Overexpression of BRD1 induces erythroid differentiation in K562. (A) Appearance of parental K562 cells (Control) and the Flag-BRD1-expressing clone (BRD1c2) used for purification of the BRD1 complex. (B) Benzidine staining of parental K562 cells (Control) and Brd1c2. The bar indicates 20 μm (C) Benzidine staining of K562 cells expressing BRD1 mutants. K562 cells were transduced with an empty vector (Control) or retroviruses expressing full-length BRD1 (BRD1), dPWWP, or dN. Transduced cells were sorted with the use of GFP as a marker antigen and expanded for benzidine staining. Bars represent mean ± SE (n = 12). (D) Growth of K562 cells expressing BRD1 or the BRD1 mutant in (C). The results are shown as the mean ± SE for triplicate cultures. (E) Overexpression of BRPF1 in K562 cells. K562 cells were transduced with a HA-BRPF1 retrovirus, and BRPF1 expression was detected by Western blotting by use of the anti-HA antibody (left). Effects of BRPF1 on erythroid differentiation of K562 cells were evaluated by benzidine staining. The data are shown as the mean ± SE for triplicate cultures. (F) Knockdown of HBO1 with the use of shRNA. K562 cells were infected with lentiviruses expressing shRNAs against HBO1 and analyzed as to the basal status of hemoglobinization by benzidine staining. The results are shown as the mean ± SE for triplicate cultures. *P < .05, **P < .005, ***P < .0005.