LSD1 directly inhibits myeloid differentiation genes in erythroid cells. (A) Relative mRNA levels of RUNX1, PU.1, LSD1, and GATA1 (normalized to 18s ribosome RNA) in sorted CFU-E cells from Tx-treated control and Lsd1-CKO mouse BM. (B) Relative mRNA levels of PU.1, RUNX1, or GATA1 (normalized to OAZ1¹⁵) in day-9 (D9) or day-11 (D11) erythroid-differentiated human CD34⁺ cells assayed by qRT-PCR. Cells were expanded in the presence of DMSO or 370 nM LSD1i. (C) Protein levels of PU.1 or GATA1 in the same cells as in (B) assayed by western blotting. (D) ChIP-qPCR analysis of LSD1, H3K4me2, and RUNX1 binding at sites in the PU.1 locus in day-11 human CD34 erythroid differentiated cells in the presence of DMSO or 370 nM LSD1i. (E) Colony numbers of CFU-GM and erythroid colony per 1000 CD34⁺ erythroid differentiated cells from day 4 or day 7 treated with DMSO or 370 nM LSD1i. Data are mean ± standard deviation. (F) LSD1 maintains normal erythropoiesis by repressing PU.1 transcription in erythroid progenitors. LSD1 gene deletion or protein inhibition leads to aberrant activation of PU.1, likely through RUNX1, and shifts the differentiation potential from erythroid to myeloid. *P < .05, **P < .01, ***P < .001, unpaired Student t test. h, human; IgG, immunoglobulin G; n.s., not significant; TSS, PU.1 TSS; WT, wild-type; −14kb, PU.1 enhancer; +27 kb, random sequence control.