CXCL8 and interleukin-6 in B-cell chronic lymphocytic leukemia are up-reuglated through the activity of CXCL12

Interactions between stromal and tumor cells in the microenvironment play a key role in B-cell chronic lymphocytic leukemia (B-CLL) onset and progression. This complex cross-talk is based on cytokine release and intercellular contacts that contribute to regulate the mechanisms of cell survival and apoptosis. Among the cytokines involved in this network, CXCL8/IL-8 and IL-6 are particularly noteworthy as potential pro-survival molecule able to decrease apoptosis in B-CLL cells. In this study, we explored whether the CXCL12 chemokine of stromal origin can regulate the expression of CXCL8 and IL-6 in B-CLL cells. We analyzed primary peripheral blood B-cells from 19 B-CLL patients. Engagement of CXCR4 expressed by B-CLL with its own ligand CXCL12 induced a significant increased production of CXCL8 (17/19 cases) and IL-6 (15/16 cases) but was ineffective on IL-1, TNF, or IL-10 production, as simultaneously measured by cytometric bead array kit and flow cytometry analysis. The average fold-induction ± SD was 3.2 ± 1.4 (range 1.5–6.2) for CXCL8 and 3.9 ± 2.6 (range 1.4–11) for IL-6. Real time PCR analysis confirmed the CXCL8 and IL-6 increased expression also at the level of mRNA. We then investigated the role of the mitogen activated protein kinases (MAPK) p38 and JNK as well as NF-kappa B pathways that can contribute to regulate CXCL8 and IL-6 production in some cells. To this aim, we used SB203580, a compound that specifically blocks p38 enzymatic activity, SP600125, a potent and selective inhibitor of JNK, and MG132, which selectively blocks proteasome and inhibits NF-kappa B activation. Neutralization of p38 activity, but not JNK, suppressed both constitutive and inducible production of CXCL8 and IL-6, thus suggesting that the p38 pathway is required for the expression of both cytokines in B-CLL. In contrast, the blockage of NF-kappa B activation inhibits the production of IL-6 but not CXCL8. Our data show that CXCL8 and IL-6 are physiologically regulated by the CXCL12/CXCR4 axis and suggest that regulation of both cytokines requires the p38 MAPK activity whereas NF-kappa B is necessary only for the expression of IL-6. Since CXCL8 as well as IL-6 have been implicated in progression of B-CLL disease, our findings suggest that, by up-regulating these cytokines, the CXCL12/CXCR4 axis may contribute to the pathogenesis of B-CLL.