RESUMO
Translation of HAC1 mRNA in the budding yeast Saccharomyces cerevisiae is derepressed when RNase Ire1 removes its intron via nonconventional cytosolic splicing in response to accumulation of unfolded proteins inside the endoplasmic reticulum. The spliced HAC1 mRNA is translated into a transcription factor that changes the cellular gene expression patterns to increase the protein folding capacity of cells. Previously, we showed that a segment of the intronic sequence interacts with the 5'-UTR of the unspliced mRNA, resulting in repression of HAC1 translation at the initiation stage. However, the exact mechanism of translational derepression is not clear. Here, we show that at least 11-base-pairing interactions between the 5'-UTR and intron (UI) are sufficient to repress HAC1 translation. We also show that overexpression of the helicase eukaryotic initiation factor 4A derepressed translation of an unspliced HAC1 mRNA containing only 11-bp interactions between the 5'-UTR and intronic sequences. In addition, our genetic screen identifies that single mutations in the UI interaction site could derepress translation of the unspliced HAC1 mRNA. Furthermore, we show that the addition of 24 RNA bases between the mRNA 5'-cap and the UI interaction site derepressed translation of the unspliced HAC1 mRNA. Together, our data provide a mechanistic explanation for why the cap-proximal UI-RNA duplex inhibits the recruitment of translating ribosomes to HAC1 mRNA, thus keeping mRNA translationally repressed.
Assuntos
Fatores de Transcrição de Zíper de Leucina Básica , Capuzes de RNA , RNA Mensageiro , Proteínas Repressoras , Proteínas de Saccharomyces cerevisiae , Regiões 5' não Traduzidas , Fatores de Transcrição de Zíper de Leucina Básica/genética , Fatores de Transcrição de Zíper de Leucina Básica/metabolismo , Capuzes de RNA/metabolismo , Splicing de RNA , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Proteínas Repressoras/genética , Proteínas Repressoras/metabolismo , Saccharomyces cerevisiae/genética , Saccharomyces cerevisiae/metabolismo , Proteínas de Saccharomyces cerevisiae/genética , Proteínas de Saccharomyces cerevisiae/metabolismoRESUMO
In the budding yeast Saccharomyces cerevisiae, an mRNA, called HAC1, exists in a translationally repressed form in the cytoplasm. Under conditions of cellular stress, such as when unfolded proteins accumulate inside the endoplasmic reticulum (ER), an RNase Ire1 removes an intervening sequence (intron) from the HAC1 mRNA by nonconventional cytosolic splicing. Removal of the intron results in translational derepression of HAC1 mRNA and production of a transcription factor that activates expression of many enzymes and chaperones to increase the protein-folding capacity of the cell. Here, we show that Ire1-mediated RNA cleavage requires Watson-Crick base pairs in two RNA hairpins, which are located at the HAC1 mRNA exon-intron junctions. Then, we show that the translational derepression of HAC1 mRNA can occur independent of cytosolic splicing. These results are obtained from HAC1 variants that translated an active Hac1 protein from the unspliced mRNA. Additionally, we show that the phosphatidylinositol-3-kinase Vps34 and the nutrient-sensing kinases TOR and GCN2 are key regulators of HAC1 mRNA translation and consequently the ER stress responses. Collectively, our data suggest that the cytosolic splicing and the translational derepression of HAC1 mRNA are coordinated by unique and parallel networks of signaling pathways.
Assuntos
Fatores de Transcrição de Zíper de Leucina Básica/metabolismo , Regulação Fúngica da Expressão Gênica/fisiologia , Glicoproteínas de Membrana/metabolismo , Proteínas Serina-Treonina Quinases/metabolismo , Proteínas Repressoras/metabolismo , Proteínas de Saccharomyces cerevisiae/metabolismo , Serina-Treonina Quinases TOR/metabolismo , Fatores de Transcrição de Zíper de Leucina Básica/genética , Retículo Endoplasmático/metabolismo , Estresse do Retículo Endoplasmático/fisiologia , Regulação Fúngica da Expressão Gênica/genética , Glicoproteínas de Membrana/genética , Proteínas Serina-Treonina Quinases/genética , Proteínas Repressoras/genética , Saccharomyces cerevisiae/metabolismo , Proteínas de Saccharomyces cerevisiae/genéticaRESUMO
Measles virus is the causative agent of measles, a major cause of child mortality in developing countries. Two major proteins, coded by the viral genome, are nucleocapsid protein (N) and phosphoprotein (P). The N protein protects the viral genomic RNA and forms ribonucleoprotein complex (RNP) together with P protein. MeV-P protein recruits the large protein (L), i.e. viral RNA-depended RNA polymerase (RdRp), to ensure viral replication in host cell. Apoptogenic properties of N protein of Edmonston vaccine strain have been established in our lab previously. We investigated the role of MeV-P protein of Edmonston vaccine strain as modulator of apoptosis in cervical cancer cell line (HeLa) and found that MeV-P protein is anti-apoptotic and enhances cell proliferation. Measles virus is considered to be innately oncotropic virus. However, the anti-apoptotic property of MeV-P protein raises important concerns while adopting this virus as an anti-cancer therapeutic tool.
Assuntos
Vírus do Sarampo/genética , Proteínas do Nucleocapsídeo/genética , Fosfoproteínas/genética , Neoplasias do Colo do Útero/genética , Apoptose/genética , Movimento Celular/genética , Proliferação de Células/genética , RNA Polimerases Dirigidas por DNA/genética , Feminino , Genoma Viral/genética , Células HeLa , Humanos , Proteínas do Nucleocapsídeo/farmacologia , Terapia Viral Oncolítica , Fosfoproteínas/farmacologia , Retroviridae/genética , Ensaio Tumoral de Célula-Tronco , Neoplasias do Colo do Útero/imunologia , Neoplasias do Colo do Útero/terapia , Neoplasias do Colo do Útero/virologia , Vacinas Virais/genética , Vacinas Virais/imunologiaRESUMO
Measles is a highly transmissible disease caused by measles virus and remains a major cause of child mortality in developing countries. Measles virus nucleoprotein (N) encapsidates the RNA genome of the virus for providing protection from host cell endonucleases and for specific recognition of viral RNA as template for transcription and replication. This protein is over-expressed at the time of viral replication. The C-terminal of N protein is intrinsically disordered, which enables this protein to interact with several host cell proteins. It was previously proved in our laboratory that N expressing human cancerous cells undergo programmed cell death because of reactive oxygen species (ROS) generation as well as Caspase 3 activation. The phosphoprotein (P) along with N protein enclosed viral genomic RNA forming a ribonucleoprotein complex (RNP). It also establishes interaction with the large protein (L) i.e. viral RNA dependent RNA polymerase to ensure viral replication within host cells. The host cell receptors of this virus are CD46, SLAM/CD150 and PVRL4. Measles virus is latently oncotropic in nature and possesses oncolytic property by syncytia formation. We try to highlight the application of this property in developing a virotherapeutic vehicle.