Background: Cytokines released in the bone marrow and thymic microenvironments play a key role in the growth of T-cell acute lymphoblastic leukemia. Among such cytokines, interleukin-8 is highly expressed in T-cell acute lymphoblastic leukemia cells refractory to chemotherapy. In this study we explored whether bone marrow stromal cells can regulate IL-8 expression in T-cell acute lymphoblastic leukemia and investigated the role of the stromal CXCL12 chemokine in this event. We also investigated the roles of the nuclear factor-kappaB and Jun-N-terminal kinase (JNK)/activating protein (AP)-1 signaling pathways, which contribute to regulate interleukin-8 production in some cells.
Design and methods: We analyzed the expression of interleukin-8 in primary cells from ten adult patients with T-cell acute lymphoblastic leukemia when these cells were cultured with bone marrow stromal cells or stimulated with exogenous CXCL12. Interleukin-8 mRNA was analyzed by a colorimetric assay. Cytokine production was assayed by cytometric antibody array and flow cytometry. Nuclear factor-kappaB and JNK/AP-1 activation was investigated by using specific inhibitors of these pathways, immunoblotting, electrophoretic mobility-shift assay and cell transfection assays.
Results: Bone marrow stromal cells upregulated interleukin-8 mRNA in T-cell acute lymphoblastic leukemia cells through the activity of CXCR4, the CXCL12 receptor, as assessed by the use of neutralizing antibodies. Exogenous CXCL12 induced a significant increase in the production of IL-8 mRNA and protein in all T-cell acute lymphoblastic leukemia cases. We showed that CXCL12 activates the nuclear factor-kappaB and JNK/AP-1 pathways, and that these events are required for increased expression of interleukin-8. Furthermore, the nuclear factor-kappaB and AP-1 elements of the interleukin-8 promoter are necessary for both constitutive and CXCL12-induced interleukin-8 expression.
Conclusions: Interleukin-8 is physiologically regulated by the CXCL12/CXCR4 axis and the nuclear factor-kappaB and JNK/AP-1 pathways are required for interleukin-8 expression in T-cell acute lymphoblastic leukemia. We propose that, by upregulating interleukin-8, the bone marrow microenvironment and the CXCL12/CXCR4 axis may play a role in the pathogenesis of T-cell acute lymphoblastic leukemia.