Chronic lymphocytic leukemia is characterized by the accumulation of monoclonal malignant CD5+ B cells that show resistance to apoptosis in vivo. Berg 36 (ZFP36L1, TIS11b, BRF1, cMG1, ERF1) is a zinc finger containing early response gene that was cloned from PMA-stimulated B chronic lymphocytic leukemia cells. Induced expression of this gene has been linked to calcium ionophore and anti-CD20-induced apoptosis of human B lymphoma cells. Berg36 protein has, in common with two other members of the small gene family (TIS11, TIS11d), been reported to function as an mRNA-binding protein that may promote instability of cytokine mRNAs. We have therefore studied the regulation of Berg36 expression in B-CLL cells in vitro, in response to cytokines and other signals that regulate apoptosis. B-CLL cells from 12 patients were purified and incubated with the following agents either alone or in combinations for a number of hours; IL-4, CD40 ligand, PMA or anti-CD20 antibody (rituximab). Apoptosis was measured after 24 hours by Annexin/PI staining and Berg-36 expression by Northern blot analysis. Spontaneous apoptosis in unstimulated B-CLL cells was 20.9±5.1%. Co-incubation of B-CLL cells with IL-4 reduced the percentage of apoptotic cells to 6.2±1.2%, but had no effect on Berg-36 expression. In contrast, both PMA and CD40 stimulation reduced the percentage of apoptotic cells (to 14.8±3.4% and 10.2±4.2% respectively), and markedly induced Berg36 expression. On the other hand, anti-CD20 antibody induced apoptosis (36.2±6.6%), but also induced Berg36 expression. Specific inhibitors of various intracellular signalling molecules confirmed that induction of Berg36 by different agents was mediated through different signalling pathways. In conclusion, expression of Berg36 can be induced in B-CLL cells by stimuli that induce either survival or apoptosis in these cells.

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