Knockdown of EIF3G inhibits the intracellular protein translation of H1299 cells
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ABSTRACT: eIF3 is the largest translation initiation factor in mammalian cells, consisting of 13 subunits. This translation initiation factor is involved in multiple processes of protein translation in cells, including translation initiation, termination, and ribosome recycling. Several studies have reported that multiple subunits of eIF3 exhibit abnormal expression in tumor cells and play an important role in the occurrence and development of tumors. In this study, it was found that changes in the expression level of EIF3G significantly affected the growth of non-small cell lung cancer. Knockdown of EIF3G inhibited the intracellular protein translation process of non-small cell lung cancer cells H1299. Through the study of translatome, it was found that knockdown of EIF3G significantly affected the cell cycle processes in H1299 cells. In vitro cell experiments also showed that changes in the expression level of EIF3G influences the cell cycle distribution of H1299 cells. This study is the first to explore the impact of knockdown of EIF3G on the translatome of H1299 cells.
Project description:Translation initiation in eukaryotes is multi-step pathway and the most regulated phase of translation. Eukaryotic initiation factor 3 is the largest and most complex of the translation initiation factors, and it contributes to events throughout the initiation pathway. In particular, eIF3 appears to play critical roles in mRNA recruitment. More recently, eIF3 has been implicated in driving the selective translation of specific classes of mRNAs. However, unraveling the mechanism of these diverse contributions — and disentangling the roles of the individual subunits of the eIF3 complex — remains challenging. We employed ribosome profiling of budding yeast cells expressing two distinct mutations targeting the eIF3 complex. These mutations either disrupt the entire complex or subunits positioned near the mRNA-entry channel of the ribosome which appear to relocate during or in response to mRNA binding and start-codon recognition. Disruption of either the entire eIF3 complex or specific targeting of these subunits affects mRNAs with long 5’-untranslated regions and whose translation is more dependent on eIF4A, eIF4B, and Ded1 but less dependent on eIF4G, eIF4E, and PABP. Disruption of the entire eIF3 complex further affects mRNAs involved in mitochondrial processes and with structured 5’-untranslated regions. Comparison of the suite of mRNAs most sensitive to both mutations with those uniquely sensitive to disruption of the entire complex sheds new light on the specific roles of individual subunits of the eIF3 complex.
Project description:eIF3, whose subunits are frequently overexpressed in cancer, regulates mRNA translation from initiation to termination, but mRNAeIF3, whose subunits are frequently overexpressed in cancer, regulates mRNA translation from initiation to termination, but mRNA-selective functions of individual subunits remain poorly defined. Using multi-omic profiling upon acute depletion of eIF3 subunits, we observed that while eIF3a, b, e, and f markedly differed in their impact on eIF3 holo-complex formation and translation, they were each required for cancer cell proliferation and tumor growth. -selective functions of individual subunits remain poorly defined. Using multi-omic profiling upon acute depletion of eIF3 subunits, we observed that while eIF3a, b, e, and f markedly differed in their impact on eIF3 holo-complex formation and translation, they were each required for cancer cell proliferation and tumor growth.
Project description:Improper regulation of translation initiation, a vital check-point of protein synthesis in the cell, has been linked to a number of cancers. Overexpression of protein subunits of eukaryotic translation initiation factor 3 (eIF3) has been associated with increased translation of mRNAs involved in cell proliferation. In addition to playing a major role in general translation initiation by serving as a scaffold for the assembly of translation initiation complexes, eIF3 regulates translation of specific cellular mRNAs and viral RNAs. Mutations in the N-terminal Helix-Loop-Helix (HLH) RNA-binding motif of the EIF3A subunit in eIF3 interfere with Hepatitis C Virus Internal Ribosome Entry Site (IRES) mediated translation initiation in vitro. Here we use RNA-seq and ribosome profiling of engineered lentiviral HEK293T cells to show that the EIF3A HLH motif controls translation of a small set of cellular transcripts enriched in oncogenic mRNAs, including MYC.
Project description:A prominent hallmark of cancer is deregulated protein synthesis. It is well established that various translation initiation factors (eIFs) are either overexpressed or under-expressed in numerous types of cancer. Recent studies suggest that rather than representing an indirect consequence of neoplasia, imbalanced expression of eIFs significantly contributes to cellular transformation, tumor development, cancer cell survival, metastasis and tumor angiogenesis. Among them, eIF3 stands out as the largest complex composed of 12 subunits with a modular assembly, where aberrant expression of one subunit leads to partially functional subcomplexes. Here we took advantage of well-established knockdowns of subunits d, e and h of human eIF3, all implicated in cancer, and investigated their impact on differential gene expression translatome-wide by Ribo-Seq. We demonstrate that eIF3e and eIF3d knock-downs result in reduced translation efficiency of numerous components of the MAPK signaling pathway, a pathway often upregulated in cancer, and pathways preventing genotoxic stress. Concurrently, depletion of eIF3d increased translation of proteins associated with membrane organelles, whereas eIF3e depletion increased expression of numerous ribosomal proteins, implicating eIF3e in controlling the balanced production of mature ribosomes. Overall, our data illustrate that individual eIF3 subunits exert specific translational control over a broad range of cellular transcripts.
Project description:Exon junction complexes (EJCs) deposited on spliced mRNAs play multifunctional roles in the regulation of gene expression. Whereas the formation and components of EJCs are well characterized, the underlying molecular mechanisms for gene regulation remain poorly understood. Here we find that a eukaryotic translation initiation factor (eIF) 4A3, a core component of EJC directly interacts with eIF3g, a subunit of eIF3 complex. This interaction serves as a linker between the EJC and eIF3 complex, consequently driving an internal ribosomal recruitment. Accordingly, artificially tethered EJC component or cellular EJC deposited on mRNA after splicing promotes internal initiation of translation in a way that is resistant to cellular stress induced by serum starvation. We also demonstrate that translatable endogenous or reporter circular RNAs depend on EJC for their association with polysomes. Our results uncover an internal initiation driven by EJC, expanding the protein-coding potential of human transcriptome including circular RNAs.
Project description:Microarray comparisons of transcript level in wild-type Arabidopsis and eif3h mutant plants. Goal:; To detect any change in transcript level between WT and eif3h mutant. BACKGROUND: The eukaryotic translation initiation factor eIF3 has multiple roles during the initiation of translation of cytoplasmic mRNAs. However, the contributions of individual subunits of eIF3 to the translation of specific mRNAs remain poorly understood. RESULTS: Working with stable reporter transgenes in Arabidopsis thaliana it was demonstrated that the h subunit of; eIF3 contributes to the efficient translation initiation of mRNAs harboring upstream open reading frames (uORFs) in their 5â leader sequence. uORFs, which can function as devices for translational regulation, are present in over 30% of Arabidopsis mRNAs, and are enriched among mRNAs for transcriptional regulators and protein modifying enzymes. Microarray comparisons of polysome loading in wild-type and eif3h mutant plants revealed that eIF3h generally helps to maintain efficient polysome loading of mRNAs harboring multiple uORFs. Independently, eIF3h also boosted polysome loading of mRNAs with long coding sequences. Moreover, the lesion in eIF3h revealed a concerted upregulation of translation for specific functional subgroups of mRNAs, including ribosomal proteins and proteins involved in photosynthesis. CONCLUSIONS: The intact eIF3h protein contributes to efficient translation initiation on 5â leader sequences harboring multiple uORFs, although mRNA features independent of uORFs were also implicated. Moreover, our data suggest that regulons of translational control can be revealed by mutations in generic translation initiation factors. Experiment Overall Design: Total RNA samples were isolated from 10-day-old wild-type and eif3h mutant plants
Project description:Reprograming of protein synthesis is an essential cellular process to tolerate and resist to stressing conditions. A variety of mechanisms are known to regulate translation at initiation but cells can also control proteins synthesis after the initiation checkpoint. We previously showed that K63 ubiquitin can modify ribosome proteins in response to oxidative stress. However, the mechanism by how K63 ubiquitin impacts ribosome function is entirely unknown. Here we characterized > 1000 K63 ubiquitin sites in the yeast Saccharomyces cerevisiae by mass spectrometry, and showed that many sites clustered at the head of the 40S subunit in response to H2O2. Moreover, ribosomes lacking K63 ubiquitin were depleted in proteins from the translation initiation factor eIF3, particularly Tif35 (eIF3g), which impacted ribosome stability, and protein production. Our results provided new insights on the role of K63 ubiquitin in regulating the resistance to oxidative stress via a post-initiation control of translation.
Project description:Int6/yin6 encodes the eIF3e subunits of the eukaryotic translation initiation factor 3 complex (eIF3). To assess the impact of eIF3e on the global transcriptome, RNA seq of total mRNA was performed.
Project description:Microarray comparisons of polysome loading in wild-type Arabidopsis and eif3h mutant; Goal: ; To find the target mRNAs that are translationally regulated by eIF3h. BACKGROUND: The eukaryotic translation initiation factor eIF3 has multiple roles during the initiation of translation of cytoplasmic mRNAs. However, the contributions of individual subunits of eIF3 to the translation of specific mRNAs remain poorly understood. RESULTS: Working with stable reporter transgenes in Arabidopsis thaliana it was demonstrated that the h subunit of; eIF3 contributes to the efficient translation initiation of mRNAs harboring upstream open reading frames (uORFs) in their 5â leader sequence. uORFs, which can function as devices for translational regulation, are present in over 30% of Arabidopsis mRNAs, and are enriched among mRNAs for transcriptional regulators and protein modifying enzymes. Microarray comparisons of polysome loading in wild-type and eif3h mutant plants revealed that eIF3h generally helps to maintain efficient polysome loading of mRNAs harboring multiple uORFs. Independently, eIF3h also boosted polysome loading of mRNAs with long coding sequences. Moreover, the lesion in eIF3h revealed a concerted upregulation of translation for specific functional subgroups of mRNAs, including ribosomal proteins and proteins involved in photosynthesis. CONCLUSIONS: The intact eIF3h protein contributes to efficient translation initiation on 5â leader sequences harboring multiple uORFs, although mRNA features independent of uORFs were also implicated. Moreover, our data suggest that regulons of translational control can be revealed by mutations in generic translation initiation factors. Experiment Overall Design: Polysomal and non-polysomal RNA samples were isolated from 10-day-old wild-type and eif3h mutant plants. The translation state (ratio between the polysome and non-polysome, PL/NP) for each gene in the WT and in the mutant was separately established, and then the translation states between the genotype were compared.