RARβ knockdown by siRNA diminished fenretinide-induced apoptosis. (A)Establishment of RARβ-deficient Huh-7 cells. Silencing of RARβ was achieved by transfecting Huh-7 cells with individual pre-designed RARβ siRNAs (#3935, #4030, and #4124) or scramble siRNA as the negative control. The knockdown efficiency of RARβ (i.e. RARβ mRNA level reduction) by each siRNA was presented as the percentage of RARβ mRNA level in scramble siRNA-transfected cells 48 hours post-transfection. (B)Scramble or RARβ siRNA transfected Huh-7 cells were treated with either DMSO or fenretinide for 24 hours followed by TUNEL assay. TUNEL staining was representative result from two independent experiments. The histograms depict the relative fold of TUNEL positive cells between fenretinide and DMSO treatment in individual siRNA transfected Huh-7 cells. TUNEL positive cell counting was presented as mean ± S.E.M. from four independent countings (* p < 0.05, compared with DMSO treatment of scramble siRNA-transfected Huh-7 cells; # p < 0.05, compared with fenretinide treatment of scramble siRNA-transfected Huh-7 cells).