Tissue-specific expression of the endoglin promoter. Endoglin⁺ (BAEC, HUVEC, and HMEC-1) and endoglin⁻ (K562, HepG2, and keratinocytes) cells were transiently transfected with the pCD105 (−400/+341) endoglin promoter construct. Luciferase activity was determined 48 hours after transfection. Correction for transfection efficiency was made by cotransfection with a β-galactosidase expression vector. In addition, cells were transfected in parallel with the pGL2-SV40 vector, which contains the SV40 viral promoter activity, as a positive control. The promoterless pXP2 plasmid was also included as a negative control. This is a representative experiment of four separate experiments.