PECAM-1 inhibits Bax overexpression—induced apoptosis. HEK 293 cells were transiently transfected with 1 μg of the control vector pcDNA3, with 1 μg of Bax-encoding plasmid alone, or with 1 μg of Bax plasmid together with 4 μg of expression plasmids encoding PECAM-1 or XIAP. (A) PECAM-1 expression suppressed DEVD hydrolysis as effectively as did XIAP, (B) cells coexpressing Bax and PECAM-1 exhibited significantly less nuclear condensation than did cells expressing Bax alone (original magnification, × 40), and (C) there were no major changes in the expression of major proapoptotic or antiapoptotic family members correlating with PECAM-1 expression that could account for PECAM-1—mediated cytoprotection.