ABT-737 reverses resistance to apoptosis caused by Bim knockdown. (A) WT HEL cells (open bars) and HEL cells stably transfected with vectors constitutively expressing either scrambled (pSuper-bim75; 1 stably transfected clone analyzed: Scrambled; gray bars) or shRNA sequences targeting Bim (pSuper-bim73, clone #1: shBim; black bars) were treated with increasing doses of ABT-737 for 24 hours. Apoptosis was assessed by an annexin V assay. Data are mean ± SD of annexin V⁺ cells. Error bars represent SD (n = 3). (B) HEL cells stably transfected with pSuper-bim73 constitutively expressing scrambled shRNA (sc) were treated with increasing doses of JAK inhibitor I in the absence of ABT-737 (gray bars). HEL cells stably transfected with pSuper-bim75 (clone #1), constitutively expressing shRNA targeting Bim (shBim), were treated with increasing doses of JAK inhibitor I in the absence (black bars) or presence (hatched bars) of 0.3μM ABT-737 for 24 hours. Apoptosis was assessed by an annexin V assay. Data are mean ± SD of annexin V⁺ cells. Error bars represent SD (n = 3). JAK inhibitor alone versus JAK inhibitor I and ABT-737: *P < .05, ***P < .001.