Interaction of interleukin-7 and interleukin-3 with the CXCL12-induced proliferation of B-cell progenitor acute lymphoblastic leukemia

Background and Objectives The chemokine stroma-derived factor 1 alpha (SDF-1 alpha or CXCL12) is essential for proliferation of B lineage acute lymphoblastic leukemia (ALL) cells in their physiological microenvironment, bone marrow stroma. CXCL12 synergizes with cytokines that stimulate myeloid cells, but its interaction with cytokines affecting lymphoid cells has not been examined. We investigated whether interleukin (IL)-7 and IL-3 interact with CXCL12 to regulate ALL proliferation. Design and Methods The survival of ALL cells in serum-free cultures, with or without stromal support and cytokines, was assessed by flow cytometry, and proliferation by H-3-thymidine incorporation. Signaling mechanisms were assessed by western blotting of phosphorylated forms of signaling molecules and by the use of specific inhibitors. Results CXCL12, IL-3, and IL-7 had only marginal effects on ALL cell survival under serum-free conditions. However, these molecules individually induced significant proliferative responses in stromal cultures of 11 cases of ALL. The combination of CXCL12 with IL-7 or IL-3 produced a variety of responses, with clear synergistic or additive interactions observed in four cases. Synergistic proliferation in response to CXCL12 plus IL-7 was associated with enhanced phosphorylation of the mitogen-activated protein kinases, ERK-1/2 and p38, and AKT, and was partially inhibited by pretreatment of cells with inhibitors for p38 MAPK and phosphatidylinositol 3-kinase, implicating these pathways in the proliferation in response to IL-7 plus CXCL12. Interpretation and Conclusions These findings indicate a complex interaction between signaling from the CXCR4 receptor on ALL cells with those initiated by the cytokines IL-7 and IL-3, suggesting that CXCL12 may facilitate ALL proliferation by enhancing cytokine-signaling pathways in responsive cases.