EIF4E AND EIF4GI HAVE DISTINCT AND DIFFERENTIAL IMPRINTS ON MULTIPLE MYELOMA'S PROTEOME AND SIGNALING
ABSTRACT: Accumulating data indicate translation plays a role in cancer biology, particularly its rate limiting stage of initiation. Despite this evolving recognition, the function and importance of specific translation initiation factors is unresolved. The eukaryotic translation initiation complex eIF4F consists of eIF4E and eIF4G at a 1:1 ratio. Although it is expected that they display interdependent functions, several publications suggest independent mechanisms. This study is the first to directly assess the relative contribution of eIF4F components to the expressed cellular proteome, transcription factors, microRNAs, and phenotype in a malignancy known for extensive protein synthesis- multiple myeloma (MM). Previously, we have shown that eIF4E/eIF4GI attenuation (siRNA/ Avastin) deleteriously affected MM cells' fate and reduced levels of eIF4E/eIF4GI established targets. Here, we demonstrated that eIF4E/eIF4GI indeed have individual influences on cell proteome. We used an objective, high throughput assay of mRNA microarrays to examine the significance of eIF4E/eIF4GI silencing to several cellular facets such as transcription factors, microRNAs and phenotype. We showed different imprints for eIF4E and eIF4GI in all assayed aspects. These results promote our understanding of the relative contribution and importance of eIF4E and eIF4GI to the malignant phenotype and shed light on their function in eIF4F translation initiation complex. This study concentrated on a particular cancer model and studied the role of eIF4E and eIF4GI in the design of the cells' proteome. We used an unbiased, high throughput system to evaluate the individual importance of eIF4E and eIF4GI levels in MM. We used models of eIF4E or eIF4GI knocked down (KD) MM cell line RPMI 8226 and profiled their respective translated transcription factors (TF), often tumor suppressors or oncogenes. Furthermore, we assessed the KDs' microRNAs repertoires and cells' phenotype. Significant differences were observed between eIF4E and eIF4GI knockdown imprints.
Project description:Translation factors eIF4E and eIF4G form eIF4F, which binds to mRNAs to promote ribosome recruitment and translation initiation. We were interested in analysing the effects of stresses on eIF4F interactions with individual mRNAs. We used a RIP-seq approach to assess how mRNA associations with eIF4E, eIF4G1 and eIF4G2 change in response to three stresses: 1) addition of hydrogen peroxide; 2) amino acids withdrawal; and, 3) glucose withdrawal. We find that acute stress leads to changes in eIF4FmRNA interactions that are shared among each factor and across the stresses imposed.
Project description:Regulatory T cells expressing the transcription factor Foxp3 play indispensable roles for the induction and maintenance of immunological self-tolerance and immune homeostasis. Genome-wide mRNA expression-studies have defined canonical signatures of T-cell subsets. Changes in steady-state mRNA levels do, however, often not reflect those of corresponding proteins due to post-transcriptional mechanisms including mRNA translation. Here, we unveil a unique translational signature, contrasting CD4+Foxp3+ regulatory T (TFoxp3+) and CD4+Foxp3- non-regulatory T (TFoxp3-) cells, which imprints subset-specific protein expression. We further show that translation of eukaryotic translation initiation factor 4E (eIF4E) is induced during T-cell activation and, in turn, regulates translation of cell cycle related mRNAs and proliferation in both TFoxp3- and TFoxp3+ cells. Unexpectedly, eIF4E also affects Foxp3 expression and thereby lineage identity. Thus, mRNA-specific translational control directs both common and distinct cellular processes in CD4+ T-cell subset. CD4+/Foxp3+ and CD4+Foxp3- cells were studied ex vivo or activated in vitro for 36h. Both polysome-associated and cytoplasmic RNA was isolated to enables studies of translational control
Project description:One of the most regulated steps of translation initiation is the recruitment of an mRNA by the translation machinery. In eukaryotes, this step is mediated by the 5´end cap-binding factor eIF4E bound to the bridge protein eIF4G and forming the eIF4F complex. In plants, different isoforms of eIF4E and eIF4G form the antigenically distinct eIF4F and eIF(iso)4F complexes proposed to mediate selective translation. Using a microarray analysis of polyribosome- and non-polyribosome-purified mRNAs from 15 day-old Arabidopsis thaliana wild type [WT] and eIF(iso)4E knockout mutant [AteIF(iso)4E-1] seedlings we found 79 transcripts shifted from polyribosomes toward non-polyribosomes, and 47 mRNAs with the opposite behavior in the mutant. The translationally decreased mRNAs were overrepresented in root-preferentially expressed genes and proteins from the endomembrane system, including several transporters such as the phosphate transporter PHOSPHATE1 (PHO1), Sucrose transporter 3 (SUC3), the ABC transporter-like with ATPase activity (MRP11) and five electron transporters, as well as signal transduction-, protein modification- and transcription-related proteins. For transcriptional analysis used total RNA of AteIF(iso)4E-1 seedlings of 15 days old to known the changes on transcripts leves by the eIF(iso)4E absence, using as control Wt seedlings. The experiments were performed in duplicate, and swap analysis were done. For translational analysis, used non-polysomal and polysomal RNA of AteIF(iso)4E-1 seedlings of 15 days old in order to known the transcripts that are modified in their translational levels by the eIF(iso)4E absence, using as control non polysomal and polysomal RNA of Wt seddlings.
Project description:This work explores the therapeutic potential for the translation initiation factor eIF4E in multiple myeloma (MM). We show that targeting eIF4E is deleterious to MM cells and causes reduction of targets with established importance to the disease progression. We demonstrate that eIF4E inhibition may be achieved by treating the MM cells with the already clinically employed anti-viral drug Ribavirin. Results indicate that tetraspanin overexpression in MM cell lines increased global protein synthesis; CD81N1/CD82N1 also caused a decrease in peIF4E, its regulators and targets; direct inhibition of eIF4E (siRNA, Ribavirin) deleteriously affected MM cell lines; and Ribavirin attenuated viability and induced death of primary BM MM cells. Overall design: Multiple Myeloma cell lines RPMI 8226 and CAG were each transiently transfected with purified plasmids of tetraspanins: pEGFP-N1 (N1, control), CD81N1-eGFP (81N1) or CD82N1-eGFP (82N1) (Clontech). Transfected cells were separated by Sorter Flow Cytometer 24 hours after transfection. Total RNA was extracted from sorted transfected cells with the Qiagen kit. Three separate experiments were analyzed by Whole Genome Affymetrix microarray chips (N1, 81N1, 82N1 in each cell line).
Project description:This work explores the therapeutic potential for the translation initiation factor eIF4E in multiple myeloma (MM). We show that targeting eIF4E is deleterious to MM cells and causes reduction of targets with established importance to the disease progression. We demonstrate that eIF4E inhibition may be achieved by treating the MM cells with the already clinically employed anti-viral drug Ribavirin. Results indicate that tetraspanin overexpression in MM cell lines increased global protein synthesis; CD81N1/CD82N1 also caused a decrease in peIF4E, its regulators and targets; direct inhibition of eIF4E (siRNA, Ribavirin) deleteriously affected MM cell lines; and Ribavirin attenuated viability and induced death of primary BM MM cells. Multiple Myeloma cell lines RPMI 8226 and CAG were each transiently transfected with purified plasmids of tetraspanins: pEGFP-N1 (N1, control), CD81N1-eGFP (81N1) or CD82N1-eGFP (82N1) (Clontech). Transfected cells were separated by Sorter Flow Cytometer 24 hours after transfection. Total RNA was extracted from sorted transfected cells with the Qiagen kit. Three separate experiments were analyzed by Whole Genome Affymetrix microarray chips (N1, 81N1, 82N1 in each cell line).
Project description:mRNA translation plays a major role in homeostasis, whereas its dysregulation underpins a variety of pathological states including cancer, metabolic syndrome and neurological disorders. Ternary complex (TC) and eIF4F complex assembly are two major rate-limiting steps in translation initiation that are thought to be regulated by eIF2α phosphorylation, and the mTOR/4E-BP pathway, respectively2. However, how TC and eIF4F assembly are coordinated remains largely unknown. Using polysome-profiling, we show that on a genome-wide scale mTOR suppresses translation of mRNAs, which are translationally activated under short-term ER stress when TC recycling is attenuated by eIF2α phosphorylation. During acute nutrient or growth factor stimulation, mTORC1 induces eIF2β phosphorylation, which increases recruitment of NCK1 to eIF2, decreases eIF2α phosphorylation and bolsters TC recycling. Accordingly, eIF2β appears to act as a previously unidentified mediator of mTORC1 on protein synthesis and proliferation. In addition, we demonstrate a formerly undocumented role for CK2 in regulation of translation initiation, whereby CK2 stimulates phosphorylation of eIF2β and simultaneously bolsters eIF4F complex assembly via the mTORC1/4E-BP pathway. These findings imply a previously unrecognized mode of translation regulation whereby mTORC1 and CK2 coordinate TC and eIF4F complex assembly to stimulate cell proliferation. Overall design: Comparisons of polysome-associated and cytoplasmic mRNA from starved cells or cells stimulated with insulin in the presence or absence of Torin-1.
Project description:In eukaryotic cells, protein synthesis typically begins with the binding of eIF4F to the 7-methylguanylate (m7G)cap found on the 5’ end of the majority of mRNAs. Surprisingly, overall translational output remains robust under eIF4F inhibition. The sustained protein synthesis has been largely attributed to cap-independent translation mediated by internal ribosome entry sites (IRES). However, the IRES-driven translation is substrate-specific and largely incompatible with the broad spectrum of eIF4F-resistant translatomes.Here, we report that N6-methyladenosine (m6A)-mediated translation prevails on capped mRNAs and is resistant to eIF4F inactivation.Depletion of the methyltransferase METTL3 selectively inhibits translation of mRNAs bearing 5’UTR methylation, but not mRNAs with 5’ terminal oligopyrimidine (TOP) elements. Mechanistically, we identify ABCF1 as a critical mediator of m6A-promoted translation under both stress and physiological conditions. Supporting the role of ABCF1 in m6A-mediated cap-independent translation, ABCF1-sensitive transcripts largely overlap with METTL3-responsible mRNA targets. By illustrating the scope and the mechanism of translation initiation that is neither cap- nor IRES-dependent, these findingsreshape our current perceptions of cellular translational pathways Overall design: Ribo-seq and RNA-seq in Scramble, ABCF1 and METTL3 knockdown.
Project description:Hepatitis C Virus protein NS5A was found to upregulate assembly of cap binding initiation complex eIF4F in Huh7.5 cells. NS5A also was found to associate with translation machinery. To understand consequences of NS5A mediation in host translation, we analyzed mRNA associated with polysome fractions of NS5A expressing Huh7.5 cells and compared them with the corresponding fractions from control cells. Agilent-027114 Genotypic Technology designed Custom Human Whole Genome 8x60k Microarray
Project description:The mRNA 5′ cap is normally essential for eukaryotic mRNA translation, stabilization and transport and both the cap and eIF4E are important elements of post-transcriptional gene regulation. To further our understanding of mRNA translation in the human malaria parasite Plasmodium falciparum, we have investigated the parasite translation initiation factor eIF4E and its interaction with 5′ capped mRNA. We have purified P. falciparum eIF4E as a recombinant protein and demonstrated that it has canonical mRNA 5′ cap binding activity. We used this protein to purify P. falciparum full-length 5′ capped mRNAs from total parasite RNA. Microarray analysis comparing total and eIF4E-purified 5′ capped mRNAs shows that a subset of 34 features were more than two-fold under-represented in the purified RNA sample, including 19 features representative of nuclear transcripts. The uncapped nuclear transcripts may represent a class of mRNAs targeted for storage and cap removal. Keywords: total RNA vs purified capped mRNA The microarray data were obtained from four hybridizations using RNA from two independent GST-PfeIF4E purifications from separate malaria cultures.
Project description:Aberrant activation of the translation initiation machinery is a common property of malignant cells, and is essential for breast carcinoma cells to manifest a malignant phenotype. How does sustained activation of the rate limiting step in protein synthesis so fundamentally alter a cell? In this report, we test the post transcriptional operon theory as a possible mechanism, employing a model system in which apoptosis resistance is conferred on NIH 3T3 cells by ectopic expression of eIF4E. We show (i) there is a set of 255 transcripts that manifest an increase in translational efficiency during eIF4E-mediated escape from apoptosis; (ii) there is a novel prototype 55 nt RNA consensus hairpin structure that is overrepresented in the 5'-untranslated region of translationally activated transcripts; (iii) the identified consensus hairpin structure is sufficient to target a reporter mRNA for translational activation under pro-apoptotic stress, but only when eIF4E is deregulated; and (iv) that osteopontin, one of the translationally activated transcripts harboring the identified consensus hairpin structure functions as one mediator of the apoptosis resistance seen in our model. Our findings offer genome-wide insights into the mechanism of eIF4E-mediated apoptosis resistance and provide a paradigm for the systematic study of posttranscriptional control in normal biology and disease. Keywords: common reference, various polyribosome fractions Overall design: To globally address the issue of which transcripts mediate the anti-apoptotic functions of eIF4E, we used a model in which NIH 3T3 cells ectopically overexpress translation initiation factor 4E (eIF4E) resulting in an apoptosis-resistant and tumorigenic phenotype. We performed a comprehensive study of apoptosis resistance in the NIH 3T3/4E model using an array containing 15k cDNAs and ESTs (NIH 15k collection printed at The Ontario Cancer Institute). To facilitate data analysis in the two-color competitive hybridization microarray approach employed, we used a universal standard mRNA [non-stratified poly(A) selected RNA derived from NIH 3T3 cells cultured in full growth medium]. We compared signals generated from this standard to both the light (fractions 4–6, <1 ribosome/transcript) and the heavy (fractions 7–10, >1 ribosomes/transcript) polyribosome fractions of RNA from NIH 3T3 and NIH 3T3/4E cells cultured either in complete growth medium or after 16 h of serum starvation, a time point before any evidence of cytochrome c release from the mitochondria, a signature step at the apex of the cell death program. We selected the 16 h time point in order to identify genes that might govern the decision to enter the apoptotic pathway, and exclude those involved in the actual process of cell execution.