Effects of human FLT3 ligand on myeloid leukemia cell growth: heterogeneity in response and synergy with other hematopoietic growth factors

Abstract

A novel hematopoietic growth factor for primitive hematopoietic progenitor cells, the ligand for the flt3/flk2 receptor, (FL), has been recently purified and its gene has been cloned. In the present study, we investigated the effects of FL on the proliferation and differentiation of normal and leukemic myeloid progenitor cells. We demonstrate that FL is a potent stimulator of the in vitro growth of granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin- 3 (IL-3), or G-CSF-dependent granulocyte-macrophage committed precursors from Lin- CD34+ bone marrow cells of normal donors. By contrast, FL does not affect the growth of erythroid-committed progenitors even in the presence of erythropoietin. The effect of FL on the proliferation and on the in vitro growth of clonogenic leukemic precursor cells was studied in 54 acute myeloid leukemia (AML) cases. Fresh leukemia blasts from 36 of 45 patients with AML significantly responded to FL without any relation to the French-American-British (FAB) subtype. FL stimulated the proliferation of leukemic blasts in a dose-dependent fashion. Synergistic activities were seen when FL was combined with G-CSF, GM-CSF, IL-3, or stem cell factor (SCF). FL as a single factor induced or increased significantly colony formation by clonogenic precursor cells from 21 of 24 patients with AML. In the presence of suboptimal and optimal concentrations of G-CSF, GM-CSF, IL3, SCF, or a combination of all factors, FL strongly enhanced the number of leukemic colonies (up to 18-fold). We also evaluated the induction of tyrosine phosphorylated protein on FL stimulation in fresh AML cells. We demonstrate that, on FL stimulation, a band of phosphorylated protein(s) of about 90 kD can be detected in FL- responsive, but not in FL-unresponsive cases. This study suggests that FL may be an important factor for the growth of myeloid leukemia cells, either as a direct stimulus or as a synergistic factor with other cytokines.

GENETIC PROFILEOF ACUTE MYELOID LEUKEMIA

“…After the ligand–receptor interaction, the FLT3 receptor dimerizes, leading to autophosphorylation of tyrosine residues and triggers the phosphorylation/activation of cellular targets such as mitogen‐activated protein (MAP) kinase and STAT5. Reported ITD and point mutations in FLT3 constitutively activate the receptor, leading to proliferative and antiapoptotic signaling (85–87).…”

Tandem duplication of the FLT3 gene is found in acute lymphoblastic leukaemia as well as acute myeloid leukaemia but not in myelodysplastic syndrome or juvenile chronic myelogenous leukaemia in children

“…The interaction of FLT3 and its ligand (FL) regulates growth of pluripotent haemopoietic stem cells, early progenitor cells and immature lymphocytes (Rosnet et al, 1993;Brasel et al, 1995;Drexler, 1996), as well as ᭧ 1999 Blackwell Science Ltd Correspondence: Dr Yasuhide Hayashi, Department of Paediatrics, Faculty of Medicine, University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-8655, Japan. leukaemic cells (Piacibello et al, 1995;Carow et al, 1996;Dehmal et al, 1996;Drexler, 1996;Mckenna et al, 1996;Stacchini et al, 1996).…”

Hematopoietic Growth Factors and Blast Progenitors in Acute Leukemia

“…Differences in the effects of HGFs on AML blast progenitors can also be detected in other ways. As mentioned above, leukemic stem cells in AML that are stimulated to proliferate, undergo either a self-renewal (birth) or a determination (death) process during cell divi- Thrombopoietin, TPO (c-mplligand) growth stimulation (not restricted to AML-M7) [123][124][125][126][127] autocrine growth stimulation [166) growth enhancement with other cytokines [125,127) induction of megakaryocytic differentiation [123,124) Erythrpoietin, EPO no growth stimulation on its own [128,129) growth stimulation of erythroid leukemia cells [130) growth enhancement with other cytokines (not restricted to AML-M6) [128,129] Flt3 ligand, FL growth stimulation [111,112] synergistic growth enhancement with other cytokines [ [119][120][121][122] induction of differentiation towards eosinophils in sorne patients with AML-M2 [120,121] or AML-M6 [119] induction of monocytic differentiation [122] IL-6 little growth stimulation on its own [89,100,113,114] growth stimulation or inhibition in sorne patients [87,100,150] indirect growth stimulation [168] enhancement [87,89,100,[113][114]…”

“…This group of HGFs includes stem cell factor (SCF, also variously referred to as c-kit ligand, steel factor, mast cell growth factor, etc.) [89,[101][102][103][104][105][106][107][108][109][110], flt3 ligand [111,112), IL-6 [87,89,100,[113][114][115], IL-11 [89,115,116) and IL-12 [89). The synergism indicates the presence of subpopulations of blast progenitors requiring more than one HGF to form colonies, possibly based on the following mechanism; synergistic factors do not stimulate cell growth but rather upregulate the receptors for other cytokines, which in tum stimulate colony formation when activated through binding with their ligands.…”