BCL-2 is a downstream target of ATF5 that mediates the prosurvival function of ATF5 in a cell type-dependent manner

Decreased ATF5 level contributes to improved mitochondrial function in oocytes exposed to vitrification stress

Background

Mitochondrial unfolded protein response (mtUPR) plays an essential role in the response of mitochondria to stress-induced damage. Activating of transcription factor 5 (ATF5) can help to sustain mitochondrial function and regulate organelle recovery under mitochondrial stress. Vitrification is a stressor that disrupts mitochondrial activity and cell homeostasis. However, little is known about the function of ATF5 in response to the extreme biophysical and chemical stresses during oocyte vitrification.

Methods

The expression of ATF5 and mtUPR biomarkers were measured in fresh and vitrified oocytes. Subsequently, oocytes with ATF5 deficiency were constructed by siRNA microinjection, and the function of ATF5 in mitochondrial function and oocyte development were analyzed in vitrified oocytes. Furthermore, transcriptome analysis was performed to uncover the molecular network regulated by ATF5 in response to oocyte vitrification.

Results

In the present study, the mitochondrial membrane potential and ATP levels were decreased in ATF5 knockdown oocytes, in line with the phenotypes observed in vitrified oocytes. In addition, ATF5 knockdown resulted in decreased mitochondrial temperature, reduced unfolded protein levels, abnormal mitochondrial dynamics (fusion and fission), and increased autophagy. Subsequent experiments indicated that mtUPR was suppressed in oocytes with ATF5 knockdown. Interestingly, ATF5 was aberrantly upregulated in oocytes exposed to vitrification stress. Reduced ATF5 expression to a homeostatic level in vitrified oocytes led to accumulated unfolded protein levels and increased mitochondrial membrane potential. Moreover, increased mitochondrial dynamics and an increased germinal vesicle breakdown (GVBD) rate were detected after in vitro maturation. Transcriptome analysis revealed that ATF5 is involved in the vitrification stress response, and ATF5 regulated the in vitro maturation potential in vitrified oocytes through the cAMP-PKA and PI3K/AKT pathways.

Discussion

Our findings indicate that mtUPR was initiated in response to vitrification stimuli, and downregulated ATF5 level to a homeostatic state contributes to improved mitochondrial function in oocytes exposed to vitrification stress. Our results highlight the crucial role of ATF5 in the regulation of mitochondrial function in vitrified oocytes through mediating mtUPR.

ATF family members as therapeutic targets in cancer: From mechanisms to pharmacological interventions

The activating transcription factor (ATF)/ cAMP-response element binding protein (CREB) family represents a large group of basic zone leucine zip (bZIP) transcription factors (TFs) with a variety of physiological functions, such as endoplasmic reticulum (ER) stress, amino acid stress, heat stress, oxidative stress, integrated stress response (ISR) and thus inducing cell survival or apoptosis. Interestingly, ATF family has been increasingly implicated in autophagy and ferroptosis in recent years. Thus, the ATF family is important for homeostasis and its dysregulation may promote disease progression including cancer. Current therapeutic approaches to modulate the ATF family include direct modulators, upstream modulators, post-translational modifications (PTMs) modulators. This review summarizes the structural domain and the PTMs feature of the ATF/CREB family and comprehensively explores the molecular regulatory mechanisms. On this basis, their pathways affecting proliferation, metastasis, and drug resistance in various types of cancer cells are sorted out and discussed. We then systematically summarize the status of the therapeutic applications of existing ATF family modulators and finally look forward to the future prospect of clinical applications in the treatment of tumors by modulating the ATF family.

ATF5 promotes malignant T cell survival through the PI3K/AKT/mTOR pathway in cutaneous T cell lymphoma

Backgrounds

Cutaneous T cell lymphoma (CTCL) is a non-Hodgkin lymphoma characterized by skin infiltration of malignant T cells. The biological overlap between malignant T cells and their normal counterparts has brought obstacles in identifying tumor-specific features and mechanisms, limiting current knowledge of CTCL pathogenesis. Transcriptional dysregulation leading to abnormal gene expression profiles contributes to the initiation, progression and drug resistance of cancer. Therefore, we aimed to identify tumor-specific transcription factor underlying CTCL pathology.

Methods

We analyzed and validated the differentially expressed genes (DEGs) in malignant T cells based on single-cell sequencing data. Clinical relevance was evaluated based on progression-free survival and time to next treatment. To determine the functional importance, lentivirus-mediated gene knockdown was conducted in two CTCL cell lines Myla and H9. Cell survival was assessed by examining cell viability, colony-forming ability, in-vivo tumor growth in xenograft models, apoptosis rate and cell-cycle distribution. RNA sequencing was employed to investigate the underlying mechanisms.

Results

Activating transcription factor 5 (ATF5) was overexpressed in malignant T cells and positively correlated with poor treatment responses in CTCL patients. Mechanistically, ATF5 promoted the survival of malignant T cells partially through the PI3K/AKT/mTOR pathway, and imparted resistance to endoplasmic reticulum (ER) stress-induced apoptosis.

Conclusions

These findings revealed the tumor-specific overexpression of the transcription factor ATF5 with its underlying mechanisms in promoting tumor survival in CTCL, providing new insight into the understanding of CTCL's pathology.

Dpep Inhibits Cancer Cell Growth and Survival via Shared and Context-Dependent Transcriptome Perturbations

Dpep is a cell-penetrating peptide targeting transcription factors ATF5, CEBPB, and CEBPD, and that selectively promotes the apoptotic death of multiple tumor cell types in vitro and in vivo. As such, it is a potential therapeutic. To better understand its mechanism of action, we used PLATE-seq to compare the transcriptomes of six cancer cell lines of diverse origins before and after Dpep exposure. This revealed a context-dependent pattern of regulated genes that was unique to each line, but that exhibited a number of elements that were shared with other lines. This included the upregulation of pro-apoptotic genes and tumor suppressors as well as the enrichment of genes associated with responses to hypoxia and interferons. Downregulated transcripts included oncogenes and dependency genes, as well as enriched genes associated with different phases of the cell cycle and with DNA repair. In each case, such changes have the potential to lie upstream of apoptotic cell death. We also detected the regulation of unique as well as shared sets of transcription factors in each line, suggesting that Dpep may initiate a cascade of transcriptional responses that culminate in cancer cell death. Such death thus appears to reflect context-dependent, yet shared, disruption of multiple cellular pathways as well as of individual survival-relevant genes.

Transcriptome-wide association study identifies novel candidate susceptibility genes for migraine

Genome-wide association studies (GWASs) have identified more than 130 genetic susceptibility loci for migraine; however, how most of these loci impact migraine development is unknown. To identify novel genes associated with migraine and interpret the transcriptional products of those genes, we conducted a transcriptome-wide association study (TWAS). We performed tissue-specific and multi-tissue TWAS analyses to assess associations between imputed gene expression from 53 tissues and migraine susceptibility using FUSION software. Meta-analyzed GWAS summary statistics from 26,052 migraine cases and 487,214 controls, all of European ancestry and from two cohorts (the Kaiser Permanente GERA and the UK Biobank), were used. We evaluated the associations for genes after conditioning on variant-level effects from GWAS, and we tested for colocalization of GWAS migraine-associated loci and expression quantitative trait loci (eQTLs). Across tissue-specific and multi-tissue analyses, we identified 53 genes for which genetically predicted gene expression was associated with migraine after correcting for multiple testing. Of these 53 genes, 10 (ATF5, CNTNAP1, KTN1-AS1, NEIL1, NEK4, NNT, PNKP, RUFY2, TUBG2, and VAT1) did not overlap known migraine-associated loci identified from GWAS. Tissue-specific analysis identified 45 gene-tissue pairs and cardiovascular tissues represented the highest proportion of the Bonferroni-significant gene-tissue pairs (n = 22 [49%]), followed by brain tissues (n = 6 [13%]), and gastrointestinal tissues (n = 4 [9%]). Colocalization analyses provided evidence of shared genetic variants underlying eQTL and GWAS signals in 18 of the gene-tissue pairs (40%). Our TWAS reports novel genes for migraine and highlights the important contribution of brain, cardiovascular, and gastrointestinal tissues in migraine susceptibility.

The potential roles of ATF family in the treatment of Alzheimer's disease

Activating transcription factors, ATFs, is a family of transcription factors that activate gene expression and transcription by recognizing and combining the cAMP response element binding proteins (CREB). It is present in various viruses as a cellular gene promoter. ATFs is involved in regulating the mammalian gene expression that is associated with various cell physiological processes. Therefore, ATFs play an important role in maintaining the intracellular homeostasis. ATF2 and ATF3 is mostly involved in mediating stress responses. ATF4 regulates the oxidative metabolism, which is associated with the survival of cells. ATF5 is presumed to regulate apoptosis, and ATF6 is involved in the regulation of endoplasmic reticulum stress (ERS). ATFs is actively studied in oncology. At present, there has been an increasing amount of research on ATFs for the treatment of neurological diseases. Here, we have focused on the different types of ATFs and their association with Alzheimer's disease (AD). The level of expression of different ATFs have a significant difference in AD patients when compared to healthy control. Recent studies have suggested that ATFs are implicated in the pathogenesis of AD, such as neuronal repair, maintenance of synaptic activity, maintenance of cell survival, inhibition of apoptosis, and regulation of stress responses. In this review, the potential role of ATFs for the treatment of AD has been highlighted. In addition, we have systematically reviewed the progress of research on ATFs in AD. This review will provide a basic and innovative understanding on the pathogenesis and treatment of AD.

Targeting Transcription Factors ATF5, CEBPB and CEBPD with Cell-Penetrating Peptides to Treat Brain and Other Cancers

Developing novel therapeutics often follows three steps: target identification, design of strategies to suppress target activity and drug development to implement the strategies. In this review, we recount the evidence identifying the basic leucine zipper transcription factors ATF5, CEBPB, and CEBPD as targets for brain and other malignancies. We describe strategies that exploit the structures of the three factors to create inhibitory dominant-negative (DN) mutant forms that selectively suppress growth and survival of cancer cells. We then discuss and compare four peptides (CP-DN-ATF5, Dpep, Bpep and ST101) in which DN sequences are joined with cell-penetrating domains to create drugs that pass through tissue barriers and into cells. The peptide drugs show both efficacy and safety in suppressing growth and in the survival of brain and other cancers in vivo, and ST101 is currently in clinical trials for solid tumors, including GBM. We further consider known mechanisms by which the peptides act and how these have been exploited in rationally designed combination therapies. We additionally discuss lacunae in our knowledge about the peptides that merit further research. Finally, we suggest both short- and long-term directions for creating new generations of drugs targeting ATF5, CEBPB, CEBPD, and other transcription factors for treating brain and other malignancies.

ATF5 is a regulator of ER stress and β-cell apoptosis in different mouse models of genetic- and diet-induced obesity and diabetes mellitus

Endoplasmic reticulum (ER) stress is closely associated with type 2 diabetes (T2D). Activating transcription factor 5 (ATF5) is a member of the ATF/cAMP response element binding protein (CREB) family whose levels are increased upon stress in pancreatic islets from mice. Intriguingly, ATF5 deficiency has been shown to contribute to increased ER stress and apoptosis in mouse islet micro-organs. We hypothesized that either deficiency or overexpression of ATF5 is equally deleterious for pancreatic islets in terms of ER stress and apoptosis. To test this, we used a number of in vitro and in vivo models whereby ATF5 levels were overexpressed. We also determined the regulation of ATF5 in the context of metabolic derangements by using various mouse models of obesity and T2D. Our in vitro results show that ATF5 overexpression promoted palmitic acid (PA)-induced lipotoxic apoptosis. In vivo, global ATF5 overexpression in mice was lethal and pancreas-specific ATF5 overexpressing mice exhibit increased β-cell apoptosis. Interestingly, ATF5 is downregulated in all mouse models of severe obesity and T2D used in the current study. In conclusion, a tight control on ATF5 levels might be considered when developing novel agents targeting ATF5 for prevention and treatment of metabolic diseases.

The Journey of Mitochondrial Protein Import and the Roadmap to Follow

Mitochondria are double membrane-bound organelles that play critical functions in cells including metabolism, energy production, regulation of intrinsic apoptosis, and maintenance of calcium homeostasis. Mitochondria are fascinatingly equipped with their own genome and machinery for transcribing and translating 13 essential proteins of the oxidative phosphorylation system (OXPHOS). The rest of the proteins (99%) that function in mitochondria in the various pathways described above are nuclear-transcribed and synthesized as precursors in the cytosol. These proteins are imported into the mitochondria by the unique mitochondrial protein import system that consists of seven machineries. Proper functioning of the mitochondrial protein import system is crucial for optimal mitochondrial deliverables, as well as mitochondrial and cellular homeostasis. Impaired mitochondrial protein import leads to proteotoxic stress in both mitochondria and cytosol, inducing mitochondrial unfolded protein response (UPR^mt). Altered UPR^mt is associated with the development of various disease conditions including neurodegenerative and cardiovascular diseases, as well as cancer. This review sheds light on the molecular mechanisms underlying the import of nuclear-encoded mitochondrial proteins, the consequences of defective mitochondrial protein import, and the pathological conditions that arise due to altered UPR^mt.

ATF5 is a regulator of exercise-induced mitochondrial quality control in skeletal muscle

OBJECTIVES

The Mitochondrial Unfolded Protein Response (UPR^mt) is a compartment-specific mitochondrial quality control (MQC) mechanism that uses the transcription factor ATF5 to induce the expression of protective enzymes to restore mitochondrial function. Acute exercise is a stressor that has the potential to temporarily disrupt organellar protein homeostasis, however, the roles of ATF5 and the UPR^mt in maintaining basal mitochondrial content, function and exercise-induced MQC mechanisms in skeletal muscle are not known.

METHODS

ATF5 KO and WT mice were examined at rest or after a bout of acute endurance exercise. We measured protein content in whole muscle, nuclear, cytosolic and mitochondrial fractions, in addition to mRNA transcript levels in whole muscle. Using isolated mitochondria, we quantified rates of oxygen consumption and ROS emission to observe the effects of the absence of ATF5 on organelle function.

RESULTS

ATF5 KO mice exhibited a larger and less functional muscle mitochondrial pool, most likely a culmination of enhanced biogenesis via increased PGC-1α expression, and attenuated mitophagy. The absence of ATF5 resulted in a reduction in antioxidant proteins and increases in mitochondrial ROS emission, cytosolic cytochrome c, and the expression of mitochondrial chaperones. KO muscle also displayed enhanced exercise-induced stress kinase signaling, but a blunted mitophagic and UPR^mt gene expression response, complemented by significant increases in the basal mRNA abundance and nuclear localization of ATF4. Instead of promoting its nuclear translocation, acute exercise caused the enrichment of ATF5 in mitochondrial fractions. We also identified PGC-1α as an additional regulator of the basal expression of UPR^mt genes.

CONCLUSION

The transcription factor ATF5 retains a critical role in the maintenance of mitochondrial homeostasis and the appropriate response of muscle to acute exercise for the optimization of mitochondrial quality control.

TGFBR3 supports anoikis through suppressing ATF4 signaling

Epithelial morphogenesis and oncogenic transformation can cause loss of cell adhesion, and detached cells are eliminated by anoikis. Here, we reveal that transforming growth factor beta receptor 3 (TGFBR3) acts as an anoikis mediator through the coordination of activating transcription factor 4 (ATF4). In breast cancer, TGFBR3 is progressively lost, but elevated TGFBR3 is associated with a histologic subtype characterized by cellular adhesion defects. Dissecting the impact of extracellular matrix (ECM) deprivation, we demonstrate that ECM loss promotes TGFBR3 expression, which in turn differentiates cell aggregates to a prosurvival phenotype and drives the intrinsic apoptotic pathway. We demonstrate that inhibition of TGFBR3 impairs epithelial anoikis by activating ATF4 signaling. These preclinical findings provide a rationale for therapeutic inhibition of ATF4 in the subgroup of breast cancer patients with low TGFBR3 expression.

The mitochondrial unfolded protein response (UPRmt): shielding against toxicity to mitochondria in cancer

Mitochondria are essential for tumor growth and progression. However, the heavy demand for mitochondrial activity in cancer leads to increased production of mitochondrial reactive oxygen species (mtROS), accumulation of mutations in mitochondrial DNA, and development of mitochondrial dysfunction. If left unchecked, excessive mtROS can damage and unfold proteins in the mitochondria to an extent that becomes lethal to the tumor. Cellular systems have evolved to combat mtROS and alleviate mitochondrial stress through a quality control mechanism called the mitochondrial unfolded protein response (UPR^mt). The UPR^mt system is composed of chaperones and proteases, which promote protein folding or eliminate mitochondrial proteins damaged by mtROS, respectively. UPR^mt is conserved and activated in cancer in response to mitochondrial stress to maintain mitochondrial integrity and support tumor growth. In this review, we discuss how mitochondria become dysfunctional in cancer and highlight the tumor-promoting functions of key components of the UPR^mt.

Mitochondria: intracellular sentinels of infections

Structure and integrity of the mitochondrial network play important roles in many cellular processes. Loss of integrity can lead to the activation of a variety of signalling pathways and affect the cell’s response to infections. The activation of such mitochondria-mediated cellular responses has implications for infection recognition, signal transduction and pathogen control. Although we have a basic understanding of mitochondrial factors such as mitochondrial DNA or RNA that may be involved in processes like pro-inflammatory signalling, the diverse roles of mitochondria in host defence remain unclear. Here we will first summarise the functions of mitochondria in the host cell and provide an overview of the major known mitochondrial stress responses. We will then present recent studies that have contributed to the understanding of the role of mitochondria in infectious diseases and highlight a number of recently investigated models of bacterial and viral infections.

Emerging roles of activating transcription factor (ATF) family members in tumourigenesis and immunity: Implications in cancer immunotherapy

Activating transcription factors, ATFs, are a group of bZIP transcription factors that act as homodimers or heterodimers with a range of other bZIP factors. In general, ATFs respond to extracellular signals, indicating their important roles in maintaining homeostasis. The ATF family includes ATF1, ATF2, ATF3, ATF4, ATF5, ATF6, and ATF7. Consistent with the diversity of cellular processes reported to be regulated by ATFs, the functions of ATFs are also diverse. ATFs play an important role in cell proliferation, apoptosis, differentiation and inflammation-related pathological processes. The expression and phosphorylation status of ATFs are also related to neurodegenerative diseases and polycystic kidney disease. Various miRNAs target ATFs to regulate cancer proliferation, apoptosis, autophagy, sensitivity and resistance to radiotherapy and chemotherapy. Moreover, ATFs are necessary to maintain cell redox homeostasis. Therefore, deepening our understanding of the regulation and function of ATFs will provide insights into the basic regulatory mechanisms that influence how cells integrate extracellular and intracellular signals into genomic responses through transcription factors. Under pathological conditions, especially in cancer biology and response to treatment, the characterization of ATF dysfunction is important for understanding how to therapeutically utilize ATF2 or other pathways controlled by transcription factors. In this review, we will demonstrate how ATF1, ATF2, ATF3, ATF4, ATF5, ATF6, and ATF7 function in promoting or suppressing cancer development and identify their roles in tumour immunotherapy.

The Basis and Advances in Clinical Application of Cytomegalovirus-Specific Cytotoxic T Cell Immunotherapy for Glioblastoma Multiforme

A high percentage of malignant gliomas are infected by human cytomegalovirus (HCMV), and the endogenous expression of HCMV genes and their products are found in these tumors. HCMV antigen expression and its implications in gliomagenesis have emerged as a promising target for adoptive cellular immunotherapy (ACT) strategies in glioblastoma multiforme (GB) patients. Since antigen-specific T cells in the tumor microenvironments lack efficient anti-tumor immune response due to the immunosuppressive nature of glioblastoma, CMV-specific ACT relies on in vitro expansion of CMV-specific CD8+ T cells employing immunodominant HCMV antigens. Given the fact that several hurdles remain to be conquered, recent clinical trials have outlined the feasibility of CMV-specific ACT prior to tumor recurrence with minimal adverse effects and a substantial improvement in median overall survival and progression-free survival. This review discusses the role of HCMV in gliomagenesis, disease prognosis, and recent breakthroughs in harnessing HCMV-induced immunogenicity in the GB tumor microenvironment to develop effective CMV-specific ACT.

Targeting the Integrated Stress Response in Cancer Therapy

The integrated stress response (ISR) is an evolutionarily conserved intra-cellular signaling network which is activated in response to intrinsic and extrinsic stresses. Various stresses are sensed by four specialized kinases, PKR-like ER kinase (PERK), general control non-derepressible 2 (GCN2), double-stranded RNA-dependent protein kinase (PKR) and heme-regulated eIF2α kinase (HRI) that converge on phosphorylation of serine 51 of eIF2α. eIF2α phosphorylation causes a global reduction of protein synthesis and triggers the translation of specific mRNAs, including activating transcription factor 4 (ATF4). Although the ISR promotes cell survival and homeostasis, when stress is severe or prolonged the ISR signaling will shift to regulate cellular apoptosis. We review the ISR signaling pathway, regulation and importance in cancer therapy.

EBF1 is expressed in pericytes and contributes to pericyte cell commitment

Early B-cell factor-1 (EBF1) is a transcription factor with an important role in cell lineage specification and commitment during the early stage of cell maturation. Originally described during B-cell maturation, EBF1 was subsequently identified as a crucial molecule for proper cell fate commitment of mesenchymal stem cells into adipocytes, osteoblasts and muscle cells. In vessels, EBF1 expression and function have never been documented. Our data indicate that EBF1 is highly expressed in peri-endothelial cells in both tumor vessels and in physiological conditions. Immunohistochemistry, quantitative reverse transcription polymerase chain reaction (RT-qPCR) and fluorescence-activated cell sorting (FACS) analysis suggest that EBF1-expressing peri-endothelial cells represent bona fide pericytes and selectively express well-recognized markers employed in the identification of the pericyte phenotype (SMA, PDGFRβ, CD146, NG2). This observation was also confirmed in vitro in human placenta-derived pericytes and in human brain vascular pericytes (HBVP). Of note, in accord with the key role of EBF1 in the cell lineage commitment of mesenchymal stem cells, EBF1-silenced HBVP cells showed a significant reduction in PDGFRβ and CD146, but not CD90, a marker mostly associated with a prominent mesenchymal phenotype. Moreover, the expression levels of VEGF, angiopoietin-1, NG2 and TGF-β, cytokines produced by pericytes during angiogenesis and linked to their differentiation and activation, were also significantly reduced. Overall, the data suggest a functional role of EBF1 in the cell fate commitment toward the pericyte phenotype.

Systems Biomedicine of Primary and Metastatic Colorectal Cancer Reveals Potential Therapeutic Targets

Colorectal cancer (CRC) is one of the major causes of cancer deaths across the world. Patients' survival at time of diagnosis depends mainly on stage of the tumor. Therefore, understanding the molecular mechanisms from low-grade to high-grade stages of cancer that lead to cellular migration from one tissue/organ to another tissue/organ is essential for implementing therapeutic approaches. To this end, we performed a unique meta-analysis flowchart by identifying differentially expressed genes (DEGs) between normal, primary (primary sites), and metastatic samples (Colorectal metastatic lesions in liver and lung) in some Test datasets. DEGs were employed to construct a protein-protein interaction (PPI) network. A smaller network containing 39 DEGs was then extracted from the PPI network whose nodes expression induction or suppression alone or in combination with each other would inhibit tumor progression or metastasis. These DEGs were then verified by gene expression profiling, survival analysis, and multiple Validation datasets. We suggested for the first time that downregulation of mitochondrial genes, including ETHE1, SQOR, TST, and GPX3, would help colorectal cancer cells to produce more energy under hypoxic conditions through mechanisms that are different from "Warburg Effect". Augmentation of given antioxidants and repression of P4HA1 and COL1A2 genes could be a choice of CRC treatment. Moreover, promoting active GSK-3β together with expression control of EIF2B would prevent EMT. We also proposed that OAS1 expression enhancement can induce the anti-cancer effects of interferon-gamma, while suppression of CTSH hinders formation of focal adhesions. ATF5 expression suppression sensitizes cancer cells to anchorage-dependent death signals, while LGALS4 induction recovers cell-cell junctions. These inhibitions and inductions would be another combinatory mechanism that inhibits EMT and cell migration. Furthermore, expression inhibition of TMPO, TOP2A, RFC3, GINS1, and CKS2 genes could prevent tumor growth. Besides, TRIB3 suppression would be a promising target for anti-angiogenic therapy. SORD is a poorly studied enzyme in cancer, found to be upregulated in CRC. Finally, TMEM131 and DARS genes were identified in this study whose roles have never been interrogated in any kind of cancer, neither as a biomarker nor curative target. All the mentioned mechanisms must be further validated by experimental wet-lab techniques.

Cell-Penetrating CEBPB and CEBPD Leucine Zipper Decoys as Broadly Acting Anti-Cancer Agents

Simple Summary

The gene-regulatory factors ATF5, CEBPB and CEBPD promote survival, growth, metastasis and treatment resistance of a range of cancer cell types. Presently, no drugs target all three at once. Here, with the aim of treating cancers, we designed novel cell-penetrating peptides that interact with and inactivate all three. The peptides Bpep and Dpep kill a range of cancer cell types in culture and in animals. In animals with tumors, they also significantly increase survival time. In contrast, they do not affect survival of non-cancer cells and have no apparent side effects in animals. The peptides work in combination with other anti-cancer treatments. Mechanism studies of how the peptides kill cancer cells indicate a decrease in survival proteins and increase in death proteins. These studies support the potential of Bpep and Dpep as novel, safe agents for the treatment of a variety of cancer types, both as mono- and combination therapies.

Abstract

Transcription factors are key players underlying cancer formation, growth, survival, metastasis and treatment resistance, yet few drugs exist to directly target them. Here, we characterized the in vitro and in vivo anti-cancer efficacy of novel synthetic cell-penetrating peptides (Bpep and Dpep) designed to interfere with the formation of active leucine-zipper-based dimers by CEBPB and CEBPD, transcription factors implicated in multiple malignancies. Both peptides similarly promoted apoptosis of multiple tumor lines of varying origins, without such effects on non-transformed cells. Combined with other treatments (radiation, Taxol, chloroquine, doxorubicin), the peptides acted additively to synergistically and were fully active on Taxol-resistant cells. The peptides suppressed expression of known direct CEBPB/CEBPD targets IL6, IL8 and asparagine synthetase (ASNS), supporting their inhibition of transcriptional activation. Mechanisms by which the peptides trigger apoptosis included depletion of pro-survival survivin and a required elevation of pro-apoptotic BMF. Bpep and Dpep significantly slowed tumor growth in mouse models without evident side effects. Dpep significantly prolonged survival in xenograft models. These findings indicate the efficacy and potential of Bpep and Dpep as novel agents to treat a variety of cancers as mono- or combination therapies.

Influence of genetic variants in asparaginase pathway on the susceptibility to asparaginase-related toxicity and patients' outcome in childhood acute lymphoblastic leukemia

BACKGROUND

Asparaginase (ASNase) is a key component in the treatment protocols of childhood acute lymphoblastic leukemia (ALL). Asparagine synthetase (ASNS) and the basic region leucine zipper activating transcription factor 5 (ATF5) mediate the anti-leukemic effect of ASNase. Only a few reports studied the association between polymorphisms in these genes and treatment-related toxicity and response. Therefore, the current study aimed to investigate the association of ASNS and ATF5 polymorphisms with the susceptibility to ASNase-related toxicity and disease outcome in a population of childhood ALL Egyptian patients.

METHODS

In this study, 88 children with ALL were enrolled and genotyped for ASNS T629A and ATF5 C362T polymorphisms using allelic discrimination assay.

RESULTS

The studied polymorphisms did not associate with hypersensitivity or thrombosis, while the ATF5 C362T polymorphism was associated significantly with decreased ASNase-associated pancreatitis (AAP) risk under the dominant model. Patients carrying TT/CT genotypes of ATF5 C362T polymorphism had a significantly better overall survival (OS) and longer event-free survival (EFS) compared to patients with CC genotype. Multivariate analysis confirmed the independent prognostic value of the ATF5 C362T dominant model.

CONCLUSION

ATF5 362TT and CT genotypes were associated with decreased risk to develop AAP and better disease outcome demonstrating a low risk for events and superior survival.

Mitochondrial unfolded protein response: A novel pathway in metabolism and immunity

Mitochondrial unfolded protein response (mitoUPR) is a mitochondria stress response to maintain mitochondrial proteostasis during stress. Increasing evidence suggests that mitoUPR participates in diverse physiological processes especially metabolism and immunity. Although mitoUPR regulates metabolism in many aspects, it is mainly reflected in the regulation of energy metabolism. During stress, mitoUPR alters energy metabolism via suppressing oxidative phosphorylation (OXPHOS) or increasing glycolysis. MitoUPR also alters energy metabolism and regulates diverse metabolic diseases such as diabetes, cancers, fatty liver and obesity. In addition, mitoUPR also participates in immune process during stress. MitoUPR can induce innate immune response during various infections and may regulate inflammatory response during diverse inflammations. Considering the pleiotropic actions of mitoUPR, mitoUPR may supply diverse therapeutic targets for metabolic diseases and immune diseases.

ELF1 Transcription Factor Enhances the Progression of Glioma via ATF5 promoter

A key transcriptional activator, activating transcription factor 5 (ATF5), is aberrantly overexpressed in glioma and supports both poor prognosis and antiapototic potential. Unfortunately, data on ATF5 is largely based on its regulatory mechanism. Further investigation of the upstream regulatory factor for ATF5 transcription in glioma is required. Clinical data for patients with diagnosed glioma were obtained from The Cancer Genome Atlas (TCGA). Additionally, transcription factors potentially regulating the ATF5 promoter in glioma were screened with bioinformatics. A further experimental study was performed to investigate both the role of E74-like factor 1 (ELF1) and the binding of ELF1 and the ATF5 promoter in glioma. We show that ATF5 expression is upregulated in glioma tissues and associated with tumor malignancy and worse prognosis. As a putative upstream regulator, silencing ELF1 inhibits glioma cell growth and migration with ATF5 involvement. Moreover, ELF1 upregulation is also associated with poor prognosis in glioma. Importantly, the luciferase assay and chromatin immunoprecipitation (ChIP) reveal that the ATF5 gene promoter is essential for ELF1-dependent activation of ATF5 gene transcription. These results indicate that a high expression of ELF1 may be related to the malignant behavior of human glioma and ELF1 promotes glioma development mediated by transactivation of the ATF5 gene.

Mitochondrial unfolded protein response: An emerging pathway in human diseases

Mitochondrial unfolded protein response (UPR^mt) is a mitochondria stress response, which the transcriptional activation programs of mitochondrial chaperone proteins and proteases are initiated to maintain proteostasis in mitochondria. Additionally, the activation of UPR^mt delays aging and extends lifespan by maintaining mitochondrial proteostasis. Growing evidences suggests that UPR^mt plays an important role in diverse human diseases, especially ageing-related diseases. Therefore, this review focuses on the role of UPR^mt in ageing and ageing-related neurodegenerative diseases such as Alzheimer's disease, Huntington's disease and Parkinson's disease. The activation of UPR^mt and the high expression of UPR^mt components contribute to longevity extension. The activation of UPR^mt may ameliorate Alzheimer's disease, Parkinson's disease and Huntington's disease. Besides, UPR^mt is also involved in the occurrence and development of cancers and heart diseases. UPR^mt contributes to the growth, invasive and metastasis of cancers. UPR^mt has paradoxical roles in heart diseases. UPR^mt not only protects against heart damage, but may sometimes aggravates the development of heart diseases. Considering the pleiotropic actions of UPR^mt system, targeting UPR^mt pathway may be a potent therapeutic avenue for neurodegenerative diseases, cancers and heart diseases.

The mitochondrial unfolded protein response and its diverse roles in cellular stress

Mitochondrial function is centrally involved in many cellular processes, such as energy production, metabolism of nucleotides, amino acids, and lipids, calcium buffering, and regulation of cell death. Multiple mechanisms are engaged under conditions of mitochondrial dysfunction to restore cellular and, subsequently, systemic functions. The mitochondrial unfolded protein response is a homeostatic mechanism that has attracted a lot of interest recently and has been described in several organisms, including humans. The mitochondrial unfolded protein response serves as a first-line-of-defence mechanism against stress to restore mitochondrial proteostasis and functions. Here, we discuss the canonical mechanisms via which the mitochondrial unfolded protein response is activated under stress and examine recent evidence that links the response with other processes that promote survival and the recovery of the mitochondrial network (i.e. the integrated stress response and mitophagy).

Expression patterns of activating transcription factor 5 (atf5a and atf5b) in zebrafish

The Activating Transcription Factor 5 (ATF5) is a basic leucine-zipper (bZIP) transcription factor (TF) with proposed stress-protective, anti-apoptotic and oncogenic roles which were all established in cell systems. In whole animals, Atf5 function seems highly context dependent. Atf5 is strongly expressed in the rodent nose and mice knockout (KO) pups have defective olfactory sensory neurons (OSNs), smaller olfactory bulbs (OB), while adults are smell deficient. It was therefore proposed that Atf5 plays an important role in maturation and maintenance of OSNs. Atf5 expression was also described in murine liver and bones where it appears to promote differentiation of progenitor cells. By contrast in the rodent brain, Atf5 was first described as uniquely expressed in neuroprogenitors and thus, proposed to drive their proliferation and inhibit their differentiation. However, it was later also found in mature neurons stressing the need for additional work in whole animals. ATF5 is well conserved with two paralogs, atf5a and atf5b in zebrafish. Here, we present the expression patterns for both from 6 h (hpf) to 5day post-fertilization (dpf). We found early expression for both genes, and from 1dpf onwards overlapping expression patterns in the inner ear and the developing liver. In the brain, at 24hpf both atf5a and atf5b were expressed in the forebrain, midbrain, and hindbrain. However, from 2dpf and onwards we only detected atf5a expression namely in the olfactory bulbs, the mesencephalon, and the metencephalon. We further evidenced additional differential expression for atf5a in the sensory neurons of the olfactory organs, and for atf5b in the neuromasts, that form the superficial sensory organ called the lateral line (LL). Our results establish the basis for future functional analyses in this lower vertebrate.

Mitochondrial Stress Response and Cancer

Cancer cells survive and adapt to many types of stress including hypoxia, nutrient deprivation, metabolic, and oxidative stress. These stresses are sensed by diverse cellular signaling processes, leading to either degradation of mitochondria or alleviation of mitochondrial stress. This review discusses signaling during sensing and mitigation of stress involving mitochondrial communication with the endoplasmic reticulum, and how retrograde signaling upregulates the mitochondrial stress response to maintain mitochondrial integrity. The importance of the mitochondrial unfolded protein response, an emerging pathway that alleviates cellular stress, will be elaborated with respect to cancer. Detailed understanding of cellular pathways will establish mitochondrial stress response as a key mechanism for cancer cell survival leading to cancer progression and resistance, and provide a potential therapeutic target in cancer.

TooManyCells identifies and visualizes relationships of single-cell clades

Identifying and visualizing transcriptionally similar cells is instrumental for accurate exploration of the cellular diversity revealed by single-cell transcriptomics. However, widely used clustering and visualization algorithms produce a fixed number of cell clusters. A fixed clustering 'resolution' hampers our ability to identify and visualize echelons of cell states. We developed TooManyCells, a suite of graph-based algorithms for efficient and unbiased identification and visualization of cell clades. TooManyCells introduces a visualization model built on a concept intentionally orthogonal to dimensionality-reduction methods. TooManyCells is also equipped with an efficient matrix-free divisive hierarchical spectral clustering different from prevalent single-resolution clustering methods. TooManyCells enables multiresolution and multifaceted exploration of single-cell clades. An advantage of this paradigm is the immediate detection of rare and common populations that outperforms popular clustering and visualization algorithms, as demonstrated using existing single-cell transcriptomic data sets and new data modeling drug-resistance acquisition in leukemic T cells.

Dominant-Negative ATF5 Compromises Cancer Cell Survival by Targeting CEBPB and CEBPD

The basic leucine zipper transcription factor ATF5 is overexpressed in many tumor types and interference with its expression or function inhibits cancer cell survival. As a potential therapeutic approach to exploit these findings, we created dominant-negative (DN) ATF5 forms lacking DNA-binding ability that retain the ATF5 leucine zipper, and thus associate with and sequester ATF5's requisite leucine zipper-binding partners. Preclinical studies with DN-ATF5, including a cell-penetrating form, show in vitro and in vivo efficacy in compromising cancer cell survival. However, DN-ATF5's targets, and particularly those required for tumor cell survival, have been unknown. We report that cells lacking ATF5 succumb to DN-ATF5, indicating that ATF5 itself is not DN-ATF5's obligate target. Unbiased pull-down assays coupled with mass spectrometry and immunoblotting revealed that DN-ATF5 associates in cells with the basic leucine zipper proteins CEBPB and CEBPD and coiled-coil protein CCDC6. Consistent with DN-ATF5 affecting tumor cell survival by suppressing CEBPB and CEBPD function, DN-ATF5 interferes with CEBPB and CEBPD transcriptional activity, while CEBPB or CEBPD knockdown promotes apoptotic death of multiple cancer cells lines, but not of normal astrocytes. We propose a two-pronged mechanism by which DN-ATF5 kills tumor cells. One is by inhibiting heterodimer formation between ATF5 and CEBPB and CDBPD, thus suppressing ATF5-dependent transcription. The other is by blocking the formation of transcriptionally active CEBPB and CEBPD homodimers as well as heterodimers with partners in addition to ATF5. IMPLICATIONS: This study indicates that the potential cancer therapeutic DN-ATF5 acts by associating with and blocking the transcriptional activities of CEBPB and CEBPD.

Dominant-negative ATF5 rapidly depletes survivin in tumor cells

Survivin (BIRC5, product of the BIRC5 gene) is highly expressed in many tumor types and has been widely identified as a potential target for cancer therapy. However, effective anti-survivin drugs remain to be developed. Here we report that both vector-delivered and cell-penetrating dominant-negative (dn) forms of the transcription factor ATF5 that promote selective death of cancer cells in vitro and in vivo cause survivin depletion in tumor cell lines of varying origins. dn-ATF5 decreases levels of both survivin mRNA and protein. The depletion of survivin protein appears to be driven at least in part by enhanced proteasomal turnover and depletion of the deubiquitinase USP9X. Survivin loss is rapid and precedes the onset of cell death triggered by dn-ATF5. Although survivin downregulation is sufficient to drive tumor cell death, survivin over-expression does not rescue cancer cells from dn-ATF5-promoted apoptosis. This indicates that dn-ATF5 kills malignant cells by multiple mechanisms that include, but are not limited to, survivin depletion. Cell-penetrating forms of dn-ATF5 are currently being developed for potential therapeutic use and the present findings suggest that they may pose an advantage over treatments that target only survivin.

Disruption of oncogenic liver-intestine cadherin (CDH17) drives apoptotic pancreatic cancer death

Liver-intestine cadherin (CDH17) has been known to function as a tumor stimulator and diagnostic marker for almost two decades. However, its function in highly malignant pancreatic cancer (PC) has yet to be elucidated. Using different strategies including siRNA, shRNA, and CRISPR technology, we successfully induced knockdown and knockout of CDH17 in Panc02-H7 cells and established the corresponding stable cell lines. With these cells, we demonstrated that loss of CDH17 function not only suppressed Panc02-H7 cell growth in vitro but also significantly slowed orthotopic tumor growth in vivo, resulting in the significant life extension. In vitro studies demonstrated that impairing CDH17 inhibited cell proliferation, colony formation, and motility by mechanistically modulating pro- and anti-apoptosis events in PC cells, as CDH17 suppression obviously increased expression of Bad, cytochrome C, cleaved caspase 3, and cleaved PARP, and reduced expression of Bcl-2, Survivin, and pAkt. In vivo studies showed CDH17 knockout resulted in apoptotic PC tumor death through activating caspase-3 activity. Taken together, CDH17 functions as an oncogenic molecule critical to PC growth by regulating tumor apoptosis signaling pathways and CDH17 could be targeted to develop an anti-PC therapeutic approach.

Expression of activating transcription factor 5 (ATF5) is increased in astrocytomas of different WHO grades and correlates with survival of glioblastoma patients

Background

ATF5 suppresses differentiation of neuroprogenitor cells and is overexpressed in glioblastoma (GBM). A reduction of its expression leads to apoptotic GBM cell death. Data on ATF5 expression in astrocytoma WHO grade II (low-grade astrocytoma [LGA]) are scarce and lacking on recurrent GBM.

Patients and methods

ATF5 mRNA was extracted from frozen samples of patients’ GBM (n=79), LGA (n=40), and normal brain (NB, n=10), quantified by duplex qPCR and correlated with retrospectively collected clinical data. ATF5 protein expression was evaluated by measuring staining intensity on immunohistochemistry.

Results

ATF5 mRNA was overexpressed in LGA (sevenfold, P<0.001) and GBM (tenfold, P<0.001) compared to NB, which was confirmed on protein level. Although ATF5 mRNA expression in GBM showed a considerable fluctuation range, groups of varying biological behavior, that is, local/multifocal growth or primary tumor/relapse and the tumor localization at diagnosis, were not significantly different. ATF5 mRNA correlated with the patients’ age (r=0.339, P=0.028) and inversely with Ki67-staining (r=−0.421, P=0.007). GBM patients were allocated to a low and a high ATF5 expression group by the median ATF5 overexpression compared to NB. Kaplan–Meier analysis and Cox regression indicated that ATF5 mRNA expression significantly correlated with short-term survival (t,12 months, median survival 18 vs 13 months, P=0.022, HR 2.827) and progression-free survival (PFS) (12 vs 6 months, P=0.024). This advantage vanished after 24 months (P=0.084).

Conclusion

ATF5 mRNA expression could be identified as an additional, though not independent factor correlating with overall survival and PFS. Since its inhibition might lead to the selective death of glioma cells, it might serve as a potential ubiquitous therapeutic target in astrocytic tumors.

Dysregulation of Transcription Factors: A Key Culprit Behind Neurodegenerative Disorders

Neurodegenerative diseases (NDs) are considered heterogeneous disorders characterized by progressive pathological changes in neuronal systems. Transcription factors are protein molecules that are important in regulating the expression of genes. Although the clinical manifestations of NDs vary, the pathological processes appear similar with regard to neuroinflammation, oxidative stress, and proteostasis, to which, as numerous studies have discovered, transcription factors are closely linked. In this review, we summarized and reviewed the roles of transcription factors in NDs, and then we elucidated their functions during pathological processes, and finally we discussed their therapeutic values in NDs.

A PDX1-ATF transcriptional complex governs β cell survival during stress

Objective

Loss of insulin secretion due to failure or death of the insulin secreting β cells is the central cause of diabetes. The cellular response to stress (endoplasmic reticulum (ER), oxidative, inflammatory) is essential to sustain normal β cell function and survival. Pancreatic and duodenal homeobox 1 (PDX1), Activating transcription factor 4 (ATF4), and Activating transcription factor 5 (ATF5) are transcription factors implicated in β cell survival and susceptibility to stress. Our goal was to determine if a PDX1-ATF transcriptional complex or complexes regulate β cell survival in response to stress and to identify direct transcriptional targets.

Methods

Pdx1, Atf4 and Atf5 were silenced by viral delivery of gRNAs or shRNAs to Min6 insulinoma cells or primary murine islets. Gene expression was assessed by qPCR, RNAseq analysis, and Western blot analysis. Chromatin enrichment was measured in the Min6 β cell line and primary isolated mouse islets by ChIPseq and ChIP PCR. Immunoprecipitation was used to assess interactions among transcription factors in Min6 cells and isolated mouse islets. Activation of caspase 3 by immunoblotting or by irreversible binding to a fluorescent inhibitor was taken as an indication of commitment to an apoptotic fate.

Results

RNASeq identified a set of PDX1, ATF4 and ATF5 co-regulated genes enriched in stress and apoptosis functions. We further identified stress induced interactions among PDX1, ATF4, and ATF5. PDX1 chromatin occupancy peaks were identified over composite C/EBP-ATF (CARE) motifs of 26 genes; assessment of a subset of these genes revealed co-enrichment for ATF4 and ATF5. PDX1 occupancy over CARE motifs was conserved in the human orthologs of 9 of these genes. Of these, Glutamate Pyruvate Transaminase 2 (Gpt2), Cation transport regulator 1 (Chac1), and Solute Carrier Family 7 Member 1 (Slc7a1) induction by stress was conserved in human islets and abrogated by deficiency of Pdx1, Atf4, and Atf5 in Min6 cells. Deficiency of Gpt2 reduced β cell susceptibility to stress induced apoptosis in both Min6 cells and primary islets.

Conclusions

Our results identify a novel PDX1 stress inducible complex (es) that regulates expression of stress and apoptosis genes to govern β cell survival.

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PDX1 binds to composite CEBP/ATF (CARE) sites of stress and apoptosis genes.

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A novel stress inducible transcriptional complex involving PDX1, ATF4, and ATF5 is discovered.

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Novel stress induced targets of the complex involved in fate decisions are identified.

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Silencing of one of these targets, Gpt2, protects β cells from apoptosis due to stress.

Human cytomegalovirus immediate-early protein promotes survival of glioma cells through interacting and acetylating ATF5

Human cytomegalovirus (HCMV), a widespread beta-herpes virus, infects a high percentage of gliomas. HCMV is specifically detected in human gliomas at a low level of expression raises the possibility that it may regulate the malignant phenotype in a chronic manner. Although HCMV is not recognized as an oncogenic virus, it might dysregulate signaling pathways involved in initiation and promotion of malignancy.Here, our immunohistochemical staining reveals that nucleus staining of the HCMV 86-kDa immediate-early protein (IE86) is markedly increased in GBM (58.56%) compared with that in nontumorous samples (4.20%) and low-grade glioma(19.56%). IE86 staining positively correlates with the staining of activating transcription factor 5 (ATF5) which is essential for glioma cell viability and proliferation suggesting that HCMV IE86 could have important implications in glioma biology. Moreover, we find that the IE86 overexpression enhances glioma cell's growth in vitro and in vivo. We demonstrate that IE86 protein physically interacts with, and acetylates ATF5 thereby promoting glioma cell survival. Therefore, our findings illustrate the biological significance of HCMV infection in accelerating glioma progression, and provide novel evidence that HCMV infection may serve as a therapeutic target in human glioma.

SUMO2/3 modification of activating transcription factor 5 (ATF5) controls its dynamic translocation at the centrosome

Activating transcription factor 5 (ATF5) is a member of the ATF/cAMP response element-binding protein family of transcription factors. ATF5 regulates stress responses and cell survival, proliferation, and differentiation and also plays a role in viral infections, cancer, diabetes, schizophrenia, and the olfactory system. Moreover, it was found to also have a critical cell cycle-dependent structural function at the centrosome. However, the mechanism that controls the localization of ATF5 at the centrosome is unclear. Here we report that ATF5 is small ubiquitin-like modifier (SUMO) 2/3-modified at a conserved SUMO-targeting consensus site in various types of mammalian cells. We found that SUMOylation of ATF5 is elevated in the G₁ phase of the cell cycle and diminished in the G₂/M phase. ATF5 SUMOylation disrupted the interaction of ATF5 with several centrosomal proteins and dislodged ATF5 from the centrosome at the end of the M phase. Of note, blockade of ATF5 SUMOylation deregulated the centrosome cycle, impeded ATF5 translocation from the centrosome, and caused genomic instability and G₂/M arrest in HeLa cells. Our results indicate that ATF5 SUMOylation is an essential mechanism that regulates ATF5 localization and function at the centrosome.

Regression/eradication of gliomas in mice by a systemically-deliverable ATF5 dominant-negative peptide

Malignant gliomas have poor prognosis and urgently require new therapies. Activating Transcription Factor 5 (ATF5) is highly expressed in gliomas, and interference with its expression/function precipitates targeted glioma cell apoptosis in vitro and in vivo. We designed a novel deliverable truncated-dominant-negative (d/n) form of ATF5 fused to a cell-penetrating domain (Pen-d/n-ATF5-RP) that can be intraperitoneally/subcutaneously administered to mice harboring malignant gliomas generated; (1) by PDGF-B/sh-p53 retroviral transformation of endogenous neural progenitor cells; and (2) by human U87-MG xenografts. In vitro Pen-d/n-ATF5-RP entered into glioma cells and triggered massive apoptosis. In vivo, subcutaneously-administered Pen-d/n-ATF5-RP passed the blood brain barrier, entered normal brain and tumor cells, and then caused rapid selective tumor cell death. MRI verified elimination of retrovirus-induced gliomas within 8-21 days. Histopathology revealed growth-suppression of intracerebral human U87-MG cells xenografts. For endogenous PDGF-B gliomas, there was no recurrence or mortality at 6-12 months versus 66% mortality in controls at 6 months. Necropsy and liver-kidney blood enzyme analysis revealed no adverse effects on brain or other tissues. Our findings thus identify Pen-d/n-ATF5-RP as a potential therapy for malignant gliomas.

The neuroprotective transcription factor ATF5 is decreased and sequestered into polyglutamine inclusions in Huntington's disease

Activating transcription factor-5 (ATF5) is a stress-response transcription factor induced upon different cell stressors like fasting, amino-acid limitation, cadmium or arsenite. ATF5 is also induced, and promotes transcription of anti-apoptotic target genes like MCL1, during the unfolded protein response (UPR) triggered by endoplasmic reticulum stress. In the brain, high ATF5 levels are found in gliomas and also in neural progenitor cells, which need to decrease their ATF5 levels for differentiation into mature neurons or glia. This initially led to believe that ATF5 is not expressed in adult neurons. More recently, we reported basal neuronal ATF5 expression in adult mouse brain and its neuroprotective induction during UPR in a mouse model of status epilepticus. Here we aimed to explore whether ATF5 is also expressed by neurons in human brain both in basal conditions and in Huntington's disease (HD), where UPR has been described to be partially impaired due to defective ATF6 processing. Apart from confirming that ATF5 is present in human adult neurons, here we report accumulation of ATF5 within the characteristic polyglutamine-containing neuronal nuclear inclusions in brains of HD patients and mice. This correlates with decreased levels of soluble ATF5 and of its antiapoptotic target MCL1. We then confirmed the deleterious effect of ATF5 deficiency in a Caenorhabditis elegans model of polyglutamine-induced toxicity. Finally, ATF5 overexpression attenuated polyglutamine-induced apoptosis in a cell model of HD. These results reflect that decreased ATF5 in HD-probably secondary to sequestration into inclusions-renders neurons more vulnerable to mutant huntingtin-induced apoptosis and that ATF5-increasing interventions might have therapeutic potential for HD.

Blood-brain barrier transport and neuroprotective potential of blackberry-digested polyphenols: an in vitro study

PURPOSE

Epidemiological and intervention studies have attempted to link the health effects of a diet rich in fruits and vegetables with the consumption of polyphenols and their impact in neurodegenerative diseases. Studies have shown that polyphenols can cross the intestinal barrier and reach concentrations in the bloodstream able to exert effects in vivo. However, the effective uptake of polyphenols into the brain is still regarded with some reservations. Here we describe a combination of approaches to examine the putative transport of blackberry-digested polyphenols (BDP) across the blood-brain barrier (BBB) and ultimate evaluation of their neuroprotective effects.

METHODS

BDP was obtained by in vitro digestion of blackberry extract and BDP major aglycones (hBDP) were obtained by enzymatic hydrolysis. Chemical characterization and BBB transport of extracts were evaluated by LC-MSⁿ. BBB transport and cytoprotection of both extracts was assessed in HBMEC monolayers. Neuroprotective potential of BDP was assessed in NT2-derived 3D co-cultures of neurons and astrocytes and in primary mouse cerebellar granule cells. BDP-modulated genes were evaluated by microarray analysis.

RESULTS

Components from BDP and hBDP were shown to be transported across the BBB. Physiologically relevant concentrations of both extracts were cytoprotective at endothelial level and BDP was neuroprotective in primary neurons and in an advanced 3D cell model. The major canonical pathways involved in the neuroprotective effect of BDP were unveiled, including mTOR signaling and the unfolded protein response pathway. Genes such as ASNS and ATF5 emerged as novel BDP-modulated targets.

CONCLUSIONS

BBB transport of BDP and hBDP components reinforces the health benefits of a diet rich in polyphenols in neurodegenerative disorders. Our results suggest some novel pathways and genes that may be involved in the neuroprotective mechanism of the BDP polyphenol components.

The transcription factor ATF5: role in cellular differentiation, stress responses, and cancer

Activating transcription factor 5 (ATF5) is a cellular prosurvival transcription factor within the basic leucine zipper (bZip) family that is involved in cellular differentiation and promotes cellular adaptation to stress. Recent studies have characterized the oncogenic role of ATF5 in the development of several different types of cancer, notably glioblastoma. Preclinical assessment of a systemically deliverable dominant-negative ATF5 (dnATF5) biologic has found that targeting ATF5 results in tumor regression and tumor growth inhibition of glioblastoma xenografts in mouse models. In this review, we comprehensively and critically detail the current scientific literature on ATF5 in the context of cellular differentiation, survival, and response to stressors in normal tissues. Furthermore, we will discuss how the prosurvival role of ATF5 aides in cancer development, followed by current advances in targeting ATF5 using dominant-negative biologics, and perspectives on future research.

Physiological/pathological ramifications of transcription factors in the unfolded protein response

Numerous environmental, physiological, and pathological insults disrupt protein-folding homeostasis in the endoplasmic reticulum (ER), referred to as ER stress. Eukaryotic cells evolved a set of intracellular signaling pathways, collectively termed the unfolded protein response (UPR), to maintain a productive ER protein-folding environment through reprogramming gene transcription and mRNA translation. The UPR is largely dependent on transcription factors (TFs) that modulate expression of genes involved in many physiological and pathological conditions, including development, metabolism, inflammation, neurodegenerative diseases, and cancer. Here we summarize the current knowledge about these mechanisms, their impact on physiological/pathological processes, and potential therapeutic applications.

Comprehensive Behavioral Analysis of Activating Transcription Factor 5-Deficient Mice

Activating transcription factor 5 (ATF5) is a member of the CREB/ATF family of basic leucine zipper transcription factors. We previously reported that ATF5-deficient (ATF5^-/-) mice demonstrated abnormal olfactory bulb development due to impaired interneuron supply. Furthermore, ATF5^-/- mice were less aggressive than ATF5^+/+ mice. Although ATF5 is widely expressed in the brain, and involved in the regulation of proliferation and development of neurons, the physiological role of ATF5 in the higher brain remains unknown. Our objective was to investigate the physiological role of ATF5 in the higher brain. We performed a comprehensive behavioral analysis using ATF5^-/- mice and wild type littermates. ATF5^-/- mice exhibited abnormal locomotor activity in the open field test. They also exhibited abnormal anxiety-like behavior in the light/dark transition test and open field test. Furthermore, ATF5^-/- mice displayed reduced social interaction in the Crawley’s social interaction test and increased pain sensitivity in the hot plate test compared with wild type. Finally, behavioral flexibility was reduced in the T-maze test in ATF5^-/- mice compared with wild type. In addition, we demonstrated that ATF5^-/- mice display disturbances of monoamine neurotransmitter levels in several brain regions. These results indicate that ATF5 deficiency elicits abnormal behaviors and the disturbance of monoamine neurotransmitter levels in the brain. The behavioral abnormalities of ATF5^-/- mice may be due to the disturbance of monoamine levels. Taken together, these findings suggest that ATF5^-/- mice may be a unique animal model of some psychiatric disorders.

Targeting ATF5 in Cancer

The expression of activating transcription factor 5 (ATF5) correlates negatively with patient survival in different types of cancer. ATF5 is important for the survival and proliferation of cancer cells, and can be targeted to selectively trigger cancer cell apoptosis while sparing normal cells. Cell-penetrating peptides combined with a dominant negative ATF5 cargo have recently shown efficacy against brain, breast, melanoma, and prostate cancers.

Mitochondrial dysfunction in cancer: Potential roles of ATF5 and the mitochondrial UPR

Mitochondria form a cellular network of organelles, or cellular compartments, that efficiently couple nutrients to energy production in the form of ATP. As cancer cells rely heavily on glycolysis, historically mitochondria and the cellular pathways in place to maintain mitochondrial activities were thought to be more relevant to diseases observed in non-dividing cells such as muscles and neurons. However, more recently it has become clear that cancers rely heavily on mitochondrial activities including lipid, nucleotide and amino acid synthesis, suppression of mitochondria-mediated apoptosis as well as oxidative phosphorylation (OXPHOS) for growth and survival. Considering the variety of conditions and stresses that cancer cell mitochondria may incur such as hypoxia, reactive oxygen species and mitochondrial genome mutagenesis, we examine potential roles for a mitochondrial-protective transcriptional response known as the mitochondrial unfolded protein response (UPR^mt) in cancer cell biology.

Expression and targeting of transcription factor ATF5 in dog gliomas

BACKGROUND

Activating transcription factor 5 (ATF5) is a transcription factor that is highly expressed in undifferentiated neural progenitor/stem cells as well as a variety of human cancers including gliomas.

AIMS

In this study, we examined the expression and localization of ATF5 protein in canine gliomas, and targeting of ATF5 function in canine glioma cell lines.

MATERIALS AND METHODS

Paraffin-embedded canine brain glioma tissue sections and western blots of tumours and glioma cells were immunoassayed with anti-ATF5 antibody. Viability of glioma cells was tested with a synthetic cell-penetrating ATF5 peptide (CP-d/n ATF5) ATF5 antagonist.

RESULTS

ATF5 protein expression was in the nucleus and cytoplasm and was present in normal adult brain and tumour samples, with significantly higher expression in tumours as shown by western immunoblotting. CP-d/n ATF5 was found to decrease cell viability in canine glioma cell lines in vitro in a dose-dependent manner.

CONCLUSION

Similarities in expression of ATF5 in rodent, dog and human tumours, and cross species efficacy of the CP-d/n ATF5 peptide support the development of this ATF5-targeting approach as a novel and translational therapy in dog gliomas.

ATF5 regulates β-cell survival during stress

The stress response and cell survival are necessary for normal pancreatic β-cell function, glucose homeostasis, and prevention of diabetes. The homeodomain transcription factor and human diabetes gene pancreas/duodenum homeobox protein 1 (Pdx1) regulates β-cell survival and endoplasmic reticulum stress susceptibility, in part through direct regulation of activating transcription factor 4 (Atf4). Here we show that Atf5, a close but less-studied relative of Atf4, is also a target of Pdx1 and is critical for β-cell survival under stress conditions. Pdx1 deficiency led to decreased Atf5 transcript, and primary islet ChIP-sequencing localized PDX1 to the Atf5 promoter, implicating Atf5 as a PDX1 target. Atf5 expression was stress inducible and enriched in β cells. Importantly, Atf5 deficiency decreased survival under stress conditions. Loss-of-function and chromatin occupancy experiments positioned Atf5 downstream of and parallel to Atf4 in the regulation of eIF4E-binding protein 1 (4ebp1), a mammalian target of rapamycin (mTOR) pathway component that inhibits protein translation. Accordingly, Atf5 deficiency attenuated stress suppression of global translation, likely enhancing the susceptibility of β cells to stress-induced apoptosis. Thus, we identify ATF5 as a member of the transcriptional network governing pancreatic β-cell survival during stress.

Activating Transcription Factor-5 Knockdown Reduces Aggressiveness of Mammary Tumor Cells and Attenuates Mammary Tumor Growth

Activating transcription factor-5 (ATF5) is an anti-apoptotic factor and has been implicated in enhancing the survival of cancer cells under stress and in regulating the autophagy process. Targeting ATF5 in anticancer therapy may be particularly attractive because of its differential role in cancer cells than in non-transformed cells, thus allowing specificity of the treatment. Using the delivery of short hairpin RNA vectors into the Mvt1 and Met1 cell lines, we tested the role of ATF5 in the development of mammary tumors in vivo and in regulating proliferation and migration of these cells in vitro. In this study, we demonstrate that knockdown of ATF5 (ATF5-KD) in both cell lines results in a decreased tumor volume and weight, as well as in a reduced proliferation rate and migratory potential of the cells. In addition, ATF5-KD led to an increased autophagy flux and a shift in the sub-populations comprising Mvt1 cells from the aggressive CD24-positive cells toward less aggressive CD24-negative cells. Taken together, these findings suggest that ATF5 plays an important role in enhancing mammary tumor cells overall aggressiveness and in promoting mammary tumor growth and emphasize the possible benefit of anti-ATF5 therapy in breast cancer patients, particularly, against tumors characterized with the positive expression of cell surface CD24.

Differential expression of two activating transcription factor 5 isoforms in papillary thyroid carcinoma

BACKGROUND

Activating transcription factor 5 (ATF5) is a member of the activating transcription/cAMP response element-binding protein family of basic leucine zipper proteins that plays an important role in cell survival, differentiation, proliferation, and apoptosis. The ATF5 gene generates two transcripts: ATF5 isoform 1 and ATF5 isoform 2. A number of studies indicate that ATF5 could be an attractive target for therapeutic intervention in several tumor types; however, so far, the role of ATF5 has not been investigated in papillary thyroid carcinoma (PTC).

METHODS

Quantitative real-time reverse transcription polymerase chain reaction and immuno-histochemical staining were used to study ATF5 mRNA and protein expression in PTC.

RESULTS

We report here that ATF5 is expressed more in PTC tissue than in normal thyroid tissue. Furthermore, this is the first study that describes the presence of both ATF5 isoforms in PTC.

CONCLUSION

These findings could provide potential applications in PTC cancer treatment.

DNA methylation level of promoter region of activating transcription factor 5 in glioma

Transcription factors, which represent an important class of proteins that play key roles in controlling cellular proliferation and cell cycle modulation, are attractive targets for cancer therapy. Previous researches have shown that the expression level of activating transcription factor 5 (ATF5) was frequently increased in glioma and its acetylation level was related to glioma. The purposes of this study were to explore the methylation level of ATF5 in clinical glioma tissues and to explore the effect of ATF5 methylation on the expression of ATF5 in glioma. Methylation of the promoter region of ATF5 was assayed by bisulfite-specific polymerase chain reaction (PCR) sequencing analysis in 35 cases of glioma and 5 normal tissues. Quantitative real-time PCR (qRT-PCR) was also performed to detect ATF5 mRNA expression in 35 cases of glioma and 5 normal tissues. Clinical data were collected from the patients and analyzed. The percentages of methylation of the ATF5 gene in the promoter region in healthy control, patients with well-differentiated glioma, and those with poorly differentiated glioma were 87.78%, 73.89%, and 47.70%, respectively. Analysis of the methylation status of the promoter region of the ATF5 gene showed a gradually decreased methylation level in poorly differentiated glioma, well-differentiated glioma, and normal tissues (P<0.05). There was also a significant difference between well-differentiated glioma and poorly differentiated glioma (P<0.05). ATF5 mRNA expression in glioma was significantly higher than that in the normal tissues (P<0.05). This study provides the first evidence that the methylation level of ATF5 decreased, and its mRNA expression was evidently up-regulated in glioma.

Translational control by eIF2α in neurons: Beyond the stress response

The translation of mRNAs is a tightly controlled process that responds to multiple signaling pathways. In neurons, this control is also exerted locally due to the differential necessity of proteins in axons and dendrites. The phosphorylation of the alpha subunit of the translation initiation factor 2 (eIF2α) is one of the mechanisms of translational control. The phosphorylation of eIF2α has classically been viewed as a stress response, halting translation initiation. However, in the nervous system this type of regulation has been related to other mechanisms besides stress response, such as behavior, memory consolidation and nervous system development. Additionally, neurodegenerative diseases have a major stress component, thus eIF2α phosphorylation plays a preeminent role and its modulation is currently viewed as a new opportunity for therapeutic interventions. This review consolidates current information regarding eIF2α phosphorylation in neurons and its impact in neurodegenerative diseases. © 2016 Wiley Periodicals, Inc.