title: Identification of CD25 as STAT5-Dependent Growth Regulator of Leukemic Stem Cells in Ph+ CML.
abstract: OBJECTIVE
  In chronic myelogenous leukemia (CML), leukemic stem cells (LSC) represent a critical target of therapy. However, little is known about markers and targets expressed by LSCs. The aim of this project was to identify novel relevant markers of CML LSCs.
  
  
  METHODS
  CML LSCs were examined by flow cytometry, qPCR, and various bioassays. In addition, we examined the multipotent CD25(+)CML cell line KU812.
  
  
  RESULTS
  In contrast to normal hematopoietic stem cells, CD34(+)/CD38(-)CML LSCs expressed the IL-2 receptor alpha chain, IL-2RA (CD25). STAT5 was found to induce expression of CD25 in Lin(-)/Sca-1(+)/Kit(+)stem cells in C57Bl/6 mice. Correspondingly, shRNA-induced STAT5 depletion resulted in decreased CD25 expression in KU812 cells. Moreover, the BCR/ABL1 inhibitors nilotinib and ponatinib were found to decrease STAT5 activity and CD25 expression in KU812 cells and primary CML LSCs. A CD25-targeting shRNA was found to augment proliferation of KU812 cellsin vitroand their engraftmentin vivoin NOD/SCID-IL-2Rγ(-/-)mice. In drug-screening experiments, the PI3K/mTOR blocker BEZ235 promoted the expression of STAT5 and CD25 in CML cells. Finally, we found that BEZ235 produces synergistic antineoplastic effects on CML cells when applied in combination with nilotinib or ponatinib.
  
  
  CONCLUSIONS
  CD25 is a novel STAT5-dependent marker of CML LSCs and may be useful for LSC detection and LSC isolation in clinical practice and basic science. Moreover, CD25 serves as a growth regulator of CML LSCs, which may have biologic and clinical implications and may pave the way for the development of new more effective LSC-eradicating treatment strategies in CML.
authors.affiliation: Division of Hematology and Hemostaseology, Department of Internal Medicine I, Medical University of Vienna, Vienna, Austria.
authors.forename: Irina
authors.initials: I
authors.lastname: Sadovnik
authors.affiliation: Institute of Pharmacology and Toxicology, University of Veterinary Medicine Vienna, Vienna, Austria.
authors.forename: Andrea
authors.initials: A
authors.lastname: Hoelbl-Kovacic
authors.affiliation: Ludwig Boltzmann Cluster Oncology, Medical University of Vienna, Vienna, Austria. Department of Radiation Oncology, Medical University of Vienna, Vienna, Austria.
authors.forename: Harald
authors.initials: H
authors.lastname: Herrmann
authors.affiliation: Division of Hematology and Hemostaseology, Department of Internal Medicine I, Medical University of Vienna, Vienna, Austria. Ludwig Boltzmann Cluster Oncology, Medical University of Vienna, Vienna, Austria.
authors.forename: Gregor
authors.initials: G
authors.lastname: Eisenwort
authors.affiliation: Division of Hematology and Hemostaseology, Department of Internal Medicine I, Medical University of Vienna, Vienna, Austria. Ludwig Boltzmann Cluster Oncology, Medical University of Vienna, Vienna, Austria.
authors.forename: Sabine
authors.initials: S
authors.lastname: Cerny-Reiterer
authors.affiliation: Institute of Pharmacology and Toxicology, University of Veterinary Medicine Vienna, Vienna, Austria. Cambridge Institute for Medical Research and Wellcome Trust/MRC Stem Cell Institute; Department of Haematology, University of Cambridge, Cambridge, United Kingdom.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Warsch
authors.affiliation: Department of Laboratory Medicine, Medical University of Vienna, Vienna, Austria.
authors.forename: Gregor
authors.initials: G
authors.lastname: Hoermann
authors.affiliation: Department of Laboratory Medicine, Medical University of Vienna, Vienna, Austria.
authors.forename: Georg
authors.initials: G
authors.lastname: Greiner
authors.affiliation: Division of Hematology and Hemostaseology, Department of Internal Medicine I, Medical University of Vienna, Vienna, Austria. Ludwig Boltzmann Cluster Oncology, Medical University of Vienna, Vienna, Austria.
authors.forename: Katharina
authors.initials: K
authors.lastname: Blatt
authors.affiliation: Division of Hematology and Hemostaseology, Department of Internal Medicine I, Medical University of Vienna, Vienna, Austria. Ludwig Boltzmann Cluster Oncology, Medical University of Vienna, Vienna, Austria.
authors.forename: Barbara
authors.initials: B
authors.lastname: Peter
authors.affiliation: Division of Hematology and Hemostaseology, Department of Internal Medicine I, Medical University of Vienna, Vienna, Austria.
authors.forename: Gabriele
authors.initials: G
authors.lastname: Stefanzl
authors.affiliation: Division of Hematology and Hemostaseology, Department of Internal Medicine I, Medical University of Vienna, Vienna, Austria.
authors.forename: Daniela
authors.initials: D
authors.lastname: Berger
authors.affiliation: Department of Laboratory Medicine, Medical University of Vienna, Vienna, Austria.
authors.forename: Martin
authors.initials: M
authors.lastname: Bilban
authors.affiliation: Division of Hematology and Hemostaseology, Department of Internal Medicine I, Medical University of Vienna, Vienna, Austria. Ludwig Boltzmann Cluster Oncology, Medical University of Vienna, Vienna, Austria.
authors.forename: Susanne
authors.initials: S
authors.lastname: Herndlhofer
authors.affiliation: Division of Haematology, Department of Internal Medicine, Medical University of Graz, Graz, Austria.
authors.forename: Heinz
authors.initials: H
authors.lastname: Sill
authors.affiliation: Division of Hematology and Hemostaseology, Department of Internal Medicine I, Medical University of Vienna, Vienna, Austria. Ludwig Boltzmann Cluster Oncology, Medical University of Vienna, Vienna, Austria.
authors.forename: Wolfgang R
authors.initials: WR
authors.lastname: Sperr
authors.affiliation: Institute of Gynecology and Obstetrics, Medical University of Vienna, Vienna, Austria.
authors.forename: Berthold
authors.initials: B
authors.lastname: Streubel
authors.affiliation: Department of Laboratory Medicine, Medical University of Vienna, Vienna, Austria.
authors.forename: Christine
authors.initials: C
authors.lastname: Mannhalter
authors.affiliation: College of Medical, Veterinary and Life Sciences, Institute of Cancer Sciences, University of Glasgow, Glasgow, Scotland, United Kingdom.
authors.forename: Tessa L
authors.initials: TL
authors.lastname: Holyoake
authors.affiliation: Institute of Pharmacology and Toxicology, University of Veterinary Medicine Vienna, Vienna, Austria.
authors.forename: Veronika
authors.initials: V
authors.lastname: Sexl
authors.affiliation: Division of Hematology and Hemostaseology, Department of Internal Medicine I, Medical University of Vienna, Vienna, Austria. Ludwig Boltzmann Cluster Oncology, Medical University of Vienna, Vienna, Austria. peter.valent@meduniwien.ac.at.
authors.forename: Peter
authors.initials: P
authors.lastname: Valent
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology; D015415:Biomarkers; D045744:Cell Line, Tumor; D004195:Disease Models, Animal; D015195:Drug Design; D004357:Drug Synergism; D015870:Gene Expression; D015973:Gene Expression Regulation, Leukemic / Q000187:drug effects; D016313:Genes, abl; D064593:Heterografts; D006801:Humans; D016130:Immunophenotyping; D053645:Interleukin-2 Receptor alpha Subunit / Q000235:genetics / Q000378:metabolism*; D015464:Leukemia, Myelogenous, Chronic, BCR-ABL Positive / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D051379:Mice; D014411:Neoplastic Stem Cells / Q000378:metabolism*; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D050799:STAT5 Transcription Factor / Q000235:genetics / Q000378:metabolism*
chemical_list: D000970:Antineoplastic Agents; D015415:Biomarkers; D053645:Interleukin-2 Receptor alpha Subunit; D047428:Protein Kinase Inhibitors; D050799:STAT5 Transcription Factor