RelB, Together with Rela, Maintains the Cellular Survival In Chronic Lymphocytic Leukemia

Abstract 3583

RelA, a classical NF-κB subunit, has been shown to function critically in cellular survival and drug-resistance of B-cell chronic lymphocytic leukemia (B-CLL). The significance of RelB, contributing to the alternative NF-κB activity, has not been addressed in B-CLL yet. The protein expression levels of NF-κB subunits in 60 B-CLL samples were examined in this study. According to the RelA and RelB expression status in the nuclear extracts of peripheral blood and bone marrow, the B-CLL samples were classified as RelA⁺/RelB⁻, RelA⁺/RelB⁺, and RelA⁻/RelB⁻ subgroups. The frequencies of the individual group were 30%, 30%, and 40%. In RelA⁺/RelB⁺ subgroup, both the RelA DNA-binding complex and the RelB DNA-binding complex were further detected in the nuclear extracts of B-CLL cells by electrophoretic mobility super-shift assay. Fresh CD19⁺ B-CLL cells from different subgroups were cultured for 48 hours ex vivo, the spontaneous apoptosis were quantified by Annexin-V/PI staining and the frequencies of apoptosis were 48±4.5% (RelA⁺/RelB⁻), 24±8.6% (RelA⁺/RelB⁺), and 65±5.0% (RelA⁻/RelB⁻) individually. In addition, when fresh B-CLL cells were incubated with MG-132, a proteosome inhibitor, a significant reduction of cellular survival in RelA⁺/RelB⁻ and RelA⁺/RelB⁺ group was observed in a dose and time-dependent manner. B-CLL cells from RelA⁺/RelB⁺ group were cultured for 0, 6 and 24 hours in the presence of CD40L (250μ g/ml), the cellular survival was not affected and the protein expression levels of NF-κB family members stayed unchanged. While the CD19⁺ B-CLL cells from RelA⁺/RelB⁻ group were cultured with CD40L, a modest decrease in apoptosis and a slightly increased RelB expression in cytoplasm and nucleus after 24-hour treatment were identified. The induction of RelA and RelB expression, companied by an evident decrease in apoptosis, was detected in cells from RelA⁻/RelB⁻ group. The alternative NF-κB signaling pathway, in terms of RelB/p52 nuclear translocation, functions specifically in lymphoid organogenesis and B-cell development. In this study, we show that RelB expression is detected in B-CLL cells and partially maintain the basal survival. CD40L triggers the expression of RelB, correlating with the enhanced survival. Taken together, not only RelA but also RelB subunit of NF-κB family plays an important role in the cellular behavior of B-CLL cells.