X-Linked Inhibitor of Apoptosis Protein Is an Important Regulator of Vascular Endothelial Growth Factor–Dependent Bovine Aortic Endothelial Cell Survival

Abstract

Abstract-Vascular endothelial growth factor (VEGF) is a critical regulator of endothelial cell biology and vascular function. Chronic VEGF treatment has been shown to inhibit tumor necrosis factor-induced apoptosis in endothelial cells. However, the mechanism for this cell survival is unclear. Interestingly, VEGF also enhances the expression of X-linked inhibitor of apoptosis (XIAP), a well-established antiapoptotic factor. XIAP has been shown to suppress apoptosis by blocking caspase activity in cancer cells, but it remains under studied in the endothelium. Therefore, we hypothesized that VEGF affects important endothelial functions, such as apoptosis and cell migration, by regulating XIAP expression and downstream caspase activity. To test this hypothesis, caspase activity, apoptosis, and cell migration were assessed following XIAP overexpression or depletion in bovine aortic endothelial cells. Much like VEGF treatment, ectopic expression of XIAP blocked tumor necrosis factor-induced apoptosis. Surprisingly, the mechanism was caspase-independent. In addition, XIAP-associated cell survival was the result of enhanced nitric oxide (NO) production, and XIAP was partially localized in caveolae. In these lipid rafts, XIAP interacted with a regulator of NO production, caveolin-1, via a binding motif (FtFgtwiY, where the bold letters represent aromatic amino acids) in the baculoviral IAP repeat-3 domain. Endothelial NO synthase binding to caveolin-1 was competitively inhibited by XIAP, suggesting that XIAP acts as a modulator of NO production by releasing endothelial NO synthase from caveolin-1. Further studies showed that endothelial cell migration was also controlled by XIAP-dependent NO. Taken Key Words: VEGF Ⅲ XIAP Ⅲ caveolin-1 Ⅲ nitric oxide Ⅲ apoptosis E xtensive study of apoptosis has revealed a dichotomy of functions in the vascular system. In the endothelium, apoptosis contributes significantly to vascular pathology, as well as normal physiological function. In atherosclerotic plaques, apoptosis weakens the endothelial cell layer, promoting plaque rupture and atherothrombosis. 1 In contrast, apoptosis also acts as an important physiological mediator, eliminating unbalanced, harmful cells and maintaining vascular homeostasis. 2 Thus, the definition of apoptosis as an either physiological or pathological phenomenon requires careful dissection of distinct vascular apoptotic processes.Vascular endothelial growth factor (VEGF) is an endothelial cytokine that acts through the activation of VEGF receptor tyrosine kinases, eg, flkA/KDR and flt-1. 3 It is an important regulator of angiogenesis 4 and cell survival, or antiapoptosis, [5][6][7] and has been shown to act as a survival factor for newly formed blood vessels. Additional studies have found that VEGF also upregulates antiapoptotic proteins such as the inhibitors of apoptosis (IAPs) in human umbilical vein endothelial cells (HUVECs). 8 Cellular IAP homologs have been identified in many organisms, from yeasts to higher-order animals. 9 An important family m...

Extract from Prunus mume Sieb. et Zucc. Fruit Prevents LPS-induced Homotypic Aggregation of Monocytic THP-1 Cells via Suppression of Nitric Oxide Production and NF-κB Activation

“…The fluorescence of collected supernatants was measured using a spectrofluorophotometer (RF 5301PC Shimadzu) at excitation and emission of 495 and 515 nm (slit 10 nm), respectively. NO content was calculated via fluorescence intensity [19]. were compared.…”

The Rac1 hypervariable region in targeting and signaling

“…[91][92][93] Interestingly, Caveolin1 binds to XIAP in the context of VEGF-induced cell survival of endothelial cells. 94 XIAP also binds to Rac1, in a nucleotide-independent fashion 91 but the domain in Rac1 that is required for this association was not identified. Importantly, Caveolin1 links XIAP to integrins and FAK (Focal Adhesion Kinase), regulating integrin function and adhesion in endothelial cells.…”

In vivo gene delivery of XIAP protects against myocardial apoptosis and infarction following ischemia/reperfusion in conscious rabbits

“…In addition to a direct inhibition to myocyte apoptosis, XIAP has been demonstrated to have effects in vascular endothelial cells, which could indirectly provide protection to myocytes subjected to ischemia/reperfusion. These effects include a modulation of endothelial apoptosis and cell signaling molecules, and an increase in NO production by releasing endothelial NO from caveolin-1 (Hofer-Warbinek, et al 2000; Kim, et al 2008; Stehlik, et al 1998). …”