The PARP inhibitor PJ34 causes a PARP1-independent, p21 dependent mitotic arrest

► Mitotic growth arrest by PJ34 is PARP1 + 2 independent. ► PJ34 growth arrest occurs in cells from diverse genetic backgrounds. ► PJ34 causes a G2/M growth arrest, independent of ATM, p53 or Chk1. ► PJ34 growth arrest is caffeine sensitive and UCN01 insensitive. ► ATR is necessary for PJ34 growth arrest. ► PJ34 activates p21 gene expression by both p53 dependent and independent pathways.