Eukaryotic translation initiation factor 3 subunit D overexpression is associated with the occurrence and development of ovarian cancer

eIF3d: A driver of noncanonical cap-dependent translation of specific mRNAs and a trigger of biological/pathological processes

Eukaryotic initiation factor 3d (eIF3d), a known RNA-binding subunit of the eIF3 complex, is a 66 to 68-kDa protein with an RNA-binding motif and a cap-binding domain. Compared with other eIF3 subunits, eIF3d is relatively understudied. However, recent progress in studying eIF3d has revealed a number of intriguing findings on its role in maintaining eIF3 complex integrity, global protein synthesis, and in biological and pathological processes. It has also been reported that eIF3d has noncanonical functions in regulating translation of a subset of mRNAs by binding to 5'-UTRs or interacting with other proteins independent of the eIF3 complex and additional functions in regulating protein stability. The noncanonical regulation of mRNA translation or protein stability may contribute to the role of eIF3d in biological processes such as metabolic stress adaptation and in disease onset and progression including severe acute respiratory syndrome coronavirus 2 infection, tumorigenesis, and acquired immune deficiency syndrome. In this review, we critically evaluate the recent studies on these aspects of eIF3d and assess prospects in understanding the function of eIF3d in regulating protein synthesis and in biological and pathological processes.

Initiation and elongation factor co-expression correlates with recurrence and survival in epithelial ovarian cancer

High grade epithelial ovarian cancer (EOC) represents a diagnostic and therapeutic challenge due to its aggressive features and short recurrence free survival (RFS) after primary treatment. Novel targets to inform our understanding of the EOC carcinogenesis in the translational machinery can provide us with independent prognostic markers and provide drugable targets. We have identified candidate eukaryotic initiation factors (eIF) and eukaryotic elongation factors (eEF) in the translational machinery for differential expression in EOC through in-silico analysis. We present the analysis of 150 ovarian tissue microarray (TMA) samples on the expression of the translational markers eIF2α, eIF2G, eIF5 (eIF5A and eIF5B), eIF6 and eEF1A1. All translational markers were differentially expressed among non-neoplastic ovarian samples and tumour samples (borderline tumours and EOC). In EOC, expression of eIF5A was found to be significantly correlated with recurrence free survival (RFS) and expression of eIF2G and eEF1A1 with overall survival (OS). Expression correlation among factor subunits showed that the correlation of eEF1A1, eIF2G, EIF2α and eIF5A were significantly interconnected. eIF5A was also correlated with eIF5B and eIF6. Our study demonstrates that EOCs have different translational profile compared to benign ovarian tissue and that eIF5A is a central dysregulated factor of the translation machinery.

EIF3D promotes the progression of preeclampsia by inhibiting of MAPK/ERK1/2 pathway

Preeclampsia (PE) has been recognized as one of the main reasons for neonatal and maternal mortality and morbidity. This study intended to identify certain genes that correlated with the pathogenesis of PE, and disclose the underlying mechanisms. The GSE14776 and GSE65271 datasets were obtained from the Gene Expression Omnibus database. Venn diagram analysis was performed to identify the differently expressed genes. The potential pathways were analyzed by Gene set enrichment analysis software. The expression of eukaryotic translation initiation factor 3 subunit D (EIF3D) in tissues and cells was respectively tested by immunohistochemistry and the quantitative real-time PCR. Cell transfection was utilized to alter the expression of EIF3D. Cell proliferation, invasion and migration were respectively tested by MTT, EdU, transwell and wound healing assays. Tube formation assay was utilized to determine the tube formation capacity of HTR-8/SVneo cells. ELISA was employed for determination of the concentration of Angiotensin (ANG)-1. Moreover, the expression of EIF3D, proliferation-, metastasis-, tube formation- and MAPK/ERK1/2 pathway-related proteins were measured utilizing western blot. EIF3D was selected in this study. EIF3D was upregulated in placentas tissues collected from patients with PE. EIF3D upregulation observably repressed the proliferation, invasion, migration, wound healing and tube formation of HTR-8/SVneo cells, and the expression of their associated proteins. Besides, the concentration of ANG-1, and the ratios of phosphorylated-ERK1/2 and phosphorylated-MEK1/MEK1 were also markedly lowered by EIF3D upregulation. Whereas, EIF3D knockdown exerted the opposite effects, and these effects were distinctly counteracted by ERK1/2 inhibitor SC-221593 treatment. In conclusion, these observations manifested that EIF3D upregulation might have repressed the progression of PE through modulation of MAPK/ERK1/2 pathway.

Knockdown of ribosomal protein S6 suppresses proliferation, migration, and invasion in epithelial ovarian cancer

Background

Ovarian cancer typically is diagnosed late because insensitivity and lack of specificity of current biomarkers prior to its clinical detection. Ribosomal protein S6 (RPS6) is a ribosomal protein involved in the ribosomal 40S subunit, but its biological role in epithelial ovarian cancer (EOC) is still unknown.

Results

RPS6 was elevated in EOC compared to normal ovarian tissues and adenomas. Higher expression of RPS6 predicted worse prognosis in EOC. The level of RPS6 was correlated with clinical stage, histological type and pathological grade. Knockdown of RPS6 reduced the proliferation of ovarian cancer cell lines SKOV-3 and HO8910, and inhibit the migration and invasion ability. It revealed that cells arrested at G0G1 phase after knockdown of RPS6, and the expressions of CyclinD1, Cyclin E, CDK2, CDK4, CDK6 and pRb were also reduced.

Conclusions

RPS6 is involved in EOC and knockdown of RPS6 could inhibit the proliferation, invasion and migration ability of EOC in vitro by inducing G0/G1 phase arrest. RPS6 is expected to be a novel biomarker and molecular target to the EOC.

Overexpression of eIF3D in Lung Adenocarcinoma Is a New Independent Prognostic Marker of Poor Survival

The eukaryotic initiation factor 3 (eIF3) is the largest and most complex translation initiation factor in mammalian cells. It consists of 13 subunits and among which several were implicated to have significant prognostic effects on multiple human cancer entities. To examine the expression profiles of eIF3 subunits and determine their prognostic value in patients with lung adenocarcinoma (LUAD), the genomic data, survival data, and related clinical information were obtained from The Cancer Genome Atlas (TCGA) project for a secondary analysis. The results showed that among ten aberrantly expressed eIF3 subunits in tumours compared with adjacent normal counterparts (p < 0.05), only upregulated eIF3D could predict poor overall survival (OS) outcome independent of multiple clinicopathological parameters (HR = 2.043, 95% CI: 1.132-3.689, p = 0.018). Chi-square analysis revealed that the highly expressed eIF3D group had larger ratios of patients with advanced pathological stage (68/40 vs. 184/206, p = 0.0046), residual tumour (13/4 vs. 163/176, p = 0.0257), and targeted molecular therapy (85/65 vs. 138/164, p = 0.0357). In silico analysis demonstrated that the altered expression of eIF3D was at least regulated by both copy number alterations (CNAs) and the hypomethylation of cg14297023 site. In conclusion, high eIF3D expression might serve as a valuable independent prognostic indicator of shorter OS in patients with LUAD.

Cullin-3/KCTD10 complex is essential for K27-polyubiquitination of EIF3D in human hepatocellular carcinoma HepG2 cells

Eukaryotic translation initiation factor 3 subunit D (EIF3D) binds to the 5'-cap of specific mRNAs, initiating their translation into polypeptides. From a pathological standpoint, EIF3D has been observed to be essential for cell growth in various cancer types, and cancer patients with high EIF3D mRNA levels exhibit poor prognosis, indicating involvement of EIF3D in oncogenesis. In this study, we found, by mass spectrometry, that Cullin-3 (CUL3)/KCTD10 ubiquitin (Ub) ligase forms a complex with EIF3D. We also demonstrated that EIF3D is K27-polyubiquitinated at the lysine 153 and 275 residues in a KCTD10-dependent manner in human hepatocellular carcinoma HepG2 cells. Similar to other cancers, high expression of EIF3D significantly correlated with poor prognosis in hepatocellular carcinoma patients, and depletion of EIF3D drastically suppressed HepG2 cell proliferation. These results indicate that EIF3D is a novel substrate of CUL3/KCTD10 Ub ligase and suggest involvement of K27-polyubiquitinated EIF3D in the development of hepatocellular carcinoma.

Eukaryotic translation initiation factor 3 subunit G promotes human colorectal cancer

In this study, we investigated the role of eukaryotic translation initiation factor 3 subunit G (EIF3G) in colorectal cancer. Immunohistochemical analysis showed higher EIF3G expression in stage IV human colorectal cancer tissues than in adjacent normal tissues (P<0.01). EIF3G short hairpin RNA (shRNA) knockdown in HCT116 colon cancer cells reduced proliferation and increased apoptosis as compared to control. EIF3G knockdown also increased autophagy and reduced mTOR signaling, as evidenced by low phospho-AKT, phospho-S6K and phospho-4EBP1 levels. Functional experiments indicated that overexpression of EIF3G promoted HCT-116 cells proliferation, migration and xenograft tumor growth. Finally, we observed lower xenograft tumor weights and volumes with EIF3G-silenced HCT116 cells than with control cells. These findings demonstrate that EIF3G promotes colon cancer growth and is a potential therapeutic target.

Embraced by eIF3: structural and functional insights into the roles of eIF3 across the translation cycle

Protein synthesis is mediated via numerous molecules including the ribosome, mRNA, tRNAs, as well as translation initiation, elongation and release factors. Some of these factors play several roles throughout the entire process to ensure proper assembly of the preinitiation complex on the right mRNA, accurate selection of the initiation codon, errorless production of the encoded polypeptide and its proper termination. Perhaps, the most intriguing of these multitasking factors is the eukaryotic initiation factor eIF3. Recent evidence strongly suggests that this factor, which coordinates the progress of most of the initiation steps, does not come off the initiation complex upon subunit joining, but instead it remains bound to 80S ribosomes and gradually falls off during the first few elongation cycles to: (1) promote resumption of scanning on the same mRNA molecule for reinitiation downstream—in case of translation of upstream ORFs short enough to preserve eIF3 bound; or (2) come back during termination on long ORFs to fine tune its fidelity or, if signaled, promote programmed stop codon readthrough. Here, we unite recent structural views of the eIF3–40S complex and discus all known eIF3 roles to provide a broad picture of the eIF3’s impact on translational control in eukaryotic cells.