X-linked Inhibitor (X-link + inhibitor)

Distribution by Scientific Domains

Selected Abstracts

Prostacyclin inhibits endothelial cell XIAP ubiquitination and degradation

Jun-Yang Liou
To understand the role of prostacyclin (PGI2) in protecting endothelial cells from apoptosis, we evaluated the effects of carbaprostacyclin (cPGI2) on H2O2 -induced human umbilical vein endothelial cell (HUVEC) apoptosis. cPGI2 suppressed H2O2 -induced annexin V-positive cells in a concentration- and time-dependent manner. Pre-treatment of HUVEC with 50 M cPGI2 for 4 h produced the maximal anti-apoptotic effect. Authentic PGI2 generated by adenoviral transfer of PGI2 synthetic genes exerted a similar protective effect. cPGI2 inhibited Smac/DIABLO release from mitochondria, caspase 3 activation, focal adhesion protein degradation, and cell detachment. cPGI2 selectively protected X-linked inhibitor of apoptosis protein (X-linked IAP, XIAP) from H2O2 -induced ubiquitination, and preserved XIAP protein levels. PD-98059 but not H-89 abrogated the protective action of cPGI2. cPGI2 increased ERK phosphorylation which was blocked by PD-98059. HUVEC stably transfected with dominant negative Ras abrogated XIAP preservation by cPGI2 while constitutive active Ras increased ERK phosphorylation and protected XIAP from degradation. Our results demonstrate for the first time that PGI2 inhibits XIAP ubiquitination and degradation via the Ras/MEK-1/ERK signaling pathway. Preservation of XIAP proteins represents a key mechanism by which PGI2 protects endothelial cells from oxidant-induced apoptosis. J. Cell. Physiol. 212:840,848, 2007. 2007 Wiley-Liss, Inc. [source]

Influence of cardiac-specific overexpression of insulin-like growth factor 1 on lifespan and aging-associated changes in cardiac intracellular Ca2+ homeostasis, protein damage and apoptotic protein expression

AGING CELL, Issue 6 2007
Qun Li
Summary A fall in circulating levels of cardiac survival factor insulin-like growth factor 1 (IGF-1) contributes to cardiac aging. To better understand the role of IGF-1 in cardiac aging, we examined the influence of cardiac IGF-1 overexpression on lifespan, cardiomyocyte intracellular Ca2+ homeostasis, protein damage, apoptosis and expression of pro- and anti-apoptotic proteins in young and old mice. Mouse survival rate was constructed by the Kaplan,Meier curve. Intracellular Ca2+ was evaluated by fura-2 fluorescence. Protein damage was determined by protein carbonyl formation. Apoptosis was assessed by caspase-8 expression, caspase-3 and TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling) assay. Pro- and anti-apoptotic proteins including Bax, p53, pp53, Bcl2, Omi/HtrA2, apoptosis repressor with caspase recruitment domain (ARC) and X-linked inhibitor of apoptosis protein (XIAP) were assessed by Western blot. Aging decreased plasma in IGF-1 levels, elevated myocyte resting intracellular Ca2+ levels, reduced electrically stimulated rise in intracellular Ca2+ and delayed intracellular Ca2+ decay associated with enhanced protein carbonyl formation, caspase-8 expression and caspase-3 activity in FVB mice, all of which with the exception of elevated resting intracellular Ca2+ were attenuated by IGF-1. Aging up-regulated expression of Bax, Bcl2 and ARC, down-regulated XIAP expression and did not affect p53, pp53 and Omi/HtrA2. The IGF-1 transgene attenuated or nullified aging-induced changes in Bax, Bcl2 and XIAP. Our data suggest a beneficial role for IGF-1 in aging-induced survival, cardiac intracellular Ca2+ homeostasis, protein damage and apoptosis possibly related to pro- and anti-apoptotic proteins. [source]

ADAM15 exerts an antiapoptotic effect on osteoarthritic chondrocytes via up-regulation of the X-linked inhibitor of apoptosis

Beate Bhm
Objective To investigate the capacity of ADAM15, a disintegrin metalloproteinase that is up-regulated in osteoarthritic (OA) cartilage, to protect chondrocytes against apoptosis induced by growth factor deprivation and genotoxic stress. Methods Caspase 3/7 activity was determined in primary OA and ADAM15-transfected T/C28a4 chondrocytes upon exposure to the DNA-damaging agent camptothecin or serum withdrawal. Camptothecin-induced cytotoxicity was determined by measuring cellular ATP content. (Anti-)apoptotic proteins were analyzed by immunoblotting, and levels of messenger RNA (mRNA) for X-linked inhibitor of apoptosis (XIAP) were determined using real-time polymerase chain reaction. RNA interference was applied for down-regulation of ADAM15 and XIAP expression. Immunohistochemistry analysis of normal and OA cartilage samples was performed using XIAP- and ADAM15-specific antibodies. Results ADAM15-transfected chondrocytes cultured on a collagen matrix displayed significantly reduced caspase 3/7 activity upon serum or intermittent matrix withdrawal, compared with vector-transfected control cells. Apoptosis induction by camptothecin exposure also led to significantly elevated caspase 3/7 activity and reduced cell viability of the vector-transfected compared with ADAM15-transfected chondrocytes. Increased levels of activated caspase 3 and cleaved poly(ADP-ribose) polymerase were detected in the vector controls. XIAP, an inhibitor of activated caspase 3, was significantly up-regulated (,3-fold) at the protein and mRNA levels in ADAM15-transfected chondrocytes upon camptothecin treatment. Specific down-regulation of either ADAM15 or XIAP in OA chondrocytes led to significant sensitization to camptothecin-induced caspase 3/7 activity. Immunohistochemical analysis revealed low to moderate XIAP expression in normal specimens and markedly increased XIAP staining, colocalizing with ADAM15, in OA cartilage. Conclusion ADAM15 conveys antiapoptotic properties to OA chondrocytes that might sustain their potential to better resist the influence of death-inducing stimuli under pathophysiologic conditions. [source]

The 423Q polymorphism of the X-linked inhibitor of apoptosis gene influences monocyte function and is associated with periodic fever

Massimo Ferretti
Objective Hereditary periodic fever syndromes (HPFs) develop as a result of uncontrolled activation of the inflammatory response, with a substantial contribution from interleukin-1, or tumor necrosis factor , (TNF,). The HPFs include familial Mediterranean fever (FMF), hyperimmunoglobulinemia D with periodic fever syndrome (HIDS), TNF receptor,associated syndrome (TRAPS), and cryopyrinopathies, which are attributable to mutations of the MEFV, MVK, TNFRSF1A, and CIAS1 genes, respectively. However, in many patients, the mutated gene has not been determined; therefore, the condition in these patients with an HPF-like clinical picture is referred to as idiopathic periodic fever (IPF). The aim of this study was to assess involvement of X-linked inhibitor of apoptosis (XIAP), which plays a role in caspase inhibition and NF-,B signaling, both of which are processes that influence the development of inflammatory cells. Methods The XIAP gene (X-linked) was sequenced in 87 patients with IPF, 46 patients with HPF (13 with HIDS, 17 with TRAPS, and 16 with FMF), and 182 healthy control subjects. The expression of different alleles was evaluated by sequencing XIAP -specific complementary DNA mini-libraries and by real-time polymerase chain reaction and Western blot analyses. The functional effect of XIAP on caspase 9 activity was assessed by a fluorimetric assay, and cytokine secretion was evaluated by enzyme-linked immunosorbent assay. Results Sequencing disclosed a 1268A>C variation that caused a Q423P amino acid substitution. The frequency of 423Q-homozygous female patients and 423Q-hemizygous male patients was significantly higher in the IPF group than in the control group (69% versus 51%; odds ratio 2.17, 95% confidence interval 1.23,3.87, P = 0.007), whereas no significant difference was detected in the HPF group (59%) compared with controls. In primary lymphocytes and transfected cell lines, 423Q, as compared with 423P, was associated with higher XIAP protein and messenger RNA expression and lower caspase 9 activation. In lipopolysaccharide-activated monocytes, 423Q was associated with higher secretion of TNF,. Conclusion These results suggest that 423Q is a predisposing factor for IPF development, possibly through its influence on monocyte function. [source]

The role of neutrophil apoptosis in juvenile-onset systemic lupus erythematosus

Angela Midgley
Objective Accumulation of apoptotic cells may lead to the development of systemic lupus erythematosus (SLE) through a breakdown in immune tolerance. Altered neutrophil apoptosis may contribute to nuclear autoantigen exposure, ultimately leading to autoantibody generation. This study aimed to determine whether neutrophil apoptosis is altered in patients with juvenile-onset SLE as compared with controls. Methods Apoptosis was measured in neutrophils from patients with juvenile-onset SLE (n = 12), adult-onset SLE (n = 6), and pediatric patients with inflammatory (n = 12) and noninflammatory (n = 12) conditions. Annexin V staining and flow cytometry were used to determine neutrophil apoptosis. Proapoptotic and antiapoptotic proteins were measured in sera and in neutrophil cell lysates. Results Neutrophil apoptosis was significantly increased in patients with juvenile-onset SLE as compared with the noninflammatory controls at time 0. Incubation of neutrophils with sera from patients with juvenile-onset SLE further increased neutrophil apoptosis as compared with incubation with sera from pediatric controls. Concentrations of TRAIL and FasL were significantly increased in sera from patients with juvenile-onset SLE, whereas interleukin-6, tumor necrosis factor ,, and granulocyte,macrophage colony-stimulating factor (GM-CSF) were significantly decreased. Addition of GM-CSF to sera from patients with juvenile-onset SLE significantly decreased neutrophil apoptosis as compared with juvenile-onset SLE sera alone. The expression of proapoptotic proteins (caspase 3, Fas, and FADD) was elevated in juvenile-onset SLE neutrophils, whereas the expression of antiapoptotic proteins (cellular inhibitor of apoptosis 1 and 2 and X-linked inhibitor of apoptosis) was decreased. Neutrophil apoptosis correlated with biomarkers of disease activity (erythrocyte sedimentation rate and double-stranded DNA concentration) and the British Isles Lupus Assessment Group disease activity score. Conclusion Our data demonstrate an imbalance in proapoptotic and antiapoptotic factors in both neutrophils and sera from patients with juvenile-onset SLE. This imbalance results in increased neutrophil apoptosis in these patients. Correlations with markers of disease activity indicate that altered neutrophil apoptosis in juvenile-onset SLE patients may play a pathogenic role in this condition. [source]

Chemical sensitization and regulation of TRAIL-induced apoptosis in a panel of B-lymphocytic leukaemia cell lines

Jian Kang
Summary., Tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) effectively kills tumour cells but not normal cells. We investigated TRAIL sensitivity and the TRAIL-induced apoptosis signalling pathway in a panel of B-lymphocytic leukaemia cell lines. Depending upon TRAIL sensitivity, leukaemia cells could be divided into three groups: highly sensitive, moderately sensitive and resistant. TRAIL receptor-2 (DR5) plays an important role in transducing apoptosis signals. DR5 was internalized into the cytoplasm where it recruited FAS-associated death domain protein (FADD) under TRAIL stimulation in both sensitive and resistant cells. However, the active form of caspase-8 was recruited to FADD and only sensitive cells showed increased caspase-8 activity upon TRAIL stimulation. The caspase-8 specific inhibitor, Z-IETD, impaired caspase-8 activation and completely abrogated TRAIL-induced apoptosis. These results suggest that TRAIL resistance in B-lymphocytic leukaemia cells is due to negative regulation at the level of caspase-8 activation and that caspase-8 activation is an indispensable process in TRAIL-induced apoptosis. However, FADD-like interleukin-1 ,-converting enzyme inhibitory protein (c-FLIPL) was similarly expressed and down-regulated after TRAIL stimulation in both sensitive and resistant cells. Interestingly, in some cell lines, TRAIL sensitivity and caspase-8 activity was enhanced or restored with the treatment of cycloheximide (CHX). In addition, X-linked inhibitor of apoptosis (XIAP) levels decreased significantly and rapidly following treatment with CHX. Down-regulation of XIAP may be responsible for enhancement or restoration of TRAIL sensitivity after CHX treatment in B-lymphocytic leukaemia cells. [source]

Structural and Biophysical Characterization of XIAP BIR3 G306E Mutant: Insights in Protein Dynamics and Application for Fragment-Based Drug Design

Cathy D. Moore
Previous reports describe modulators of X-linked inhibitor of apoptosis (XIAP),caspase interaction designed from the AVPI N-terminal peptide sequence of second mitochondria-derived activator of caspase. A fragment-based drug design strategy was initiated to identify therapeutic non-peptidomimetic antagonists of X-linked inhibitor of apoptosis protein,protein interactions. Fragments that bind to the AVPI binding site of BIR3 (bacculoviral inhibitory repeat) were identified, and to further localize the fragment binding within the AVPI binding site, a point mutation was designed which alters the dynamics of flexible loops and blocks PI region of the binding cleft, thus enabling definition of weakly bound small molecules in the AV portion of the binding cleft. Nuclear magnetic resonance analysis confirmed the G306E mutation stabilizes the AV pocket. Biophysical characterization of the mutant confirms conformation change within the PI sub-pocket as evidenced by a significant diminishment in binding affinity of AVPI mimetics, yet the binding affinity of the smaller AV mimetics is maintained or slightly improved in the mutant compared with wild-type. Additional data from non-covalent mass spectrometry analysis shows enhanced binding of AV mimetics to the G306E mutant over the wild-type. The presented data outline a protein engineering strategy that allowed mapping of AV-replacements with better sensitivity and precision. [source]