title: Hypoxia influences stem cell-like properties in multidrug resistant K562 leukemic cells.
abstract: OBJECTIVE
  The present study investigates the potential role of hypoxia in maintaining stem cell-like properties and therapeutic resistance in K562 leukemic cell.
  
  
  METHODS
  Western blot, flow cytometry and cell viability assays were used to investigate the effects of hypoxia (1% O2) on cell proliferation, drug resistance and expression of the hypoxia inducible factor-2α (HIF-2α), the octamer-binding transcription factor 4 (Oct4), CD133, CD34 and the ATP-binding cassette sub-family G member 2 (ABCG2) as well as Smad2 phosphorylation in the drug resistant cell line K562/DOX and its parental cell line.
  
  
  RESULTS
  Hypoxia induced growth inhibition and significantly upregulated HIF-2α, CD133, Oct4, CD34 and ABCG2 expression in the wild type K562 cells (p<0.05). The IC50 of doxorubicin was also enhanced about 2.5-fold in hypoxia. In contrast, the K562/DOX cells, which showed significantly higher ABCG2 expression and IC50 for various drugs, no significant difference in cell proliferation was observed between hypoxia and normoxia. The hypoxia-induced upregulation of HIF-2α, CD133, Oct4, CD34 and ABCG2 expression was significantly lower than in the wild type cells (p<0.05). Moreover, hypoxia induced the phosphorylation of Smad2 and additional treatment with SD-208, an inhibitor of the TGF-β receptor I kinase, resulted in a dose-dependent downregulation of CD133 and Oct4 in the K562/DOX cells.
  
  
  CONCLUSIONS
  Hypoxia plays an important role in enhancing the stem cell-like properties and to induce multidrug resistance of leukemia cells. The activation of the TGF-β/Smad2 signaling pathway may be involved in the regulation of this pathophysiological process.
authors.affiliation: Department of Hematology, the First Affiliated Hospital of Zhengzhou University, Zhengzhou, China. x.y.cui@medisin.uio.no
authors.forename: Xue Yan
authors.initials: XY
authors.lastname: Cui
authors.forename: Grethe
authors.initials: G
authors.lastname: Skretting
authors.forename: Ying
authors.initials: Y
authors.lastname: Jing
authors.forename: Hui
authors.initials: H
authors.lastname: Sun
authors.forename: Per Morten
authors.initials: PM
authors.lastname: Sandset
authors.forename: Ling
authors.initials: L
authors.lastname: Sun
mesh_terms: D018952:Antigens, CD34 / Q000378:metabolism; D000970:Antineoplastic Agents / Q000494:pharmacology*; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics / Q000378:metabolism; D015687:Cell Hypoxia; D049109:Cell Proliferation / Q000187:drug effects; D018432:Drug Resistance, Multiple / Q000235:genetics; D019008:Drug Resistance, Neoplasm / Q000235:genetics; D015973:Gene Expression Regulation, Leukemic / Q000187:drug effects; D006801:Humans; D020128:Inhibitory Concentration 50; D020014:K562 Cells; D007938:Leukemia / Q000378:metabolism; D014411:Neoplastic Stem Cells / Q000187:drug effects* / Q000378:metabolism*; D015398:Signal Transduction; D051899:Smad2 Protein / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000378:metabolism; D000099162:Endothelial PAS Domain-Containing Protein 1
chemical_list: D018952:Antigens, CD34; D000970:Antineoplastic Agents; D051792:Basic Helix-Loop-Helix Proteins; D051899:Smad2 Protein; D016212:Transforming Growth Factor beta; D000099162:Endothelial PAS Domain-Containing Protein 1
keywords: 3-(4,5-dimethylthiazol-2-yl)-2,5- diphenyltetrazolium bromide; ABC; AML; ATP-Binding Cassette; Acute myeloid leukemia; Ara-C; BM; DMSO; DOX; Drug concentrations inhibiting cell growth by 50%; Hypoxia; IC(50); Leukemia; MDR; MTT; MTX; Multi-drug resistance; PAGE; Stem cell-like properties; TBS-T; TGF-β; VCR; bone marrow; cytosine arabinoside; dimethyl sulfoxide; doxorubicin; methotrexate; multi-drug resistant; polyacrylamide gel electrophoresis; transforming growth factor-β; tris-buffered saline-Tween; vincristine