Abstract
To understand the role of prostacyclin (PGI~2~) in protecting endothelial cells from apoptosis, we evaluated the effects of carbaprostacyclin (cPGI~2~) on H~2~O~2~‐induced human umbilical vein endothelial cell (HUVEC) apoptosis. cPGI~2~ suppressed H~2~O~2~‐induced annexin V‐positive cells in a concentration‐ and time‐dependent manner. Pre‐treatment of HUVEC with 50 µM cPGI~2~ for 4 h produced the maximal anti‐apoptotic effect. Authentic PGI~2~ generated by adenoviral transfer of PGI~2~ synthetic genes exerted a similar protective effect. cPGI~2~ inhibited Smac/DIABLO release from mitochondria, caspase 3 activation, focal adhesion protein degradation, and cell detachment. cPGI~2~ selectively protected X‐linked inhibitor of apoptosis protein (X‐linked IAP, XIAP) from H~2~O~2~‐induced ubiquitination, and preserved XIAP protein levels. PD‐98059 but not H‐89 abrogated the protective action of cPGI~2~. cPGI~2~ increased ERK phosphorylation which was blocked by PD‐98059. HUVEC stably transfected with dominant negative Ras abrogated XIAP preservation by cPGI~2~ while constitutive active Ras increased ERK phosphorylation and protected XIAP from degradation. Our results demonstrate for the first time that PGI~2~ inhibits XIAP ubiquitination and degradation via the Ras/MEK‐1/ERK signaling pathway. Preservation of XIAP proteins represents a key mechanism by which PGI~2~ protects endothelial cells from oxidant‐induced apoptosis. J. Cell. Physiol. 212:840–848, 2007. © 2007 Wiley‐Liss, Inc.