Identification of XAF1 as an antagonist of XIAP anti-Caspase activity

TRIM32 protein sensitizes cells to tumor necrosis factor (TNFα)-induced apoptosis via its RING domain-dependent E3 ligase activity against X-linked inhibitor of apoptosis (XIAP)

TRIM32, which belongs to the tripartite motif (TRIM) protein family, has the RING finger, B-box, and coiled-coil domain structures common to this protein family, along with an additional NHL domain at the C terminus. TRIM32 reportedly functions as an E3 ligase for actin, a protein inhibitor of activated STAT y (PIASy), dysbindin, and c-Myc, and it has been associated with diseases such as muscular dystrophy and epithelial carcinogenesis. Here, we identify a new substrate of TRIM32 and propose a mechanism through which TRIM32 might regulate apoptosis. Our overexpression and knockdown experiments demonstrate that TRIM32 sensitizes cells to TNFα-induced apoptosis. The RING domain is necessary for this pro-apoptotic function of TRM32 as well as being responsible for its E3 ligase activity. TRIM32 colocalizes and directly interacts with X-linked inhibitor of apoptosis (XIAP), a well known cancer therapeutic target, through its coiled-coil and NHL domains. TRIM32 overexpression enhances XIAP ubiquitination and subsequent proteasome-mediated degradation, whereas TRIM32 knockdown has the opposite effect, indicating that XIAP is a substrate of TRIM32. In vitro reconstitution assay reveals that XIAP is directly ubiquitinated by TRIM32. Our novel results collectively suggest that TRIM32 sensitizes TNFα-induced apoptosis by antagonizing XIAP, an anti-apoptotic downstream effector of TNFα signaling. This function may be associated with TRIM32-mediated tumor suppressive mechanism.

Caspase-3 deficiency reveals a physiologic role for Smac/DIABLO in regulating programmed cell death

Inhibitor of apoptosis protein (IAP)-binding proteins such as Grim, Reaper and HID have been shown to exert a critical role in regulating caspase activity in species such as D. Melanogaster. However, a comparable role for the mammalian homologue of second mitochondrial-derived activator of caspase/direct IAP-binding protein with low pI (Smac/DIABLO) has yet to be clearly established in vivo. Despite tremendous interest in recent years in the use of so-called Smac mimetics to enhance chemotherapeutic potency, our understanding of the true physiologic nature of Smac/DIABLO in regulating programmed cell death (PCD) remains elusive. In order to critically evaluate the role of Smac/DIABLO in regulating mammalian PCD, deficiency of caspase-3 was used as a sensitizing mutation in order to reduce aggregate levels of executioner caspase activity. We observe that combinatorial deletion of Diablo and Casp3, but neither alone, results in perinatal lethality in mice. Consistent with this, examination of both intrinsic and extrinsic forms of PCD in lines of murine embryonic fibroblasts demonstrate that loss of Smac/DIABLO alters both caspase-dependent and caspase-independent intrinsic PCD. Comparative small interfering RNA inhibition studies of X-linked inhibitor of apoptosis, cellular inhibitor of apoptosis (cIAP)-1, cIAP-2, caspase-6 and -7 in both wild-type and Casp3/Diablo DKO mouse embryonic fibroblast lineages, supports a model in which Smac/DIABLO acts to enhance the early phase executioner caspase activity through the modulation of inhibitory interactions between specific IAP family members and executioner caspases-3 and -7.

Curcumin suppresses growth of mesothelioma cells in vitro and in vivo, in part, by stimulating apoptosis

Malignant pleural mesothelioma (MPM) is an aggressive, asbestos-related malignancy of the thoracic pleura. Although, platinum-based agents are the first line of therapy, there is an urgent need for second-line therapies to treat the drug-resistant MPM. Cell cycle as well as apoptosis pathways are frequently altered in MPM and thus remain attractive targets for intervention strategies. Curcumin, the major component in the spice turmeric, alone or in combination with other chemotherapeutics has been under investigation for a number of cancers. In this study, we investigated the biological and molecular responses of MPM cells to curcumin treatments and the mechanisms involved. Flow-cytometric analyses coupled with western immunoblotting and gene-array analyses were conducted to determine mechanisms of curcumin-dependent growth suppression of human (H2373, H2452, H2461, and H226) and murine (AB12) MPM cells. Curcumin inhibited MPM cell growth in a dose- and time-dependent manner while pretreatment of MPM cells with curcumin enhanced cisplatin efficacy. Curcumin activated the stress-activated p38 kinase, caspases 9 and 3, caused elevated levels of proapoptotic proteins Bax, stimulated PARP cleavage, and apoptosis. In addition, curcumin treatments stimulated expression of novel transducers of cell growth suppression such as CARP-1, XAF1, and SULF1 proteins. Oral administration of curcumin inhibited growth of murine MPM cell-derived tumors in vivo in part by stimulating apoptosis. Thus, curcumin targets cell cycle and promotes apoptosis to suppress MPM growth in vitro and in vivo. Our studies provide a proof-of-principle rationale for further in-depth analysis of MPM growth suppression mechanisms and their future exploitation in effective management of resistant MPM.

Early response of bovine alveolar macrophages to infection with live and heat-killed Mycobacterium bovis

Bovine tuberculosis (TB) is a disease of economic importance and a significant animal health and welfare issue. The alveolar macrophage (AlvMϕ) plays a vital role in the immune response to TB and recent studies provide insights into the interactions between Mϕ and Mycobacterium bovis. Here we reveal the early transcriptional response of bovine AlvMϕ to M. bovis infection. We demonstrate up-regulation of immune response genes, including chemokines, members of the NF-κB pathway which may be involved in their transcription and also pro- and anti-apoptotic genes. M. bovis may therefore induce multiple mechanisms to manipulate the host immune response. We compared the response of AlvMϕ to infection with live and heat-killed M. bovis to determine transcriptional differences dependent on the viable pathogen. Several chemokines up-regulated following live M. bovis infection were not up-regulated after heat-killed M. bovis stimulation; hence the Mϕ seems to differentiate between the two stimuli.

ARTS and Siah collaborate in a pathway for XIAP degradation

ARTS (apoptosis-related protein in the TGF-β signaling pathway) is a mitochondrial protein that binds XIAP (X-linked inhibitor of apoptosis protein) upon entering the cytosol, thus promoting cell death. Expression of ARTS is lost in some malignancies. Here, we show that ARTS binds to XIAP at BIR1, a domain distinct from the caspase-binding sites. Furthermore, ARTS interacts with the E3 ligase Siah-1 (seven in absentia homolog 1) to induce ubiquitination and degradation of XIAP. Cells lacking either Siah or ARTS contain higher steady-state levels of XIAP. Thus, ARTS serves as an adaptor to bridge Siah-1 to XIAP, targeting it for destruction.

XAF1 expression and regulatory effects of somatostatin on XAF1 in prostate cancer cells

Background

Somatostatin prevents cell proliferation by inducing apoptosis. Downregulation of the XAF1 transcript may occur during the development of prostate cancer. It is interesting to evaluate the potential regulatory effects of somatostatin on XAF1 expression during the development of prostate cancer cells.

Methods

XAF1 mRNA and protein expression in human prostate epithelial cells RWPE-1, androgen dependent prostate cancer LNCaP, and androgen independent DU145 and PC3 cells were evaluated using RT-PCR and Western blot. The regulation of XAF1 mRNA and protein expression by somatostatin and its analogue Octreotide was evaluated.

Results

Substantial levels of XAF1 mRNA and proteins were detected in RWPE-1 cells, whereas prostate cancer cells LNCaP, DU145 and PC3 exhibited lower XAF1 expression. Somatostatin and Octreotide up-regulated XAF1 mRNA and protein expression in all prostate cancer cell lines.

Conclusions

XAF1 down-regulation may contribute to the prostate cancer development. The enhanced XAF1 expression by somatostatin indicates a promising strategy for prostate cancer therapy.

Molecular profiling of cytomegalovirus-induced human CD8+ T cell differentiation

CD8+ T cells play a critical role in the immune response to viral pathogens. Persistent human cytomegalovirus (HCMV) infection results in a strong increase in the number of virus-specific, quiescent effector-type CD8+ T cells with constitutive cytolytic activity, but the molecular pathways involved in the induction and maintenance of these cells are unknown. We show here that HCMV infection induced acute and lasting changes in the transcriptomes of virus-reactive T cells collected from HCMV-seropositive patients at distinct stages of infection. Enhanced cell cycle and metabolic activity was restricted to the acute phase of the response, but at all stages, HCMV-specific CD8+ T cells expressed the Th1-associated transcription factors T-bet (TBX21) and eomesodermin (EOMES), in parallel with continuous expression of IFNG mRNA and IFN-γ-regulated genes. The cytolytic proteins granzyme B and perforin as well as the fractalkine-binding chemokine receptor CX3CR1 were found in virus-reactive cells throughout the response. During HCMV latency, virus-specific CD8+ T cells lacked the typical features of exhausted cells found in other chronic infections. Persistent effector cell traits together with the permanent changes in chemokine receptor usage of virus-specific, nonexhausted, long-lived CD8+ T cells may be crucial to maintain lifelong protection from HCMV reactivation.

The enigmatic roles of caspases in tumor development

One function ascribed to apoptosis is the suicidal destruction of potentially harmful cells, such as cancerous cells. Hence, their growth depends on evasion of apoptosis, which is considered as one of the hallmarks of cancer. Apoptosis is ultimately carried out by the sequential activation of initiator and executioner caspases, which constitute a family of intracellular proteases involved in dismantling the cell in an ordered fashion. In cancer, therefore, one would anticipate caspases to be frequently rendered inactive, either by gene silencing or by somatic mutations. From clinical data, however, there is little evidence that caspase genes are impaired in cancer. Executioner caspases have only rarely been found mutated or silenced, and also initiator caspases are only affected in particular types of cancer. There is experimental evidence from transgenic mice that certain initiator caspases, such as caspase-8 and -2, might act as tumor suppressors. Loss of the initiator caspase of the intrinsic apoptotic pathway, caspase-9, however, did not promote cellular transformation. These data seem to question a general tumor-suppressive role of caspases. We discuss several possible ways how tumor cells might evade the need for alterations of caspase genes. First, alternative splicing in tumor cells might generate caspase variants that counteract apoptosis. Second, in tumor cells caspases might be kept in check by cellular caspase inhibitors such as c-FLIP or XIAP. Third, pathways upstream of caspase activation might be disrupted in tumor cells. Finally, caspase-independent cell death mechanisms might abrogate the selection pressure for caspase inactivation during tumor development. These scenarios, however, are hardly compatible with the considerable frequency of spontaneous apoptosis occurring in several cancer types. Therefore, alternative concepts might come into play, such as compensatory proliferation. Herein, apoptosis and/or non-apoptotic functions of caspases may even promote tumor development. Moreover, experimental evidence suggests that caspases might play non-apoptotic roles in processes that are crucial for tumorigenesis, such as cell proliferation, migration, or invasion. We thus propose a model wherein caspases are preserved in tumor cells due to their functional contributions to development and progression of tumors.

Expression of inhibitor of apoptosis family proteins in human oral squamous cell carcinogenesis

BACKGROUND

The purpose of this study was to determine inhibitor of apoptosis (IAP) expression, its relationship with p53, and epigenetic change in oral carcinogenesis that remain to be elucidated.

METHODS

We measured IAP and p53 expression in 44 oral potentially malignant disorders and their corresponding malignant-transformed oral squamous cell carcinomas (OSCCs), and in 44 other non-transformed oral potentially malignant disorders. IAP and p53 expression in 10 fresh OSCCs, together with epigenetic change of their mutation, were also determined.

RESULTS

Normal mucosa did not express IAP/mutated p53. Oral potentially malignant disorders that underwent transformation exhibited high IAPs (>90%) and less-consistent mutated-p53 (34%) expression, whereas transformed OSCCs exhibited high IAP and mutated-p53 expression. Fresh OSCCs exhibited 80% to 100% IAP mRNA expression and 50% protein, mRNA, and p53 mutation expression. Normal tissues revealed DNA methylation of IAP, whereas cancerous tissues overexpressing IAP exhibited hypomethylation.

CONCLUSION

This study showed that IAP expression is an early event in oral carcinogenesis and that epigenetic and genetic pathways are associated with IAP expression in OSCC.

Antagonists of IAP proteins as cancer therapeutics

Inhibitor of apoptosis (IAP) proteins play pivotal roles in cellular survival by blocking apoptosis, modulating signal transduction, and affecting cellular proliferation. Through their interactions with inducers and effectors of apoptosis IAP proteins can effectively suppress apoptosis triggered by diverse stimuli including death receptor signaling, irradiation, chemotherapeutic agents, or growth factor withdrawal. Evasion of apoptosis, in part due to the action of IAP proteins, enhances resistance of cancer cells to treatment with chemotherapeutic agents and contributes to tumor progression. Additionally, IAP genes are known to be subject to amplification, mutation, and chromosomal translocation in human malignancies and autoimmune diseases. In this review we will discuss the role of IAP proteins in cancer and the development of antagonists targeting IAP proteins for cancer treatment.

XIAP expression is post-transcriptionally upregulated in childhood ALL and is associated with glucocorticoid response in T-cell ALL

BACKGROUND

Resistance to glucocorticoid induced apoptosis is one of the major risk factors for relapse and poor outcome in childhood acute lymphoblastic leukemia (ALL). Overexpression of X-linked inhibitor of apoptosis protein (XIAP) has been shown to be associated with chemotherapy resistance in several malignancies.

PROCEDURE

XIAP protein and mRNA expression were determined in leukemic blasts of 51 childhood ALL patients and normal bone marrow mononuclear cells. XIAP expression was correlated with glucocorticoid response and outcome.

RESULTS

XIAP protein but not mRNA expression was found to be highly increased in childhood ALL compared to control bone marrow mononuclear cells (MNC) (median: 3.5 vs. 0.14 ng/10(5) MNC, P < 0.0001) indicating a post-transcriptional regulation of XIAP expression. In patients with T-cell ALL, poor prednisone response was associated with increased XIAP expression (median: 2.8 in good vs. 5.8 in poor responders; P = 0.005). Similarly, T-cell ALL patients suffering adverse events showed higher initial XIAP levels than patients in continuous complete remission (CCR) (median: 2.7 in patients in CCR vs. 5.6 in patients suffering adverse events; P = 0.007). XIAP inhibition using the low-molecular-weight SMAC mimetic LBW242 resulted in a significant increase of prednisone-induced apoptosis in vitro.

CONCLUSION

In childhood ALL compared to control bone marrow, the expression of the apoptosis inhibitor XIAP is highly increased by post-transcriptional regulation. The association with poor in vivo glucocorticoid response and outcome in T-cell ALL suggests XIAP inhibition as a promising novel approach for the treatment of resistant ALL.

RNF152, a novel lysosome localized E3 ligase with pro-apoptotic activities

RING finger protein 152 (RNF152) is a novel RING finger protein and has not been well characterized. We report here that RNF152 is a canonical RING finger protein and has E3 ligase activity. It is polyubiqitinated partly through Lys-48-linked ubiquitin chains in vivo and this phenomenon is dependent on its RING finger domain and transmembrane domain. RNF152 is localized in lysosomes and co-localized with LAMP3, a lysosome marker. Moreover, over-expression of RNF152 in Hela cells induces apoptosis. These results suggest that RNF152 is a lysosome localized E3 ligase with pro-apoptotic activities. It is the first E3 ligase identified so far that is involved in lysosome-related apoptosis.

Transcriptome dysregulation by anthrax lethal toxin plays a key role in induction of human endothelial cell cytotoxicity

We have investigated how Bacillus anthracis lethal toxin (LT) triggers caspase-3 activation and the formation of thick actin cables in human endothelial cells. By DNA array analysis we show that LT has a major impact on the cell transcriptome and we identify key host genes involved in LT cytotoxic effects. Indeed, upregulation of TRAIL and downregulation of XIAP both participate in LT-induced caspase-3 activation. LT induces a downregulation of the immediate early gene and master regulator of transcription egr1. Importantly, its re-expression in LT-intoxicated cells blocks caspase-3 activation. In parallel, we found that the formation of actin cables induced by LT occurs in the absence of direct activation of RhoA/ROCK signalling. We show that knock-down of cortactin and rhophilin-2 under conditions of calponin-1 expression defines the minimal set of genes regulated by LT for actin cable formation. Together our data establish that the modulation of the cell transcriptome by LT plays a key role in triggering human endothelial cell toxicity.

Molecular targeted therapies for diffuse large B-cell lymphoma based on apoptosis profiles

Diffuse large B-cell lymphoma (DLBCL) is the most common type of adult non-Hodgkin lymphoma and is treated with chemotherapy in combination with rituximab. Despite this aggressive therapy, the disease is fatal in 30-40% of patients. Inhibition of the apoptosis signalling pathways is strongly related to response to chemotherapy and eventual clinical outcome. In order to survive, lymphoma cells depend on disruption of the apoptosis pathway by mutations in apoptosis inducing genes or by continuous expression of anti-apoptotic proteins. The development of molecules targeting these apoptosis inhibitors provides a very promising opportunity to specifically target tumour cells without toxicity to non-malignant cells in DLBCL patients. Sensitivity for most of these antagonists can be predicted based on biological markers, suggesting the possibility of pre-defining patients who will most likely benefit from these targeted therapies. Experimental therapies aimed at restoring the upstream apoptosis pathway or targeting apoptosis inhibitors are currently being tested in clinical trials and are expected to be effective particularly in chemotherapy-refractory DLBCL, providing hope for patients who are refractory to current therapies.

Tumor suppressor XIAP-Associated factor 1 (XAF1) cooperates with tumor necrosis factor-related apoptosis-inducing ligand to suppress colon cancer growth and trigger tumor regression

BACKGROUND

XIAP-associated factor 1 (XAF1) antagonizes the anticaspase activity of XIAP (X-linked inhibitor of apoptosis) and functions as a tumor suppressor in colon cancer. The tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is known as a potential anticancer agent. In this study, the synergistic effect of XAF1 and TRAIL on colon cancer growth was investigated.

METHODS

Adeno-XAF1 virus was generated and purified. Cell apoptosis was detected by flow-cytometry and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling assay. Protein expression of the different genes was determined by Western blot analysis. Tumorigenesis and tumor growth were assessed in subcutaneous nude mouse xenograft experiments.

RESULTS

Stable overexpression of XAF1-sensitized colon cancer cells to TRAIL-induced apoptosis significantly increased the activity of caspase 3, 7, 8, and 9; released cytochrome c; and down-regulated XIAP, survivin, and c-IAP-2. The restoration of XAF1 expression mediated by adenovirus (adeno-XAF1) directly induced apoptosis, and synergized TRAIL-induced apoptosis in colon cancer cells. Ex vivo transduction of adeno-XAF1 suppressed colon cancer formation in vivo. Furthermore, adeno-XAF1 treatment of mice significantly inhibited tumor growth, strongly enhanced TRAIL-induced apoptosis and antitumor activity in colon cancer xenograft models in vivo, and markedly prolonged the survival. Notably, the combined treatment with adeno-XAF1 and TRAIL completely eradicated the established tumors without detectable toxicity in normal tissue.

CONCLUSIONS

The combined restoration of XAF1 expression and TRAIL treatment may be a potent strategy for colon cancer therapy.

XAF1 as a prognostic biomarker and therapeutic target in pancreatic cancer

XAF1 (X chromosome-linked inhibitor of apoptosis [XIAP]-associated factor 1) is a novel XIAP modulator that negatively regulates the anti-apoptotic effects of XIAP and sensitizes cells to other cell death triggers. It has been reported to be downregulated in a variety of human cancer cell lines. However, the role of XAF1 in pancreatic carcinogenesis remains unclear. In the present study, we investigated the prognostic values of XAF1 expression and its regulation in cancer cell growth and apoptosis both in vitro and in vivo. From the immunohistochemistry staining of tissue microarray, 40 of 89 (44.9%) pancreatic specimens showed low levels of XAF1 expression. Statistical analysis suggested the downregulation of XAF1 was significantly correlated with tumor staging (P = 0.047) and those patients with low XAF1 levels had shorter survival times (P = 0.0162). Multivariate analysis indicated that XAF1 expression was an independent prognostic indicator of the survival of patients with pancreatic cancer (P = 0.007). Furthermore, we found that restoration of XAF1 expression mediated by Ad5/F35 virus suppressed cell proliferation and induced cell cycle arrest and apoptosis, accompanied by the activation of caspases 3, 8, and 9 and poly(ADP-ribose) polymerase as well as increased level of cytochrome c and Bid cleavage. Notably, XAF1 restoration robustly decreased survivin expression rather than XIAP. In addition, in vivo s.c. xenografts from Ad5/F35-XAF1 treatment, which showed less cellular proliferation and enhanced apoptosis, were significantly smaller than those from control groups. Our findings document that XAF1 is a valuable prognostic marker in pancreatic cancer and could be a potential candidate for cancer gene therapy.

Targeted proteasome inhibition by Velcade induces apoptosis in human mesothelioma and breast cancer cell lines

INTRODUCTION

Thoracic malignancies and human breast cancer (HBC) continue to be aggressive solid tumors that are poor responders to the existing conventional standard chemotherapeutic approaches. Malignant pleural mesothelioma (MPM) is an asbestos-related tumor of the thoracic pleura that lacks effective treatment options. Altered ubiquitin proteasome pathway is frequently encountered in many malignancies including HBC and MPM and thus serves as an important target for therapeutic intervention strategies. Although proteasome inhibitor Velcade (Bortezomib) has been under clinical investigation for a number of cancers, limited preclinical studies with this agent have thus far been conducted in HBC and MPM malignancies.

PURPOSE

To study the biological and molecular responses of MPM and HBC cells to Velcade treatments, and to identify mechanisms involved in transducing growth inhibitory effects of this agent.

METHODS

Flow-cytometric analyses coupled with western immunoblotting and gene-array methodologies were utilized to determine mechanisms of Velcade-dependent growth suppression of five MPM (H2595, H2373, H2452, H2461, and H2714) and two breast cancer (MDA MB-468, SKBR-3) cell lines.

RESULTS

Our data revealed significant reduction in cell growth properties that were dose and time dependent. Velcade treatment resulted in G2M phase arrest, increased expression of cyclin-dependent kinase inhibitor p21 and pro-apoptotic protein Bax. Pretreatment of mesothelioma cells with Velcade showed synergistic effect with cisplatin combination regimens. High-throughput gene expression profiling among Velcade treated and untreated mesothelioma cell lines resulted in identification of novel transducers of apoptosis such as CARP-1, XAF1, and Troy proteins.

CONCLUSIONS

Velcade targets cell cycle and apoptosis signaling to suppress MPM and HBC growth in part by activating novel transducers of apoptosis. This pilot study has paved way for further in-depth analysis of the downstream target molecules associated with presensitization of mesothelioma cells in finding effective therapeutic treatment options for both mesothelioma and recalcitrant breast cancers.

XIAP associates with GSK3 and inhibits the promotion of intrinsic apoptotic signaling by GSK3

This study examined if there are interactions between two key proteins that oppositely regulate intrinsic apoptosis, X-linked inhibitor of apoptosis protein (XIAP), a key suppressor of apoptosis that binds to inhibit active caspases, and glycogen synthase kinase-3 (GSK3), which promotes intrinsic apoptosis. Immunoprecipitation of GSK3beta revealed that XIAP associates with GSK3beta, as do two other members of the IAP family, cIAP-1, and cIAP-2. Cell fractionation revealed that XIAP is predominantly cytosolic, cIAP-1 is predominantly nuclear and nearly all of the nuclear cIAP-1 and cIAP-2 are associated with GSK3. Expression of individual domains of XIAP demonstrated that the RING domain of XIAP associates with GSK3. Inhibition of GSK3 did not alter the binding of XIAP to active caspase-9 or caspase-3 after stimulation of apoptosis with staurosporine. However, inhibition of GSK3 reduced apoptosis and apoptosome formation, including the recruitments of caspase-9 and XIAP to Apaf-1, in response to staurosporine treatment. Cell free measurements of apoptosome-induced caspase-3 activation demonstrated that GSK3 acts upstream of the apoptosome to facilitate intrinsic apoptotic signaling. This facilitation was blocked by overexpression of XIAP. These findings indicate that the RING domain of XIAP (and probably cIAP-1 and cIAP-2) associates with GSK3, GSK3 acts upstream of the apoptosome to promote intrinsic apoptosis, and the association between XIAP and GSK3 may block the pro-apoptotic function of GSK3.

A small molecule inhibitor of XIAP induces apoptosis and synergises with vinorelbine and cisplatin in NSCLC

Background:

Evasion of apoptosis contributes to the pathogenesis of solid tumours including non-small cell lung cancer (NSCLC). Malignant cells resist apoptosis through over-expression of inhibitor of apoptosis proteins (IAPs), such as X-linked IAP (XIAP).

Methods:

A phenylurea-based small molecule inhibitor of XIAP, XIAP antagonist compound (XAC) 1396-11, was investigated preclincally to determine its ability to sensitise to clinically relevant cytotoxics, potentially allowing dose reduction while maintaining therapeutic efficacy.

Results:

XIAP protein expression was detected in six NSCLC cell lines examined. The cytotoxicity of XAC 1396-11 against cultured NSCLC cell lines in vitro was concentration- and time-dependent in both short-term and clonogenic assays. XAC 1396-11-induced apoptosis was confirmed by PARP cleavage and characteristic nuclear morphology. XAC 1396-11 synergised with vinorelbine±cisplatin in H460 and A549 NSCLC cells. The mechanism of synergy was enhanced apoptosis, shown by increased cleavage of caspase-3 and PARP and by the reversal of synergy by a pan-caspase inhibitor. Synergy between XAC 1396-11 and vinorelbine was augmented by optimising drug scheduling with superior effects when XAC 1396-11 was administered before vinorelbine.

Conclusion:

These preclinical data suggest that XIAP inhibition in combination with vinorelbine holds potential as a therapeutic strategy in NSCLC.

Simultaneous activation of p53 and inhibition of XIAP enhance the activation of apoptosis signaling pathways in AML

Activation of p53 by murine double minute (MDM2) antagonist nutlin-3a or inhibition of X-linked inhibitor of apoptosis (XIAP) induces apoptosis in acute myeloid leukemia (AML) cells. We demonstrate that concomitant inhibition of MDM2 by nutlin-3a and of XIAP by small molecule antagonists synergistically induced apoptosis in p53 wild-type OCI-AML3 and Molm13 cells. Knockdown of p53 by shRNA blunted the synergy, and down-regulation of XIAP by antisense oligonucleotide (ASO) enhanced nutlin-3a-induced apoptosis, suggesting that the synergy was mediated by p53 activation and XIAP inhibition. This is supported by data showing that inhibition of both MDM2 and XIAP by their respective ASOs induced significantly more cell death than either ASO alone. Importantly, p53 activation and XIAP inhibition enhanced apoptosis in blasts from patients with primary AML, even when the cells were protected by stromal cells. Mechanistic studies demonstrated that XIAP inhibition potentiates p53-induced apoptosis by decreasing p53-induced p21 and that p53 activation enhances XIAP inhibition-induced cell death by promoting mitochondrial release of second mitochondria-derived activator of caspases (SMAC) and by inducing the expression of caspase-6. Because both XIAP and p53 are presently being targeted in ongoing clinical trials in leukemia, the combination strategy holds promise for expedited translation into the clinic.

Microarray analysis identifies changes in inflammatory gene expression in response to amyloid-beta stimulation of cultured human retinal pigment epithelial cells

PURPOSE

Age-related macular degeneration (AMD) is a common cause of irreversible vision loss in the elderly. The hypothesis was that in vitro stimulation of RPE cells with Abeta(1-40), a constituent of drusen, promotes changes in gene expression and cellular pathways associated with the pathogenesis of AMD, including oxidative stress, inflammation, and angiogenesis.

METHODS

Confluent human RPE cells were stimulated with Abeta(1-40), or the reverse peptide Abeta(40-1), and genome wide changes in gene expression were studied with gene microarrays. Selected genes were verified by qRT-PCR and ELISA. Pathway analysis with gene set enrichment analysis (GSEA) and ingenuity revealed top functional pathways in RPE after Abeta(1-40) stimulation.

RESULTS

RPE cells stimulated with Abeta(1-40) (0.3 microM) for 24 hours resulted in 63 upregulated and 22 downregulated previously known genes. The upregulated genes were predominantly in inflammatory and immune response categories, but other categories were also represented, including apoptosis, cell signaling, cell proliferation, and signal transduction. Categories of downregulated genes included immune response, transporters, metabolic functions and transcription factors. ELISA confirmed that secreted levels of IL-8 were two times higher than control levels. GSEA and ingenuity analysis confirmed that the top affected pathways in RPE cells after Abeta(1-40) stimulation were inflammation and immune response related. Surprisingly, few angiogenic pathways were activated at the doses and exposure times studied.

CONCLUSIONS

Abeta(1-40) promotes RPE gene expression changes in pathways associated with immune response, inflammation, and cytokine and interferon signaling pathways. Results may relate to in vivo mechanisms associated with the pathogenesis of AMD.

5-Aza-2'-deoxycytidine sensitizes busulfan-resistant myeloid leukemia cells by regulating expression of genes involved in cell cycle checkpoint and apoptosis

Busulfan (Bu) is a DNA-alkylating drug used in myeloablative pretransplant conditioning therapy for patients with myeloid leukemia (ML). A major obstacle to successful treatment is cellular Bu-resistance. To investigate the possible contribution of DNA hypermethylation to Bu-resistance, we examined the cytotoxic activity of combined 5-aza-2'-deoxycytidine (DAC) and Bu. Exposure of Bu-resistant B5/Bu250(6) ML cells to 0.5 microM DAC resulted in G2-arrest and apoptosis. The observed G2-arrest was associated with hypomethylation and subsequent expression of epigenetically controlled genes including p16(INK4A), activation of the p53 pathway, and phosphorylation of CDC2. The DAC-mediated apoptosis was partly due to hypomethylation and up-regulation of XAF1, which resulted in down-regulation of the anti-apoptotic proteins XIAP, cIAP1 and cIAP2. The pro-apoptotic PUMA and BNIP3 proteins were up-regulated while pro-survival STAT3 and c-MYC were suppressed. Combination of 0.05 microM DAC and 5 microg/ml Bu resulted in synergistic cytotoxicity, which was associated with PARP1 cleavage and activation of caspases 3 and 8, suggesting induction of an apoptotic response. P53 inhibition in B5/Bu250(6) cells using pifithrin-alpha alleviated these effects, suggesting a role for p53 therein; this observation was supported by the relative resistance of p53-null K562 cells to [DAC+Bu] combinations and by the effects of an anti-p53 shRNA on the OCI-AML3 cell line. We conclude that the synergistic effects of [DAC+Bu] are p53-dependent and involve cell cycle arrest, apoptosis induction and down-regulation of pro-survival genes. Our results suggest that, depending on tumor p53 status, incorporation of DAC might synergistically improve the cytoreductive efficacy of Bu-based pretransplant regimen in patients with ML.

Down-regulation of the pro-apoptotic XIAP associated factor-1 (XAF1) during progression of clear-cell renal cancer

BACKGROUND

Decreased expression of the interferon-stimulated, putative tumour suppressor gene XAF1 has been shown to play a role during the onset, progression and treatment failure in various malignancies. However, little is yet known about its potential implication in the tumour biology of clear-cell renal cell cancer (ccRCC).

METHODS

This study assessed the expression of XAF1 protein in tumour tissue obtained from 291 ccRCC patients and 68 normal renal tissue samples, utilizing immunohistochemistry on a tissue-micro-array. XAF1 expression was correlated to clinico-pathological tumour features and prognosis.

RESULTS

Nuclear XAF1 expression was commonly detected in normal renal- (94.1%) and ccRCC (91.8%) samples, without significant differences of expression levels. Low XAF1 expression in ccRCC tissue, however, was associated with progression of tumour stage (p = 0.040) and grade (p < 0.001). Low XAF1 tumour levels were also prognostic of significantly shortened overall survival times in univariate analysis (p = 0.018), but did not provide independent prognostic information.

CONCLUSION

These data suggest down-regulation of XAF1 expression to be implicated in ccRCC progression and implies that its re-induction may provide a therapeutic approach. Although the prognostic value of XAF1 in ccRCC appears to be limited, its predictive value remains to be determined, especially in patients with metastatic disease undergoing novel combination therapies of targeted agents with Interferon-alpha.

Identification of XAF1 as a novel cell cycle regulator through modulating G(2)/M checkpoint and interaction with checkpoint kinase 1 in gastrointestinal cancer

BACKGROUND AND AIMS

X-linked inhibitor of apoptosis-associated factor 1 (XAF1) was first recognized as an antagonist of X-linked inhibitor of apoptosis in suppressing caspase 3 activity. It has lower expression in cancer cells than normal tissue. Overexpression of XAF1 can inhibit cancer cell growth and sensitize tumor necrosis factor-related apoptosis-inducing ligand- or etoposide-induced apoptosis. The aim of this study is to elucidate the mechanism of XAF1 in regulating cell growth.

METHODS

Stable transfectants of gastrointestinal (GI) cancer cell lines AGS and SW1116 expressing XAF1 and vector control were generated. Cell growth, apoptosis, mitotic status and cell cycle distribution were assessed. The interaction between XAF1 and G(2)/M checkpoint proteins was evaluated by immunoblotting, kinase assay and co-immunoprecipitation assay. Mitotic catastrophe was identified by occurrence of aberrant nuclei and centrosomal amplification.

RESULTS

Our results showed that overexpression of XAF1 suppressed serum-dependent cancer cell growth, induced mitotic catastrophe and G(2)/M cell cycle arrest. Interestingly, XAF1 was predominantly expressed in G(2)/M phase after cell cycle synchronization. XAF1 interacted with and activated checkpoint kinase 1 (Chk1), inactivated Cdc25C and lead to inactivation of Cdc2-cyclin B complex. Suppression of Chk1 abrogated XAF1-induced G(2)/M arrest.

CONCLUSIONS

Our findings implicate XAF1 as a novel cell cycle modulator that is recruited in G(2)/M phase and thus unravel a novel function pathway of XAF1, suggesting the potential role of XAF1 as the target for the management of GI cancers.

Restoration of XAF1 expression induces apoptosis and inhibits tumor growth in gastric cancer

XAF1 (XIAP-associated factor 1) is a novel XIAP binding protein that can antagonize XIAP and sensitize cells to other cell death triggers. Our previous results have shown that aberrant hypermethylation of the CpG sites in XAF1 promoter is strongly associated with lower expression of XAF1 in gastric cancers. In our study, we investigated the effect of restoration of XAF1 expression on growth of gastric cancers. We found that the restoration of XAF1 expression suppressed anchorage-dependent and -independent growth and increased sensitivity to TRAIL and drug-induced apoptosis. Stable cell clones expressing XAF1 exhibited delayed tumor initiation in nude mice. Restoration of XAF1 expression mediated by adenovirus vector greatly increased apoptosis in gastric cancer cell lines in a time- and dose-dependent manner and sensitized cancer cells to TRAIL and drugs-induced apoptosis. Adeno-XAF1 transduction induced cell cycle G2/M arrest and upregulated the expression of p21 and downregulated the expression of cyclin B1 and cdc2. Notably, adeno-XAF1 treatment significantly inhibited tumor growth, strongly enhanced the antitumor activity of TRAIL in a gastric cancer xenograft model in vivo, and significantly prolonged the survival time of animals bearing tumor xenografts. Complete eradication of established tumors was achieved on combined treatment with adeno-XAF1 and TRAIL. Our results document that the restoration of XAF1 inhibits gastric tumorigenesis and tumor growth and that XAF1 is a promising candidate for cancer gene therapy.

Chronic crude garlic-feeding modified adult male rat testicular markers: mechanisms of action

BACKGROUND

Garlic or Allium sativum (As) shows therapeutic effects such as reduction of blood pressure or hypercholesterolemia but side-effects on reproductive functions remain poorly investigated. Because of garlic's chemical complexity, the processing methods and yield in preparations differ in efficacy and safety. In this context, we clarify the mechanisms of action of crushed crude garlic on testicular markers.

METHODS

During one month of treatment, 24 male rats were fed 5%, 10% and 15% crude garlic.

RESULTS

We showed that crude garlic-feeding induced apoptosis in testicular germ cells (spermatocytes and spermatids). This cell death process was characterized by increased levels of active CASP3 but not CASP6. Expression of the caspase inhibitors BIRC3 and BIRC2 was increased at all doses of As while expression of XIAP and BIRC5 was unchanged. Moreover, expression of the IAP inhibitor DIABLO was increased at doses 10% and 15% of As. The germ cell death process induced by As might be related to a decrease in testosterone production because of the reduced expression of steroidogenic enzymes (Star, Cyp11a, Hsd3b5 and Hsd17b). Evaluation of Sertoli markers showed that TUBB3 and GSTA2 expression was unchanged. In contrast, AMH, RHOX5 and CDKN1B expression was decreased while GATA4 expression was increased.

CONCLUSION

In summary, we showed that feeding with crude garlic inhibited Leydig steroidogenic enzyme expression and Sertoli cell markers. These alterations might induce apoptosis in testicular germ cells.

Inhibitors of apoptosis proteins (IAPs) expression and their prognostic significance in hepatocellular carcinoma

Background

Similarly to other tumor types, an imbalance between unrestrained cell proliferation and impaired apoptosis appears to be a major unfavorable feature of hepatocellular carcinoma (HCC). The members of IAP family are key regulators of apoptosis, cytokinesis and signal transduction. IAP survival action is antagonized by specific binding of Smac/DIABLO and XAF1. This study aimed to investigate the gene and protein expression pattern of IAP family members and their antagonists in a series of human HCCs and to assess their clinical significance.

Methods

Relative quantification of IAPs and their antagonist genes was assessed by quantitative Real Time RT-PCR (qPCR) in 80 patients who underwent surgical resection for HCC. The expression ratios of XIAP/XAF1 and of XIAP/Smac were also evaluated. Survivin, XIAP and XAF1 protein expression were investigated by immunohistochemistry. Correlations between mRNA levels, protein expression and clinicopathological features were assessed. Follow-up data were available for 69 HCC patients. The overall survival analysis was estimated according to the Kaplan-Meier method.

Results

Survivin and Livin/ML-IAP mRNAs were significantly over-expressed in cancer tissues compared to non-neoplastic counterparts. Although Survivin immunoreactivity did not correlate with qPCR data, a significant relation was found between higher Survivin mRNA level and tumor stage, tumor grade and vascular invasion.

The mRNA ratio XIAP/XAF1 was significantly higher in HCCs than in cirrhotic tissues. Moreover, high XIAP/XAF1 ratio was an indicator of poor prognosis when overall survival was estimated and elevated XIAP immunoreactivity was significantly associated with shorter survival.

Conclusion

Our study demonstrates that alterations in the expression of IAP family members, including Survivin and Livin/ML-IAP, are frequent in HCCs. Of interest, we could determine that an imbalance in XIAP/XAF1 mRNA expression levels correlated to overall patient survival, and that high XIAP immunoreactivity was a poor prognostic factor.

X-linked inhibitor of apoptosis protein expression after ischemic injury in the human and rat developing brain

X-linked inhibitor of apoptosis protein (XIAP) is a potent suppressor of neuronal death. The aim of this study was to investigate the expression of XIAP after ischemia in the human and rat developing brain. Autopsy specimens from 19 children with neuropathologic diagnosis of focal cerebral ischemic infarct were processed immunohistochemically for XIAP expression. XIAP positive cells were compared in pathologically classified acute (1-4 d), subacute (5-30 d), and chronic (months) strokes vs. age-matched controls with normal brain histology. For the animal studies, ischemia was induced in 1-wk-old rats by unilateral carotid artery occlusion and transient hypoxia. XIAP expression was quantified at four time points after ischemia in the infarct core and peri-infarct area. Neuronal XIAP expression was higher in the penumbra of subacute human infarcts compared with controls (p < 0.05). XIAP expression in the peri-infarct of rat pup was highest at 7 d postischemic injury (p < 0.05). The increase in XIAP expression was associated with a reduction in activated caspase-3 in ischemic neonatal rat brain. Our results demonstrate that XIAP expression postischemic injury is delayed in both species and may continue for several days. Therefore, potentiation of XIAP expression may be neuroprotective in the developing brain.

Tumor resistance to apoptosis

One of the hallmarks of human cancers is the intrinsic or acquired resistance to apoptosis. Evasion of apoptosis may contribute to carcinogenesis, tumor progression and also to treatment resistance, since most current anticancer therapies including chemotherapy, radio- and immunotherapy primarily act by activating cell death pathways including apoptosis in cancer cells. Hence, a better understanding of the molecular mechanisms underlying tumor resistance to apoptotic cell death is expected to provide the basis for a rational approach to develop molecular targeted therapies.

Combination of DNA methylation inhibitor 5-azacytidine and arsenic trioxide has synergistic activity in myeloma

XAF1 is a newly identified candidate tumour-suppressor gene that can antagonise XIAP and sensitise cells to cell death triggers. This study was undertaken to study the effect of 5-azacytidine (AZA) on XAF1 expression in myeloma cells and efficacy of 5-AZA and arsenic trioxide (ATO) combination treatment in myeloma in vivo and in vitro. XAF1 expression was analysed by semi-quantitative PCR and western blotting. Methylation specific PCR was used to detect methylation status of XAF1 promoter CpG islands. RPMI 8226 and XG-7 cells were treated with various concentrations of 5-AZA and ATO. Expression of XAF1 mRNA variants were confirmed by gel electrophoresis and sequencing. Untreated RPMI 8226 cell expresses two variants of XAF1 mRNA. Untreated XG-7 cell has no expression of XAF1. Hypermethylation of XAF1 promoter CpG islands was detected in both cell lines. Both cell lines express full-length XAF1 transcript after treated with 2.5 mumol/L 5-AZA for 72 h. Our studies demonstrated that 5-AZA exhibits anti-myeloma synergy with ATO. In addition, ATO alone, 5-AZA alone, or combination of 5-AZA and ATO was effective in slowing myeloma growth and prolonging survival of myeloma-loaded nude mice. The findings suggested that 5-AZA and ATO may be an effective combination in the therapy of myeloma patients.

c-Jun N-terminal kinase (JNK1) upregulates XIAP-associated factor 1 (XAF1) through interferon regulatory factor 1 (IRF-1) in gastrointestinal cancer

BACKGROUND AND AIMS

X-linked inhibitor of apoptosis protein-associated factor 1 (XAF1) is a tumor suppressor that can sensitize cancer cell to apoptosis. Intrinsic expression of XAF1 in cancer cell is low. Our purpose is to determine the effect of c-Jun N-terminal kinase 1 (JNK1) on XAF1 expression and the putative mechanism.

METHODS

XAF1 expression in gastrointestinal (GI) cancer cell line AGS and SW1116 was detected by reverse transcription-polymerase chain reaction (PCR), real-time PCR and immunoblotting. The role of JNK1 was assessed by ectopic overexpression with wild-type (JNK1-WT) and dominant-negative (JNK1-DN) JNK1 constructs. The effects of JNK1 activator, interferon (IFN)-alpha, tumor necrosis factor (TNF)-alpha and phorbol-12-myristate-13-acetate (PMA), or JNK1 inhibitor, SP600125, were evaluated. An XAF1 promoter reporter pLUC107 with WT or mutated interferon regulatory factor 1-binding element (IRF-E) was used to assess JNK1-induced transcription by dual luciferase assay.

RESULT

Ectopic overexpression of JNK1-WT or treatment with IFN-alpha, TNF-alpha and PMA induced whereas SP600125 suppressed intrinsic and induced XAF1 expression. Induction of XAF1 required de novo protein synthesis. Moreover, JNK1 stimulated whereas SP600125 suppressed XAF1 promoter activity. JNK1 stimulated interferon regulatory factor 1 (IRF-1) expression, whereas both IRF-1 small-interfering RNA and site mutation of IRF-E within XAF1 promoter abrogated the effect of JNK1.

CONCLUSION

JNK1 stimulated and mediated the effects of IFN and TNF-alpha on XAF1 expression through transcriptional regulation by induction of IRF-1. The linkage of JNK1, IRF-1 and XAF1 in the same signal pathway may unravel a novel mechanism in regulation of apoptosis and differentiation of GI cancers.

Inhibitor of apoptosis proteins in hematological malignancies

Apoptosis or programmed cell death is a key mechanism to control tissue homeostasis, for example, in the hematopoietic system. Thus, resistance to apoptosis can contribute to the development of leukemia or lymphoma. Inhibitors of apoptosis (IAP) proteins block cell death pathways at a central node by interfering with the activation of effector caspases. As increased expression levels of IAPs are found in hematological malignancies and have been correlated with poor prognosis, IAPs could be exploited as therapeutic targets and prognostic markers. Various strategies have been developed to target IAPs for therapeutic purposes in leukemia and lymphoma cells, including small-molecule inhibitors and antisense oligonucleotides. These agents could directly induce apoptosis in malignant cells or sensitize these cells to other cytotoxic agents. Thus, IAPs present promising targets for the development of new biomarkers and cancer therapeutics in hematological malignancies.

Stable XIAP knockdown clones of HCT116 colon cancer cells are more sensitive to TRAIL, taxanes and irradiation in vitro

PURPOSE

To develop a model of X-linked inhibitor of apoptosis (XIAP) down regulation in colorectal cancer cell lines. This may be used to determine whether combination strategies have clinical potential.

METHODS

A series of clones were developed using short hairpin RNA (shRNA) against XIAP stably expressed in HCT116 cells. XIAP mRNA and protein levels were established by RT-PCR and Immunoblot, respectively. GeneChip microarrays confirmed XIAP knockdown and absence of compensation by other IAP members.

RESULTS

Four XIAP knockdown cell lines show 82-93% reduction in XIAP mRNA and 67-89% reduction in protein when compared to four luciferase control cell lines. XIAP knockdown sensitises cells to rhTRAIL by a factor of 3, to paclitaxel and docetaxel by a factor of >2 and, to a lesser extent, radiotherapy (20% enhancement).

CONCLUSIONS

Clinical trials with XIAP antisense continue, and these data suggest combination studies with agents such as rhTRAIL and taxanes should be undertaken.

IAP-targeted therapies for cancer

DNA damage, chromosomal abnormalities, oncogene activation, viral infection, substrate detachment and hypoxia can all trigger apoptosis in normal cells. However, cancer cells acquire mutations that allow them to survive these threats that are part and parcel of the transformation process or that may affect the growth and dissemination of the tumor. Eventually, cancer cells accumulate further mutations that make them resistant to apoptosis mediated by standard cytotoxic chemotherapy or radiotherapy. The inhibitor of apoptosis (IAP) family members, defined by the presence of a baculovirus IAP repeat (BIR) protein domain, are key regulators of cytokinesis, apoptosis and signal transduction. Specific IAPs regulate either cell division, caspase activity or survival pathways mediated through binding to their BIR domains, and/or through their ubiquitin-ligase RING domain activity. These protein-protein interactions and post-translational modifications are the subject of intense investigations that shed light on how these proteins contribute to oncogenesis and resistance to therapy. In the past several years, we have seen multiple approaches of IAP antagonism enter the clinic, and the rewards of such strategies are about to reap benefit. Significantly, small molecule pan-IAP antagonists that mimic an endogenous inhibitor of the IAPs, called Smac, have demonstrated an unexpected ability to sensitize cancer cells to tumor necrosis factor-alpha and to promote autocrine or paracrine production of this cytokine by the tumor cell and possibly, other cells too. This review will focus on these and other developmental therapeutics that target the IAPs in cancer.

Impact of XIAP protein levels on the survival of myeloma cells

BACKGROUND

XIAP is the best characterized and the most potent direct endogenous caspase inhibitor and is considered a key actor in the control of apoptotic threshold in cancer cells. In this report, we specifically addressed XIAP regulation and function in myeloma cells.

DESIGN AND METHODS

XIAP and its endogenous inhibitor XAF-1 protein levels and their regulation were assessed by immunoblot analysis in myeloma cell lines or primary myeloma cells. XIAP knockdown by RNA interference was used to evaluate XIAP impact on in vitro drug sensitivity and in vivo tumor growth.

RESULTS

Our results indicate that myeloma cells expressed high levels of XIAP protein that were tightly regulated during growth factor stimulation or stress condition. Of note, an increased XIAPlevel was evidenced during the blockade of the canonical cap-dependent translation by the mTOR inhibitor rapamycin, supporting the hypothesis of a functional IRES sequence in XIAP mRNA. In addition, caspase-mediated XIAP cleavage correlated to an apoptotic process occurring upon cell treatment with the proteasome inhibitor bortezomib. Importantly, XIAP knockdown using RNA interference enhanced drug sensitivity and decreased tumor formation in NOD/SCID mice. Finally, myeloma cells also expressed the XIAP inhibitor XAF-1 that interacted with XIAP in viable myeloma cells.

CONCLUSIONS

Altogether, our data argue for a delicate control of XIAP function in myeloma cells and stimulate interest in targeting XIAP in myeloma treatment.

Decreased expression of CXXC4 promotes a malignant phenotype in renal cell carcinoma by activating Wnt signaling

The Wnt signaling pathway is involved in normal embryonic development and controls the homeostatic self-renewal of stem cells in adult tissues. Constitutive activation of Wnt signaling contributes to cancer development and progression. We identified a CXXC4 homozygous deletion at 4q24 in an aggressive renal cell carcinoma (RCC) using single-nucleotide polymorphism (SNP) arrays. CXXC4 encodes Idax, which negatively regulates Wnt signaling by binding to the PDZ domain of Dishevelled. CXXC4 mRNA levels in tumor samples were significantly lower in patients with metastases compared with those without (P=0.0016). Patients whose tumors had lower CXXC4 expression than normal kidney showed a poorer cause-specific survival outcome than those with higher expression (P=0.0095). Decreased expression of CXXC4 also correlated with cytoplasmic staining of beta-catenin. Knockdown of CXXC4 induced the nuclear translocation of beta-catenin and altered expression of a set of genes involved in cell proliferation, invasion and survival. Furthermore, reduced expression of CXXC4 by small interfering RNAs promoted cell proliferation and inhibited apoptosis after 5-FU and doxorubicin treatment in RCC cells. These data suggest that CXXC4 plays a critical role in tumor progression of RCC through Wnt signaling. Wnt signaling could thus be a potential molecular target in RCC indicating decreased CXXC4 expression.

Mechanisms of neuronal death in disease: defining the models and the players

Dysregulation of life and death at the cellular level leads to a variety of diseases. In the nervous system, aberrant neuronal death is an outstanding feature of neurodegenerative diseases. Since the discovery of the caspase family of proteases, much effort has been made to determine how caspases function in disease, including neurodegenerative diseases. Although many papers have been published examining caspases in neuronal death and disease, the pathways have not been fully clarified. In the present review, we examine the potential players in the death pathways, the current tools for examining these players and the models for studying neurological disease. Alzheimer's disease, the most common neurodegenerative disorder, and cerebral ischaemia, the most common cause of neurological death, are used to illustrate our current understanding of death signalling in neurodegenerative diseases. A better understanding of the neuronal death pathways would provide targets for the development of therapeutic interventions for these diseases.

Role of Smac/DIABLO in cancer progression

Second mitochondria-derived activator of caspase/direct inhibitor of apoptosis-binding protein with low pI (Smac/DIABLO) is a proapoptogenic mitochondrial protein that is released to the cytosol in response to diverse apoptotic stimuli, including commonly used chemotherapeutic drugs. In the cytosol, Smac/DIABLO interacts and antagonizes inhibitors of apoptosis proteins (IAPs), thus allowing the activation of caspases and apoptosis. This activity has prompted the synthesis of peptidomimetics that could potentially be used in cancer therapy. For these reasons, several authors have analyzed the expression levels of Smac/DIABLO in samples of patients from different tumors. Although dissimilar results have been found, a tissue-specific role of this protein emerges from the data. The objective of this review is to present the current knowledge of the Smac/DIABLO role in cancer and its possible use as a marker or therapeutic target for drug design.

X-linked inhibitor of apoptosis protein levels and protein kinase C activity regulate the sensitivity of human endometrial carcinoma cells to tumor necrosis factor alpha-induced apoptosis

Endometrial carcinomas are often chemoresistant. TNFalpha shows potent antitumor activity against various cancers, and if it demonstrates good antitumor activity against endometrial cancer, the cytokine could represent a valuable alternative therapeutic approach. We have tested the ability of TNFalpha to induce apoptosis in endometrial carcinoma cells, and examined a putative role for X-linked inhibitor of apoptosis protein (XIAP) in regulating cellular sensitivity to the cytokine. Exposure to TNFalpha triggered TNF-R1-dependent activation of caspases-8, -9, and -3, down-regulated Akt and XIAP proteins and induced dose-dependent and time-dependent apoptosis in Ishikawa cells. On the opposite, TNFalpha up-regulated XIAP in Hec-1A cells; in these cells, the cytokine induced delayed TNF-R1-dependent activation of caspase-8, and failed to activate caspases -9 and -3 and to induce apoptosis. However, XIAP small interfering RNA restored TNFalpha-induced caspase signaling and apoptosis in Hec-1A cells; XIAP small interfering RNA also increased TNFalpha-induced apoptosis in Ishikawa cells. In addition, inhibition of protein kinase C activity enhanced TNFalpha-induced down-regulation of XIAP and potentiated apoptosis induction, in both Ishikawa and Hec-1A cells. Finally, we found XIAP immunoreactivity in epithelial cells from a large number of human endometrial tumor tissue samples, indicating that XIAP is produced by endometrial tumor cells in vivo. This could allow XIAP to play a putative in vivo role in counteracting TNFalpha-induced apoptosis in endometrial tumor cells; in this case, direct or indirect targeting of XIAP should potentiate the antitumor effect of TNFalpha.

Expression of cIAP-1 correlates with nodal metastasis in squamous cell carcinoma of the tongue

Cellular inhibitor-of-apoptosis protein 1 (cIAP-1) is a member of the inhibitor-of- apoptosis protein family, which predominantly regulates apoptosis. It has been suggested that expression of cIAP-1 correlates with certain clinicopathological features. The possible significance of cIAP-1 expression in cervical lymph node metastasis of tongue squamous cell carcinoma (SCC) is investigated. Seventy-five tongue SCCs were analyzed by immunohistochemistry. cIAP-1 immunoreactivity patterns were nuclear in 38 (51%), cytoplasmic in 47 (63%), and concurrent in 37 (49%) cases. Nuclear, cytoplasmic and concurrent cIAP-1 immunoreactions were significantly correlated with lymph node metastasis in tongue SCCs (P=0.0011, 0.0012, and 0.0006, respectively). The cleaved caspase-3, which is a marker of tumor apoptosis, and Ki-67 index, which is a marker of tumor proliferation, were immunohistochemically examined in 21 tongue SCCs with concurrent nuclear and cytoplasmic cIAP-1 expression and with metastasis, and in 23 tongue SCCs without concurrent nuclear and cytoplasmic cIAP-1 expression and without metastasis. Concurrent cIAP-1 expression was inversely correlated with caspase-3 (P=0.0066), but was positively correlated with Ki-67 expression (P=0.0028). The mode of invasion was associated with lymph node metastasis (P=0.014) and differentiation (P=0.013), but was not correlated with cIAP-1 expression. There was no statistically significant correlation between nuclear or cytoplasmic cIAP-1 expression and the clinicopathological factors of gender, age, clinical stage or differentiation. These results suggest that both patterns of cIAP-1 are useful markers for predicting cervical lymph node metastasis in tongue SCC.