Mutation and expression of the beta-catenin-interacting protein ICAT in human colorectal tumors

Disruption of PABPN1 phase separation by SNRPD2 drives colorectal cancer cell proliferation and migration through promoting alternative polyadenylation of CTNNBIP1

Generally shortened 3' UTR due to alternative polyadenylation (APA) is widely observed in cancer, but its regulation mechanisms for cancer are not well characterized. Here, with profiling of APA in colorectal cancer tissues and poly(A) signal editing, we firstly identified that the shortened 3' UTR of CTNNIBP1 in colorectal cancer promotes cell proliferation and migration. We found that liquid-liquid phase separation (LLPS) of PABPN1 is reduced albeit with higher expression in cancer, and the reduction of LLPS leads to the shortened 3' UTR of CTNNBIP1 and promotes cell proliferation and migration. Notably, the splicing factor SNRPD2 upregulated in colorectal cancer, can interact with glutamic-proline (EP) domain of PABPN1, and then disrupt LLPS of PABPN1, which attenuates the repression effect of PABPN1 on the proximal poly(A) sites. Our results firstly reveal a new regulation mechanism of APA by disruption of LLPS of PABPN1, suggesting that regulation of APA by interfering LLPS of 3' end processing factor may have the potential as a new way for the treatment of cancer.

RNA-binding motif protein 10 represses tumor progression through the Wnt/β- catenin pathway in lung adenocarcinoma

RNA-binding motif protein 10 (RBM10), one of the members of the RNA-binding protein (RBP) family, has a tumor suppressor role in multiple cancers. However, the functional role of RBM10 in lung adenocarcinoma (LUAD) and the underlying molecular mechanism remains unclear. In this study, we observed that RBM10 is significantly downregulated in LUAD tissues compared with normal tissues. Low RBM10 expression is significantly associated with poor outcome of LUAD patients. In vitro and in vivo experiments show that RBM10 inhibits cell proliferation, metastasis and EMT progression in LUAD. Mechanistically, we demonstrate that RBM10 interacts with β-catenin interacting protein 1 (CTNNBIP1) and positively regulates its expression, disrupting the binding of β-catenin to the transcription factor TCF/LEF, thereby inactivating the Wnt/β-catenin pathway. In conclusion, this is the first study reporting the role of RBM10 in suppressing LUAD progression at least via partly inactivating the Wnt/β-catenin pathway, which provides new insights into the tumorigenesis and metastasis of LUAD. Thus, RBM10 may be a promising new therapeutic target or clinical biomarker for LUAD therapy in the future.

Overexpression of ICAT Inhibits the Progression of Colorectal Cancer by Binding with β-Catenin in the Cytoplasm

Inhibitor of β-catenin and T-cell factor (ICAT) was first found as a polypeptide that blocks β-catenin–TCF interaction. Abundant evidence has shown that ICAT has different functions in diverse cancers’ progression. Nevertheless, the roles it plays in colorectal cancer (CRC) have not been described. Here, we documented that ICAT expression was higher in CRC tissue than in the adjacent normal tissue and that prognosis was better in high-ICAT expression patients. The overexpression of ICAT inhibited CRC cell proliferation both in vitro and in vivo. Wnt pathway transcriptional activity was suppressed in the CRC cells with ICAT overexpression, where the CCND1 and MYC expression, which occurs downstream of the Wnt signaling pathway, was inhibited. Co-immunoprecipitation experiments showed that ICAT bound with β-catenin in stable overexpression cell lines; immunofluorescence showed the co-localization of ICAT and β-catenin in the cytoplasm. Overall, our study reveals that ICAT inhibits CRC cell proliferation by binding to cytoplasm-located β-catenin, and prevents its translocation, which results in Wnt signaling pathway inactivation. It may provide a scientific foundation for focusing on ICAT in treatments for CRC.

Functional genetic variants of CTNNBIP1 predict platinum treatment response of Chinese epithelial ovarian cancer patients

Chemotherapy resistance remains a blockade for successful treatment and longer overall survival of patients with epithelial ovarian cancer (EOC). CTNNBIP1 is an inhibitor of β-catenin that is a chemotherapeutic target for EOC treatment. In the present study, we investigated associations between single nucleotide polymorphisms (SNPs) of CTNNBIP1 and platinum treatment response of Han Chinese EOC patients and subsequently performed functional prediction and validation of the resultant SNPs. We found that CTNNBIP1 rs935072 AT/TT variant genotypes were associated with platinum treatment response in the multivariate logistic regression analysis of EOC patients. Specifically, the CTNNBIP1 rs935072 AT/TT genotypes were associated with a decreased risk of developing chemoresistance ([adjusted odds ratio (OR)] = 0.89, 95% confidence interval (CI) = 0.82-0.97 and P=0.010), compared with the AA genotype. Further experiments showed that the underlying mechanism for the CTNNBIP1 rs935072 A>T change in chemotherapy treatment response resulted from a lower binding affinity of miR-27a-3p, thereby leading to up-regulation of the CTNNBIP1 expression. We further found that overexpression of CTNNBIP1 sensitized ovarian cancer cells to platinum treatment. Thus, the present study provides evidence that functional variants of CTNNBIP1 may regulate the expression of CTNNBIP1, a possible mechanism affecting platinum treatment response of EOC patients.

miR‑296‑3p promotes the proliferation of glioblastoma cells by targeting ICAT

MicroRNAs (miRNA/miRs) serve an important function in the regulation of gene expression, and have been indicated to mediate a number of cellular biological processes, including cell proliferation, the cell cycle, cell apoptosis and cell differentiation. The altered expression of miRNAs has been revealed to result in a variety of human diseases, including glioblastoma multiforme (GBM). The present study indicated an increase in miR‑296‑3p in glioma tumor types compared with normal brain, particularly in the samples from patients with high grade GBM. Antagonizing miR‑296‑3p was demonstrated to induce cell growth arrest and cell cycle redistribution in U251 cells. The miR‑296‑3p antagonist altered the expression of a number of key genes that are involved in cell cycle control, including cyclin D1 and p21. Additionally, the decrease of miR‑296‑3p increased inhibitor of β‑catenin and T cell factor (ICAT) expression, and increased miR‑296‑3p‑inhibited ICAT expression in U251 cells. Bioinformatics analysis indicated that ICAT is a target gene of miR‑296‑3p, which was further validated using a dual‑luciferase reporter assay. Through the regulation of ICAT, the miR‑296‑3p antagonist decreased β‑catenin protein expression and increased the expression of its target genes. Silencing ICAT was indicated to reverse the miR‑296‑3p downregulation‑induced inactivation of Wnt signaling and cell growth arrest in glioma cells. The present study also indicated a negative correlation between ICAT mRNA levels and miR‑296‑3p levels in glioma tumor types. In conclusion, the present study identified an oncogenic function of miR‑296‑3p in glioblastoma via the direct regulation of ICAT.

Piplartine suppresses proliferation and invasion of hepatocellular carcinoma by LINC01391-modulated Wnt/β-catenin pathway inactivation through ICAT

Although piplartine is regarded as an anticancer agent, the relationship between long noncoding RNAs (lncRNAs), which are involved in various diseases (e.g., tumors) and piplartine in hepatocellular carcinoma (HCC) remains unclear. We identified LINC01391 using microarray analysis and validated its expression by qRT-PCR. Functional assays were applied to evaluate the biological effects of LINC01391 and inhibitory of β-catenin and T-cell factor (ICAT) on HepG2 and SMMC-7721 cells. The binding relationship between LINC01391 and ICAT was determined by RNA pull-down and RNA immunoprecipitation (RIP). Results showed that piplartine attenuated cell proliferation and invasion but promoted cell apoptosis. Upregulation of LINC01391 induced by piplartine inhibited HCC cell proliferation, invasion in vitro, and tumor growth in vivo. LINC01391 interacted with ICAT and promoted its inhibitory effect on the Wnt/β-catenin pathway, as enhanced interaction between β-catenin and ICAT, and dampened interaction of β-catenin and TCF/LEF were induced by overexpression of LINC01391. Knockdown of ICAT also promoted cell proliferation in vitro and tumor growth in vivo. Our study supported a role for piplartine and LINC01391 in HCC treatment. We found that LINC01391 inhibited the Wnt/β-catenin pathway and suppressed tumor growth via ICAT.

Inhibitor of β-catenin and TCF (ICAT) promotes cervical cancer growth and metastasis by disrupting E-cadherin/β-catenin complex

The inhibitor of β-catenin and TCF (ICAT) blocks the binding of TCF to β-catenin and has been demonstrated as a suppressor of the Wnt/β-catenin signaling pathway. It has been reported to exert a different function around a wide variety of cancers. However, its function and underlying mechanisms in human cervical cancer remains unknown. In the present study, the expression of ICAT in 41 human cervical cancer tissues and 30 normal cervical tissues was evaluated by immunohistochemical analysis. ICAT was found highly expressed in cancer tissues. ICAT overexpression significantly promoted SiHa cell proliferation in vitro by causing G1 arrest, and enhanced cell migration and invasion whereas, ICAT knockdown induced opposite effects in Caski cells which have higher expression of ICAT. Downregulation or overexpression of ICAT resulted in an altered expression of the epithelial-mesenchymal transition (EMT). Furthermore, immunoprecipitation assays revealed that ICAT pormoted cervical cancer EMT by competing in E-cadhenin binding to β-caterin. Overexpression of ICAT in SiHa cells promoted tumor growth and EMT was also demonstrated by the xenograft mouse experiment. These results demonstrate that ICAT contributed to the progression of cervical cancer and may play a role in the regulation of EMT by distrupting the E-cadherin/β-catenin complex. It may be a novel potential therapeutic target for therapy in human cervical cancer.

Frequent inactivation of MCC/CTNNBIP1 and overexpression of phospho-beta-catenin(Y654) are associated with breast carcinoma: Clinical and prognostic significance

Transcriptional activation of β-catenin is a hallmark of Wnt/β-catenin pathway activation. The MCC (Mutated in colorectal cancers) and CTNNBIP1 (catenin, beta interacting protein 1) are two candidate genes which inhibit the transcriptional activity of nuclear β-catenin. The importance of MCC and CTNNBIP1 in breast cancer (BC) development has not yet been studied in detail. For this reason, in present study, the alterations (deletion/methylation/mutation/expression) of MCC and CTNNBIP1 were analyzed in BC of Indian patients (N=120) followed by expression/mutation analysis of β-catenin. Then transcriptional activity of β-catenin was checked by expression analysis of its target genes (EGFR, C-MYC and CCND1) in the same set of samples. Frequent methylation (44-45%) than deletion (20-32%) with overall alterations of 52-55% was observed in MCC/CTNNBIP1 in the BC samples. The alterations of MCC/CTNNBIP1 showed significant correlation with increased nuclear β-catenin/p-β-catenin(Y654) expression. Also, a significant correlation was seen between nuclear β-catenin expression and overexpression of its target genes like EGFR, MYC and CCND1 in the BC samples (P<0.0001). An upregulation of MCC and CTNNBIP1 expression by 5-Aza-2'-deoxycytidine treatment of MCF7 and MDA-MB-231 cell lines lead to downregulation of β-catenin and its target genes. The expression of nuclear p-β-catenin(Y654), EGFR, MYC and CCND1 were significantly high in TNBC (Triple negative BC) and Her2+ compared to Luminal A/B+ subtypes. The TNBC patients in stage III/IV having reduced expression of MCC in the tumors showed poor prognosis. Thus, our data suggests that inactivation of MCC/CTNNBIP1 could be an important event in activation of β-catenin mediated transcription of target genes in BC.

Wnt-induced deubiquitination FoxM1 ensures nucleus β-catenin transactivation

A key step of Wnt signaling activation is the recruitment of β-catenin to the Wnt target-gene promoter in the nucleus, but its mechanisms are largely unknown. Here, we identified FoxM1 as a novel target of Wnt signaling, which is essential for β-catenin/TCF4 transactivation. GSK3 phosphorylates FoxM1 on serine 474 which induces FoxM1 ubiquitination mediated by FBXW7. Wnt signaling activation inhibits FoxM1 phosphorylation by GSK3-Axin complex and leads to interaction between FoxM1 and deubiquitinating enzyme USP5, thereby deubiquitination and stabilization of FoxM1. FoxM1 accumulation in the nucleus promotes recruitment of β-catenin to Wnt target-gene promoter and activates the Wnt signaling pathway by protecting the β-catenin/TCF4 complex from ICAT inhibition. Subsequently, the USP5-FoxM1 axis abolishes the inhibitory effect of ICAT and is required for Wnt-mediated tumor cell proliferation. Therefore, Wnt-induced deubiquitination of FoxM1 represents a novel and critical mechanism for controlling canonical Wnt signaling and cell proliferation.

Expressional STAT3/STAT5 Ratio is an Independent Prognostic Marker in Colon Carcinoma

BACKGROUND

Signal transducer and activator of transcription proteins (STATs) are crucial regulators of cell growth and differentiation; however, their specific prognostic impact in human colon cancer has only been studied to limited extent. We aimed to assess the prognostic significance of specific STAT expression patterns in colon carcinoma.

METHODS

Protein expression patterns of activated STAT1, STAT3, STAT4, and STAT5 in human colon carcinoma tissue and corresponding healthy mucosa (n = 104) were assessed using multiplex bead-based immunoassay technologies. Expression patterns were correlated with clinical and survival data. Immunohistochemistry was performed to assess spatial expression of STAT3 and STAT5.

RESULTS

STAT3 was underexpressed whereas STAT4 and STAT5 were overexpressed in colon carcinoma tissue. Primary tumors from patients with distant metastases (M1) displayed significantly increased expression of STAT1 and STAT3 but decreased expression of STAT4 and STAT5. Increased tumor expression of STAT1 or STAT3 was associated with impaired patient survival, whereas increased expression of STAT4 or STAT5 correlated with improved survival. Multivariate analysis identified an increased STAT3/STAT5 expressional ratio as an adverse prognostic marker in colon cancer patients.

CONCLUSIONS

The tumor progression-associated transcription factors STAT3, STAT4, and STAT5 are differently expressed in colon carcinoma tissue and colon mucosa. Moreover, the STAT3/STAT5 expression ratio is an independent prognostic marker in colon cancer patients.

ICAT inhibits glioblastoma cell proliferation by suppressing Wnt/β-catenin activity

Inhibitor of β-catenin and T-cell factor (ICAT) is a key component of Wnt/β-catenin signaling. ICAT blocks the formation of the β-catenin/TCF complex and has been demonstrated to be involved in embryonic development and carcinogenesis. As an inhibitor of canonical Wnt signaling, ICAT was presumed to be a tumor-suppressor gene. However, the ICAT functions in human glioma remain unknown. In this study, we evaluated the expression of ICAT in 305 human glioma tissues and found that negative ICAT expression correlated with higher grade glioma and poor survival in patients with glioma. Then we transfected glioma cells with ICAT plasmid. Western blotting showed an increased ICAT protein expression level in glioma cells. MTT assay, flow cytometry and cell invasion assay were used to detect cell proliferation, cell cycle distribution, apoptosis and invasion. Our studies confirmed that ICAT inhibits glioma cell proliferation and invasion, and it induces cell apoptosis and cell cycle progression arrest. Besides, ICAT slowed down tumor growth in a glioblastoma xenograft model. Therefore, our study demonstrates that ICAT may serve as a tumor-suppressor in human glioma suggesting a promising direction for targeting therapy in glioma.

MiR-424-5p reversed epithelial-mesenchymal transition of anchorage-independent HCC cells by directly targeting ICAT and suppressed HCC progression

Resistance to anoikis and Epithelial-mesenchymal transition (EMT) are two processes critically involved in cancer metastasis. In this study, we demonstrated that after anchorage deprival, hepatocellular carcinoma (HCC) cells not only resisted anoikis, but also exhibited EMT process. Microarray expression profiling revealed that expression of miR-424-5p was significantly decreased in anoikis-resistant HCC cells. Ectopic overexpression of miR-424-5p was sufficient to reverse resistance to anoikis, block EMT process and inhibit malignant behaviors of HCC cells. Target analysis showed that a potent β-catenin inhibitor, ICAT/CTNNBIP1 was a direct target of miR-424-5p. Further study demonstrated that miR-424-5p reversed resistance to anoikis and EMT of HCCs by directly targeting ICAT and further maintaining the E-cadherin/β-catanin complex on the cellular membrance. In vivo study further demonstrated that miR-424-5p significantly inhibited the tumorigenicity of HCC cells in nude mice. Clinical investigation demonstrated that miR-424-5p was significantly downregulated in HCC tissues compared with that of the non-cancerous liver tissues, and this decreased expression of miR-424-5p was significantly correlated with higher pathological grades and more advanced TNM stages. Therefore, aberrant expression of miR-424-5p is critically involved in resistance to anoikis and EMT during the metastatic process of HCC, and its downregulation significantly contributes to liver cancer progression.

Physiological inhibitors of Wnt signaling

Wnt signaling is crucial for cell proliferation and differentiation. It represents a complex network with mechanisms of self-regulation through positive and negative feedback. Recent increasing interest in this signaling pathway has led to the discovery of many new proteins that down-regulate Wnt activity. Here, we provide a short description of the most important and best-studied inhibitors, group them according to the target molecule within the Wnt cascade, and discuss their clinical potential. Although most of the inhibitors discussed here may also interact with proteins from other signaling pathways, we focus only on their ability to modulate Wnt signaling.

An oncogenic hub: beta-catenin as a molecular target for cancer therapeutics

The Wnt/beta-catenin signaling pathway plays diverse roles in embryonic development and in maintenance of organs and tissues in adults. Activation of this signaling cascade inhibits degradation of the pivotal component beta-catenin, which in turn stimulates transcription of downstream target genes. Over the past two decades, intensive worldwide investigations have yielded considerable progress toward understanding the cellular and molecular mechanisms of Wnt signaling and its involvement in the pathogenesis of a range of human diseases. Remarkably, beta-catenin signaling is aberrantly activated in greater than 70% of colorectal cancers and to a lesser extent in other tumor types, promoting cancer cell proliferation, survival and migration. Accordingly, beta-catenin has gained recognition as an enticing molecular target for cancer therapeutics. Disruption of protein-protein interactions essential for beta-catenin activity holds immense promise for the development of novel anti-cancer drugs. In this review, we focus on the regulation of beta-catenin-dependent transcriptional activation and discuss potential therapeutic opportunities to block this signaling pathway in cancer.

Glutamine Regulates the Human Epithelial Intestinal HCT-8 Cell Proteome under Apoptotic Conditions

Glutamine plays a key role in the metabolism of rapidly dividing cells, including enterocytes and lymphocytes, which may contribute to its beneficial clinical effects. Gut mucosal homeostasis is achieved through a balance between cell proliferation and apoptosis. In T cells, glutamine up-regulates antiapoptotic proteins and down-regulates proapoptotic proteins. In gut mucosa, glutamine prevents apoptosis in rat epithelial cell lines, whereas glutamine starvation induces apoptosis through caspase activation. Finally glutamine specifically prevents tumor necrosis factor-alpha-related apoptosis in the human intestinal cell line HT-29. Comparative functional proteomics enables the characterization of each differentially expressed protein in intestinal cells in response to modifications of nutritional environment. The influence of glutamine on intestinal proteome expression in apoptotic conditions has not been studied and evaluated. This comparative proteomics study was performed in the human epithelial intestinal cell line HCT-8 under experimental apoptotic conditions to investigate the influence of glutamine on protein expression during apoptosis. The pharmaconutritional effects of glutamine were determined under 2 mm (physiological concentration) and 10 mm (pharmaconutritional concentration) conditions. About 1,800 protein spots were revealed in both conditions. Comparative assessments indicated that 28 proteins were differentially expressed significantly (i.e. at least 2-fold modulated and Student's t test with p </= 0.05) in response to an increase of glutamine concentration in the culture medium. Twenty-four proteins were identified by mass spectrometry and associated databases. From these proteins, 34% are involved in cell cycle and apoptosis mechanisms, 17% are involved in signal transduction, and 13% are involved in cytoskeleton organization. These data were integrated in a proposed schema of the interactome under apoptotic conditions. In conclusion, this study provides the first holistic picture of proteome modulation by glutamine in a human enterocytic cell line under apoptotic conditions and supports further evaluation of nutritional modulation of human intestinal proteome in various pathological conditions where apoptosis may be involved.

LZIC regulates neuronal survival during zebrafish development

Development of the brain and central nervous system is a complex process involving localized gene expression and regulated cell death and proliferation. Here, we describe a gene involved in neuronal survival, the zebrafish ortholog of the human lzic gene. Zebrafish lzic is expressed ubiquitously during early development and later becomes enriched in the developing brain. Using antisense morpholino oligonucleotides, we demonstrate that zebrafish lzic is required zygotically for the survival of distinct neuronal populations. LZIC is closely related to ICAT, a physiological inhibitor of the Wnt pathway that interacts physically and functionally with beta-catenin to prevent the transcription of Wnt target genes. LZIC's ICAT-homologous region is highly similar to ICAT with particular conservation of residues that are used by ICAT for beta-catenin-binding. Surprisingly, despite this high similarity, LZIC does not interact with beta-catenin in vitro or in vivo. Our results reveal that LZIC, a protein conserved in vertebrates, is required for neuronal survival in zebrafish.

Role for ICAT in beta-catenin-dependent nuclear signaling and cadherin functions

Inhibitor of beta-catenin and TCF-4 (ICAT) is a 9-kDa polypeptide that inhibits beta-catenin nuclear signaling by binding beta-catenin and competing its interaction with the transcription factor TCF (T cell factor), but basic characterization of the endogenous protein and degree to which it alters other beta-catenin functions is less well understood. At the subcellular level, we show that ICAT localizes to both cytoplasmic and nuclear compartments. In intestinal tissue, ICAT is upregulated in the mature, nondividing enterocyte population lining intestinal villi and is absent in the beta-catenin/TCF signaling-active crypt region, suggesting that its protein levels may be inversely related with beta-catenin signaling activity. However, ICAT protein levels are not altered by activation or inhibition of Wnt signaling in cultured cells, suggesting that ICAT expression is not a direct target of the Wnt/beta-catenin pathway. In cells where beta-catenin levels are elevated by Wnt, a fraction of this beta-catenin pool is associated with ICAT, suggesting that ICAT may buffer the cell from increased levels of beta-catenin. Distinct from TCF and cadherin, ICAT does not protect the soluble pool of beta-catenin from degradation by the adenomatous polyposis coli containing "destruction complex." Although ICAT inhibits beta-catenin binding to the cadherin as well as TCF in vitro, stable overexpression of ICAT in Madin-Darby canine kidney (MDCK) epithelial cells shows no obvious alterations in the cadherin complex, suggesting that the ability of ICAT to inhibit beta-catenin binding to the cadherin may be restricted in vivo. MDCK cells overexpressing ICAT do, however, exhibit enhanced cell scattering on hepatocyte growth factor treatment, suggesting a possible role in the regulation of dynamic rather than steady-state cell-cell adhesions. These findings confirm ICAT's primary role in beta-catenin signaling inhibition and further suggest that ICAT may have consequences for cadherin-based adhesive function in certain circumstances, implying a broader role than previously described.