Fig. 4. BMP-9 activates Smad1 and Smad5, and upregulates ID1 and endoglin in endothelial cells. (A-C) BAECs (A), HUVECs (B) or HDMVECs (C) were incubated with increasing doses of BMP-9 and BMP-6 as indicated in the figure. After 45 minutes, cells were lysed and samples subjected to SDS-PAGE and subsequent western blotting. Membranes were either probed with an antibody that specifically recognises phosphorylated Smad1 and Smad5 or with an antibody directed against ID1. An anti--actin antibody was used to confirm equal loading. (D) Effect of BMP-9 and TGF- on endoglin mRNA expression in BAECs as measured by quantitative real-time PCR.