The alternative reading frame tumor suppressor antagonizes hypoxia-induced cancer cell migration via interaction with the COOH-terminal binding protein corepressor

Identification and characterization of a new potent inhibitor targeting CtBP1/BARS in melanoma cells

BACKGROUND

The C-terminal-binding protein 1/brefeldin A ADP-ribosylation substrate (CtBP1/BARS) acts both as an oncogenic transcriptional co-repressor and as a fission inducing protein required for membrane trafficking and Golgi complex partitioning during mitosis, hence for mitotic entry. CtBP1/BARS overexpression, in multiple cancers, has pro-tumorigenic functions regulating gene networks associated with "cancer hallmarks" and malignant behavior including: increased cell survival, proliferation, migration/invasion, epithelial-mesenchymal transition (EMT). Structurally, CtBP1/BARS belongs to the hydroxyacid-dehydrogenase family and possesses a NAD(H)-binding Rossmann fold, which, depending on ligands bound, controls the oligomerization of CtBP1/BARS and, in turn, its cellular functions. Here, we proposed to target the CtBP1/BARS Rossmann fold with small molecules as selective inhibitors of mitotic entry and pro-tumoral transcriptional activities.

METHODS

Structured-based screening of drug databases at different development stages was applied to discover novel ligands targeting the Rossmann fold. Among these identified ligands, N-(3,4-dichlorophenyl)-4-{[(4-nitrophenyl)carbamoyl]amino}benzenesulfonamide, called Comp.11, was selected for further analysis. Fluorescence spectroscopy, isothermal calorimetry, computational modelling and site-directed mutagenesis were employed to define the binding of Comp.11 to the Rossmann fold. Effects of Comp.11 on the oligomerization state, protein partners binding and pro-tumoral activities were evaluated by size-exclusion chromatography, pull-down, membrane transport and mitotic entry assays, Flow cytometry, quantitative real-time PCR, motility/invasion, and colony assays in A375MM and B16F10 melanoma cell lines. Effects of Comp.11 on tumor growth in vivo were analyzed in mouse tumor model.

RESULTS

We identify Comp.11 as a new, potent and selective inhibitor of CtBP1/BARS (but not CtBP2). Comp.11 directly binds to the CtBP1/BARS Rossmann fold affecting the oligomerization state of the protein (unlike other known CtBPs inhibitors), which, in turn, hinders interactions with relevant partners, resulting in the inhibition of both CtBP1/BARS cellular functions: i) membrane fission, with block of mitotic entry and cellular secretion; and ii) transcriptional pro-tumoral effects with significantly hampered proliferation, EMT, migration/invasion, and colony-forming capabilities. The combination of these effects impairs melanoma tumor growth in mouse models.  CONCLUSIONS: This study identifies a potent and selective inhibitor of CtBP1/BARS active in cellular and melanoma animal models revealing new opportunities to study the role of CtBP1/BARS in tumor biology and to develop novel melanoma treatments.

Transcriptional corepressor activity of CtBP1 is regulated by ISG15 modification

C-terminal binding protein 1 (CtBP1) is a critical transcriptional corepressor of many tumor suppressor genes and plays diverse roles in the progression of cancers. The transcriptional repression function of CtBP1 is mediated by recruiting histone-modifying enzymes, such as histone deacetylases and histone methyltransferases, to target genes by binding with DNA-interacting factors. Several post-translational modifications of CtBP1 have been identified, including ubiquitination, phosphorylation, and SUMOylation. This paper reports that CtBP1 is conjugated by ISG15. Endogenous CtBP1 was modified by ISG15 after interferon-α treatment in HeLa cells. The ISGylation process of CtBP1 was regulated by deISGylation enzyme USP18 and ISG15 E3 ligase EFP. Interestingly, CtBP1 ISGylation affected the binding affinity between CtBP1 and some components of CtBP1-associated transcriptional complexes. HDAC1 and LSD1 bound more efficiently to ISG15-conjugated CtBP1 than non-conjugated CtBP1. On the other hand, binding between CtBP1 and HDAC4 was unaffected by ISG15 modification. Furthermore, ISG15 modification enhanced the transcriptional repression activity of CtBP1 on several target genes related to EMT and apoptosis. These findings suggest that the ISG15 modification of CtBP1 modulates the function and activity of CtBP1 and that CtBP1 ISGylation may provide a new insight for CtBP1-mediated cancers.

C-terminal binding protein 2 promotes high-glucose-triggered cell proliferation, angiogenesis and cellular adhesion of human retinal endothelial cell line

PURPOSE

The proliferation and angiogenesis of human retinal endothelial cells (HRECs) are critical for the pathophysiology of diabetic retinopathy (DR). C-terminal binding protein 2 (CtBP2) has multiple biologic functions, but its effect on HRECs under high-glucose (HG) conditions is unclear.

METHODS

The cell viability, angiogenesis, cellular adhesion and CtBP2 expression levels of HRECs were measured following treatment with different concentrations of glucose. Small interfering CtBP2-targeting RNA, wide-type and function mutant plasmid of CtBP2 were constructed and then were transfected into HRECs to evaluate the effects of CtBP2 on cell functions of HRECs.

RESULTS

The expression of CtBP2 in HRECs was increased after HG treatment. HG treatment significantly increased cell proliferation, angiogenesis, and decreased relative gene expressions in gap junctions, tight junctions and adherens junctions. After CtBP2 was inhibited via siRNA, the changes induced by HG were partially restored. Conversely, only wild-type CtBP2 could increase cell proliferation and angiogenesis under HG condition. Mechanistically, we also found that CtBP2 exerted its functions to effect HG-induced changes via Akt signaling pathway.

CONCLUSION

This study implicates that CtBP2 promotes HG-induced cell proliferation, angiogenesis and cellular adhesion, and CtBP2 might be a potential target in the prevention of DR.

Circular RNA circHERC4 as a novel oncogenic driver to promote tumor metastasis via the miR-556-5p/CTBP2/E-cadherin axis in colorectal cancer

BACKGROUND

The main cause of death in colorectal cancer patients is metastasis. Accumulating evidences suggest that circRNA plays pivotal roles in cancer initiation and development. However, the underlying molecular mechanisms of circRNAs that orchestrate cancer metastasis remain vague and need further clarification.

METHODS

Two paired CRC and adjacent normal tissues were used to screen the upregulated circRNAs by circRNA-seq; then, cell invasion assay was applied to confirm the functional invasion-related circRNAs. According to the above methods, circHERC4 (hsa_circ_0007113) was selected for further research. Next, we investigated the clinical significance of circHERC4 in a large cohort of patients with CRC. The oncogenic activity of circHERC4 was investigated in both CRC cell lines and animal xenograft studies. Finally, we explored the molecular mechanisms underlying circHERC4 as a malignant driver.

RESULTS

We demonstrated that circHERC4 was aberrantly elevated in CRC tissues (P < 0.001), and was positively associated with lymph node metastasis and advanced tumor grade (P < 0.01). Notably, the expression of circHERC4 was associated with worse survival in patients with CRC. Silencing of circHERC4 significantly inhibited the proliferation and migration of two highly aggressive CRC cell lines and reduced liver and lung metastasis in vivo. Mechanistically, we revealed that circHERC4 inactivated the tumor suppressor, miR-556-5p, leading to the activation of CTBP2/E-cadherin pathway which promotes tumor metastasis in CRC.

CONCLUSIONS

CircHERC4 exerts critical roles in promoting tumor aggressiveness through miR-556-5p/CTBP2/E-cadherin pathway and is a prognostic biomarker of the disease, suggesting that circHERC4 may serve as an exploitable therapeutic target for patients with CRC.

The transrepression and transactivation roles of CtBPs in the pathogenesis of different diseases

Gene transcription is strictly controlled by transcriptional complexes, which are assemblies of transcription factors, transcriptional regulators, and co-regulators. Mammalian genomes encode two C-terminal-binding proteins (CtBPs), CtBP1 and CtBP2, which are both well-known transcriptional corepressors of oncogenic processes. Their overexpression in tumors is associated with malignant behavior, such as uncontrolled cell proliferation, migration, and invasion, as well as with an increase in the epithelial-mesenchymal transition. CtBPs coordinate with other transcriptional regulators, such as histone deacetylases (HDACs) and histone acetyltransferases (p300 and CBP [CREBP-binding protein]) that contain the PXDLS motif, and with transcription factors to assemble transcriptional complexes that dock onto the promoters of genes to initiate gene transcription. Emerging evidence suggests that CtBPs function as both corepressors and coactivators in different biological processes ranging from apoptosis to inflammation and osteogenesis. Therapeutic targeting of CtBPs or the interactions required to form transcriptional complexes has also shown promising effects in preventing disease progression. This review summarizes the most recent progress in the study of CtBP functions and therapeutic inhibitors in different biological processes. This knowledge may enable a better understanding of the complexity of the roles of CtBPs, while providing new insights into therapeutic strategies that target CtBPs.

Genetic variants in epithelial-mesenchymal transition genes as predictors of clinical outcomes in localized prostate cancer

BACKGROUND

Epithelial-mesenchymal transition (EMT) plays a pivotal role in the progression of prostate cancer (PCa). However, little is known about genetic variants in the EMT pathway as predictors of aggressiveness, biochemical recurrence (BCR) and disease reclassification in localized PCa.

PATIENTS AND METHODS

In this multistage study, we evaluated 5186 single nucleotide polymorphisms (SNPs) from 264 genes related to EMT pathway to identify SNPs associated with PCa aggressiveness and BCR in the MD Anderson PCa (MDA-PCa) patient cohort (N = 1762), followed by assessment of the identified SNPs with disease reclassification in the active surveillance (AS) cohort (N = 392).

RESULTS

In the MDA-PCa cohort, 312 SNPs were associated with high D'Amico risk (P < 0.05), among which, 14 SNPs in 10 genes were linked to BCR risk. In the AS cohort, 2 of 14 identified SNPs (rs76779889 and rs7083961) in C-terminal Binding Proteins 2 gene were associated with reclassification risk. The associations of rs76779889 with different endpoints were: D'Amico high versus low, odds ratio [95% confidence interval (CI)] = 2.89 (1.32-6.34), P = 0.008; BCR, hazard ratio (HR) (95% CI) = 2.88 (1.42-5.85), P = 0.003; and reclassification, HR (95% CI) = 2.83 (1.40-5.74), P = 0.004. For rs7083961, the corresponding risk estimates were: D'Amico high versus low, odds ratio (95% CI) = 1.69 (1.12-2.57), P = 0.013; BCR, HR (95% CI) = 1.87 (1.15-3.02), P = 0.011 and reclassification, HR (95% CI) = 1.72 (1.09-2.72), P = 0.020. There were cumulative effects of these two SNPs on modulating these endpoints.

CONCLUSION

Genetic variants in EMT pathway may influence the risks of localized PCa's aggressiveness, BCR and disease reclassification, suggesting their potential role in the assessment and management of localized PCa.

The p53 Pathway and Metabolism: The Tree That Hides the Forest

Simple Summary

The p53 pathway is a major tumor suppressor pathway that prevents the propagation of abnormal cells by regulating DNA repair, cell cycle progression, cell death, or senescence. The multiple cellular processes regulated by p53 were more recently extended to the control of metabolism, and many studies support the notion that perturbations of p53-associated metabolic activities are linked to cancer development. Converging lines of evidence support the notion that, in addition to p53, other key components of this molecular cascade are also important regulators of metabolism. Here, we illustrate the underestimated complexity of the metabolic network controlled by the p53 pathway and show how its perturbation contributes to human diseases including cancer, aging, and metabolic diseases.

Abstract

The p53 pathway is functionally inactivated in most, if not all, human cancers. The p53 protein is a central effector of numerous stress-related molecular cascades. p53 controls a safeguard mechanism that prevents accumulation of abnormal cells and their transformation by regulating DNA repair, cell cycle progression, cell death, or senescence. The multiple cellular processes regulated by p53 were more recently extended to the control of metabolism and many studies support the notion that perturbations of p53-associated metabolic activities are linked to cancer development, as well as to other pathophysiological conditions including aging, type II diabetes, and liver disease. Although much less documented than p53 metabolic activities, converging lines of evidence indicate that other key components of this tumor suppressor pathway are also involved in cellular metabolism through p53-dependent as well as p53-independent mechanisms. Thus, at least from a metabolic standpoint, the p53 pathway must be considered as a non-linear pathway, but the complex metabolic network controlled by these p53 regulators and the mechanisms by which their activities are coordinated with p53 metabolic functions remain poorly understood. In this review, we highlight some of the metabolic pathways controlled by several central components of the p53 pathway and their role in tissue homeostasis, metabolic diseases, and cancer.

Primary tumor and metastasis-sectioning the different steps of the metastatic cascade

Patients with lung cancer in the majority die of metastases. Treatment options include surgery, chemo- and radiotherapy, targeted therapy by tyrosine kinase inhibitors (TKIs), and immuno-oncologic treatment. Despite the success with these treatment options, cure of lung cancer is achieved in only a very small proportion of patients. In most patients’ recurrence and metastasis will occur, and finally kill the patient. Metastasis is a multistep procedure. It requires a change in adhesion of tumor cells for detachment from their neighboring cells. The next step is migration either as single cells [epithelial-mesenchymal transition (EMT)], or as cell clusters (hybrid-EMT or bulk migration). A combination of genetic changes is required to facilitate migration. Then tumor cells have to orient themselves along matrix proteins, detect oxygen concentrations, prevent attacks by immune cells, and induce a tumor-friendly switch of stroma cells (macrophages, myofibroblasts, etc.). Having entered the blood stream tumor cells need to adapt to shear stress, avoid being trapped by coagulation, but also use coagulation in small veins for adherence to endothelia, and express homing molecules for extravasation. Within a metastatic site, tumor cells need a well-prepared niche to establish a metastatic focus. Tumor cells again have to establish a vascular net for maintaining nutrition and oxygen supply, communicate with stroma cells, grow out and set further metastases. In this review the different steps will be discussed with a focus on pulmonary carcinomas. The vast amount of research manuscripts published so far are not easy to analyze: in most reports’ single steps of the metastatic cascade are interpreted as evidence for the whole process; for example, migration is interpreted as evidence for metastasis. In lung cancer most often latency periods are shorter, in between 1–5 years. In other cases, despite widespread migration occurs, tumor cells die within the circulation and do not reach a metastatic site. Therefore, migration is a requisite, but does not necessarily predict metastasis. The intention of this review is to point to these different aspects and hopefully provoke research directed into a more functional analysis of the metastatic process.

p53 is regulated by aerobic glycolysis in cancer cells by the CtBP family of NADH-dependent transcriptional regulators

High rates of glycolysis in cancer cells are a well-established characteristic of many human tumors, providing rapidly proliferating cancer cells with metabolites that can be used as precursors for anabolic pathways. Maintenance of high glycolytic rates depends on the lactate dehydrogenase-catalyzed regeneration of NAD⁺ from GAPDH-generated NADH because an increased NADH:NAD⁺ ratio inhibits GAPDH. Here, using human breast cancer cell models, we identified a pathway in which changes in the extramitochondrial-free NADH:NAD⁺ ratio signaled through the CtBP family of NADH-sensitive transcriptional regulators to control the abundance and activity of p53. NADH-free forms of CtBPs cooperated with the p53-binding partner HDM2 to suppress p53 function, and loss of these forms in highly glycolytic cells resulted in p53 accumulation. We propose that this pathway represents a "glycolytic stress response" in which the initiation of a protective p53 response by an increased NADH:NAD⁺ ratio enables cells to avoid cellular damage caused by mismatches between metabolic supply and demand.

GMBP1-conjugated manganese oxide nanoplates for in vivo monitoring of gastric cancer MDR using magnetic resonance imaging

Multidrug resistance (MDR) is a huge challenge for gastric cancer chemotherapy. Therefore, MDR accurate monitoring is of great significance for the treatment of gastric cancer. GMBP1, an extracellular internalization peptide, can target MDR gastric cancer cells through specific binding to GRP78, which is an MDR-related protein that is overexpressed in gastric cancer cells. Herein, we constructed GMBP1 conjugated Mn₃O₄ nanoplates (Mn₃O₄@PEG-GMBP1 NPs) for in vivo monitoring of MDR gastric cancer through magnetic resonance imaging (MRI). The generated Mn₃O₄@PEG-GMBP1 NPs had a size of about 11 nm and exhibited a good colloidal stability in PBS and in 10% FBS medium. Serial in vivo MRI studies in mice demonstrated that the magnetic resonance signal intensity, at the tumor site, reached a peak at 3 h after tail vein injection of Mn₃O₄@PEG-GMBP1 NPs. The specific targeting ability of MDR gastric cancer cells (SGC7901/ADR) by Mn₃O₄@PEG-GMBP1 NPs was authenticated in vitro, in vivo and by immunofluorescence analysis experiments. The systematic safety evaluation indicated that the toxicity of Mn₃O₄@PEG-GMBP1 NPs in mice was negligible. Therefore, the GMBP1 conjugated Mn₃O₄ nanoplates can be clinically used for accurate imaging and monitoring of MDR gastric cancer.

An Intricate Connection between Alternative Splicing and Phenotypic Plasticity in Development and Cancer

During tumor progression, hypoxia, nutrient deprivation or changes in the extracellular environment (i.e., induced by anti-cancer drugs) elicit adaptive responses in cancer cells. Cellular plasticity increases the chance that tumor cells may survive in a challenging microenvironment, acquire new mechanisms of resistance to conventional drugs, and spread to distant sites. Re-activation of stem pathways appears as a significant cause of cellular plasticity because it promotes the acquisition of stem-like properties through a profound phenotypic reprogramming of cancer cells. In addition, it is a major contributor to tumor heterogeneity, depending on the coexistence of phenotypically distinct subpopulations in the same tumor bulk. Several cellular mechanisms may drive this fundamental change, in particular, high-throughput sequencing technologies revealed a key role for alternative splicing (AS). Effectively, AS is one of the most important pre-mRNA processes that increases the diversity of transcriptome and proteome in a tissue- and development-dependent manner. Moreover, defective AS has been associated with several human diseases. However, its role in cancer cell plasticity and tumor heterogeneity remains unclear. Therefore, unravelling the intricate relationship between AS and the maintenance of a stem-like phenotype may explain molecular mechanisms underlying cancer cell plasticity and improve cancer diagnosis and treatment.

Association of Single-Nucleotide Polymorphism REX1 rs6815391, OCT4 rs13409 or rs3130932, and CTBP2 rs3740535 with Primary Lung Cancer Susceptibility: A Case-Control Study in a Chinese Population

The purpose of the current study is to explore the contribution of single-nucleotide polymorphisms (SNPs) of REX1 rs6815391, OCT4 rs13409 or rs3130932, and CTBP2 rs3740535 to the risk of lung cancer. A questionnaire survey was used to obtain basic information of the included subjects. A case control study was performed in 1121 patients and 1121 controls. All subjects were subjected to blood sampling for genomic DNA extraction and genotyping of the cancer stem cell-associated gene SNPs, including REX1 rs6815391, OCT4 rs13409 or rs3130932, and CTBP2 rs3740535 by real-time PCR. The association with the risk of primary lung cancer and interaction with environmental factors were assessed using unconditional logistic regression for the odds ratios and corresponding 95% confidence intervals. The genotype frequency distribution of OCT4 rs13409 loci was statistically significant, but there was no significant difference in the rest of the loci between lung cancer patients and healthy controls. The OCT4 gene was also related with lung cancer susceptibility in the genetic model after adjusting for lung cancer-related factors. Despite the presence of the dominant or recessive model, the four loci polymorphisms were associated with pollution near the place of residence, house type, worse ventilation situation, smoking, passive smoking, cooking oil fumes (COF), and family history of cancer, which increased the risk of lung cancer. Nonmarried status, 18.5≤BMI, COF, smoking, passive smoking, family history of cancer, and history of lung disease were independent risk factors of lung cancer susceptibility. Additionally, college degree or above, no pollution near the place of residence, protective genotype 1 or 2, and well ventilation can reduce the occurrence of lung cancer. There is an interaction between the four loci and environmental factors, and OCT4 rs13409 is a risk factor of primary lung cancer.

CTBP1 Confers Protection for Hippocampal and Cortical Neurons in Rat Models of Alzheimer's Disease

OBJECTIVE

Alzheimer's disease (AD) is an age-related devastating neurodegenerative disorder. The hippocampus and cerebral cortex are the most closely related brain regions of cognitive function and neurogenesis. The present study investigated the role of C-terminal-binding protein 1 (CTBP1) in AD.

METHODS

AD rat models were established through intracerebroventricular injection of β-amyloid polypeptide Aβ(25-35) and intragastric administration of aluminum chloride solution, and the expression pattern that CTBP1 showed in the hippocampus and cerebral cortex was determined. The learning and memory abilities of AD rats after CTBP1 overexpression were assessed. Hippocampal and cortical neurons were transfected with siRNA against CTBP1 or CTBP1-overexpressing plasmids in order to study the effects of CTBP1 elevation or depletion on neuron morphological changes, apoptosis, and viability. The expression of CTBP1, proapoptotic factor (B-cell lymphoma 2; Bcl-2), and antiapoptotic factors (Bcl-2-associated X protein [Bax] and caspase-3) was subsequently evaluated.

RESULTS

CTBP1 was poorly expressed in the hippocampus and cerebral cortex. AD rats displayed enhanced learning and memory abilities following CTBP1 overexpression. Furthermore, overexpression of CTBP1 improved morphological changes of hippocampal and cortical neurons, increased neuron activity, and inhibited neuron apoptosis in AD rats. Moreover, the expression of Bax and caspase-3 decreased, yet Bcl-2 increased.

CONCLUSION

Collectively, CTBP1 plays a protective role in the degeneration of hippocampal and cortical neurons whereby overexpressed CTBP1 attenuated the hippocampal and cortical neuron apoptosis and enhanced neuron activity, highlighting the potential of CTBP1 as a target for AD treatment.

An intestinal stem cell niche in Apc mutated neoplasia targetable by CtBP inhibition

C-terminal binding protein 2 (CtBP2) drives intestinal polyposis in the Apc^min mouse model of human Familial Adenomatous Polyposis. As CtBP2 is targetable by an inhibitor of its dehydrogenase domain, understanding CtBP2’s role in adenoma formation is necessary to optimize CtBP-targeted therapies in Apc mutated human neoplasia. Tumor initiating cell (TIC) populations were substantially decreased in Apc^minCtbp2^+/- intestinal epithelia. Moreover, normally nuclear Ctbp2 was mislocalized to the cytoplasm of intestinal crypt stem cells in Ctbp2^+/- mice, both Apc^min and wildtype, correlating with low/absent CD133 expression in those cells, and possibly explaining the lower burden of polyps in Apc^min Ctbp2^+/- mice. The CtBP inhibitor 4-chloro-hydroxyimino phenylpyruvate (4-Cl-HIPP) also robustly downregulated TIC populations and significantly decreased intestinal polyposis in Apc^min mice. We have therefore demonstrated a critical link between polyposis, intestinal TIC’s and Ctbp2 gene dosage or activity, supporting continued efforts targeting CtBP in the treatment or prevention of Apc mutated neoplasia.

HBV Upregulates CtBP2 Expression via the X Gene

Background

Hepatitis B virus (HBV) infection causes acute and chronic liver diseases that can eventually develop into cirrhosis and hepatocellular carcinoma (HCC), but the carcinogenesis of HBV is not fully understood. Carboxyl-terminal-binding protein 2 (CtBP2) plays an important role in tumorigenesis and progression. The aim of this study was to investigate the effect of HBV on CtBP2 expression and to explore its mechanism.

Methods

Real-time quantitative reverse transcription polymerase chain reaction (RT-qPCR) and western blotting were used to evaluate the CtBP2 mRNA and protein expression levels in tissues and cells. The HBV infectious clone pHBV1.3 and plasmids expressing a single gene of the HBV genome were cotransfected with the CtBP2 gene promoter pGL3-CtBP2 into the human hepatoma cell line HepG2, and luciferase activity was determined using a luminometer.

Results

CtBP2 expression was higher in HBV-related HCC tissues than in paracancerous tissues. CtBP2 expression was higher in HepG2.2.15 cells integrated with the HBV genome than in HepG2 cells. pHBV1.3 upregulated CtBP2 mRNA and protein expression. The HBV X gene significantly activated CtBP2 gene promoter activity, and CtBP2 mRNA and protein expression were upregulated by the HBV X gene. This activation effect was enhanced by the increase in the dose of the X gene, showing metrological dependence.

Conclusion

HBV may be involved in the occurrence and development of HCC by upregulating CtBP2 expression.

Colorectal cancer mutational profiles correlate with defined microbial communities in the tumor microenvironment

Variation in the gut microbiome has been linked to colorectal cancer (CRC), as well as to host genetic variation. However, we do not know whether, in addition to baseline host genetics, somatic mutational profiles in CRC tumors interact with the surrounding tumor microbiome, and if so, whether these changes can be used to understand microbe-host interactions with potential functional biological relevance. Here, we characterized the association between CRC microbial communities and tumor mutations using microbiome profiling and whole-exome sequencing in 44 pairs of tumors and matched normal tissues. We found statistically significant associations between loss-of-function mutations in tumor genes and shifts in the abundances of specific sets of bacterial taxa, suggestive of potential functional interaction. This correlation allows us to statistically predict interactions between loss-of-function tumor mutations in cancer-related genes and pathways, including MAPK and Wnt signaling, solely based on the composition of the microbiome. In conclusion, our study shows that CRC microbiomes are correlated with tumor mutational profiles, pointing towards possible mechanisms of molecular interaction.

The Role of CtBP1 in Oncogenic Processes and Its Potential as a Therapeutic Target

Transcriptional corepressor proteins have emerged as an important facet of cancer etiology. These corepressor proteins are often altered by loss- or gain-of-function mutations, leading to transcriptional imbalance. Thus, research directed at expanding our current understanding of transcriptional corepressors could impact the future development of new cancer diagnostics, prognostics, and therapies. In this review, our current understanding of the CtBP corepressors, and their role in both development and disease, is discussed in detail. Importantly, the role of CtBP1 overexpression in adult tissues in promoting the progression of multiple cancer types through their ability to modulate the transcription of developmental genes ectopically is explored. CtBP1 overexpression is known to be protumorigenic and affects the regulation of gene networks associated with "cancer hallmarks" and malignant behavior, including increased cell survival, proliferation, migration, invasion, and the epithelial-mesenchymal transition. As a transcriptional regulator of broad developmental processes capable of promoting malignant growth in adult tissues, therapeutically targeting the CtBP1 corepressor has the potential to be an effective method for the treatment of diverse tumor types. Although efforts to develop CtBP1 inhibitors are still in the early stages, the current progress and the future perspectives of therapeutically targeting this transcriptional corepressor are also discussed. Mol Cancer Ther; 16(6); 981-90. ©2017 AACR.

C-terminal binding protein-2 promotes cell proliferation and migration in breast cancer via suppression of p16INK4A

C-terminal binding protein-2 (CtBP2) enhances cancer proliferation and metastasis. The role and mechanism of CtBP2 in breast cancer remains to be elucidated. Western blot and immunochemistry were employed to evaluate the level of CtBP2 and p16^INK4A in breast cancer. Genetic manipulation was used to study the expression of p16^INK4A and its downstream genes regulated by CtBP2. Functional assays, including colony formation, wound healing, transwell invasion, anchorage-independent growth assay and a xenograft tumor model were used to determine the oncogenic role of CtBP2 in breast cancer progression. The expression of CtBP2 was increased in breast cancer tissues and cell lines. The expression of p16^INK4A were inversely correlated CtBP2 (r² = 0.43, P < 0.01). The expression of both CtBP2 and p16^INK4A were significantly related to histological differentiation (P < 0.01 and P = 0.004, respectively) and metastasis (P = 0.046 and 0.047, respectively). The overall survival rate was lower in patients with increased CtBP2 expression and lower p16^INK4A expression. Knockdown of CtBP2 resulted in the activation of p16^INK4A and down–regulation of cell cycle regulators cyclin D, cyclin E and cyclin-dependent kinase 2 and 4. This down-regulation also led to a decreased transition of the G1-S phase in breast cancer cells. Moreover, gain-of-function experiments showed that CtBP2 suppressed p16^INK4A and matrix metalloproteinase-2, subsequently enhancing the migration in breast cancer. However, the silence of CtBP2 abrogated this effect. Collectively, these findings provide insight into the role CtBP2 plays in promoting proliferation and migration in breast cancer by the inhibition of p16^INK4A.

CtBP2 ameliorates palmitate-induced insulin resistance in HepG2 cells through ROS mediated JNK pathway

Oxidative stress plays a significant role in the development of hepatic insulin resistance, but the underlying molecular mechanisms remain poorly understood. In this study, we discovered that C-terminal-binding protein 2 (CtBP2) level was decreased in insulin resistance. Taking into account the relationship between CtBP family protein (ANGUSTIFOLIA) and reactive oxygen species (ROS) accumulation, we conjectured CtBP2 was involved in insulin resistance through ROS induced stress. In order to verify this hypothesis, we over-expressed CtBP2 in palmitate (PA) treated HepG2 cells. Here, we found that over-expression of CtBP2 ameliorated insulin sensitivity by increasing phosphorylation of glycogen synthase kinase 3β (GSK3β) and protein kinase B (AKT). These data suggest that CtBP2 plays a critical role in the development of insulin resistance. Moreover, CtBP2 reversed the effects of PA on ROS level, lipid accumulation, hepatic glucose uptake and gluconeogenesis. We also found that over-expression of CtBP2 could suppress PA induced c-jun NH2 terminal kinase (JNK) activation. Furthermore, JNK inhibitor SP600125 was shown to promote the effect of CtBP2 on insulin signaling. Thus, we demonstrated that CtBP2 ameliorated PA-induced insulin resistance via ROS-dependent JNK pathway.

CtBP- an emerging oncogene and novel small molecule drug target: Advances in the understanding of its oncogenic action and identification of therapeutic inhibitors

C-terminal Binding Proteins (CtBP) 1 and 2 are oncogenic transcriptional co-regulators overexpressed in many cancer types, with their expression level correlating to worse prognostic outcomes and aggressive tumor features. CtBP negatively regulates the expression of many tumor suppressor genes, while coactivating genes that promote proliferation, epithelial-mesenchymal transition, and cancer stem cell self-renewal activity. In light of this evidence, the development of novel inhibitors that mitigate CtBP function may provide clinically actionable therapeutic tools. This review article focuses on the progress made in understanding CtBP structure, role in tumor progression, and discovery and development of CtBP inhibitors that target CtBP's dehydrogenase activity and other functions, with a focus on the theory and rationale behind the designs of current inhibitors. We provide insight into the future development and use of rational combination therapy that may further augment the efficacy of CtBP inhibitors, specifically addressing metastasis and cancer stem cell populations within tumors.

Transforming activity and therapeutic targeting of C-terminal-binding protein 2 in Apc-mutated neoplasia

Overexpression of the transcriptional coregulators C-terminal binding proteins 1 and 2 (CtBP) occurs in many human solid tumors and is associated with poor prognosis. CtBP modulates oncogenic gene expression programs and is an emerging drug target, but its oncogenic role is unclear. Consistent with oncogenic potential, exogenous CtBP2 transformed primary mouse and human cells to anchorage independence similarly to mutant H-Ras. To investigate CtBP’s contribution to in vivo tumorigenesis, Apc^min/+ mice, which succumb to massive intestinal polyposis, were bred to Ctbp2^+/− mice. CtBP interacts with Adenomatous Polyposis Coli (APC) protein, and is stabilized in both APC-mutated human colon cancers and Apc^min/+ intestinal polyps. Ctbp2 heterozygosity increased the median survival of Apc^min/+ mice from 21 to 48 weeks, and reduced polyp formation by 90%, with Ctbp2^+/− polyps exhibiting reduced levels of β-catenin and its oncogenic transcriptional target, cyclin D1. Ctbp’s potential as a therapeutic target was studied by treating Apc^min/+ mice with the CtBP small molecule inhibitors 4-methlythio-2-oxobutyric acid and 2-hydroxy-imino phenylpyruvic acid, both of which reduced polyposis by more than half compared with vehicle treatment. Phenocopying Ctbp2 deletion, both Ctbp inhibitors caused substantial decreases in the protein level of Ctbp2, as well its oncogenic partner β-catenin, and the effects of the inhibitors on CtBP and β-catenin levels could be modeled in an APC mutated human colon cancer cell line. CtBP2 is thus a druggable transforming oncoprotein critical for the evolution of neoplasia driven by Apc mutation.

Chemoprevention in African American Men With Prostate Cancer

BACKGROUND

Recommendations for cancer screening are uncertain for the early detection or prevention of prostate cancer in African American men. Thus, chemoprevention strategies are needed to specifically target African American men.

METHODS

The evidence was examined on the biological etiology of disparities in African Americans related to prostate cancer. Possible chemopreventive agents and biomarkers critical to prostate cancer in African American men were also studied.

RESULTS

High-grade prostatic intraepithelial neoplasia may be more prevalent in African American men, even after controlling for age, prostate-specific antigen (PSA) level, abnormal results on digital rectal examination, and prostate volume. Prostate cancer in African American men can lead to the overexpression of signaling receptors that may mediate increased proliferation, angiogenesis, and decreased apoptosis. Use of chemopreventive agents may be useful for select populations of men.

CONCLUSIONS

Green tea catechins are able to target multiple pathways to address the underlying biology of prostate carcinogenesis in African American men, so they may be ideal as a chemoprevention agent in these men diagnosed with high-grade prostatic intraepithelial neoplasia.

Ikaros and its interacting partner CtBP target the metalloprotease ADAMTS10 to modulate pituitary cell function

We have previously described the expression and up-regulation of the C-terminal Binding Protein (CtBP) in response to pituitary hypoxia. This co-repressor interacts with the hematopoietic factor Ikaros to target several components implicated in cellular growth and apoptotic pathways. To identify common transcriptional pituitary targets we performed promoter arrays using Ikaros and CtBP chromatin immunoprecipitated (ChIP) DNA from pituitary AtT20 cells. This approach yielded a finite list of gene targets common to both transcription factors. Of these, the metalloprotease ADAMTS10 emerged as a validated target. We show the ability of Ikaros to bind the ADAMTS10 promoter, influence its transfected activity, and induce endogenous gene expression. ADAMTS10 is expressed in primary pituitary cells and is down-regulated in Ikaros null mice. Further, knockdown of ADAMTS10 in AtT20 cells recapitulates the impact of Ikaros deficiency on POMC/ACTH hormone expression. These results uncover a novel role for the metalloprotease ADAMTS10 in the pituitary. Additionally, they position this metalloprotease as a potential functional integrator of the Ikaros-CtBP chromatin remodeling network.

Progression and metastasis of lung cancer

Metastasis in lung cancer is a multifaceted process. In this review, we will dissect the process in several isolated steps such as angiogenesis, hypoxia, circulation, and establishment of a metastatic focus. In reality, several of these processes overlap and occur even simultaneously, but such a presentation would be unreadable. Metastasis requires cell migration toward higher oxygen tension, which is based on changing the structure of the cell (epithelial-mesenchymal transition), orientation within the stroma and stroma interaction, and communication with the immune system to avoid attack. Once in the blood stream, cells have to survive trapping by the coagulation system, to survive shear stress in small blood vessels, and to find the right location for extravasation. Once outside in the metastatic locus, tumor cells have to learn the communication with the “foreign” stroma cells to establish vascular supply and again express molecules, which induce immune tolerance.

Discovery and functional identification of fecundity-related genes in the brown planthopper by large-scale RNA interference

Recently, transcriptome and proteome data have increasingly been used to identify potential novel genes related to insect phenotypes. However, there are few studies reporting the large-scale functional identification of such genes in insects. To identify novel genes related to fecundity in the brown planthopper (BPH), Nilaparvata lugens, 115 genes were selected from the transcriptomic and proteomic data previously obtained from high- and low-fecundity populations in our laboratory. The results of RNA interference (RNAi) feeding experiments showed that 91.21% of the genes were involved in the regulation of vitellogenin (Vg) expression and may influence BPH fecundity. After RNAi injection experiments, 12 annotated genes were confirmed as fecundity-related genes and three novel genes were identified in the BPH. Finally, C-terminal binding protein (CtBP) was shown to play an important role in BPH fecundity. Knockdown of CtBP not only led to lower survival, underdeveloped ovaries and fewer eggs laid but also resulted in a reduction in Vg protein expression. The novel gene resources gained from this study will be useful for constructing a Vg regulation network and may provide potential target genes for RNAi-based pest control.

Expression and prognostic significance of CTBP2 in human gliomas

Deregulated expression of C-terminal-binding protein 2 (CTBP2) has been observed previously in a number of tumors, such as hepatocellular carcinoma and prostatic cancer, in the colorectal cancer SW480 cell line and in the human embryonic kidney 293 cell line. In the present study, western blot analysis and immunohistochemistry were performed to investigate whether gliomas exhibit deregulated CTBP2 expression. Kaplan-Meier survival analyses were performed to evaluate the associations between CTBP2 expression, clinicopathological data and patient survival in glioma patients. The results revealed that CTBP2 expression was significantly upregulated in high grade glioma tissues compared with that in low grade glioma and normal brain tissues. Furthermore, increased CTBP2 expression in gliomas was significantly associated with a higher World Health Organization (WHO) tumor grade (P<0.005) and poorer disease-specific survival (P<0.005). In conclusion, these results suggest that CTBP2 may act as an intrinsic regulator of progression in glioma cells and thus may serve as an important prognostic factor for the disease.

GGNBP2 acts as a tumor suppressor by inhibiting estrogen receptor α activity in breast cancer cells

Gametogenetin-binding protein 2 (GGNBP2) is encoded in human chromosome 17q12-q23, a region known as a breast and ovarian cancer susceptibility locus. GGNBP2, also referred to ZFP403, has a single C2H2 zinc finger and a consensus LxxLL nuclear receptor-binding motif. Here, we demonstrate that GGNBP2 expression is reduced in primary human breast tumors and in breast cancer cell lines, including T47D, MCF-7, LCC9, LY2, and MDA-MB-231 compared with normal, immortalized estrogen receptor α (ERα) negative MCF-10A and MCF10F breast epithelial cells. Overexpression of GGNBP2 inhibits the proliferation of T47D and MCF-7 ERα positive breast cancer cells without affecting MCF-10A and MCF10F. Stable GGNBP2 overexpression in T47D cells inhibits 17β-estradiol (E2)-stimulated proliferation as well as migration, invasion, anchorage-independent growth in vitro, and xenograft tumor growth in mice. We further demonstrate that GGNBP2 protein physically interacts with ERα, inhibits E2-induced activation of estrogen response element-driven reporter activity, and attenuates ER target gene expression in T47D cells. In summary, our in vitro and in vivo findings suggest that GGNBP2 is a novel breast cancer tumor suppressor functioning as a nuclear receptor corepressor to inhibit ERα activity and tumorigenesis.

Design, synthesis, and biological evaluation of substrate-competitive inhibitors of C-terminal Binding Protein (CtBP)

C-terminal Binding Protein (CtBP) is a transcriptional co-regulator that downregulates the expression of many tumor-suppressor genes. Utilizing a crystal structure of CtBP with its substrate 4-methylthio-2-oxobutyric acid (MTOB) and NAD(+) as a guide, we have designed, synthesized, and tested a series of small molecule inhibitors of CtBP. From our first round of compounds, we identified 2-(hydroxyimino)-3-phenylpropanoic acid as a potent CtBP inhibitor (IC50=0.24μM). A structure-activity relationship study of this compound further identified the 4-chloro- (IC50=0.18μM) and 3-chloro- (IC50=0.17μM) analogues as additional potent CtBP inhibitors. Evaluation of the hydroxyimine analogues in a short-term cell growth/viability assay showed that the 4-chloro- and 3-chloro-analogues are 2-fold and 4-fold more potent, respectively, than the MTOB control. A functional cellular assay using a CtBP-specific transcriptional readout revealed that the 4-chloro- and 3-chloro-hydroxyimine analogues were able to block CtBP transcriptional repression activity. This data suggests that substrate-competitive inhibition of CtBP dehydrogenase activity is a potential mechanism to reactivate tumor-suppressor gene expression as a therapeutic strategy for cancer.

Compartmentation of metabolites in regulating epigenome of cancer

Covalent modification of DNA and histones are important epigenetic events and the genome wide reshaping of epigenetic markers is common in cancer. The epigenetic markers are produced by enzymatic reactions and some of these reactions require the presence of metabolites as cofactors (termed Epigenetic Enzyme Required Metabolites, EERMs). Recent studies found that the abundance of these EERMs correlates with epigenetic enzyme activities. Also, the subcellular compartmentation, especially the nuclear localization of these EERMs may play a role in regulating the activities of epigenetic enzymes. Moreover, gene specific recruitment of enzymes which produce the EERMs in the proximity of the epigenetic modification events accompanying the gene expression regulation, were proposed. Therefore, it is of importance to summarize these findings of the EERMs in regulating the epigenetic modifications at both DNA and histone levels, and to understand how EERMs contribute to cancer development by addressing their global versus local distribution.

CtBP2 is an independent prognostic marker that promotes GLI1 induced epithelial-mesenchymal transition in hepatocellular carcinoma

C-terminal binding protein 2 (CtBP2) is a transcriptional co-repressor that promotes cancer cell migration and invasion by inhibiting multiple tumor suppressor genes that contribute to cell mobility and adhesion. In this investigation, we showed thatCtBP2 expression was increased significantly in HCC tissues when compared to matched normal adjacent liver tissues. We also showed that CtBP2 expression is associated with worse HCC patient prognosis after liver resection. CtBP2 over-expression induced epithelial-mesenchymal transition (EMT) in Huh7 cells and, correspondingly, silencing CtBP2 suppressed EMT in MHCC97H cells. ChIP assays revealed that GLI1 increased CtBP2 transcription by directly binding its promoter. Furthermore, interaction of CtBP2 and Snail Family Zinc Finger 1 (SNAI1), both of which were found to be positively regulated by GLI1, was confirmed by Co-IP assay. SNAI1 knockdown revealed that SNAI1 was essential for CtBP2 induction of the EMT phenotype of HCC cells, and CtBP2 knockdown reversed GLI1-SNAI1 driven EMT in Huh7 cells. Finally, in vivo experiments demonstrated that enhanced CtBP2expression promoted HCC xenograft growth and induced EMT. In conclusion, CtBP2 may serve as a prognostic marker for post liver resection HCC and may play a role during GLI1-driven EMT as a transcriptional co-repressor of SNAI1.

CtBP2 overexpression is associated with tumorigenesis and poor clinical outcome of prostate cancer

INTRODUCTION

The aim of the study was to evaluate the expression of CtBP2 in prostate cancer and to determine its relationship with clinicopathologic parameters.

MATERIAL AND METHODS

The expression of CtBP2 in 119 prostate cancer tissues and 41 normal tissues was examined by qPCR and Western blot analysis, and the results were correlated with clinicopathologic parameters.

RESULTS

CtBP2 expression in prostate cancer tissues was higher than that in normal samples. CtBP2 overexpression was closely correlated with serum prostatic specific antigen (PSA) (p = 0.018), advanced tumor stage (T3) (p = 0.025), higher Gleason scores (p = 0.019), positive extraprostatic extension (p = 0.012), positive vascular invasion (p = 0.011) and perineural invasion (p = 0.035). However, no significant association was found between CtBP2 abnormal expression and other parameters, including age (p = 0.776), positive lymph node (p = 0.872) and positive surgical margin (p = 0.37). Moreover, CtBP2 overexpression was significantly associated with poor clinical outcome of prostate cancer (p = 0.0168).

CONCLUSIONS

CtBP2 is overexpressed in prostate cancer, and its increased expression is closely associated with tumor progression and the outcome of prostate cancer.

Mechanism study of peptide GMBP1 and its receptor GRP78 in modulating gastric cancer MDR by iTRAQ-based proteomic analysis

Background

Multidrug resistance (MDR) is a major obstacle to the treatment of gastric cancer (GC). Using a phage display approach, we previously obtained the peptide GMBP1, which specifically binds to the surface of MDR gastric cancer cells and is subsequently internalized. Furthermore, GMBP1 was shown to have the potential to reverse the MDR phenotype of gastric cancer cells, and GRP78 was identified as the receptor for this peptide. The present study aimed to investigate the mechanism of peptide GMBP1 and its receptor GRP78 in modulating gastric cancer MDR.

Methods

Fluorescence-activated cell sorting (FACS) and immunofluorescence staining were used to investigate the subcellular location and mechanism of GMBP1 internalization. iTRAQ was used to identify the MDR-associated downstream targets of GMBP1. Differentially expressed proteins were identified in GMBP1-treated compared to untreated SGC7901/ADR and SGC7901/VCR cells. GO and KEGG pathway analyses of the differentially expressed proteins revealed the interconnection of these proteins, the majority of which are involved in MDR. Two differentially expressed proteins were selected and validated by western blotting.

Results

GMBP1 and its receptor GRP78 were found to be localized in the cytoplasm of GC cells, and GRP78 can mediate the internalization of GMBP1 into MDR cells through the transferrin-related pathway. In total, 3,752 and 3,749 proteins were affected in GMBP1-treated SGC7901/ADR and SGC7901/VCR cells, respectively, involving 38 and 79 KEGG pathways. Two differentially expressed proteins, CTBP2 and EIF4E, were selected and validated by western blotting.

Conclusion

This study explored the role and downstream mechanism of GMBP1 in GC MDR, providing insight into the role of endoplasmic reticulum stress protein GRP78 in the MDR of cancer cells.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-015-1361-3) contains supplementary material, which is available to authorized users.

Interaction with CCNH/CDK7 facilitates CtBP2 promoting esophageal squamous cell carcinoma (ESCC) metastasis via upregulating epithelial-mesenchymal transition (EMT) progression

CtBP2, as a transcriptional corepressor of epithelial-specific genes, has been reported to promote tumor due to upregulating epithelial-mesenchymal transition (EMT) in cancer cells. CtBP2 was also demonstrated to contribute to the proliferation of esophageal squamous cell carcinoma (ESCC) cells through a negative transcriptional regulation of p16(INK4A). In this study, for the first time, we reported that CtBP2 expression, along with CCNH/CDK7, was higher in ESCC tissues with lymph node metastases than in those without lymph node metastases. Moreover, both CtBP2 and CCNH/CDK7 were positively correlated with E-cadherin, tumor grade, and tumor metastasis. However, the concrete mechanism of CtBP2's role in enhancing ESCC migration remains incompletely understood. We confirmed that CCNH/CDK7 could directly interact with CtBP2 in ESCC cells in vivo and in vitro. Furthermore, our data demonstrate for the first time that CtBP2 enhanced the migration of ESCC cells in a CCNH/CDK7-dependent manner. Our results indicated that CCNH/CDK7-CtBP2 axis may augment ESCC cell migration, and targeting the interaction of both may provide a novel therapeutic target of ESCC.

CtBP2 contributes to malignant development of human esophageal squamous cell carcinoma by regulation of p16INK4A

C-terminal binding protein-2 (CtBP2), as a transcriptional co-repressor, has been shown to mediate the repression of p16(INK4A) , a tumor suppressor gene product, in primary human cells. Here we aimed to investigate how the correlation between CtBP2 and p16(INK4A) influenced the development of esophageal squamous cell carcinoma (ESCC). Immunohistochemistry of ESCC tissue sections indicated that the CtBP2 and p16(INK4A) expressions were inversely correlated to each other with a linear regression coefficient of -0.747 (P < 0.05), and Western blot analysis revealed that CtBP2 was higher expressed in tumorous tissues than in adjacent non-tumorous tissues. Either CtBP2 or p16(INK4A) expression was significantly related to histological differentiation (P = 0.016 or 0.001) and to the expression of Ki-67, a proliferating marker (P = 0.006 or 0.02), and patients with higher CtBP2 and lower p16(INK4A) expressions had shorter overall survival. We also observed that CtBP2 modulated the cell proliferation and cell cycle in ECA109 cells, an ESCC cell line, by inhibiting p16(INK4A) . Overexpression or knockdown of CtBP2 in ECA109 cells was found to inhibit or activate the mRNA or protein expression of p16(INK4A) , which in turn altered the cell proliferation and cell cycle in ECA109 cells, as measured by flow cytometry and cell count assay. Additionally, after ECA109 cells silenced for CtBP2 were treated with cisplatin (an anti-ESCC agent), the p16(INK4A) expression was up-regulated, and the cell apoptosis was promoted, thus confirming the repression of p16(INK4A) by CtBP2. Collectively, all results suggested that CtBP2 might contribute to the progression of ESCC through a negative transcriptional regulation of p16(INK4A).

CtBP2 could promote prostate cancer cell proliferation through c-Myc signaling

C-terminal binding protein-2 (CtBP2) is a CtBP-family member which plays a significant role in tumor initiation, progression and response to therapy. However, little has been known about the potential oncobiological role of CtBP2 and its mechanism in human prostate cancer. In this study, we observed the overexpression of CtBP2 in prostate cancer and demonstrated that its expression was closely correlated with several malignant behaviors, e.g., increased serum PSA level, advanced tumor stage (T3), higher Gleason scores and poor outcome. Furthermore, downregulation of CtBP2 expression in prostate cancer PC3 cells could markedly inhibit their proliferation by inducing apoptosis in vitro. Additionally, CtBP2 inhibition could decrease the level of c-Myc and its direct transcriptional target, HSPC111. Taken together, our investigations demonstrated that low-expression of CtBP2 could highly inhibit proliferation of prostate cancer by c-Myc induced signaling, suggesting that targeting CtBP2 may yield a viable anti-tumor strategy by restraining tumor progression in prostate cancer.

High expression and prognostic role of CAP1 and CtBP2 in breast carcinoma: associated with E-cadherin and cell proliferation

Overexpression of C-terminal binding protein-2 (CtBP2) has been noted to correlate with cancer metastasis in several human cancers including breast cancer. The aim of this study was to examine the effect of cyclase-associated protein 1 (CAP1) overexpression on CtBP2 expression and related mechanism in the metastasis of breast cancer. Immunohistochemical analysis was performed in 100 human breast carcinoma samples, and the data were correlated with clinicopathologic features. Furthermore, Western blot analysis was performed for CAP1 and CtBP2 in breast carcinoma samples and cell lines to evaluate their protein levels and molecular interaction. We found that the expression of CAP1 was positively related to CtBP2 expression (P<0.01); moreover, CAP1 expression was significantly correlated with histologic grade (P<0.01) and negatively related to E-cadherin expression (P<0.01). Meanwhile, CtBP2 expression obtained similar results. Kaplan-Meier survival analysis showed that overexpression of CAP1 and CtBP2 exhibited a significant correlation with poor prognosis in human breast cancer (P<0.01). While in vitro, we employed siRNA technique to knockdown CAP1 and CtBP2 expressions and observed their effects on MDA-MB-231 cells growth. CtBP2 depletion by siRNA-inhibited cell proliferation, resulted in increased E-cadherin levels. Moreover, knockdown of CAP1 resulted in decreased CtBP2 and increased E-cadherin expression. On the basis of these results, we suggested that CAP1's oncogenic abilities appear to be triggered at least in part by the modulation of CtBP2 and E-cadherin, which might serve as a future target for breast cancer.

Presynaptic [Ca(2+)] and GCAPs: aspects on the structure and function of photoreceptor ribbon synapses

Changes in intracellular calcium ions [Ca²⁺] play important roles in photoreceptor signaling. Consequently, intracellular [Ca²⁺] levels need to be tightly controlled. In the light-sensitive outer segments (OS) of photoreceptors, Ca²⁺ regulates the activity of retinal guanylate cyclases thus playing a central role in phototransduction and light-adaptation by restoring light-induced decreases in cGMP. In the synaptic terminals, changes of intracellular Ca²⁺ trigger various aspects of neurotransmission. Photoreceptors employ tonically active ribbon synapses that encode light-induced, graded changes of membrane potential into modulation of continuous synaptic vesicle exocytosis. The active zones of ribbon synapses contain large electron-dense structures, synaptic ribbons, that are associated with large numbers of synaptic vesicles. Synaptic coding at ribbon synapses differs from synaptic coding at conventional (phasic) synapses. Recent studies revealed new insights how synaptic ribbons are involved in this process. This review focuses on the regulation of [Ca²⁺] in presynaptic photoreceptor terminals and on the function of a particular Ca²⁺-regulated protein, the neuronal calcium sensor protein GCAP2 (guanylate cyclase-activating protein-2) in the photoreceptor ribbon synapse. GCAP2, an EF-hand-containing protein plays multiple roles in the OS and in the photoreceptor synapse. In the OS, GCAP2 works as a Ca²⁺-sensor within a Ca²⁺-regulated feedback loop that adjusts cGMP levels. In the photoreceptor synapse, GCAP2 binds to RIBEYE, a component of synaptic ribbons, and mediates Ca²⁺-dependent plasticity at that site. Possible mechanisms are discussed.

Variation in HNF1B and Obesity May Influence Prostate Cancer Risk in African American Men: A Pilot Study

Background. Prostate cancer (PCa) racial disparity is multifactorial, involving biological, sociocultural, and lifestyle determinants. We investigated the association between selected potentially functional polymorphisms (SNPs) and prostate cancer (PCa) risk in Black (AAM) and White (EAM) men. We further explored if these associations varied by the body mass index (BMI) and height. Methods. Age-matched DNA samples from 259 AAM and 269 EAM were genotyped for 10 candidate SNPs in 7 genes using the TaqMan allelic differentiation analysis. The dominant, recessive, and additive age-adjusted unconditional logistic regression models were fitted. Results. Three SNPs showed statistically significant associations with PCa risk: in AAM, HNF1B rs7501939 (OR = 2.42, P = 0.0046) and rs4430796 (OR = 0.57, P = 0.0383); in EAM, CTBP2 rs4962416 (OR = 1.52, P = 0.0384). In addition, high BMI in AAM (OR = 1.06, P = 0.022) and height in EAM (OR = 0.92, P = 0.0434) showed significant associations. Interestingly, HNF1B rs7501939 was associated with PCa exclusively in obese AAM (OR = 2.14, P = 0.0103). Conclusion. Our results suggest that variation in the HNF1B may influence PCa risk in obese AAM.

Mechanisms that link the oncogenic epithelial-mesenchymal transition to suppression of anoikis

The oncogenic epithelial-mesenchymal transition (EMT) contributes to tumor progression in various context-dependent ways, including increased metastatic potential, expansion of cancer stem cell subpopulations, chemo-resistance and disease recurrence. One of the hallmarks of EMT is resistance of tumor cells to anoikis. This resistance contributes to metastasis and is a defining property not only of EMT but also of cancer stem cells. Here, we review the mechanistic coupling between EMT and resistance to anoikis. The discussion focuses on several key aspects. First, we provide an update on new pathways that lead from the loss of E-cadherin to anoikis resistance. We then discuss the relevance of transcription factors that are crucial in wound healing in the context of oncogenic EMT. Next, we explore the consequences of the breakdown of cell-polarity complexes upon anoikis sensitivity, through the Hippo, Wnt and transforming growth factor β (TGF-β) pathways, emphasizing points of crossregulation. Finally, we summarize the direct regulation of cell survival genes through EMT-inducing transcription factors, and the roles of the tyrosine kinases focal adhesion kinase (FAK) and TrkB neurotrophin receptor in EMT-related regulation of anoikis. Emerging from these studies are unifying principles that will lead to improvements in cancer therapy by reprogramming sensitivity of anoikis.

The corepressor CTBP2 is a coactivator of retinoic acid receptor/retinoid X receptor in retinoic acid signaling

Retinoids play key roles in development, differentiation, and homeostasis through regulation of specific target genes by the retinoic acid receptor/retinoid X receptor (RAR/RXR) nuclear receptor complex. Corepressors and coactivators contribute to its transcriptional control by creating the appropriate chromatin environment, but the precise composition of these nuclear receptor complexes remains to be elucidated. Using an RNA interference-based genetic screen in mouse F9 cells, we identified the transcriptional corepressor CTBP2 (C-terminal binding protein 2) as a coactivator critically required for retinoic acid (RA)-induced transcription. CTBP2 suppression by RNA interference confers resistance to RA-induced differentiation in diverse murine and human cells. Mechanistically, we find that CTBP2 associates with RAR/RXR at RA target gene promoters and is essential for their transactivation in response to RA. We show that CTBP2 is indispensable to create a chromatin environment conducive for RAR/RXR-mediated transcription by recruiting the histone acetyltransferase p300. Our data reveal an unexpected function of the corepressor CTBP2 as a coactivator for RAR/RXR in RA signaling.

An integrated computational/experimental model of lymphoma growth

Non-Hodgkin's lymphoma is a disseminated, highly malignant cancer, with resistance to drug treatment based on molecular- and tissue-scale characteristics that are intricately linked. A critical element of molecular resistance has been traced to the loss of functionality in proteins such as the tumor suppressor p53. We investigate the tissue-scale physiologic effects of this loss by integrating in vivo and immunohistological data with computational modeling to study the spatiotemporal physical dynamics of lymphoma growth. We compare between drug-sensitive Eμ-myc Arf-/- and drug-resistant Eμ-myc p53-/- lymphoma cell tumors grown in live mice. Initial values for the model parameters are obtained in part by extracting values from the cellular-scale from whole-tumor histological staining of the tumor-infiltrated inguinal lymph node in vivo. We compare model-predicted tumor growth with that observed from intravital microscopy and macroscopic imaging in vivo, finding that the model is able to accurately predict lymphoma growth. A critical physical mechanism underlying drug-resistant phenotypes may be that the Eμ-myc p53-/- cells seem to pack more closely within the tumor than the Eμ-myc Arf-/- cells, thus possibly exacerbating diffusion gradients of oxygen, leading to cell quiescence and hence resistance to cell-cycle specific drugs. Tighter cell packing could also maintain steeper gradients of drug and lead to insufficient toxicity. The transport phenomena within the lymphoma may thus contribute in nontrivial, complex ways to the difference in drug sensitivity between Eμ-myc Arf-/- and Eμ-myc p53-/- tumors, beyond what might be solely expected from loss of functionality at the molecular scale. We conclude that computational modeling tightly integrated with experimental data gives insight into the dynamics of Non-Hodgkin's lymphoma and provides a platform to generate confirmable predictions of tumor growth.

Non-Hodgkin's lymphoma is a cancer that develops from white blood cells called lymphocytes in the immune system, whose role is to fight disease throughout the body. This cancer can spread throughout the whole body and be very lethal – in the US, one third of patients will die from this disease within five years of diagnosis. Chemotherapy is a usual treatment for lymphoma, but the cancer can become highly resistant to it. One reason is that a critical gene called p53 can become mutated and help the cancer to survive. In this work we investigate how cells with this mutation affect the cancer growth by performing experiments in mice and using a computer model. By inputting the model parameters based on data from the experiments, we are able to accurately predict the growth of the tumor as compared to tumor measurements in living mice. We conclude that computational modeling integrated with experimental data gives insight into the dynamics of Non-Hodgkin's lymphoma, and provides a platform to generate confirmable predictions of tumor growth.

The role of C-terminal binding protein 2 in Schwann cell differentiation after sciatic nerve crush

C-terminal binding protein 2 (CtBP2), as a transcriptional repressor, plays an essential role in development and tumorigenesis. However, its distribution and function in peripheral system lesion and repair are still unknown. Here, we investigated the spatiotemporal expression of CtBP2 in rat sciatic nerve crush model. Western blot analysis revealed that CtBP2 was expressed in normal sciatic nerve. It gradually decreased, reached minimal levels at 7 days after crush, and then returned to the normal level at 4 weeks. We observed that CtBP2 is mainly expressed in Schwann cells (SCs). In vitro, we induced SC differentiation via cyclic adenosine monophosphate (cAMP) and found that CtBP2 expression was downregulated during the process of differentiation. CtBP2-specific siRNA inhibited the cAMP-induced expression of the immature SC marker P75(NTR), and exogenous CtBP2 expression upregulated the expression of P75(NTR). Taken together, we hypothesized that peripheral nerve crush-induced downregulation of CtBP2 in the sciatic nerve was associated with SC differentiation, and CtBP2 likely played an important role in peripheral nerve injury and regeneration.

CtBP2 Promotes Human Cancer Cell Migration by Transcriptional Activation of Tiam1

The mammalian COOH-terminal binding proteins (CtBPs) CtBP1 and CtBP2 are metabolically regulated transcriptional co-repressors that are degraded upon acute exposure to the alternative reading frame (ARF) tumor suppressor. We reported previously that CtBP stimulates cell migration in certain contexts via repression of PTEN transcription and activation of the phosphatidylinositol 3-kinase (PI3K) pathway. We have now identified an additional and direct mechanism for CtBP stimulation of cell migration via regulation of T-cell lymphoma invasion and metastasis 1 (Tiam1) protein. Tiam1 is a guanine nucleotide exchange factor (GEF) for Rac GTPase that plays a critical role in regulating cell adhesion, invasion, and migration and has been directly implicated in the promotion of cancer progression and metastasis. We noted a strict positive correlation between CtBP2 and Tiam1 expression levels and that CtBP promotion of cell migration required CtBP-dependent transcriptional activation of Tiam1. RNA interference (RNAi)-mediated knockdown of CtBP2 in human colon or lung carcinoma cells led to decreased Tiam1 protein and mRNA expression, while overexpression of CtBP2 increased Tiam1 expression levels. RNAi and overexpression studies also demonstrated that Tiam1 is a key downstream mediator of CtBP2-mediated cell migration. An analysis of the Tiam1 promoter revealed binding sites for the CtBP-interacting Kruppel-like factor 8 (KLF8), and a Tiam1 promoter luciferase reporter was induced in the presence of both KLF8 and CtBP2, consistent with KLF8-dependent CtBP transactivation of Tiam1. Chromatin immunoprecipitation analyses demonstrated CtBP2 occupancy of the Tiam1 promoter that was dependent on the presence of KLF8. Our results indicate that Tiam1 is a transcriptional activation target of CtBP2 and that this interaction promotes the pro-oncogenic function of CtBP2 leading to cancer cell migration. Transcriptional activation thus plays a role in CtBP pro-oncogenic functions along with the previously characterized CtBP co-repressor function.

Interactions between genome-wide significant genetic variants and circulating concentrations of insulin-like growth factor 1, sex hormones, and binding proteins in relation to prostate cancer risk in the National Cancer Institute Breast and Prostate Cancer Cohort Consortium

Genome-wide association studies (GWAS) have identified many single nucleotide polymorphisms (SNPs) associated with prostate cancer risk. There is limited information on the mechanistic basis of these associations, particularly about whether they interact with circulating concentrations of growth factors and sex hormones, which may be important in prostate cancer etiology. Using conditional logistic regression, the authors compared per-allele odds ratios for prostate cancer for 39 GWAS-identified SNPs across thirds (tertile groups) of circulating concentrations of insulin-like growth factor 1 (IGF-1), insulin-like growth factor binding protein 3 (IGFBP-3), testosterone, androstenedione, androstanediol glucuronide, estradiol, and sex hormone-binding globulin (SHBG) for 3,043 cases and 3,478 controls in the Breast and Prostate Cancer Cohort Consortium. After allowing for multiple testing, none of the SNPs examined were significantly associated with growth factor or hormone concentrations, and the SNP-prostate cancer associations did not differ by these concentrations, although 4 interactions were marginally significant (MSMB-rs10993994 with androstenedione (uncorrected P = 0.008); CTBP2-rs4962416 with IGFBP-3 (uncorrected P = 0.003); 11q13.2-rs12418451 with IGF-1 (uncorrected P = 0.006); and 11q13.2-rs10896449 with SHBG (uncorrected P = 0.005)). The authors found no strong evidence that associations between GWAS-identified SNPs and prostate cancer are modified by circulating concentrations of IGF-1, sex hormones, or their major binding proteins.

CtBP1 interacts with Ikaros and modulates pituitary tumor cell survival and response to hypoxia

C-terminal binding protein (CtBP) is a transcriptional corepressor that plays an important role in mammalian development and tumorigenesis. We demonstrate that CtBP is expressed in adenohypophyseal cells and is expressed at high levels in human corticotroph, somatotroph, and lactotroph pituitary adenomas. CtBP interacts with Ikaros isoforms in GH4 and AtT20 pituitary tumor cells. Ikaros and CtBP1 expression is coordinately induced by hypoxia, and this response is abrogated by CtBP1 deficiency. Forced reduction of CtBP1 leads to reduced cell growth, up-regulation of Sprouty 2, and down-regulation of ectonucleotide pyrophosphatase phosphodiesterase 2 (Enpp2). Consistent with diminished Enpp2 activity, CtBP1-deficient pituitary cells are more susceptible to hypoxia-induced apoptosis, which is rescued by Enpp2-derived lysophosphatidic acid treatment. These results identify putative oncogenic properties of CtBP1 and provide new insights into the overlapping functions of two members of the chromatin remodeling network in the response to hypoxic pituitary tumor cell drive.

The ARF tumor suppressor inhibits tumor cell colonization independent of p53 in a novel mouse model of pancreatic ductal adenocarcinoma metastasis

Pancreatic ductal adenocarcinoma (PDAC) is an incurable, highly metastatic disease that is largely resistant to existing treatments. A better understanding of the genetic basis of PDAC metastasis should facilitate development of improved therapies. To that end, we developed a novel mouse xenograft model of PDAC metastasis to expedite testing of candidate genes associated with the disease. Human PDAC cell lines BxPC-3, MiaPaCa-2, and Panc-1 stably expressing luciferase were generated and introduced by intracardiac injections into immunodeficient mice to model hematogenous dissemination of cancer cells. Tumor development was monitored by bioluminescence imaging. Bioluminescent MiaPaCa-2 cells most effectively recapitulated PDAC tumor development and metastatic distribution in vivo. Tumors formed in nearly 90% of mice and in multiple tissues, including normal sites of PDAC metastasis. Effects of p14ARF, a known suppressor of PDAC, were tested to validate the model. In vitro, p14ARF acted through a CtBP2-dependent, p53-independent pathway to inhibit MiaPaCa-2-invasive phenotypes, which correlated with reduced tumor cell colonization in vivo. These findings establish a new bioluminescent mouse tumor model for rapidly assessing the biological significance of suspected PDAC metastasis genes. This system may also provide a valuable platform for testing innovative therapies.

Meta-analysis of genome-wide and replication association studies on prostate cancer

BACKGROUND

Genome-wide and replication association studies (GWAs) have identified multiple loci at which common variants modestly influence the risk of developing prostate cancer (PCa). To enhance the power to identify loci associated with PCa, we constructed a meta-analysis of GWAs on PCa.

METHODS

Articles evaluating the effects of genome-wide SNPs on PCa were identified by searching the PubMed database. After extraction of relevant data, main and subgroup meta-analyses were performed to assess the effects of relevant SNPs on PCa.

RESULTS

21 eligible articles containing 71 subgroups were included in this meta-analysis. Significant associations were found between 31 SNPs and PCa. They were rs445114, rs620861, rs983085, rs1016343, rs1447295, rs1859962, rs2660753, rs2710646, rs2735839, rs3760511, rs4242382, rs4430796, rs4962416, rs5945572, rs5945619, rs6470494, rs6501455, rs6983267, rs6983561, rs7000448, rs7214479, rs7501939, rs7920517, rs7931342, rs9364554, rs9623117, rs10090154, rs10486567, rs10896449, rs10993994, and rs16901979. The weighted odds ratios for above SNPs ranged between 0.64 and 1.88 (all P < 0.05). Subgroup analysis further indicated that the significant associations of some SNPs existed only in specific ancestry population (P < 10⁻⁵).

CONCLUSIONS

The current meta-analysis demonstrated the moderate effects of above 31 SNPs on PCa and 14 independent PCa risk loci were identified.

Therapeutic targeting of C-terminal binding protein in human cancer

The CtBP transcriptional corepressors promote cancer cell survival and migration/invasion. CtBP senses cellular metabolism via a regulatory dehydrogenase domain, and is antagonized by p14/p19(ARF) tumor suppressors. The CtBP dehydrogenase substrate 4-methylthio-2-oxobutyric acid (MTOB) can act as a CtBP inhibitor at high concentrations, and is cytotoxic to cancer cells. MTOB induced apoptosis was p53-independent, correlated with the derepression of the proapoptotic CtBP repression target Bik, and was rescued by CtBP overexpression or Bik silencing. MTOB did not induce apoptosis in mouse embryonic fibroblasts (MEFs), but was increasingly cytotoxic to immortalized and transformed MEFs, suggesting that CtBP inhibition may provide a suitable therapeutic index for cancer therapy. In human colon cancer cell peritoneal xenografts, MTOB treatment decreased tumor burden and induced tumor cell apoptosis. To verify the potential utility of CtBP as a therapeutic target in human cancer, the expression of CtBP and its negative regulator ARF was studied in a series of resected human colon adenocarcinomas. CtBP and ARF levels were inversely-correlated, with elevated CtBP levels (compared with adjacent normal tissue) observed in greater than 60% of specimens, with ARF absent in nearly all specimens exhibiting elevated CtBP levels. Targeting CtBP may represent a useful therapeutic strategy in human malignancies.

An ARF/CtBP2 complex regulates BH3-only gene expression and p53-independent apoptosis

The alternative reading frame (ARF) tumor suppressor exerts both p53-dependent and p53-independent functions. The corepressor C-terminal binding protein (CtBP) interacts with ARF, resulting in proteasome-mediated degradation of CtBP. ARF can induce apoptosis in p53-null colon cancer cells, in a manner dependent on ARF interaction with CtBP. Bik was uniquely identified in an apoptotic gene array as coordinately upregulated in colon cancer cells after either CtBP2 knockdown or ARF overexpression. Validating the array findings, ARF induced Bik mRNA and protein expression, and this activity required an intact CtBP binding domain. Apoptosis induced by CtBP deficiency was substantially impaired when Bik expression was simultaneously silenced. An analysis of the Bik promoter revealed binding sites for the CtBP-interacting basic Kruppel-like factor (BKLF). A Bik promoter luciferase reporter was repressed by BKLF and CtBP2, and ARF reversed CtBP-associated repression. Chromatin immunoprecipitation analyses showed that CtBP was recruited to the Bik promoter largely by BKLF. Expression profiling of BH3-only gene expression in ARF-expressing or CtBP-deficient cells revealed that Bik was uniquely regulated by ARF/CtBP in colon cancer cells, whereas additional BH3-only proteins (Bim, Bmf) showed CtBP-dependent repression in osteosarcoma cells. ARF antagonism of CtBP repression of Bik and other BH3-only genes may have a critical role in ARF-induced p53-independent apoptosis and tumor suppression.