eIF3d is an mRNA cap-binding protein that is required for specialized translation initiation.

Eukaryotic mRNAs contain a 5' cap structure that is crucial for recruitment of the translation machinery and initiation of protein synthesis. mRNA recognition is thought to require direct interactions between eukaryotic initiation factor 4E (eIF4E) and the mRNA cap. However, translation of numerous capped mRNAs remains robust during cellular stress, early development, and cell cycle progression despite inactivation of eIF4E. Here we describe a cap-dependent pathway of translation initiation in human cells that relies on a previously unknown cap-binding activity of eIF3d, a subunit of the 800-kilodalton eIF3 complex. A 1.4 Å crystal structure of the eIF3d cap-binding domain reveals unexpected homology to endonucleases involved in RNA turnover, and allows modelling of cap recognition by eIF3d. eIF3d makes specific contacts with the cap, as exemplified by cap analogue competition, and these interactions are essential for assembly of translation initiation complexes on eIF3-specialized mRNAs such as the cell proliferation regulator c-Jun (also known as JUN). The c-Jun mRNA further encodes an inhibitory RNA element that blocks eIF4E recruitment, thus enforcing alternative cap recognition by eIF3d. Our results reveal a mechanism of cap-dependent translation that is independent of eIF4E, and illustrate how modular RNA elements work together to direct specialized forms of translation initiation.

Reciprocal signaling between mTORC1 and MNK2 controls cell growth and oncogenesis.

eIF4E plays key roles in protein synthesis and tumorigenesis. It is phosphorylated by the kinases MNK1 and MNK2. Binding of MNKs to eIF4G enhances their ability to phosphorylate eIF4E. Here, we show that mTORC1, a key regulator of mRNA translation and oncogenesis, directly phosphorylates MNK2 on Ser74. This suppresses MNK2 activity and impairs binding of MNK2 to eIF4G. These effects provide a novel mechanism by which mTORC1 signaling impairs the function of MNK2 and thereby decreases eIF4E phosphorylation. MNK2[S74A] knock-in cells show enhanced phosphorylation of eIF4E and S6K1 (i.e., increased mTORC1 signaling), enlarged cell size, and increased invasive and transformative capacities. MNK2[Ser74] phosphorylation was inversely correlated with disease progression in human prostate tumors. MNK inhibition exerted anti-proliferative effects in prostate cancer cells in vitro. These findings define a novel feedback loop whereby mTORC1 represses MNK2 activity and oncogenic signaling through eIF4E phosphorylation, allowing reciprocal regulation of these two oncogenic pathways.

Targeting eIF4F translation initiation complex with SBI-756 sensitises B lymphoma cells to venetoclax.

BACKGROUND: The BCL2 inhibitor venetoclax has shown efficacy in several hematologic malignancies, with the greatest response rates in indolent blood cancers such as chronic lymphocytic leukaemia. There is a lower response rate to venetoclax monotherapy in diffuse large B-cell lymphoma (DLBCL). METHODS: We tested inhibitors of cap-dependent mRNA translation for the ability to sensitise DLBCL and mantle cell lymphoma (MCL) cells to apoptosis by venetoclax. We compared the mTOR kinase inhibitor (TOR-KI) MLN0128 with SBI-756, a compound targeting eukaryotic translation initiation factor 4G1 (eIF4G1), a scaffolding protein in the eIF4F complex. RESULTS: Treatment of DLBCL and MCL cells with SBI-756 synergised with venetoclax to induce apoptosis in vitro, and enhanced venetoclax efficacy in vivo. SBI-756 prevented eIF4E-eIF4G1 association and cap-dependent translation without affecting mTOR substrate phosphorylation. In TOR-KI-resistant DLBCL cells lacking eIF4E binding protein-1, SBI-756 still sensitised to venetoclax. SBI-756 selectively reduced translation of mRNAs encoding ribosomal proteins and translation factors, leading to a reduction in protein synthesis rates in sensitive cells. When normal lymphocytes were treated with SBI-756, only B cells had reduced viability, and this correlated with reduced protein synthesis. CONCLUSIONS: Our data highlight a novel combination for treatment of aggressive lymphomas, and establishes its efficacy and selectivity using preclinical models.

4Ei-10 interdiction of oncogenic cap-mediated translation as therapy for non-small cell lung cancer.

In order to suppress 5' cap-mediated translation a highly available inhibitor of the interaction between the 5' mRNA cap and the eIF4E complex has been developed. 4Ei-10 is a member of the class of ProTide compounds and has elevated membrane permeability and is a strong active chemical antagonist for eIF4E. Once taken up by cells it is converted by anchimeric activation of the lipophilic 2-(methylthio) ethyl protecting group and after that Hint1 P-N bond cleavage to N7-(p-chlorophenoxyethyl) guanosine 5'-monophosphate (7-Cl-Ph-Ethyl-GMP). Using this powerful interaction, it has been demonstrated that 4Ei-10 inhibits non-small cell lung cancer (NSCLC) cell growth. In addition, treatment of NSCLC cells with 4Ei-10 results in suppression of translation and diminished expression of a cohort of cellular proteins important to maintaining the malignant phenotype and resisting apoptosis such as Bcl-2, survivin, and ornithine decarboxylase (ODC). Finally, as a result of targeting the translation of anti-apoptotic proteins, NSCLC cells are synergized to be more sensitive to the existing anti-neoplastic treatment gemcitabine currently used in NSCLC therapy.

eIF4E-eIF4G complex inhibition synergistically enhances the effect of sorafenib in hepatocellular carcinoma.

The clinical efficacy of sorafenib in hepatocellular carcinoma (HCC) is disappointing due to its low response rate and high rates of adverse effects. The eukaryotic translation initiation factor 4F (eIF4F) complex, mainly consisting of eIF4E-eukaryotic translation initiation factor 4G (eIF4G) interaction, is involved in the induction of drug resistance. Herein, we aimed to demonstrate that eIF4E-eIF4G complex inhibition enhanced the effect of sorafenib. The antiproliferation effect of combined treatment was evaluated by MTT assay and colony formation assay. Flow cytometry was used to detect the early cell apoptosis and cell cycle. The specific mechanism was demonstrated using western blot and lentivirus transfection. The combination of sorafenib with eIF4E-eIF4G inhibitors 4E1RCat (structural) or 4EGI-1 (competitive) synergistically inhibited the cell viability and colony formation ability of HCC cells. Moreover, the combined treatment induced more early apoptosis than sorafenib alone through downregulating the Bcl-2 expression. Besides, the coadministration of sorafenib and 4E1RCat or 4EGI-1 synergistically inhibited the expressions of eIF4E, eIF4G and phospho-4E-BP1 in HCC cells while blocking the phosphorylation of 4E-BP1 with lentiviral transfection failed to increase the sensitivity of HCC cells to sorafenib treatment. PI3K-AKT-mTOR signaling was also inhibited by the combined treatment. In a word, eIF4E-eIF4G complex inhibition synergistically enhances the effect of sorafenib in HCC treatment.

Discovery of Lysine-Targeted eIF4E Inhibitors through Covalent Docking.

Eukaryotic translation initiation factor 4E (eIF4E) binds the m7GTP cap structure at the 5'-end of mRNAs, stimulating the translation of proteins implicated in cancer cell growth and metastasis. eIF4E is a notoriously challenging target, and most of the reported inhibitors are negatively charged guanine analogues with negligible cell permeability. To overcome these challenges, we envisioned a covalent targeting strategy. As there are no cysteines near the eIF4E cap binding site, we developed a covalent docking approach focused on lysine. Taking advantage of a "make-on-demand" virtual library, we used covalent docking to identify arylsulfonyl fluorides that target a noncatalytic lysine (Lys162) in eIF4E. Guided by cocrystal structures, we elaborated arylsulfonyl fluoride 2 to 12, which to our knowledge is the first covalent eIF4E inhibitor with cellular activity. In addition to providing a new tool for acutely inactivating eIF4E in cells, our computational approach may offer a general strategy for developing selective lysine-targeted covalent ligands.

Preclinical evidence that MNK/eIF4E inhibition by cercosporamide enhances the response to antiangiogenic TKI and mTOR inhibitor in renal cell carcinoma.

Eukaryotic translation initiation factor 4E (eIF4E) is deregulated in patients with renal cell carcinoma (RCC) and associated with poor prognosis, and is activated and regulated by Mnk kinases. In this study, we investigated the anti-RCC potential of a unique Mnk inhibitor cercosporamide. We showed that cercosporamide is active against RCC cells via suppressing growth, survival and migration. Combination indices value indicated that the combination of cercosporamide with sunitinib or temsirolimus are synergistic in RCC. In two independent RCC xenograft mouse models, complete tumor growth arrest or reverse was observed throughout the duration of drug treatment in the combination of cercosporamide with sunitinib or temsirolimus groups. Of note, cercosporamide inhibited RCC angiogenesis via negatively regulating a number of RCC endothelial cellular events including morphogenesis, migration, growth and survival. Mechanistically, we found that cercosporamide suppressed pro-angiogenic factors VEGF and HIFα, inhibited EMT and reduced pro-survival and cell cycle proteins; and furthermore this was attributed to cercosporamide's ability in inhibiting eIF4E. This work demonstrates the anti-RCC activity of cercosporamide through targeting both RCC tumor cells and angiogenesis, and provides the first preclinical proof-of-concept of evidence of Mnk inhibition for RCC treatment.

Suppression of oncogenic protein translation via targeting eukaryotic translation initiation factor 4E overcomes chemo-resistance in nasopharyngeal carcinoma.

Resistance to adjuvant chemotherapy remains therapeutic challenge in nasopharyngeal carcinoma (NPC). In this work, we demonstrate that targeting eukaryotic translation initiation factor 4E (eIF4E) is a potential sensitizing strategy to overcome chemoresistance in NPC. We observe the aberrant activation of eIF4E and translational upregulation of eIF4E-regulated oncogenes in NPC cell after pro-longed exposure of cisplatin. Functional analysis demonstrates that eIF4E depletion effectively inhibits proliferation and induces apoptosis in cisplatin-resistant NPC cells. Consistently, eIF4E knockdown significantly enhances cisplatin efficacy in cisplatin-sensitive cells. We identify eIF4E as a therapeutically actionable targets by showing that ribavirin, an anti-viral drug, phenocopies the effects of eIF4E knockdown in NPC. We further demonstrate that ribavirin acts on chemoresistant NPC cells through suppressing eIF4E activity and oncogenic protein translation. Using two independent NPC xenograft mouse models, we show that ribavirin not only is effective in inhibiting chemoresistant NPC growth but also significantly augments the inhibitory effects of cisplatin efficacy in vivo without causing significant toxicity in mice. Taken together, our work shows an activation of eIF4E-mediated growth and survival mechanisms in response to chemotherapy and suggests that inhibition of eIF4E activity represents an attractive sensitizing strategy for NPC treatment. Our findings also suggest that ribavirin is a useful addition to the treatment armamentarium for NPC.

Autism-related deficits via dysregulated eIF4E-dependent translational control.

Hyperconnectivity of neuronal circuits due to increased synaptic protein synthesis is thought to cause autism spectrum disorders (ASDs). The mammalian target of rapamycin (mTOR) is strongly implicated in ASDs by means of upstream signalling; however, downstream regulatory mechanisms are ill-defined. Here we show that knockout of the eukaryotic translation initiation factor 4E-binding protein 2 (4E-BP2)-an eIF4E repressor downstream of mTOR-or eIF4E overexpression leads to increased translation of neuroligins, which are postsynaptic proteins that are causally linked to ASDs. Mice that have the gene encoding 4E-BP2 (Eif4ebp2) knocked out exhibit an increased ratio of excitatory to inhibitory synaptic inputs and autistic-like behaviours (that is, social interaction deficits, altered communication and repetitive/stereotyped behaviours). Pharmacological inhibition of eIF4E activity or normalization of neuroligin 1, but not neuroligin 2, protein levels restores the normal excitation/inhibition ratio and rectifies the social behaviour deficits. Thus, translational control by eIF4E regulates the synthesis of neuroligins, maintaining the excitation-to-inhibition balance, and its dysregulation engenders ASD-like phenotypes.

Inhibition of eukaryotic translation initiation factor 4E is effective against chemo-resistance in colon and cervical cancer.

Although cancer patients initially respond well to chemotherapy, they eventually develop resistance and relapse. In this work, we demonstrate that eIF4E-targeting therapy is a potential sensitizing strategy for overcoming chemoresistance and progression in cancer. We show that ribavirin, an anti-viral drug and pharmacological eIF4E inhibitor, effectively inhibits proliferation and decreases viability of paclitaxel-resistant cervical cancer and 5-FU-resistant colon cancer cells while is less toxic to human fibroblast cells. Importantly, oral administration of ribavirin significantly inhibits paclitaxel-resistant colon and 5-FU-resistant cervical cancer growth in xenograft mouse cancer model without causing significant toxicity in mice. Consistently, combination of ribavirin with paclitaxel or 5-FU sensitizes colon and cervical cancer cells to chemotherapeutic agents treatment in vitro and in vivo. We further confirm that the mechanism of the action of ribavirin in chemoresistant cancer cells is through suppressing eIF4E function. In addition, specific eIF4E knockdown via two independent siRNA mimics the effects of ribavirin in chemoresistant colon and cervical cancer cells. Cell cycle analysis indicate that ribavirin enhances the anti-proliferative effect of 5-FU by additionally arresting cells at G2/M phase via increasing cyclin B1, p-histone H3(Ser10) and Mad2 levels. Our work demonstrates that eIF4E inhibition using inhibitor or siRNA, either as single agent or in combination, could sensitize chemoresistant cancer cells to paclitaxel or 5-FU treatment and thereby improving the efficacy of chemodrug. Our findings demonstrate the therapeutic value of inhibiting eIF4E, particularly in chemoresistant cancers. Our findings also suggest ribavirin as a promising sensitizing drug for cancer treatment.

Ribavirin augments doxorubicin's efficacy in human hepatocellular carcinoma through inhibiting doxorubicin-induced eIF4E activation.

Activation of eukaryotic translation initiation factor 4E (eIF4E) is a cellular survival mechanism in response to chemotherapy in cancers. In this work, we demonstrate that targeting eIF4E by ribavirin sensitizes hepatocellular carcinoma (HCC) cell response to doxorubicin. Ribavirin inhibits growth and survival of HCC cells, and to a greater extent than in normal liver cells. Its combination with doxorubicin achieves greater efficacy than single drug in vitro and in vivo. Ribavirin suppresses phosphorylation of molecules involved in Akt/mTOR/eIF4E pathway. Overexpression of the phosphomimetic form (S209D) but not the nonphosphorylatable form (S209A) eIF4E significantly reverses the inhibitory effects of ribavirin. Interestingly, doxorubicin significantly increases p-eIF4E(S209) level in a dose- and time-dependent manner, suggesting that doxorubicin induces eIF4E activation in HCC cells. In addition, eIF4E activation induced by doxorubicin in HCC cells is inhibited by ribavirin. Our work demonstrates the greater efficacy of ribavirin and doxorubicin combination and its underlying mechanisms.

AEG-1 induces gastric cancer metastasis by upregulation of eIF4E expression.

Gastric cancer is the third leading cause of cancer-related deaths worldwide, and patients with lymph node, peritoneal and distant metastasis have a poor prognosis. Overexpression of Astrocyte-elevated gene-1 (AEG-1) has been reported to be correlated with the progression and metastasis of gastric cancer. However, its mechanisms are quite unclear. In this study, we found that elevated expression of AEG-1 was correlated with metastasis in human gastric cancer tissues. Moreover, gain- or loss-of-function of AEG-1, respectively, promoted or suppressed epithelial-mesenchymal transition (EMT), migration and invasion of gastric cancer cells. AEG-1 positively regulated eIF4E, MMP-9 and Twist expression. Manipulating eIF4E expression by transfection of overexpression constructs or siRNAs partially eliminated AEG-1-regulated EMT, cell migration and invasion. In addition, overexpression or knockdown of eIF4E promoted or suppressed EMT, cell migration and invasion in parallel with upregulation of MMP-9 and Twist expression, while manipulating eIF4E expression partially abrogated AEG-1-induced MMP-9 and Twist. Finally, silencing of AEG-1 expression not only inhibited tumour growth in parallel with downregulation of eIF4E, MMP-9 and Twist expression in a xenograft nude mouse model, but also suppressed lymph node and peritoneal metastasis of gastric cancer in an orthotopic nude mouse model. These findings suggest that AEG-1 promotes gastric cancer metastasis through upregulation of eIF4E-mediated MMP-9 and Twist, which provides new diagnostic markers and therapeutic targets for cancer metastasis.

Structure of the eukaryotic translation initiation factor eIF4E in complex with 4EGI-1 reveals an allosteric mechanism for dissociating eIF4G.

The interaction of the eukaryotic translation initiation factor eIF4E with the initiation factor eIF4G recruits the 40S ribosomal particle to the 5' end of mRNAs, facilitates scanning to the AUG start codon, and is crucial for eukaryotic translation of nearly all genes. Efficient recruitment of the 40S particle is particularly important for translation of mRNAs encoding oncoproteins and growth-promoting factors, which often harbor complex 5' UTRs and require efficient initiation. Thus, inhibiting the eIF4E/eIF4G interaction has emerged as a previously unpursued route for developing anticancer agents. Indeed, we discovered small-molecule inhibitors of this eIF4E/eIF4G interaction (4EGIs) that inhibit translation initiation both in vitro and in vivo and were used successfully in numerous cancer-biology and neurobiology studies. However, their detailed molecular mechanism of action has remained elusive. Here, we show that the eIF4E/eIF4G inhibitor 4EGI-1 acts allosterically by binding to a site on eIF4E distant from the eIF4G binding epitope. Data from NMR mapping and high-resolution crystal structures are congruent with this mechanism, where 4EGI-1 attaches to a hydrophobic pocket of eIF4E between ß-sheet2 (L60-T68) and α-helix1 (E69-N77), causing localized conformational changes mainly in the H78-L85 region. It acts by unfolding a short 310-helix (S82-L85) while extending α-helix1 by one turn (H78-S82). This unusual helix rearrangement has not been seen in any previous eIF4E structure and reveals elements of an allosteric inhibition mechanism leading to the dislocation of eIF4G from eIF4E.

Identification of Downstream Genes of the mTOR Pathway that Predict Recurrence and Progression in Non-Muscle Invasive High-Grade Urothelial Carcinoma of the Bladder.

Microarray analysis was used to investigate the lack of identified mammalian target of rapamycin (mTOR) pathway downstream genes to overcome cross-talk at non-muscle invasive high-grade (HG)-urothelial carcinoma (UC) of the bladder, gene expression patterns, gene ontology, and gene clustering by triple (p70S6K, S6K, and eIF4E) small interfering RNAs (siRNAs) or rapamycin in 5637 and T24 cell lines. We selected mTOR pathway downstream genes that were suppressed by siRNAs more than 2-fold, or were up-regulated or down-regulated by rapamycin more than 2-fold. We validated mTOR downstream genes with immunohistochemistry using a tissue microarray (TMA) of 125 non-muscle invasive HG-UC patients and knockout study to evaluate the synergistic effect with rapamycin. The microarray analysis selected mTOR pathway downstream genes consisting of 4 rapamycin up-regulated genes (FABP4, H19, ANXA10, and UPK3A) and 4 rapamycin down-regulated genes (FOXD3, ATP7A, plexin D1, and ADAMTS5). In the TMA, FABP4, and ATP7A were more expressed at T1 and FOXD3 was at Ta. ANXA10 and ADAMTS5 were more expressed in tumors ≤ 3 cm in diameter. In a multivariate Cox regression model, ANXA10 was a significant predictor of recurrence and ATP7A was a significant predictor of progression in non-muscle invasive HG-UC of the bladder. In an ATP7A knock-out model, rapamycin treatment synergistically inhibited cell viability, wound healing, and invasion ability compared to rapamycin only. Activity of the ANXA10 and ATP7A mTOR pathway downstream genes might predict recurrence and progression in non-muscle invasive HG-UC of the bladder. ATP7A knockout overcomes rapamycin cross-talk.

Modulation of tumor eIF4E by antisense inhibition: A phase I/II translational clinical trial of ISIS 183750-an antisense oligonucleotide against eIF4E-in combination with irinotecan in solid tumors and irinotecan-refractory colorectal cancer.

The eukaryotic translation initiation factor 4E (eIF4E) is a potent oncogene that is found to be dysregulated in 30% of human cancer, including colorectal carcinogenesis (CRC). ISIS 183750 is a second-generation antisense oligonucleotide (ASO) designed to inhibit the production of the eIF4E protein. In preclinical studies we found that EIF4e ASOs reduced expression of EIF4e mRNA and inhibited proliferation of colorectal carcinoma cells. An additive antiproliferative effect was observed in combination with irinotecan. We then performed a clinical trial evaluating this combination in patients with refractory cancer. No dose-limiting toxicities were seen but based on pharmacokinetic data and tolerability the dose of irinotecan was reduced to 160 mg/m(2) biweekly. Efficacy was evaluated in 15 patients with irinotecan-refractory colorectal cancer. The median time of disease control was 22.1 weeks. After ISIS 183750 treatment, peripheral blood levels of eIF4E mRNA were decreased in 13 of 19 patients. Matched pre- and posttreatment tumor biopsies showed decreased eIF4E mRNA levels in five of nine patients. In tumor tissue, the intracellular and stromal presence of ISIS 183750 was detected by IHC in all biopsied patients. Although there were no objective responses stable disease was seen in seven of 15 (47%) patients who were progressing before study entry, six of whom were stable at the time of the week 16 CT scan. We were also able to confirm through mandatory pre- and posttherapy tumor biopsies penetration of the ASO into the site of metastasis.

Targeting translation: eIF4E as an emerging anticancer drug target.

The translation initiation factor eIF4E mediates a rate-limiting process that drives selective translation of many oncongenic proteins such as cyclin D1, survivin and VEGF, thereby contributing to tumour growth, metastasis and therapy resistance. As an essential regulatory hub in cancer signalling network, many oncogenic signalling pathways appear to converge on eIF4E. Therefore, targeting eIF4E-mediated cap-dependent translation is considered a promising anticancer strategy. This paper reviews the strategies that can be used to target eIF4E, highlighting agents that target eIF4E activity at each distinct level.

Requirement of Mammalian target of rapamycin complex 1 downstream effectors in cued fear memory reconsolidation and its persistence.

Memory retrieval, often termed reconsolidation, can render previously consolidated memories susceptible to manipulation that can lead to alterations in memory strength. Although it is known that reconsolidation requires mammalian target of rapamycin complex 1 (mTORC1)-dependent translation, the specific contributions of its downstream effectors in reconsolidation are unclear. Using auditory fear conditioning in mice, we investigated the role of eukaryotic translation initiation factor 4E (eIF4E)-eIF4G interactions and p70 S6 kinase polypeptide 1 (S6K1) in reconsolidation. We found that neither 4EGI-1 (2-[(4-(3,4-dichlorophenyl)-thiazol-2-ylhydrazono)-3-(2-nitrophenyl)]propionic acid), an inhibitor of eFI4E-eIF4G interactions, nor PF-4708671 [2-((4-(5-ethylpyrimidin-4-yl)piperazin-1-yl)methyl)-5-(trifluoromethyl)-1H-benzo[d]imidazole], an inhibitor of S6K1, alone blocked the reconsolidation of auditory fear memory. In contrast, using these drugs in concert to simultaneously block eIF4E-eIF4G interactions and S6K1 immediately after memory reactivation significantly attenuated fear memory reconsolidation. Moreover, the combination of 4EGI-1 and PF-4708671 further destabilized fear memory 10 d after memory reactivation, which was consistent with experiments using rapamycin, an mTORC1 inhibitor. Furthermore, inhibition of S6K1 immediately after retrieval resulted in memory destabilization 10 d after reactivation, whereas inhibition of eIF4E-eIF4G interactions did not. These results indicate that the reconsolidation of fear memory requires concomitant association of eIF4E to eIF4G as well as S6K1 activity and that the persistence of memory at longer intervals after memory reactivation also requires mTORC1-dependent processes that involve S6K1. These findings suggest a potential mechanism for how mTORC1-dependent translation is fine tuned to alter memory persistence.

Signalling to eIF4E in cancer.

Translational control plays a critical role in the regulation of gene expression in eukaryotes and affects many essential cellular processes, including proliferation, apoptosis and differentiation. Under most circumstances, translational control occurs at the initiation step at which the ribosome is recruited to the mRNA. The eukaryotic translation initiation factor 4E (eIF4E), as part of the eIF4F complex, interacts first with the mRNA and facilitates the recruitment of the 40S ribosomal subunit. The activity of eIF4E is regulated at many levels, most profoundly by two major signalling pathways: PI3K (phosphoinositide 3-kinase)/Akt (also known and Protein Kinase B, PKB)/mTOR (mechanistic/mammalian target of rapamycin) and Ras (rat sarcoma)/MAPK (mitogen-activated protein kinase)/Mnk (MAPK-interacting kinases). mTOR directly phosphorylates the 4E-BPs (eIF4E-binding proteins), which are inhibitors of eIF4E, to relieve translational suppression, whereas Mnk phosphorylates eIF4E to stimulate translation. Hyperactivation of these pathways occurs in the majority of cancers, which results in increased eIF4E activity. Thus, translational control via eIF4E acts as a convergence point for hyperactive signalling pathways to promote tumorigenesis. Consequently, recent works have aimed to target these pathways and ultimately the translational machinery for cancer therapy.

Integrin ß6 can be translationally regulated by eukaryotic initiation factor 4E: Contributing to colonic tumor malignancy.

It is well known that both eukaryotic initiation factor 4E (eIF4E) and integrin αvß6 can contribute to malignant behavior of colon cancer. We have found that integrin αvß6 and eIF4E were co-expressed and positively correlated in colon cancer tissues. Recently, deregulation of the protein synthesis apparatus has begun to gain attention as a major participant in cancer development and progression. However, the regulation of integrin ß6 expression at translational level has never been investigated before. In present study, gene-silencing technique for eIF4E by small interfering RNA (siRNA) was used in all the subsequent experiments, in order to investigate whether eIF4E could translationally regulate expression of integrin ß6 in colon cancer SW480 and HT-29 cell lines. Additionally, the subsequent effects of eIF4E knockdown on cellular malignant behavior were observed. siRNA in SW480 and HT-29 transfectants. Subsequently, protein expression of ß6 was markedly suppressed, while mRNA expression of ß6 showed no significant variation before and after eIF4E RNA interfering. Therefore, it could be seen that eIF4E could upregulate the expression of ß6, without effect on ß6 mRNA expression. More importantly, after treated with eIF4E siRNA, cellular migratory capacity on fibronectin of HT-29 and ß6-transfected SW480 as well as their survival to 5-FU was decreased distinctly. Expression of integrin ß6 could be translationally regulated by eIF4E, which subsequently contributed to tumor malignancy through enhancing cellular migration, survival, anti-apoptosis, and chemoresistance of colon cancer in vitro. Thus, targeting eIF4E in integrin αvß6 expressing tumors can be a potential therapeutic strategy for patients with colon cancer.

P70S6K and Elf4E dual inhibition is essential to control bladder tumor growth and progression in orthotopic mouse non-muscle invasive bladder tumor model.

We investigated how the dual inhibition of the molecular mechanism of the mammalian target of the rapamycin (mTOR) downstreams, P70S6 kinase (P70S6K) and eukaryotic initiation factor 4E (eIF4E), can lead to a suppression of the proliferation and progression of urothelial carcinoma (UC) in an orthotopic mouse non-muscle invasive bladder tumor (NMIBT) model. A KU-7-luc cell intravesically instilled orthotopic mouse NMIBC model was monitored using bioluminescence imaging (BLI) in vivo by interfering with different molecular components using rapamycin and siRNA technology. We then analyzed the effects on molecular activation status, cell growth, proliferation, and progression. A high concentration of rapamycin (10 µM) blocked both P70S6K and elF4E phosphorylation and inhibited cell proliferation in the KU-7-luc cells. It also reduced cell viability and proliferation more than the transfection of siRNA against p70S6K or elF4E. The groups with dual p70S6K and elF4E siRNA, and rapamycin reduced tumor volume and lamina propria invasion more than the groups with p70S6K or elF4E siRNA instillation, although all groups reduced photon density compared to the control. These findings suggest that both the mTOR pathway downstream of eIF4E and p70S6K can be successfully inhibited by high dose rapamycin only, and p70S6K and Elf4E dual inhibition is essential to control bladder tumor growth and progression.