/2009; 107(1):75-80. DOI:10.1073/pnas.0912589107 · 9.81 Impact Factor
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    ABSTRACT: Embryonic development of the pancreas is marked by an early phase of dramatic morphogenesis, in which pluripotent progenitor cells of the developing pancreatic epithelium give rise to the full array of mature exocrine and endocrine cell types. The genetic determinants of acinar and islet cell lineages are somewhat well defined; however, the molecular mechanisms directing ductal formation and differentiation remain to be elucidated. The complex ductal architecture of the pancreas is established by a reiterative program of progenitor cell expansion and migration known as branching morphogenesis, or tubulogenesis, which proceeds in mouse development concomitantly with peak Pdx1 transcription factor expression. We therefore evaluated Pdx1 expression with respect to lineage-specific markers in embryonic sections of the pancreas spanning this critical period of duct formation and discovered an unexpected population of nonislet Pdx1-positive cells displaying physical traits of branching. We then established a 3D cell culture model of branching morphogenesis using primary pancreatic duct cells and identified a transient surge of Pdx1 expression exclusive to branching cells. From these observations we propose that Pdx1 might be involved temporally in a program of gene expression sufficient to facilitate the biochemical and morphological changes necessary for branching morphogenesis.
    Molecular biology of the cell 09/2009; 20(22):4838-44. DOI:10.1091/mbc.E09-03-0203 · 5.98 Impact Factor
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    ABSTRACT: Zebrafish provide a highly versatile model in which to study vertebrate development. Many recent studies have elucidated early events in the organogenesis of the zebrafish pancreas; however, several aspects of early endocrine pancreas formation in the zebrafish are not homologous to the mammalian system. To better identify mechanisms of islet formation in the zebrafish, with true homology to those observed in mammals, we have temporally and spatially characterized zebrafish secondary islet formation. As is the case in the mouse, we show that Notch inhibition leads to precocious differentiation of endocrine tissues. Furthermore, we have used transgenic fish expressing fluorescent markers under the control of a Notch-responsive element to observe the precursors of these induced endocrine cells. These pancreatic Notch-responsive cells represent a novel population of putative progenitors that are associated with larval pancreatic ductal epithelium, suggesting functional homology between secondary islet formation in zebrafish and the secondary transition in mammals. We also show that Notch-responsive cells persist in the adult pancreas and possess the classical characteristics of centroacinar cells, a cell type believed to be a multipotent progenitor cell in adult mammalian pancreas.
    Mechanisms of development 08/2009; 126(10):898-912. DOI:10.1016/j.mod.2009.07.002 · 2.24 Impact Factor
  • Mechanisms of Development 08/2009; 126. DOI:10.1016/j.mod.2009.06.358 · 2.24 Impact Factor
  • Gastroenterology 05/2009; 136(5). DOI:10.1016/S0016-5085(09)60144-X · 13.93 Impact Factor
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    ABSTRACT: Optical clarity of larvae makes the zebrafish ideal for real-time analyses of vertebrate organ function through the use of fluorescent reporters of enzymatic activities. A key function of digestive organs is to couple the generation of enzymes with mechanical processes that enable nutrient availability and absorption. However, it has been extremely difficult, and in many cases not possible, to directly observe digestive processes in a live vertebrate. Here we describe a new method to visualize intestinal protein and lipid processing simultaneously in live zebrafish larvae using a quenched fluorescent protein (EnzChek) and phospholipid (PED6). By employing these reagents, we found that wild-type larvae exhibit significant variation in intestinal phospholipase and protease activities within a group but display a strong correlation between the activities within individuals. Furthermore, we found that pancreas function is essential for larval digestive protease activity but not for larval intestinal phospholipase activity. Although fat-free (ffr) mutant larvae were previously described to exhibit impaired lipid processes, we found they also had significantly reduced protease activity. Finally, we selected and evaluated compounds that were previously suggested to have altered phospholipase activity and are known or suspected to have inflammatory effects in the intestinal tract including nonsteroidal anti-inflammatory drugs, and identified a compound that significantly increases intestinal phospholipid processing. Thus the multiple fluorescent reporter-based methodology facilitates the rapid analysis of digestive organ function in live zebrafish larvae.
    AJP Gastrointestinal and Liver Physiology 01/2009; 296(2):G445-53. DOI:10.1152/ajpgi.90513.2008 · 3.74 Impact Factor
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    ABSTRACT: Pancreatic ductal adenocarcinoma (PDAC) is believed to arise through a multistep model comprised of putative precursor lesions known as pancreatic intraepithelial neoplasia (PanIN). Recent genetically engineered mouse models of PDAC demonstrate a comparable morphologic spectrum of murine PanIN (mPanIN) lesions. The histogenesis of PanIN and PDAC in both mice and men remains controversial. The most faithful genetic models activate an oncogenic Kras(G12D) knockin allele within the pdx1- or ptf1a/p48-expression domain of the entire pancreatic anlage during development, thus obscuring the putative cell(s)-of-origin from which subsequent mPanIN lesions arise. In our study, activation of this knockin Kras(G12D) allele in the Elastase- and Mist1-expressing mature acinar compartment of adult mice resulted in the spontaneous induction of mPanIN lesions of all histological grades, although invasive carcinomas per se were not seen. We observed no requirement for concomitant chronic exocrine injury in the induction of mPanIN lesions from the mature acinar cell compartment. The acinar cell derivation of the mPanINs was established through lineage tracing in reporter mice, and by microdissection of lesional tissue demonstrating Cre-mediated recombination events. In contrast to the uniformly penetrant mPanIN phenotype observed following developmental activation of Kras(G12D) in the Pdx1-expressing progenitor cells, the Pdx1-expressing population in the mature pancreas (predominantly islet beta cells) appears to be relatively resistant to the effects of oncogenic Kras. We conclude that in the appropriate genetic context, the differentiated acinar cell compartment in adult mice retains its susceptibility for spontaneous transformation into mPanIN lesions, a finding with potential relevance vis-à-vis the origins of PDAC.
    Proceedings of the National Academy of Sciences 12/2008; 105(48):18913-8. DOI:10.1073/pnas.0810097105 · 9.81 Impact Factor
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    ABSTRACT: There are currently few therapeutic options for patients with pancreatic cancer, and new insights into the pathogenesis of this lethal disease are urgently needed. Toward this end, we performed a comprehensive genetic analysis of 24 pancreatic cancers. We first determined the sequences of 23,219 transcripts, representing 20,661 protein-coding genes, in these samples. Then, we searched for homozygous deletions and amplifications in the tumor DNA by using microarrays containing probes for approximately 10(6) single-nucleotide polymorphisms. We found that pancreatic cancers contain an average of 63 genetic alterations, the majority of which are point mutations. These alterations defined a core set of 12 cellular signaling pathways and processes that were each genetically altered in 67 to 100% of the tumors. Analysis of these tumors' transcriptomes with next-generation sequencing-by-synthesis technologies provided independent evidence for the importance of these pathways and processes. Our data indicate that genetically altered core pathways and regulatory processes only become evident once the coding regions of the genome are analyzed in depth. Dysregulation of these core pathways and processes through mutation can explain the major features of pancreatic tumorigenesis.
    Science 10/2008; 321(5897):1801-6. DOI:10.1126/science.1164368 · 31.48 Impact Factor
  • Jacqueline M Garonzik Wang, Steven D Leach
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    ABSTRACT: This article gives a brief overview of the common histologic subtypes seen in truncal sarcomas and discusses fundamental diagnostic and treatment principles. It also provides a general review of abdominal desmoids. For both truncal sarcomas and desmoids, recurrence rates are high, and definitive recommendations regarding optimal treating are lacking. A multidisciplinary approach to these entities therefore is critical to select appropriate therapeutic strategies for individual patients.
    Surgical Clinics of North America 07/2008; 88(3):571-82, vi-vii. DOI:10.1016/j.suc.2008.04.001 · 1.93 Impact Factor
  • Developmental Biology 07/2008; 319(2):571-571. DOI:10.1016/j.ydbio.2008.05.367 · 3.64 Impact Factor
  • Sherri-Gae Scott, Steven D. Leach
    Developmental Biology 07/2008; 319(2):593-594. DOI:10.1016/j.ydbio.2008.05.502 · 3.64 Impact Factor
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    ABSTRACT: Although the cell of origin for pancreatic cancer remains unknown, prior studies have suggested that pancreatic neoplasia may be initiated in progenitor-like cells. To examine the effects of oncogene activation within the pancreatic progenitor pool, we devised a system for real-time visualization of both normal and oncogenic KRAS-expressing pancreatic progenitor cells in living zebrafish embryos. By using BAC transgenes under the regulation of ptf1a regulatory elements, we expressed either extended green fluorescent protein (eGFP) alone or eGFP fused to oncogenic KRAS in developing zebrafish pancreas. After their initial specification, normal eGFP-labeled pancreatic progenitor cells were observed to actively migrate away from the forming endodermal gut tube, and subsequently underwent characteristic exocrine differentiation. In contrast, pancreatic progenitor cells expressing oncogenic KRAS underwent normal specification and migration, but failed to differentiate. This block in differentiation resulted in the abnormal persistence of an undifferentiated progenitor pool, and was associated with the subsequent formation of invasive pancreatic cancer. These tumors showed several features in common with the human disease, including evidence of abnormal Hedgehog pathway activation. These results provide a unique view of the tumor-initiating effects of oncogenic KRAS in a living vertebrate organism, and suggest that zebrafish models of pancreatic cancer may prove useful in advancing our understanding of the human disease.
    Gastroenterology 06/2008; 134(7):2080-90. DOI:10.1053/j.gastro.2008.02.084 · 13.93 Impact Factor
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    ABSTRACT: The mechanisms regulating pancreatic endocrine versus exocrine fate are not well defined. By analyzing the effects of Ptf1a partial loss of function, we uncovered novel roles for this transcription factor in determining pancreatic fates. In a newly identified hypomorphic ptf1a mutant, pancreatic cells that would normally express ptf1a and become exocrine cells, express the endocrine marker Isl1, indicating a cell fate switch. Surprisingly, a milder reduction of Ptf1a leads to an even greater increase of ectopic endocrine cells, suggesting that Ptf1a also plays a role in promoting endocrine development. We propose that low levels of Ptf1a promote endocrine fate, whereas high levels repress endocrine fate and promote exocrine fate.
    Genes & Development 06/2008; 22(11):1445-50. DOI:10.1101/gad.1663208 · 12.64 Impact Factor

Publication Stats

8k Citations
996.12 Total Impact Points

Institutions

  • 2014
    • Memorial Sloan-Kettering Cancer Center
      New York, New York, United States
  • 2003–2013
    • Johns Hopkins Medicine
      • • McKusick-Nathans Institute of Genetic Medicine
      • • Department of Surgery
      • • Department of Cell Biology
      Baltimore, MD, United States
  • 2001–2013
    • Johns Hopkins University
      • • Department of Surgery
      • • McKusick-Nathans Institute of Genetic Medicine
      • • Department of Cell Biology
      Baltimore, Maryland, United States
  • 2009
    • University of Pennsylvania
      • Division of Gastroenterology
      Philadelphia, PA, United States
  • 2008
    • Philipps University of Marburg
      Marburg, Hesse, Germany
    • Bryn Mawr College
      • Department of Biology
      Bryn Mawr, Pennsylvania, United States
  • 1998–2005
    • Vanderbilt University
      • • Department of Surgery
      • • Department of Radiology and Radiological Sciences
      • • Division of Surgical Oncology
      Nashville, MI, United States
  • 2004
    • University Pompeu Fabra
      Barcino, Catalonia, Spain
  • 1997–2001
    • Gateway-Vanderbilt Cancer Treatment Center
      Clarksville, Tennessee, United States
  • 1995–1998
    • University of Texas MD Anderson Cancer Center
      • • Department of Surgery
      • • Department of Surgical Oncology
      Houston, TX, United States