E2F Family Of Transcription Factors Research Articles

A bioinformatics analysis for diagnostic roles of the E2F family in esophageal cancer.

Esophageal cancer (EC) is the eighth most commonly occurring cancer worldwide and the sixth leading cause of cancer-related deaths. The therapeutic effect of EC patients is not ideal, and new biomarkers are needed to guide diagnosis and prognosis of EC patients. E2F family transcription factors are among the most important links in the cell cycle regulatory network. E2Fs dysregulation not only promotes the early stages of tumor development but also the progression of benign tumors to malignant tumors. E2F is expected to be a new biomarker. The prognostic significance of the E2F family in EC requires further research. We analyzed The Cancer Genome Atlas (TCGA), Gene Expression Profiling Interactive Analysis (GEPIA), and GeneMANIA databases to obtain RNA-sequencing data and clinical data. The clinical data included age, gender, race, stage, type, status, etc. The prognosis outcome included overall survival (OS) and progression-free interval (PFI). Subsequently, we conducted further research on gene expressions, enrichment analysis, interaction network, and prognostic values by R software, containing ggplot2, ComplexHeatmap, DESeq2, pROC R package, based on t-test, Wilcoxon rank sum test, Spearman rank correlation analysis, log-rank test and COX model. We found that mRNA transcription levels of E2F1, E2F3-8 were more highly expressed in esophageal carcinoma (ESCA) tissues than in normal tissues. E2F8 expression was correlated with tumor stage [Pr(>F)=0.00856]. E2F-related genes played a role in development and differentiation, and were prevalent in the endoplasmic reticulum lumen, Golgi lumen, and lipoprotein particle, catalyzing translation activities and lipid metabolism. Each gene was found to be related to each other to some degree. The GeneMANIA network analysis revealed links between E2Fs and other genes. We compared the correlations between 24 kinds of tumor-infiltrating immune cells and E2Fs. E2F1 (AUC =0.945, CI: 0.890-1.000) and E2F7 (AUC =0.958, CI: 0.920-0.996) exhibited higher predictive power accuracy. However, only E2F7 was closely related to OS [HR =1.91 (1.16-3.16), P=0.011]. We discover that E2F7 is a prognostic biomarker. E2F family may take part in the development of EC through lipid metabolism pathways, which is helpful to predict the prognosis of EC patients and guide accurate diagnosis and treatment.

PP2A-B55 and its adapter proteins IER2 and IER5 regulate the activity of RB family proteins and the expression of cell cycle-related genes.

The retinoblastoma (RB) tumour suppressor protein regulates cell proliferation, motility, differentiation and apoptosis. The phosphorylation state of RB is modulated by kinases and phosphatases, and RB exhibits phosphorylation-sensitive interactions with E2F family transcription factors. Here, we characterize RB dephosphorylation by protein phosphatase 2A (PP2A). The growth factor-inducible immediate early response (IER) proteins IER2 and IER5 possess an adapter-like function in which IER proteins bind to both PP2A and its target proteins and enhance PP2A activity towards the proteins. IER2 interacts with RB and facilitates dephosphorylation of RB at T821/T826 by PP2A. In IER2 knockdown cells, elevated phosphorylation of RB resulted in reduced binding of RB to the promoters and derepression of cyclin D1 and p21. IER5 binds to both RB and RB-like 1 (p107/RBL1), enhances dephosphorylation of these proteins by PP2A and represses the expression of various cell cycle-related genes. However, IER2-regulated dephosphorylation at T821/T826 is not necessary for the repression function of RB in cell mobility-related gene expression. Our data identify PP2A adapter proteins as critical regulators of RB family proteins and suggest that the phosphorylation status of RB differentially affects gene expression.

Metformin Improves the Senescence of Renal Tubular Epithelial Cells in a High-Glucose State Through E2F1.

Diabetic kidney disease is a major cause of chronic kidney condition and the most common complication of diabetes. The cellular senescence participates in the process of diabetic kidney disease, but the specific mechanism is not yet clear. Cell cycle-related protein E2F transcription factor 1 (E2F1) is a member of the E2F transcription factor family, it plays a key role in cellular damage under HG conditions. In this study, we explored whether metformin improves a high-glucose-induced senescence and fibrosis of renal tubular epithelial cells through cell cycle-related protein E2F1. In the in vivo experiments, the recombinant adeno-associated virus (AAV-shE2F1) knockdown E2F1 gene was injected into the tail vein of 16-weeks-old db/db mice for 8 weeks. The 16-week-old db/db mice were administered metformin (260 mg/kg/d) continuously for 8 weeks. The normal control group (NC) and diabetic model group (DM) were set up simultaneously. Mice renal tubular epithelial cells (mRTECs) were cultured in vitro. The cells were randomly divided into the following groups: normal glucose (NG, containing 5.5 mmol/L glucose), high glucose group (HG, containing 30 mmol/L glucose), NG/HG metformin intervention group (NG/HG + Met), NG/HG negative control siRNA transfection group (NG/HG + Control), NG/HG E2F1 siRNA transfection group (NG/HG + siRNA E2F1), HG metformin intervention and overexpression E2F1 plasmid transfection group (HG + Met + overexpress-E2F1). The expression of related indexes were detected by Western blot, real-time polymerase chain reaction (PCR), immunohistochemistry, and immunofluorescence. The results showed that E2F1 knockdown or metformin reduces the degree of renal fibrosis, DNA damage, and cellular senescence in the DM group; metformin also reduced the expression of E2F1. If E2F1 was overexpressed, the effects of metformin in delaying fibrosis and reducing DNA damage and cellular senescence could be weakened. Thus, metformin alleviates high-glucose-induced senescence and fibrosis of renal tubular epithelial cells by downregulating the expression of E2F1.

Defining the molecular underpinnings controlling cardiomyocyte proliferation.

Shortly after birth, mammalian cardiomyocytes (CM) exit the cell cycle and cease to proliferate. The inability of adult CM to replicate renders the heart particularly vulnerable to injury. Restoration of CM proliferation would be an attractive clinical target for regenerative therapies that can preserve contractile function and thus prevent the development of heart failure. Our review focuses on recent progress in understanding the tight regulation of signaling pathways and their downstream molecular mechanisms that underly the inability of CM to proliferate in vivo. In this review, we describe the temporal expression of cell cycle activators e.g., cyclin/Cdk complexes and their inhibitors including p16, p21, p27 and members of the retinoblastoma gene family during gestation and postnatal life. The differential impact of members of the E2f transcription factor family and microRNAs on the regulation of positive and negative cell cycle factors is discussed. This review also highlights seminal studies that identified the coordination of signaling mechanisms that can potently activate CM cell cycle re-entry including the Wnt/Ctnnb1, Hippo, Pi3K-Akt and Nrg1-Erbb2/4 pathways. We also present an up-to-date account of landmark studies analyzing the effect of various genes such as Argin, Dystrophin, Fstl1, Meis1, Pitx2 and Pkm2 that are responsible for either inhibition or activation of CM cell division. All these reports describe bona fide therapeutically targets that could guide future clinical studies toward cardiac repair.

Retinoblastoma-E2F Transcription Factor Interplay Is Essential for Testicular Development and Male Fertility.

The retinoblastoma (RB) protein family members (pRB, p107 and p130) are key regulators of cell cycle progression, but also play crucial roles in apoptosis, and stem cell self-renewal and differentiation. RB proteins exert their effects through binding to E2F transcription factors, which are essential developmental and physiological regulators of tissue and organ homeostasis. According to the canonical view, phosphorylation of RB results in release of E2Fs and induction of genes needed for progress of the cell cycle. However, there are eight members in the E2F transcription factor family with both activator (E2F1-3a) and repressor (E2F3b–E2F8) roles, highlighting the functional diversity of RB-E2F pathway. In this review article we summarize the data showing that RB-E2F interaction is a key cell-autonomous mechanism responsible for establishment and maintenance of lifelong male fertility. We also review the expression pattern of RB proteins and E2F transcription factors in the testis and male germ cells. The available evidence supports that RB and E2F family members are widely and dynamically expressed in the testis, and they are known to have versatile roles during spermatogenesis. Knowledge of the function and significance of RB-E2F interplay for testicular development and spermatogenesis comes primarily from gene knock-out (KO) studies. Several studies conducted in Sertoli cell-specific pRB-KO mice have demonstrated that pRB-mediated inhibition of E2F3 is essential for Sertoli cell functional maturation and cell cycle exit, highlighting that RB-E2F interaction in Sertoli cells is paramount to male fertility. Similarly, ablation of either pRB or E2F1 in the germline results in progressive testicular atrophy due to germline stem cell (GSC) depletion, emphasizing the importance of proper RB-E2F interplay for germline maintenance and lifelong sperm production. In summary, while balanced RB-E2F interplay is essential for cell-autonomous maintenance of GSCs and, the pRB-E2F3 system in Sertoli cells is critical for providing GSC niche thus laying the basis for spermatogenesis.

ATR activity controls stem cell quiescence via the cyclin F–SCF complex

A key property of adult stem cells is their ability to persist in a quiescent state for prolonged periods of time. The quiescent state is thought to contribute to stem cell resilience by limiting accumulation of DNA replication–associated mutations. Moreover, cellular stress response factors are thought to play a role in maintaining quiescence and stem cell integrity. We utilized muscle stem cells (MuSCs) as a model of quiescent stem cells and find that the replication stress response protein, ATR (Ataxia Telangiectasia and Rad3-Related), is abundant and active in quiescent but not activated MuSCs. Concurrently, MuSCs display punctate RPA (replication protein A) and R-loop foci, both key triggers for ATR activation. To discern the role of ATR in MuSCs, we generated MuSC-specific ATR conditional knockout (ATRcKO) mice. Surprisingly, ATR ablation results in increased MuSC quiescence exit. Phosphoproteomic analysis of ATRcKO MuSCs reveals enrichment of phosphorylated cyclin F, a key component of the Skp1–Cul1–F-box protein (SCF) ubiquitin ligase complex and regulator of key cell-cycle transition factors, such as the E2F family of transcription factors. Knocking down cyclin F or inhibiting the SCF complex results in E2F1 accumulation and in MuSCs exiting quiescence, similar to ATR-deficient MuSCs. The loss of ATR could be counteracted by inhibiting casein kinase 2 (CK2), the kinase responsible for phosphorylating cyclin F. We propose a model in which MuSCs express cell-cycle progression factors but ATR, in coordination with the cyclin F–SCF complex, represses premature stem cell quiescence exit via ubiquitin–proteasome degradation of these factors.

Curcumin selectively induces colon cancer cell apoptosis and S cell cycle arrest by regulates Rb/E2F/p53 pathway

ObjectiveCurcumin is a natural active product extracted from turmeric, has been reported to have anticancer properties against various tumors. However, the effect of curcumin on colon cancer remains still unclear. Our aimed to investigate the anti-colon cancer properties of curcumin in vitro, and determine the molecular mechanisms underlying these effects. MethodsViability assays including CCK8 and LDH were used to measure cell proliferation. Flow cytometry was performed to detect cell apoptosis and cell cycle distribution. qRT-PCR and Western blotting was used for measuring genes/protein expression/activation in apoptotic and pro-carcinogenic cellular signaling pathways. Finally, the results were confirmed using a xenograft tumor model that comprised of mice. ResultsIn vitro, Our data showed that curcumin preferentially and, in a dose, dependent way inhibited colon cancer cells proliferation, but was not toxic to normal colon mucosa epithelial cells. Curcumin induced apoptosis through a p53-mediated mechanism, pro-apoptotic proteins Bax was upregulated, and cell cycle arrest at S phase by inhibited the expression of cell cycle related proteins, phosphorylation of Rb signaling pathway proteins and E2F family transcription factors. Finally, the mouse xenograft model confirmed the suppressive effect of curcumin on tumor growth in vivo. ConclusionCurcumin may be a potential strategy for the treatment of colon cancer.

Single-cell RNA-seq reveals heterogeneity in hiPSC-derived muscle progenitors and E2F family as a key regulator of proliferation.

Human pluripotent stem cell-derived muscle progenitor cells (hiPSC-MuPCs) resemble fetal-stage muscle progenitor cells and possess in vivo regeneration capacity. However, the heterogeneity of hiPSC-MuPCs is unknown, which could impact the regenerative potential of these cells. Here, we established an hiPSC-MuPC atlas by performing single-cell RNA sequencing of hiPSC-MuPC cultures. Bioinformatic analysis revealed four cell clusters for hiPSC-MuPCs: myocytes, committed, cycling, and noncycling progenitors Using FGFR4 as a marker for noncycling progenitors and cycling cells and CD36 as a marker for committed and myocyte cells, we found that FGFR4+ cells possess a higher regenerative capacity than CD36+ cells. We also identified the family of E2F transcription factors are key regulators of hiPSC-MuPC proliferation. Our study provides insights on the purification of hiPSC-MuPCs with higher regenerative potential and increases the understanding of the transcriptional regulation of hiPSC-MuPCs.

Evaluation and Comparison of PBK and E2F7 Gene Expression Between Early and Advanced Stages of Colorectal Cancer

Background and Aim PBK is a mitogen-activated protein kinase (MAPKK) among MEK1/2 and MEK7 and can phosphorylate P38, JNK, and ERK in many cellular functions. The E2F transcription factor family also belongs to a class of cellular regulators acting as oncogenes and tumor suppressors. This study aims to investigate the expression of PBK and E2F7 in the early stages of colorectal cancer (CRC) compared to advanced stages based on the experimental and TCGA (The Cancer Genome Atlas) database. Methods & Materials A total of 32 tissue samples of patients with CRC with the approval of a pathobiologist were collected according to the examination and criteria reported from different stages. After RNA extraction and cDNA synthesis, the RT-qPCR technique was used to evaluate the expression of the desired genes in the study groups. A receiver operating characteristic (ROC) curve analysis was also used to determine the ability of each of the selected genes to differentiate the two populations: stage I+II and stage III+IV. Ethical Considerations In all stages of this research, codes of ethics of research and publication were observed. Results In this study, it was shown that the expression of PBK and E2F7 significantly increased in stage I+II samples compared to stage III+IV. These data were confirmed by laboratory results and information extracted from the TCGA database. Also, based on the area under curve obtained from the ROC curves, these two genes are significantly distinguishable between stage I+II and III+IV populations in CRC. Conclusion According to the results of this study, PBK and E2F7 genes are good markers in the diagnosis of CRC.

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.

E2F transcription factor 1 is involved in the phenotypic modulation of esophageal squamous cell carcinoma cells via microRNA-375

ABSTRACT E2F family of transcription factors modulates multiple cellular functions associated with cell cycle and apoptosis. Here, we focused on the relevance of E2F1 to esophageal squamous cell carcinoma (ESCC) and identification of E2F1-mediated network in this study. Query of Gene Expression Omnibus database revealed that E2F1 was the core gene that was upregulated in ESCC. E2F1 downregulation inhibited ESCC cell activity. microRNA (miR)-375 was confirmed to be a downstream target of E2F1. E2F1 bound to miR-375 promoter and inhibited miR-375 transcription. Moreover, miR-375 inhibitor mitigated the repressive impacts of si-E2F1 on ESCC cells in part. Further study showed that sestrin 3 (SESN3) could interact with miR-375, and its knockdown annulled the stimulative effect of miR-375 inhibitor on ESCC development. Finally, E2F1 and SESN3 downregulation inhibited the phosphatidylinositol 3 kinase (PI3K)/AKT pathway activity in cells, while miR-375 inhibitor promoted PI3K/AKT pathway activation. These findings suggest that E2F1 inhibited miR-375 expression and promoted SESN3 expression to activate the PI3K/AKT pathway in ESCC.

Cancer cells with defective RB and CDKN2A are resistant to the apoptotic effects of rapamycin

Inhibition of mammalian target of rapamycin complex 1 (mTORC1) with rapamycin in the absence of transforming growth factor-β (TGFβ) signaling induces apoptosis in many cancer cell lines. In the presence of TGFβ, rapamycin induces G1 cell cycle arrest; however, in the absence of TGFβ, cells do not arrest in G1 and progress into S-phase where rapamycin is cytotoxic rather than cytostatic. However, we observed that DU145 prostate and NCI-H2228 lung cancer cells were resistant to the cytotoxic effect of rapamycin. Of interest, the rapamycin-resistant DU145 and NCI-H2228cells have mutations in the RB and CDKN2A tumor suppressor genes. The gene products of RB and CDKN2A (pRb and p14ARF) suppress E2F family transcription factors that promote cell cycle progression from G1 into S. Restoration of wild type RB or inhibition of E2F activity in DU145 and NCI-H2228cells led to rapamycin sensitivity. These data provide evidence that the combination of mutant RB and mutant CDKN2A in cancer cells leads to rapamycin resistance, which has implications for precision medicine approaches to anti-cancer therapies.

Single Cell Characterization of Myeloma and Its Precursor Conditions Reveals Transcriptional Signatures of Early Tumorigenesis

Our understanding of disease progression in multiple myeloma (MM) and its precursor conditions, monoclonal gammopathy of undetermined significance (MGUS) and smoldering multiple myeloma (SMM), is classically founded on bulk analysis studies. Low disease burden at the precursor stages has precluded comprehensive analyses of the transcriptomic events underlying malignant transformation. Here, we use single-cell RNA sequencing data from 29,387 bone marrow plasma cells from 26 patients with MGUS, SMM, or MM and 9 healthy controls to characterize the transcriptional transformation at each step of progression.Due to varying disease burdens, many samples contained a mixture of healthy and neoplastic plasma cells. We leveraged this impurity to perform a patient-specific characterization of the disease, comparing each patient's neoplastic and healthy plasma cells. This approach isolated the disease phenotype in each patient, which is usually confounded by biological and technical variability when comparing tumors to samples from healthy donors.We found that neoplastic cells from patients with MGUS and SMM already exhibit phenotypic changes similar to those of advanced myeloma. We observed upregulation of genes corresponding to known MM subtypes, such as CCND1 in patients with t(11;14) translocations and other known driver genes such as HIST1H1C. We also found universal downregulation of certain genes such as CD27, a member of the tumor necrosis factor receptor family associated with the differentiation of B cells into plasma cells, which may signify a common loss of a normal plasma phenotype across samples with different driver events and stages.Pathway analysis of differentially expressed genes further revealed that biological pathways related to myeloma were altered as early as MGUS. We observed that SMM patients with hyperdiploidy exhibit upregulation of ribosomal proteins, as reported in advanced disease. Upregulated genes in select MGUS and SMM samples were enriched for the eukaryotic translation initiation factor 3 (eIF3) complex, which plays important roles in translation, as well as proteasome activity, a function central to the survival of MM and targeted by therapies such as bortezomib. We observed enrichment of the E2F family of transcription factors in MGUS and SMM samples; these are master regulators of proliferation that have been suggested as therapeutic targets in myeloma. Five samples were enriched for genes associated with extracellular exosomes, which has been reported to play an important role in cancer cell signaling and to contribute to osteolysis and drug resistance in MM. Pathway enrichment of genes downregulated in neoplastic cell populations revealed weakened response to endoplasmic reticulum and oxidative stress, presumably allowing myeloma cells to tolerate high volumes of abnormal protein production without apoptosing.To further identify shared gene expression patterns across samples, we employed a Bayesian Non-Negative Matrix Factorization method to decompose our data into 31 gene signatures that capture its variability. In addition to recovering signatures corresponding to known MM subtypes, demonstrating that our method captures cohesive transcriptional networks, we find signatures that capture disease biology shared across subtypes. Most notably, we identified a signature that is active in healthy plasma cells across disease stages and dramatically lost in MM and precursor cells. The top genes in this signature include CD27 and CD79A, which are associated with the B cell lineage and whose downregulation may signify dedifferentiation of premalignant cells as early as MGUS, and JSRP1, CTSH, and HCST, genes as of yet unreported to be involved in plasma and MM cell biology. This phenotype would be obscured at early disease stages by bulk analysis. We validated the discovery and behavior of this signature in an external single-cell dataset from Ledergor et al. (Nature Medicine 2018).In summary, using single-cell RNA sequencing, we discovered that canonical MM pathways are altered as early as MGUS and identified a signature of genes which distinguishes healthy and neoplastic cells even at early disease stages. Our identification of patient-specific transcriptional changes as early as MGUS paves the way for future work exploring personalized treatment approaches prior to malignant disease. DisclosuresHaradhvala: Constellation Pharmaceuticals a MorphoSys Company: Consultancy. Zavidij: Constellation Pharmaceuticals: Current Employment. Sontag: curai health: Current holder of individual stocks in a privately-held company; Takeda Pharmaceuticals: Research Funding; Genentech: Research Funding; IBM: Research Funding. Ghobrial: AbbVie, Adaptive, Aptitude Health, BMS, Cellectar, Curio Science, Genetch, Janssen, Janssen Central American and Caribbean, Karyopharm, Medscape, Oncopeptides, Sanofi, Takeda, The Binding Site, GNS, GSK: Consultancy. Getz: IBM, Pharmacyclics: Research Funding; Scorpion Therapeutics: Consultancy, Current holder of individual stocks in a privately-held company, Membership on an entity's Board of Directors or advisory committees.

Comprehensive Analysis of Regulatory Factors and Immune-Associated Patterns to Decipher Common and BRCA1/2 Mutation-Type-Specific Critical Regulation in Breast Cancer.

Background: BRCA1/2 mutations are closely related to high lifetime risk of breast cancer (BC). The objective of this study was to identify the genes, regulators, and immune-associated patterns underlying disease pathology in BC with BRCA1/2 somatic mutations and their associations with clinical traits.Methods: RNA sequencing data and clinical information from The Cancer Genome Atlas (TCGA; N = 36 BRCA1-mutant BC; N = 49 BRCA2-mutant BC; and N = 117 BRCA1/2-wild-type BC samples) were used for discovery, which included consensus network analysis, function enrichment, and analysis of hub genes; other TCGA data (N = 117 triple-negative BC) and two Gene Expression Omnibus database expression profiles were used as validation cohorts.Results: Consensus network analysis helped to identify specific co-expressed modules that showed positive correlations with tumor stage, number of positive lymph nodes, and margin status in BRCA1/2-mutant BC but lacking correlations in BRCA1/2-wild-type BC. Functional enrichment suggested potential mechanisms in BRCA1/2 carriers that could regulate the cell cycle, immune response, cellular metabolic processes, and cell migration, via enriched pathways including p53 and JAK–STAT signaling. Consensus network analysis identified the specific and common carcinogenic mechanisms involving BRCA mutations. Regulators cross-linking these modules include E2F or IRF transcription factor family, associated with cell cycle or immune response regulation module, respectively. Eight hub genes, including ISG15, BUB1, and TTK, were upregulated in several BRCA1/2-mutant BC datasets and showed prognostic value in BC. Furthermore, their genetic expression was related to higher levels of immune infiltration in BRCA1/2-mutant BC, which manifested as recruitment of T helper cells (Th1 cells), follicular helper T cells, and regulatory T cells, and T cell exhaustion. Moreover, important indicators for evaluation of BC immunotherapy, tumor mutational burden and neoantigen load also positively correlated with expression of some hub genes.Conclusion: We constructed a BRCA1/2 mutation-type-specific co-expressed gene network with related transcription factors and immune-associated patterns that could regulate and influence tumor metastasis and immune microenvironment, providing novel insights into the pathological process of this disease and the corresponding BRCA mutations.

The Role of Retinoblastoma Protein in Cell Cycle Regulation: An Updated Review.

Selected transcription factors have critical roles to play in organism survival by regulating the expression of genes that control the adaptations needed to handle stress conditions. The retinoblastoma (Rb) protein coupled with the E2F transcription factor family was demonstrated to have roles in controlling the cell cycle during freezing and associated environmental stresses (anoxia, dehydration). Rb phosphorylation or acetylation at different sites provides a mechanism for repressing cell proliferation that is under the control of E2F transcription factors in animals facing stresses that disrupt cellular energetics or cell volume controls. Other central regulators of the cell cycle including Cyclins, Cyclin-dependent kinases (Cdks), and checkpoint proteins detect DNA damage or any improper replication, blocking further progression of cell cycle and interrupting cell proliferation. This review provides an insight into the molecular regulatory mechanisms of cell cycle control, focusing on Rb-E2F along with Cyclin-Cdk complexes typically involved in development and differentiation that need to be regulated in order to survive extreme cellular stress.

Differential regulation of mammalian and avian ATOH1 by E2F1 and its implication for hair cell regeneration in the inner ear

The mammalian inner ear has a limited capacity to regenerate its mechanosensory hair cells. This lack of regenerative capacity underlies the high incidence of age-related hearing loss in humans. In contrast, non-mammalian vertebrates can form new hair cells when damage occurs, a mechanism that depends on re-activation of expression of the pro-hair cell transcription factor Atoh1. Here, we show that members of the E2F transcription factor family, known to play a key role in cell cycle progression, regulate the expression of Atoh1. E2F1 activates chicken Atoh1 by directly interacting with a cis-regulatory region distal to the avian Atoh1 gene. E2F does not activate mouse Atoh1 gene expression, since this regulatory element is absent in mammals. We also show that E2F1 expression changes dynamically in the chicken auditory epithelium during ototoxic damage and hair cell regeneration. Therefore, we propose a model in which the mitotic regeneration of non-mammalian hair cells is due to E2F1-mediated activation of Atoh1 expression, a mechanism which has been lost in mammals.

Prognostic Value of E2F Transcription Factor Expression in Pancreatic Adenocarcinoma.

BackgroundPancreatic adenocarcinoma (PAAD) is one of the deadliest types of cancer. In the early stages, patients often have atypical symptoms, making diagnosis difficult. The prognosis of diagnosed patients is very poor and treating PAAD is challenging. Therefore, determining reliable risk factors related to PAAD development is critical for improving patient prognosis. E2F family transcription factors (TFs) are essential regulators of DNA synthesis and cell cycle progression in eukaryotic cells, and they have been identified as prognostic biomarkers associated with multiple cancer types. However, further research is necessary to establish the prognostic relevance of these TFs in PAAD patients.Material/MethodsWe assessed PAAD patient transcriptional and outcome data using the TIMER, ONCOMINE, STRING, GEPIA, cBioPortal, Kaplan-Meier Plotter, GSCALite, and starBase databases.ResultsPAAD tumor tissues exhibited increased expression of E2F1/3/5/7/8 relative to that in normal tissues, while the expression of E2F2/3/6/8 was associated with a more advanced tumor stage. Survival analyses indicated that PAAD patients expressing higher levels of E2F1/2/3/7/8 exhibited shorter overall survival (OS) and disease-free survival (DFS) than patients expressing lower levels of these TFs. In addition, E2F4 and E2F6 overexpression was associated with poorer DFS and OS, respectively. We also found that the expression of E2Fs was significantly correlated with immune infiltrates, including CD8+ T cells, CD4+ T cells, B cells, dendritic cells, neutrophils, and macrophages.ConclusionsOur study may provide new insights into the optimal choice of immunotherapy and promising novel targets for therapeutic intervention in PAAD patients.

Emerging Role of E2F Family in Cancer Stem Cells.

The E2F family of transcription factors (E2Fs) consist of eight genes in mammals. These genes encode ten proteins that are usually classified as transcriptional activators or transcriptional repressors. E2Fs are important for many cellular processes, from their canonical role in cell cycle regulation to other roles in angiogenesis, the DNA damage response and apoptosis. A growing body of evidence demonstrates that cancer stem cells (CSCs) are key players in tumor development, metastasis, drug resistance and recurrence. This review focuses on the role of E2Fs in CSCs and notes that many signals can regulate the activities of E2Fs, which in turn can transcriptionally regulate many different targets to contribute to various biological characteristics of CSCs, such as proliferation, self-renewal, metastasis, and drug resistance. Therefore, E2Fs may be promising biomarkers and therapeutic targets associated with CSCs pathologies. Finally, exploring therapeutic strategies for E2Fs may result in disruption of CSCs, which may prevent tumor growth, metastasis, and drug resistance.

BSCI-05. ABL2-HSF1-E2F signaling axis promotes lung adenocarcinoma brain metastasis

Brain metastases are the most common intracranial tumors in adults and are associated with increased patient morbidity and mortality. Limited therapeutic options are currently available for the treatment of brain metastasis. We have identified an actionable signaling pathway utilized by metastatic tumor cells whereby the transcriptional regulator Heat Shock Factor 1 (HSF1) drives a transcriptional program, divergent from its canonical role as the master regulator of the heat shock response, leading to enhanced expression of a subset of E2F transcription factor family gene targets. We showed that HSF1 is required for survival and outgrowth by metastatic lung cancer cells in the brain parenchyma. Unexpectedly, we identified the ABL2 tyrosine kinase as an upstream regulator of HSF1 protein expression, and showed that the Src-homology 3 (SH3) domain of ABL2 directly interacts with HSF1 protein at a non-canonical, proline-independent SH3 interaction motif. Importantly, knockdown of ABL2 impairs expression of HSF1 protein and HSF1-E2F transcriptional gene targets. Notably, we found that pharmacologic inhibition of the ABL kinases using selective ABL allosteric inhibitors, but not ATP-competitive inhibitors, ablates the physical interaction between ABL2 and HSF1, leading to markedly decreased expression of HSF1, E2F1 and E2F8 proteins in brain-metastatic lung cancer cells, and depletion of HSF1-E2F transcriptional targets. These findings highlight potential differences affecting intra- and inter-molecular protein-protein interactions induced by allosteric versus ATP-competitive kinase inhibitors that have important therapeutic implications. Importantly, the targetable nature of the ABL2-HSF1-E2F signaling network identifies ABL allosteric inhibitors as a potentially effective therapy for the treatment of metastatic lung cancers characterized by high expression of HSF1.

A TIMM17A Regulatory Network Contributing to Breast Cancer

BackgroundTranslocase of inner mitochondrial membrane 17A (TIMM17A) is overexpressed in breast cancer (BRCA), and upregulation can increase the aggressiveness of BRCA cells. This study examined the influence of the TIMM17A gene network on BRCA outcome.MethodsExpression levels of TIMM17A were compared between normal and tumor tissues from the OncomineTM database, and the association with patient survival was analyzed using Kaplan–Meier Plotter. Clinical factors influencing TIMM17A expression were studied by UALCAN. cBioPotal was then used to identify genes interacting with TIMM17A, and network relationships were assessed using the R clusterProfiler package. The association between TIMM17A mutation and mRNA expression in BRCA was examined using the LinkFinder application in LinkedOmics, and coexpressed genes were assessed for functional enrichment using the LinkInterpreter application. Furthermore, TIMM17A expression correlation with cell cycle phase distribution was performed by flow cytometry. Finally, the target networks of kinases, microRNAs (miRNAs), and transcription factors were identified using GeneMANIA. The expression and correlation of potential miRNAs and targets were further validated in BRCA cell lines by qRT-PCR.ResultsExpression of TIMM17A was significantly elevated in BRCA compared with normal tissue (p < 0.05), and overexpression was associated with both poor overall survival (OS) and shorter distant metastasis-free survival (DMFS) (p < 0.05). Expression of TIMM17A was not associated with age, sex, BRCA subclass, clinical stage, or patient ethnicity. The coexpressed TIMM17A network was enriched in genes targeted by cell cycle regulators such as CDK1, miR-331, and E2F family transcription factors (FDR < 0.001). Furthermore, flow cytometry revealed a strong association between higher TIMM17A expression and faster cell cycle progression in these BRCA cell lines. In addition, expression of TIMM17A protein was correlated with CDK1 protein expression in BRCA cell lines as measured by western blotting.ConclusionElevated TIMM17A expression accelerates the progression of BRCA, thereby reducing OS and DMFS. The TIMM17A-associated networks identified here provide clues to the molecular pathogenesis of BRCA and potential targets for BRCA treatment.