title: Oncogenic KRAS promotes malignant brain tumors in zebrafish.
abstract: BACKGROUND
  Zebrafish have been used as a vertebrate model to study human cancers such as melanoma, rhabdomyosarcoma, liver cancer, and leukemia as well as for high-throughput screening of small molecules of therapeutic value. However, they are just emerging as a model for human brain tumors, which are among the most devastating and difficult to treat. In this study, we evaluated zebrafish as a brain tumor model by overexpressing a human version of oncogenic KRAS (KRAS(G12V)).
  
  
  METHODS
  Using zebrafish cytokeratin 5 (krt5) and glial fibrillary acidic protein (gfap) gene promoters, we activated Ras signaling in the zebrafish central nervous system (CNS) through transient and stable transgenic overexpression. Immunohistochemical analyses were performed to identify activated pathways in the resulting brain tumors. The effects of the MEK inhibitor U0126 on oncogenic KRAS were evaluated.
  
  
  RESULTS
  We demonstrated that transient transgenic expression of KRAS(G12V) in putative neural stem and/or progenitor cells induced brain tumorigenesis. When expressed under the control of the krt5 gene promoter, KRAS(G12V) induced brain tumors in ventricular zones (VZ) at low frequency. The majority of other tumors were composed mostly of spindle and epithelioid cells, reminiscent of malignant peripheral nerve sheath tumors (MPNSTs). In contrast, when expressed under the control of the gfap gene promoter, KRAS(G12V) induced brain tumors in both VZs and brain parenchyma at higher frequency. Immunohistochemical analyses indicated prominent activation of the canonical RAS-RAF-ERK pathway, variable activation of the mTOR pathway, but no activation of the PI3K-AKT pathway. In a krt5-derived stable and inducible transgenic line, expression of oncogenic KRAS resulted in skin hyperplasia, and the MEK inhibitor U0126 effectively suppressed this pro-proliferative effects. In a gfap-derived stable and inducible line, expression of oncogenic KRAS led to significantly increased mitotic index in the spinal cord.
  
  
  CONCLUSIONS
  Our studies demonstrate that zebrafish could be explored to study cellular origins and molecular mechanisms of brain tumorigenesis and could also be used as a platform for studying human oncogene function and for discovering oncogenic RAS inhibitors.
authors: Department of Chemical Biology & Therapeutics, St. Jude Children's Research Hospital, Memphis, TN, 38105, USA. bensheng.ju@stjude.org.
authors: Bensheng
authors: B
authors: Ju
authors: Department of Molecular Physiology & Biophysics, Vanderbilt University School of Medicine, Nashville, TN, 37232, USA. wenbiao.chen@vanderbilt.edu.
authors: Wenbiao
authors: W
authors: Chen
authors: Department of Pathology, St Jude Children's Research Hospital, Memphis, TN, 38105, USA. brent.orr@stjude.org.
authors: Brent A
authors: BA
authors: Orr
authors: Fish Disease Research Group, Department of Microbiology, Oregon State University, Corvallis, OR, 97331, USA. spitsbej@onid.orst.edu.
authors: Jan M
authors: JM
authors: Spitsbergen
authors: Department of Chemical Biology & Therapeutics, St. Jude Children's Research Hospital, Memphis, TN, 38105, USA. sujuan.jia@stjude.org.
authors: Sujuan
authors: S
authors: Jia
authors: Department of Developmental Neurobiology, St. Jude Children's Research Hospital, Memphis, TN, 38105, USA. ceden@nikon.net.
authors: Christopher J
authors: CJ
authors: Eden
authors: Department of Chemical Biology & Therapeutics, St. Jude Children's Research Hospital, Memphis, TN, 38105, USA. hannah.henson@uky.edu.|Integrated Program in Biomedical Sciences, University of Tennessee Health Science Center, Memphis, TN, 38163, USA. hannah.henson@uky.edu.
authors: Hannah E
authors: HE
authors: Henson
authors: Department of Chemical Biology & Therapeutics, St. Jude Children's Research Hospital, Memphis, TN, 38105, USA. michael.taylor@wisc.edu.|Current address: Pharmaceutical Sciences Division, School of Pharmacy, University of Wisconsin-Madison, Madison, WI, 53705, USA. michael.taylor@wisc.edu.
authors: Michael R
authors: MR
authors: Taylor
mesh_terms: D000818:Animals; D030801:Animals, Genetically Modified; D001921:Brain / Q000378:metabolism / Q000473:pathology; D001932:Brain Neoplasms / Q000188:drug therapy / Q000235:genetics* / Q000473:pathology*; D002471:Cell Transformation, Neoplastic / Q000235:genetics; D004195:Disease Models, Animal; D004354:Drug Screening Assays, Antitumor; D015870:Gene Expression; D006801:Humans; D007150:Immunohistochemistry; D053555:Keratin-5 / Q000235:genetics; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism; D011401:Promoter Regions, Genetic; D011518:Proto-Oncogene Proteins / Q000235:genetics* / Q000378:metabolism; D016283:Proto-Oncogene Proteins p21(ras); D015398:Signal Transduction; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism; D019076:Transgenes; D015027:Zebrafish; D018631:ras Proteins / Q000235:genetics* / Q000378:metabolism
chemical_list: C117307:KRAS protein, human; D053555:Keratin-5; D009419:Nerve Tissue Proteins; D011518:Proto-Oncogene Proteins; D058570:TOR Serine-Threonine Kinases; D016283:Proto-Oncogene Proteins p21(ras); D018631:ras Proteins
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