Suppression of DBR1 mRNA expression by DBR1 siRNA. (A) GHOST-R5X4 cells were transfected with various concentrations of DBR1 siRNA pHyper-D123 (0.8 μg/ml, 1.6 μg/ml, 3.2 μg/ml, 6.4 μg/ml, 12.8 μg/ml) or mock transfected. Forty-eight hours post transfection, RNA was isolated, treated with Dnase I and used as template in real-time quantitative RT-PCR. Each reaction included 300 ng RNA, 0.5 μM each gene-specific primer for DBR1 and GAPDH amplification. GAPDH was used as an internal control. (B) GHOST-R5X4 cells were transfected with 12.8 μg/ml DBR1 siRNA pHyper-D1, pHyper-D2, pHyper-D3, pHyper-D123 or control pHyper and cells were collected at the indicated time points. RNA was isolated, treated with Dnase I and analyzed by real-time quantitative RT-PCR. Results shown are from triplicate samples in a representative experiment. Error bars indicate standard deviations. Results that are significant by Student's t-test are indicated by asterisks (p < 0.05).