PARP1 and precursor B-cell acute lymphoblastic leukemia: However, the pattern of PARP1 expression was distinct for B-ALL cells relative to BMSC, increasing significantly in response to X-radiation (measured at 30 min) as well as following proliferative stress (at 24 h in sham) (Fig. 4f)(Supplementary Fig. S15c), suggesting a reliance on PARP1 expression for B-ALL cell survival following stress.