PARP1 and systemic lupus erythematosus: However, neither proliferation (Ki67) nor apoptosis [cleaved poly(ADP-ribose) polymerase 1 (PARP1) and cleaved caspase-3] differed in SLE B cells when compared to HC, indicating that ATR/Chk1 pathway deregulation may not have a significant impact on these processes in SLE and that other cell responses may be affected (Fig. 2, C and D).