Regulation of G(1) arrest and apoptosis in hypoxia by PERK and GCN2-mediated eIF2alpha phosphorylation

GCN2 kinase activation mediates pulmonary vascular remodeling and pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is characterized by progressive increase of pulmonary vascular resistance and remodeling that result in right heart failure. Recessive mutations of EIF2AK4 gene (encoding general control nonderepressible 2 kinase, GCN2) are linked to heritable pulmonary veno-occlusive disease (PVOD) in patients but rarely in patients with PAH. The role of GCN2 kinase activation in the pathogenesis of PAH remains unclear. Here, we show that GCN2 was hyperphosphorylated and activated in pulmonary vascular endothelial cells (ECs) of hypoxic mice, monocrotaline-treated rats, and patients with idiopathic PAH. Unexpectedly, loss of GCN2 kinase activity in Eif2ak4-/- mice with genetic disruption of the kinase domain induced neither PVOD nor pulmonary hypertension (PH) but inhibited hypoxia-induced PH. RNA-sequencing analysis suggested endothelin-1 (Edn1) as a downstream target of GCN2. GCN2 mediated hypoxia-induced Edn1 expression in human lung ECs via HIF-2α. Restored Edn1 expression in ECs of Eif2ak4-/- mice partially reversed the reduced phenotype of hypoxia-induced PH. Furthermore, GCN2 kinase inhibitor A-92 treatment attenuated PAH in monocrotaline-treated rats. These studies demonstrate that GCN2 kinase activation mediates pulmonary vascular remodeling and PAH at least partially through Edn1. Thus, targeting GCN2 kinase activation is a promising therapeutic strategy for treatment of PAH in patients without EIF2AK4 loss-of-function mutations.

Loss of Gcn2 exacerbates gossypol induced oxidative stress, apoptosis and inflammation in zebrafish

Gossypol, a naturally occurring compound found in cottonseed meal, shows promising therapeutic potential for human diseases. However, within the aquaculture industry, it is considered an antinutritional factor. The incorporation of cottonseed meal into fish feed introduces gossypol, which induces intracellular stresses and hinders overall health of farmed fish. The aim of this study is to determine the role of General control nonderepressible 2 (gcn2), a sensor for intracellular stresses in gossypol-induced stress responses in fish. In the present study, we established two gcn2 knockout zebrafish lines. A feeding trial was conducted to assess the growth-inhibitory effect of gossypol in both wild type and gcn2 knockout zebrafish. The results showed that in the absence of gcn2, zebrafish exhibited increased oxidative stress and apoptosis when exposed to gossypol, resulting in higher mortality rates. In feeding trial, dietary gossypol intensified liver inflammation in gcn2-/- zebrafish, diminishing their growth and feed conversion. Remarkably, administering the antioxidant N-acetylcysteine (NAC) was effective in reversing the gossypol induced oxidative stress and apoptosis, thereby increasing the gossypol tolerance of gcn2-/- zebrafish. Exposure to gossypol induces more severe mitochondrial stress in gcn2-/- zebrafish, thereby inducing metabolic disorders. These results reveal that gcn2 plays a protective role in reducing gossypol-induced oxidative stress and apoptosis, attenuating inflammation responses, and enhancing the survivability of zebrafish in gossypol-challenged conditions. Therefore, maintaining appropriate activation of Gcn2 may be beneficial for fish fed diets containing gossypol.

Protein aggregation and biomolecular condensation in hypoxic environments (Review)

Due to molecular forces, biomacromolecules assemble into liquid condensates or solid aggregates, and their corresponding formation and dissolution processes are controlled. Protein homeostasis is disrupted by increasing age or environmental stress, leading to irreversible protein aggregation. Hypoxic pressure is an important factor in this process, and uncontrolled protein aggregation has been widely observed in hypoxia‑related conditions such as neurodegenerative disease, cardiovascular disease, hypoxic brain injury and cancer. Biomolecular condensates are also high‑order complexes assembled from macromolecules. Although they exist in different phase from protein aggregates, they are in dynamic balance under certain conditions, and their activation or assembly are considered as important regulatory processes in cell survival with hypoxic pressure. Therefore, a better understanding of the relationship between hypoxic stress, protein aggregation and biomolecular condensation will bring marked benefits in the clinical treatment of various diseases. The aim of the present review was to summarize the underlying mechanisms of aggregate assembly and dissolution induced by hypoxic conditions, and address recent breakthroughs in understanding the role of aggregates in hypoxic‑related diseases, given the hypotheses that hypoxia induces macromolecular assemblage changes from a liquid to a solid phase, and that adenosine triphosphate depletion and ATP‑driven inactivation of multiple protein chaperones play important roles among the process. Moreover, it is anticipated that an improved understanding of the adaptation in hypoxic environments could extend the overall survival of patients and provide new strategies for hypoxic‑related diseases.

When autophagy meets placenta development and pregnancy complications

Autophagy is a common biological phenomenon in eukaryotes that has evolved and reshaped to maintain cellular homeostasis. Under the pressure of starvation, hypoxia, and immune damage, autophagy provides energy and nutrients to cells, which benefits cell survival. In mammals, autophagy is an early embryonic nutrient supply system involved in early embryonic development, implantation, and pregnancy maintenance. Recent studies have found that autophagy imbalance in placental tissue plays a key role in the occurrence and development of pregnancy complications, such as gestational hypertension, gestational obesity, premature birth, miscarriage, and intrauterine growth restriction. This mini-review summarizes the molecular mechanism of autophagy regulation, the autophagy pathways, and related factors involved in placental tissue and comprehensively describes the role of autophagy in pregnancy complications.

HIF: a master regulator of nutrient availability and metabolic cross-talk in the tumor microenvironment

A role for hypoxia-inducible factors (HIFs) in hypoxia-dependent regulation of tumor cell metabolism has been thoroughly investigated and covered in reviews. However, there is limited information available regarding HIF-dependent regulation of nutrient fates in tumor and stromal cells. Tumor and stromal cells may generate nutrients necessary for function (metabolic symbiosis) or deplete nutrients resulting in possible competition between tumor cells and immune cells, a result of altered nutrient fates. HIF and nutrients in the tumor microenvironment (TME) affect stromal and immune cell metabolism in addition to intrinsic tumor cell metabolism. HIF-dependent metabolic regulation will inevitably result in the accumulation or depletion of essential metabolites in the TME. In response, various cell types in the TME will respond to these hypoxia-dependent alterations by activating HIF-dependent transcription to alter nutrient import, export, and utilization. In recent years, the concept of metabolic competition has been proposed for critical substrates, including glucose, lactate, glutamine, arginine, and tryptophan. In this review, we discuss how HIF-mediated mechanisms control nutrient sensing and availability in the TME, the competition for nutrients, and the metabolic cross-talk between tumor and stromal cells.

Potent GCN2 Inhibitor Capable of Reversing MDSC-Driven T Cell Suppression Demonstrates In Vivo Efficacy as a Single Agent and in Combination with Anti-Angiogenesis Therapy

General control nonderepressible 2 (GCN2) protein kinase is a cellular stress sensor within the tumor microenvironment (TME), whose signaling cascade has been proposed to contribute to immune escape in tumors. Herein, we report the discovery of cell-potent GCN2 inhibitors with excellent selectivity against its closely related Integrated Stress Response (ISR) family members heme-regulated inhibitor kinase (HRI), protein kinase R (PKR), and (PKR)-like endoplasmic reticulum kinase (PERK), as well as good kinome-wide selectivity and favorable PK. In mice, compound 39 engages GCN2 at levels ≥80% with an oral dose of 15 mg/kg BID. We also demonstrate the ability of compound 39 to alleviate MDSC-related T cell suppression and restore T cell proliferation, similar to the effect seen in MDSCs from GCN2 knockout mice. In the LL2 syngeneic mouse model, compound 39 demonstrates significant tumor growth inhibition (TGI) as a single agent. Furthermore, TGI mediated by anti-VEGFR was enhanced by treatment with compound 39 demonstrating the complementarity of these two mechanisms.

Endoplasmic Reticulum Stress of Gut Enterocyte and Intestinal Diseases

The endoplasmic reticulum, a vast reticular membranous network from the nuclear envelope to the plasma membrane responsible for the synthesis, maturation, and trafficking of a wide range of proteins, is considerably sensitive to changes in its luminal homeostasis. The loss of ER luminal homeostasis leads to abnormalities referred to as endoplasmic reticulum (ER) stress. Thus, the cell activates an adaptive response known as the unfolded protein response (UPR), a mechanism to stabilize ER homeostasis under severe environmental conditions. ER stress has recently been postulated as a disease research breakthrough due to its significant role in multiple vital cellular functions. This has caused numerous reports that ER stress-induced cell dysfunction has been implicated as an essential contributor to the occurrence and development of many diseases, resulting in them targeting the relief of ER stress. This review aims to outline the multiple molecular mechanisms of ER stress that can elucidate ER as an expansive, membrane-enclosed organelle playing a crucial role in numerous cellular functions with evident changes of several cells encountering ER stress. Alongside, we mainly focused on the therapeutic potential of ER stress inhibition in gastrointestinal diseases such as inflammatory bowel disease (IBD) and colorectal cancer. To conclude, we reviewed advanced research and highlighted future treatment strategies of ER stress-associated conditions.

Role of indoleamine 2,3-dioxygenase in ischemia-reperfusion injury of renal tubular epithelial cells

The present study evaluated indoleamine 2,3-dioxygenase 1 (IDO) kinetics and how it affects cell survival during the two distinct phases of ischemia-reperfusion (I-R) injury. Primary renal proximal tubular epithelial cells (RPTECs) were cultured under anoxia or reoxygenation with or without the IDO inhibitor 1-DL-methyltryptophan, the aryl-hydrocarbon receptor (AhR) inhibitor CH223191 or the ferroptosis inhibitor α-tocopherol. Using cell imaging, colorimetric assays, PCR and western blotting, it was demonstrated that IDO was upregulated and induced apoptosis during anoxia. The related molecular pathway entails tryptophan degradation, general control non-derepressible-2 kinase (GCN2K) activation, increased level of phosphorylated eukaryotic translation initiation factor 2α, activating transcription factor (ATF)4, ATF3, C/EBP homologous protein, phosphorylated p53, p53, Bax, death receptor-5 and eventually activated cleaved caspase-3. Reoxygenation also upregulated IDO, which, in this case, induced ferroptosis. The related molecular pathway encompasses kynurenine production, AhR activation, cytochrome p450 enzymes increase, reactive oxygen species generation and eventually ferroptosis. In conclusion, in RPTECs, both anoxia and reoxygenation upregulated IDO, which in turn induced GCN2K-mediated apoptosis and AhR-mediated ferroptosis. Since both phases of I-R injury share IDO upregulation as a common point, its inhibition may prove a useful therapeutic strategy for preventing or attenuating I-R injury.

Raloxifene prevents stress granule dissolution, impairs translational control and promotes cell death during hypoxia in glioblastoma cells

Glioblastoma (GBM) is the most common primary malignant brain tumor, and it has a uniformly poor prognosis. Hypoxia is a feature of the GBM microenvironment, and previous work has shown that cancer cells residing in hypoxic regions resist treatment. Hypoxia can trigger the formation of stress granules (SGs), sites of mRNA triage that promote cell survival. A screen of 1120 FDA-approved drugs identified 129 candidates that delayed the dissolution of hypoxia-induced SGs following a return to normoxia. Amongst these candidates, the selective estrogen receptor modulator (SERM) raloxifene delayed SG dissolution in a dose-dependent manner. SG dissolution typically occurs by 15 min post-hypoxia, however pre-treatment of immortalized U251 and U3024 primary GBM cells with raloxifene prevented SG dissolution for up to 2 h. During this raloxifene-induced delay in SG dissolution, translational silencing was sustained, eIF2α remained phosphorylated and mTOR remained inactive. Despite its well-described role as a SERM, raloxifene-mediated delay in SG dissolution was unaffected by co-administration of β-estradiol, nor did β-estradiol alone have any effect on SGs. Importantly, the combination of raloxifene and hypoxia resulted in increased numbers of late apoptotic/necrotic cells. Raloxifene and hypoxia also demonstrated a block in late autophagy similar to the known autophagy inhibitor chloroquine (CQ). Genetic disruption of the SG-nucleating proteins G3BP1 and G3BP2 revealed that G3BP1 is required to sustain the raloxifene-mediated delay in SG dissolution. Together, these findings indicate that modulating the stress response can be used to exploit the hypoxic niche of GBM tumors, causing cell death by disrupting pro-survival stress responses and control of protein synthesis.

The role of host eIF2α in viral infection

Background

eIF2α is a regulatory node that controls protein synthesis initiation by its phosphorylation or dephosphorylation. General control nonderepressible-2 (GCN2), protein kinase R-like endoplasmic reticulum kinase (PERK), double-stranded RNA (dsRNA)-dependent protein kinase (PKR) and heme-regulated inhibitor (HRI) are four kinases that regulate eIF2α phosphorylation.

Main body

In the viral infection process, dsRNA or viral proteins produced by viral proliferation activate different eIF2α kinases, resulting in eIF2α phosphorylation, which hinders ternary tRNA^Met-GTP-eIF2 complex formation and inhibits host or viral protein synthesis. The stalled messenger ribonucleoprotein (mRNP) complex aggregates under viral infection stress to form stress granules (SGs), which encapsulate viral RNA and transcription- and translation-related proteins, thereby limiting virus proliferation. However, many viruses have evolved a corresponding escape mechanism to synthesize their own proteins in the event of host protein synthesis shutdown and SG formation caused by eIF2α phosphorylation, and viruses can block the cell replication cycle through the PERK-eIF2α pathway, providing a favorable environment for their own replication. Subsequently, viruses can induce host cell autophagy or apoptosis through the eIF2α-ATF4-CHOP pathway.

Conclusions

This review summarizes the role of eIF2α in viral infection to provide a reference for studying the interactions between viruses and hosts.

Targeting Protein Synthesis in Colorectal Cancer

Under physiological conditions, protein synthesis controls cell growth and survival and is strictly regulated. Deregulation of protein synthesis is a frequent event in cancer. The majority of mutations found in colorectal cancer (CRC), including alterations in the WNT pathway as well as activation of RAS/MAPK and PI3K/AKT and, subsequently, mTOR signaling, lead to deregulation of the translational machinery. Besides mutations in upstream signaling pathways, deregulation of global protein synthesis occurs through additional mechanisms including altered expression or activity of initiation and elongation factors (e.g., eIF4F, eIF2α/eIF2B, eEF2) as well as upregulation of components involved in ribosome biogenesis and factors that control the adaptation of translation in response to stress (e.g., GCN2). Therefore, influencing mechanisms that control mRNA translation may open a therapeutic window for CRC. Over the last decade, several potential therapeutic strategies targeting these alterations have been investigated and have shown promising results in cell lines, intestinal organoids, and mouse models. Despite these encouraging in vitro results, patients have not clinically benefited from those advances so far. In this review, we outline the mechanisms that lead to deregulated mRNA translation in CRC and highlight recent progress that has been made in developing therapeutic strategies that target these mechanisms for tumor therapy.

eIF2α phosphorylation and the regulation of translation

We discuss novel insight into the role and consequences of the phosphorylation of the translation initiation factor eIF2α in the context of stress responses and cell-cycle regulation. eIF2α is centrally located to regulate translation and its phosphorylation in response to different environmental challenges is one of the best characterized stress-response pathways. In addition to its role in stress management, eIF2α phosphorylation is also linked to cell-cycle progression and memory consolidation in the nervous system. The best known consequences of eIF2α phosphorylation are downregulation of global translation and stimulation of translation of some mRNAs. However, recent evidence shows that (i) eIF2α phosphorylation is not always required for the downregulation of global translation after exposure to stress and (ii) eIF2α phosphorylation does not necessarily lead to the downregulation of global translation. These results suggest that the textbook view of eIF2α phosphorylation needs to be revised and that there must be additional regulatory mechanisms at play.

Unique wreath-like smooth muscle proliferation of the pulmonary vasculature in pulmonary veno-occlusive disease versus pulmonary arterial hypertension

BACKGROUND/PURPOSE

Pulmonary veno-occlusive disease (PVOD) is a rare but fatal cause of pulmonary hypertension reported to be linked to mutations of eukaryotic initiation factor 2 alpha kinase 4 (EIF2AK4), also known as general control nonderepressible 2 kinase (GCN2). PVOD is difficult to diagnose and often initially misdiagnosed as other types of idiopathic pulmonary arterial hypertension (IPAH). To rapidly and correctly identify PVOD patients and explore the possible pathogenesis, we thoroughly investigated histopathological features and GCN2 protein levels in non-PAH, PVOD and PAH patients.

METHODS

Lung specimens were examined for histopathological changes, including those of pulmonary arteries and veins, by Masson's trichrome, modified Verhoeff's and α-SMA staining in the PVOD, IPAH, and non-PAH groups. GCN2 and α-SMA expression in lung tissue was examined by immunohistochemistry and western blotting.

RESULTS

PVOD and IPAH patients showed significant intimal and medial thickening of muscular pulmonary arteries compared with non-PAH patients. PVOD patients had more prominent intimal and medial thickening of muscular pulmonary veins than the other two groups. Interestingly, specialized muscle bundles surrounding the tunica adventitia of the pulmonary artery and vein were observed in PVOD patients. A significant decrease in GCN2 expression in the PVOD group was confirmed by immunohistochemistry and western blotting.

CONCLUSION

Our study is the first to show remarkable histological structures, including the wreath-like arrangement of a hyperplastic muscle bundle in the adventitia of pulmonary arteries, in PVOD patients as a diagnostic clue and to disclose the biological difference between PAH and PVOD in a Taiwanese population.

Genomic signatures of high-altitude adaptation in Ethiopian sheep populations

BACKGROUND

Ethiopian sheep populations such as Arsi-Bale, Horro and Adilo (long fat-tailed, LFT) inhabit mid to high-altitude areas; and Menz sheep (MZ, short fat-tailed) are adapted to cool sub-alpine environments. In contrast, Blackhead Somali sheep (BHS, fat-rumped) thrive well in arid and semi-arid areas characterized by high temperature and low precipitation. The genomic investigation of Ethiopian sheep populations may help to identify genes and biological pathways enable to adapt to the different ecological conditions.

OBJECTIVE

To uncover genomic regions and genes showing evidence of positive selection for altitude adaptation in Ethiopian sheep populations.

METHODS

A total of 72 animals inhabiting high-versus low-altitude environments were genotyped on an Ovine Infinium HD array (~ 600 K). Pairwise genetic differentiation (Fst) was calculated in sliding windows of 20 SNPs and the upper 1% smoothed Fst values were considered to represent positive selection signatures. Genes within < 25 kb of the most differentiated SNPs were considered as selection candidates.

RESULTS

Signatures of selection were detected in genes known to be associated high with altitude adaptation in MZ-BHS pair comparison (PPP1R12A, RELN, PARP2, and DNAH9) and in LFT-BHS pair comparison (VAV3, MSRB3,EIF2AK4, MET, and TACR1). The candidate genes (MITF, FGF5, MTOR, TRHDE, and TUBB3) associated with altitude adaptation and shared between the MZ-BHS and LTF-BHS pair comparisons were also detected as under selection. Further functional analyses reveal that the candidate genes were involved in biological processes and pathways relevant to adaptation under extreme altitudes, including respiratory system development and smoothened signaling pathway.

CONCLUSION

The results of the present study could aid in-depth understanding and exploitation of the underlying genetic mechanisms for sheep and other livestock species adaptation to high-altitude environments.

Endoplasmic Reticulum Stress and Autophagy

In 1945, K. R. Porter et al. observed mouse embryonic fibroblasts (MEFs) and found that the cytoplasmic part of the cell had an unreported reticular structure, so it was named endoplasmic reticulum (ER). The major functions of the endoplasmic reticulum are: synthesis of intracellular proteins and the modification and processing of proteins. It is an important organelle in eukaryotic cells. It is a three-dimensional network structure in which complex and closed intracellular tubular intimal systems are intertwined. When cells are subjected to various strong stimulating factors such as nutrient deficiencies, Ca²⁺ metabolic imbalance, toxin stimulation, and sustained oxidative stress stimulation, the cell homeostasis will be broken. In order to survive, a series of cell self-protection event will be initiated including the endoplasmic reticulum stress (ERS). The UPR can further promote the expression of the proteins which can help the misfolded and unfolded proteins restore to its normal structure through the activation of PERK, IRE1, and ATF6. However, the co-working of UPR and the ubiquitin-proteasome system still cannot make the endoplasmic reticulum restoring to its normal state, when the stimuli persist or are too strong. The damaged endoplasmic reticulum can be partially engulfed by the autophagic vesicles for degradation when the ERS persists. The degraded endoplasmic reticulum fragments can be reassembled into a new endoplasmic reticulum to restore the normal state of it. Hence, it seems that the autophagy has become the last mean to restore the homeostasis of endoplasmic reticulum.

Triazolo[4,5-d]pyrimidines as Validated General Control Nonderepressible 2 (GCN2) Protein Kinase Inhibitors Reduce Growth of Leukemia Cells

Cellular stress signals activate adaptive signaling pathways of the mammalian integrated stress response (ISR), of which the unfolded protein response (UPR) is a subset. These pathways converge at the phosporylation of eIF2α. Drug-like, potent and selective chemical inhibitors (valid chemical probes) targeting major ISR kinases have been previously identified, with the exception of GCN2. We synthesized and evaluated a series of GCN2 inhibitors based on a triazolo[4,5-d]pyrimidine scaffold. Several compounds potently inhibited GCN2 in vitro and displayed good selectivity over the related kinases PERK, HRI, and IRE1. The compounds inhibited phosporylation of eIF2α in HEK293T cells with an IC₅₀ < 150 nM, validating them as chemical probes for cellular studies. These probes were screened against the National Cancer Institute NCI-60 human cancer cell line panel. Uniform growth inhibition was observed in the leukemia group of cell lines. Growth inhibition in the most sensitive cell lines coincided with high GCN2 mRNA expression levels. Oncomine analysis revealed high GCN2 expression accompanied by lower asparagine synthetase (ASNS) expression in patient-derived acute lymphoblastic leukemias with B-Cell origins (B-ALL) as well. Notably, asparaginase, which depletes amino acids and triggers GCN2 activity, is a licensed, first-line B-ALL treatment. Thus, we hypothesize that leukemias exhibiting high GCN2 expression and low ASNS expression may be susceptible to pharmacologic GCN2 inhibition.

Genome-wide scan reveals divergent selection among taurine and zebu cattle populations from different regions

In this study, to identify genomic signatures of divergent selection, we genotyped 10 cattle breeds/populations (n = 275), representing eight Ethiopian cattle populations (n = 229) and two zebu populations (n = 46) adapted to tropical and sub-tropical environments, using the high-density single-nucleotide polymorphisms (SNPs) derived mainly from Bos indicus breeds, and using five reference taurine breeds (n = 212). Population genetic differentiation (F_ST ) values across sliding windows were estimated between zebu and reference combined taurine breeds. The most differentiated regions (F_ST  ≥ 0.53), representing the top 1% smoothed F_ST values, were considered to represent regions under diversifying selection. In total, 285 and 317 genes were identified in the comparisons of Ethiopian cattle with taurine and Asian zebu with taurine respectively. Some of these genes are involved in stress responses/thermo-tolerance and DNA damage repair (HSPA4, HSF1, CMPK1 and EIF2AK4), pigmentation (ERBB3 and MYO1A), reproduction/fertility (UBE2D3, ID3 and PSPC1), immune response (PIK3CD and AKIRIN2) and body stature and size (MBP2, LYN and NPM1). Additionally, the candidate genes were associated with functional terms (e.g. cellular response to stress, DNA repair, inflammatory response) important for physiological adaptation to environmental stresses. The results of our study may shed light on the influence of artificial and natural selection in shaping the genomic diversity of modern cattle breeds and also may serve as a basis for further genetic investigation of traits of tropical adaptation in cattle.

Blocking autophagy enhances the pro-apoptotic effect of bufalin on human gastric cancer cells through endoplasmic reticulum stress

Bufalin has been used to treat cancer for several years. However, the molecular mechanisms for its anti-tumor function are not fully understood. This work aimed to investigate the effect of bufalin on the proliferation and apoptosis of human gastric cancer (HGC) cells and the roles of endoplasmic reticulum (ER) stress and autophagy in bufalin-induced apoptosis. HGC cell lines, SGC7901 and BGC823, were treated with different concentrations of bufalin or 80 nmol/l bufalin for 1, 2, 3 and 4 days. Cell counting kit-8 (CCK-8) assay and direct cell counting method were used to detect proliferation. Cell cycle arrest and apoptosis was detected using flow cytometry. Protein levels of caspase-3, -8, Bax/Bcl-2, Beclin-1, LC3, inositol-requiring enzyme 1 (IRE1) and C/EBP homologous protein (CHOP) were determined using western blotting. Autophagy was blocked using 3-methyladenine (3MA) or Atg5 siRNA to evaluate the effect of autophagy on bufalin-induced apoptosis. The IRE1 and CHOP were knocked down using specific siRNA to determine the pathway involved in bufalin-induced autophagy. It was found that bufalin significantly suppressed proliferation of SGC7901 and BGC823 cells and induced apoptosis in a time- and dose-dependent manner. The mechanism responsible for bufalin-induced apoptosis was the formation of ER stress via the IRE1-JNK pathway. Moreover, autophagy was activated during ER stress, and blocking autophagy significantly exacerbated bufalin-induced apoptosis.

Summary: Bufalin suppressed human gastric cancer cells and induced apoptosis. The mechanism was related to ER stress formation via the IRE1-JNK pathway. Blocking autophagy exacerbated bufalin-induced apoptosis.

The Integrated Stress Response in Hypoxia-Induced Diffuse White Matter Injury

Currently no treatments exist for preterm infants with diffuse white matter injury (DWMI) caused by hypoxia. Due to the improved care of preterm neonates and increased recognition by advanced imaging techniques, the prevalence of DWMI is increasing. A better understanding of the pathophysiology of DWMI is therefore of critical importance. The integrated stress response (ISR), a conserved eukaryotic response to myriad stressors including hypoxia, may play a role in hypoxia-induced DWMI and may represent a novel target for much needed therapies. In this study, we use in vitro and in vivo hypoxic models of DWMI to investigate whether the ISR is involved in DWMI. We demonstrate that hypoxia activates the ISR in primary mouse oligodendrocyte precursor cells (OPCs) in vitro and that genetically inhibiting the ISR in differentiating OPCs increases their susceptibility to in vitro hypoxia. We also show that a well established in vivo mild chronic hypoxia (MCH) mouse model and a new severe acute hypoxia (SAH) mouse model of DWMI activates the initial step of the ISR. Nonetheless, genetic inhibition of the ISR has no detectable effect on either MCH- or SAH-induced DWMI. In addition, we demonstrate that genetic enhancement of the ISR does not ameliorate MCH- or SAH-induced DWMI. These studies suggest that, while the ISR protects OPCs from hypoxia in vitro, it does not appear to play a major role in either MCH- or SAH-induced DWMI and is therefore not a likely target for therapies aimed at improving neurological outcome in preterm neonates with hypoxia-induced DWMI.SIGNIFICANCE STATEMENT Diffuse white matter injury (DWMI) caused by hypoxia is a leading cause of neurological deficits following premature birth. An increased understanding of the pathogenesis of this disease is critical. The integrated stress response (ISR) is activated by hypoxia and protects oligodendrocyte lineage cells in other disease models. This has led to an interest in the potential role of the ISR in DWMI. Here we examine the ISR in hypoxia-induced DWMI and show that while the ISR protects oligodendrocyte lineage cells from hypoxia in vitro, genetic inhibition or enhancement of the ISR has no effect on hypoxia-induced DWMI in vivo, suggesting that the ISR does not play a major role in and is not a likely therapeutic target for DWMI.

Preconditioning of primary human renal proximal tubular epithelial cells without tryptophan increases survival under hypoxia by inducing autophagy

PURPOSE

Hypoxia plays a significant role in the pathogenesis of acute kidney injury (AKI). Autophagy protects from AKI. Amino acid deprivation induces autophagy. The effect of L-tryptophan depletion on survival and autophagy in cultures of renal proximal tubular epithelial cells (RPTECs) under hypoxia was evaluated.

METHODS

RPTECs were preconditioned in a medium containing or not tryptophan, following culture under hypoxia and treatment with or without the autophagy inhibitor chloroquine. Cell survival was assessed by cell imaging, the level of certain proteins by western blotting and cellular ATP fluorometrically.

RESULTS

Preconditioning of RPTECs in a medium without tryptophan activated general control nonderepressible 2 kinase and induced changes that favored autophagy and cell survival under hypoxic conditions. Additionally, it increased cellular ATP, while it inhibited apoptosis. Inhibition of autophagy nullified the induced increase in cellular ATP and cell survival by the absence of tryptophan. The absence of tryptophan increased p53, although its effect on p53's transcriptional targets was heterogeneous. In accordance with the decreased apoptosis, expression of p21 increased, while expression of Bax decreased. The expression of BNIP3L, which may be pro-apoptotic or pro-autophagic, increased. Considering the decreased apoptosis, it is likely that tryptophan depletion enhances autophagy through a p53-mediated increase of BNIP3L.

CONCLUSION

Preconditioning of primary human RPTECs in a medium without tryptophan increases their survival under hypoxia by inducing autophagy. Identifying new molecular mechanisms that protect renal tissue from hypoxia could be proved clinically important in the prevention of AKI.

Integrated stress response of vertebrates is regulated by four eIF2α kinases

The integrated stress response (ISR) is a cytoprotective pathway initiated upon phosphorylation of the eukaryotic translation initiation factor 2 (eIF2α) residue designated serine-51, which is critical for translational control in response to various stress conditions. Four eIF2α kinases, namely heme-regulated inhibitor (HRI), protein kinase R (PKR), PKR-like endoplasmic reticulum kinase, (PERK) and general control non-depressible 2 (GCN2), have been identified thus far, and they are known to be activated by heme depletion, viral infection, endoplasmic reticulum stress, and amino acid starvation, respectively. Because eIF2α is phosphorylated under various stress conditions, the existence of an additional eIF2α kinase has been suggested. To validate the existence of the unidentified eIF2α kinase, we constructed an eIF2α kinase quadruple knockout cells (4KO cells) in which the four known eIF2α kinase genes were deleted using the CRISPR/Cas9-mediated genome editing. Phosphorylation of eIF2α was completely abolished in the 4KO cells by various stress stimulations. Our data suggests that the four known eIF2α kinases are sufficient for ISR and that there are no additional eIF2α kinases in vertebrates.

EIF2AK4 mutation in pulmonary veno-occlusive disease: A case report and review of the literature

BACKGROUND

Pulmonary veno-occlusive disease (PVOD) is a rare and devastating cause of pulmonary arterial hypertension with a non-specific clinical presentation and a relatively specific presentation in high-resolution thoracic CT scan images. Definitive diagnosis is made by histological examination in previous. According to the 2015 ESC/ERS Guidelines, detection of a mutation in the eukaryotic translation initiation factor 2 alpha kinase 4 (EIF2AK4) without histological confirmation is recommended to validate the diagnosis of PVOD.

METHODS

We report the case of a 27-year-old man who was admitted for persistent cough and dyspnea that had lasted for 5 months and had developed and experienced progressive dyspnea for the last 2 months. The echocardiogram and right heart catheterization without vasodilator challenge confirmed the diagnosis of pulmonary arterial hypertension. Other tests, such as high-resolution thoracic CT scan, V/Q scan, pulmonary function test with diffusion capacity, and blood tests, excluded other associated diseases which could have caused pulmonary hypertension.

RESULTS

The initial diagnosis at admission was idiopathic pulmonary arterial hypertension and an oral vasodilator (sildenafil) was given. However, the dyspnea subsequently worsened, and the patient was transferred to a regional lung transplant center, where he died of heart failure 1 week later. Using exome sequencing, we found an EIF2AK4 mutation, which was sufficient to confirm the diagnosis of PVOD.

CONCLUSION

This is the first reported case of EIF2AK4 mutation in PVOD in a Chinese patient population. We found the frameshift EIF2AK4 mutation c.1392delT (p.Arg465fs) in this case. Up to now, there has been a paucity of data on this rare disease, and the exact role of EIF2AK4 loss-of-function mutations in the pathogenesis of PVOD is still unknown. More investigations should be conducted in the future.

Tauroursodeoxycholic acid reduces the invasion of MDA-MB-231 cells by modulating matrix metalloproteinases 7 and 13

Tauroursodeoxycholic acid (TUDCA) is a conjugated form of UDCA that modulates several signaling pathways and acts as a chemical chaperone to relieve endoplasmic reticulum (ER) stress. The present study showed that TUDCA reduced the invasion of the MDA-MB-231 metastatic breast cancer cell line under normoxic and hypoxic conditions using an in vitro invasion assay. Quantitative polymerase chain reaction assay revealed that the reduced invasion following TUDCA treatment was associated with a decreased expression of matrix metalloproteinase (MMP)-7 and -13, which play important roles in invasion and metastasis. Inhibitors and short hairpin RNAs were used to show that the effect of TUDCA in the reduction of invasion appeared to be dependent on the protein kinase RNA-like ER kinase pathway, a downstream ER stress signaling pathway. Thus, TUDCA is a candidate anti-metastatic agent to target the ER stress pathway.

Hypoxia reduces ER-to-Golgi protein trafficking and increases cell death by inhibiting the adaptive unfolded protein response in mouse beta cells

AIMS/HYPOTHESIS

Hypoxia may contribute to beta cell failure in type 2 diabetes and islet transplantation. The adaptive unfolded protein response (UPR) is required for endoplasmic reticulum (ER) homeostasis. Here we investigated whether or not hypoxia regulates the UPR in beta cells and the role the adaptive UPR plays during hypoxic stress.

METHODS

Mouse islets and MIN6 cells were exposed to various oxygen (O2) tensions. DNA-damage inducible transcript 3 (DDIT3), hypoxia-inducible transcription factor (HIF)1α and HSPA5 were knocked down using small interfering (si)RNA; Hspa5 was also overexpressed. db/db mice were used.

RESULTS

Hypoxia-response genes were upregulated in vivo in the islets of diabetic, but not prediabetic, db/db mice. In isolated mouse islets and MIN6 cells, O2 deprivation (1-5% vs 20%; 4-24 h) markedly reduced the expression of adaptive UPR genes, including Hspa5, Hsp90b1, Fkbp11 and spliced Xbp1. Coatomer protein complex genes (Copa, Cope, Copg [also known as Copg1], Copz1 and Copz2) and ER-to-Golgi protein trafficking were also reduced, whereas apoptotic genes (Ddit3, Atf3 and Trb3 [also known as Trib3]), c-Jun N-terminal kinase (JNK) phosphorylation and cell death were increased. Inhibition of JNK, but not HIF1α, restored adaptive UPR gene expression and ER-to-Golgi protein trafficking while protecting against apoptotic genes and cell death following hypoxia. DDIT3 knockdown delayed the loss of the adaptive UPR and partially protected against hypoxia-induced cell death. The latter response was prevented by HSPA5 knockdown. Finally, Hspa5 overexpression significantly protected against hypoxia-induced cell death.

CONCLUSIONS/INTERPRETATION

Hypoxia inhibits the adaptive UPR in beta cells via JNK and DDIT3 activation, but independently of HIF1α. Downregulation of the adaptive UPR contributes to reduced ER-to-Golgi protein trafficking and increased beta cell death during hypoxic stress.

Role of GCN2-Independent Signaling Through a Noncanonical PERK/NRF2 Pathway in the Physiological Responses to Dietary Methionine Restriction

Restricting availability of essential amino acids (EAAs) limits aminoacylation of tRNAs by their cognate EAAs and activates the nutrient-sensing kinase, general control nonderepressible 2 (GCN2). Activated GCN2 phosphorylates eukaryotic initiation factor 2 (eIF2), altering gene-specific translation and initiating a transcriptional program collectively described as the integrated stress response (ISR). Central GCN2 activation by EAA deprivation is also linked to an acute aversive feeding response. Dietary methionine restriction (MR) produces a well-documented series of physiological responses (increased energy intake and expenditure, decreased adiposity, and increased insulin sensitivity), but the role of GCN2 in mediating them is unknown. Using Gcn2(-/-) mice, we found that the absence of GCN2 had no effect on the ability of MR to reduce body weight or adiposity, increase energy intake and expenditure, increase hepatic transcription and release of fibroblast growth factor 21, or improve insulin sensitivity. Interestingly, hepatic eIF2 phosphorylation by MR was uncompromised in Gcn2(-/-) mice. Instead, protein kinase R-like endoplasmic reticulum (ER) kinase (PERK) was activated in both intact and Gcn2(-/-) mice. PERK activation corresponded with induction of the ISR and the nuclear respiratory factor 2 antioxidant program but not ER stress. These data uncover a novel glutathione-sensing mechanism that functions independently of GCN2 to link dietary MR to its metabolic phenotype.

Hypoxia Activates Calpains in the Nerve Fiber Layer of Monkey Retinal Explants

PURPOSE

The vascular ischemic hypothesis attributes nerve damage in the retina to decreased blood flow in the ophthalmic artery, reduced oxygenation, and impaired axonal transport. Activation of calpain enzymes contributes to retinal cell death during hypoxia. However, we still do not know in which specific retinal layers calpains are activated. Thus, the purpose of the present study was to investigate where and when calpains are activated in an improved culture model of hypoxic monkey retina.

METHODS

Monkey retinal explants were cultured on microporous membranes with the retinal ganglion cell (RGC) side facing up. Explants were incubated under hypoxic conditions, with or without additional reoxygenation. When it was used, the calpain inhibitor SNJ-1945 was maintained throughout the culture period. Immunohistochemistry and immunoblotting assays for α-spectrin, calpains 1 and 2, calpastatin, β-III tubulin, and γ-synuclein were performed with specific antibodies. Cell death was assessed by TUNEL staining.

RESULTS

Under normoxic conditions, TUNEL-positive cells were minimal in our improved culture conditions. As early as 8 hours after hypoxia, the 150-kDa calpain-specific α-spectrin breakdown product appeared in the nerve fiber layer (NFL), where calpains 1 and 2 were localized. TUNEL-positive RGCs then increased at later time periods. The calpain inhibitor SNJ-1945 ameliorated changes induced by hypoxia or hypoxia/reoxygenation.

CONCLUSIONS

During hypoxia/reoxygenation in an improved, relevant monkey model, calpains were first activated in the NFL, followed by death of the parent RGCs. This observation suggest that calpain-induced degeneration of retinal nerve fibers may be an underlying mechanism for RGC death in hypoxic retinal neuropathies.

IMA901: a multi-peptide cancer vaccine for treatment of renal cell cancer

Despite a major improvement in the treatment of advanced kidney cancer by the recent introduction of targeted agents such as multi-kinase inhibitors, long-term benefits are still limited and a significant unmet medical need remains for this disease. Cancer immunotherapy has shown its potential by the induction of long-lasting responses in a small subset of patients, however, the unspecific immune interventions with (high dose) cytokines used so far are associated with significant side effects. Specific cancer immunotherapy may circumvent these problems by attacking tumor cells while sparing normal tissue with the use of multi-peptide vaccination being one of the most promising strategies. We here summarize the clinical and translational data from phase I and II trials investigating IMA901. Significant associations of clinical benefit with detectable T cell responses against the IMA901 peptides and encouraging survival data in treated patients has prompted the start of a randomized, controlled phase III trial in 1st line advanced RCC with survival results expected toward the end of 2015. Potential combination strategies with the recently discovered so-called checkpoint inhibitors are also discussed.

A Critical Role of the mTOR/eIF2α Pathway in Hypoxia-Induced Pulmonary Hypertension

Enhanced proliferation of pulmonary arterial vascular smooth muscle cells (PASMCs) is a key pathological component of vascular remodeling in hypoxia-induced pulmonary hypertension (HPH). Mammalian targeting of rapamycin (mTOR) signaling has been shown to play a role in protein translation and participate in the progression of pulmonary hypertension. Eukaryotic translation initiation factor-2α (eIF2α) is a key factor in regulation of cell growth and cell cycle, but its role in mTOR signaling and PASMCs proliferation remains unknown. Pulmonary hypertension (PH) rat model was established by hypoxia. Rapamycin was used to treat rats as an mTOR inhibitor. Proliferation of primarily cultured rat PASMCs was induced by hypoxia, rapamycin and siRNA of mTOR and eIF2α were used in loss-of-function studies. The expression and activation of eIF2α, mTOR and c-myc were analyzed. Results showed that mTOR/eIF2α signaling was significantly activated in pulmonary arteries from hypoxia exposed rats and PASMCs cultured under hypoxia condition. Treatment with mTOR inhibitor for 21 days attenuated vascular remodeling, suppressed mTOR and eIF2α activation, inhibited c-myc expression in HPH rats. In hypoxia-induced PASMCs, rapamycin and knockdown of mTOR and eIF2α by siRNA significantly abolished proliferation and increased c-myc expression. These results suggest a critical role of the mTOR/eIF2αpathway in hypoxic vascular remodeling and PASMCs proliferation of HPH.

p58IPK is an inhibitor of the eIF2α kinase GCN2 and its localization and expression underpin protein synthesis and ER processing capacity

One of the key cellular responses to stress is the attenuation of mRNA translation and protein synthesis via the phosphorylation of eIF2α (eukaryotic translation initiation factor 2α). This is mediated by four eIF2α kinases and it has been suggested that each kinase is specific to the cellular stress imposed. In the present study, we show that both PERK (PKR-like endoplasmic reticulum kinase/eIF2α kinase 3) and GCN2 (general control non-derepressible 2/eIF2α kinase 4) are required for the stress responses associated with conditions encountered by cells overexpressing secreted recombinant protein. Importantly, whereas GCN2 is the kinase that is activated following cold-shock/hypothermic culturing of mammalian cells, PERK and GCN2 have overlapping functions since knockdown of one of these at the mRNA level is compensated for by the cell by up-regulating levels of the other. The protein p58IPK {also known as DnaJ3C [DnaJ heat-shock protein (hsp) 40 homologue, subfamily C, member 3]} is known to inhibit the eIF2α kinases PKR (dsRNA-dependent protein kinase/eIF2α kinase 2) and PERK and hence prevent or delay eIF2α phosphorylation and consequent inhibition of translation. However, we show that p58IPK is a general inhibitor of the eIF2α kinases in that it also interacts with GCN2. Thus forced overexpression of cytoplasmic p58 delays eIF2α phosphorylation, suppresses GCN2 phosphorylation and prolongs protein synthesis under endoplasmic reticulum (ER), hypothermic and prolonged culture stress conditions. Taken together, our data suggest that there is considerable cross talk between the eIF2α kinases to ensure that protein synthesis is tightly regulated. Their activation is controlled by p58 and the expression levels and localization of this protein are crucial in the capacity the cells to respond to cellular stress via control of protein synthesis rates and subsequent folding in the ER.

Database screening of herbal monomers regulating autophagy by constructing a "disease-gene-drug" network

Background

Studies suggest an important role of autophagy as a target for cancer therapy. We constructed a "disease-gene-drug" network using the modular approach of bioinformatics and screened herbal monomers demonstrating functions related to autophagy regulation.

Methods

Based on the microarray results of the gene expression omnibus (GEO) database (GSE2435 and GSE31040, starvation-induced autophagy model), we used the human protein reference database (HPRD) to obtain the protein-protein interaction (PPI) network. In addition, we used the CFinder software to identify several functional modules, performed gene ontology-biological process (GO-BP) functional enrichment analysis using the DAVID software, constructed a herbal monomer-module gene regulatory network using literature search and the Cytoscape software, and then analyzed the relationships between autophagy, genes, and herbal monomers.

Results

We screened 544 differentially expressed genes related to autophagy, 375 pairs of differentially expressed genes, and 7 gene modules, wherein the functions of module 3 (composed of 7 genes) were enriched in "cell death". Using the constructed herbal monomer-module gene regulatory network, we found that 30 herbal monomers can simultaneously regulate these 7 genes, indicating a potential regulatory role in autophagy.

Conclusions

Database screening using the disease-gene-drug network can provide new strategies and ideas for the application of herbal medicines in cancer therapy.

ER Stress Response in Human Cellular Models of Senescence

The aging process is characterized by progressive accumulation of damaged biomolecules in the endoplasmic reticulum, as result of increased oxidative stress accompanying cellular senescence. In agreement, we hypothesized that WI-38 human cellular models of replicative senescence and stress-induced premature senescence (SIPS) induced by hydrogen peroxide (H2O2-SIPS) or copper sulfate (CuSO4-SIPS) would present endoplasmic reticulum chaperoning mechanisms impairment and unfolded protein response activation. Results show that in replicative senescence and CuSO4-SIPS, immunoglobulin binding protein, calnexin, protein disulfide isomerase, and ER oxireductin-1 levels adjust to restore proteostasis and inositol-requiring enzyme-1 (IRE1)-, activating transcription factor 6 (ATF6)-, and pancreatic ER kinase (PERK)-mediated unfolded protein response are activated. However, H2O2-SIPS does not exhibit IRE1 and ATF6 pathways activation but a PERK-mediated upregulation of CCAAT/enhancer-binding protein homologous protein, showing that CuSO4-SIPS mimics better the endoplasmic reticulum molecular events of replicative senescence than H2O2-SIPS. Moreover, unfolded protein response activation is required for both SIPS models induction, because PERK and IRE1 inhibitors decreased senescence-associated beta-galactosidase appearance. In CuSO4-SIPS, the decrease in senescence levels is associated with PERK-driven, but IRE1 independent, cell cycle arrest while in H2O2-SIPS cell proliferation is PERK independent. These results add a step further on the molecular mechanisms that regulate senescence induction; moreover, they validate CuSO4-SIPS model as a useful tool to study cellular stress responses during aging, hoping to postpone age-related health decline.

Keeping the eIF2 alpha kinase Gcn2 in check

The protein kinase Gcn2 is present in virtually all eukaryotes and is of increasing interest due to its involvement in a large array of crucial biological processes. Some of these are universally conserved from yeast to humans, such as coping with nutrient starvation and oxidative stress. In mammals, Gcn2 is important for e.g. long-term memory formation, feeding behaviour and immune system regulation. Gcn2 has been also implicated in diseases such as cancer and Alzheimer's disease. Studies on Gcn2 have been conducted most extensively in Saccharomyces cerevisiae, where the mechanism of its activation by amino acid starvation has been revealed in most detail. Uncharged tRNAs stimulate Gcn2 which subsequently phosphorylates its substrate, eIF2α, leading to reduced global protein synthesis and simultaneously to increased translation of specific mRNAs, e.g. those coding for Gcn4 in yeast and ATF4 in mammals. Both proteins are transcription factors that regulate the expression of a myriad of genes, thereby enabling the cell to initiate a survival response to the initial activating cue. Given that Gcn2 participates in many diverse processes, Gcn2 itself must be tightly controlled. Indeed, Gcn2 is regulated by a vast network of proteins and RNAs, the list of which is still growing. Deciphering molecular mechanisms underlying Gcn2 regulation by effectors and inhibitors is fundamental for understanding how the cell keeps Gcn2 in check ensuring normal organismal function, and how Gcn2-associated diseases may develop or may be treated. This review provides a critical evaluation of the current knowledge on mechanisms controlling Gcn2 activation or activity.

6-Shogaol induces apoptosis in human leukemia cells through a process involving caspase-mediated cleavage of eIF2α

Background

6-Shogaol is a promising antitumor agent isolated from dietary ginger (Zingiber officinale). However, little is known about the efficacy of 6-shogaol on leukemia cells. Here we investigated the underlying mechanism of 6-shogaol induced apoptosis in human leukemia cells in vitro and in vivo.

Methods

Three leukemia cell lines and primary leukemia cells were used to investigate the apoptosis effect of 6-shogaol. A shotgun approach based on label-free proteome with LC-CHIP Q-TOF MS/MS was employed to identify the cellular targets of 6-shogaol and the differentially expressed proteins were analyzed by bioinformatics protocols.

Results

The present study indicated that 6-shogaol selectively induced apoptosis in transformed and primary leukemia cells but not in normal cells. Eukaryotic translation initiation factor 2 alpha (eIF2α), a key regulator in apoptosis signaling pathway, was significantly affected in both Jurkat and U937 proteome profiles. The docking results suggested that 6-shogaol might bind well to eIF2α at Ser51 of the N-terminal domain. Immunoblotting data indicated that 6-shogaol induced apoptosis through a process involving dephosphorylation of eIF2α and caspase activation–dependent cleavage of eIF2α. Furthermore, 6-shogaol markedly inhibited tumor growth and induced apoptosis in U937 xenograft mouse model.

Conclusion

The potent anti-leukemia activity of 6-shogaol found both in vitro and in vivo in our study make this compound a potential anti-tumor agent for hematologic malignancies.

The eIF2α kinases: their structures and functions

Cell signaling in response to an array of diverse stress stimuli converges on the phosphorylation of the α-subunit of eukaryotic initiation factor 2 (eIF2). Phosphorylation of eIF2α on serine 51 results in a severe decline in de novo protein synthesis and is an important strategy in the cell's armory against stressful insults including viral infection, the accumulation of misfolded proteins, and starvation. The phosphorylation of eIF2α is carried out by a family of four kinases, PERK (PKR-like ER kinase), PKR (protein kinase double-stranded RNA-dependent), GCN2 (general control non-derepressible-2), and HRI (heme-regulated inhibitor). Each primarily responds to a distinct type of stress or stresses. Thus, while significant sequence similarity exists between the eIF2α kinases in their kinase domains, underlying their common role in phosphorylating eIF2α, additional unique features determine the regulation of these four proteins, that is, what signals activate them. This review will describe the structure of each eIF2α kinase and discuss how this is linked to their activation and function. In parallel to the general translational attenuation elicited by eIF2α kinase activation the translation of stress-induced mRNAs, most notably activating transcription factor 4 (ATF4) is enhanced and these set in motion cascades of gene expression constituting the integrated stress response (ISR), which seek to remediate stress and restore homeostasis. Depending on the cellular context and concurrent signaling pathways active, however, translational attenuation can also facilitate apoptosis. Accordingly, the role of the kinases in determining cell fate will also be discussed.

Overcoming intratumor heterogeneity of polygenic cancer drug resistance with improved biomarker integration

Improvements in technology and resources are helping to advance our understanding of cancer-initiating events as well as factors involved with tumor progression, adaptation, and evasion of therapy. Tumors are well known to contain diverse cell populations and intratumor heterogeneity affords neoplasms with a diverse set of biologic characteristics that can be used to evolve and adapt. Intratumor heterogeneity has emerged as a major hindrance to improving cancer patient care. Polygenic cancer drug resistance necessitates reconsidering drug designs to include polypharmacology in pursuit of novel combinatorial agents having multitarget activity to overcome the diverse and compensatory signaling pathways in which cancer cells use to survive and evade therapy. Advances will require integration of different biomarkers such as genomics and imaging to provide for more adequate elucidation of the spatially varying location, type, and extent of diverse intratumor signaling molecules to provide for a rationale-based personalized cancer medicine strategy.

Eukaryotic translation initiation factors in cancer development and progression

Eukaryotic gene expression is a complicated process primarily regulated at the levels of gene transcription and mRNA translation. The latter involves four main steps: initiation, elongation, termination and recycling. Translation regulation is primarily achieved during initiation which is orchestrated by 12 currently known eukaryotic initiation factors (eIFs). Here, we review the current state of eIF research and present a concise summary of the various eIF subunits. As eIFs turned out to be critically implicated in different oncogenic processes the various eIF members and their contribution to onset and progression of cancer are featured.

RNA profiles of porcine embryos during genome activation reveal complex metabolic switch sensitive to in vitro conditions

Fertilization is followed by complex changes in cytoplasmic composition and extensive chromatin reprogramming which results in the abundant activation of totipotent embryonic genome at embryonic genome activation (EGA). While chromatin reprogramming has been widely studied in several species, only a handful of reports characterize changing transcriptome profiles and resulting metabolic changes in cleavage stage embryos. The aims of the current study were to investigate RNA profiles of in vivo developed (ivv) and in vitro produced (ivt) porcine embryos before (2-cell stage) and after (late 4-cell stage) EGA and determine major metabolic changes that regulate totipotency. The period before EGA was dominated by transcripts responsible for cell cycle regulation, mitosis, RNA translation and processing (including ribosomal machinery), protein catabolism, and chromatin remodelling. Following EGA an increase in the abundance of transcripts involved in transcription, translation, DNA metabolism, histone and chromatin modification, as well as protein catabolism was detected. The further analysis of members of overlapping GO terms revealed that despite that comparable cellular processes are taking place before and after EGA (RNA splicing, protein catabolism), different metabolic pathways are involved. This strongly suggests that a complex metabolic switch accompanies EGA. In vitro conditions significantly altered RNA profiles before EGA, and the character of these changes indicates that they originate from oocyte and are imposed either before oocyte aspiration or during in vitro maturation. IVT embryos have altered content of apoptotic factors, cell cycle regulation factors and spindle components, and transcription factors, which all may contribute to reduced developmental competence of embryos produced in vitro. Overall, our data are in good accordance with previously published, genome-wide profiling data in other species. Moreover, comparison with mouse and human embryos showed striking overlap in functional annotation of transcripts during the EGA, suggesting conserved basic mechanisms regulating establishment of totipotency in mammalian development.

Phosphorylation of eIF2α attenuates statin-induced apoptosis by inhibiting the stabilization and translocation of p53 to the mitochondria

Statins are effective cholesterol-lowering drugs that exert pleiotropic effects, including cytotoxicity to cancer cells. We previously reported that simvastatin triggered the mitochondrial apoptotic pathway in MethA fibrosarcoma cells, which was accompanied by the translocation of stabilized p53 to the mitochondria. In this study, we investigated whether statins induce the endoplasmic reticulum (ER) stress response and the mechanisms by which this response is linked to the stabilization of p53 and its translocation to the mitochondria. Statins induced typical ER stress-related proteins, such as BiP/78 kDa glucose-regulated protein (Grp78) and CCAAT/ enhancer-binding protein homologous protein (CHOP), as well as the phosphorylation of protein kinase RNA-like endoplasmic reticulum kinase (PERK), eIF2α and JNK. The statin-induced phosphorylation of eIF2α and JNK was inhibited by supplementation with components of the mevalonate pathway, such as mevalonate, farnesyl pyrophosphate (FPP) and geranylgeranyl pyrophosphate (GGPP). Salubrinal, an inhibitor of the dephosphorylation of eIF2α, suppressed the loss of mitochondrial membrane potential and the translocation of stabilized p53 and Bax to the mitochondria; however, SP600125, a JNK kinase inhibitor, did not exert this effect. Furthermore, the eIF2α knockdown sensitized cells to simvastatin-induced apoptosis and the overexpression of a non-phosphorylatable eIF2α-mutant [serine 51(Ser51)/alanine] enhanced the stabilization of p53 and its translocation to the mitochondria in response to simvastatin treatment. Taken together, these data indicate that eIF2α phosphorylation in the context of the ER stress response plays a role in cell survival by counteracting the p53-mediated mitochondrial apoptosis in response to statins.

Changes in translational control after pro-apoptotic stress

In stressed cells, a general decrease in the rate of protein synthesis occurs due to modifications in the activity of translation initiation factors. Compelling data now indicate that these changes also permit a selective post-transcriptional expression of proteins necessary for either cell survival or completion of apoptosis when cells are exposed to severe or prolonged stress. In this review, we summarize the modifications that inhibit the activity of the main canonical translation initiation factors, and the data explaining how certain mRNAs encoding proteins involved in either cell survival or apoptosis can be selectively translated.

The PERK-eIF2α phosphorylation arm is a pro-survival pathway of BCR-ABL signaling and confers resistance to imatinib treatment in chronic myeloid leukemia cells

Activation of adaptive mechanisms plays a crucial role in cancer progression and drug resistance by allowing cell survival under stressful conditions. Therefore, inhibition of the adaptive response is considered as a prospective therapeutic strategy. The PERK-eIF2α phosphorylation pathway is an important arm of the unfolded protein response (UPR), which is induced under conditions of endoplasmic reticulum (ER) stress. Our previous work showed that ER stress is induced in chronic myeloid leukemia (CML) cells. Herein, we demonstrate that the PERK-eIF2α phosphorylation pathway is upregulated in CML cell lines and CD34⁺ cells from CML patients and is associated with CML progression and imatinib resistance. We also show that induction of apoptosis by imatinib results in the downregulation of the PERK-eIF2α phosphorylation arm. Furthermore, we demonstrate that inactivation of the PERK-eIF2α phosphorylation arm decreases the clonogenic and proliferative capacities of CML cells and sensitizes them to death by imatinib. These findings provide evidence for a pro-survival role of PERK-eIF2α phosphorylation arm that contributes to CML progression and development of imatinib resistance. Thus, the PERK-eIF2α phosphorylation arm may represent a suitable target for therapeutic intervention for CML disease.

Anti-tumorigenic effects of Type 1 interferon are subdued by integrated stress responses

Viral and pharmacological inducers of protein kinase RNA-activated (PKR)-like ER kinase (PERK) were shown to accelerate the phosphorylation-dependent degradation of the IFNAR1 chain of the Type 1 interferon (IFN) receptor and to limit cell sensitivity to IFN. Here we report that hypoxia can elicit these effects in a PERK-dependent manner. The altered fate of IFNAR1 affected by signaling downstream of PERK depends on phosphorylation of eIF2α (eukaryotic translational initiation factor 2-α) and ensuing activation of p38α kinase. Activators of other eIF2α kinases such as PKR or GCN2 (general control nonrepressed-2) are also capable of eliminating IFNAR1 and blunting IFN responses. Modulation of constitutive PKR activity in human breast cancer cells stabilizes IFNAR1 and sensitizes these cells to IFNAR1-dependent anti-tumorigenic effects. Although downregulation of IFNAR1 and impaired IFNAR1 signaling can be elicited in response to amino-acid deficit, the knockdown of GCN2 in melanoma cells reverses these phenotypes. We propose that, in cancer cells and the tumor microenvironment, activation of diverse eIF2α kinases followed by IFNAR1 downregulation enables multiple cellular components of tumor tissue to evade the direct and indirect anti-tumorigenic effects of Type 1 IFN.

Expression profiling and biochemical analysis suggest stress response as a potential mechanism inhibiting proliferation of polyamine-depleted cells

Polyamines are small organic polycations that are absolutely required for cell growth and proliferation; yet the basis for this requirement is mostly unknown. Here, we combined a genome-wide expression profiling with biochemical analysis to reveal the molecular basis for inhibited proliferation of polyamine-depleted cells. Transcriptional responses accompanying growth arrest establishment in polyamine-depleted cells or growth resumption following polyamine replenishment were monitored and compared. Changes in the expression of genes related to various fundamental cellular processes were established. Analysis of mirror-symmetric expression patterns around the G(1)-arrest point identified a set of genes representing a stress-response signature. Indeed, complementary biochemical analysis demonstrated activation of the PKR-like endoplasmic reticulum kinase arm of the unfolded protein response and of the stress-induced p38 MAPK. These changes were accompanied by induction of key growth-inhibitory factors such as p21 and Gadd45a and reduced expression of various cyclins, most profoundly cyclin D1, setting the basis for the halted proliferation. However, although the induced stress response could arrest growth, polyamine depletion also inhibited proliferation of PKR-like endoplasmic reticulum kinase and p38α-deficient cells and of cells harboring a nonphosphorylatable mutant eIF2α (S51A), suggesting that additional yet unidentified mechanisms might inhibit proliferation of polyamine-depleted cells. Despite lengthy persistence of the stress and activation of apoptotic signaling, polyamine-depleted cells remained viable, apparently due to induced expression of protective genes and development of autophagy.

Toxicogenomics discrimination of potential hepatocarcinogenicity of non-genotoxic compounds in rat liver

Long-term carcinogenicity testing of a compound is exceedingly time-consuming and costly, and requires many test animals, whereas the Ames test, which is based on the assumption that any substance that is mutagenic may also exert carcinogenic potential, is useful as a short-term screening assay but has major drawbacks. Although, in fact, 90% of compounds that give a positive Ames test cause cancer in laboratory animals, a good proportion of compounds that give a negative Ames test are also carcinogens; that is, there is no good correlation between carcinogenicity and negative Ames test results. As an alternative to these two approaches, we have tried applying toxicogenomics to predict the carcinogenicity of a compound from the gene expression profile induced in vivo. To establish our model, male Sprague-Dawley rats were orally administered test compounds (12 hepatocarcinogens and 26 non-hepatocarcinogens) for 28 days. Analysis of liver gene expression data by Support Vector Machines (SVM) dividing compounds into 'for training' and 'for test' (20 cases assigned randomly) allowed a set of marker genes to be tested for prediction of hepatocarcinogenicity. The developed prediction model was then validated with reference to the concordance rate with training data and test data, and a good performance was obtained. We will have new gene expression data and continue the validation of our model.

Genetic network and gene set enrichment analysis to identify biomarkers related to cigarette smoking and lung cancer

OBJECTIVES

Cigarette smoking is the most demonstrated risk factor for the development of lung cancer, while the related genetic mechanisms are still unclear.

METHODS

The preprocessed microarray expression dataset was downloaded from Gene Expression Omnibus database. Samples were classified according to the disease state, stage and smoking state. A new computational strategy was applied for the identification and biological interpretation of new candidate genes in lung cancer and smoking by coupling a network-based approach with gene set enrichment analysis.

MEASUREMENTS

Network analysis was performed by pair-wise comparison according to the disease states (tumor or normal), smoking states (current smokers or nonsmokers or former smokers), or the disease stage (stages I-IV). The most activated metabolic pathways were identified by gene set enrichment analysis.

RESULTS

Panels of top ranked gene candidates in smoking or cancer development were identified, including genes involved in cell proliferation and drug metabolism like cytochrome P450 and WW domain containing transcription regulator 1. Semaphorin 5A and protein phosphatase 1F are the common genes represented as major hubs in both the smoking and cancer related network. Six pathways, e.g. cell cycle, DNA replication, RNA transport, protein processing in endoplasmic reticulum, vascular smooth muscle contraction and endocytosis were commonly involved in smoking and lung cancer when comparing the top ten selected pathways.

CONCLUSION

New approach of bioinformatics for biomarker identification and validation can probe into deep genetic relationships between cigarette smoking and lung cancer. Our studies indicate that disease-specific network biomarkers, interaction between genes/proteins, or cross-talking of pathways provide more specific values for the development of precision therapies for lung.

The critical roles of endoplasmic reticulum chaperones and unfolded protein response in tumorigenesis and anticancer therapies

Cancer progression is characterized by rapidly proliferating cancer cells that are in need of increased protein synthesis. Therefore, enhanced endoplasmic reticulum (ER) activity is required to facilitate the folding, assembly and transportation of membrane and secretory proteins. These functions are carried out by ER chaperones. It is now becoming clear that the ER chaperones have critical functions outside of simply facilitating protein folding. For example, cancer progression requires glucose regulated protein (GRP) 78 for cancer cell survival and proliferation, as well as angiogenesis in the microenvironment. GRP78 can translocate to the cell surface acting as a receptor regulating oncogenic signaling and cell viability. Calreticulin, another ER chaperone, can translocate to the cell surface of apoptotic cancer cells and induce immunogenic cancer cell death and antitumor responses in vivo. Tumor-secreted GRP94 has been shown to elicit antitumor immune responses when used as antitumor vaccines. Protein disulfide isomerase is another ER chaperone that demonstrates pro-oncogenic and pro-survival functions. Because of intrinsic alterations of cellular metabolism and extrinsic factors in the tumor microenvironment, cancer cells are under ER stress, and they respond to this stress by activating the unfolded protein response (UPR). Depending on the severity and duration of ER stress, the signaling branches of the UPR can activate adaptive and pro-survival signals, or induce apoptotic cell death. The protein kinase RNA-like ER kinase signaling branch of the UPR has a dual role in cancer proliferation and survival, and is also required for ER stress-induced autophagy. The activation of the inositol-requiring kinase 1α branch promotes tumorigenesis, cancer cell survival and regulates tumor invasion. In summary, perturbance of ER homeostasis has critical roles in tumorigenesis, and therapeutic modulation of ER chaperones and/or UPR components presents potential antitumor treatments.

Oncolytic herpes simplex virus counteracts the hypoxia-induced modulation of glioblastoma stem-like cells

Glioblastoma (GBM), a fatal malignant brain tumor, contains abundant hypoxic regions that provide a "niche" to promote both the maintenance and enrichment of glioblastoma stem-like cells (GSCs) and confer resistance to chemo- and radiotherapy. Since GSCs, with an ability to resist conventional therapies, may be responsible for tumor recurrence, targeting GSCs located in such a hypoxic environment may be critical to improving the therapeutic outcome for GBM patients. Oncolytic viral therapies have been tested in the clinic as a promising therapeutic approach for GBM. In this study, we analyzed and compared the therapeutic effects of oncolytic herpes simplex virus (oHSV) type 1 G47Δ (γ34.5(-)ICP6(-)LacZ(+)α47(-)) in patient-derived GSCs under normoxia (21% oxygen) and hypoxia (1% oxygen). GSCs cultured in hypoxia showed an increased ability to form neurospheres and expressed higher levels of the putative stem cell marker CD133 compared with GSCs cultured in normoxia. G47Δ exhibited a comparable ability to infect, replicate, and kill GSCs in normoxia and hypoxia in vitro. Importantly, G47Δ could counteract hypoxia-mediated enhancement of the stem-like properties of GSCs, inhibiting their self-renewal and stem cell marker expression. Using orthotopic human GSC xenografts in mice, we demonstrated that intratumoral injection of G47ΔUs11fluc, a newly developed G47Δ derivative that expresses firefly luciferase driven by a true late viral promoter, led to an equivalent frequency of viral infection and replication in hypoxic and nonhypoxic tumor areas. These findings suggest that oHSV G47Δ represents a promising therapeutic strategy to target and kill GSCs, not only in normoxic areas of GBM but also within the hypoxic niche.

Oxidative stress induces unfolding protein response and inflammation in nasal polyposis

BACKGROUND

Nasal polyposis, a chronic inflammatory disease affecting the upper airways, is a valuable and accessible model to investigate the mechanisms underlying chronic inflammation. The main objective of this study was to investigate a potential involvement of the unfolded protein response (UPR) in the context of oxidative stress and inflammation in nasal epithelial cells from nasal polyps (NP).

METHODS

Epithelial cells from NP (n = 20) and normal mucosa (Controls, n = 15) in primary culture were analyzed by global proteomic approach and cell biology techniques for the glucose-regulated protein 78 (GRP78), the spliced X-box-binding protein 1 (sXBP-1), the glucose-regulated protein 94 (GRP94), and the calreticulin (immunoblot, mass spectrometry, immunocytochemistry).

RESULTS

Proteomics analysis of human nasal epithelial cells in culture revealed the activation of the unfolded protein response in NP. Systematic cell biology and biochemical analysis of two markers (GRP78, sXBP-1) in the presence and absence of oxidative stress in NP showed a susceptibility of the unfolded protein response to oxidative stress compared to controls at least partially linked to an abnormal redox state of the protein disulfide-isomerase 4. This unfolded protein response was correlated with mitochondrial depolarization and secretion of interleukin 8 (IL-8) and leukotriene B4 (LTB4) and was prevented by mitochondrial antioxidant.

CONCLUSIONS

We show the existence of UPR in nasal epithelial cells that is linked to oxidative stress leading to IL-8 and LTB4 secretions. These mechanisms may participate in chronic inflammation in nasal polyposis.