Stromal cells prevent apoptosis of AML cells by up-regulation of anti-apoptotic proteins

Abstract

The aim of this study was to study interactions between stromal bone marrow microenvironment and leukemic cells. We tested the hypothesis that stromal cells prevent apoptosis of AML cells by up-regulating anti-apoptotic proteins in leukemic blasts. In HL-60 and NB-4 cells, serum deprivation-and ara-Cinduced apoptosis was diminished when cells were cocultured with murine MS-5 stromal cells (P Ͻ 0.02). This effect was reproduced with conditioned medium from MS-5 cells. Cocultivation with stromal cells induced Bcl-2 expression levels, both by PCR analysis and flow cytometry. In primary AML (n = 14), ara-C-induced apoptosis was significantly lower in cells cocultured with MS-5 cells than in controls (P Ͻ 0.001). This effect was partially preserved when leukemic cells were separated from stromal cells by a microporous insert (in 5/9 samples, P = 0.04). In addition, Bcl-2 levels were significantly higher in stroma-supported than in control CD34+ AML cells (P Ͻ 0.01). Bcl-X L levels were higher in 5/7 samples grown on stromal layers. Of note, in AML patients resistant to induction chemotherapy (n = 6), Bcl-2 increased significantly after cultivation with stromal cells, but no such increase was noted in cells from chemotherapy-sensitive patients. In conclusion, MS-5 stromal cells prevented apoptosis in HL-60 cells and in primary AML blasts via modulation of Bcl-2 family proteins. The observed association of high Bcl-2 expression in stroma-supported AML blasts in vitro with resistance to chemotherapy in vivo suggests that the same mechanisms may be operational in vivo.

CXCL12+ stromal cells as bone marrow niche for CD34+ hematopoietic cells and their association with disease progression in myelodysplastic syndromes

“…23 The previous study also showed that coculture with CXCL12-producing stromal cell diminished ara-C-induced apoptosis in leukemic cells by BCL-2 upregulation. 19 Therefore, under a similar mechanism, increased expression of CXCL12 might be associated with the chemoresistance of CD34 þ hematopoietic cells in MDS/ AML-MRC bone marrow. CXCL12-abundant reticular cells are known to be major producers of SCF in the bone marrow, 5 and we found that the MDS bone marrow expresses high levels of SCF.…”

CXCR4 downregulation of let-7a drives chemoresistance in acute myeloid leukemia

“…Our group and others have shown that culturing of AML cells with SDF-1α (also known as CXCL12) promotes their survival, whereas adding neutralizing CXCR4 antibodies, SDF-1α antibodies, or the CXCR4 inhibitor AMD3100 significantly decreases it. BMderived mesenchymal stromal cells can also protect AML cells from chemotherapeutic drug-induced apoptosis (6,7). Moreover, weekly administration of anti-human CXCR4 antibody to mice previously engrafted with human AML cells leads to a dramatic decrease of human AML cells in BM, blood, and spleen in a dose-and time-dependent manner (8,9).…”

CXCR4 is a prognostic marker in acute myelogenous leukemia

“…About 35% to 50% of AML patients display a normal karyotype, which can further be subdivided using predictive molecular markers, such as mutations in the fetal liver tyrosine kinase-3 (FLT3) gene and the mixed-lineage leukemia (MLL) gene. 6,7 Several studies indicated that adhesion to marrow stromal cells affects the survival and proliferation of AML cells 8,9 and protects AML cells from chemotherapy in vitro 10 and in vivo. 11 Adhesion molecules, particularly the very late antigen-4 (VLA-4) and VLA-5 integrins, are considered essential for AML cell adhesion to respective stromal ligands (fibronectin) 12 and for protection of AML cells from spontaneous or drug-induced apoptosis.…”