SMAD7 and SMAD4 antagonistically control hepcidin mRNA expression. Huh7 cells were transfected with siRNAs targeting SMAD4, SMAD7, or SMAD4 and SMAD7 or a scrambled siRNA as a control. Seventy-two hours after siRNA transfection, total RNA was isolated. SMAD4, SMAD7, and hepcidin mRNA levels were determined by quantitative real-time PCR analysis and normalized to the housekeeping gene GAPDH. Results are presented as fold change (± SD) compared with samples transfected with control siRNA. The mean of 3 independent experiments is shown. Significant changes are marked by *(P < .05) or **(P < .005).