STAT-3 activates NF-kB in chronic lymphocytic leukemia cells

NF-kB plays a major role in the pathogenesis of B-cell neoplasms. A broad array of mostly extracellular stimuli has been reported to activate NF-kB, to various degrees, in chronic lymphocytic leukemia (CLL) cells. Because CLL cells harbor high levels of unphosphorylated STAT-3 (USTAT-3) and USTAT-3 was reported to activate NF-kB, we sought to determine whether USTAT-3 activates NF-kB in CLL. Using the electrophoretic mobility shift assay (EMSA), we studied peripheral blood low-density cells from 15 patients with CLL and found that CLL cell nuclear extracts from all the samples bound to an NF-kB DNA probe, suggesting that NF-kB is constitutively activated in CLL. Immunoprecipitation studies showed that STAT-3 bound NF-kB p65, and confocal microscopy studies detected USTAT-3/NF-kB complexes in the nuclei of CLL cells, thereby confirming these findings. Furthermore, infection of CLL cells with retroviral STAT-3-short hairpin RNA attenuated the binding of NF-kB to DNA, as assessed by EMSA, and downregulated mRNA levels of NF-kB- regulated genes, as assessed by quantitative PCR. Taken together, our data suggest that USTAT-3 binds to the NF-kB p50/p65 dimers and that the USTAT-3/NF-kB complexes bind to DNA and activate NF-kB- regulated genes in CLL cells. Mol Cancer Res; 9(4); 507-15