Endoglin overexpression increases the BMP9 response. (A) NIH-3T3 cells were transiently transfected with pGL3(BRE)-luc, pRL-TK-luc, pALK1, and either pCDNA₃ empty vector or pEndoglin. After 4 hours, cells were treated with BMP9 (0.03 ng/mL) or BMP2 (10 ng/mL) for 15 hours. The firefly luciferase activity was normalized to renilla luciferase activity. Results are presented as mean values ± SD. (B) Overexpression of human endoglin transcripts in transfected cells was controlled using semiquantitative PCR. mHPRT was amplified to normalize for the amount of RNA used as starting material.