Flt3 ligand stimulates proliferation and inhibits apoptosis of acute myeloid leukemia cells: regulation of Bcl-2 and Bax.
Flt3/flk-2 ligand (flt3-L) is a potent costimulator of normal bone marrow (BM) myeloid progenitors. Flt3-L is produced by BM stromal cells and its receptor is expressed in the majority of acute myeloid leukemia (AML) cases. Therefore, flt3-L may play a role in the paracrine and/or autocrine loops sustaining leukemic cell growth. We evaluated the effects of recombinant human flt3-L on proliferation, apoptosis, and Bcl-2 and Bax expression in primary AML cells and compared them with those of stem cell factor (SCF). Mononuclear BM cells from patients with newly diagnosed AML were cultured in serum-free conditions with flt3-L, SCF, granulocyte colony-stimulating factor (G-CSF) and granulocyte macrophage-colony-stimulating factor (GM-CSF) alone and in combination. In 9 of 10 samples, flt3-L significantly increased [3H]thymidine uptake (geometric mean stimulation index, 7.5; range, 2.4 to 41.5). Flt3-L also increased the number of AML blast colonies by 126% (range, 61% to 181%). In these 9 samples, flt3-L significantly enhanced the proliferative response triggered by G-CSF or GM-CSF. Flt3-L prevented apoptosis in AML blasts. It reduced the number of apoptotic cells by 36% +/- 3.9% compared with control cultures. Combining flt3-L with G-CSF or GM-CSF doubled the antiapoptotic effect. Cellular Bcl-2 and Bax levels were determined separately for apoptotic and nonapoptotic cells by flow cytometry. Cells undergoing spontaneous apoptosis had low Bcl-2 and high Bax levels, whereas nonapoptotic cells had high Bcl-2 and low Bax levels. Flt3-L alone or in combination with G-CSF or GM-CSF did not upregulate Bcl-2. However, Bax expression decreased in viable cells in the presence of these cytokines and the lowest level was achieved when a combination of flt3 and GM-CSF was used. Proliferative and viability effects of flt3-L were similar to those of SCF. Our results demonstrate that flt3-L acts as a stimulatory factor for primary AML cells. The antiapoptotic effects of flt3-L or its combinations with G-CSF or GM-CSF correlate with their ability to prevent upregulation of Bax.
Lisovsky
M
M
Department of Hematology, University of Texas M.D. Anderson Cancer Center, Houston 77030, USA.
Estrov
Z
Z
Zhang
X
X
Consoli
U
U
Sanchez-Williams
G
G
Snell
V
V
Munker
R
R
Goodacre
A
A
Savchenko
V
V
Andreeff
M
M
D000208:Acute Disease; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D017209:Apoptosis / Q000187:drug effects*; D002455:Cell Division / Q000187:drug effects; D016895:Culture Media, Serum-Free; D005260:Female; D015973:Gene Expression Regulation, Leukemic / Q000187:drug effects*; D016179:Granulocyte Colony-Stimulating Factor / Q000494:pharmacology; D016178:Granulocyte-Macrophage Colony-Stimulating Factor / Q000494:pharmacology; D006801:Humans; D007951:Leukemia, Myeloid / Q000235:genetics / Q000473:pathology*; D008297:Male; D008565:Membrane Proteins / Q000494:pharmacology*; D008875:Middle Aged; D009363:Neoplasm Proteins / Q000096:biosynthesis* / Q000235:genetics; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis* / Q000235:genetics / Q000502:physiology; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000096:biosynthesis* / Q000235:genetics; D020794:Receptor Protein-Tyrosine Kinases / Q000502:physiology; D011993:Recombinant Fusion Proteins / Q000494:pharmacology; D019089:Stem Cell Factor / Q000494:pharmacology; D014407:Tumor Cells, Cultured / Q000187:drug effects; D051028:bcl-2-Associated X Protein; D051941:fms-Like Tyrosine Kinase 3
C494826:BAX protein, human; D016895:Culture Media, Serum-Free; D008565:Membrane Proteins; D009363:Neoplasm Proteins; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D011993:Recombinant Fusion Proteins; D019089:Stem Cell Factor; D051028:bcl-2-Associated X Protein; C084881:flt3 ligand protein; D016179:Granulocyte Colony-Stimulating Factor; D016178:Granulocyte-Macrophage Colony-Stimulating Factor; C497970:FLT3 protein, human; D020794:Receptor Protein-Tyrosine Kinases; D051941:fms-Like Tyrosine Kinase 3