BCR-ABL activation of SIRT1 involves STAT5 signaling. (A) Luciferase reporter constructs of SIRT1 promoter (2852-94 bp) were transfected into K562 cells, followed by mock or imatinib treatment for 30 hours. Relative promoter activity was calculated by normalizing luciferase activity to the Renilla control. (B) Effect of STAT5 knockdown on SIRT1 promoter luciferase activity in K562 cells. (C) Effect of deleting both STAT5-binding sites on SIRT1 promoter luciferase activity in K562 cells. (D-E) Effect of STAT5 knockdown on endogenous SIRT1 expression in K562 (D) and KCL-22 cells (E). (F) ChIP assay of STAT5A and 5B on SIRT1 promoter. Anti-Flag Ab was used as a ChIP control. (G) BCR-ABL dose effect on SIRT1 expression. High- and low-GFP–expressing CD34⁺ cells were sorted (supplemental Figure 5) for analysis. BCR-ABL levels were validated by CRKL phosphorylation, and blots were reprobed for SIRT1 and STAT5 expression and modifications.