Role of the RANKL/RANK system in the induction of interleukin-8 (IL-8) in B chronic lymphocytic leukemia (B-CLL) cells.

B chronic lymphocytic leukemia (B-CLL) cells express several members of the tumor necrosis factor (TNF) family, such as CD40L, CD30L, and TRAIL. By using the cDNA microarray technology, B-CLL samples were found to overexpress receptor activator of nuclear factor kB (NF-kB) ligand (RANKL), as compared to normal CD19(+) B cells. These findings were validated at the protein level by Western blot and flow cytometry analyses. Moreover, unlike primary normal B cells, leukemic B-CLL cells showed surface expression of RANK, the cognate transmembrane receptor of RANKL. When added in vitro to B-CLL cultures, either alone or in association with chlorambucil or fludarabine, recombinant RANKL did not significantly modulate cell viability, and it minimally affected the IL-8 expression/release. On the other hand, treatment with RANK-Fc chimera potently upregulated the release of IL-8 in the B-CLL culture supernatants, suggesting involvement of reverse signaling through transmembrane RANKL in IL-8 induction. In turn, exposure of B-CLL cells to recombinant IL-8 significantly decreased spontaneous apoptosis as well as chlorambucil- and fludarabine-mediated cytoxicity in B-CLL cells. Since IL-8 has been implicated in progression of B-CLL disease, our findings suggest that, by upregulating IL-8, the RANKL/RANK system may contribute to the pathogenesis of B-CLL.