MLL3 acts as a recessive gene mutated in FLT3-ITD subgroup. (A) Xenografts (4 weeks) were established using MV4-11 cells stably expressing either scramble or MLL3 shRNA. Scale is in centimeters. (B) Weight of individual tumors in each group (mean ± SD; P = .0098). (C) Relative mRNA expression of MLL3 (quantitative PCR) in xenografts. Values represent mean ± SD; n = 3. *P < .05. (D) Quantitative PCR showed relative increase in mRNA levels of HOXA7, HOXA9, and MEIS, and relative decrease in the mRNA levels of p21 and p53 (growth-inhibitory genes). Data represent mean ± SD; n = 3. *P < .05; **P ≤ .01. (E,F) Knockdown of murine MLL3 in 32D cells stably expressing murine FLT3-ITD caused increased cell growth in liquid culture. Data represent mean ± SD; n = 3. *P ≤ .05; **P ≤ .01. (G) Methylcellulose colony formation assay of 32D cells (stably expressing murine FLT3-ITD) transfected with either scramble siRNA or siRNA MLL3. Data represent mean ± SD; n = 3. *P ≤ .05. (H) Survival curves of AML patients either with or without MLL3 mutations. (I) Relapse-free survival curves of AML patients either with or without MLL3 mutations.