Fig. 7: PARP1 cleavage promotes apoptosis via a positive feedback loop.

a PARP1 cleavage, caspase 3 activation, and RIG-I activation were examined in wild-type U2OS cells and U2OS cells expressing non-cleavable PARP1 (D214N) at different time points during 5 μg/mL poly(dA-dT)-induced apoptosis. b Myc-tagged POLR3B, POLR3F, or POLR3G subunit was expressed in U2OS cells. ADP-ribosylation of Pol III was examined by IP and western blotting with the indicated antibodies in a time course in cells treated with 5 μg/mL poly(dA-dT). c Induction of IFN-β by poly(dA-dT) was analyzed by luciferase reporter assay in wild-type or PARP1-null cells. d Induction of IFN-β by poly(dA-dT) was examined in U2OS cells with or without 1-h treatment with 1 µM olaparib. e Induction of IFN-β by poly(dA-dT) was determined in PARP1-null cells reconstructed with wild-type PARP1 or the D214N mutant. f Apoptotic cells were examined by Annexin V-FITC/PI double staining in parental U2OS cells or PARP1 knockout cells. g Apoptotic cells were examined by Annexin V-FITC/PI double staining in U2OS cells with or without 1-h treatment with 1 µM olaparib. h Apoptotic cells were examined by Annexin V-FITC/PI double staining in the PARP1-null cells reconstructed with wild-type PARP1 or the D214N mutant. Note that the apoptotic cells were harvested after 6-h treatment with 5 μg/mL poly(dA-dT) in c–h. Data are represented as means ± SD as indicated from three independent experiments. Significance of differences was evaluated by Student’s t-test. *P < 0.05; **P < 0.01; ***P < 0.001.