Activin B uses the classic BMP type I receptors to regulate BMP signaling and hepcidin expression in human hepatoma-derived cells. HepG2 cells were pretreated with LDN-193189 (100nM) or vehicle for 30 minutes and then stimulated with activin B (50 ng/mL) or vehicle for 2.5, 4, or 6 hours. (A) Hepcidin (Hamp) mRNA levels were measured by quantitative RT-PCR. Values shown are −ΔΔCt (ie, −[ΔCt treatment − ΔCt vehicle]) ± SD obtained from 3 independent experiments. Means of −ΔΔCt were compared with 0 by Student t tests. **P < .01; *P < .05. The fold change induced by treatment can be obtained by raising 2 to the power −ΔΔCt. (B) Protein extracts were prepared from these cells. Phospho–Smad1/5/8 and total Smad5 were detected by immunoblot techniques.