Compound K induced apoptosis in HL-60 cells. (A) The chemical structure of Compound K. (B) Cells were treated with various concentrations (10, 15, 20 μM) of Compound K for the indicated times. Extents (%) of DNA fragmentation were determined by fluorometric method using DAPI, as described in Methods. Data are presented as means ± SD of three independent experiments. *P < 0.05, **P < 0.01 and ***P < 0.001 vs. the control group; the significances of differences between treatments were determined using the Student's t-test. (C) Cells were treated with or without 20 μM Compound K for the indicated times. Fragmentation of genomic DNA was extracted and resolved on 2% agarose gels. Apoptotic DNA fragmentation was visualized by ethidium bromide staining. (D) Cells treated with or without 20 μM of Compound K for the indicated times were co-stained with PI and FITC-conjugated Annexin V, which specifically detected the translocation of phosphatidylserine (PS). Cells were then examined by flow cytometry (LR; low right, UR; upper right).