title: Inverse relationship between myeloid maturation and leukotriene C4 synthase expression in normal and leukemic myelopoiesis-consistent overexpression of the enzyme in myeloid cells from patients with chronic myeloid leukemia.
abstract: OBJECTIVE
  Leukotriene (LT) C(4) synthase (LTC(4)S) is the key enzyme in the biosynthesis of LTC(4), which has been reported to stimulate the growth of human myeloid progenitor cells and is specifically overproduced in chronic myeloid leukemia (CML). The aim of this study was to clarify the expression of LTC(4)S during normal and leukemic myelopoiesis and to investigate the correlation between abnormal LTC(4)S expression in CML myeloid cells and the activity of the disease-specific tyrosine kinase p210 BCR-ABL.
  
  
  METHODS
  Immature and mature myeloid cell subpopulations were isolated with magnetic cell sorting from healthy volunteer bone marrow (n = 11) and CML patient peripheral blood (n = 8), respectively. The cells were subjected to analysis of LTC(4)S protein expression and activity. Expression of LTC(4)S was investigated in CD16(+) neutrophils from CML patients before and after 1 month of medication with imatinib mesylate (STI571), which is a specific inhibitor of p210 BCR-ABL.
  
  
  RESULTS
  Among normal cells, the highest enzyme activity was observed in the most immature, CD34(+) progenitor cell-enriched and CD15(+) myelocyte-enriched fractions. Subsequently, LTC(4)S activity decreased with increasing maturity, with only negligible amounts of LTC(4) produced in CD16(+) neutrophils. LTC(4)S was expressed at the protein level in the immature myeloid cell fractions but not in CD16(+) cells. In CML cells, LTC(4)S activity and expression were consistently elevated. Thus, the CML CD34(+) and CD15(+) cell fractions, as well as the CD11b(+) myelocyte/metamyelocyte-enriched fractions, produced 6 to 10 times as much LTC(4) as the corresponding normal cells. Again, enzyme expression was highest in the most immature cells, although evident LTC(4)S expression and activity remained in CML CD16(+) neutrophils. Interestingly, treatment of five CML patients with imatinib mesylate down-regulated the abnormal neutrophil LTC(4)S expression and activity.
  
  
  CONCLUSIONS
  Expression of LTC(4)S in immature myelopoid cells is in line with a role for this enzyme in myelopoiesis. In addition, consistent overexpression of LTC(4)S in CML and the correlation to p210 BCR-ABL activity suggests that LTC(4)S may be involved in leukemic pathogenesis.
authors.affiliation: Division of Physiological Chemistry II, Department of Medical Biochemistry and Biophysics, Scheele Laboratory, Karolinska Institutet, S-171 77 Stockholm, Sweden. Susanne.Tornhamre@mbb.ki.se
authors.forename: Susanne
authors.initials: S
authors.lastname: Tornhamre
authors.forename: Leif
authors.initials: L
authors.lastname: Stenke
authors.forename: Anna
authors.initials: A
authors.lastname: Granzelius
authors.forename: Mikael
authors.initials: M
authors.lastname: Sjölinder
authors.forename: Barbro
authors.initials: B
authors.lastname: Näsman-Glaser
authors.forename: Cecilia
authors.initials: C
authors.lastname: Roos
authors.forename: Susanne
authors.initials: S
authors.lastname: Widell
authors.forename: Jan Ake
authors.initials: JA
authors.lastname: Lindgren
mesh_terms: D018952:Antigens, CD34; D001549:Benzamides; D016022:Case-Control Studies; D002454:Cell Differentiation / Q000187:drug effects; D015973:Gene Expression Regulation, Leukemic / Q000187:drug effects; D005982:Glutathione Transferase / Q000235:genetics* / Q000502:physiology; D006801:Humans; D000068877:Imatinib Mesylate; D015464:Leukemia, Myelogenous, Chronic, BCR-ABL Positive / Q000201:enzymology* / Q000209:etiology / Q000473:pathology; D016256:Lewis X Antigen; D022423:Myeloid Cells / Q000166:cytology / Q000201:enzymology*; D038042:Myelopoiesis / Q000187:drug effects / Q000502:physiology*; D009504:Neutrophils / Q000201:enzymology / Q000473:pathology; D010879:Piperazines / Q000494:pharmacology / Q000627:therapeutic use; D011743:Pyrimidines / Q000494:pharmacology / Q000627:therapeutic use; D017452:Receptors, IgG
chemical_list: D018952:Antigens, CD34; D001549:Benzamides; D016256:Lewis X Antigen; D010879:Piperazines; D011743:Pyrimidines; D017452:Receptors, IgG; D000068877:Imatinib Mesylate; D005982:Glutathione Transferase; C041116:leukotriene-C4 synthase