Figure 5.

Activin B (ACT B) uses the activin type I receptor ALK7 to stimulate SMAD3 signaling but the BMP type I receptors ALK2 and ALK3 to stimulate hepcidin in Hep3B cells. Hep3B cells were transfected with control siRNA (CTRL), siALK4, siALK7, siAKL2, siALK3, or siALK6 (40nM) either alone (A and D) or in combination with CAGA-Luc and pRL-TK (B, C, E, and F). Forty-eight hours after transfection, cells were incubated in the absence or presence of 5-ng/mL ACT B, BMP6, or activin A (ACT A) as indicated for 6 hours, followed by measurement of HAMP relative to RPL19 mRNA levels by qRT-PCR (A and D) or relative luciferase activity (B, C, E, and F). Data are expressed and analyzed as described in Figure 4.