BCL-2 translation is mediated via internal ribosome entry during cell stress

Harnessing Synthetic Riboswitches for Tunable Gene Regulation in Mammalian Cells

RNA switches regulated by specific inducer molecules have become a powerful synthetic biology tool for precise gene regulation in mammalian systems. The engineered RNA switches can be integrated with natural RNA-mediated gene regulatory functions as a modular and customizable approach to probe and control cellular behavior. RNA switches have been used to advance synthetic biology applications, including gene therapy, bio-production, and cellular reprogramming. This review explores recent progress in the design and functional implementation of synthetic riboswitches in mammalian cells based on diverse RNA regulation mechanisms by highlighting recent studies and emerging technologies. We also discuss challenges such as off-target effects, system stability, and ligand delivery in complex biological environments. In conclusion, this review emphasizes the potential of synthetic riboswitches as a platform for customizable gene regulation in diverse biomedical applications.

A versatile toolbox for determining IRES activity in cells and embryonic tissues

Widespread control of gene expression through translation has emerged as a key level of spatiotemporal regulation of protein expression. A prominent mechanism by which ribosomes can confer gene regulation is via internal ribosomal entry sites (IRESes), whose functions have however, remained difficult to rigorously characterize. Here we present a set of technologies in embryos and cells, including IRES-mediated translation of circular RNA (circRNA) reporters, single-molecule messenger (m)RNA isoform imaging, PacBio long-read sequencing, and isoform-sensitive mRNA quantification along polysome profiles as a new toolbox for understanding IRES regulation. Using these techniques, we investigate a broad range of cellular IRES RNA elements including Hox IRESes. We show IRES-dependent translation in circRNAs, as well as the relative expression, localization, and translation of an IRES-containing mRNA isoform in specific embryonic tissues. We thereby provide a new resource of technologies to elucidate the roles of versatile IRES elements in gene regulation and embryonic development.

PERK-Olating Through Cancer: A Brew of Cellular Decisions

The type I protein kinase PERK is an endoplasmic reticulum (ER) transmembrane protein that plays a multifaceted role in cancer development and progression, influencing tumor growth, metastasis, and cellular stress responses. The activation of PERK represents one of the three signaling pathways induced during the unfolded protein response (UPR), which is triggered, in particular, in tumor cells that constitutively experience various intracellular and extracellular stresses that impair protein folding within the ER. PERK activation can lead to both pro-survival and proapoptotic outcomes, depending on the cellular context and the extent of ER stress. It helps the reprogramming of the gene expression in cancer cells, thereby ensuring survival in the face of oncogenic stress, such as replicative stress and DNA damage, and also microenvironmental challenges, including hypoxia, angiogenesis, and metastasis. Consequently, PERK contributes to tumor initiation, transformation, adaptation to the microenvironment, and chemoresistance. However, sustained PERK activation in cells can also impair cell proliferation and promote apoptotic death by various interconnected processes, including mitochondrial dysfunction, translational inhibition, the accumulation of various cellular stresses, and the specific induction of multifunctional proapoptotic factors, such as CHOP. The dual role of PERK in promoting both tumor progression and suppression makes it a complex target for therapeutic interventions. A comprehensive understanding of the intricacies of PERK pathway activation and their impact is essential for the development of effective therapeutic strategies, particularly in diseases like cancer, where the ER stress response is deregulated in most, if not all, of the solid and liquid tumors. This article provides an overview of the knowledge acquired from the study of animal models of cancer and tumor cell lines cultured in vitro on PERK's intracellular functions and their impact on cancer cells and their microenvironment, thus highlighting potential new therapeutic avenues that could target this protein.

Stress response regulation of mRNA translation: Implications for antioxidant enzyme expression in cancer

From tumorigenesis to advanced metastatic stages, tumor cells encounter stress, ranging from limited nutrient and oxygen supply within the tumor microenvironment to extrinsic and intrinsic oxidative stress. Thus, tumor cells seize regulatory pathways to rapidly adapt to distinct physiologic conditions to promote cellular survival, including manipulation of mRNA translation. While it is now well established that metastatic tumor cells must up-regulate their antioxidant capacity to effectively spread and that regulation of antioxidant enzymes is imperative to disease progression, relatively few studies have assessed how translation and the hijacking of RNA systems contribute to antioxidant responses of tumors. Here, we review the major stress signaling pathways involved in translational regulation and discuss how these are affected by oxidative stress to promote prosurvival changes that manipulate antioxidant enzyme expression. We describe how tumors elicit these adaptive responses and detail how stress-induced translation can be regulated by kinases, RNA-binding proteins, RNA species, and RNA modification systems. We also highlight opportunities for further studies focused on the role of mRNA translation and RNA systems in the regulation of antioxidant enzyme expression, which may be of particular importance in the context of metastatic progression and therapeutic resistance.

Ribosome specialization in cancer: a spotlight on ribosomal proteins

In the past few decades, our view of ribosomes has changed substantially. Rather than passive machines without significant variability, it is now acknowledged that they are heterogeneous, and have direct regulatory capacity. This 'ribosome heterogeneity' comes in many flavors, including in both the RNA and protein components of ribosomes, so there are many paths through which ribosome specialization could arise. It is easy to imagine that specialized ribosomes could have wide physiological roles, through the translation of specific mRNA populations, and there is now evidence for this in several contexts. Translation is highly dysregulated in cancer, needed to support oncogenic phenotypes and to overcome cellular stress. However, the role of ribosome specialization in this is not clear. In this review we focus on specialized ribosomes in cancer. Specifically, we assess the impact that post-translational modifications and differential ribosome incorporation of ribosomal proteins (RPs) have in this disease. We focus on studies that have shown a ribosome-mediated change in translation of specific mRNA populations, and hypothesize how such a process could be driving other phenotypes. We review the impact of RP-mediated heterogeneity in both intrinsic and extrinsic oncogenic processes, and consider how this knowledge could be leveraged to benefit patients.

eIF4A controls translation of estrogen receptor alpha and is a therapeutic target in advanced breast cancer

The majority of human breast cancers are dependent on hormone-stimulated estrogen receptor alpha (ER) and are sensitive to its inhibition. Treatment resistance arises in most advanced cancers due to genetic alterations that promote ligand independent activation of ER itself or ER target genes. Whereas re-targeting of the ER ligand binding domain (LBD) with newer ER antagonists can work in some cases, these drugs are largely ineffective in many genetic backgrounds including ER fusions that lose the LBD or in cancers that hyperactivate ER targets. By identifying the mechanism of ER translation, we herein present an alternative strategy to target ER and difficult to treat ER variants. We find that ER translation is cap-independent and mTOR inhibitor insensitive, but dependent on 5' UTR elements and sensitive to pharmacologic inhibition of the translation initiation factor eIF4A, an mRNA helicase. EIF4A inhibition rapidly reduces expression of ER and short-lived targets of ER such as cyclin D1 and other components of the cyclin D-CDK complex in breast cancer cells. These effects translate into suppression of growth of a variety of ligand-independent breast cancer models including those driven by ER fusion proteins that lack the ligand binding site. The efficacy of eIF4A inhibition is enhanced when it is combined with fulvestrant-an ER degrader. Concomitant inhibition of ER synthesis and induction of its degradation causes synergistic and durable inhibition of ER expression and tumor growth. The clinical importance of these findings is confirmed by results of an early clinical trial (NCT04092673) of the selective eIF4A inhibitor zotatifin in patients with estrogen receptor positive metastatic breast cancer. Multiple clinical responses have been observed on combination therapy including durable regressions. These data suggest that eIF4A inhibition could be a useful new strategy for treating advanced ER+ breast cancer.

Multiple regulatory roles of the transfer RNA-derived small RNAs in cancers

With the development of sequencing technology, transfer RNA (tRNA)-derived small RNAs (tsRNAs) have received extensive attention as a new type of small noncoding RNAs. Based on the differences in the cleavage sites of nucleases on tRNAs, tsRNAs can be divided into two categories, tRNA halves (tiRNAs) and tRNA-derived fragments (tRFs), each with specific subcellular localizations. Additionally, the biogenesis of tsRNAs is tissue-specific and can be regulated by tRNA modifications. In this review, we first elaborated on the classification and biogenesis of tsRNAs. After summarizing the latest mechanisms of tsRNAs, including transcriptional gene silencing, post-transcriptional gene silencing, nascent RNA silencing, translation regulation, rRNA regulation, and reverse transcription regulation, we explored the representative biological functions of tsRNAs in tumors. Furthermore, this review summarized the clinical value of tsRNAs in cancers, thus providing theoretical support for their potential as novel biomarkers and therapeutic targets.

Cell death or survival: Insights into the role of mRNA translational control

Cellular stress is an intrinsic part of cell physiology that underlines cell survival or death. The ability of mammalian cells to regulate global protein synthesis (aka translational control) represents a critical, yet underappreciated, layer of regulation during the stress response. Various cellular stress response pathways monitor conditions of cell growth and subsequently reshape the cellular translatome to optimize translational outputs. On the molecular level, such translational reprogramming involves an intricate network of interactions between translation machinery, RNA-binding proteins, mRNAs, and non-protein coding RNAs. In this review, we will discuss molecular mechanisms, signaling pathways, and targets of translational control that contribute to cellular adaptation to stress and to cell survival or death.

Circulating microvesicles miR139-3p from bronchopulmonary dysplasia aggravates pulmonary vascular simplification by targeting 4E binding protein 1

BACKGROUND

Microvesicles (MVs) play a crucial role in bronchopulmonary dysplasia (BPD). There are many MVs in circulating plasma, and they are in direct contact with lung endothelial cells. However, the molecular mechanism and causative effect of circulating MVs on BPD remain unclear.

METHODS

Clinical plasma samples were collected, circulating MVs were isolated, and microRNA (miRNA) sequencing was performed. The BPD model was established, and different MVs were administered. Alveoli and pulmonary vessels were examined by hematoxylin-eosin staining, and body weight and length were measured. In vitro, gene expression was disrupted by miRNA mimics, miRNA inhibitors or plasmid transfection. Cell proliferation and protein expression were detected by cell scratch assay, accurate 5-ethynyl-2-deoxyuridine test, western blotting, or immunofluorescence assay.

RESULTS

BPD-derived MVs further aggravated pulmonary vascular simplification, while circulating MVs from control mice mitigated pulmonary vascular simplification. Micro-RNA sequencing and independent sample verification revealed that miR139-3p, but not miR6125 or miR193b-3p, was the most critical effector molecule in MVs. Mechanism studies showed that eukaryotic translation initiation factor 4E binding protein 1 was the target gene for miR139-3p. In addition, we found that supplementation of miR139-3p inhibitor partially alleviated pulmonary vascular simplification.

CONCLUSIONS

These results indicate that circulating MVs are involved in forming BPD by carrying miR139-3p molecules and support miR139-3p inhibitors as a potential therapeutic strategy for alleviating pulmonary vascular simplification in BPD.

Translation of paired box 6 (PAX6) mRNA is IRES-mediated and inhibited by cymarin in breast cancer cells

Paired box 6 (PAX6) is a member of the PAX family and plays an essential role in cancer cell cycle progression, colony formation, proliferation and invasion. Its expression is upregulated in many cancers including breast cancer, but the process of PAX6 mRNA translation has rarely been studied. We found that PAX6 translation level increased in MCF-7 breast cancer cells treated with the chemotherapeutic drug adriamycin (ADM), which might be attributable to internal ribosome entry site (IRES)-mediated translation. By modifying a bicistronic luciferase plasmid that is widely used to examine IRES activity, we found that the 469-base 5'-UTR of PAX6 mRNA contains an IRES element and that core IRES activity is located between nucleotides 159 and 333. Moreover, PAX6 IRES activity was induced during ADM treatment, which may be the main reason for the elevated level of PAX6 protein. We also found that cymarin, a cardiac glycoside, acts as an inhibitor of PAX6 protein expression by impairing its IRES-mediated translation. Furthermore, MCF-7 cell proliferation was suppressed during treatment with cymarin. These results provide novel insights into the translation mechanism of PAX6 in breast cancer cells and suggest that cymarin is a promising candidate for the treatment of breast cancer via targeting the expression of PAX6.

Enhanced bypass of PD-L1 translation reduces the therapeutic response to mTOR kinase inhibitors

Increased PD-L1 expression in cancer cells is known to enhance immunosuppression, but the mechanism underlying PD-L1 upregulation is incompletely characterized. We show that PD-L1 expression is upregulated through internal ribosomal entry site (IRES)-mediated translation upon mTORC1 inhibition. We identify an IRES element in the PD-L1 5'-UTR that permits cap-independent translation and promotes continuous production of PD-L1 protein despite effective inhibition of mTORC1. eIF4A is found to be a key PD-L1 IRES-binding protein that enhances PD-L1 IRES activity and protein production in tumor cells treated with mTOR kinase inhibitors (mTORkis). Notably, treatment with mTORkis in vivo elevates PD-L1 levels and reduces the number of tumor-infiltrating lymphocytes in immunogenic tumors, but anti-PD-L1 immunotherapy restores antitumor immunity and enhances the therapeutic efficacy of mTORkis. These findings report a molecular mechanism for regulating PD-L1 expression through bypassing mTORC1-mediated cap-dependent translation and provide a rationale for targeting PD-L1 immune checkpoint to improve mTOR-targeted therapy.

The role of eIF4F-driven mRNA translation in regulating the tumour microenvironment

Cells can rapidly adjust their proteomes in dynamic environments by regulating mRNA translation. There is mounting evidence that dysregulation of mRNA translation supports the survival and adaptation of cancer cells, which has stimulated clinical interest in targeting elements of the translation machinery and, in particular, components of the eukaryotic initiation factor 4F (eIF4F) complex such as eIF4E. However, the effect of targeting mRNA translation on infiltrating immune cells and stromal cells in the tumour microenvironment (TME) has, until recently, remained unexplored. In this Perspective article, we discuss how eIF4F-sensitive mRNA translation controls the phenotypes of key non-transformed cells in the TME, with an emphasis on the underlying therapeutic implications of targeting eIF4F in cancer. As eIF4F-targeting agents are in clinical trials, we propose that a broader understanding of their effect on gene expression in the TME will reveal unappreciated therapeutic vulnerabilities that could be used to improve the efficacy of existing cancer therapies.

Kozak Similarity Score Algorithm Identifies Alternative Translation Initiation Codons Implicated in Cancers

Ribosome profiling and mass spectroscopy have identified canonical and noncanonical translation initiation codons (TICs) that are upstream of the main translation initiation site and used to translate oncogenic proteins. There have previously been conflicting reports about the patterns of nucleotides that surround noncanonical TICs. Here, we use a Kozak Similarity Score algorithm to find that nearly all of these TICs have flanking nucleotides closely matching the Kozak sequence. Remarkably, the nucleotides flanking alternative noncanonical TICs are frequently closer to the Kozak sequence than the nucleotides flanking TICs used to translate the gene’s main protein. Of note, the 5′ untranslated region (5‘UTR) of cancer-associated genes with an upstream TIC tend to be significantly longer than the same region in genes not associated with cancer. The presence of a longer-than-typical 5′UTR increases the likelihood of ribosome binding to upstream noncanonical TICs, and may be a distinguishing feature of a number of genes overexpressed in cancer. Noncanonical TICs that are located in the 5′UTR, although thought by some to be disadvantageous and suppressed by evolution, may translate oncogenic proteins because of their flanking nucleotides.

Therapy resistance: opportunities created by adaptive responses to targeted therapies in cancer

Normal cells explore multiple states to survive stresses encountered during development and self-renewal as well as environmental stresses such as starvation, DNA damage, toxins or infection. Cancer cells co-opt normal stress mitigation pathways to survive stresses that accompany tumour initiation, progression, metastasis and immune evasion. Cancer therapies accentuate cancer cell stresses and invoke rapid non-genomic stress mitigation processes that maintain cell viability and thus represent key targetable resistance mechanisms. In this Review, we describe mechanisms by which tumour ecosystems, including cancer cells, immune cells and stroma, adapt to therapeutic stresses and describe three different approaches to exploit stress mitigation processes: (1) interdict stress mitigation to induce cell death; (2) increase stress to induce cellular catastrophe; and (3) exploit emergent vulnerabilities in cancer cells and cells of the tumour microenvironment. We review challenges associated with tumour heterogeneity, prioritizing actionable adaptive responses for optimal therapeutic outcomes, and development of an integrative framework to identify and target vulnerabilities that arise from adaptive responses and engagement of stress mitigation pathways. Finally, we discuss the need to monitor adaptive responses across multiple scales and translation of combination therapies designed to take advantage of adaptive responses and stress mitigation pathways to the clinic.

Protein synthesis control in cancer: selectivity and therapeutic targeting

Translational control of mRNAs is a point of convergence for many oncogenic signals through which cancer cells tune protein expression in tumorigenesis. Cancer cells rely on translational control to appropriately adapt to limited resources while maintaining cell growth and survival, which creates a selective therapeutic window compared to non-transformed cells. In this review, we first discuss how cancer cells modulate the translational machinery to rapidly and selectively synthesize proteins in response to internal oncogenic demands and external factors in the tumor microenvironment. We highlight the clinical potential of compounds that target different translation factors as anti-cancer therapies. Next, we detail how RNA sequence and structural elements interface with the translational machinery and RNA-binding proteins to coordinate the translation of specific pro-survival and pro-growth programs. Finally, we provide an overview of the current and emerging technologies that can be used to illuminate the mechanisms of selective translational control in cancer cells as well as within the microenvironment.

Research progress on the tsRNA classification, function, and application in gynecological malignant tumors

A large number of small non-coding RNAs derived from tRNAs, called tRNA-derived small RNA (tsRNAs), have been identified by high-throughput RNA sequencing of cell lines. Further research has revealed that they are not produced via random tRNA degradation, but through degradation by specific nuclease cleavages, such as Elac Ribonuclease Z 2 (ELAC2)/RNase Z, RNase L, Dicer, and angiogenin (ANG), the tsRNAs can be classified into the following types based on the location from which they have been derived from the parental tRNA: tRF-1s, tRF-3s, tRF-5s, tiRNA, and tRF-2s/i-tRFs. Moreover, tsRNAs are a type of small RNAs with diverse functions, including gene expression regulation, anti-apoptosis, translation inhibition, participation in epigenetic regulation, initial virus reverse transcription, promote virus replication and cell-to-cell communication. Certain types of tsRNAs are overexpressed in cancer tissues, but are underexpressed in normal tissues. Therefore, the relationship between tsRNAs and the occurrence and development of cancer has attracted significant research attention. Research advancements have contributed to further discoveries of the biological activities of tsRNAs, but the mechanisms of their biogenesis and functions have not been fully elucidated. This article reviews the classification and biological functions of tsRNAs, and introduces the research progress in gynecological malignancies.

The two faces of the Integrated Stress Response in cancer progression and therapeutic strategies

In recent years considerable progress has been made in identifying the impact of mRNA translation in tumour progression. Cancer cells hijack the pre-existing translation machinery to thrive under the adverse conditions originating from intrinsic oncogenic programs, that increase their energetic demand, and from the hostile microenvironment. A key translation program frequently dysregulated in cancer is the Integrated Stress Response, that reprograms translation by attenuating global protein synthesis to decrease metabolic demand while increasing translation of specific mRNAs that support survival, migration, immune escape. In this review we provide an overview of the Integrated Stress Response, emphasise its dual role during tumorigenesis and cancer progression, and highlight the therapeutic strategies available to target it.

Multifaceted control of mRNA translation machinery in cancer

The mRNA translation machinery is tightly regulated through several, at times overlapping, mechanisms that modulate its efficiency and accuracy. Due to their fast rate of growth and metabolism, cancer cells require an excessive amount of mRNA translation and protein synthesis. However, unfavorable conditions, such as hypoxia, amino acid starvation, and oxidative stress, which are abundant in cancer, as well as many anti-cancer treatments inhibit mRNA translation. Cancer cells adapt to the various internal and environmental stresses by employing specialised transcript-specific translation to survive and gain a proliferative advantage. We will highlight the major signaling pathways and mechanisms of translation that regulate the global or mRNA-specific translation in response to the intra- or extra-cellular signals and stresses that are key components in the process of tumourigenesis.

Modes of Regulated Cell Death in Cancer

Cell suicide pathways, termed regulated cell death (RCD), play a critical role in organismal development, homeostasis, and pathogenesis. Here, we provide an overview of key RCD modalities, namely apoptosis, entosis, necroptosis, pyroptosis, and ferroptosis. We explore how various RCD modules serve as a defense mechanism against the emergence of cancer as well as the manner in which they can be exploited to drive oncogenesis. Furthermore, we outline current therapeutic agents that activate RCD and consider novel RCD-based strategies for tumor elimination. SIGNIFICANCE: A variety of antitumor therapeutics eliminate cancer cells by harnessing the devastating potential of cellular suicide pathways, emphasizing the critical importance of RCD in battling cancer. This review supplies a mechanistic perspective of distinct RCD modalities and explores the important role they play in tumorigenesis. We discuss how RCD modules serve as a double-edged sword as well as novel approaches aimed at selectively manipulating RCD for tumor eradication.

Amplification of 8p11.23 in cancers and the role of amplicon genes

Copy number alterations are widespread in cancer genomes and are part of the genomic instability underlying the pathogenesis of neoplastic diseases. Recurrent copy number alterations of specific chromosomal loci may result in gains of oncogenes or losses of tumor suppressor genes and become entrenched in the genomic framework of certain types of cancers. The locus at chromosome 8p11.23 presents recurrent amplifications most commonly in squamous lung carcinomas, breast cancers, squamous esophageal carcinomas, and urothelial carcinomas. Amplification is rare in other cancers. The amplified segment involves several described oncogenes that may promote cancer cell survival and proliferation, as well as less well characterized genes that could also contribute to neoplastic processes. Genes proposed to be "drivers" in 8p11.23 amplifications include ZNF703, FGFR1 and PLPP5. Additional genes in the locus that could be functionally important in neoplastic networks include co-chaperone BAG4, lysine methyltransferase NSD3, ASH2L, a member of another methyltransferase complex, MLL and the mRNA processing and translation regulators LSM1 and EIF4EBP1. In this paper, genes located in the amplified segment of 8p11.23 will be examined for their role in cancer and data arguing for their importance for cancers with the amplification will be presented.

Ionizing Radiation and Translation Control: A Link to Radiation Hormesis?

Protein synthesis, or mRNA translation, is one of the most energy-consuming functions in cells. Translation of mRNA into proteins is thus highly regulated by and integrated with upstream and downstream signaling pathways, dependent on various transacting proteins and cis-acting elements within the substrate mRNAs. Under conditions of stress, such as exposure to ionizing radiation, regulatory mechanisms reprogram protein synthesis to translate mRNAs encoding proteins that ensure proper cellular responses. Interestingly, beneficial responses to low-dose radiation exposure, known as radiation hormesis, have been described in several models, but the molecular mechanisms behind this phenomenon are largely unknown. In this review, we explore how differences in cellular responses to high- vs. low-dose ionizing radiation are realized through the modulation of molecular pathways with a particular emphasis on the regulation of mRNA translation control.

Dance with the Devil: Stress Granules and Signaling in Antiviral Responses

Cells have evolved highly specialized sentinels that detect viral infection and elicit an antiviral response. Among these, the stress-sensing protein kinase R, which is activated by double-stranded RNA, mediates suppression of the host translation machinery as a strategy to limit viral replication. Non-translating mRNAs rapidly condensate by phase separation into cytosolic stress granules, together with numerous RNA-binding proteins and components of signal transduction pathways. Growing evidence suggests that the integrated stress response, and stress granules in particular, contribute to antiviral defense. This review summarizes the current understanding of how stress and innate immune signaling act in concert to mount an effective response against virus infection, with a particular focus on the potential role of stress granules in the coordination of antiviral signaling cascades.

Role of the RNA-binding protein La in cancer pathobiology

RNA-binding proteins are important regulators of RNA metabolism and are of critical importance in all steps of the gene expression cascade. The role of aberrantly expressed RBPs in human disease is an exciting research field and the potential application of RBPs as a therapeutic target or a diagnostic marker represents a fast-growing area of research.Aberrant overexpression of the human RNA-binding protein La has been found in various cancer entities including lung, cervical, head and neck, and chronic myelogenous leukaemia. Cancer-associated La protein supports tumour-promoting processes such as proliferation, mobility, invasiveness and tumour growth. Moreover, the La protein maintains the survival of cancer cells by supporting an anti-apoptotic state that may cause resistance to chemotherapeutic therapy.The human La protein represents a multifunctional post-translationally modified RNA-binding protein with RNA chaperone activity that promotes processing of non-coding precursor RNAs but also stimulates the translation of selective messenger RNAs encoding tumour-promoting and anti-apoptotic factors. In our model, La facilitates the expression of those factors and helps cancer cells to cope with cellular stress. In contrast to oncogenes, able to initiate tumorigenesis, we postulate that the aberrantly elevated expression of the human La protein contributes to the non-oncogenic addiction of cancer cells. In this review, we summarize the current understanding about the implications of the RNA-binding protein La in cancer progression and therapeutic resistance. The concept of exploiting the RBP La as a cancer drug target will be discussed.

Targeted inhibition of mRNA translation initiation factors as a novel therapeutic strategy for mature B-cell neoplasms

Cancer development is frequently associated with dysregulation of mRNA translation to enhance both increased global protein synthesis and translation of specific mRNAs encoding oncoproteins. Thus, targeted inhibition of mRNA translation is viewed as a promising new approach for cancer therapy. In this article we review current progress in investigating dysregulation of mRNA translation initiation in mature B-cell neoplasms, focusing on chronic lymphocytic leukemia, follicular lymphoma and diffuse large B-cell lymphoma. We discuss mechanisms and regulation of mRNA translation, potential pathways by which genetic alterations and the tumor microenvironment alters mRNA translation in malignant B cells, preclinical evaluation of drugs targeted against specific eukaryotic initiation factors and current progress towards clinical development. Overall, inhibition of mRNA translation initiation factors is an exciting and promising area for development of novel targeted anti-tumor drugs.

The Prognostic Significance of Eukaryotic Translation Initiation Factors (eIFs) in Endometrial Cancer

Whilst the role of eukaryotic translation initiation factors (eIFs) has already been investigated in several human cancers, their role in endometrial cancer (EC) is relatively unknown. In the present retrospective study, 279 patients with EC (1180 samples) were included (mean age: 63.0 years, mean follow-up: 6.1 years). Samples were analysed for expression of 7 eIFs subunits (eIF2α, eIF3c, eIF3h, eIF4e, eIF4g, eIF5, eIF6) through immunohistochemistry and western blotting. Fifteen samples of healthy endometrium served as controls. Density and intensity were assessed and mean combined scores (CS) calculated for each patient. Upon immunohistochemistry, median eIF5 CS were significantly higher in EC as compared with non-neoplastic tissue (NNT, p < 0.001), whilst median eIF6 CS were significantly lower in EC (p < 0.001). Moreover, eIF5 (p = 0.002), eIF6 (p = 0.032) and eIF4g CS (p = 0.014) were significantly different when comparing NNT with EC grading types. Median eIF4g CS was higher in type II EC (p = 0.034). Upon western blot analysis, eIF4g (p < 0.001), peIF2α (p < 0.001) and eIF3h (p < 0.05) were significantly overexpressed in EC, while expression of eIF3c was significantly reduced in EC as compared with NNT (p < 0.001). The remaining eIFs were non-significant. Besides tumour stage (p < 0.001) and patient's age (p < 0.001), high eIF4g CS-levels were independently associated with poor prognosis (HR: 1.604, 95%CI: 1.037-2.483, p = 0.034). The other eIFs had no prognostic significance. Notably, the independent prognostic significance of eIF4g was lost when adding tumour type. Considering the difficulties in differentiating EC type I and II, eIF4g may serve as a novel prognostic marker indicating patient outcome.

Alternative Mechanisms of mRNA Translation Initiation in Cellular Stress Response and Cancer

Throughout evolution, eukaryotic cells have devised different mechanisms to cope with stressful environments. When eukaryotic cells are exposed to stress stimuli, they activate adaptive pathways that allow them to restore cellular homeostasis. Most types of stress stimuli have been reported to induce a decrease in overall protein synthesis accompanied by induction of alternative mechanisms of mRNA translation initiation. Here, we present well-studied and recent examples of such stress responses and the alternative translation initiation mechanisms they induce, and discuss the consequences of such regulation for cell homeostasis and oncogenic transformation.

Alternatively spliced variants of the 5'-UTR of the ARPC2 mRNA regulate translation by an internal ribosome entry site (IRES) harboring a guanine-quadruplex motif

The 5'-UTR of the actin-related protein 2/3 complex subunit 2 (ARPC2) mRNA exists in two variants. Using a bicistronic reporter construct, the present study demonstrates that the longer variant of the 5'-UTR harbours an internal ribosome entry site (IRES) which is lacking in the shorter one. Multiple control assays confirmed that only this variant promotes cap-independent translation. Furthermore, it includes a guanine-rich region that is capable of forming a guanine-quadruplex (G-quadruplex) structure which was found to contribute to the IRES activity. To investigate the cellular function of the IRES element, we determined the expression level of ARPC2 at various cell densities. At high cell density, the relative ARPC2 protein level increases, supporting the presumed function of IRES elements in driving the expression of certain genes under stressful conditions that compromise cap-dependent translation. Based on chemical probing experiments and computer-based predictions, we propose a structural model of the IRES element, which includes the G-quadruplex motif exposed from the central stem-loop element. Taken together, our study describes the functional relevance of two alternative 5'-UTR splice variants of the ARPC2 mRNA, one of which contains an IRES element with a G-quadruplex as a central motif, promoting translation under stressful cellular conditions.

Inhibition of Caspase-2 Translation by the mRNA Binding Protein HuR: A Novel Path of Therapy Resistance in Colon Carcinoma Cells?

An increased expression and cytoplasmic abundance of the ubiquitous RNA binding protein human antigen R (HuR) is critically implicated in the dysregulated control of post- transcriptional gene expression during colorectal cancer development and is frequently associated with a high grade of malignancy and therapy resistance. Regardless of the fact that HuR elicits a broad cell survival program by increasing the stability of mRNAs coding for prominent anti-apoptotic factors, recent data suggest that HuR is critically involved in the regulation of translation, particularly, in the internal ribosome entry site (IRES) controlled translation of cell death regulatory proteins. Accordingly, data from human colon carcinoma cells revealed that HuR maintains constitutively reduced protein and activity levels of caspase-2 through negative interference with IRES-mediated translation. This review covers recent advances in the understanding of mechanisms underlying HuR's modulatory activity on IRES-triggered translation. With respect to the unique regulatory features of caspase-2 and its multiple roles (e.g., in DNA-damage-induced apoptosis, cell cycle regulation and maintenance of genomic stability), the pathophysiological consequences of negative caspase-2 regulation by HuR and its impact on therapy resistance of colorectal cancers will be discussed in detail. The negative HuR-caspase-2 axis may offer a novel target for tumor sensitizing therapies.

miR-125a-5p Functions as Tumor Suppressor microRNA And Is a Marker of Locoregional Recurrence And Poor prognosis in Head And Neck Cancer

MicroRNAs (miRNAs) are short single-stranded RNAs, measuring 21 to 23 nucleotides in length and regulate gene expression at the post-transcriptional level through mRNA destabilization or repressing protein synthesis. Dysregulation of miRNAs can lead to tumorigenesis through changes in regulation of key cellular processes such as cell proliferation, cell survival, and apoptosis. miR-125a-5p has been implicated as a tumor suppressor miRNA in malignancies such as non-small cell lung cancer and colon cancer. However, the role of miR-125a-5p has not been fully investigated in head and neck squamous cell carcinoma (HNSCC). We performed microRNA microarray profiling of HNSCC tumor samples obtained from a prospective clinical trial evaluating the role of postoperative radiotherapy in head and neck cancer. We also mined through The Cancer Genome Atlas to evaluate expression and survival data. Biological experiments, including cell proliferation, flow cytometry, cell migration and invasion, clonogenic survival, and fluorescent microscopy, were conducted using HN5 and UM-SCC-22B cell lines. miR-125a-5p downregulation was associated with recurrent disease in a panel of high-risk HNSCC and then confirmed poor survival associated with low expression in HNSCC via the Cancer Genome Atlas, suggesting that miR-125a-5p acts as a tumor suppressor miRNA. We then demonstrated that miR-125a-5p regulates cell proliferation through cell cycle regulation at the G₁/S transition. We also show that miR-125a-5p can alter cell migration and modulate sensitivity to ionizing radiation. Finally, we identified putative mRNA targets of miR-125a-5p, including ERBB2, EIF4EBP1, and TXNRD1, which support the tumor suppressive mechanism of miR-125a-5p. Functional validation of ERBB2 suggests that miR-125a-5p affects cell proliferation and sensitivity to ionizing radiation, in part, through ERBB2. Our data suggests that miR-125a-5p acts as a tumor suppressor miRNA, has potential as a diagnostic tool and may be a potential therapeutic target for the management and treatment of squamous cell carcinoma of the head and neck.

tiRNAs: A novel class of small noncoding RNAs that helps cells respond to stressors and plays roles in cancer progression

tRNA-derived stress-induced RNAs (tiRNAs), important components of tRNA-derived fragments, are gaining popularity for their functions as small noncoding RNAs involved in cancer progression. Under cellular stress, tiRNAs are generated when mature tRNA is specifically cleaved by angiogenin and suggested to act as transducers or effectors involved in cellular stress responses. tiRNAs facilitate cells to respond to stresses mainly via reprogramming translation, inhibiting apoptosis, degrading mRNA, and generating stress granules. This review introduces the cellular biogenesis, molecular mechanisms, and biological roles of tiRNAs in stress response and disease regulation. A better understanding of their roles in regulating cancer may provide novel biomarkers or therapeutic targets for diagnosis and treatment.

The ribosomal RPL10 R98S mutation drives IRES-dependent BCL-2 translation in T-ALL

The R98S mutation in ribosomal protein L10 (RPL10 R98S) affects 8% of pediatric T-cell acute lymphoblastic leukemia (T-ALL) cases, and was previously described to impair cellular proliferation. The current study reveals that RPL10 R98S cells accumulate reactive oxygen species which promotes mitochondrial dysfunction and reduced ATP levels, causing the proliferation defect. RPL10 R98S mutant leukemia cells can survive high oxidative stress levels via a specific increase of IRES-mediated translation of the anti-apoptotic factor B-cell lymphoma 2 (BCL-2), mediating BCL-2 protein overexpression. RPL10 R98S selective sensitivity to the clinically available Bcl-2 inhibitor Venetoclax (ABT-199) was supported by suppression of splenomegaly and the absence of human leukemia cells in the blood of T-ALL xenografted mice. These results shed new light on the oncogenic function of ribosomal mutations in cancer, provide a novel mechanism for BCL-2 upregulation in leukemia, and highlight BCL-2 inhibition as a novel therapeutic opportunity in RPL10 R98S defective T-ALL.

Cap-Independent mRNA Translation in Germ Cells

Cellular mRNAs in plants and animals have a 5'-cap structure that is accepted as the recognition point to initiate translation by ribosomes. Consequently, it was long assumed that the translation initiation apparatus was built solely for a cap-dependent (CD) mechanism. Exceptions that emerged invoke structural damage (proteolytic cleavage) to eukaryotic initiation factor 4 (eIF4) factors that disable cap recognition. The residual eIF4 complex is thought to be crippled, but capable of cap-independent (CI) translation to recruit viral or death-associated mRNAs begrudgingly when cells are in great distress. However, situations where CI translation coexists with CD translation are now known. In such cases, CI translation is still a minor mechanism in the major background of CD synthesis. In this review, I propose that germ cells do not fit this mold. Using observations from various animal models of oogenesis and spermatogenesis, I suggest that CI translation is a robust partner to CD translation to carry out the translational control that is so prevalent in germ cell development. Evidence suggests that CI translation provides surveillance of germ cell homeostasis, while CD translation governs the regulated protein synthesis that ushers these meiotic cells through the remarkable steps in sperm/oocyte differentiation.

Control of nucleolar stress and translational reprogramming by lncRNAs

Under adverse environmental conditions, cells activate stress re-sponses that favour adaptation or, in case of irreversible damage, induce cell death. Multiple stress response pathways converge to downregulate ribo-some biogenesis and translation since these are the most energy consuming processes in the cell. This adaptive response allows preserving genomic stabil-ity and saving energy for the recovery. It follows that the nucleolus is a major sensor and integrator of stress responses that are then transmitted to the translation machinery through an intricate series of conserved events. Long non-coding RNAs (lncRNAs) are emerging as important regulators of stress-induced cascades, for their ability to mediate post-transcriptional responses. Consistently, many of them are specifically expressed under stress conditions and a few have been already functionally linked to these processes, thus fur-ther supporting a role in stress management. In this review we survey differ-ent archetypes of lncRNAs specifically implicated in the regulation of nucleo-lar functions and translation reprogramming during stress responses.

Potential role of cyclin F mRNA expression in the survival of skin melanoma patients: Comprehensive analysis of the pathways altered due to cyclin F upregulation

Cyclin F is a part of the Skp, Cullin, F-box containing ligase complex. The activity of cyclin F includes cell cycle control, centrosome duplication and response to DNA damage. The cyclin F expression pattern is very similar to cyclin A, but cyclin F is an orphan cyclin without its cyclin-dependent kinase partner. There is little evidence concerning the role of cyclin F in cancer. In the present study, for the first time, we present analysis from The Cancer Genome Atlas (TCGA) data in the context of expression of cyclin F mRNA in melanoma patients. Our original in silico analysis, not published elsewhere before, revealed that high expression of cyclin F in melanoma patients is associated with worse overall survival. Cyclin F and ribonucleotide reductase family member 2 (RRM2) compose a functional axis responsible for nucleotide metabolism. Impairment in this pathway may contribute to increased DNA damage repair and drug resistance. Additionally, we analyzed the expression of RRM2 mRNA and discovered that high expression of RRM2 is associated with worse overall survival. To shed more light on cyclin F overexpression in melanoma, we analyzed all protein data available in the TCGA melanoma dataset. It was found that in patients with upregulated cyclin F mRNA, we noted increased activity of pathways related to cell cycle and DNA damage repair. These data will support further in vitro and in vivo studies on the involvement of cyclin F in skin cutaneous melanoma.

Translational control of aberrant stress responses as a hallmark of cancer

Altered mRNA translational control is emerging as a critical factor in cancer development and progression. Targeting specific elements of the translational machinery, such as mTORC1 or eIF4E, is emerging as a new strategy for innovative cancer therapy. While translation of most mRNAs takes place through cap-dependent mechanisms, a sub-population of cellular mRNA species, particularly stress-inducible mRNAs with highly structured 5'-UTR regions, are primarily translated through cap-independent mechanisms. Intriguingly, many of these mRNAs encode proteins that are involved in tumour cell adaptation to microenvironmental stress, and thus linked to aggressive behaviour including tumour invasion and metastasis. This necessitates a rigorous search for links between microenvironmental stress and aggressive tumour phenotypes. Under stress, cells block global protein synthesis to preserve energy while maintaining selective synthesis of proteins that support cell survival. One highly conserved mechanism to regulate protein synthesis under cell stress is to sequester mRNAs into cytosolic aggregates called stress granules (SGs), where their translation is silenced. SGs confer survival advantages and chemotherapeutic resistance to tumour cells under stress. Recently, it has been shown that genetically blocking SG formation dramatically reduces tumour invasive and metastatic capacity in vivo. Therefore, targeting SG formation might represent a potential treatment strategy to block cancer metastasis. Here, we present the critical link between selective mRNA translation, stress adaptation, SGs, and tumour progression. Further, we also explain how deciphering mechanisms of selective mRNA translation occurs under cell stress holds great promise for the identification of new targets in the treatment of cancer. Copyright © 2018 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

The La protein counteracts cisplatin-induced cell death by stimulating protein synthesis of anti-apoptotic factor Bcl2

Up-regulation of anti-apoptotic factors is a critical mechanism of cancer cell resistance and often counteracts the success of chemotherapeutic treatment. Herein, we identified the cancer-associated RNA-binding protein La as novel factor contributing to cisplatin resistance. Our data demonstrate that depletion of the RNA-binding protein La in head and neck squamous cell carcinoma cells (HNSCC) increases the sensitivity toward cisplatin-induced cell death paralleled by reduced expression of the anti-apoptotic factor Bcl2. Furthermore, it is shown that transient expression of Bcl2 in La-depleted cells protects against cisplatin-induced cell death. By dissecting the underlying mechanism we report herein, that the La protein is required for Bcl2 protein synthesis in cisplatin-treated cells. The RNA chaperone La binds in close proximity to the authentic translation start site and unwinds a secondary structure embedding the authentic AUG. Altogether, our data support a novel model, whereby cancer-associated La protein contributes to cisplatin resistance by stimulating the translation of anti-apoptotic factor Bcl2 in HNSCC cells.

Eukaryotic Elongation Factor 2 Kinase (eEF2K) in Cancer

Eukaryotic elongation factor 2 kinase (eEF2K) is a highly unusual protein kinase that negatively regulates the elongation step of protein synthesis. This step uses the vast majority of the large amount of energy and amino acids required for protein synthesis. eEF2K activity is controlled by an array of regulatory inputs, including inhibition by signalling through mammalian target of rapamycin complex 1 (mTORC1). eEF2K is activated under conditions of stress, such as energy depletion or nutrient deprivation, which can arise in poorly-vascularised tumours. In many such stress conditions, eEF2K exerts cytoprotective effects. A growing body of data indicates eEF2K aids the growth of solid tumours in vivo. Since eEF2K is not essential (in mice) under ‘normal’ conditions, eEF2K may be a useful target in the treatment of solid tumours. However, some reports suggest that eEF2K may actually impair tumorigenesis in some situations. Such a dual role of eEF2K in cancer would be analogous to the situation for other pathways involved in cell metabolism, such as autophagy and mTORC1. Further studies are needed to define the role of eEF2K in different tumour types and at differing stages in tumorigenesis, and to assess its utility as a therapeutic target in oncology.

The N6-methyladenosine (m6A)-forming enzyme METTL3 controls myeloid differentiation of normal hematopoietic and leukemia cells

N6-methyladenosine (m6A) is an abundant nucleotide modification in mRNA that is required for the differentiation of mouse embryonic stem cells. However, it remains unknown whether the m6A modification controls the differentiation of normal and/or malignant myeloid hematopoietic cells. Here we show that shRNA-mediated depletion of the m6A-forming enzyme METTL3 in human hematopoietic stem/progenitor cells (HSPCs) promotes cell differentiation, coupled with reduced cell proliferation. Conversely, overexpression of wild-type METTL3, but not of a catalytically inactive form of METTL3, inhibits cell differentiation and increases cell growth. METTL3 mRNA and protein are expressed more abundantly in acute myeloid leukemia (AML) cells than in healthy HSPCs or other types of tumor cells. Furthermore, METTL3 depletion in human myeloid leukemia cell lines induces cell differentiation and apoptosis and delays leukemia progression in recipient mice in vivo. Single-nucleotide-resolution mapping of m6A coupled with ribosome profiling reveals that m6A promotes the translation of c-MYC, BCL2 and PTEN mRNAs in the human acute myeloid leukemia MOLM-13 cell line. Moreover, loss of METTL3 leads to increased levels of phosphorylated AKT, which contributes to the differentiation-promoting effects of METTL3 depletion. Overall, these results provide a rationale for the therapeutic targeting of METTL3 in myeloid leukemia.

Sequence features of viral and human Internal Ribosome Entry Sites predictive of their activity

Translation of mRNAs through Internal Ribosome Entry Sites (IRESs) has emerged as a prominent mechanism of cellular and viral initiation. It supports cap-independent translation of select cellular genes under normal conditions, and in conditions when cap-dependent translation is inhibited. IRES structure and sequence are believed to be involved in this process. However due to the small number of IRESs known, there have been no systematic investigations of the determinants of IRES activity. With the recent discovery of thousands of novel IRESs in human and viruses, the next challenge is to decipher the sequence determinants of IRES activity. We present the first in-depth computational analysis of a large body of IRESs, exploring RNA sequence features predictive of IRES activity. We identified predictive k-mer features resembling IRES trans-acting factor (ITAF) binding motifs across human and viral IRESs, and found that their effect on expression depends on their sequence, number and position. Our results also suggest that the architecture of retroviral IRESs differs from that of other viruses, presumably due to their exposure to the nuclear environment. Finally, we measured IRES activity of synthetically designed sequences to confirm our prediction of increasing activity as a function of the number of short IRES elements.

Translational Dysregulation in Cancer: Molecular Insights and Potential Clinical Applications in Biomarker Development

Although transcript levels have been traditionally used as a surrogate measure of gene expression, it is increasingly recognized that the latter is extensively and dynamically modulated at the level of translation (messenger RNA to protein). Over the recent years, significant progress has been made in dissecting the complex posttranscriptional mechanisms that regulate gene expression. This advancement in knowledge came hand in hand with the progress made in the methodologies to study translation both at gene-specific as well as global genomic level. The majority of translational control is exerted at the level of initiation; nonetheless, protein synthesis can be modulated at the level of translation elongation, termination, and recycling. Sequence and structural elements and epitranscriptomic modifications of individual transcripts allow for dynamic gene-specific modulation of translation. Cancer cells usurp the regulatory mechanisms that govern translation to carry out translational programs that lead to the phenotypic hallmarks of cancer. Translation is a critical nexus in neoplastic transformation. Multiple oncogenes and signaling pathways that are activated, upregulated, or mutated in cancer converge on translation and their transformative impact "bottlenecks" at the level of translation. Moreover, this translational dysregulation allows cancer cells to adapt to a diverse array of stresses associated with a hostile microenviroment and antitumor therapies. All elements involved in the process of translation, from the transcriptional template, the components of the translational machinery, to the proteins that interact with the transcriptome, have been found to be qualitatively and/or quantitatively perturbed in cancer. This review discusses the regulatory mechanisms that govern translation in normal cells and how translation becomes dysregulated in cancer leading to the phenotypic hallmarks of malignancy. We also discuss how dysregulated mediators or components of translation can be utilized as biomarkers with potential diagnostic, prognostic, or predictive significance. Such biomarkers have the potential advantage of uniform applicability in the face of inherent tumor heterogeneity and deoxyribonucleic acid instability. As translation becomes increasingly recognized as a process gone awry in cancer and agents are developed to target it, the utility and significance of these potential biomarkers is expected to increase.

More than just scanning: the importance of cap-independent mRNA translation initiation for cellular stress response and cancer

The scanning model for eukaryotic mRNA translation initiation states that the small ribosomal subunit, along with initiation factors, binds at the cap structure at the 5' end of the mRNA and scans the 5' untranslated region (5'UTR) until an initiation codon is found. However, under conditions that impair canonical cap-dependent translation, the synthesis of some proteins is kept by alternative mechanisms that are required for cell survival and stress recovery. Alternative modes of translation initiation include cap- and/or scanning-independent mechanisms of ribosomal recruitment. In most cap-independent translation initiation events there is a direct recruitment of the 40S ribosome into a position upstream, or directly at, the initiation codon via a specific internal ribosome entry site (IRES) element in the 5'UTR. Yet, in some cellular mRNAs, a different translation initiation mechanism that is neither cap- nor IRES-dependent seems to occur through a special RNA structure called cap-independent translational enhancer (CITE). Recent evidence uncovered a distinct mechanism through which mRNAs containing N 6-methyladenosine (m6A) residues in their 5'UTR directly bind eukaryotic initiation factor 3 (eIF3) and the 40S ribosomal subunit in order to initiate translation in the absence of the cap-binding proteins. This review focuses on the important role of cap-independent translation mechanisms in human cells and how these alternative mechanisms can either act individually or cooperate with other cis-acting RNA regulons to orchestrate specific translational responses triggered upon several cellular stress states, and diseases such as cancer. Elucidation of these non-canonical mechanisms reveals the complexity of translational control and points out their potential as prospective novel therapeutic targets.

Anti-angiogenic Therapy in Cancer: Downsides and New Pivots for Precision Medicine

Primary solid tumors originate close to pre-existing tissue vasculature, initially growing along such tissue blood vessels, and this phenomenon is important for the metastatic potential which frequently occurs in highly vascularized tissues. Unfortunately, preclinic and clinic anti-angiogenic approaches have not been very successful, and multiple factors have been found to contribute to toxicity and tumor resistance. Moreover, tumors can highlight intrinsic or acquired resistances, or show adaptation to the VEGF-targeted therapies. Furthermore, different mechanisms of vascularization, activation of alternative signaling pathways, and increased tumor aggressiveness make this context even more complex. On the other hand, it has to be considered that the transitional restoration of normal, not fenestrated, microvessels allows the drug to reach the tumor and act with the maximum efficiency. However, these effects are time-limited and different, depending on the various types of cancer, and clearly define a specific “normalization window.” So, new horizons in the therapeutic approaches consist on the treatment of the tumor with pro- (instead of anti-) angiogenic therapies, which could strengthen a network of well-structured blood vessels that facilitate the transport of the drug.

4E-BP1, a multifactor regulated multifunctional protein

Eukaryotic translation initiation factor 4E (eIF4E)-binding protein 1 (4E-BP1) is a member of a family of translation repressor proteins, and a well-known substrate of mechanistic target of rapamycin (mTOR) signaling pathway. Phosphorylation of 4E-BP1 causes its release from eIF4E to allow cap-dependent translation to proceed. Recently, 4E-BP1 was shown to be phosphorylated by other kinases besides mTOR, and overexpression of 4E-BP1 was found in different human carcinomas. In this review, we summarize the novel findings on mTOR independent 4E-BP1 phosphorylation in carcinomas. The implications of overexpression and possible multi-function of 4E-BP1 are also discussed.

Angiogenin is upregulated during the alloreactive immune response and has no effect on the T-cell expansion phase, whereas it affects the contraction phase by inhibiting CD4+ T-cell apoptosis

Under growth conditions, angiogenin is translocated into the nucleus, where it enhances ribosomal RNA transcription, facilitating increased protein synthesis and cellular proliferation. During stress conditions, angiogenin is sequestered in the cytoplasm, where it cleaves transfer RNA (tRNA) to produce tRNA-derived, stress-induced small RNAs (tiRNAs) that inhibit global protein synthesis, but increase the translation of anti-apoptotic factors. In the present study, the role of angiogenin in the human alloreactive immune response was evaluated using mixed lymphocyte reactions (MLRs) and neamine, an inhibitor of angiogenin nuclear translocation. In MLRs, angiogenin production was significantly (P<0.001) increased compared with resting peripheral blood mononuclear cells. The addition of neamine had no effect on cell proliferation, but did significantly (P<0.001) increase expression of Bcl-2-associated X protein and protein levels of activated caspase-3 in CD4+ T-cells isolated from the MLRs, indicating that angiogenin reduces apoptosis. In conclusion, angiogenin is upregulated during the alloreactive immune response, in which it does not affect the T-cell expansion phase, but inhibits the T-cell contraction phase by protecting against CD4+ T-cell apoptosis.

eIF4E binding protein 1 expression is associated with clinical survival outcomes in colorectal cancer

eIF4E binding protein 1 (4E-BP1), is critical for cap-dependent and cap-independent translation. This study is the first to demonstrate that 4E-BP1 expression correlates with colorectal cancer (CRC) progression. Compared to its expression in normal colon epithelial cells, 4E-BP1 was upregulated in CRC cell lines and was detected in patient tumor tissues. Furthermore, high 4E-BP1 expression was statistically associated with poor prognosis. Hypoxia has been considered as an obstacle for cancer therapeutics. Our previous data showed that YXM110, a cryptopleurine derivative, exhibited anticancer activity via 4E-BP1 depletion. Here, we investigated whether YXM110 could inhibit protein synthesis under hypoxia. 4E-BP1 expression was notably decreased by YXM110 under hypoxic conditions, implying that cap-independent translation could be suppressed by YXM110. Moreover, YXM110 repressed hypoxia-inducible factor 1α (HIF-1α) expression, which resulted in decreased downstream vascular endothelial growth factor (VEGF) expression. These observations highlight 4E-BP1 as a useful biomarker and therapeutic target, indicating that YXM110 could be a potent CRC therapeutic drug.

IRES inhibition induces terminal differentiation and synchronized death in triple-negative breast cancer and glioblastoma cells

Internal ribosome entry site (IRES)-mediated translation is a specialized mode of protein synthesis which malignant cells depend on to survive adverse microenvironmental conditions. Our lab recently reported the identification of a group of compounds which selectively interfere with IRES-mediated translation, completely blocking de novo IGF1R synthesis, and differentially modulating synthesis of the two c-Myc isoforms. Here, we examine the phenotypic consequences of sustained IRES inhibition in human triple-negative breast carcinoma and glioblastoma cells. A sudden loss of viability affects the entire tumor cell population after ∼72-h continuous exposure to the lead compound. The extraordinarily steep dose-response relationship (Hill-Slope coefficients −15 to −35) and extensive physical connections established between the cells indicate that the cells respond to IRES inhibition collectively as a population rather than as individual cells. Prior to death, the treated cells exhibit prominent features of terminal differentiation, with marked gains in cytoskeletal organization, planar polarity, and formation of tight junctions or neuronal processes. In addition to IGF1R and Myc, specific changes in connexin 43, BiP, CHOP, p21, and p27 also correlate with phenotypic outcome. This unusual mode of tumor cell death is absolutely dependent on exceeding a critical threshold in cell density, suggesting that a quorum-sensing mechanism may be operative. Death of putative tumor stem cells visualized in situ helps to explain the inability of tumor cells to recover and repopulate once the compound is removed. Together, these findings support the concept that IRES-mediated translation is of fundamental importance to maintenance of the undifferentiated phenotype and survival of undifferentiated malignant cells.

Activation of Pim Kinases Is Sufficient to Promote Resistance to MET Small-Molecule Inhibitors

Mesenchymal-epithelial transition (MET) blockade offers a new targeted therapy particularly in those cancers with MET amplification. However, the efficacy and the duration of the response to MET inhibitors are limited by the emergence of drug resistance. Here, we report that resistance to small-molecule inhibitors of MET can arise from increased expression of the prosurvival Pim protein kinases. This resistance mechanism was documented in non-small cell lung cancer and gastric cancer cells with MET amplification. Inhibition of Pim kinases enhanced cell death triggered by short-term treatment with MET inhibitors. Pim kinases control the translation of antiapoptotic protein Bcl-2 at an internal ribosome entry site and this mechanism was identified as the basis for Pim-mediated resistance to MET inhibitors. Protein synthesis was increased in drug-resistant cells, secondary to a Pim-mediated increase in cap-independent translation. In cells rendered drug resistant by chronic treatment with MET inhibitors, genetic or pharmacologic inhibition of Pim kinases was sufficient to restore sensitivity in vitro and in vivo. Taken together, our results rationalize Pim inhibition as a strategy to augment responses and blunt acquired resistance to MET inhibitors in cancer.