Fig. 4.

Effect of apigenin-mediated inhibition of HDAC activity on XIAP expression in human prostate cancer PC-3 cells. a Effect of apigenin on class I HDAC activity. The cells were treated with 20 μM apigenin for specified times and HDAC enzyme assay was performed. Time-dependent decrease in HDAC activity was observed in PC-3 cells after apigenin treatment. The experiment was repeated twice with similar results. Bars represent mean ± SE, **P < 0.001 versus control. Inset figure shows protein expression for HDAC1 after 20 μM apigenin treatment at specified times. Time-dependent decrease in HDAC1 expression was observed after apigenin treatment. b Effect of HDAC1 knockdown and treatment with apigenin and embelin on HDAC1, CBP and XIAP protein expression. The cells were treated with 20 μM apigenin, 20 μM embelin for 24 h and transient knockdown of HDAC1 was achieved by siRNA treatment and Western blotting was performed. HDAC1 knockdown resulted in decrease in XIAP, whereas apigenin treatment caused decrease in protein expression of HDAC1 and XIAP and embelin treatment resulted in inhibition of XIAP protein expression. β-actin was used as loading control. c Cell viability was performed by MTT assay. Apigenin and embelin treatment resulted in decrease cell survival whereas HDAC1 knockdown did not result in appreciable decrease in cell viability. The experiments were repeated three times with similar results. Bars represent mean ± SE, **P < 0.001 versus control. d Occupancy of CBP/p300, acetylated histone H3, and HDAC1 at the XIAP promoter in PC-3 cells. Apigenin (20 μM) treatment caused decrease occupancy of HDAC1 on the XIAP promoter as shown by ChIP assay. Details are described in “Materials and methods” section