Role of PARP-14 in IL-4–stimulated proliferation. (A) Failure of anti-μ–stimulated B lacking PARP-14 to respond to IL-4 with increased proliferation. Thymidine incorporation into cells from WT and PARP-14–null mice 32 hours after stimulation with anti-IgM (1 μg/mL) or anti-IgM + IL-4. Data are shown both as mean (± SEM) cpm from an assay representative of 3 independent experiments (left panel) and as the net effect of IL-4 (IL-4–stimulated proliferation) in each of the 3 replicate experiments (right panel). Each error bar indicates SD. *P < .05, for difference between means for WT versus PARP-14–null samples in each case. (B) Normal G₁/S-transition response of PARP-14 null B cells to anti-IgM plus IL-4. The same conditions for measurement of proliferation of anti-IgM + IL-4–stimulated B cells were used as in panel A, except that, instead of tritiated thymidine, cultures were pulsed with BrdU, surface stained to reveal B cells, and processed to determine the fraction of the B-cell population that incorporated BrdU. Shown are FACS profiles of anti-BrdU signal gated on B220⁺ cells from 1 experiment representative of 3 independent repeats; there also was no difference in the percentage of BrdU⁺ events in the B220(−) gate. (C) Anti-IgM–stimulated B lymphocytes depend on PARP-14 for survival signaling by IL-4. Splenocytes from WT and PARP-14 KO were cultured (20 hours) with anti-IgM (1 μg/mL) or anti-IgM + IL-4 (5 ng/mL), and analyzed by TUNEL. FACS profiles show TUNEL data (fluorescence intensity of avidin-FITC) from the B220⁺ gate in a representative experiment of 3 independent experiments. Inset numbers indicate both the percentage of events TUNEL-positive in the samples, and mean fluorescence intensity for the overall population.