FRAT2 confers chemoresistance through Rac activation. (A) The proportion of leukemic MLL-ENL cells surviving exposure to the indicated concentrations of doxorubicin and NSC23766 (NSC) after 24 hours, normalized to cells treated with vehicle alone. Error bars represent SD of mean values (n = 3). (B) Bar chart showing IC₅₀ values for graph in panel A. Error bars represent SD of mean values (n = 3). **P < .01 versus control. (C) Percentage of viable leukemic MLL-ENL cells after 24 hours of exposure to the indicated concentrations of NSC. Error bars represent SD of mean values (n = 3). (D) The proportion of leukemic MLL-ENL cells transduced with Scrambled (Sc) or Frat2 (F2b) shRNA retroviral vectors surviving exposure to the indicated concentrations of doxorubicin. Error bars represent SD of mean values (n = 3). At 48 hours after shRNA transduction, cells were selected with puromycin for 72 hours and then used in the analysis. (E) Bar chart showing IC₅₀ values for graph in panel D. Error bars represent SD of mean values (n = 3). **P < .01 versus control. (F) Western blot analysis of Rac1 and Rac2 GTP and total Rac in preleukemic and leukemic wild-type B6ME (B6) and F123ME (F123) cells. Numbers represent densitometric quantitation of Rac GTP levels normalized to total Rac protein bands. α-tubulin served as a loading control. Data were obtained from individual preleukemic and leukemic cell lines in each case and are representative of 3 independent experiments. (G) Graph showing the proportion of leukemic wild-type B6ME and F123ME cells surviving exposure to the indicated concentrations of doxorubicin after 24 hours, normalized to cells treated with vehicle alone. Responses for 3 independent B6ME and F123ME leukemic cell lines are shown. Error bars represent SD of mean values (n = 3). Data are representative of 4 independent experiments. (H) Bar chart showing IC₅₀ values for graph in panel G. Error bars represent SD of mean values (n = 3 independent cell lines). **P < .01 versus control. (I) Western blot analysis of MCL expression in 2 independently generated leukemic B6ME and 2 F123ME cell lines. α-tubulin served as a loading control. Numbers represent densitometric quantitation of MCL1 levels normalized to α-tubulin.