Prostacyclin inhibits endothelial cell XIAP ubiquitination and degradation

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.