Flt3 ligand stimulates proliferation and inhibits apoptosis of acute myeloid leukemia cells: regulation of Bcl-2 and Bax.

Abstract

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.

• Authors: M Lisovsky, Z Estrov, X Zhang, U Consoli, G Sanchez-Williams, V Snell, R Munker, A Goodacre, V Savchenko, M Andreeff
• Journal: Blood (Blood) Vol. 88 Issue 10 Pg. 3987-97 (Nov 15 1996) ISSN: 0006-4971 [Print] United States
• PMID: 8916965 (Publication Type: Comparative Study, Journal Article, Research Support, Non-U.S. Gov't, Research Support, U.S. Gov't, P.H.S.)

Chemical References

• BAX protein, human
• Culture Media, Serum-Free
• Membrane Proteins
• Neoplasm Proteins
• Proto-Oncogene Proteins
• Proto-Oncogene Proteins c-bcl-2
• Recombinant Fusion Proteins
• Stem Cell Factor
• bcl-2-Associated X Protein
• flt3 ligand protein
• Granulocyte Colony-Stimulating Factor
• Granulocyte-Macrophage Colony-Stimulating Factor
• FLT3 protein, human
• Receptor Protein-Tyrosine Kinases
• fms-Like Tyrosine Kinase 3

Topics

• Acute Disease
• Adult
• Aged
• Aged, 80 and over
• Apoptosis (drug effects)
• Cell Division (drug effects)
• Culture Media, Serum-Free
• Female
• Gene Expression Regulation, Leukemic (drug effects)
• Granulocyte Colony-Stimulating Factor (pharmacology)
• Granulocyte-Macrophage Colony-Stimulating Factor (pharmacology)
• Humans
• Leukemia, Myeloid (genetics, pathology)
• Male
• Membrane Proteins (pharmacology)
• Middle Aged
• Neoplasm Proteins (biosynthesis, genetics)
• Proto-Oncogene Proteins (biosynthesis, genetics, physiology)
• Proto-Oncogene Proteins c-bcl-2 (biosynthesis, genetics)
• Receptor Protein-Tyrosine Kinases (physiology)
• Recombinant Fusion Proteins (pharmacology)
• Stem Cell Factor (pharmacology)
• Tumor Cells, Cultured (drug effects)
• bcl-2-Associated X Protein
• fms-Like Tyrosine Kinase 3