Anti-apoptotic function of the E2F transcription factor 4 (E2F4)/p130, a member of retinoblastoma gene family in cardiac myocytes

Single-cell RNA sequencing reveals the transcriptional heterogeneity of Tbx18-positive cardiac cells during heart development

The T-box family transcription factor 18 (Tbx18) has been found to play a critical role in regulating the development of the mammalian heart during the primary stages of embryonic development while the cellular heterogeneity and landscape of Tbx18-positive (Tbx18+) cardiac cells remain incompletely characterized. Here, we analyzed prior published single-cell RNA sequencing (scRNA-seq) mouse heart data to explore the heterogeneity of Tbx18+ cardiac cell subpopulations and provide a comprehensive transcriptional landscape of Tbx18+ cardiac cells during their development. Bioinformatic analysis methods were utilized to identify the heterogeneity between cell groups. Based on the gene expression characteristics, Tbx18+ cardiac cells can be classified into a minimum of two distinct cell populations, namely fibroblast-like cells and cardiomyocytes. In terms of temporal heterogeneity, these cells exhibit three developmental stages, namely the MEM stage, ML_P0 stage, and P stage Tbx18+ cardiac cells. Furthermore, Tbx18+ cardiac cells encompass several cell types, including cardiac progenitor-like cells, cardiomyocytes, and epicardial/stromal cells, as determined by specific transcriptional regulatory networks. The scRNA-seq results revealed the involvement of extracellular matrix (ECM) signals and epicardial epithelial-to-mesenchymal transition (EMT) in the development of Tbx18+ cardiac cells. The utilization of a lineage-tracing model served to validate the crucial function of Tbx18 in the differentiation of cardiac cells. Consequently, these findings offer a comprehensive depiction of the cellular heterogeneity within Tbx18+ cardiac cells.

RBL2 Regulates Cardiac Sensitivity to Anthracycline Chemotherapy

Background

Anthracycline chemotherapies cause heart failure in a subset of cancer patients. We previously reported that the anthracycline doxorubicin (DOX) induces cardiotoxicity through the activation of cyclin-dependent kinase 2 (CDK2).

Objectives

The aim of this study was to determine whether retinoblastoma-like 2 (RBL2/p130), an emerging CDK2 inhibitor, regulates anthracycline sensitivity in the heart.

Methods

Rbl2-/- mice and Rbl2+/+ littermates received DOX (5 mg/kg/wk for 4 weeks intraperitoneally, 20 mg/kg cumulative). Heart function was monitored with echocardiography. The association of RBL2 genetic variants with anthracycline cardiomyopathy was evaluated in the SJLIFE (St. Jude Lifetime Cohort Study) and CPNDS (Canadian Pharmacogenomics Network for Drug Safety) studies.

Results

The loss of endogenous Rbl2 increased basal CDK2 activity in the mouse heart. Mice lacking Rbl2 were more sensitive to DOX-induced cardiotoxicity, as evidenced by rapid deterioration of heart function and loss of heart mass. The disruption of Rbl2 exacerbated DOX-induced mitochondrial damage and cardiomyocyte apoptosis. Mechanistically, Rbl2 deficiency enhanced CDK2-dependent activation of forkhead box O1 (FOXO1), leading to up-regulation of the proapoptotic protein Bim. The inhibition of CDK2 desensitized Rbl2-depleted cardiomyocytes to DOX. In wild-type cardiomyocytes, DOX exposure induced Rbl2 expression in a FOXO1-dependent manner. Importantly, the rs17800727 G allele of the human RBL2 gene was associated with reduced anthracycline cardiotoxicity in childhood cancer survivors.

Conclusions

Rbl2 is an endogenous CDK2 inhibitor in the heart and represses FOXO1-mediated proapoptotic gene expression. The loss of Rbl2 increases sensitivity to DOX-induced cardiotoxicity. Our findings suggest that RBL2 could be used as a biomarker to predict the risk of cardiotoxicity before the initiation of anthracycline-based chemotherapy.

E2F4 regulates cell cycle to mediate embryonic development in pigs

In mammals, E2 factor (E2F) acts as a cell cycle regulator. E2F transcription factor 4 (E2F4) is a member of the E2F family of transcription factors and usually represents predominant E2F activity in cells. The E2F4 gene has been extensively studied in animals and is associated with multiple functions, such as cell cycle regulation and apoptosis; however, little is known about its role during embryonic development. In this study, we investigated the function of E2F4 and its mechanism of action in porcine embryo development. For this purpose, we knocked down E2F4 by microinjecting double-stranded RNA of E2F4 at the 1-cell stage. The results showed that E2F4 knockdown in porcine embryos led to a significant decrease in the blastocyst rate and total cell number. Defective E2F4 expression reduced the level of G1/S checkpoints (cyclin E-cyclin-dependent kinase 2) and cell cycle-related gene expression at the 4-cell embryo stage and blastocyst. Moreover, a decrease in E2F4 expression increased phosphorylated H2A.X variant histones and activated ataxia telangiectasia mutated (ATM) and p53-p21 pathway. In addition, E2F4 depletion caused a significant decrease in histone acetylation. Taken together, E2F4 plays a critical role as a transcriptional activator in the development of porcine embryos, an observation that contradicts its well-established role as a transcription repressor.

E2F4DN Transgenic Mice: A Tool for the Evaluation of E2F4 as a Therapeutic Target in Neuropathology and Brain Aging

E2F4 was initially described as a transcription factor with a key function in the regulation of cell quiescence. Nevertheless, a number of recent studies have established that E2F4 can also play a relevant role in cell and tissue homeostasis, as well as tissue regeneration. For these non-canonical functions, E2F4 can also act in the cytoplasm, where it is able to interact with many homeostatic and synaptic regulators. Since E2F4 is expressed in the nervous system, it may fulfill a crucial role in brain function and homeostasis, being a promising multifactorial target for neurodegenerative diseases and brain aging. The regulation of E2F4 is complex, as it can be chemically modified through acetylation, from which we present evidence in the brain, as well as methylation, and phosphorylation. The phosphorylation of E2F4 within a conserved threonine motif induces cell cycle re-entry in neurons, while a dominant negative form of E2F4 (E2F4DN), in which the conserved threonines have been substituted by alanines, has been shown to act as a multifactorial therapeutic agent for Alzheimer’s disease (AD). We generated transgenic mice neuronally expressing E2F4DN. We have recently shown using this mouse strain that expression of E2F4DN in 5xFAD mice, a known murine model of AD, improved cognitive function, reduced neuronal tetraploidization, and induced a transcriptional program consistent with modulation of amyloid-β (Aβ) peptide proteostasis and brain homeostasis recovery. 5xFAD/E2F4DN mice also showed reduced microgliosis and astrogliosis in both the cerebral cortex and hippocampus at 3-6 months of age. Here, we analyzed the immune response in 1 year-old 5xFAD/E2F4DN mice, concluding that reduced microgliosis and astrogliosis is maintained at this late stage. In addition, the expression of E2F4DN also reduced age-associated microgliosis in wild-type mice, thus stressing its role as a brain homeostatic agent. We conclude that E2F4DN transgenic mice represent a promising tool for the evaluation of E2F4 as a therapeutic target in neuropathology and brain aging.

Loss of Rbl2 (Retinoblastoma-Like 2) Exacerbates Myocardial Ischemia/Reperfusion Injury

Background The postmitotic state of adult cardiomyocytes, maintained by the cell cycle repressor Rbl2 (retinoblastoma-like 2), is associated with considerable resistance to apoptosis. However, whether Rbl2 regulates cardiomyocyte apoptosis remains unknown. Methods and Results Here, we show that ablation of Rbl2 increased cardiomyocyte apoptosis following acute myocardial ischemia/reperfusion injury, leading to diminished cardiac function and exaggerated ventricular remodeling in the long term. Mechanistically, ischemia/reperfusion induced expression of the proapoptotic protein BCL2 interacting protein 3 (Bnip3), which was augmented by deletion of Rbl2. Because the Bnip3 promoter contains an adenoviral early region 2 binding factor (E2F)-binding site, we further showed that loss of Rbl2 upregulated the transcriptional activator E2F1 but downregulated the transcriptional repressor E2F4. In cultured cardiomyocytes, treatment with H₂O₂ markedly increased the levels of E2F1 and Bnip3, resulting in mitochondrial depolarization and apoptosis. Depletion of Rbl2 significantly augmented H₂O₂-induced mitochondrial damage and apoptosis in vitro. Conclusions Rbl2 deficiency enhanced E2F1-mediated Bnip3 expression, resulting in aggravated cardiomyocyte apoptosis and ischemia/reperfusion injury. Our results uncover a novel antiapoptotic role for Rbl2 in cardiomyocytes, suggesting that the cell cycle machinery may directly regulate apoptosis in postmitotic cardiomyocytes. These findings may be exploited to develop new strategies to limit ischemia/reperfusion injury in the treatment of acute myocardial infarction.

E2F4 regulates the cell cycle and DNA replication in the silkworm, Bombyx mori

The E2F family of transcription factors is crucial for cell cycle progression and cell fate decisions. Although E2Fs have been widely studied in mammals, there have been few studies performed in insects. Here, we determined the function of E2F4 in the silkworm, Bombyx mori. We demonstrate that E2F proteins are highly conserved among species from lower animals to higher mammals. Overexpression of the BmE2F4 gene led to cell cycle arrest in the G1 phase, whereas interfering with the BmE2F4 mRNA led to accumulation of cells in the S phase. These results indicate that BmE2F4 is important in cell cycle regulation. We also demonstrate that the BmE2F4 gene is involved in DNA replication of BmN-SWU1 cells and DNA synthesis in the silk gland. Furthermore, we identified a protein called Bm14-3-3ζ that can interact with BmE2F4 and allow it to localize in the nucleus. Overexpression of the Bm14-3-3ζ gene led to cell cycle arrest in the G1 phase, while knocking down the gene increased the proportion of cells in S phase. These findings provide important insights into the function of E2F transcription factors and increase our understanding of their involvement in cell cycle regulation.

E2F4 transcription factor is a prognostic biomarker related to immune infiltration of head and neck squamous cell carcinoma

To investigate the relationship between the transcription factor, E2F4, and head and neck squamous cell carcinoma (HNSCC), and to preliminarily explore the signaling pathways and immunological role of E2F4. The mRNA expression of E2F4 in HNSCC was evaluated by searching Gene Expression Omnibus (GEO) and The Cancer Genome Atlas (TCGA) datasets. E2F4 protein expression was analyzed by immunohistochemistry using the CMU1h-ENT database. The association between E2F4 expression and tumor infiltration of immune cells was analyzed. Intracellular signaling by E2F4 was explored using KEGG and GO analysis. The correlation of E2F4 expression with clinical characteristics and its prognostic role were validated and analyzed in TCGA database. From the analysis of GEO and TCGA data, E2F4 expression was found to be up-regulated in HNSCC tumor tissues, and its level was associated with T, Grade, and M staging. Kaplan–Meier curve and Cox analyses indicated that the high expression of E2F4 was related to a poor prognosis. Thus, E2F4 was considered a potential prognostic factor for HNSCC. Immunohistochemical staining showed that E2F4 was mainly localized in the cell nucleus; it was highly expressed in HNSCC tissues, with a significant difference noted from that in pericancerous mucosa tissues. A correlation was observed between the differential expression of E2F4 and the immune infiltration of HNSCC. As revealed by KEGG and GO analysis, differential enrichment was found in the cell cycle, spliceosome, meiosis, microbial polysaccharide synthesis, and WNT signaling pathway, as well as in cyclic adenosine monophosphate, ERBB2, VEGF, GCNP and MYC pathways. E2F4 plays an important role in tumor progression and may be a critical biological prognostic factor for HNSCC. In addition, it functions in the nucleus as a transcription factor, regulates immune cells, and could be a promising molecular target for the diagnosis and treatment of HNSCC.

The Role and Clinical Implications of the Retinoblastoma (RB)-E2F Pathway in Gastric Cancer

Gastric cancer is the most common malignant tumor in the digestive tract, with very high morbidity and mortality in developing countries. The pathogenesis of gastric cancer is a complex biological process mediated by abnormal regulation of proto-oncogenes and tumor suppressor genes. Although there have been some in-depth studies on gastric cancer at the molecular level, the specific mechanism has not been fully elucidated. RB family proteins (including RB, p130, and p107) are involved in cell cycle regulation, a process that largely depends on members of the E2F gene family that encode transcriptional activators and repressors. In gastric cancer, inactivation of the RB-E2F pathway serves as a core transcriptional mechanism that drives cell cycle progression, and is regulated by cyclins, cyclin-dependent kinases, cyclin-dependent kinase inhibitors, p53, Helicobacter pylori and some other upstream molecules. The E2F proteins are encoded by eight genes (i.e. E2F1 to E2F8), each of which may play a specific role in gastric cancer. Interestingly, a single E2F such as E2F1 can activate or repress transcription, and enhance or inhibit cell proliferation, depending on the cell environment. Thus, the function of the E2F transcription factor family is very complex and needs further exploration. Importantly, the presence of H. pylori in stomach mucosa may affect the RB and p53 tumor suppressor systems, thereby promoting the occurrence of gastric cancer. This review aims to summarize recent research progress on important roles of the complex RB-E2F signaling network in the development and effective treatment of gastric cancer.

Dynamic effects of genetic variation on gene expression revealed following hypoxic stress in cardiomyocytes

One life-threatening outcome of cardiovascular disease is myocardial infarction, where cardiomyocytes are deprived of oxygen. To study inter-individual differences in response to hypoxia, we established an in vitro model of induced pluripotent stem cell-derived cardiomyocytes from 15 individuals. We measured gene expression levels, chromatin accessibility, and methylation levels in four culturing conditions that correspond to normoxia, hypoxia, and short- or long-term re-oxygenation. We characterized thousands of gene regulatory changes as the cells transition between conditions. Using available genotypes, we identified 1,573 genes with a cis expression quantitative locus (eQTL) in at least one condition, as well as 367 dynamic eQTLs, which are classified as eQTLs in at least one, but not in all conditions. A subset of genes with dynamic eQTLs is associated with complex traits and disease. Our data demonstrate how dynamic genetic effects on gene expression, which are likely relevant for disease, can be uncovered under stress.

ZBTB7A, a potential biomarker for prognosis and immune infiltrates, inhibits progression of endometrial cancer based on bioinformatics analysis and experiments

Backgroud

ZBTB protein is an important member of the C2H2 zinc finger protein family. As a transcription factor, it is widely involved in the transcriptional regulation of genes, cell proliferation, differentiation, and apoptosis. The ZBTB7A has been largely linked to different kinds of tumors due to its diverse function. However, the value for ZBTB7A in uterine corpus endometrial carcinoma (UCEC) is unclear.

Methods

In our work, we assessed the importance of ZBTB7A in UCEC. Firstly, Using Oncomine and Tumor Immunoassay Resource (TIMER) databases to evaluate the expression of ZBTB7A. Secondly, we explored the co-expression network of ZBTB7A through the cBioPortal online tool, Metascape, and LinkedOmics. TIMER was also used to explore the relationship between ZBTB7A and tumor immune invasion, and to detect the correlation between the ZBTB7A and the marker genes related to immune infiltration. Finally, CCK8, migration, ChIP assays were introduced to partly validate ZBTB7A function in endometrial cancer cells.

Results

We found the ZBTB7A expression in TIMER was associated with various cancers, especially UCEC. The decreased expression of ZBTB7A was markedly related to the stage and prognosis of UCEC. Furthermore, ZBTB7A was also related to the expression of various immune markers such as Neutrophils, Dendritic cell, T cell (general), Th1, Th2, and Treg. Finally, we verified that ZBTB7A repressed E2F4 transcription and inhibited cells proliferation and migration. These results indicate that ZBTB7A may play a vital role in regulating immune cell infiltration in UCEC, and is a valuable prognostic marker.

Conclusions

In summary, we demonstrate that ZBTB7A is notably downregulated in UCEC, plays a vital role in regulating immune cell infiltration, possesses diagnostic and prognostic values and attenuates E2F4 transcription and cell proliferation, migration in vitro.

Resveratrol Attenuates High Glucose-Induced Vascular Endothelial Cell Injury by Activating the E2F3 Pathway

Type 2 diabetes mellitus (T2DM) is the most common metabolic disease. High glucose-induced macrovascular disease and microangiopathy are major complications of diabetes. E2F3, a member of the E2F transcription factor family, is closely related to cardiovascular diseases. Resveratrol, a nonflavonoid polyphenolic compound widely found in plants, has been shown to have cardiovascular protection. However, there are few studies on whether resveratrol can effectively treat diabetic angiopathy, and the specific mechanism involved needs further study. This study investigated whether E2F3 transcription factors are involved in the process of vascular endothelial injury induced by high glucose and observed its effects on the proliferation of vascular endothelial cells. Then, it analyzed whether resveratrol can inhibit high glucose-induced vascular endothelial cell injury by regulating the E2F3 pathway. We demonstrated that the expression level of the E2F3 transcription factor was significantly inhibited in high glucose state. Resveratrol inhibited high glucose-induced vascular endothelial cell injury by upregulating the E2F3 pathway. High glucose can induce vascular endothelial injury by inhibiting E2F3 gene expression, while resveratrol can inhibit high glucose-induced vascular endothelial injury by activating the E2F3 pathway.

Molecular cloning, expression, and characterization of E2F transcription factor 4 from Antheraea pernyi

The E2F transcription factor family is distributed widely in eukaryotes and has been well studied among mammals. In the present study, the E2F transcription factor 4 (E2F4) gene was isolated from fat bodies of Antheraea pernyi and sequenced. E2F4 comprised a 795 bp open reading frame encoding a deduced amino acid sequence of 264 amino acid residues. The recombinant protein was expressed in Escherichia coli (Transetta DE3), and anti-E2F4 antibodies were prepared. The deduced amino acid sequence displayed significant homology to an E2F4-like protein from Bombyx mori L. Quantitative real-time polymerase chain reaction analysis revealed that E2F4 expression was highest in the integument, followed by the fat body, silk glands, and haemocytes. The expression of E2F4 was upregulated in larvae challenged by bacterial (Escherichia coli, Micrococcus luteus), viral (nuclear polyhedrosis virus), and fungal (Beauveria bassiana) pathogens. These observations indicated that E2F4 is an inducible protein in the immune response of A. pernyi and probably in other insects.

Identification of target genes downstream of semaphorin6A/PlexinA2 signaling in zebrafish

BACKGROUND

Semaphorin (Sema)/Plexin (Plxn) signaling is important for many aspects of neuronal development, however, the transcriptional regulation imposed by this signaling pathway is unknown. Previously, we identified an essential role for Sema6A/PlxnA2 signaling in regulating proliferation and cohesion of retinal precursor cells (RPCs) during early eye development. This study used RNA isolated from control, Sema6A-deficient and PlxnA2-deficient zebrafish embryos in a microarray analysis to identify genes that were differentially expressed when this signaling pathway was disrupted.

RESULTS

We uncovered a set of 58 transcripts, and all but 1 were up-regulated in both sema6A and plxnA2 morphants. We validated gene expression changes in subset of candidates that are suggested to be involved in proliferation, migration or neuronal positioning. We further functionally evaluated one gene, rasl11b, as contributing to disrupted proliferation in sema6A and plxna2 morphants. Our results suggest rasl11b negatively regulates proliferation of RPCs in the developing zebrafish eye.

CONCLUSIONS

Microarray analysis has generated a resource of target genes downstream of Sema6A/PlxnA2 signaling, which can be further investigated to elucidate the downstream effects of this well-studied neuronal and vascular guidance signaling pathway. Developmental Dynamics 246:539-549, 2017. © 2017 Wiley Periodicals, Inc.

Understanding cardiomyocyte proliferation: an insight into cell cycle activity

Cardiomyocyte proliferation and regeneration are key to the functional recovery of myocardial tissue from injury. In the recent years, studies on cardiomyocyte proliferation overturned the traditional belief that adult cardiomyocytes permanently withdraw from the cell cycle activity. Hence, targeting cardiomyocyte proliferation is one of the potential therapeutic strategies for myocardial regeneration and repair. To achieve this, a deep understanding of the fundamental mechanisms involved in cardiomyocyte cell cycle as well as differences between neonatal and adult cardiomyocytes' cell cycle activity is required. This review focuses on the recent progress in understanding of cardiomyocyte cell cycle activity at different life stages viz., gestation, birth, and adulthood. The temporal expression/activities of major cell cycle activators (cyclins and CDKs), inhibitors (p21, p27, p57, p16, and p18), and cell-cycle-associated proteins (Rb, p107, and p130) in cardiomyocytes during gestation and postnatal life are described in this review. The influence of different transcription factors and microRNAs on the expression of cell cycle proteins is demonstrated. This review also deals major pathways (PI3K/AKT, Wnt/β-catenin, and Hippo-YAP) associated with cardiomyocyte cell cycle progression. Furthermore, the postnatal alterations in structure and cellular events responsible for the loss of cell cycle activity are also illustrated.

Signaling Pathways in Cardiac Myocyte Apoptosis

Cardiovascular diseases, the number 1 cause of death worldwide, are frequently associated with apoptotic death of cardiac myocytes. Since cardiomyocyte apoptosis is a highly regulated process, pharmacological intervention of apoptosis pathways may represent a promising therapeutic strategy for a number of cardiovascular diseases and disorders including myocardial infarction, ischemia/reperfusion injury, chemotherapy cardiotoxicity, and end-stage heart failure. Despite rapid growth of our knowledge in apoptosis signaling pathways, a clinically applicable treatment targeting this cellular process is currently unavailable. To help identify potential innovative directions for future research, it is necessary to have a full understanding of the apoptotic pathways currently known to be functional in cardiac myocytes. Here, we summarize recent progress in the regulation of cardiomyocyte apoptosis by multiple signaling molecules and pathways, with a focus on the involvement of these pathways in the pathogenesis of heart disease. In addition, we provide an update regarding bench to bedside translation of this knowledge and discuss unanswered questions that need further investigation.

Novel functions for the transcription factor E2F4 in development and disease

The E2F family of transcription factors is a key determinant of cell proliferation in response to extra- and intra-cellular signals. Within this family, E2F4 is a transcriptional repressor whose activity is critical to engage and maintain cell cycle arrest in G0/G1 in conjunction with members of the retinoblastoma (RB) family. However, recent observations challenge this paradigm and indicate that E2F4 has a multitude of functions in cells besides this cell cycle regulatory role, including in embryonic and adult stem cells, during regenerative processes, and in cancer. Some of these new functions are independent of the RB family and involve direct activation of target genes. Here we review the canonical functions of E2F4 and discuss recent evidence expanding the role of this transcription factor, with a focus on cell fate decisions in tissue homeostasis and regeneration.

RB1 dual role in proliferation and apoptosis: cell fate control and implications for cancer therapy

Inactivation of the retinoblastoma (RB1) tumor suppressor is one of the most frequent and early recognized molecular hallmarks of cancer. RB1, although mainly studied for its role in the regulation of cell cycle, emerged as a key regulator of many biological processes. Among these, RB1 has been implicated in the regulation of apoptosis, the alteration of which underlies both cancer development and resistance to therapy. RB1 role in apoptosis, however, is still controversial because, depending on the context, the apoptotic cues, and its own status, RB1 can act either by inhibiting or promoting apoptosis. Moreover, the mechanisms whereby RB1 controls both proliferation and apoptosis in a coordinated manner are only now beginning to be unraveled. Here, by reviewing the main studies assessing the effect of RB1 status and modulation on these processes, we provide an overview of the possible underlying molecular mechanisms whereby RB1, and its family members, dictate cell fate in various contexts. We also describe the current antitumoral strategies aimed at the use of RB1 as predictive, prognostic and therapeutic target in cancer. A thorough understanding of RB1 function in controlling cell fate determination is crucial for a successful translation of RB1 status assessment in the clinical setting.

The Histone Demethylase PHF8 Is Essential for Endothelial Cell Migration

Epigenetic marks critically control gene expression and thus the cellular activity state. The functions of many epigenetic modifiers in the vascular system have not yet been studied. We screened for histone modifiers in endothelial cells and observed a fairly high expression of the histone plant homeodomain finger protein 8 (PHF8). Given its high expression, we hypothesize that this histone demethylase is important for endothelial cell function. Overexpression of PHF8 catalyzed the removal of methyl-groups from histone 3 lysine 9 (H3K9) and H4K20, whereas knockdown of the enzyme increased H3K9 methylation. Knockdown of PHF8 by RNAi also attenuated endothelial proliferation and survival. As a functional readout endothelial migration and tube formation was studied. PHF8 siRNA attenuated the capacity for migration and developing of capillary-like structures. Given the impact of PHF8 on cell cycle genes, endothelial E2F transcription factors were screened, which led to the identification of the gene repressor E2F4 to be controlled by PHF8. Importantly, PHF8 maintains E2F4 but not E2F1 expression in endothelial cells. Consistently, chromatin immunoprecipitation revealed that PHF8 reduces the H3K9me2 level at the E2F4 transcriptional start site, demonstrating a direct function of PHF8 in endothelial E2F4 gene regulation. Conclusion: PHF8 by controlling E2F4 expression maintains endothelial function.

Interplay between the E2F pathway and β-adrenergic signaling in the pathological hypertrophic response of myocardium

The E2F/Pocket protein (Rb) pathway regulates cell growth, differentiation, and death by modulating gene expression. We previously examined this pathway in the myocardium via manipulation of the unique E2F repressor, E2F6, which is believed to repress gene activity independently of Rb. Mice with targeted expression of E2F6 in postnatal myocardium developed dilated cardiomyopathy (DCM) without hypertrophic growth. We assessed the mechanisms of the apparent failure of compensatory hypertrophic growth as well as their response to the β-adrenergic agonist isoproterenol. As early as 2 weeks, E2F6 transgenic (Tg) mice present with dilated thinner left ventricles and significantly reduced ejection fraction and fractional shortening which persists at 6 weeks of age, but with no apparent increase in left ventricle weight: body weight (LVW:BW). E2F6-Tg mice treated with isoproterenol (6.1 mg/kg/day) show double the increase in LVW:BW than their Wt counterparts (32% vs 16%, p-value: 0.007). Western blot analysis revealed the activation of the adrenergic pathway in Tg heart tissue under basal conditions with ~2-fold increase in the level of β2-adrenergic receptors (p-value: 8.9E-05), protein kinase A catalytic subunit (PKA-C) (p-value: 0.0176), activated c-Src tyrosine-protein kinase (p-value: 0.0002), extracellular receptor kinase 2 (ERK2) (p-value: 0.0005), and induction of the anti-apoptotic protein Bcl2 (p-value 0. 0.00001). In contrast, a ~60% decrease in the cardiac growth regulator: AKT1 (p-value 0.0001) and a ~four fold increase in cyclic AMP dependent phosphodiesterase 4D (PDE4D), the negative regulator of PKA activity, were evident in the myocardium of E2F6-Tg mice. The expression of E2F3 was down-regulated by E2F6, but was restored by isoproterenol. Further, Rb expression was down-regulated in Tg mice in response to isoproterenol implying a net activation of the E2F pathway. Thus the unique regulation of E2F activity by E2F6 renders the myocardium hypersensitive to adrenergic stimulus resulting in robust hypertrophic growth. These data reveal a novel interplay between the E2F pathway, β2-adrenergic/PKA/PDE4D, and ERK/c-Src axis in fine tuning the pathological hypertrophic growth response. E2F6 deregulates E2F3 such that pro-hypertrophic growth and survival are enhanced via β2-adrenergic signaling however this response is outweighed by the induction of anti-hypertrophic signals so that left ventricle dilation proceeds without any increase in muscle mass.

Regulation of the human ABCB10 gene by E2F transcription factors

Here, we report for the first time a functional study of transcriptional regulation of the human ABCB10 gene. We cloned a functional promoter sequence, and then showed that E2F2, E2F3 and E2F4 can activate transcription from the ABCB10 promoter. We identified sites responsible for this activation and confirmed direct binding of E2F4 to these sites in EMSA and ChIP assays. Finally, by silencing the expression of E2F factors we demonstrated their importance in maintenance of the basal ABCB10 expression. This study provides important atypical examples of E2F4 being a transcriptional activator rather than repressor as well as directly binding to a promoter and regulating it through an alternative and classical DNA consensus response element sequences. It also provides a mechanistic link between E2F4 and ABCB10, both of which are involved in the same physiological phenomena: erythroid lineage differentiation and maturation as well as protection against cardiomyocyte cell death.

Dysregulation of histone acetyltransferases and deacetylases in cardiovascular diseases

Cardiovascular disease (CVD) remains a leading cause of mortality worldwide despite advances in its prevention and management. A comprehensive understanding of factors which contribute to CVD is required in order to develop more effective treatment options. Dysregulation of epigenetic posttranscriptional modifications of histones in chromatin is thought to be associated with the pathology of many disease models, including CVD. Histone acetyltransferases (HATs) and deacetylases (HDACs) are regulators of histone lysine acetylation. Recent studies have implicated a fundamental role of reversible protein acetylation in the regulation of CVDs such as hypertension, pulmonary hypertension, diabetic cardiomyopathy, coronary artery disease, arrhythmia, and heart failure. This reversible acetylation is governed by enzymes that HATs add or HDACs remove acetyl groups respectively. New evidence has revealed that histone acetylation regulators blunt cardiovascular and related disease states in certain cellular processes including myocyte hypertrophy, apoptosis, fibrosis, oxidative stress, and inflammation. The accumulating evidence of the detrimental role of histone acetylation in cardiac disease combined with the cardioprotective role of histone acetylation regulators suggests that the use of histone acetylation regulators may serve as a novel approach to treating the millions of patients afflicted by cardiac diseases worldwide.