siRNA silencing of both BMPRII and ActRIIA abolishes the BMP9 response. NIH-3T3 cells were transiently transfected with control, BMPRII, or ActRIIA siRNAs. After 24 hours, NIH-3T3 cells were then transiently transfected with pGL3(BRE)-luc, pRL-TK-luc, and pALK1. After 4 hours, cells were treated with BMP9 (0.5 ng/mL) for 15 hours. The luciferase activities were then measured as described in “Materials and methods.” The firefly luciferase activity was normalized to renilla luciferase activity. Data show 1 representative experiment ± SD of 3.