Abstract 14442: X-Box Binding Protein 1 Splicing Triggers an Autophagic Response-Mediated Survival in Endothelial Cells
Endothelial cell dysfunction is an initial step on the development of atherosclerosis. Sustained activation of X-box binding protein 1 (XBP1) splicing, which is a key signal transducer in endoplasmic reticulum stress response, leads to endothelial apoptosis and atherosclerosis development. Autophagy is characterized as a survival response and also as a pathway culminating in cell death. In the present study, we aimed to assess the hypothesis whether XBP1 splicing activates autophagy in endothelial cells, and to investigate its role in the cell survival and apoptosis. XBP1 splicing was introduced to human umbilical vein endothelial cells by adenoviral gene transfer. Autophagic vesicle formation was observed 48 and 72 hours post infection. Moreover, autophagy gene expression such as Beclin 1, LC3-beta, NIX, ATGF-tv1, autophagy-related 5 (ATG5) and autophagy-related 12 (ATG12) was induced by XBP1 splicing at RNA and protein levels. Additional experiments have revealed that endothelial cells transfected with the LC3beta-GFP construct showed a high GPF expression of autophagic vesicle formation only in the presence of spliced XBP1 compared with the non-infected cells. Moreover, our results showed that endostatin, a well-characterized endogenous inhibitor of angiogenesis that induces apoptosis, activated autophagy genes 4 hours after treatment, through XBP1 splicing in an IRE1-alpha dependent manner. Knockdown of XBP1 or IRE1alpha by ShRNA in endothelial cells ablated endostatin-induced autophagy responsive genes expression and enhanced the apoptotic effect of endostatin. In conclusion, these results suggest that activation of XBP1 splicing triggers an autophagic survival signal pathway, providing novel insights into the elucidation of the mechanisms involved in endothelial cell survival. Key words: endostatin, IRE1alpha, cell survival, cell apoptosis
- © 2010 by American Heart Association, Inc.