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1.
Mol Cell ; 75(6): 1203-1217.e5, 2019 09 19.
Artigo em Inglês | MEDLINE | ID: mdl-31494035

RESUMO

In response to foreign and endogenous double-stranded RNA (dsRNA), protein kinase R (PKR) and ribonuclease L (RNase L) reprogram translation in mammalian cells. PKR inhibits translation initiation through eIF2α phosphorylation, which triggers stress granule (SG) formation and promotes translation of stress responsive mRNAs. The mechanisms of RNase L-driven translation repression, its contribution to SG assembly, and its regulation of dsRNA stress-induced mRNAs are unknown. We demonstrate that RNase L drives translational shut-off in response to dsRNA by promoting widespread turnover of mRNAs. This alters stress granule assembly and reprograms translation by allowing translation of mRNAs resistant to RNase L degradation, including numerous antiviral mRNAs such as interferon (IFN)-ß. Individual cells differentially activate dsRNA responses revealing variation that can affect cellular outcomes. This identifies bulk mRNA degradation and the resistance of antiviral mRNAs as the mechanism by which RNase L reprograms translation in response to dsRNA.


Assuntos
Reprogramação Celular , Endorribonucleases/metabolismo , Interferon beta/biossíntese , Biossíntese de Proteínas , RNA Mensageiro/metabolismo , eIF-2 Quinase/metabolismo , Células A549 , Endorribonucleases/genética , Células HEK293 , Humanos , Interferon beta/genética , Estabilidade de RNA , RNA de Cadeia Dupla/genética , RNA de Cadeia Dupla/metabolismo , RNA Mensageiro/genética , eIF-2 Quinase/genética
2.
J Virol ; 98(3): e0188323, 2024 Mar 19.
Artigo em Inglês | MEDLINE | ID: mdl-38376197

RESUMO

Many viruses, including mammarenaviruses, have evolved mechanisms to counteract different components of the host cell innate immunity, which is required to facilitate robust virus multiplication. The double-stranded RNA (dsRNA) sensor protein kinase receptor (PKR) pathway plays a critical role in the cell anti-viral response. Whether PKR can restrict the multiplication of the Old World mammarenavirus lymphocytic choriomeningitis virus (LCMV) and the mechanisms by which LCMV may counteract the anti-viral functions of PKR have not yet been investigated. Here we present evidence that LCMV infection results in very limited levels of PKR activation, but LCMV multiplication is enhanced in the absence of PKR. In contrast, infection with a recombinant LCMV with a mutation affecting the 3'-5' exonuclease (ExoN) activity of the viral nucleoprotein resulted in robust PKR activation in the absence of detectable levels of dsRNA, which was associated with severely restricted virus multiplication that was alleviated in the absence of PKR. However, pharmacological inhibition of PKR activation resulted in reduced levels of LCMV multiplication. These findings uncovered a complex role of the PKR pathway in LCMV-infected cells involving both pro- and anti-viral activities.IMPORTANCEAs with many other viruses, the prototypic Old World mammarenavirus LCMV can interfere with the host cell innate immune response to infection, which includes the dsRNA sensor PKR pathway. A detailed understanding of LCMV-PKR interactions can provide novel insights about mammarenavirus-host cell interactions and facilitate the development of effective anti-viral strategies against human pathogenic mammarenaviruses. In the present work, we present evidence that LCMV multiplication is enhanced in PKR-deficient cells, but pharmacological inhibition of PKR activation unexpectedly resulted in severely restricted propagation of LCMV. Likewise, we document a robust PKR activation in LCMV-infected cells in the absence of detectable levels of dsRNA. Our findings have revealed a complex role of the PKR pathway during LCMV infection and uncovered the activation of PKR as a druggable target for the development of anti-viral drugs against human pathogenic mammarenaviruses.


Assuntos
Arenaviridae , Coriomeningite Linfocítica , Humanos , Arenaviridae/metabolismo , Linhagem Celular , Proteínas Quinases/metabolismo , Interações Hospedeiro-Patógeno , Vírus da Coriomeningite Linfocítica/metabolismo , Proteínas de Transporte , Antivirais , eIF-2 Quinase/genética , eIF-2 Quinase/metabolismo
3.
Genes Dev ; 31(17): 1717-1731, 2017 09 01.
Artigo em Inglês | MEDLINE | ID: mdl-28982758

RESUMO

Although it was long thought that eukaryotic translation almost always initiates at an AUG start codon, recent advancements in ribosome footprint mapping have revealed that non-AUG start codons are used at an astonishing frequency. These non-AUG initiation events are not simply errors but instead are used to generate or regulate proteins with key cellular functions; for example, during development or stress. Misregulation of non-AUG initiation events contributes to multiple human diseases, including cancer and neurodegeneration, and modulation of non-AUG usage may represent a novel therapeutic strategy. It is thus becoming increasingly clear that start codon selection is regulated by many trans-acting initiation factors as well as sequence/structural elements within messenger RNAs and that non-AUG translation has a profound impact on cellular states.


Assuntos
Fenômenos Fisiológicos Celulares/genética , Eucariotos/genética , Biossíntese de Proteínas/genética , Códon de Iniciação/genética , Isoformas de Proteínas/genética , Estresse Fisiológico/genética
4.
J Biol Chem ; 298(6): 102016, 2022 06.
Artigo em Inglês | MEDLINE | ID: mdl-35525273

RESUMO

Ubiquitin-fold modifier 1 (UFM1) is a recently identified ubiquitin-like posttranslational modification with important biological functions. However, the regulatory mechanisms governing UFM1 modification of target proteins (UFMylation) and the cellular processes controlled by UFMylation remain largely unknown. It has been previously shown that a UFM1-specific protease (UFSP2) mediates the maturation of the UFM1 precursor and drives the de-UFMylation reaction. Furthermore, it has long been thought that UFSP1, an ortholog of UFSP2, is inactive in many organisms, including human, because it lacks an apparent protease domain when translated from the canonical start codon (445AUG). Here, we demonstrate using the combination of site-directed mutagenesis, CRISPR/Cas9-mediated genome editing, and mass spectrometry approaches that translation of human UFSP1 initiates from an upstream near-cognate codon, 217CUG, via eukaryotic translation initiation factor eIF2A-mediated translational initiation rather than from the annotated 445AUG, revealing the presence of a catalytic protease domain containing a Cys active site. Moreover, we show that both UFSP1 and UFSP2 mediate maturation of UFM1 and de-UFMylation of target proteins. This study demonstrates that human UFSP1 functions as an active UFM1-specific protease, thus contributing to our understanding of the UFMylation/de-UFMylation process.


Assuntos
Cisteína Endopeptidases , Peptídeo Hidrolases , Proteínas , Códon de Iniciação/genética , Cisteína Endopeptidases/genética , Cisteína Endopeptidases/metabolismo , Endopeptidases/metabolismo , Humanos , Peptídeo Hidrolases/metabolismo , Biossíntese de Proteínas , Processamento de Proteína Pós-Traducional , Proteínas/metabolismo , Ubiquitina/metabolismo
5.
Dev Dyn ; 251(2): 377-389, 2022 02.
Artigo em Inglês | MEDLINE | ID: mdl-34278643

RESUMO

BACKGROUND: EIF2A is an unconventional translation factor required for initiation of protein synthesis from non-AUG codons from a variety of transcripts, including oncogenes and stress related transcripts in mammalian cells. Its function in multicellular organisms has not been reported. RESULTS: Here, we identify and characterize mutant alleles of the CG7414 gene, which encodes the Drosophila EIF2A ortholog. We identified that CG7414 undergoes sex-specific splicing that regulates its male-specific expression. We characterized a Mi{Mic} transposon insertion that disrupts the coding regions of all predicted isoforms and is a likely null allele, and a PBac transposon insertion into an intron, which is a hypomorph. The Mi{Mic} allele is homozygous lethal, while the viable progeny from the hypomorphic PiggyBac allele are male sterile and female fertile. In dEIF2A mutant flies, sperm failed to individualize due to defects in F-actin cones and failure to form and maintain cystic bulges, ultimately leading to sterility. CONCLUSIONS: These results demonstrate that EIF2A is essential in a multicellular organism, both for normal development and spermatogenesis, and provide an entrée into the elucidation of the role of EIF2A and unconventional translation in vivo.


Assuntos
Proteínas de Drosophila , Drosophila , Animais , Drosophila/metabolismo , Proteínas de Drosophila/genética , Proteínas de Drosophila/metabolismo , Feminino , Masculino , Mamíferos/metabolismo , Fatores de Iniciação de Peptídeos/genética , Espermatogênese/genética , Espermatozoides/metabolismo
6.
FASEB J ; 35(11): e21990, 2021 11.
Artigo em Inglês | MEDLINE | ID: mdl-34665898

RESUMO

Eukaryotic initiation factor 2A (eIF2A) is a 65 kDa protein that functions in minor initiation pathways, which affect the translation of only a subset of messenger ribonucleic acid (mRNAs), such as internal ribosome entry site (IRES)-containing mRNAs and/or mRNAs harboring upstream near cognate/non-AUG start codons. These non-canonical initiation events are important for regulation of protein synthesis during cellular development and/or the integrated stress response. Selective eIF2A knockdown in cellular systems significantly inhibits translation of such mRNAs, which rely on alternative initiation mechanisms for their translation. However, there exists a gap in our understanding of how eIF2A functions in mammalian systems in vivo (on the organismal level) and ex vivo (in cells). Here, using an eIF2A-knockout (KO) mouse model, we present evidence implicating eIF2A in the biology of aging, metabolic syndrome and central tolerance. We discovered that eIF2A-KO mice have reduced life span and that eIF2A plays an important role in maintenance of lipid homeostasis, the control of glucose tolerance, insulin resistance and also reduces the abundance of B lymphocytes and dendritic cells in the thymic medulla of mice. We also show the eIF2A KO affects male and female mice differently, suggesting that eIF2A may affect sex-specific pathways. Interestingly, our experiments involving pharmacological induction of endoplasmic reticulum (ER) stress with tunicamycin did not reveal any substantial difference between the response to ER stress in eIF2A-KO and wild-type mice. The identification of eIF2A function in the development of metabolic syndrome bears promise for the further identification of specific eIF2A targets responsible for these changes.


Assuntos
Metabolismo dos Lipídeos , Longevidade , Síndrome Metabólica/metabolismo , Proteínas Serina-Treonina Quinases/fisiologia , Animais , Feminino , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Fatores Sexuais
7.
Int J Mol Sci ; 21(6)2020 Mar 17.
Artigo em Inglês | MEDLINE | ID: mdl-32192132

RESUMO

Initiation of protein synthesis in eukaryotes is a complex process requiring more than 12 different initiation factors, comprising over 30 polypeptide chains. The functions of many of these factors have been established in great detail; however, the precise role of some of them and their mechanism of action is still not well understood. Eukaryotic initiation factor 2A (eIF2A) is a single chain 65 kDa protein that was initially believed to serve as the functional homologue of prokaryotic IF2, since eIF2A and IF2 catalyze biochemically similar reactions, i.e., they stimulate initiator Met-tRNAi binding to the small ribosomal subunit. However, subsequent identification of a heterotrimeric 126 kDa factor, eIF2 (α,ß,γ) showed that this factor, and not eIF2A, was primarily responsible for the binding of Met-tRNAi to 40S subunit in eukaryotes. It was found however, that eIF2A can promote recruitment of Met-tRNAi to 40S/mRNA complexes under conditions of inhibition of eIF2 activity (eIF2α-phosphorylation), or its absence. eIF2A does not function in major steps in the initiation process, but is suggested to act at some minor/alternative initiation events such as re-initiation, internal initiation, or non-AUG initiation, important for translational control of specific mRNAs. This review summarizes our current understanding of the eIF2A structure and function.


Assuntos
Fator de Iniciação 2 em Eucariotos/metabolismo , Animais , Proteínas de Transporte/metabolismo , Fator de Iniciação 2 em Eucariotos/química , Fator de Iniciação 2 em Eucariotos/genética , Evolução Molecular , Técnicas de Silenciamento de Genes , Humanos , Mamíferos , Camundongos Knockout , Iniciação Traducional da Cadeia Peptídica , Fator de Iniciação 2 em Procariotos/química , Fator de Iniciação 2 em Procariotos/metabolismo , Ligação Proteica , Biossíntese de Proteínas , RNA Mensageiro/química , RNA Mensageiro/metabolismo , RNA de Transferência/metabolismo , Transdução de Sinais , Estresse Fisiológico , Relação Estrutura-Atividade , Sítio de Iniciação de Transcrição , Leveduras/genética , Leveduras/metabolismo
8.
J Cell Mol Med ; 23(9): 6060-6071, 2019 09.
Artigo em Inglês | MEDLINE | ID: mdl-31211507

RESUMO

The integrated stress response (ISR) is critical for cancer cell survival during stress stimuli and has been implicated in the resistance to cancer therapeutics, in which the mechanism, however, is poorly understood. Here, we showed that paclitaxel, the major chemotherapy drug for breast cancer, induced ISR and phosphorylated ser51 residue of EIF2S1 by EIF2AK3 and EIF2AK4. When exposed to paclitaxel, cancer cells activated the EIF2AK3/EIF2AK4-pEIF2S1-ATF4 axis and maintained redox homoeostasis by inducing expression of the major antioxidant enzymes HMOX1, SHMT2 and SLC7A11. Paclitaxel-mediated cell death was significantly increased following loss of ISR or ATF4 expression. This sensitizing effect could be partially rescued by Trolox, a ROS scavenger. We demonstrated that the alternative initiation factor EIF2A was essential for cancer cell survival after paclitaxel-mediated ISR both in vitro and in vivo. Moreover, patients with breast cancer exhibited higher ISR after chemotherapy, and the elevated mRNA levels of HMOX1, SHMT2 and EIF2A were correlated with poor prognosis. Collectively, our findings reveal a novel mechanism for paclitaxel resistance and suggest that targeting EIF2A combined with ISR agonist may be a potential treatment regimen to overcome drug resistance for breast cancer.


Assuntos
Neoplasias da Mama/tratamento farmacológico , Fator de Iniciação 2 em Eucariotos/genética , Paclitaxel/farmacologia , Proteínas Serina-Treonina Quinases/genética , eIF-2 Quinase/genética , Fator 4 Ativador da Transcrição/genética , Sistema y+ de Transporte de Aminoácidos/genética , Neoplasias da Mama/genética , Neoplasias da Mama/patologia , Linhagem Celular Tumoral , Sobrevivência Celular/efeitos dos fármacos , Resistencia a Medicamentos Antineoplásicos/genética , Feminino , Regulação Neoplásica da Expressão Gênica/efeitos dos fármacos , Glicina Hidroximetiltransferase/genética , Heme Oxigenase-1/genética , Xenoenxertos , Humanos , Paclitaxel/efeitos adversos , Transdução de Sinais/efeitos dos fármacos
9.
Cell Mol Life Sci ; 75(23): 4287-4300, 2018 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-30019215

RESUMO

The initiator tRNA (Met-tRNA i Met ) at the P site of the small ribosomal subunit plays an important role in the recognition of an mRNA start codon. In bacteria, the initiator tRNA carrier, IF2, facilitates the positioning of Met-tRNA i Met on the small ribosomal subunit. Eukarya contain the Met-tRNA i Met carrier, eIF2 (unrelated to IF2), whose carrier activity is inhibited under stress conditions by the phosphorylation of its α-subunit by stress-activated eIF2α kinases. The stress-resistant initiator tRNA carrier, eIF2A, was recently uncovered and shown to load Met-tRNA i Met on the 40S ribosomal subunit associated with a stress-resistant mRNA under stress conditions. Here, we report that eIF2A interacts and functionally cooperates with eIF5B (a homolog of IF2), and we describe the functional domains of eIF2A that are required for its binding of Met-tRNA i Met , eIF5B, and a stress-resistant mRNA. The results indicate that the eukaryotic eIF5B-eIF2A complex functionally mimics the bacterial IF2 containing ribosome-, GTP-, and initiator tRNA-binding domains in a single polypeptide.


Assuntos
Proteínas de Caenorhabditis elegans/metabolismo , Fator de Iniciação 2 em Eucariotos/metabolismo , Fatores de Iniciação em Eucariotos/metabolismo , RNA de Transferência de Metionina/metabolismo , eIF-2 Quinase/metabolismo , Sequência de Aminoácidos , Animais , Western Blotting , Caenorhabditis elegans/genética , Caenorhabditis elegans/metabolismo , Proteínas de Caenorhabditis elegans/genética , Fator de Iniciação 2 em Eucariotos/genética , Fatores de Iniciação em Eucariotos/genética , Células HEK293 , Humanos , Mutação , Ligação Proteica , Interferência de RNA , RNA de Transferência de Metionina/genética , Homologia de Sequência de Aminoácidos , eIF-2 Quinase/genética
10.
Neurobiol Dis ; 116: 155-165, 2018 08.
Artigo em Inglês | MEDLINE | ID: mdl-29792928

RESUMO

Expansion of a hexanucleotide repeat (HRE), GGGGCC, in the C9ORF72 gene is recognized as the most common cause of familial amyotrophic lateral sclerosis (FALS), frontotemporal dementia (FTD) and ALS-FTD, as well as 5-10% of sporadic ALS. Despite the location of the HRE in the non-coding region (with respect to the main C9ORF72 gene product), dipeptide repeat proteins (DPRs) that are thought to be toxic are translated from the HRE in all three reading frames from both the sense and antisense transcript. Here, we identified a CUG that has a good Kozak consensus sequence as the translation initiation codon. Mutation of this CTG significantly suppressed polyglycine-alanine (GA) translation. GA was translated when the G4C2 construct was placed as the second cistron in a bicistronic construct. CRISPR/Cas9-induced knockout of a non-canonical translation initiation factor, eIF2A, impaired GA translation. Transfection of G4C2 constructs induced an integrated stress response (ISR), while triggering the ISR led to a continuation of translation of GA with a decline in conventional cap-dependent translation. These in vitro observations were confirmed in chick embryo neural cells. The findings suggest that DPRs translated from an HRE in C9ORF72 aggregate and lead to an ISR that then leads to continuing DPR production and aggregation, thereby creating a continuing pathogenic cycle.


Assuntos
Proteína C9orf72/genética , Proteína C9orf72/metabolismo , Dipeptídeos/genética , Dipeptídeos/metabolismo , Biossíntese de Proteínas/fisiologia , Animais , Morte Celular/fisiologia , Embrião de Galinha , Células HEK293 , Humanos , Camundongos , Camundongos Knockout
11.
Int J Mol Sci ; 19(12)2018 Dec 13.
Artigo em Inglês | MEDLINE | ID: mdl-30551605

RESUMO

A variety of cellular stresses lead to global translation attenuation due to phosphorylation of the alpha subunit of eukaryotic initiation factor 2 (eIF2), which decreases the availability of the eIF2-GTP-Met-tRNAi ternary complex. However, a subset of mRNAs continues to be translated by non-canonical mechanisms under these conditions. In fact, although translation initiation of activating transcription factor 4 (ATF4) is normally repressed by an upstream open reading frame (uORF), a decreased availability of ternary complex leads to increased translation of the main ATF4-coding ORF. We show here that siRNA-mediated depletion of eIF5B-which can substitute for eIF2 in delivering Met-tRNAi-leads to increased levels of ATF4 protein in mammalian cells. This de-repression is not due to phosphorylation of eIF2α under conditions of eIF5B depletion. Although eIF5B depletion leads to a modest increase in the steady-state levels of ATF4 mRNA, we show by polysome profiling that the depletion of eIF5B enhances ATF4 expression primarily at the level of translation. Moreover, eIF5B silencing increases the expression of an ATF4-luciferase translational reporter by a mechanism requiring the repressive uORF2. Further experiments suggest that eIF5B cooperates with eIF1A and eIF5, but not eIF2A, to facilitate the uORF2-mediated repression of ATF4 translation.


Assuntos
Fator 4 Ativador da Transcrição/genética , Endonucleases/metabolismo , Fator de Iniciação 1 em Eucariotos/metabolismo , Fatores de Iniciação em Eucariotos/metabolismo , Fatores de Iniciação de Peptídeos/metabolismo , Proteínas de Ligação a RNA/metabolismo , DNA Polimerase Dirigida por RNA/metabolismo , Fator 4 Ativador da Transcrição/metabolismo , Linhagem Celular , Células HEK293 , Humanos , Fatores de Iniciação de Peptídeos/genética , Fosforilação , Polirribossomos/metabolismo , Biossíntese de Proteínas , RNA Interferente Pequeno/farmacologia , Proteínas de Ligação a RNA/genética , Fator de Iniciação de Tradução Eucariótico 5A
12.
Apoptosis ; 22(6): 753-768, 2017 06.
Artigo em Inglês | MEDLINE | ID: mdl-28391375

RESUMO

Post-traumatic stress disorder (PTSD) is characterized with abnormal learning and memory. Impairments in learning and memory are closely associated with apoptosis in the medial prefrontal cortex (mPFC). We previously examined the endoplasmic reticulum (ER) stress was involved in the apoptosis in the mPFC of PTSD. The PERK pathway plays the important role in the ER stress-induced apoptosis. The aim of the present study was to explore the role of PERK pathway in neuronal apoptosis in the mPFC of rat models of PTSD. We used the single prolonged stress (SPS) to mimic PTSD in rats and studied the effects of the PERK pathway in mPFC. Learning and memory behavior were examined by Morris water maze and novel object recognition tests. Apoptosis in mPFC was detected by TUNEL staining. Our results showed decreased learning memory and increased apoptosis of mPFC neurons in rats exposed to SPS. SPS exposure upregulate mRNA expressions of PERK, p-PERK, eIF2α, p-eIF2α, nuclear ATF4 and C/EBP-homologous protein (CHOP) in mPFC neurons, but the protein levels of these molecules showed difference in magnitude and time course. GSK2606414 (an antagonist of PERK) treatment successfully reversed the above changes. These results suggested that the PERK pathway mediated SPS-induced neural apoptosis in the mPFC. These findings will be helpful in understanding mPFC-related pathogenesis of PTSD.


Assuntos
Neurônios/enzimologia , Neurônios/patologia , Córtex Pré-Frontal/fisiopatologia , Transdução de Sinais , Estresse Fisiológico , eIF-2 Quinase/metabolismo , Fator 4 Ativador da Transcrição/metabolismo , Adenina/análogos & derivados , Adenina/farmacologia , Animais , Caspase 12/metabolismo , Núcleo Celular/efeitos dos fármacos , Núcleo Celular/metabolismo , Estresse do Retículo Endoplasmático/efeitos dos fármacos , Fator de Iniciação 2 em Eucariotos/metabolismo , Indóis/farmacologia , Masculino , Aprendizagem em Labirinto/efeitos dos fármacos , Memória/efeitos dos fármacos , Neurônios/efeitos dos fármacos , Fosforilação/efeitos dos fármacos , Córtex Pré-Frontal/efeitos dos fármacos , Córtex Pré-Frontal/patologia , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Ratos Wistar , Transdução de Sinais/efeitos dos fármacos , Estresse Fisiológico/efeitos dos fármacos , Fator de Transcrição CHOP/genética , Fator de Transcrição CHOP/metabolismo , Regulação para Cima/efeitos dos fármacos , Regulação para Cima/genética
13.
Biochem Biophys Res Commun ; 487(1): 47-53, 2017 05 20.
Artigo em Inglês | MEDLINE | ID: mdl-28389244

RESUMO

Little is known about the role of oxytocin (OT) in colostrum during early gut colonization. We previously showed that transient OT receptor (OTR) expression on newborn rat enterocytes coincides with the milk-suckling period, and that OT activates endoplasmic reticulum stress sensors in cultured enterocytes. Here, we explored whether colostrum-OT attenuates stress in newborn villi primed and unprimed by colostrum by measuring levels of stress markers including BiP (an ER chaperone), eIF2a (translation initiation factor), and pPKR (eIF2a kinase). We also measured two inflammation-signaling proteins NF-κB and its inhibitor IκB. To test the impact of colostrum on autophagy, we measured a marker of autophagy initiation, LC3A. Colostrum increased inactive p-eIF2a, p-PKR and IκB and reduced p-IκB, BiP and LC3A. LPS increased and OT decreased p-IkB. BiP (GRP78) was higher in unprimed than primed villi. Together, these data suggest that colostrum OT attenuates the impact of inflammation on postnatal gut villi and that OT enhances autophagy to protect against amino acid insufficiency-induced stress during the interval between birth and the first feeding.


Assuntos
Colostro/metabolismo , Estresse do Retículo Endoplasmático/imunologia , Mediadores da Inflamação/imunologia , Mucosa Intestinal/imunologia , Ocitocina/administração & dosagem , Animais , Animais Recém-Nascidos , Autofagia/efeitos dos fármacos , Autofagia/imunologia , Relação Dose-Resposta a Droga , Estresse do Retículo Endoplasmático/efeitos dos fármacos , Feminino , Proteínas de Choque Térmico/imunologia , Mucosa Intestinal/efeitos dos fármacos , Masculino , Microvilosidades/efeitos dos fármacos , Ratos , Ratos Sprague-Dawley
14.
Biotechnol Biotechnol Equip ; 28(4): 622-626, 2014 Jul 04.
Artigo em Inglês | MEDLINE | ID: mdl-26019549

RESUMO

Eukaryotic initiation factors eIF2A and eIF2 both play important roles in the mRNA translation of protein synthesis, whereas the functions of eIF2A are usually overlooked, as both functions of binding methyionly-tRNAi (Met-tRNAi) to 40S are similar under the same complementary factor and nucleotide requirements. Recently, the functions of eIF2A were reported to differ from those of eIF2 in manners when binding Met-tRNAi to 40S. Given that eukaryotic initiation factor eIF2 has been well known, eIF2A was still deficient in understanding of its sequence, structure and functions. In this work, we collected a high salt-tolerant grass Leymus chinensis (Trin.) as the object of study, and cloned and sequenced the eIF2A gene from this species. Based on the DNA alignment and analysis of eIF2A gene sequences from other organisms, an effective primer set was newly designed. Using this primer set, a DNA fragment with length of about 500 bp was obtained, and we have submitted this sequencing result to NCBI GenBank database (accession number: KF279515). The Basic Local Alignment Search Tool (BLAST) result showed that our sequence is highly identical to eIF2A gene sequences that existed in NCBI GenBank database. This work would help to further understand the function of eIF2A, and provide more potential target genes for studying their functions in relation to stress tolerance mechanisms.

15.
Int J Biol Macromol ; 273(Pt 1): 132968, 2024 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-38871097

RESUMO

Eukaryotic Initiation Translation Factor 2A (EIF2A) is considered to be primarily responsible for the initiation of translation when a cell is subjected to stressful conditions. However, information regarding this protein is still incomplete. Using a combination of proteomic approaches, we demonstrated that EIF2A is the molecular target of the naturally occurring bioactive compound cannabidiolic acid (CBDA) within human glioblastoma cells. This finding allowed us to undertake a study aimed at obtaining further information on the functions that EIF2A plays in tumor cells. Indeed, our data showed that CBDA is able to activate EIF2A when the cells are in no-stress conditions. It induces conformational changes in the protein structure, thus increasing EIF2A affinity towards the proteins participating in the Eukaryotic Translation Machinery. Consequently, following glioblastoma cells incubation with CBDA we observed an enhanced neosynthesis of proteins involved in the stress response, nucleic acid translation and organization, and protein catabolism. These changes in gene expression resulted in increased levels of ubiquitinated proteins and accumulation of the autophagosome. Our results, in addition to shedding light on the molecular mechanism underlying the biological effect of a phytocannabinoid in cancer cells, demonstrated that EIF2A plays a critical role in regulation of protein homeostasis.


Assuntos
Fator de Iniciação 2 em Eucariotos , Glioblastoma , Humanos , Glioblastoma/metabolismo , Glioblastoma/patologia , Fator de Iniciação 2 em Eucariotos/metabolismo , Linhagem Celular Tumoral , Proteostase/efeitos dos fármacos , Biossíntese de Proteínas/efeitos dos fármacos , Proteômica/métodos
16.
Elife ; 122024 Jan 24.
Artigo em Inglês | MEDLINE | ID: mdl-38266075

RESUMO

Initiating translation of most eukaryotic mRNAs depends on recruitment of methionyl initiator tRNA (Met-tRNAi) in a ternary complex (TC) with GTP-bound eukaryotic initiation factor 2 (eIF2) to the small (40S) ribosomal subunit, forming a 43S preinitiation complex (PIC) that attaches to the mRNA and scans the 5'-untranslated region (5' UTR) for an AUG start codon. Previous studies have implicated mammalian eIF2A in GTP-independent binding of Met-tRNAi to the 40S subunit and its recruitment to specialized mRNAs that do not require scanning, and in initiation at non-AUG start codons, when eIF2 function is attenuated by phosphorylation of its α-subunit during stress. The role of eIF2A in translation in vivo is poorly understood however, and it was unknown whether the conserved ortholog in budding yeast can functionally substitute for eIF2. We performed ribosome profiling of a yeast deletion mutant lacking eIF2A and isogenic wild-type (WT) cells in the presence or absence of eIF2α phosphorylation induced by starvation for amino acids isoleucine and valine. Whereas starvation of WT confers changes in translational efficiencies (TEs) of hundreds of mRNAs, the eIF2AΔ mutation conferred no significant TE reductions for any mRNAs in non-starved cells, and it reduced the TEs of only a small number of transcripts in starved cells containing phosphorylated eIF2α. We found no evidence that eliminating eIF2A altered the translation of mRNAs containing putative internal ribosome entry site (IRES) elements, or harboring uORFs initiated by AUG or near-cognate start codons, in non-starved or starved cells. Thus, very few mRNAs (possibly only one) appear to employ eIF2A for Met-tRNAi recruitment in yeast cells, even when eIF2 function is attenuated by stress.


Assuntos
Fator de Iniciação 2 em Eucariotos , Saccharomyces cerevisiae , Animais , Saccharomyces cerevisiae/genética , Códon de Iniciação/genética , Fator de Iniciação 2 em Eucariotos/genética , Fosforilação , Regiões 5' não Traduzidas , Guanosina Trifosfato , Mamíferos
17.
Biochem Biophys Res Commun ; 438(3): 500-6, 2013 Aug 30.
Artigo em Inglês | MEDLINE | ID: mdl-23916707

RESUMO

Pro-apoptotic signaling instigated by endoplasmic reticulum (ER) stress is tightly governed by the BH3-only proteins like Noxa and Bim, which help trigger apoptosis, in part by inactivating mitochondria protecting proteins like Mcl-1. Bim/Noxa-based pro-apoptotic signaling has been implicated for various ER stressors but not yet for those causing "ER-focused" production of severe oxidative stress. In the present study we found that photo-oxidative (phox)-ER stress induced by hypericin-based photodynamic therapy is associated with activation of PERK (an ER sessile, stress sensor), robust induction of CHOP (a pro-apoptotic transcription factor) and induction of Bim and Noxa (accompanied by an eventual drop in Mcl-1 levels). Interestingly Noxa, but not Bim, contributed toward phox-ER stress induced apoptosis, regulated by PERK in a CHOP-independent, temporally-defined manner. These observations shed further light on complex signaling pathways elicited byphox-ER stress and vouch for directing more investigation toward the role of PERK in cell death governance.


Assuntos
Proteínas Reguladoras de Apoptose/fisiologia , Estresse do Retículo Endoplasmático/fisiologia , Proteínas Proto-Oncogênicas c-bcl-2/fisiologia , Animais , Antracenos , Proteína 11 Semelhante a Bcl-2 , Chaperona BiP do Retículo Endoplasmático , Estresse do Retículo Endoplasmático/efeitos dos fármacos , Humanos , Proteínas de Membrana/fisiologia , Camundongos , Perileno/análogos & derivados , Perileno/farmacologia , Proteínas Proto-Oncogênicas/fisiologia , Transdução de Sinais , Regulação para Cima , eIF-2 Quinase/fisiologia
18.
Cell Rep ; 42(8): 112987, 2023 08 29.
Artigo em Inglês | MEDLINE | ID: mdl-37581984

RESUMO

Many positive-strand RNA viruses, including all known coronaviruses, employ programmed -1 ribosomal frameshifting (-1 PRF) to regulate the translation of polycistronic viral RNAs. However, only a few host factors have been shown to regulate -1 PRF. Through a genome-wide CRISPR-Cas9 knockout screen, we have identified host factors that either suppress or enhance severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) -1 PRF. Among them, eukaryotic translation initiation factor 2A (eIF2A) specifically and directly enhances -1 PRF independent of changes in initiation. Consistent with the crucial role of efficient -1 PRF in transcriptase/replicase expression, loss of eIF2A reduces SARS-CoV-2 replication in cells. Furthermore, transcriptome-wide analysis shows that eIF2A preferentially binds CG-rich RNA motifs, including a region within 18S ribosomal RNA near the contacts between the SARS-CoV-2 frameshift-stimulatory element (FSE) and the ribosome. Thus, our results indicate a role for eIF2A in modulating the translation of specific RNAs independent of its role during initiation.


Assuntos
COVID-19 , Fator de Iniciação 2 em Eucariotos , Mudança da Fase de Leitura do Gene Ribossômico , SARS-CoV-2 , Humanos , COVID-19/genética , Sequências Reguladoras de Ácido Nucleico , RNA Viral/genética , SARS-CoV-2/genética , Fator de Iniciação 2 em Eucariotos/genética
19.
Front Oral Health ; 2: 765931, 2021.
Artigo em Inglês | MEDLINE | ID: mdl-35048066

RESUMO

Translation of cellular RNA to protein is an energy-intensive process through which synthesized proteins dictate cellular processes and function. Translation is regulated in response to extracellular effectors and availability of amino acids intracellularly. Most eukaryotic mRNA rely on the methyl 7-guanosine (m7G) nucleotide cap to recruit the translation machinery, and the uncoupling of translational control that occurs in tumorigenesis plays a significant role in cancer treatment response. This article provides an overview of the mammalian translation initiation process and the primary mechanisms by which it is regulated. An outline of how deregulation of initiation supports tumorigenesis and how initiation at a downstream open reading frame (ORF) of Tousled-like kinase 1 (TLK1) leads to treatment resistance is discussed.

20.
F1000Res ; 10: 1162, 2021.
Artigo em Inglês | MEDLINE | ID: mdl-34900236

RESUMO

In eukaryotes, stalled and collided ribosomes are recognized by several conserved multicomponent systems, which either block protein synthesis in situ and resolve the collision locally, or trigger a general stress response. Yeast ribosome-binding GTPases RBG1 (DRG1 in mammals) and RBG2 (DRG2) form two distinct heterodimers with TMA46 (DFRP1) and GIR2 (DFRP2), respectively, both involved in mRNA translation. Accumulated evidence suggests that the dimers play partially redundant roles in elongation processivity and resolution of ribosome stalling and collision events, as well as in the regulation of GCN1-mediated signaling involved in ribosome-associated quality control (RQC). They also genetically interact with SLH1 (ASCC3) helicase, a key component of RQC trigger (RQT) complex disassembling collided ribosomes. Here, we present RNA-Seq and ribosome profiling (Ribo-Seq) data from S. cerevisiae strains with individual deletions of the TMA46 and GIR2 genes. Raw RNA-Seq and Ribo-Seq data as well as gene-level read counts are available in NCBI Gene Expression Omnibus (GEO) repository under GEO accession GSE185458 and GSE185286.


Assuntos
Proteínas de Saccharomyces cerevisiae , Saccharomyces cerevisiae , Animais , Biossíntese de Proteínas , RNA-Seq , Ribossomos/genética , Saccharomyces cerevisiae/genética , Saccharomyces cerevisiae/metabolismo , Proteínas de Saccharomyces cerevisiae/genética , Proteínas de Saccharomyces cerevisiae/metabolismo
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