Translation initiation of ornithine decarboxylase and nucleocytoplasmic transport of cyclin D1 mRNA are increased in cells overexpressing eukaryotic initiation factor 4E

eIF4E orchestrates mRNA processing, RNA export and translation to modify specific protein production

The eukaryotic translation initiation factor eIF4E acts as a multifunctional factor that simultaneously influences mRNA processing, export, and translation in many organisms. Its multifactorial effects are derived from its capacity to bind to the methyl-7-guanosine cap on the 5'end of mRNAs and thus can act as a cap chaperone for transcripts in the nucleus and cytoplasm. In this review, we describe the multifactorial roles of eIF4E in major mRNA-processing events including capping, splicing, cleavage and polyadenylation, nuclear export and translation. We discuss the evidence that eIF4E acts at two levels to generate widescale changes to processing, export and ultimately the protein produced. First, eIF4E alters the production of components of the mRNA processing machinery, supporting a widescale reprogramming of multiple mRNA processing events. In this way, eIF4E can modulate mRNA processing without physically interacting with target transcripts. Second, eIF4E also physically interacts with both capped mRNAs and components of the RNA processing or translation machineries. Further, specific mRNAs are sensitive to eIF4E only in particular mRNA processing events. This selectivity is governed by the presence of cis-acting elements within mRNAs known as USER codes that recruit relevant co-factors engaging the appropriate machinery. In all, we describe the molecular bases for eIF4E's multifactorial function and relevant regulatory pathways, discuss the basis for selectivity, present a compendium of ~80 eIF4E-interacting factors which play roles in these activities and provide an overview of the relevance of its functions to its oncogenic potential. Finally, we summarize early-stage clinical studies targeting eIF4E in cancer.

Review: The PI3K-AKT-mTOR signal transduction pathway in canine cancer

Tumors in dogs and humans share many similar molecular and genetic features, incentivizing a better understanding of canine neoplasms not only for the purpose of treating companion animals, but also to facilitate research of spontaneously developing tumors with similar biologic behavior and treatment approaches in an immunologically competent animal model. Multiple tumor types of both species have similar dysregulation of signal transduction through phosphatidylinositol 3-kinase (PI3K), protein kinase B (PKB; AKT), and mechanistic target of rapamycin (mTOR), collectively known as the PI3K-AKT-mTOR pathway. This review aims to delineate the pertinent aspects of the PI3K-AKT-mTOR signaling pathway in health and in tumor development. It will then present a synopsis of current understanding of PI3K-AKT-mTOR signaling in important canine cancers and advancements in targeted inhibitors of this pathway.

The eukaryotic translation initiation factor eIF4E unexpectedly acts in splicing thereby coupling mRNA processing with translation: eIF4E induces widescale splicing reprogramming providing system-wide connectivity between splicing, nuclear mRNA export and translation

Recent findings position the eukaryotic translation initiation factor eIF4E as a novel modulator of mRNA splicing, a process that impacts the form and function of resultant proteins. eIF4E physically interacts with the spliceosome and with some intron-containing transcripts implying a direct role in some splicing events. Moreover, eIF4E drives the production of key components of the splicing machinery underpinning larger scale impacts on splicing. These drive eIF4E-dependent reprogramming of the splicing signature. This work completes a series of studies demonstrating eIF4E acts in all the major mRNA maturation steps whereby eIF4E drives production of the RNA processing machinery and escorts some transcripts through various maturation steps. In this way, eIF4E couples the mRNA processing-export-translation axis linking nuclear mRNA processing to cytoplasmic translation. eIF4E elevation is linked to worse outcomes in acute myeloid leukemia patients where these activities are dysregulated. Understanding these effects provides new insight into post-transcriptional control and eIF4E-driven cancers.

eIF4E as a molecular wildcard in metazoans RNA metabolism

The evolutionary origin of eukaryotes spurred the transition from prokaryotic-like translation to a more sophisticated, eukaryotic translation. During this process, successive gene duplication of a single, primordial eIF4E gene encoding the mRNA cap-binding protein eukaryotic translation initiation factor 4E (eIF4E) gave rise to a plethora of paralog genes across eukaryotes that underwent further functional diversification in RNA metabolism. The ability to take different roles is due to eIF4E promiscuity in binding many partner proteins, rendering eIF4E a highly versatile and multifunctional player that functions as a molecular wildcard. Thus, in metazoans, eIF4E paralogs are involved in various processes, including messenger RNA (mRNA) processing, export, translation, storage, and decay. Moreover, some paralogs display differential expression in tissues and developmental stages and show variable biochemical properties. In this review, we discuss recent advances shedding light on the functional diversification of eIF4E in metazoans. We emphasise humans and two phylogenetically distant species which have become paradigms for studies on development, namely the fruit fly Drosophila melanogaster and the roundworm Caenorhabditis elegans.

Exploring the mTOR Signalling Pathway and Its Inhibitory Scope in Cancer

Mechanistic target of rapamycin (mTOR) is a protein kinase that regulates cellular growth, development, survival, and metabolism through integration of diverse extracellular and intracellular stimuli. Additionally, mTOR is involved in interplay of signalling pathways that regulate apoptosis and autophagy. In cells, mTOR is assembled into two complexes, mTORC1 and mTORC2. While mTORC1 is regulated by energy consumption, protein intake, mechanical stimuli, and growth factors, mTORC2 is regulated by insulin-like growth factor-1 receptor (IGF-1R), and epidermal growth factor receptor (EGFR). mTOR signalling pathways are considered the hallmark in cancer due to their dysregulation in approximately 70% of cancers. Through downstream regulators, ribosomal protein S6 kinase β-1 (S6K1) and eukaryotic translation initiation factor 4E binding protein 1 (4E-BP1), mTORC1 influences various anabolic and catabolic processes in the cell. In recent years, several mTOR inhibitors have been developed with the aim of treating different cancers. In this review, we will explore the current developments in the mTOR signalling pathway and its importance for being targeted by various inhibitors in anti-cancer therapeutics.

Medicinal chemistry approaches to target the MNK-eIF4E axis in cancer

Aberrant translation of proteins that promote cell proliferation is an essential factor that defines oncogenic processes and cancer. The process for ribosomal translation of proteins from mRNA requires an essential initiation step which is controlled by the protein eIF4E, which binds the RNA 5'-cap and forms the eIF4F complex that subsequently translates protein. Typically, eIF4E is activated by phosphorylation on Ser209 by MNK1 and MNK2 kinases. Substantial work has shown that eIF4E and MNK1/2 are dysregulated in many cancers and this axis has therefore become an active area of interest for developing new cancer therapeutics. This review summarizes and discusses recent work to develop small molecules that target different steps in the MNK-eIF4E axis as potential cancer therapeutics. The aim of this review is to cover the breadth of different molecular approaches being taken and the medicinal chemistry basis for their optimization and testing as new cancer therapeutics.

The eIF4EBP-eIF4E axis regulates CD4+ T cell differentiation through modulation of T cell activation and metabolism

CD4⁺ T cells are critical for adaptive immunity, differentiating into distinct effector and regulatory subsets. Although the transcriptional programs underlying their differentiation are known, recent research has highlighted the importance of mRNA translation in determining protein abundance. We previously conducted genome-wide analysis of translation in CD4⁺ T cells revealing distinct translational signatures distinguishing these subsets, identifying eIF4E as a central differentially translated transcript. As eIF4E is vital for eukaryotic translation, we examined how altered eIF4E activity affected T cell function using mice lacking eIF4E-binding proteins (BP^-/-). BP^-/- effector T cells showed elevated Th1 responses ex vivo and upon viral challenge with enhanced Th1 differentiation observed in vitro. This was accompanied by increased TCR activation and elevated glycolytic activity. This study highlights how regulating T cell-intrinsic eIF4E activity can influence T cell activation and differentiation, suggesting the eIF4EBP-eIF4E axis as a potential therapeutic target for controlling aberrant T cell responses.

An Aptamer against MNK1 for Non-Small Cell Lung Cancer Treatment

Lung cancer is the leading cause of cancer-related death worldwide. Its late diagnosis and consequently poor survival make necessary the search for new therapeutic targets. The mitogen-activated protein kinase (MAPK)-interacting kinase 1 (MNK1) is overexpressed in lung cancer and correlates with poor overall survival in non-small cell lung cancer (NSCLC) patients. The previously identified and optimized aptamer from our laboratory against MNK1, apMNKQ2, showed promising results as an antitumor drug in breast cancer in vitro and in vivo. Thus, the present study shows the antitumor potential of apMNKQ2 in another type of cancer where MNK1 plays a significant role, such as NSCLC. The effect of apMNKQ2 in lung cancer was studied with viability, toxicity, clonogenic, migration, invasion, and in vivo efficacy assays. Our results show that apMNKQ2 arrests the cell cycle and reduces viability, colony formation, migration, invasion, and epithelial-mesenchymal transition (EMT) processes in NSCLC cells. In addition, apMNKQ2 reduces tumor growth in an A549-cell line NSCLC xenograft model. In summary, targeting MNK1 with a specific aptamer may provide an innovative strategy for lung cancer treatment.

The N6-methyladenosine writer WTAP contributes to the induction of immune tolerance post kidney transplantation by targeting regulatory T cells

N6-methyladenosine (m6A) modification is involved in diverse immunoregulation, while the relationship between m6A modification and immune tolerance post kidney transplantation remains unclear. Expression of Wilms tumor 1-associating protein (WTAP), an m6A writer, was firstly detected in tolerant kidney transplant recipients (TOL). Then the role of WTAP on regulatory T (Treg) cell differentiation and function in CD4⁺ T cells from kidney transplant recipients with immune rejection (IR) was investigated. The potential target of WTAP and effect of WTAP on immune tolerance in vivo were subsequently verified. WTAP was upregulated in CD4⁺ T cells of TOL and positively correlated with Treg cell proportion. In vitro, WTAP overexpression promoted Treg cell differentiation and enhanced Treg cell-mediated suppression toward naïve T cells. Forkhead box other 1 (Foxo1) was identified as a target of WTAP. WTAP enhanced m6A modification of Foxo1 mRNA in coding sequence (CDS) region, leading to up-regulation of Foxo1. Overexpression of m6A demethylase removed the effect of WTAP overexpression, while Foxo1 overexpression reversed these effects. WTAP overexpression alleviated allograft rejection in model mice, as evidenced by reduced inflammatory response and increased Treg population. Our study suggests that WTAP plays a positive role in induction of immune tolerance post kidney transplant by promoting Treg cell differentiation and function.

Cancer cells hijack RNA processing to rewrite the message

Typically, cancer is thought to arise due to DNA mutations, dysregulated transcription and/or aberrant signalling. Recently, it has become clear that dysregulated mRNA processing, mRNA export and translation also contribute to malignancy. RNA processing events result in major modifications to the physical nature of mRNAs such as the addition of the methyl-7-guanosine cap, the removal of introns and the addition of polyA tails. mRNA processing is a critical determinant for the protein-coding capacity of mRNAs since these physical changes impact the efficiency by which a given transcript can be exported to the cytoplasm and translated into protein. While many of these mRNA metabolism steps were considered constitutive housekeeping activities, they are now known to be highly regulated with combinatorial and multiplicative impacts i.e. one event will influence the capacity to undergo others. Furthermore, alternative splicing and/or cleavage and polyadenylation can produce transcripts with alternative messages and new functionalities. The coordinated processing of groups of functionally related RNAs can potently re-wire signalling pathways, modulate survival pathways and even re-structure the cell. As postulated by the RNA regulon model, combinatorial regulation of these groups is achieved by the presence of shared cis-acting elements (known as USER codes) which recruit machinery for processing, export or translation. In all, dysregulated RNA metabolism in cancer gives rise to an altered proteome that in turn elicits biological responses related to malignancy. Studies of these events in cancer revealed new mechanisms underpinning malignancies and unearthed novel therapeutic opportunities. In all, cancer cells coopt RNA processing, export and translation to support their oncogenic activity.

Understanding the Polyamine and mTOR Pathway Interaction in Breast Cancer Cell Growth

The polyamines putrescine, spermidine and spermine are nutrient-like polycationic molecules involved in metabolic processes and signaling pathways linked to cell growth and cancer. One important pathway is the PI3K/Akt pathway where studies have shown that polyamines mediate downstream growth effects. Downstream of PI3K/Akt is the mTOR signaling pathway, a nutrient-sensing pathway that regulate translation initiation through 4EBP1 and p70S6K phosphorylation and, along with the PI3K/Akt, is frequently dysregulated in breast cancer. In this study, we investigated the effect of intracellular polyamine modulation on mTORC1 downstream protein and general translation state in two breast cancer cell lines, MCF-7 and MDA-MB-231. The effect of mTORC1 pathway inhibition on the growth and intracellular polyamines was also measured. Results showed that polyamine modulation alters 4EBP1 and p70S6K phosphorylation and translation initiation in the breast cancer cells. mTOR siRNA gene knockdown also inhibited cell growth and decreased putrescine and spermidine content. Co-treatment of inhibitors of polyamine biosynthesis and mTORC1 pathway induced greater cytotoxicity and translation inhibition in the breast cancer cells. Taken together, these data suggest that polyamines promote cell growth in part through interaction with mTOR pathway. Similarly intracellular polyamine content appears to be linked to mTOR pathway regulation. Finally, dual inhibition of polyamine and mTOR pathways may provide therapeutic benefits in some breast cancers.

Cryptolepine suppresses breast adenocarcinoma via inhibition of HIF-1 mediated glycolysis

As a characteristic transcription factor in solid tumors, hypoxia inducible factor-1 (HIF-1) acts as a master regulator in breast cancer progression. Cryptolepine, as a natural alkaloid, noticeably inhibited HIF-1 transcriptional activity and decreased the protein expression of hypoxia-induced HIF-1α in breast cancer cells. Further study showed that cryptolepine blocked HIF-1-mediated glycolysis and suppressed the expression of multiple glycolysis enzymes, resulting in a decrease in ATP production in hypoxic T47D and 4T1 cells. Meanwhile, cryptolepine displayed potent suppressive effect on tumor growth in a dose-dependent manner. In 4T1 tumor xenografts, cryptolepine reduced HIF-1α protein expression, and thus decreased the levels of both lactate acid and ATP productions. The mechanistic study revealed that cryptolepine could effectively suppress the process of HIF-1α mRNA translation rather than transcription, which was attributed to the inhibition on the phosphorylation of eIF4E regulated by both MAPK and mTOR signaling pathways. Collectively, current findings suggested that cryptolepine possesses the potential to treat breast cancers by modulating HIF-1 both in vitro and in vivo.

Nuclear-targeted 4E-BP1 is dephosphorylated, induces nuclear translocation of eIF4E, and alters mRNA translation

Mechanistic target of rapamycin complex 1 (mTORC1) phosphorylates and inhibits eukaryotic translation initiation factor 4E (eIF4E)-binding protein 1 (4E-BP1). This leads to the release of eIF4E from 4E-BP1 and the initiation of eIF4E-dependent mRNA translation. In this study, we examined the expression of a 4E-BP1-based reporter (mTORC1 activity reporter; TORCAR) with various localization signal tags to clarify the relationship between the localization of 4E-BP1 and its phosphorylation. Phosphorylation of 4E-BP1 at threonine 37/46 and serine 65 was efficient at lysosomes and the plasma membrane, whereas it was significantly decreased in the nucleus. In addition, the localization of endogenous eIF4E shifted from the cytoplasm to the nucleus only when nuclear-localized TORCAR was expressed. Nuclear-localized TORCAR decreased cyclin D1 protein levels and altered cell cycle distribution. These data provide an experimental tool to manipulate the localization of endogenous eIF4E without affecting mTORC1 and highlight the important role of nuclear-cytoplasmic shuttling of eIF4E.

Down-regulated Circ_0000190 promotes cervical cancer by facilitating the activity of proto-oncogene protein EIF4E

Circular RNAs (circRNAs), a new class of non-coding RNAs, have been recently confirmed to regulate cell development, functions and certain types of pathological responses. In addition, it has been proved that circ_0000190 can serve as a tumor suppressor in several cancers. However, the underlying mechanism and biological functions of it in cervical cancer (CC) remain to be revealed. In our study, relative expression of indicated molecules was detected by RT-qPCR analysis. Loss-of-function and gain-of-function experiments were conducted to detect cell functions. Mechanism experiments including RIP assay, luciferase reporter assay and pull down assay were applied to verify the interaction among the indicated molecules. Overexpressed circ_0000190 attenuated CC progression in vitro and in vivo. Circ_0000190 functioned through the modulation of miR-1252-5p/EIF4EBP2 axis. Rescue experiments found that miR-1252-5p overexpression or EIF4EBP2 knockdown could reverse the influence on CC cells caused by circ_0000190 overexpression. Interestingly, it was found that EIF4EBP2 could bind to proto-oncogene eIF4E and prevent eIF4E from forming into complex and functioning. Circ_0000190 served as a tumor suppressor in CC and down-regulated circ_0000190 expression could weaken the binding ability of EIF4EBP2 to eIF4E thus leading to CC tumorigenesis. In our investigation, a novel tumor suppressive gene circ_0000190 was recognized, which could be treated as a promising biomarker for the diagnosis of CC.

The Cap-Binding Complex CBC and the Eukaryotic Translation Factor eIF4E: Co-Conspirators in Cap-Dependent RNA Maturation and Translation

The translation of RNA into protein is a dynamic process which is heavily regulated during normal cell physiology and can be dysregulated in human malignancies. Its dysregulation can impact selected groups of RNAs, modifying protein levels independently of transcription. Integral to their suitability for translation, RNAs undergo a series of maturation steps including the addition of the m7G cap on the 5' end of RNAs, splicing, as well as cleavage and polyadenylation (CPA). Importantly, each of these steps can be coopted to modify the transcript signal. Factors that bind the m7G cap escort these RNAs through different steps of maturation and thus govern the physical nature of the final transcript product presented to the translation machinery. Here, we describe these steps and how the major m7G cap-binding factors in mammalian cells, the cap binding complex (CBC) and the eukaryotic translation initiation factor eIF4E, are positioned to chaperone transcripts through RNA maturation, nuclear export, and translation in a transcript-specific manner. To conceptualize a framework for the flow and integration of this genetic information, we discuss RNA maturation models and how these integrate with translation. Finally, we discuss how these processes can be coopted by cancer cells and means to target these in malignancy.

Apoptotic cell-derived metabolites in efferocytosis-mediated resolution of inflammation

The resolution of inflammation, as part of standard host defense mechanism, is the process to guarantee timely termination of inflammatory responses and eventual restoration of tissue homeostasis . It is mainly achieved via efferocytosis, during which pro-resolving macrophages clear apoptotic neutrophils at the inflammatory site. Unfortunately, impaired resolution can be the leading cause of chronic inflammatory disorders and some autoimmune diseases. Existing studies have provided relatively comprehensive understandings about the recognition and uptake of apoptotic neutrophils by macrophages during early phases of efferocytosis. However, lack of information concerns macrophage metabolism of apoptotic cell-derived metabolites after being released from phagolysosomes or the relationship between such metabolism and efferocytosis. Notwithstanding, three recent studies have revealed macrophage metabolism of cholesterol, fatty acids and arginine, as well as their respective functions in the context of inflammation-resolution. This review provides an overview of the resolution of inflammation, efferocytosis and the key players involved, followed by a focus on the metabolism of apoptotic cell-derived metabolites within efferocytes. Hypotheses of more potential apoptotic cell-derived metabolites and their possible roles in the resolution are also formulated. Understanding the effect of these metabolites further advances the concept that apoptotic cells act as active players to regulate resolution, and also suggests novel therapeutic strategies for diseases driven by defective resolution and even cancer that may be treated through enhanced efferocytosis.

Large-scale translatome profiling annotates the functional genome and reveals the key role of genic 3' untranslated regions in translatomic variation in plants

The translatome, a profile of the translational status of genetic information within cells, provides a new perspective on gene expression. Although many plant genomes have been sequenced, comprehensive translatomic annotations are not available for plants due to a lack of efficient translatome profiling techniques. Here, we developed a new technique termed 3' ribosome-profiling sequencing (3'Ribo-seq) for reliable, robust translatomic profiling. 3'Ribo-seq combines polysome profiling and 3' selection with a barcoding and pooling strategy. Systematic translatome profiling of different tissues of Arabidopsis, rice, and maize using conventional ribosome profiling (Ribo-seq) and 3'Ribo-seq revealed many novel translational genomic loci, thereby complementing functional genome annotation in plants. Using the low-cost, efficient 3'Ribo-seq technique and genome-wide association mapping of translatome expression (eGWAS), we performed a population-level dissection of the translatomes of 159 diverse maize inbred lines and identified 1,777 translational expression quantitative trait loci (eQTLs). Notably, local eQTLs are significantly enriched in the 3' untranslated regions of genes. Detailed eQTL analysis suggested that sequence variation around the polyadenylation (polyA) signal motif plays a key role in translatomic variation. Our study provides a comprehensive translatome annotation of plant functional genomes and introduces 3'Ribo-seq, which paves the way for deep translatomic analysis at the population level.

BAD regulates mammary gland morphogenesis by 4E-BP1-mediated control of localized translation in mouse and human models

Elucidation of non-canonical protein functions can identify novel tissue homeostasis pathways. Herein, we describe a role for the Bcl-2 family member BAD in postnatal mammary gland morphogenesis. In Bad^3SA knock-in mice, where BAD cannot undergo phosphorylation at 3 key serine residues, pubertal gland development is delayed due to aberrant tubulogenesis of the ductal epithelium. Proteomic and RPPA analyses identify that BAD regulates focal adhesions and the mRNA translation repressor, 4E-BP1. These results suggest that BAD modulates localized translation that drives focal adhesion maturation and cell motility. Consistent with this, cells within Bad^3SA organoids contain unstable protrusions with decreased compartmentalized mRNA translation and focal adhesions, and exhibit reduced cell migration and tubulogenesis. Critically, protrusion stability is rescued by 4E-BP1 depletion. Together our results confirm an unexpected role of BAD in controlling localized translation and cell migration during mammary gland development.

Metabolism of Amino Acids in Cancer

Metabolic reprogramming has been widely recognized as a hallmark of malignancy. The uptake and metabolism of amino acids are aberrantly upregulated in many cancers that display addiction to particular amino acids. Amino acids facilitate the survival and proliferation of cancer cells under genotoxic, oxidative, and nutritional stress. Thus, targeting amino acid metabolism is becoming a potential therapeutic strategy for cancer patients. In this review, we will systematically summarize the recent progress of amino acid metabolism in malignancy and discuss their interconnection with mammalian target of rapamycin complex 1 (mTORC1) signaling, epigenetic modification, tumor growth and immunity, and ferroptosis. Finally, we will highlight the potential therapeutic applications.

The eukaryotic translation initiation factor eIF4E elevates steady-state m7G capping of coding and noncoding transcripts

Methyl-7-guanosine (m7G) "capping" of coding and some noncoding RNAs is critical for their maturation and subsequent activity. Here, we discovered that eukaryotic translation initiation factor 4E (eIF4E), itself a cap-binding protein, drives the expression of the capping machinery and increased capping efficiency of ∼100 coding and noncoding RNAs. To quantify this, we developed enzymatic (cap quantification; CapQ) and quantitative cap immunoprecipitation (CapIP) methods. The CapQ method has the further advantage that it captures information about capping status independent of the type of 5' cap, i.e., it is not restricted to informing on m7G caps. These methodological advances led to unanticipated revelations: 1) Many RNA populations are inefficiently capped at steady state (∼30 to 50%), and eIF4E overexpression increased this to ∼60 to 100%, depending on the RNA; 2) eIF4E physically associates with noncoding RNAs in the nucleus; and 3) approximately half of eIF4E-capping targets identified are noncoding RNAs. eIF4E's association with noncoding RNAs strongly positions it to act beyond translation. Coding and noncoding capping targets have activities that influence survival, cell morphology, and cell-to-cell interaction. Given that RNA export and translation machineries typically utilize capped RNA substrates, capping regulation provides means to titrate the protein-coding capacity of the transcriptome and, for noncoding RNAs, to regulate their activities. We also discovered a cap sensitivity element (CapSE) which conferred eIF4E-dependent capping sensitivity. Finally, we observed elevated capping for specific RNAs in high-eIF4E leukemia specimens, supporting a role for cap dysregulation in malignancy. In all, levels of capping RNAs can be regulated by eIF4E.

Controlling TIME: How MNK Kinases Function to Shape Tumor Immunity

A number of studies have clearly established the oncogenic role for MAPK-interacting protein kinases (MNK) in human malignancies. Modulation of MNK activity affects translation of mRNAs involved in cancer development, progression, and resistance to therapies. As a result, there are ongoing efforts to develop and evaluate MNK inhibitors for cancer treatment. However, it is important to recognize that MNK activity also plays an important role in regulating the innate and adaptive immune systems. A better understanding of the role of MNK kinases and MNK-mediated signals in regulating the immune system could help mitigate undesired side effects while maximizing therapeutic efficacy of MNK inhibitors. Here, we provide a systematic review on the function of MNK kinases and their substrates in immune cells.

Nuclear eIF4E Stimulates 3'-End Cleavage of Target RNAs

The eukaryotic translation initiation factor eIF4E is nuclear and cytoplasmic where it plays roles in export and translation of specific transcripts, respectively. When we were studying its mRNA export activity, we unexpectedly discovered that eIF4E drives the protein expression of elements of the 3′-end core cleavage complex involved in cleavage and polyadenylation (CPA), including CPSF3, the enzyme responsible for cleavage, as well as its co-factors CPSF1, CPSF2, CPSF4, Symplekin, WDR33, and FIP1L1. Using multiple strategies, we demonstrate that eIF4E stimulates 3′-end cleavage of selected RNAs. eIF4E physically interacts with CPSF3, CPSF1, and uncleaved target RNA, suggesting it acts directly and indirectly on the pathway. Through these effects, eIF4E can generate better substrates for its mRNA export and translation activities. Thus, we identified an unanticipated function for eIF4E in 3′-end processing of specific target RNAs, and this function could potentially affect the expression of a broad range of oncoproteins.

Davis et al. demonstrate that the eukaryotic translation initiation factor eIF4E, which is usually associated with nuclear export and translation of specific transcripts, also acts in 3′-end processing of selected RNAs. Through these effects, eIF4E can generate better substrates for its export and translation activities and, thus, modulate the proteome.

The Organizing Principles of Eukaryotic Ribosome Recruitment

The stage at which ribosomes are recruited to messenger RNAs (mRNAs) is an elaborate and highly regulated phase of protein synthesis. Upon completion of this step, a ribosome is positioned at an appropriate initiation codon and primed to synthesize the encoded polypeptide product. In most circumstances, this step commits the ribosome to translate the mRNA. We summarize the knowledge regarding the initiation factors implicated in this activity as well as review different mechanisms by which this process is conducted.

The MNK1/2-eIF4E Axis as a Potential Therapeutic Target in Melanoma

: Melanoma is a type of skin cancer that originates in the pigment-producing cells of the body known as melanocytes. Most genetic aberrations in melanoma result in hyperactivation of the mitogen activated protein kinase (MAPK) and phosphoinositide 3-kinase (PI3K) pathways. We and others have shown that a specific protein synthesis pathway known as the MNK1/2-eIF4E axis is often dysregulated in cancer. The MNK1/2-eIF4E axis is a point of convergence for these signaling pathways that are commonly constitutively activated in melanoma. In this review we consider the functional implications of aberrant mRNA translation in melanoma and other malignancies. Moreover, we discuss the consequences of inhibiting the MNK1/2-eIF4E axis on the tumor and tumor-associated cells, and we provide important avenues for the utilization of this treatment modality in combination with other targeted and immune-based therapies. The past decade has seen the increased development of selective inhibitors to block the action of the MNK1/2-eIF4E pathway, which are predicted to be an effective therapy regardless of the melanoma subtype (e.g., cutaneous, acral, and mucosal).

The diversity, plasticity, and adaptability of cap-dependent translation initiation and the associated machinery

Translation initiation is a critical facet of gene expression with important impacts that underlie cellular responses to stresses and environmental cues. Its dysregulation in many diseases position this process as an important area for the development of new therapeutics. The gateway translation factor eIF4E is typically considered responsible for ‘global’ or ‘canonical’ m⁷G cap-dependent translation. However, eIF4E impacts translation of specific transcripts rather than the entire translatome. There are many alternative cap-dependent translation mechanisms that also contribute to the translation capacity of the cell. We review the diversity of these, juxtaposing more recently identified mechanisms with eIF4E-dependent modalities. We also explore the multiplicity of functions played by translation factors, both within and outside protein synthesis, and discuss how these differentially contribute to their ultimate physiological impacts. For comparison, we discuss some modalities for cap-independent translation. In all, this review highlights the diverse mechanisms that engage and control translation in eukaryotes.

Deeping in the Role of the MAP-Kinases Interacting Kinases (MNKs) in Cancer

The mitogen-activated protein kinase (MAPK)-interacting kinases (MNKs) are involved in oncogenic transformation and can promote metastasis and tumor progression. In human cells, there are four MNKs isoforms (MNK1a/b and MNK2a/b), derived from two genes by alternative splicing. These kinases play an important role controlling the expression of specific proteins involved in cell cycle, cell survival and cell motility via eukaryotic initiation factor 4E (eIF4E) regulation, but also through other substrates such as heterogeneous nuclear ribonucleoprotein A1, polypyrimidine tract-binding protein-associated splicing factor and Sprouty 2. In this review, we provide an overview of the role of MNK in human cancers, describing the studies conducted to date to elucidate the mechanism involved in the action of MNKs, as well as the development of MNK inhibitors in different hematological cancers and solid tumors.

Translating Translation to Mechanisms of Cardiac Hypertrophy

Cardiac hypertrophy in response to chronic pathological stress is a common feature occurring with many forms of heart disease. This pathological hypertrophic growth increases the risk for arrhythmias and subsequent heart failure. While several factors promoting cardiac hypertrophy are known, the molecular mechanisms governing the progression to heart failure are incompletely understood. Recent studies on altered translational regulation during pathological cardiac hypertrophy are contributing to our understanding of disease progression. In this brief review, we describe how the translational machinery is modulated for enhanced global and transcript selective protein synthesis, and how alternative modes of translation contribute to the disease state. Attempts at controlling translational output through targeting of mTOR and its regulatory components are detailed, as well as recently emerging targets for pre-clinical investigation.

It's Not the Destination, It's the Journey: Heterogeneity in mRNA Export Mechanisms

The process of creating a translation-competent mRNA is highly complex and involves numerous steps including transcription, splicing, addition of modifications, and, finally, export to the cytoplasm. Historically, much of the research on regulation of gene expression at the level of the mRNA has been focused on either the regulation of mRNA synthesis (transcription and splicing) or metabolism (translation and degradation). However, in recent years, the advent of new experimental techniques has revealed the export of mRNA to be a major node in the regulation of gene expression, and numerous large-scale and specific mRNA export pathways have been defined. In this chapter, we will begin by outlining the mechanism by which most mRNAs are homeostatically exported ("bulk mRNA export"), involving the recruitment of the NXF1/TAP export receptor by the Aly/REF and THOC5 components of the TREX complex. We will then examine various mechanisms by which this pathway may be controlled, modified, or bypassed in order to promote the export of subset(s) of cellular mRNAs, which include the use of metazoan-specific orthologs of bulk mRNA export factors, specific cis RNA motifs which recruit mRNA export machinery via specific trans-acting-binding factors, posttranscriptional mRNA modifications that act as "inducible" export cis elements, the use of the atypical mRNA export receptor, CRM1, and the manipulation or bypass of the nuclear pore itself. Finally, we will discuss major outstanding questions in the field of mRNA export heterogeneity and outline how cutting-edge experimental techniques are providing new insights into and tools for investigating the intriguing field of mRNA export heterogeneity.

Phosphorylation of eukaryotic initiation factor 4E is dispensable for skeletal muscle hypertrophy

The eukaryotic initiation factor 4E (eIF4E) is a major mRNA cap-binding protein that has a central role in translation initiation. Ser209 is the single phosphorylation site within eIF4E and modulates its activity in response to MAPK pathway activation. It has been reported that phosphorylation of eIF4E at Ser209 promotes translation of key mRNAs, such as cyclin D1, that regulate ribosome biogenesis. We hypothesized that phosphorylation at Ser209 is required for skeletal muscle growth in response to a hypertrophic stimulus by promoting ribosome biogenesis. To test this hypothesis, wild-type (WT) and eIF4E knocked-in (KI) mice were subjected to synergist ablation to induce muscle hypertrophy of the plantaris muscle as the result of mechanical overload; in the KI mouse, Ser209 of eIF4E was replaced with a nonphosphorylatable alanine. Contrary to our hypothesis, we observed no difference in the magnitude of hypertrophy between WT and KI groups in response to 14 days of mechanical overload induced by synergist ablation. Similarly, the increases in cyclin D1 protein levels, ribosome biogenesis, and translational capacity did not differ between WT and KI groups. Based on these findings, we conclude that phosphorylation of eIF4E at Ser209 is dispensable for skeletal muscle hypertrophy in response to mechanical overload.

Cell Fate Control by Translation: mRNA Translation Initiation as a Therapeutic Target for Cancer Development and Stem Cell Fate Control

Translation of mRNA is an important process that controls cell behavior and gene regulation because proteins are the functional molecules that determine cell types and function. Cancer develops as a result of genetic mutations, which lead to the production of abnormal proteins and the dysregulation of translation, which in turn, leads to aberrant protein synthesis. In addition, the machinery that is involved in protein synthesis plays critical roles in stem cell fate determination. In the current review, recent advances in the understanding of translational control, especially translational initiation in cancer development and stem cell fate control, are described. Therapeutic targets of mRNA translation such as eIF4E, 4EBP, and eIF2, for cancer treatment or stem cell fate regulation are reviewed. Upstream signaling pathways that regulate and affect translation initiation were introduced. It is important to regulate the expression of protein for normal cell behavior and development. mRNA translation initiation is a key step to regulate protein synthesis, therefore, identifying and targeting molecules that are critical for protein synthesis is necessary and beneficial to develop cancer therapeutics and stem cells fate regulation.

Clinical Significance of Eukaryotic Initiation Factor 4E (eIF4E) Level among Cases Suffering Basal Cell Carcinoma of Skin

BACKGROUND Eukaryotic initiation factor 4E (eIF4E) has been reported to act as a prognostic biomarker in various cancers, but its actual effect on basal cell cancer (BCC) of the skin is rarely reported. Our research measured eIF4E levels and discussed its consequence in BCC of the skin. MATERIAL AND METHODS Semi-quantitative real-time polymerase chain reaction (RT-PCR) and western blotting analysis were used to detect relative expression level of eIF4E in specimens at both mRNA and protein levels. The relationship of eIF4E level with clinical profiles was analyzed via chi-square test. Additionally, prognostic value of eIF4E was analyzed via Kaplan-Meier and cox regression analysis. RESULTS We found that eIF4E was over-expressed in tumor tissues, in comparison to bordering cancer-free tissue samples. Besides, elevated eIF4E level exhibited a strong relation to metastasis, TNM stage, and differentiation. Kaplan-Meier analysis revealed cases harboring high eIF4E levels faced shortened overall survival compared to cases of low levels (log rank test, P=0.018). Moreover, eIF4E could act as an independent biomarker for the prognosis of BCC of the skin, according to Cox regression analysis. CONCLUSIONS The level of eIF4E was upregulated and significantly correlated with the development of BCC of the skin. Thus, it might be a promising prognostic biomarker and therapy target for BCC of the skin.

Polysome-profiling in small tissue samples

Polysome-profiling is commonly used to study translatomes and applies laborious extraction of efficiently translated mRNA (associated with >3 ribosomes) from a large volume across many fractions. This property makes polysome-profiling inconvenient for larger experimental designs or samples with low RNA amounts. To address this, we optimized a non-linear sucrose gradient which reproducibly enriches for efficiently translated mRNA in only one or two fractions, thereby reducing sample handling 5-10-fold. The technique generates polysome-associated RNA with a quality reflecting the starting material and, when coupled with smart-seq2 single-cell RNA sequencing, translatomes in small tissues from biobanks can be obtained. Translatomes acquired using optimized non-linear gradients resemble those obtained with the standard approach employing linear gradients. Polysome-profiling using optimized non-linear gradients in serum starved HCT-116 cells with or without p53 showed that p53 status associates with changes in mRNA abundance and translational efficiency leading to changes in protein levels. Moreover, p53 status also induced translational buffering whereby changes in mRNA levels are buffered at the level of mRNA translation. Thus, here we present a polysome-profiling technique applicable to large study designs, primary cells and frozen tissue samples such as those collected in biobanks.

Microplitis bicoloratus bracovirus modulates innate immune suppression through the eIF4E-eIF4A axis in the insect Spodoptera litura

Eukaryotic initiation factor 4E (eIF4E) is regulated during the innate immune response. However, its translational regulation under innate immune suppression remains largely unexplored. Microplitis bicoloratus bracovirus (MbBV), a symbiotic virus harbored by the parasitoid wasp, Microplitis bicoloratus, suppresses innate immunity in parasitized Spodoptera litura. Here, we generated eIF4E dsRNA and used it to silence the eIF4E gene of S. litura, resulting in a hallmark immunosuppressive phenotype characterized by increased apoptosis of hemocytes and retardation of head capsule width development. In response to natural parasitism, loss of eIF4E function was associated with similar immunosuppression, and we detected no significant differences between the response to parasitism and treatment with eIF4E RNAi. Under MbBV infection, eIF4E overexpression significantly suppressed MbBV-induced increase in apoptosis and suppressed apoptosis to the same extent as co-expression of both eIF4E and eIF4A. There were no significant differences between MbBV-infected and uninfected larvae in which eIF4E was overexpressed. More importantly, in the eIF4E RNAi strain, eIF4A RNAi did not increase apoptosis. Collectively, our results indicate that eIF4E plays a nodal role in the MbBV-suppressed innate immune response via the eIF4E-eIF4A axis.

Impact of the secretome of activated pancreatic stellate cells on growth and differentiation of pancreatic tumour cells

Pancreatic ductal adenocarcinoma (PDAC) exists in a complex desmoplastic microenvironment. As part of it, pancreatic stellate cells (PSCs) provide a fibrotic niche, stimulated by a dynamic communication between activated PSCs and tumour cells. Investigating how PSCs contribute to tumour development and for identifying proteins that the cells secrete during cancer progression, we studied by means of complex antibody microarrays the secretome of activated PSCs. A large number of secretome proteins were associated with cancer-related functions, such as cell apoptosis, cellular growth, proliferation and metastasis. Their effect on tumour cells could be confirmed by growing tumour cells in medium conditioned with activated PSC secretome. Analyses of the tumour cells' proteome and mRNA revealed a strong inhibition of tumour cell apoptosis, but promotion of proliferation and migration. Many cellular proteins that exhibited variations were found to be under the regulatory control of eukaryotic translation initiation factor 4E (eIF4E), whose expression was triggered in tumour cells grown in the secretome of activated PSCs. Inhibition by an eIF4E siRNA blocked the effect, inhibiting tumour cell growth in vitro. Our findings show that activated PSCs acquire a pro-inflammatory phenotype and secret proteins that stimulate pancreatic cancer growth in an eIF4E-dependent manner, providing further insight into the role of stromal cells in pancreatic carcinogenesis and cancer progression.

Translational control mechanisms in cutaneous malignant melanoma: the role of eIF2α

BACKGROUND

Melanoma cells develop adaptive responses in order to cope with particular conditions of tumor microenvironment, characterized by stress conditions and deregulated proliferation. Recently, the interplay between the stress response and the gene expression programs leading to metastatic spread has been reported.

METHODS

We evaluated levels and localization of eIF2α/peIF2α in V600BRAF and wtBRAF metastatic melanoma cell lines by means of western blot and confocal microscopy analyses. Furthermore, we performed a sequence analyses and structure and dynamics studies of eIF2α protein to reveal the role of eIF2α and its correlations in different pathways involved in the invasive phase of melanoma.

RESULTS

We found peIF2α both in cytoplasm and nucleus. Nuclear localization was more represented in V600BRAF melanoma cell lines. Our studies on eIF2α protein sequence indicated the presence of a predicted bipartite NLS as well as a nuclear export signal NES and an S1 domain, typical of RNA interacting proteins. Furthermore, we found high levels of transcription factor EB (TFEB), a component of the MiT/TFE family, and low β-catenin levels in V600BRAF cells.

CONCLUSIONS

Based on our results, we suggest that peIF2α nuclear localization can be crucial in ER stress response and in driving the metastatic spread of melanoma, through lysosomal signaling and Wnt/β-catenin pathway. In conclusion, this is the first evidence of nuclear localization of peIF2α, representing a possible target for future therapeutic approaches for metastatic melanoma.

mTOR signalling and cellular metabolism are mutual determinants in cancer

Oncogenic signalling and metabolic alterations are interrelated in cancer cells. mTOR, which is frequently activated in cancer, controls cell growth and metabolism. mTOR signalling regulates amino acid, glucose, nucleotide, fatty acid and lipid metabolism. Conversely, metabolic inputs, such as amino acids, activate mTOR. In this Review, we discuss how mTOR signalling rewires cancer cell metabolism and delineate how changes in metabolism, in turn, sustain mTOR signalling and tumorigenicity. Several drugs are being developed to perturb cancer cell metabolism. However, their efficacy as stand-alone therapies, similar to mTOR inhibitors, is limited. Here, we discuss how the interdependence of mTOR signalling and metabolism can be exploited for cancer therapy.

The Impact of Post-transcriptional Control: Better Living Through RNA Regulons

Traditionally, cancer is viewed as a disease driven by genetic mutations and/or epigenetic and transcriptional dysregulation. While these are undoubtedly important drivers, many recent studies highlight the disconnect between the proteome and the genome or transcriptome. At least in part, this disconnect arises as a result of dysregulated RNA metabolism which underpins the altered proteomic landscape observed. Thus, it is important to understand the basic mechanisms governing post-transcriptional control and how these processes can be co-opted to drive cancer cell phenotypes. In some cases, groups of mRNAs that encode protein involved in specific oncogenic processes can be co-regulated at multiple processing levels in order to turn on entire biochemical pathways. Indeed, the RNA regulon model was postulated as a means to understand how cells coordinately regulate transcripts encoding proteins in the same biochemical pathways. In this review, we describe some of the basic mRNA processes that are dysregulated in cancer and the biological impact this has on the cell. This dysregulation can affect networks of RNAs simultaneously thereby underpinning the oncogenic phenotypes observed.

eIF4E-Dependent Translational Control: A Central Mechanism for Regulation of Pain Plasticity

Translational control of gene expression has emerged as a key mechanism in regulating different forms of long-lasting neuronal plasticity. Maladaptive plastic reorganization of peripheral and spinal nociceptive circuits underlies many chronic pain states and relies on new gene expression. Accordingly, downregulation of mRNA translation in primary afferents and spinal dorsal horn neurons inhibits tissue injury-induced sensitization of nociceptive pathways, supporting a central role for translation dysregulation in the development of persistent pain. Translation is primarily regulated at the initiation stage via the coordinated activity of translation initiation factors. The mRNA cap-binding protein, eukaryotic translation initiation factor 4E (eIF4E), is involved in the recruitment of the ribosome to the mRNA cap structure, playing a central role in the regulation of translation initiation. eIF4E integrates inputs from the mTOR and ERK signaling pathways, both of which are activated in numerous painful conditions to regulate the translation of a subset of mRNAs. Many of these mRNAs are involved in the control of cell growth, proliferation, and neuroplasticity. However, the full repertoire of eIF4E-dependent mRNAs in the nervous system and their translation regulatory mechanisms remain largely unknown. In this review, we summarize the current evidence for the role of eIF4E-dependent translational control in the sensitization of pain circuits and present pharmacological approaches to target these mechanisms. Understanding eIF4E-dependent translational control mechanisms and their roles in aberrant plasticity of nociceptive circuits might reveal novel therapeutic targets to treat persistent pain states.

mTOR co-targeting strategies for head and neck cancer therapy

Head and neck squamous cell carcinoma (HNSCC) is the sixth most common malignancy worldwide. There is an urgent need to develop effective therapeutic approaches to prevent and treat HNSCC. Recent deep sequencing of the HNSCC genomic landscape revealed a multiplicity and diversity of genetic alterations in this malignancy. Although a large variety of specific molecules were found altered in each individual tumor, they all participate in only a handful of driver signaling pathways. Among them, the PI3K/mTOR pathway is the most frequently activated, which plays a central role in cancer initiation and progression. In turn, targeting of mTOR may represent a precision therapeutic approach for HNSCC. Indeed, mTOR inhibition exerts potent anti-tumor activity in HNSCC experimental systems, and mTOR targeting clinical trials show encouraging results. However, advanced HNSCC patients may exhibit unpredictable drug resistance, and the analysis of its molecular basis suggests that co-targeting strategies may provide a more effective option. In addition, although counterintuitive, emerging evidence suggests that mTOR inhibition may enhance the anti-tumor immune response. These new findings raise the possibility that the combination of mTOR inhibitors and immune oncology agents may provide novel precision therapeutic options for HNSCC.

Functional 5' UTR mRNA structures in eukaryotic translation regulation and how to find them

RNA molecules can fold into intricate shapes that can provide an additional layer of control of gene expression beyond that of their sequence. In this Review, we discuss the current mechanistic understanding of structures in 5' untranslated regions (UTRs) of eukaryotic mRNAs and the emerging methodologies used to explore them. These structures may regulate cap-dependent translation initiation through helicase-mediated remodelling of RNA structures and higher-order RNA interactions, as well as cap-independent translation initiation through internal ribosome entry sites (IRESs), mRNA modifications and other specialized translation pathways. We discuss known 5' UTR RNA structures and how new structure probing technologies coupled with prospective validation, particularly compensatory mutagenesis, are likely to identify classes of structured RNA elements that shape post-transcriptional control of gene expression and the development of multicellular organisms.

Crosstalks between translation and metabolism in cancer

Albeit cancer patients' heterogeneity, all tumor cells have alterations of both metabolism and translation. The simplest explanation for this common feature is that several oncogenes coordinate a translational and metabolic reprogramming that is necessary for tumor cells to thrive. Overall, at least three oncogenic pathways, namely c-Myc, RAS and PI3K-mTOR, are known to affect both translation and metabolism by stimulating glycolysis and protein synthesis. The crosstalk between metabolite production and the translational machinery is, instead, less understood. What is known is that, on one side, translation initiation factors, such as eIF4E and eIF6, drive tumor growth and regulate metabolism through selective translation of nucleotide biosynthesis, glycolysis and fatty acid synthesis rate-limiting mRNAs, and on the other, that nutrient levels regulate the translational machinery by inducing full activity of translation factors. Therefore, translation and metabolism offer several therapeutic targets to be fully exploited in future studies.

The eukaryotic translation initiation factor eIF4E harnesses hyaluronan production to drive its malignant activity

The microenvironment provides a functional substratum supporting tumour growth. Hyaluronan (HA) is a major component of this structure. While the role of HA in malignancy is well-defined, the mechanisms driving its biosynthesis in cancer are poorly understood. We show that the eukaryotic translation initiation factor eIF4E, an oncoprotein, drives HA biosynthesis. eIF4E stimulates production of enzymes that synthesize the building blocks of HA, UDP-Glucuronic acid and UDP-N-Acetyl-Glucosamine, as well as hyaluronic acid synthase which forms the disaccharide chain. Strikingly, eIF4E inhibition alone repressed HA levels as effectively as directly targeting HA with hyaluronidase. Unusually, HA was retained on the surface of high-eIF4E cells, rather than being extruded into the extracellular space. Surface-associated HA was required for eIF4E’s oncogenic activities suggesting that eIF4E potentiates an oncogenic HA program. These studies provide unique insights into the mechanisms driving HA production and demonstrate that an oncoprotein can co-opt HA biosynthesis to drive malignancy.

Deletion of eIF2β lysine stretches creates a dominant negative that affects the translation and proliferation in human cell line: A tool for arresting the cell growth

BACKGROUND

Eukaryote initiation factor 2 subunit β (eIF2β) plays a crucial role in regulation protein synthesis, which mediates the interaction of eIF2 with mRNA. eIF2β contains evolutionarily conserved polylysine stretches in amino-terminal region and a zinc finger motif in the carboxy-terminus.

METHODS

The gene eIF2β was cloned under tetracycline transcription control and the polylysine stretches were deleted by site-directed mutagenesis (eIF2βΔ3K). The plasmid was transfected into HEK 293 TetR cells. These cells were analyzed for their proliferative and translation capacities as well as cell death rate. Experiments were performed using gene reporter assays, western blotting, flow cytometry, cell sorting, cell proliferation assays and confocal immunofluorescence.

RESULTS

eIF2βΔ3K affected negatively the protein synthesis, cell proliferation and cell survival causing G2 cell cycle arrest and increased cell death, acting in a negative dominant manner against the native protein. Polylysine stretches are also essential for eIF2β translocated from the cytoplasm to the nucleus, accumulating in the nucleolus and eIF2βΔ3K did not make this translocation.

DISCUSSION

eIF2β is involved in the protein synthesis process and should act in nuclear processes as well. eIF2βΔ3K reduces cell proliferation and causes cell death. Since translation control is essential for normal cell function and survival, the development of drugs or molecules that inhibit translation has become of great interest in the scenario of proliferative disorders. In conclusion, our results suggest the dominant negative eIF2βΔ3K as a therapeutic strategy for the treatment of proliferative disorders and that eIF2β polylysine stretch domains are promising targets for this.

Molecular targeting of hypoxia in radiotherapy

Hypoxia (low O₂) is an essential microenvironmental driver of phenotypic diversity in human solid cancers. Hypoxic cancer cells hijack evolutionarily conserved, O₂- sensitive pathways eliciting molecular adaptations that impact responses to radiotherapy, tumor recurrence and patient survival. In this review, we summarize the radiobiological, genetic, epigenetic and metabolic mechanisms orchestrating oncogenic responses to hypoxia. In addition, we outline emerging hypoxia- targeting strategies that hold promise for individualized cancer therapy in the context of radiotherapy and drug delivery.

Amplified in Breast Cancer Regulates Transcription and Translation in Breast Cancer Cells

Background

Control of mRNA translation is fundamentally altered in cancer. Insulin-like growth factor-I (IGF-I) signaling regulates key translation mediators to modulate protein synthesis (e.g. eIF4E, 4E-BP1, mTOR, and S6K1). Importantly the Amplified in Breast Cancer (AIB1) oncogene regulates transcription and is also a downstream mediator of IGF-I signaling.

Materials and Methods

To determine if AIB1 also affects mRNA translation, we conducted gain and loss of AIB1 function experiments in estrogen receptor alpha (ERα)⁺ (MCF-7L) and ERα^- (MDA-MB-231, MDA-MB-435 and LCC6) breast cancer cells.

Results

AIB1 positively regulated IGF-I-induced mRNA translation in both ERα⁺ and ERα^- cells. Formation of the eIF4E-4E-BP1 translational complex was altered in the AIB1 ERα⁺ and ERα^- knockdown cells, leading to a reduction in the eIF4E/4E-BP1 and eIF4G/4E-BP1 ratios. In basal and IGF-I stimulated MCF-7 and LCC6 cells, knockdown of AIB1 decreased the integrity of the cap-binding complex, reduced global IGF-I stimulated polyribosomal mRNA recruitment with a concomitant decrease in ten of the thirteen genes tested in polysome-bound mRNAs mapping to proliferation, cell cycle, survival, transcription, translation and ribosome biogenesis ontologies. Specifically, knockdown of AIB1 decreased ribosome-bound mRNA and steady-state protein levels of the transcription factors ERα and E2F1 in addition to reduced ribosome-bound mRNA of the ribosome biogenesis factor BYSL in a cell-line specific manner to regulate mRNA translation.

Conclusion

The oncogenic transcription factor AIB1 has a novel role in the regulation of polyribosome recruitment and formation of the translational complex. Combinatorial therapies targeting IGF signaling and mRNA translation in AIB1 expressing breast cancers may have clinical benefit and warrants further investigation.

The RNA-Binding Protein, Polypyrimidine Tract-Binding Protein 1 (PTBP1) Is a Key Regulator of CD4 T Cell Activation

We have previously shown that the RNA binding protein, polypyrimidine tract-binding protein (PTBP1) plays a critical role in regulating the expression of CD40L in activated CD4 T cells. This is achieved mechanistically through message stabilization at late times of activation as well as by altered distribution of CD40L mRNA within distinct cellular compartments. PTBP1 has been implicated in many different processes, however whether PTBP1 plays a broader role in CD4 T cell activation is not known. To examine this question, experiments were designed to introduce shRNA into primary human CD4 T cells to achieve decreased, but not complete ablation of PTBP1 expression. Analyses of shPTB-expressing CD4 T cells revealed multiple processes including cell proliferation, activation-induced cell death and expression of activation markers and cytokines that were regulated in part by PTBP1 expression. Although there was an overall decrease in the steady-state level of several activation genes, only IL-2 and CD40L appeared to be regulated by PTBP1 at the level of RNA decay suggesting that PTBP1 is critical at different regulatory steps of expression that is gene-specific. Importantly, even though the IL-2 protein levels were reduced in cells with lowered PTBP1, the steady-state level of IL-2 mRNA was significantly higher in these cells suggesting a block at the translational level. Evaluation of T cell activation in shPTB-expressing T cells revealed that PTBP1 was linked primarily to the activation of the PLCγ1/ERK1/2 and the NF-κB pathways. Overall, our results reveal the importance of this critical RNA binding protein in multiple steps of T cell activation.

The eukaryotic translation initiation factor eIF4E wears a "cap" for many occasions

The eukaryotic translation initiation factor eIF4E plays important roles in controlling the composition of the proteome. Indeed, dysregulation of eIF4E is associated with poor prognosis cancers. The traditional view has been that eIF4E acts solely in translation. However, over the last ∼25 years, eIF4E was found in the nucleus where it acts in mRNA export and in the last ∼10 years, eIF4E was found in cytoplasmic processing bodies (P-bodies) where it functions in mRNA sequestration and stability. The common biochemical thread for these activities is the ability of eIF4E to bind the 7-methylguanosine cap on the 5′ end of mRNAs. Recently, the possibility that eIF4E directly binds some mRNA elements independently of the cap has also been raised. Importantly, the effects of eIF4E are not genome-wide with a subset of transcripts targeted depending on the presence of specific mRNA elements and context-dependent regulatory factors. Indeed, eIF4E governs RNA regulons through co-regulating the expression of groups of transcripts acting in the same biochemical pathways. In addition, studies over the past ∼15 years indicate that there are multiple strategies that regulatory factors employ to modulate eIF4E activities in context-dependent manners. This perspective focuses on these new findings and incorporates them into a broader model for eIF4E function.

Importin 8 mediates m7G cap-sensitive nuclear import of the eukaryotic translation initiation factor eIF4E

Regulation of nuclear-cytoplasmic trafficking of oncoproteins is critical for growth homeostasis. Dysregulated trafficking contributes to malignancy, whereas understanding the process can reveal unique therapeutic opportunities. Here, we focus on eukaryotic translation initiation factor 4E (eIF4E), a prooncogenic protein highly elevated in many cancers, including acute myeloid leukemia (AML). Typically, eIF4E is localized to both the nucleus and cytoplasm, where it acts in export and translation of specific methyl 7-guanosine (m(7)G)-capped mRNAs, respectively. Nuclear accumulation of eIF4E in patients who have AML is correlated with increased eIF4E-dependent export of transcripts encoding oncoproteins. The subcellular localization of eIF4E closely correlates with patients' responses. During clinical responses to the m(7)G-cap competitor ribavirin, eIF4E is mainly cytoplasmic. At relapse, eIF4E reaccumulates in the nucleus, leading to elevated eIF4E-dependent mRNA export. We have identified importin 8 as a factor that directly imports eIF4E into the nucleus. We found that importin 8 is highly elevated in untreated patients with AML, leading to eIF4E nuclear accumulation. Importin 8 only imports cap-free eIF4E. Cap-dependent changes to the structure of eIF4E underpin this selectivity. Indeed, m(7)G cap analogs or ribavirin prevents nuclear entry of eIF4E, which mirrors the trafficking phenotypes observed in patients with AML. Our studies also suggest that nuclear entry is important for the prooncogenic activity of eIF4E, at least in this context. These findings position nuclear trafficking of eIF4E as a critical step in its regulation and position the importin 8-eIF4E complex as a novel therapeutic target.