Rac2 or Bcl-xL expression rescues the effects of Rac2 deficiency in MA9 cells. (A) Western blot analysis of 2 MA9 cell lines demonstrates variably decreased expression of Bcl-xL, Bcl-2, and Mcl-1 on knockdown of Rac2. Band densitometry was normalized to β-actin and NT control. Wild-type Rac2 (B) or Bcl-xL (C) rescues MA9 leukemogenesis in Rac2 KO cells. LDBM was harvested from Rac2 KO mice with C57/Bl6 mice as wild-type control, then transduced with retroviral vector expressing MA9-EGFP and a second virus expressing empty vector control (Venus), wild-type Rac2 allele (Rac2WT), or Bcl-xL. MA9 leukemia development in both the KO Rac2WT and KO Bcl-xL groups was statistically identical to WT Venus control (P = .96 and P = .92, respectively) and accelerated in comparison to the KO Venus group (P = .02 and P < .02, respectively). FACS analysis of BM specimens from the KO groups demonstrated coexpression of Rac2WT (B) or Bcl-xL (C) and MA9 (x-axis) in all tumors. (D) Western blot analysis of Rac2, Bcl-xL, and Bcl-2 in MA9 tumors from the different groups. Each lane represents a distinct tumor. Band densitometry was normalized to β-actin. (E) Control MA9 cells and those expressing ectopic Bcl-xL were treated with the Rac inhibitor, NSC23766. Significantly fewer annexin V⁺ cells were seen in MA9 + Bcl-xL lines compared with MA9 + pBabe control lines. The average with SD of 3-5 experiments is shown. (F) Western blot confirmed overexpression of Bcl-xL. NSC23766 treatment decreased Bcl-xL expression in both control pBabe and Bcl-xL transduced MA9 cells, implicating a role for Rac in posttranscriptional regulation of Bcl-xL.