Characterization and modulation of NFκB in chronic lymphocytic leukemia B cells
Complex signaling pathways mediated by TNF receptor family members such as CD40 are important regulators of lymphocyte proliferation and apoptosis. NFκB includes a family of related proteins that impact B cell transcription and differentiation. In nontransformed B cells, ligation of CD40 at the cell surface results in augmented NFκB entry into the nucleus. In this work, we examined the effects of CD40 signaling in B lymphocytes isolated from patients with chronic lymphocytic leukemia (CLL), a malignancy characterized by a clonal expansion of CD5+ B cells. We prepared nuclear extracts from freshly isolated CLL B cells and assessed NFκB activity by electrophoretic mobility shift assay (EMSA) using an Ig-κB probe. We detected high constitutive levels of NFκB in nuclei prepared from ten CLL cases. Using antibodies to specific NFκB components, we determined by EMSA that c-rel and p65 both contribute to NFκB in the tumor nuclei. To evaluate whether NFκB in the CLL B cells might be modulated by stimuli that influence NFκB in nonmalignant B cells, we treated CLL B cells in vitro with monoclonal antibody to CD40, or with dexamethasone at 10-7M. CD40 ligation augmented nuclear NFκB activity and, in the majority of cases, dexamethasone reduced nuclear NFκB. Western blots for IκB, using cytosolic extracts of the same cells, demonstrated reduced cytosolic IκB after CD40 ligation, and increased IκB after dexamethasone exposure. We conclude that NFκB is readily detected in the nuclei of CLL B cells and can be altered by specific stimuli. The capacity to modulate NFκB may be useful in developing novel therapeutic strategies.