Regulation of XAF1 expression in human colon cancer cell by interferon beta: activation by the transcription regulator STAT1

Luciferase Reporter Systems in Investigating Interferon Antiviral Innate Immunity

Luciferase reporter systems are commonly used in scientific research to investigate a variety of biological processes, including antiviral innate immunity. These systems employ the use of luciferase enzymes derived from organisms such as fireflies or renilla reniformis, which emit light upon reaction with a substrate. In the context of antiviral innate immunity, the luciferase reporter systems offer a noninvasive and highly sensitive approach for real-time monitoring of immune responses in vitro and in vivo, enabling researchers to delve into the intricate interactions and signaling pathways involved in host-virus dynamic interactions. Here, we describe the methods of the promoter-luciferase reporter and enhancer-luciferase reporter, which provide insights into the transcriptional and post-transcriptional regulation of antiviral innate immunity. Additionally, we outline the split-luciferase complementary reporter method, which was designed to explore protein-protein interactions associated with antiviral immunity. These methodologies offer invaluable knowledge regarding the molecular mechanisms underlying antiviral immune pathways and have the potential to support the development of effective antiviral therapies.

Multi-System-Level Analysis with RNA-Seq on Pterygium Inflammation Discovers Association between Inflammatory Responses, Oxidative Stress, and Oxidative Phosphorylation

A pterygium is a common conjunctival degeneration and inflammatory condition. It grows onto the corneal surface or limbus, causing blurred vision and cosmetic issues. Ultraviolet is a well-known risk factor for the development of a pterygium, although its pathogenesis remains unclear, with only limited understanding of its hereditary basis. In this study, we collected RNA-seq from both pterygial tissues and conjunctival tissues (as controls) from six patients (a total of twelve biological samples) and retrieved publicly available data, including eight pterygium samples and eight controls. We investigated the intrinsic gene regulatory mechanisms closely linked to the inflammatory reactions of pterygiums and compared Asian (Korea) and the European (Germany) pterygiums using multiple analysis approaches from different perspectives. The increased expression of antioxidant genes in response to oxidative stress and DNA damage implies an association between these factors and pterygium development. Also, our comparative analysis revealed both similarities and differences between Asian and European pterygiums. The decrease in gene expressions involved in the three primary inflammatory signaling pathways-JAK/STAT, MAPK, and NF-kappa B signaling-suggests a connection between pathway dysfunction and pterygium development. We also observed relatively higher activity of autophagy and antioxidants in the Asian group, while the European group exhibited more pronounced stress responses against oxidative stress. These differences could potentially be necessitated by energy-associated pathways, specifically oxidative phosphorylation.

XAF1 overexpression exacerbates diabetes by promoting pancreatic β-cell apoptosis

AIMS

Pancreatic β-cell apoptosis may be involved in the onset and progression of type 2 diabetes mellitus, although its mechanism remains unclear. We previously demonstrated that macrophage-derived interferon (IFN) β induced X-linked inhibitor of apoptosis-associated factor 1 (XAF1) expression in β-cells and accelerated β-cell apoptosis in vitro. Here, we explored the effects of XAF1 on β-cell function and progression of diabetes in vivo.

METHODS

Pancreatic β-cell-selective XAF1 overexpressing (Xaf1 Tg) mice were generated. Xaf1 Tg mice and their wild-type (WT) littermates were fed either a normal diet or a 40% or 60% high-fat diet (HFD). The effects of β-cell XAF1 on β-cell apoptosis and exacerbation of diabetes were investigated.

RESULTS

Palmitic acid induced IFNβ expression in macrophages, and HFD intake promoted macrophage infiltration in pancreatic islets, both of which cooperatively upregulated XAF1 expression in mouse islets. Furthermore, HFD-fed Xaf1 Tg mice demonstrated increased β-cell apoptosis, lowered insulin expression, and impaired glucose tolerance compared with WT mice fed the same diet. These effects were more pronounced in the 60%HFD group than in the 40%HFD group.

CONCLUSIONS

Pancreatic β-cell XAF1 expression was enhanced via HFD-induced, macrophage-derived IFNβ, which promoted β-cell apoptosis and led to a reduction in insulin secretion and progression of diabetes. To our knowledge, this is the first report to demonstrate an association between pancreatic β-cell XAF1 overexpression and exacerbation of diabetes, thus providing insight into the mechanism of β-cell mass reduction in diabetes.

XAF1 Protects Host against Emerging RNA Viruses by Stabilizing IRF1-Dependent Antiviral Immunity

XIAP-associated factor 1 (XAF1) is an interferon (IFN)-stimulated gene (ISG) that enhances IFN-induced apoptosis. However, it is unexplored whether XAF1 is essential for the host fighting against invaded viruses. Here, we find that XAF1 is significantly upregulated in the host cells infected with emerging RNA viruses, including influenza, Zika virus (ZIKV), and SARS-CoV-2. IFN regulatory factor 1 (IRF1), a key transcription factor in immune cells, determines the induction of XAF1 during antiviral immunity. Ectopic expression of XAF1 protects host cells against various RNA viruses independent of apoptosis. Knockout of XAF1 attenuates host antiviral innate immunity in vitro and in vivo, which leads to more severe lung injuries and higher mortality in the influenza infection mouse model. XAF1 stabilizes IRF1 protein by antagonizing the CHIP-mediated degradation of IRF1, thus inducing more antiviral IRF1 target genes, including DDX58, DDX60, MX1, and OAS2. Our study has described a protective role of XAF1 in the host antiviral innate immunity against RNA viruses. We have also elucidated the molecular mechanism that IRF1 and XAF1 form a positive feedback loop to induce rapid and robust antiviral immunity. IMPORTANCE Rapid and robust induction of antiviral genes is essential for the host to clear the invaded viruses. In addition to the IRF3/7-IFN-I-STAT1 signaling axis, the XAF1-IRF1 positive feedback loop synergistically or independently drives the transcription of antiviral genes. Moreover, XAF1 is a sensitive and reliable gene that positively correlates with the viral infection, suggesting that XAF1 is a potential diagnostic marker for viral infectious diseases. In addition to the antitumor role, our study has shown that XAF1 is essential for antiviral immunity. XAF1 is not only a proapoptotic ISG, but it also stabilizes the master transcription factor IRF1 to induce antiviral genes. IRF1 directly binds to the IRF-Es of its target gene promoters and drives their transcriptions, which suggests a unique role of the XAF1-IRF1 loop in antiviral innate immunity, particularly in the host defect of IFN-I signaling such as invertebrates.

PRD-class homeobox genes in bovine early embryos: function, evolution and overlapping roles

Eutherian Totipotent Cell Homeobox (ETCHbox) genes are mammalian-specific PRD-class homeobox genes with conserved expression in the preimplantation embryo but fast-evolving and highly divergent sequences. Here, we exploit an ectopic expression approach to examine the role of bovine ETCHbox genes and show that ARGFX and LEUTX homeodomain proteins upregulate genes normally expressed in the blastocyst; the identities of the regulated genes suggest that, in vivo, the ETCHbox genes play a role in coordinating the physical formation of the blastocyst structure. Both genes also downregulate genes expressed earlier during development and genes associated with an undifferentiated cell state, possibly via the JAK/STAT pathway. We find evidence that bovine ARGFX and LEUTX have overlapping functions, in contrast to their antagonistic roles in humans. Finally, we characterize a mutant bovine ARGFX allele which eliminates the homeodomain and show that homozygous mutants are viable. These data support the hypothesis of functional overlap between ETCHbox genes within a species, roles for ETCHbox genes in blastocyst formation and the change of their functions over evolutionary time.

Protective immune trajectories in early viral containment of non-pneumonic SARS-CoV-2 infection

The antiviral immune response to SARS-CoV-2 infection can limit viral spread and prevent development of pneumonic COVID-19. However, the protective immunological response associated with successful viral containment in the upper airways remains unclear. Here, we combine a multi-omics approach with longitudinal sampling to reveal temporally resolved protective immune signatures in non-pneumonic and ambulatory SARS-CoV-2 infected patients and associate specific immune trajectories with upper airway viral containment. We see a distinct systemic rather than local immune state associated with viral containment, characterized by interferon stimulated gene (ISG) upregulation across circulating immune cell subsets in non-pneumonic SARS-CoV2 infection. We report reduced cytotoxic potential of Natural Killer (NK) and T cells, and an immune-modulatory monocyte phenotype associated with protective immunity in COVID-19. Together, we show protective immune trajectories in SARS-CoV2 infection, which have important implications for patient prognosis and the development of immunomodulatory therapies.

Infection with SARS-COV-2 can result in self-limited upper airway infection or progress to a more systemic inflammatory condition including pneumonic COVID-19. Here the authors utilise a multi-omics approach to interrogate the immune response of patients with self-limiting upper respiratory SARS-CoV-2 infection and reveal a temporal immune trajectory they associate with viral containment and restriction from pneumonic progressive disease.

MX2 mediates establishment of interferon response profile, regulates XAF1, and can sensitize melanoma cells to targeted therapy

MX2 is an interferon inducible gene that is mostly known for its antiviral activity. We have previously demonstrated that MX2 is also associated with the tumorigenesis process in melanoma. However, it remains unknown which molecular mechanisms are regulated by MX2 in response to interferon signaling in this disease. Here, we report that MX2 is necessary for the establishment of an interferon‐induced transcriptional profile partially through regulation of STAT1 phosphorylation and other interferon‐related downstream factors, including proapoptotic tumor suppressor XAF1. MX2 and XAF1 expression tightly correlate in both cultured melanoma cell lines and in patient‐derived primary and metastatic tumors, where they also are significantly related with survival. MX2 mediates IFN growth‐inhibitory signals in both XAF1 dependent and independent ways and in a cell type and context‐dependent manner. Higher MX2 expression renders melanoma cells more sensitive to targeted therapy drugs such as vemurafenib and trametinib; however, this effect is XAF1 independent. In summary, we uncovered a new mechanism in the complex regulation of interferon signaling in melanoma that can influence both survival and response to therapy.

Embryonic periventricular endothelial cells demonstrate a unique pro-neurodevelopment and anti-inflammatory gene signature

Brain embryonic periventricular endothelial cells (PVEC) crosstalk with neural progenitor cells (NPC) promoting mutual proliferation, formation of tubular-like structures in the former and maintenance of stemness in the latter. To better characterize this interaction, we conducted a comparative transcriptome analysis of mouse PVEC vs. adult brain endothelial cells (ABEC) in mono-culture or NPC co-culture. We identified > 6000 differentially expressed genes (DEG), regardless of culture condition. PVEC exhibited a 30-fold greater response to NPC than ABEC (411 vs. 13 DEG). Gene Ontology (GO) analysis of DEG that were higher or lower in PVEC vs. ABEC identified "Nervous system development" and "Response to Stress" as the top significantly different biological process, respectively. Enrichment in canonical pathways included HIF1A, FGF/stemness, WNT signaling, interferon signaling and complement. Solute carriers (SLC) and ABC transporters represented an important subset of DEG, underscoring PVEC's implication in blood-brain barrier formation and maintenance of nutrient-rich/non-toxic environment. Our work characterizes the gene signature of PVEC and their important partnership with NPC, underpinning their unique role in maintaining a healthy neurovascular niche, and in supporting brain development. This information may pave the way for additional studies to explore their therapeutic potential in neuro-degenerative diseases, such as Alzheimer's and Parkinson's disease.

A Dual Role of Type I Interferons in Antitumor Immunity

Type I interferons (IFN-Is) are a family of cytokines that exert direct antiviral effects and regulate innate and adaptive immune responses through direct and indirect mechanisms. It is generally believed that IFN-Is repress tumor development via restricting tumor proliferation and inducing antitumor immune responses. However, recent emerging evidence suggests that IFN-Is play a dual role in antitumor immunity. That is, in the early stage of tumorigenesis, IFN-Is promote the antitumor immune response by enhancing antigen presentation in antigen-presenting cells and activating CD8⁺ T cells. However, in the late stage of tumor progression, persistent expression of IFN-Is induces the expression of immunosuppressive factors (PD-L1, IDO, and IL-10) on the surface of dendritic cells and other bone marrow cells and inhibits their antitumor immunity. This review outlines these dual functions of IFN-Is in antitumor immunity and elucidates the involved mechanisms, as well as their applications in tumor therapy.

"Do We Know Jack" About JAK? A Closer Look at JAK/STAT Signaling Pathway

Janus tyrosine kinase (JAK) family of proteins have been identified as crucial proteins in signal transduction initiated by a wide range of membrane receptors. Among the proteins in this family JAK2 has been associated with important downstream proteins, including signal transducers and activators of transcription (STATs), which in turn regulate the expression of a variety of proteins involved in induction or prevention of apoptosis. Therefore, the JAK/STAT signaling axis plays a major role in the proliferation and survival of different cancer cells, and may even be involved in resistance mechanisms against molecularly targeted drugs. Despite extensive research focused on the protein structure and mechanisms of activation of JAKs, and signal transduction through these proteins, their importance in cancer initiation and progression seem to be underestimated. This manuscript is an attempt to highlight the role of JAK proteins in cancer biology, the most recent developments in targeting JAKs, and the central role they play in intracellular cross-talks with other signaling cascades.

Silencing HS6ST3 inhibits growth and progression of breast cancer cells through suppressing IGF1R and inducing XAF1

Heparan sulfate 6-O-sulfation is biologically edited by 6-O-sulfotransferases (HS6STs) within heparan sulfate chains. Three isoforms of HS6ST have been identified. These enzymes are found to be differentially expressed in a variety of tissues. Recently, several studies have shown that dysregulation of 6-O-sulfotransferases could be involved in tumorigenesis of several cancers. This study aimed to analyze the expression and function of HS6ST3 in breast cancer. HS6ST3 was found up-regulated in T47D, MCF7 and MDA-MB231 breast cancer cell lines. HS6ST3 was then silenced in T47D and MCF7 using siRNA. Silencing HS6ST3 diminished tumor cell growth, migration and invasion, but enhanced cell adhesion and apoptosis in breast cancer. Gene microarray analysis revealed that silencing HS6ST3 significantly changed the expression of IGF1R and XAF1 in breast cancer cells. Further functional studies showed that the cellular processes were mediated by IGF1R and XAF1 after silencing HS6ST3 in breast cancer cells. Together these results indicate that HS6ST3 might be involved in the tumorigenesis of breast cancer and it could be a promising target in breast cancer therapy.

Epigenetic silencing of the XAF1 gene is mediated by the loss of CTCF binding

XAF1 is a tumour suppressor gene that compromises cell viability by modulating different cellular events such as mitosis, cell cycle progression and apoptosis. In cancer, the XAF1 gene is commonly silenced by CpG-dinucleotide hypermethylation of its promoter. DNA demethylating agents induce transcriptional reactivation of XAF1, sensitizing cancer cells to therapy. The molecular mechanisms that mediate promoter CpG methylation have not been previously studied. Here, we demonstrate that CTCF interacts with the XAF1 promoter in vivo in a methylation-sensitive manner. By transgene assays, we demonstrate that CTCF mediates the open-chromatin configuration of the XAF1 promoter, inhibiting both CpG-dinucleotide methylation and repressive histone posttranslational modifications. In addition, the absence of CTCF in the XAF1 promoter inhibits transcriptional activation induced by well-known apoptosis activators. We report for the first time that epigenetic silencing of the XAF1 gene is a consequence of the loss of CTCF binding.

X-linked inhibitor of apoptosis-associated factor l (XAFl) enhances the sensitivity of colorectal cancer cells to cisplatin

The purpose of present study was to investigate the roles of X-linked inhibitor of apoptosis-associated factor l (XAFl) in regulation apoptosis of colorectal cancer (CRC) cells after treatment with cisplatin (DDP). A total of ten paired cancerous and non-cancerous tissues were collected from patients with CRC after surgery. The levels of XAFl protein were detected by Western blot. Primary CRC cells were separated from cancer tissues, and its viability or apoptosis after treatment with DDP was determined with MTT or Annexin V/PI assays, respectively. Furthermore, we either up-regulated transfecting a XAF1 overexpression vector or down-regulated XAF1 by siRNA interference. And then, the XAF1 levels and its sensitivity to cisplatin were assessed. XAFl had a lower expression in the cancerous tissues from samples T1, T2 and T3 than their paired non-cancerous tissues N1, N2 and N3. However, the expression of XAF1 was not detected in samples T4 and N1. XAF1 levels in cancer tissues significantly decreased in comparison with normal tissues. Cell abilities of primary cells were significantly decreased in a dose-dependent manner, after treatment with a series concentrations of cisplatin (2, 5, 10 μg/mL) for 48 h. Although, after down-expression of XAFl by siRNA, cisplatin caused a significant decreases in apoptosis rates in CRC cells. The up-regulation of XAF1 distinctly increased apoptosis in CRC cells administered by cisplatin (P < 0.001). The XAFl could promoted apoptosis and enhanced chemotherapy sensitivity to cisplatin in CRC cells.

Integrative Pathway Analysis Using Graph-Based Learning with Applications to TCGA Colon and Ovarian Data

Recent method development has included multi-dimensional genomic data algorithms because such methods have more accurately predicted clinical phenotypes related to disease. This study is the first to conduct an integrative genomic pathway-based analysis with a graph-based learning algorithm. The methodology of this analysis, graph-based semi-supervised learning, detects pathways that improve prediction of a dichotomous variable, which in this study is cancer stage. This analysis integrates genome-level gene expression, methylation, and single nucleotide polymorphism (SNP) data in serous cystadenocarcinoma (OV) and colon adenocarcinoma (COAD). The top 10 ranked predictive pathways in COAD and OV were biologically relevant to their respective cancer stages and significantly enhanced prediction accuracy and area under the ROC curve (AUC) when compared to single data-type analyses. This method is an effective way to simultaneously predict binary clinical phenotypes and discover their biological mechanisms.

Aspirin enhances IFN-α-induced growth inhibition and apoptosis of hepatocellular carcinoma via JAK1/STAT1 pathway

STAT1 has a key role in exerting the antiproliferative and proapoptotic effects of interferon (IFN)-α on tumors, and its defects in expression is associated with IFN-α resistance. In this study we want to investigate whether aspirin can improve the antitumor efficiency of IFN-α on hepatocellular carcinoma (HCC) through the activation of STAT1. We found that aspirin not only significantly enhanced IFN-α-induced antiproliferation and apoptosis of HCC in vitro study but also enhanced tumor growth inhibition in nude mice. Although IFN-α alone resulted in significant phosphorylation of both STAT1 and STAT3, aspirin only prompted the IFN-α-induced phosphorylation of STAT1. Further study revealed that aspirin-prompted phosphorylation of STAT1 was activated through phosphorylation of JAK1. Furthermore, aspirin-activated STAT1 upregulated the transcription of proapoptotic IFN-stimulated gene (ISG) of X-linked inhibitor of apoptosis-associated factor-1 and downregulated the transcription of antiapoptotic ISG of G1P3, which in turn promoted the expression of Bax and activation of caspase-9 and caspase-3, thereby sensitizing HCC cells to IFN-α-induced apoptosis. Taken together, our findings suggest a novel strategy of using aspirin to overcome tumor resistance and enhance the effectiveness of IFN-α in HCC treatment through activating STAT1 gene, and have potential implications for improving future IFN-α protein and gene therapy.

Assessment of XAF1 as A Biomarker to Differentiate Hepatocellular Carcinoma from Nonneoplastic Liver Tissues

OBJECTIVE

XIAP-associated factor 1 (XAF1) expression has been shown to be related with apoptosis in hepatocellular carcinoma (HCC). However, the correlation of XAF1 expression with HCC tumor grade has not been intensively assessed. XIAP-associated factor-1 (XAF1) is an important apoptosis inducer in human HCC. The aim of this study is to determine the correlation between XAF1 expression and HCC histopathological grades.

METHODS

The mRNA levels of XAF1 in 24 paired HCC-nonneoplastic specimens were quantified by real-time reverse transcription PCR (RT-PCR). Protein levels of XAF1 in 110 paired HCC-noncancer tissues were investigated by immunostaining specimens on a tissue microarray (TMA). Correlations between XAF1 mRNA levels or protein expression and clinicopathological features were assessed by statistical analysis.

RESULTS

Both XAF1 mRNA and protein were significantly under-expressed in HCC tissues compared to their non-neoplastic counterparts. No significant relationship was found between XAF1 mRNA or protein expression and histological tumor grade.

CONCLUSION

All these data suggest that XAF1 is a potential biomarker for differentiating HCC with noncancerous tissues.

XAF1 contributes to dengue virus-induced apoptosis in vascular endothelial cells

The mechanism of vascular leakage in severe dengue infection remains unclear. Here, we used primary human umbilical vein endothelial cells (HUVECs) and the EA.hy926 cell line to study the molecular events that occur after dengue virus serotype 2 (DENV2) infection. DENV2-induced apoptosis was confirmed using nuclear staining, TUNEL assay, and electron microscopy. A genome-wide transcriptome analysis was performed using a microarray of DENV2-infected HUVECs. Notably, interferon-inducible genes were differentially expressed after DENV2 infection. Prominent among these genes was the X chromosome-linked inhibitor of apoptosis protein (XIAP)-associated factor 1 (XAF1; up-regulated 1.2-fold in the microarray analysis and ∼8-fold by qRT-PCR after DENV2 infection). XAF1 protein levels were up-regulated after DENV2 infection in both HUVECs and EA.hy926 cells. Evidence indicated interaction between XAF1 and XIAP during DENV2 infection based on their cellular localization, as observed by confocal microscopy and the coimmunoprecipitation of XIAP with an anti-XAF1 antibody. Next, recombinant EA.hy926 cell lines in which XAF1 was either knocked down or overexpressed were constructed. The expression levels of the apoptosis-related genes caspase 3, caspase 8, caspase 9, and poly-(ADP-ribose) polymerase (PARP) were down-regulated in the XAF1 knockdown (24-48 h postinfection) but were up-regulated in XAF1 overexpressing cells (36 h postinfection). This is the first study of the role of XAF1 in promoting apoptosis in vascular endothelial cells after DENV2 infection.

Network analysis of icb-1 gene function in human breast cancer cells

Icb-1 is a human gene previously described by our group to exert important functions in cancer cells of different origin. We now performed microarray-based gene expression profiling with subsequent network modeling to further elucidate the role of icb-1 in breast cancer cells. Analyzing the effect of icb-1 knockdown on the transcriptome of MCF-7 cells, we found 151 differentially expressed genes exhibiting more than twofold changes, 97 of which were up- and 54 downregulated. Most of the upregulated genes were cancer-related genes associated with poor prognosis, invasion and metastasis, building an oncogenic network of TNF target genes. On the other hand, network analysis identified the downregulated genes to be primarily involved in interferon signaling and cellular apoptosis. Confirming these network data, we observed that cells with reduced levels of icb-1 exhibited an impaired response to the apoptosis inducers tamoxifen, staurosporine, actinomycin, and camptothecin. The data of this study suggest that icb-1 might exert a tumor-suppressor function in breast cancer and that its loss might confer relative resistance of breast cancer cells to apoptotic drugs.

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.

Expression phenotype changes of EBV-transformed lymphoblastoid cell lines during long-term subculture and its clinical significance

OBJECTIVES

The EBV-transformed lymphoblastoid cell line (LCL) is a useful resource for population-based human genetic and pharmacogenetic studies. The principal objective here was to assess expression phenotype changes during long-term subculture of LCLs, and its clinical significance.

MATERIALS AND METHODS

We searched for genes that were differentially expressed in 17 LCLs at late (p161) passage compared to early passage (p4) using microarray assay, then validated them by real-time RT-PCR analysis. In addition, we estimated correlations between expression phenotypes of 20 LCL strains at early passage and 23 quantitative clinical traits from blood donors of particular LCL strains.

RESULTS

Transcript sequences of 16 genes including nuclear factor-kappaB (NF-kappaB) pathway-related genes (such as PTPN13, HERC5 and miR-146a) and carcinogenesis-related genes (such as XAF1, TCL1A, PTPN13, CD38 and miR-146a) were differentially expressed (>2-fold change) in at least 15 of the 17 LCL strains. In particular, TC2N, FCRL5, CD180, CD38 and miR-146a were downregulated in all 17 of the evaluated LCL strains. In addition, we identified clinical trait-associated expression phenotypes in LCLs.

CONCLUSION

Our results showed that LCLs acquired expression phenotype changes involving expression of NF-kappaB pathway- and carcinogenesis-related genes during long-term subculture. These differentially expressed genes can be considered to be a gene signature of LCL immortalization or EBV-induced carcinogenesis. Clinical trait-associated expression phenotypes should prove useful in the discovery of new candidate genes for particular traits.

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.

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.