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.