Effect of Brd4 inhibition on the proliferation and apoptosis of human peripheral activated CD19+ B cells
Initially, we evaluated the effect of Brd4 inhibition on B cell survival. We observed that stimulation with combinations of anti-IgM, rCD40L, CpG ODN2006, rIL-4 and rIL-2 increased the survival of cultured B cells at days 3, 5 and 7 (Fig. 1A); however, the Brd4-specific inhibitor PFI-1 did not affect the survival of costimulated B cells. We next determined the effect of Brd4 inhibition on B cell proliferation. We demonstrated that B cells stimulated with anti-IgM/anti-CD40 exerted increased proliferative capacity compared with unstimulated B cells; however, this increase was not inhibited by treatment with PFI-1 (Fig. 1B and C). We also examined the inhibitory effect of PFI-1 on B cell apoptosis, as measured by flow cytometry with annexin V/PI staining. Stimulation with anti-IgM/anti-CD40 decreased the frequency of apoptotic cells, but in cultures of activated B cells, PFI-1 did not increase the percentage of early apoptotic cells at days 3, 5 and 7 (Fig. 1D and E). We also found that treatment with JQ1, another Brd4 inhibitor, did not affect the proliferation and apoptosis of activated human peripheral CD19+ B cells (data not shown). These data suggest that Brd4 is not involved in the proliferation and apoptosis of activated human peripheral CD19+ B cells.