Effect of OLFM4 overexpression on HL-60 cell growth, differentiation, and apoptosis. (A) The cell lysates of HL-60 cells transfected with either OLFM4 expression vector or empty vector (Vec) were subjected to Western blotting analysis with OLFM4 antibody, then stripped and reprobed with β-actin antibody. (B) HL-60 cells were transfected with either OLFM4 expression plasmid or empty vector, then stably transfected cells were treated with ATRA (1μM) or vehicle for 4 days. Cell numbers were counted with trypan blue exclusion. Data represent the mean ± SD of 3 independent experiments *P < .05, when OLFM4 was compared with vector, and when OLFM4 + ATRA was compared with vector + ATRA. (C) Stably transfected HL-60 cells were treated with ATRA (1μM) or vehicle for 4 days. The expression of CD11b was analyzed by flow cytometry. A representative experiment is shown in the left panel, and the percentage of CD11b⁺ cells is presented in the right panel. Data represent mean ± SD of 3 independent experiments. *P < .05, **P < .01. (D) Stably transfected HL-60 cells were treated with ATRA (1μM) or vehicle for 4 days. Cell apoptosis was analyzed with annexin V–propidium iodide staining using flow cytometry. A representative analysis data are shown in the left panel, and the percentage of apoptotic cells is shown in the right panel. Data represent the mean ± SD of 3 independent experiments. *P < .05.