MLL-induced leukemia initiation/progression is independent of HIF-1α status, although MLL signals directly toward HIF. (A) GFP expression of a clone derived from doxycycline-inducible MLL-ENL BM cells transduced with a GFP-hypoxic reporter. Cells from this clone were grown in methylcellulose for 1 week under normoxic (20% oxygen) or hypoxic (1% oxygen) conditions in media ± doxycycline (Dox) and GFP expression analyzed by flow cytometry. (B) Kaplan-Meier survival curve of mice transplanted with MLL-AF9–expressing cells (Hif-1α^Δ/Δ, n = 6; Hif-1α^fl/fl, n = 7). The log-rank (Mantel-Cox) test was used to assess statistical significance. The development of the disease was measured by the percentage of transduced cells (GFP⁺) (C) and myeloid cells (Gr1⁺ and/or Mac1⁺) (D) in PB 3, 7, and 10 weeks after transplantation (n = 10). At 12 weeks after transplantation, a set of mice was sacrificed and the phenotype of the disease analyzed by measuring several parameters: WBC (E), GFP⁺ cells (F), and myeloid cells (Gr1⁺ and/or Mac1⁺) (G) in BM, and spleen and spleen and liver weights (H) (n = 3). Plots and columns represent mean ± SEM. Two-tailed Student t test was used to assess statistical significance.