title: Inhibition of the NADPH oxidase regulates heme oxygenase 1 expression in chronic myeloid leukemia.
abstract: BACKGROUND
  Patients with chronic myelogenous leukemia (CML) in blast crisis have a poor response to tyrosine kinase inhibitors designed to inhibit the breakpoint cluster region-v-Abelson murine leukemia viral oncogene homolog 1 (BCR-ABL1) oncogene. Recent work has demonstrated that heme oxygenase 1 (HO-1) expression is increased in BCR-ABL1-expressing cells and that the inhibition of HO-1 in CML leads to reduced cellular growth, suggesting that HO-1 may be a plausible target for therapy. The objective of the current study was to clarify the mechanism of HO-1 overexpression and the role of the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase as a contributor to this mechanism in CML.
  
  
  METHODS
  HO-1 expression was evaluated in bone marrow specimens from patients with CML in various stages of disease, in a transplantation-based model for CML, and in CML cell lines. Chemical and genetic inhibition of the NADPH oxidase was carried out in CML cells.
  
  
  RESULTS
  Specimens from patients with CML in blast crisis displayed higher levels of HO-1 staining than specimens from patients with CML in chronic or accelerated phase. HO-1 up-regulation in BCR-ABL1-expressing cells was suppressed by diphenyleneiodonium (DPI), a chemical inhibitor of the NADPH oxidase. Targeting the NADPH oxidase through RNA interference (RNAi) to Ras-related C3 botulinum toxin substrate 1 (Rac1), a dominant-negative Rac1 construct or an inhibitor of Rac1 activity also blunted HO-1 protein expression. Moreover, inhibition of the NADPH oxidase by RNAi directed toward the 47-kd cytosolic subunit of Nox (p47phox) similarly abrogated HO-1 levels.
  
  
  CONCLUSIONS
  BCR-ABL1 expression up-regulated HO-1, a survival factor for CML cells. This up-regulation was more pronounced in blast crisis CML relative to early stage disease and was mediated by the NADPH oxidase components Rac1 and p47phox. The expression of p47phox was increased in BCR-ABL1-expressing cells.
authors.affiliation: Department of Pediatrics Research, The University of Texas MD Anderson Cancer Center, Houston, Texas, USA.
authors.forename: Melissa M
authors.initials: MM
authors.lastname: Singh
authors.forename: Mary E
authors.initials: ME
authors.lastname: Irwin
authors.forename: Yin
authors.initials: Y
authors.lastname: Gao
authors.forename: Kechen
authors.initials: K
authors.lastname: Ban
authors.forename: Ping
authors.initials: P
authors.lastname: Shi
authors.forename: Ralph B
authors.initials: RB
authors.lastname: Arlinghaus
authors.forename: Hesham M
authors.initials: HM
authors.lastname: Amin
authors.forename: Joya
authors.initials: J
authors.lastname: Chandra
mesh_terms: D000818:Animals; D001752:Blast Crisis / Q000235:genetics; D001853:Bone Marrow / Q000378:metabolism; D045744:Cell Line, Tumor; D051547:Heme Oxygenase-1 / Q000378:metabolism*; D006801:Humans; D015464:Leukemia, Myelogenous, Chronic, BCR-ABL Positive / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D019255:NADPH Oxidases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D009368:Neoplasm Transplantation; D009861:Onium Compounds / Q000494:pharmacology; D017382:Reactive Oxygen Species / Q000378:metabolism; D014183:Transplantation, Heterologous; D015854:Up-Regulation
chemical_list: D009861:Onium Compounds; D017382:Reactive Oxygen Species; C007517:diphenyleneiodonium; D051547:Heme Oxygenase-1; D019255:NADPH Oxidases