MLL-r ALL cells show increased PRMT1 expression and sensitivity to PRMT1 knockdown. (A) PRMT1 expression (presented on a log scale) in GSE13204 data sets containing specimens from patients with MLL-r ALL vs healthy donors. (B) PRMT1 messenger RNA (mRNA) expression in normal peripheral blood stem cell (PBSC) CD34⁺ cells (n = 5) and MLL-r ALL primary blasts (n = 8). (C) Western blot showing PRMT1 expression in CD19⁺ blast cells from primary MLL-r B-ALL (n = 8) and non–MLL-r B-ALL (n = 6) cells compared with normal CD34⁺ (N-CD34⁺) cells from PBSC donors (n = 3). (D) Western blot analysis of PRMT1 expression in non–MLL-r (RCH-ACV, Sup-B15, and REH) and MLL-r ALL (KOCL45, KOCL50, KOCL69, RS4;11, and SEM) cell lines compared with that of normal CD34⁺ cells. (E) Western blot for PRMT1 in primary MLL-r ALL cells, primary non–MLL-r ALL cells, and normal CD34⁺ cells transduced with a vector expressing shCtrl or shPRMT1. (F) Apoptosis of normal CD34⁺, primary non–MLL-r, or MLL-r ALL cells, each transduced with shCtrl or shPRMT1, as analyzed by annexin V-Cy5/4′,6-diamidino-2-phenylindole (DAPI) labeling. (G) Apoptosis of shCtrl- or shPRMT1-expressing non–MLL-r ALL or MLL-r ALL cell lines. (H) Shown are representative fluorescence-activated cell sorted profiles for human CD45⁺/CD19⁺ cells engrafted in BM from SEM-shCtrl- or SEM-shPRMT1-transplanted mice. Q1: hCD45⁺CD19⁻; Q2: hCD45⁺CD19⁺; Q3: hCD45⁻CD19⁺; Q4: hCD45⁻CD19⁻. Percentage of human CD45⁺/CD19⁺ (hCD45⁺/hCD19⁺) cells engrafted in BM (I), spleen (SP; J), or peripheral blood (PB; K) of recipient NSG mice at 5 weeks after bone marrow transplantation (n = 5 per group). (L) Survival of NSG mice engrafted with SEM cells transduced with either shCtrl or shPRMT1 (n = 6 mice per group). Error bars represent standard error of the mean. *P < .05; **P < .01; ***P < .001; ****P < .0001. GAPDH, glyceraldehyde-3-phosphate dehydrogenase; ns, not significant.