[Function of alternative NF-κB activity in B-cell chronic lymphocytic leukemia cells]

To investigate the function of alternative NF-κB activity in B-cell chronic lymphocytic leukemia cells (B-CLL).

The mRNA expression of individual NF-κB subunits in CD5⁺CD19⁺ cells (CLL B-cells) from bone marrow (BM) of 56 patients with B-CLL was analyzed by quantitative RT-PCR. An ELISA-based NF-κB family transcription factor activity assay was performed to quantify the κB DNA-binding activity in nuclear extracts from CLL B-cells. Cell death of CLL-B cells was determined by PI staining, RelA and RelB expression at protein level of CLL B-cells by Western blot analyses.

The expression levels of RelA, p50, RelB and p52 mRNA in CLL B-cells were all higher than that of normal B cells with statistical significance (P<0.05). RelA was activated in almost all the patients detected while RelB activity was induced in part of samples. The average RelA activity in CLL B-cells was increased compared to that in normal B cells while the average RelB activity was similar to that of normal B cells. When cultured in vitro for 24, 48 and 72 hours, the frequencies of cell death of CLL B-cells from RelA⁺/RelB⁻ group were(35.54±4.43)%,(50.92±8.44)%, and(49.24±8.16)%, respectively; that of the RelA⁺/RelB⁺ group were (20.65±2.37)%, (18.17±1.36)%, and (26.55±4.08)%, respectively. When the cells from RelA+/RelB⁻ group were co-cultured with bone marrow stromal cells (hBMSCs), the frequencies of cell death of CLL B-cells were decreased compared to that of the cells cultured alone, while the frequencies of cell death of RelA⁺/RelB⁻ CLL B-cells were higher than that of CLL B-cells from RelA⁺/RelB⁺ group when co-cultured with hBMSCs. RelA and RelB expression in CLL-B cells from the RelA⁺/RelB⁻ group was induced after co-cultured with hBMSCs for 48 h. RelB was reduced in the cytoplasm and increased in the nucleus in CLL-B cells from the RelA+/RelB+ group.

The alternative NF-κB was indeed activated and presented heterogeneous in CLL B-cells from BM. Activation of RelB combined with RelA activity could provide the survival advantage to CLL B-cells from BM. Co-culture with hBMSCs could protect CLL-B cells through the induction of RelA and Rel B expressions.