BCR/ABL kinase elevates the expression of Nbs1 by stimulation of c-Myc–mediated transactivation and inhibition of caspase-dependent degradation. (A) Mre11, Nbs1, and RAD50 expression was examined by Western-blot analysis in total cell lysates from BCR/ABL (B/A)–positive or parental (P) mouse (32D, Baf3, and FL512) and human (M07e and UT7) cell lines. Cells were incubated for 12 hours in the presence or absence of growth factors (IL-3 or SCF) as indicated. Actin was detected as a loading control. (B-D) M07e parental (P) and BCR/ABL-positive (B/A) cells were starved from growth factor for 12 hours in the presence or absence of 1 μM IM (B), 1 μM epoxomycin (Epox) (C), and 20 μM Z-VAD-FMK (Z-VAD) (D). Expression of Mre11, Nbs1, RAD50, phosphotyrosine proteins (p-Tyr), p53, active caspase-3, and PARP (intact top and cleaved bottom band) was detected by Western-blot analysis. (E) The 293T cells were transiently transfected with the plasmid containing IRES-GFP (1), BCR/ABL-IRES-GFP (2), or BCR/ABL kinase–deficient mutant-IRES-GFP (3) along with the plasmids encoding the luciferase reporter gene driven by either the NBS promoter (NBSLuc1500, ■) or the NBS promoter containing the mutation in the E-box site preventing c-Myc binding (NBSLuc1500Mut, ▩). (F) M07e parental (1) and B/A-positive (2) cells were electroporated with NBSLuc1500 (■) or NBSLuc1500Mut (▩). (G) The 293T cells were transiently transfected with the plasmids containing NBSLuc1500 and IRES-GFP (1), BCR/ABL-IRES-GFP (2), or BCR/ABL-IRES-GFP and c-Myc–In373 (3). Luciferase activity is expressed in arbitrary units and results represent mean (± the standard deviation [SD]) of 3 independent experiments. P < .03 *in comparison to ■ in groups 1 and 3 in panel E and group 1 in panel F and to group 1 in panel G; **in comparison to ■ in group 2 in panels E and F and to bar 2 in panel G. Insets show the expression of BCR/ABL, c-Myc, and actin in particular groups.