X-linked Inhibitor Of Apoptosis Protein Overexpression Research Articles

Expression of X-linked inhibitor of apoptosis protein and its effect on chemotherapeutic sensitivity of bladder carcinoma

The expression of X-linked inhibitor of apoptosis protein (XIAP) gene and its effect on chemotherapeutic sensitivity in bladder carcinoma was explored. By using immunohistochemistry, the expression of XIAP was detected in 47 bladder carcinomas and 5 normal bladder tissues. The XIAP gene was transfected into bladder cancer cell line T24 by liposome and the positive clone was screened by G418. Cellular XIAP mRNA level was detected by RT-PCR. Low-dose mitomycin C was administered to induce the apoptosis of T24 cells. The in vitro growth of bladder carcinoma cells was analyzed by MTT colorimetry, and the apoptosis rate was assayed by TUNEL methods. It was found XIAP was moderately expressed in bladder carcinomas with the the positive rate being 78.73% (37/47), but the positive rate was not correlated with carcinoma stages and grades (P<0.05). XIAP mRNA level in transfected T24 cells was significantly increased by 3.8 times as compared with that in the cells not transfected with XIAP. After treatment with low-dose mitomycin C (0.005 and 0.05 mg/mL), the growth rate in XIAP no-transfected control group was increased by (11.60+/-0.25)% and (16.51+/-0.87)% (P<0.05), and the apoptosis rate was decreased by (10.1+/-0.2)% and (11.9+/-0.2%) (P<0.05) respectively as compared with XIAP transfected group. It was concluded that XIAP was expressed in most of bladder carcinoma samples. Overexpression of XIAP in T24 could significantly reduce the MMC-induced apoptosis of bladder carcinoma, suggesting its effect on the chemotherapeutic sensitivity of T24 cells.

Overexpression of XIAP expression in renal cell carcinoma predicts a worse prognosis

X-linked inhibitor of apoptosis protein (XIAP) is the most potent caspase-inhibitory IAP family member and a negative regulator of various apoptotic stimuli. Thus, XIAP overexpression in cancer cells may select for tumor cell survival following various cytotoxic therapeutic modalities. The anatomical staging system in renal cell carcinoma (RCC) currently provides good prognostic information, albeit insufficient. We hypothesize that overexpression of XIAP in RCC may serve as a molecular prognostic marker in RCC and improve the staging of RCC. This study examined the protein level of XIAP in lysates from surgical specimens of 109 patients with RCC and 109 normal kidney specimens from the same patients. The level of XIAP expression was quantified by Western blot analysis using non-fixed fresh frozen tissues of RCCs and normal kidneys. Results indicated that the mean level of XIAP expression was higher in RCC compared to autologous normal kidney, and the XIAP expression level in 38/109 (35%) of RCC was more than 2-fold greater than that in normal kidney tissue. In Stage I/II RCC, the mean XIAP expression level was almost identical to that detected in normal kidney, whereas XIAP expression in Stage III/IV was 2.5-fold higher than that in Stage I/II RCC. Levels of XIAP expression also correlated with the grade of RCC. Patients with RCC with low XIAP expression had a longer postoperative disease-specific survival as compared to those with high expression in the 5-year follow-up. The suggested role of XIAP in the regulation of resistance in apoptosis was examined in vitro following treatment of RCC cell lines with XIAP antisense oligonucleotide and the cells were sensitized to both Fas-mediated and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-mediated apoptosis. The present study demonstrates at the protein level that XIAP is overexpressed in RCC, and that high XIAP expression in RCC predicted a worse prognosis. In addition, XIAP antisense oligonucleotide sensitized RCC to Fas/TRAIL-induced apoptosis. These results suggest that XIAP expression in RCC may be used as a prognostic parameter, and that downregulation or inhibition of XIAP expression in RCC may reverse immune resistance.

The X-linked inhibitor of apoptosis protein (XIAP) is up-regulated in metastatic melanoma, and XIAP cleavage by Phenoxodiol is associated with Carboplatin sensitization

XIAP up-regulation is associated with chemotherapy resistance. Phenoxodiol causes XIAP degradation and chemotherapy sensitization in ovarian cancer. Here we assessed XIAP expression in melanomas, using tissue microarrays containing 436 melanomas and 336 nevi by a novel method of automated, quantitative analysis (AQUA). We used S100 to define pixels as melanoma (tumor mask) within the array spot, and measured XIAP expression using Cy5-conjugated antibodies within the mask. XIAP expression was significantly higher in melanomas than nevi (P < 0.0001), and higher in metastatic than primary lesions (P < 0.0001). We then assessed a panel of melanoma cell lines for XIAP expression, and found high expression in all cell lines. Three of the cell lines were assessed for Phenoxodiol and Carboplatin sensitivity; all were resistant to Carboplatin and showed variable sensitivity to Phenoxodiol. Pre-treating Phenoxodiol sensitive cells with Phenoxodiol prior to Carboplatin resulted in XIAP degradation, associated with Carboplatin sensitization and apoptosis, whereas exposing Phenoxodiol resistant cells to Phenoxodiol resulted in less XIAP degradation and minimal Carboplatin sensitization. We conclude that XIAP levels in clinical specimens are significantly higher in melanomas than their benign counterparts, and higher in metastatic than in primary specimens, suggesting an association with malignant progression and disease aggression. Melanoma resistance to Carboplatin is possibly due to XIAP over-expression. Phenoxodiol can sensitize melanoma cells to Carboplatin in vitro with corresponding XIAP degradation, although the precise target and mechanism of action of Phenoxodiol are subject to further assessment. Targeting XIAP warrants additional investigation as a therapeutic approach for metastatic melanoma.

Systems analysis of effector caspase activation and its control by X-linked inhibitor of apoptosis protein.

Activation of effector caspases is a final step during apoptosis. Single-cell imaging studies have demonstrated that this process may occur as a rapid, all-or-none response, triggering a complete substrate cleavage within 15 min. Based on biochemical data from HeLa cells, we have developed a computational model of apoptosome-dependent caspase activation that was sufficient to remodel the rapid kinetics of effector caspase activation observed in vivo. Sensitivity analyses predicted a critical role for caspase-3-dependent feedback signalling and the X-linked-inhibitor-of-apoptosis-protein (XIAP), but a less prominent role for the XIAP antagonist Smac. Single-cell experiments employing a caspase fluorescence resonance energy transfer substrate verified these model predictions qualitatively and quantitatively. XIAP was predicted to control this all-or-none response, with concentrations as high as 0.15 microM enabling, but concentrations >0.30 microM significantly blocking substrate cleavage. Overexpression of XIAP within these threshold concentrations produced cells showing slow effector caspase activation and submaximal substrate cleavage. Our study supports the hypothesis that high levels of XIAP control caspase activation and substrate cleavage, and may promote apoptosis resistance and sublethal caspase activation in vivo.

XIAP decreases caspase-12 cleavage and calpain activity in spinal cord of ALS transgenic mice

Amyotrophic lateral sclerosis (ALS) is characterized by the selective degeneration of motor neurons. The cause for nerve cell demise is not clear but involves activation of the caspase family of cysteine proteases. We have shown that ER stress and caspase-12 activation occur in ALS transgenic mice carrying the mutant copper/zinc superoxide dismutase (SOD1) gene. In these mice, we found that the antiapoptotic proteins, X-linked Inhibitor of Apoptosis Protein (XIAP) and the related protein, MIAP2 were decreased. To study the role of this, we generated double transgenic mice expressing XIAP in ALS spinal cord neurons using the Thy1 promoter. Overexpression of XIAP inhibited caspase-12 cleavage and reduced calpain activity in the ALS mice. XIAP also reduced the breakdown of calpastatin that is an inhibitor of calpain. In the double transgenic mice, life span was increased by about 12%. These data support the view that XIAP has beneficial effects in ALS and extends survival. The neuroprotective effect of XIAP involves inhibition of caspases and the stabilization of the calpastatin/calpain system that is altered in the ALS mice.

IFN-γ sensitizes MIN6N8 insulinoma cells to TNF-α-induced apoptosis by inhibiting NF-κB-mediated XIAP upregulation

Although X-linked inhibitor of apoptosis protein (XIAP) is an important intracellular suppressor of apoptosis in a variety of cell types, its role in cytokine-induced pancreatic β-cell apoptosis remains unclear. Here, we found that: (i) XIAP level was inversely correlated with tumor necrosis factor (TNF)-α-induced apoptosis in MIN6N8 insulinoma cells; (ii) adenoviral XIAP overexpression abrogated the TNF-α-induced apoptosis through inhibition of caspase activity; (iii) downregulation of XIAP by antisense oligonucleotide or Smac peptide sensitized MIN6N8 cells to TNF-α-induced apoptosis; (iv) XIAP expression was induced by TNF-α through a nuclear factor-κB (NF-κB)-dependent pathway, and interferon (IFN)-γ prevented such an induction in a manner independent of NF-κB, which presents a potential mechanism underlying cytotoxic IFN-γ/TNF-α synergism. Taken together, our results suggest that XIAP is an important modulator of TNF-α-induced apoptosis of MIN6N8 cells, and XIAP regulation in pancreatic β-cells might play an important role in pancreatic β-cell apoptosis and in the pathogenesis of type 1 diabetes.

XIAP Overexpression in Human Islets Prevents Early Posttransplant Apoptosis and Reduces the Islet Mass Needed to Treat Diabetes

The Edmonton Protocol for treatment of type 1 diabetes requires islets from two or more donors to achieve euglycemia in a single recipient, primarily because soon after portal infusion, the majority of the transplanted cells undergo apoptosis due to hypoxia and hypoxia reperfusion injury. X-linked inhibitor of apoptosis protein (XIAP) is a potent endogenous inhibitor of apoptosis that is capable of blocking the activation of multiple downstream caspases, and XIAP overexpression has previously been shown to enhance engraftment of a murine beta-cell line. In this study, human islets transduced with a XIAP-expressing recombinant adenovirus were resistant to apoptosis and functionally recovered following in vitro stresses of hypoxia and hypoxia with reoxygenation (models reperfusion injury). Furthermore Ad-XIAP transduction dramatically reduced the number of human islets required to reverse hyperglycemia in chemically diabetic immunodeficient mice. These results suggest that by transiently overexpressing XIAP in the immediate posttransplant period, human islets from a single donor might be used to effectively treat two diabetic recipients.

Sodium butyrate sensitizes human glioma cells to TRAIL-mediated apoptosis through inhibition of Cdc2 and the subsequent downregulation of survivin and XIAP

In TNF-related apoptosis-inducing ligand (TRAIL)-resistant glioma cells, co-treatment with nontoxic doses of sodium butyrate and TRAIL resulted in a marked increase of TRAIL-induced apoptosis. This combined treatment was also cytotoxic to glioma cells overexpressing Bcl-2 or Bcl-xL, but not to normal human astrocytes, thus offering an attractive strategy for safely treating resistant gliomas. Cotreatment with sodium butyrate facilitated completion of proteolytic processing of procaspase-3 that was partially blocked by treatment with TRAIL alone. We also found that treatment with sodium butyrate significantly decreased the protein levels of survivin and X-linked inhibitor of apoptosis protein (XIAP), two major caspase inhibitors. Overexpression of survivin and XIAP attenuated sodium butyrate-stimulated TRAIL-induced apoptosis, suggesting its involvement in conferring TRAIL resistance to glioma cells. Furthermore, the kinase activities of Cdc2 and Cdk2 were significantly decreased following sodium butyrate treatment, accompanying downregulation of cyclin A and cyclin B, as well as upregulation of p21. Forced expression of Cdc2 plus cyclin B, but not Cdk2 plus cyclin A, attenuated sodium butyrate/TRAIL-induced apoptosis, overriding sodium butyrate-mediated downregulation of survivin and XIAP. Therefore, Cdc2-mediated downregulation of survivin and XIAP by sodium butyrate may contribute to the recovery of TRAIL sensitivity in glioma cells.

Cisplatin inhibits the expression of X-linked inhibitor of apoptosis protein in human LNCaP cells

The purpose of the present study is to investigate the role of X-linked inhibitor of apoptosis protein (XIAP) in the regulation of apoptosis induced by cisplatin in human prostate cancer cell line (LNCaP). We examined the effects of cisplatin on cell growth and apoptosis in LNCaP by 2-(4-lodophenyl)-3-(4-nitrophenyl)-5-(2,4-disulfophenyl)-2H-tetrazolium, monosodium salt (WST-1), flow cytometric analyses, and caspase-3 activity assay. In addition, to clarify the roles of the XIAP, we established clonal cell lines that overexpressed XIAP. The effects of cisplatin on the XIAP expression in the induction of apoptosis in LNCaP were examined by RT-PCR and immunoblot analyses. Although the growth rates were reduced in a dose- and time-dependent manner by cisplatin in LNCaP sublines, the anti-proliferative effects of cisplatin were significantly decreased in XIAP stably overexpressing cell lines. In addition, we found that cisplatin-induced apoptosis following activation of caspase-3, and that the overexpression of XIAP inhibited apoptosis by attenuating caspase-3 activity. Interestingly, treatment of LNCaP cells with 10 and 100 μM cisplatin for 48 h significantly decreased the expression of XIAP at both the protein and mRNA levels in a dose-dependent manner. Furthermore, 10-μM cisplatin treatment of LNCaP decreased XIAP mRNA and protein in a time-dependent manner. These results suggest that cisplatin induces apoptosis by the inhibition of XIAP expression, and that XIAP plays an important role in the regulation of cisplatin-induced apoptosis in LNCaP cells. The ability of cisplatin to down-regulate XIAP may be an important mechanism in chemosensitivity.

The X-linked inhibitor of apoptosis protein inhibits taxol-induced apoptosis in LNCaP cells.

To clarify the roles of the X-linked inhibitor of apoptosis protein (XIAP), we investigated the effects of XIAP overexpression on taxol-induced cell growth arrest and apoptosis in the prostate cancer cell line (LNCaP). After the transfection of XIAP cDNA into LNCaP cells, we established clonal cell lines that overexpressed XIAP and examined the taxol effects on growth and apoptosis by 2-(4-lodophenyl)-3-(4-nitrophenyl)-5-(2,4-disulfophenyl)-2H-tetrazolium, monosodium salt and flow cytometric analysis. The effects of XIAP overexpression on caspase-3 were examined by immunoblot analysis and activity assay. The interaction between XIAP and caspase-3 in LNCaP cells was examined by cotransfection with myc-XIAP and caspase-3-HA cDNAs followed by immunoprecipitation and immunoblot analysis. Large amounts of XIAP were expressed in the established cell lines. Although the growth rates were reduced in a dose- and time-dependent manner by taxol, these effects were significantly decreased in XIAP stably overexpressing cell lines. In addition, we found that taxol treatment induced the cleavage of pro-caspase-3, followed by apoptosis, and that the overexpression of XIAP inhibited apoptosis by attenuating the cleavage of pro-caspase-3 and caspase-3 activity. Interestingly, XIAP bound to pro-caspase-3 in LNCaP cells transiently cotransfected with myc-XIAP and caspase-3-HA cDNAs, and this interaction was inhibited by taxol treatment. These results suggest that the overexpression of XIAP inhibits taxol-induced apoptosis through the decrease of caspase-3 activity and inhibition of the processing of pro-caspase-3.

X-Linked inhibitor of apoptosis protein is involved in mutant SOD1-mediated neuronal degeneration.

Mutations in the superoxide dismutase 1 (SOD1) gene cause the degeneration of motor neurons in familial amyotrophic lateral sclerosis (FALS). An apoptotic process including caspase-1 and -3 has been shown to participate in the pathogenesis of FALS transgenic (Tg) mouse model. Here we report that IAP proteins, potent inhibitors of apoptosis, are involved in the FALS Tg mouse pathologic process. The levels of X-linked inhibitor of apoptosis protein (XIAP) mRNA and protein were significantly decreased in the spinal cord of symptomatic G93A-SOD1 Tg mice compared with littermates. In contrast, the levels of cIAP-1 mRNA and protein were increased in symptomatic G93A-SOD1 Tg mice, whereas the levels of cIAP-2 mRNA and protein were unchanged. In situ hybridization showed that the expression of XIAP was remarkably reduced in the motor neurons of Tg mice, and the expression of cIAP-1 was strongly increased in the reactive astrocytes of Tg mice. Overexpression of XIAP markedly inhibited the cell death and caspase-3 activity in the neuro2a cells expressing mutant SOD1. Deletional mutant analysis revealed that the N-terminal domain of XIAP, the BIR1-2 domains, was essential for this inhibitory activity. These results suggest that XIAP plays a role in the apoptotic mechanism in the progression of disease in mutant SOD1 Tg mice and holds therapeutic possibilities for FALS.

X-Linked Inhibitor of Apoptosis Protein Activates the Phosphatidylinositol 3-Kinase/Akt Pathway in Rat Granulosa Cells during Follicular Development

X-linked inhibitor of apoptosis protein (XIAP) in granulosa cells is regulated by gonadotropins during follicular development, although the current understanding of the mechanisms by which XIAP suppressed granulosa cell apoptosis is incomplete. In the present study, we investigated the possible involvement of the phosphatidylinositol 3-kinase (PI 3-K) survival pathway in the regulation of granulosa cell fate. Using a fully characterized in vivo model to study the induction of follicular development and atresia in immature rats, we have demonstrated that gonadotropin treatment increased granulosa cell XIAP and phospho-Akt protein contents and suppressed apoptosis. In addition, gonadotropin withdrawal [equine CG (eCG)-primed rats treated with an anti-eCG antibody] induced granulosa cell apoptosis and significantly decreased ovarian weight. The increased apoptosis was accompanied by marked decreases in XIAP expression and phosphorylation of Akt protein. Infection of granulosa cells from eCG-primed rats with adenoviral sense XIAP [lacZ as a control; multiplicity of infection, 1–5] resulted in XIAP overexpression and increased phospho-Akt content, whereas XIAP antisense expression (multiplicity of infection, 10–40) decreased granulosa cell phospho-Akt level and induced apoptosis. Addition of the specific PI 3-K inhibitor LY294002 to the granulosa cell cultures decreased Akt phosphorylation and induced apoptosis in a dose-dependent manner. Taken together, these results demonstrate for the first time the importance and regulation of the PI 3-K survival pathway by XIAP in the control granulosa cell apoptosis.

X-linked inhibitor of apoptosis protein activates the phosphatidylinositol 3-kinase/Akt pathway in rat granulosa cells during follicular development.

X-linked inhibitor of apoptosis protein (XIAP) in granulosa cells is regulated by gonadotropins during follicular development, although the current understanding of the mechanisms by which XIAP suppressed granulosa cell apoptosis is incomplete. In the present study, we investigated the possible involvement of the phosphatidylinositol 3-kinase (PI 3-K) survival pathway in the regulation of granulosa cell fate. Using a fully characterized in vivo model to study the induction of follicular development and atresia in immature rats, we have demonstrated that gonadotropin treatment increased granulosa cell XIAP and phospho-Akt protein contents and suppressed apoptosis. In addition, gonadotropin withdrawal [equine CG (eCG)-primed rats treated with an anti-eCG antibody] induced granulosa cell apoptosis and significantly decreased ovarian weight. The increased apoptosis was accompanied by marked decreases in XIAP expression and phosphorylation of Akt protein. Infection of granulosa cells from eCG-primed rats with adenoviral sense XIAP [lacZ as a control; multiplicity of infection, 1-5] resulted in XIAP overexpression and increased phospho-Akt content, whereas XIAP antisense expression (multiplicity of infection, 10-40) decreased granulosa cell phospho-Akt level and induced apoptosis. Addition of the specific PI 3-K inhibitor LY294002 to the granulosa cell cultures decreased Akt phosphorylation and induced apoptosis in a dose-dependent manner. Taken together, these results demonstrate for the first time the importance and regulation of the PI 3-K survival pathway by XIAP in the control granulosa cell apoptosis.