CtBP2 proteome: Role of CtBP in E2F7-mediated repression and cell proliferation

The transcriptional repressor Ctbp2 as a metabolite sensor regulating cardiomyocytes proliferation and heart regeneration

BACKGROUND

C-terminal binding protein-2 (Ctbp2) is an evolutionarily conserved transcriptional repressor that regulates fundamental processes such as cell proliferation and apoptosis. However, the potential role of Ctbp2 in cardiomyocyte proliferation and heart regeneration remains unclear. In this study, we aim to explore the important role of Ctbp2 in cardiomyocyte proliferation and the regeneration of injured adult hearts.

METHODS AND RESULTS

In this study, we found that the expression of Ctbp2 in cardiomyocytes is downregulated after adulthood. Silencing Ctbp2 in cardiomyocytes on the post-natal day 1 (P1) reduced the proliferation ability of cardiomyocytes, whereas overexpressing Ctbp2 enhanced the proliferation ability of cardiomyocytes. Additionally, overexpressing Ctbp2 via adeno-associated virus-9 (AAV9) had no effect on the hearts of normal adult mice, but in the case of heart injury, overexpression of Ctbp2 in adult mice cardiomyocytes promoted cardiomyocyte proliferation. Mechanistically, the transcriptional repressor Ctbp2 acts as a metabolite sensor, and its regulation of cardiomyocyte proliferation is influenced by the metabolites NADH/NAD+ and fatty acyl-CoAs. Ctbp2 is activated by the intracellular accumulation of NADH during cardiomyocyte ischemia and hypoxia, inhibiting the transcriptional activity of the transcription factor FoxO1, thereby repressing the expression of the target genes and cell cycle negative regulators p21 and p27, allowing cardiomyocytes to re-enter the cell cycle. In contrast, normal adult cardiomyocytes mainly use fatty acid oxidation metabolism as their primary energy source, and the intracellular production of fatty acyl-CoAs inactivates Ctbp2, thus preventing it from inhibiting FoxO1 mediated cell cycle arrest.

CONCLUSION

In conclusion, this study demonstrates that the Ctbp2-FoxO1-p21/p27 axis can promote cardiomyocyte proliferation and heart regeneration. As a metabolite sensor, Ctbp2 is activated during cardiomyocyte ischemia and hypoxia, while it is inactivated under normal conditions. This controllable and transient regulation of cardiomyocyte proliferation can avoid the detrimental effects on cardiac function caused by long-term regulation of cardiomyocyte proliferation, such as hypertrophic cardiomyopathy or heart failure. This provides new targets and new ideas for addressing the issues of cardiomyocyte proliferation and heart regeneration.

E2F1 and E2F7 regulate gastric cancer cell proliferation, respectively, through transcriptional activation and transcriptional repression of MYBL2

Gastric cancer (GC) is the most common malignant tumor of the digestive tract. However, the molecular pathogenesis is not well understood. Through bioinformatic analysis and analyzing clinical tissue samples, we found that E2F1 and E2F7 as well as their potential downstream target MYBL2 were all upregulated in GC tissues and that their expressions correlated with patient prognosis. While knockdown of E2F1 or MYBL2 inhibited cell proliferation and promoted apoptosis, knockdown of E2F7 promoted cell proliferation but had no effects on apoptosis. Chromatin immunoprecipitation and dual luciferase reporter assays demonstrated that MYBL2 was transcriptionally activated and repressed by E2F1 and E2F7, respectively. Importantly, in vitro and ex vivo experiments demonstrated that the effects of E2F1 and E2F7 on GC cell proliferation were significantly attenuated by reversely modulating MYBL2 expression, indicating that MYBL2 is a direct and functionally relevant target of E2F1 and E2F7 in GC cells. Furthermore, the effects of E2F1 and E2F7 on GC cell proliferation through transcriptional regulation of MYBL2 can be mediated by the PI3K/AKT signaling pathway. Interestingly, we found differential nucleocytoplasmic distribution of E2F7 in GC cells with functional relevance. Taken together, our data suggest that targeted therapies of GC may be achieved from three different angles, E2F1, E2F7, and MYBL2 themselves, E2F1/E2F7 expression balance, and E2F7 nuclear localization.

C-terminal binding protein 2 is a novel tumor suppressor targeting the MYC-IRF4 axis in multiple myeloma

ABSTRACT

Multiple myeloma (MM) cells are addicted to MYC and its direct transactivation targets IRF4 for proliferation and survival. MYC and IRF4 are still considered "undruggable," as most small-molecule inhibitors suffer from low potency, suboptimal pharmacokinetic properties, and undesirable off-target effects. Indirect inhibition of MYC/IRF4 emerges as a therapeutic vulnerability in MM. Here, we uncovered an unappreciated tumor-suppressive role of C-terminal binding protein 2 (CTBP2) in MM via strong inhibition of the MYC-IRF4 axis. In contrast to epithelial cancers, CTBP2 is frequently downregulated in MM, in association with shortened survival, hyperproliferative features, and adverse clinical outcomes. Restoration of CTBP2 exhibited potent antitumor effects against MM in vitro and in vivo, with marked repression of the MYC-IRF4 network genes. Mechanistically, CTBP2 impeded the transcription of MYC and IRF4 by histone H3 lysine 27 deacetylation (H3K27ac) and indirectly via activation of the MYC repressor IFIT3. In addition, activation of the interferon gene signature by CTBP2 suggested its concomitant immunomodulatory role in MM. Epigenetic studies have revealed the contribution of polycomb-mediated silencing and DNA methylation to CTBP2 inactivation in MM. Notably, inhibitors of Enhance of zeste homolog 2, histone deacetylase, and DNA methyltransferase, currently under evaluation in clinical trials, were effective in restoring CTBP2 expression in MM. Our findings indicated that the loss of CTBP2 plays an essential role in myelomagenesis and deciphers an additional mechanistic link to MYC-IRF4 dysregulation in MM. We envision that the identification of novel critical regulators will facilitate the development of selective and effective approaches for treating this MYC/IRF4-addicted malignancy.

DNA Methylation in Gestational Diabetes and its Predictive Value for Postpartum Glucose Disturbances

CONTEXT

DNA methylation in the diagnosis of gestational diabetes.

OBJECTIVE

To assess the value of DNA methylation in the diagnosis of gestational diabetes (GDM) and in the prediction of maternal postpartum glucose disturbances.

METHODS

Two-stage observational study performed between July 2006 and December 2010, at University Hospital. Forty-eight randomly selected pregnant women formed the discovery cohort (24 with GDM and 24 controls) and 252 pregnant women (94 with GDM and 158 controls) formed the replication cohort. GDM women were re-evaluated 4 years postpartum. The main outcome measures were GDM, type 2 diabetes or prediabetes at 4 years postpartum.

RESULTS

We identified 3 CpG sites related to LINC00917, TRAPPC9, and LEF1 that were differentially methylated in women with GDM and abnormal glucose tolerance; and sites associated with LINC00917 and TRAPPC9 were independently associated with an abnormal glucose tolerance status 4 years postpartum after controlling for clinical variables. Moreover, the site associated with LINC00917 and the combination of the 3 sites had the highest predictive values.

CONCLUSION

Our results suggest that some of these sites may be implicated in the development of GDM and postpartum abnormal glucose tolerance.

The transcriptional corepressor CtBP2 serves as a metabolite sensor orchestrating hepatic glucose and lipid homeostasis

Biological systems to sense and respond to metabolic perturbations are critical for the maintenance of cellular homeostasis. Here we describe a hepatic system in this context orchestrated by the transcriptional corepressor C-terminal binding protein 2 (CtBP2) that harbors metabolite-sensing capabilities. The repressor activity of CtBP2 is reciprocally regulated by NADH and acyl-CoAs. CtBP2 represses Forkhead box O1 (FoxO1)-mediated hepatic gluconeogenesis directly as well as Sterol Regulatory Element-Binding Protein 1 (SREBP1)-mediated lipogenesis indirectly. The activity of CtBP2 is markedly defective in obese liver reflecting the metabolic perturbations. Thus, liver-specific CtBP2 deletion promotes hepatic gluconeogenesis and accelerates the progression of steatohepatitis. Conversely, activation of CtBP2 ameliorates diabetes and hepatic steatosis in obesity. The structure-function relationships revealed in this study identify a critical structural domain called Rossmann fold, a metabolite-sensing pocket, that is susceptible to metabolic liabilities and potentially targetable for developing therapeutic approaches.

Molecular networks of the FOXP2 transcription factor in the brain

The discovery of the FOXP2 transcription factor, and its implication in a rare severe human speech and language disorder, has led to two decades of empirical studies focused on uncovering its roles in the brain using a range of in vitro and in vivo methods. Here, we discuss what we have learned about the regulation of FOXP2, its downstream effectors, and its modes of action as a transcription factor in brain development and function, providing an integrated overview of what is currently known about the critical molecular networks.

CtBP2 confers protection against oxidative stress through interactions with NRF1 and NRF2

While molecular oxygen is essential for aerobic organisms, its utilization is inseparably connected with generation of oxidative insults. To cope with the detrimental aspects, cells evolved antioxidative defense systems, and insufficient management of the oxidative insults underlies the pathogenesis of a wide range of diseases. A battery of genes for this antioxidative defense are regulated by the transcription factors nuclear factor-erythroid 2-like 1 and 2 (NRF1 and NRF2). While the regulatory steps for the activation of NRFs have been investigated with particular emphasis on nuclear translocation and proteosomal degradation, unknown redundancy may exist considering the indispensable nature of these defense systems. Here we unraveled that C-terminal binding protein 2 (CtBP2), a transcriptional cofactor with redox-sensing capability, is an obligate partner of NRFs. CtBP2 forms transcriptional complexes with NRF1 and NRF2 that is required to promote the expression of antioxidant genes in response to oxidative insults. Our findings illustrate a basis for understanding the transcriptional regulation of antioxidative defense systems that may be exploited therapeutically.

E2F7, regulated by miR‑30c, inhibits apoptosis and promotes cell cycle of prostate cancer cells

Prostate cancer (PCa) remains a leading cause of mortality among men in the United States and Western Europe. The molecular mechanism of PCa pathogenesis has not been fully elucidated. In the present study, the expression profile of E2F transcription factor 7 (E2F7) in PCa was examined using immunohistochemistry and reverse transcription‑quantitative PCR, whilst cell cycle progression and apoptosis were determined using fluorescent cell activated sorting techniques. Cell viability was measured using Cell Counting Kit‑8 in loss‑ and gain‑of‑function studies. Dual‑luciferase reporter assay was used to verify if E2F7 was one of the potential targets of miR‑30c. The staining score of E2F7 of PCa tissues was found to be notably higher compared with that of adjacent normal tissues. Suppression of E2F7 expression in PCa cell lines led to significantly reduced proliferation rates, increased proportion of cells in the G1 phase of the cell cycle and higher apoptotic rates compared with those in negative control groups. Dual‑luciferase reporter assay revealed E2F7 to be one of the binding targets of microRNA (miR)‑30c. In addition, transfection of miR‑30c mimics into PCa cells resulted in reduced cell viability, increased proportion of cells in the G1 phase and higher apoptotic rates. By contrast, transfection with the miR‑30c inhibitor led to lower apoptosis rates of PCa cells compared with negative control groups, whilst E2F7 siRNA co‑transfection reversed stimulatory effects of miR‑30c inhibitors on cell viability. In addition, the expression of cyclin‑dependent kinase inhibitor p21 were found to be upregulated by transfection with either E2F7 siRNA or miR‑30c mimics into PCa cells. In conclusion, the present study suggested that E2F7 may be positively associated with PCa cell proliferation by inhibiting p21, whereas E2F7 is in turn under regulation by miR‑30c. These observations suggest the miR‑30c/E2F7/p21 axis to be a viable therapeutic target for PCa.

Sensory Processing at Ribbon Synapses in the Retina and the Cochlea

In recent years, sensory neuroscientists have made major efforts to dissect the structure and function of ribbon synapses which process sensory information in the eye and ear. This review aims to summarize our current understanding of two key aspects of ribbon synapses: 1) their mechanisms of exocytosis and endocytosis and 2) their molecular anatomy and physiology. Our comparison of ribbon synapses in the cochlea and the retina reveals convergent signaling mechanisms, as well as divergent strategies in different sensory systems.

C-Terminus of E1A Binding Protein 1 Stimulates Malignant Phenotype in Human Hepatocellular Carcinoma

<strong>BACKGROUND</strong> The C-terminus of E1A binding proteins (CTBPs) has recently been shown to stimulate tumorigenesis in several human tissues by participating in cell signal transduction. However, to date, the expression profile of CTBP isoforms in hepatocellular carcinoma (HCC) and the impact of CTBPs on HCC cell phenotype have not been fully explored. <strong>MATERIAL AND METHODS</strong> The expression level of CTBP1 was investigated in various HCC cell lines and HCC tissues by RT-qPCR, Western blotting, and immunohistochemistry assays. The phosphatidylinositol-3-kinase (PI3K) inhibitor LY294002 was utilized to treat hepatic astrocyte cells, and the impact of CTBP1 on proliferation and metastasis of hepatic astrocytes and HCC cells was accessed by CCK-8, clone-forming, Transwell chamber, and cell scratch assays. <strong>RESULTS</strong> Increased expression of CTBP1 was observed in HCC tissues and was a predictor of poor prognosis in HCC patients. CTBP1 modified proliferation and migratory activity of HCC cells via the PI3K/protein kinase B (Akt) signaling pathway in hepatic astrocytes. Moreover, genetic loss of CTBP1 significantly reduced the metastatic activity of HCC cells <i>in vitro</i>. <strong>CONCLUSIONS</strong> Our data suggest that the loss of CTBP1 suppresses cell proliferative and invasive activity of HCC cells via the PI3K/Akt pathway.

Exploration of the Brn4-regulated genes enhancing adult hippocampal neurogenesis by RNA sequencing

Adult hippocampal neurogenesis is essential for learning and memory, and its dysfunction is involved in neurodegenerative diseases. However, the molecular mechanisms underlying adult hippocampal neurogenesis are still largely unknown. Our previous studies indicated that the transcription factor Brn4 was upregulated and promoted neuronal differentiation of neural stem cells (NSCs) in the surgically denervated hippocampus in rats. In this study, we use high-throughput RNA sequencing to explore the molecular mechanisms underlying the enhancement of adult hippocampal neurogenesis induced by lentivirus-mediated Brn4 overexpression in vivo. After 10 days of the lentivirus injection, we found that the expression levels of genes related to neuronal development and maturation were significantly increased and the expression levels of genes related to NSC maintenance were significantly decreased, indicating enhanced neurogenesis in the hippocampus after Brn4 overexpression. Through RNA sequencing, we found that 658 genes were differentially expressed in the Brn4-overexpressed hippocampi compared with GFP-overexpressed controls. Many of these differentially expressed genes are involved in NSC division and differentiation. By using quantitative real-time PCR, we validated the expression changes of three genes, including Ctbp2, Notch2, and Gli1, all of which are reported to play key roles in neuronal differentiation of NSCs. Importantly, the expression levels of Ctbp2 and Notch2 were also significantly changed in the hippocampus of Brn4 KO mice, which indicates that the expression levels of Ctbp2 and Notch2 may be directly regulated by Brn4. Our current study provides a solid foundation for further investigation and identifies Ctbp2 and Notch2 as possible downstream targets of Brn4. © 2017 Wiley Periodicals, Inc.

Ad E1A 243R oncoprotein promotes association of proto-oncogene product MYC with the NuA4/Tip60 complex via the E1A N-terminal repression domain

The adenovirus E1A 243R oncoprotein targets TRRAP, a scaffold protein that assembles histone acetyltransferase (HAT) complexes, such as the NuA4/Tip60 complex which mediates transcriptional activity of the proto-oncogene MYC and helps determine the cancer cell phenotype. How E1A transforms cells through TRRAP remains obscure. We performed proteomic analysis with the N-terminal transcriptional repression domain of E1A 243R (E1A 1-80) and showed that E1A 1-80 interacts with TRRAP, p400, and three other members of the NuA4 complex - DMAP1, RUVBL1 and RUVBL2 - not previously shown to associate with E1A 243R. E1A 1-80 interacts with these NuA4 components and MYC through the E1A TRRAP-targeting domain. E1A 243R association with the NuA4 complex was demonstrated by co-immunoprecipitation and analysis with DMAP1, Tip60, and MYC. Significantly, E1A 243R promotes association of MYC/MAX with the NuA4/Tip60 complex, implicating the importance of the MYC/NuA4 pathway in cellular transformation by both MYC and E1A.

MiR-129 triggers autophagic flux by regulating a novel Notch-1/ E2F7/Beclin-1 axis to impair the viability of human malignant glioma cells

Abnormalities of autophagy have been implicated in an increasing number of human cancers, including glioma. To date, there is a wealth of evidence indicating that microRNAs (miRNAs) contribute significantly to autophagy in a variety of cancers. Previous studies have suggested that miR-129 functioned as an important inhibitor of the cell cycle and could promote the apoptosis of many cancer cell lines in vitro. Here, we reported that miR-129 acted as a potent inducer of autophagy. Forced expression of miR-129 could induce autophagic flux by targetedly suppressing Notch-1 in glioma cells. The autophagy induced by miR-129 could restrain the activity of mammalian target of rapamycin (mTOR) and upregulate Beclin-1. Moreover, we demonstrated that E2F transcription factor 7 (E2F7) could also trigger autophagic flux by upregulating Beclin-1 and mediating miR-129-induced autophagy. Additionally, knockdown of Notch-1 could upregulate the expression of E2F7, whereas downregulation of E2F7 alleviated shNotch-1-induced autophagic flux. In particular, knockdown of endogenous Beclin-1 could effectively reduce autophagic flux stimulated by miR-129 and E2F7. Interestingly, upon attenuation of miR-129- or E2F7-triggered autophagic flux rescued cell viability suppressed by them. More importantly, intratumoral injection of pHAGE-miR-129 lentivirus in a nude mouse xenograft model significantly restrained tumor growth and triggered autophagy. In conclusion, these findings identify a new function for miR-129 as a potent inducer of autophagy through a novel Notch-1/E2F7/Beclin-1 axis in glioma.

Ctbp2 Modulates NuRD-Mediated Deacetylation of H3K27 and Facilitates PRC2-Mediated H3K27me3 in Active Embryonic Stem Cell Genes During Exit from Pluripotency

For cells to exit from pluripotency and commit to a lineage, the circuitry of a core transcription factor (CTF) network must be extinguished in an orderly manner through epigenetic modifications. However, how this choreographed epigenetic remodeling at active embryonic stem cell (ESC) genes occurs during differentiation is poorly understood. In this study, we demonstrate that C-terminal binding protein 2 (Ctbp2) regulates nucleosome remodeling and deacetylation (NuRD)-mediated deacetylation of H3K27 and facilitates recruitment of polycomb repressive complex 2 (PRC2)-mediated H3K27me3 in active ESC genes for exit from pluripotency during differentiation. By genomewide analysis, we found that Ctbp2 resides in active ESC genes and co-occupies regions with ESC CTFs in undifferentiated ESCs. Furthermore, ablation of Ctbp2 effects inappropriate gene silencing in ESCs by sustaining high levels of H3K27ac and impeding H3K27me3 in active ESC genes, thereby sustaining ESC maintenance during differentiation. Thus, Ctbp2 preoccupies regions in active genes with the NuRD complex in undifferentiated ESCs that are directed toward H3K27me3 by PRC2 to induce stable silencing, which is pivotal for natural lineage commitment.

The EBNA3 Family: Two Oncoproteins and a Tumour Suppressor that Are Central to the Biology of EBV in B Cells

Epstein-Barr virus nuclear antigens EBNA3A , EBNA3B and EBNA3C are a family of three large latency-associated proteins expressed in B cells induced to proliferate by the virus. Together with the other nuclear antigens (EBNA-LP, EBNA2 and EBNA1), they are expressed from a polycistronic transcription unit that is probably unique to B cells. However, compared with the other EBNAs, hitherto the EBNA3 proteins were relatively neglected and their roles in EBV biology rather poorly understood. In recent years, powerful new technologies have been used to show that these proteins are central to the latency of EBV in B cells, playing major roles in reprogramming the expression of host genes affecting cell proliferation, survival, differentiation and immune surveillance. This indicates that the EBNA3s are critical in EBV persistence in the B cell system and in modulating B cell lymphomagenesis. EBNA3A and EBNA3C are necessary for the efficient proliferation of EBV-infected B cells because they target important tumour suppressor pathways--so operationally they are considered oncoproteins. In contrast, it is emerging that EBNA3B restrains the oncogenic capacity of EBV, so it can be considered a tumour suppressor--to our knowledge the first to be described in a tumour virus. Here, we provide a general overview of the EBNA3 genes and proteins. In particular, we describe recent research that has highlighted the complexity of their functional interactions with each other, with specific sites on the human genome and with the molecular machinery that controls transcription and epigenetic states of diverse host genes.