Regulated release of L13a from the 60S ribosomal subunit as a mechanism of transcript-specific translational control

Central leptin signaling deficiency induced by leptin receptor antagonist leads to hypothalamic proteomic remodeling

AIMS

Leptin irresponsiveness, which is often associated with obesity, can have significant impacts on the hypothalamic proteome of individuals, including those who are lean. While mounting evidence on leptin irresponsiveness has focused on obese individuals, understanding the early molecular and proteomic changes associated with deficient hypothalamic leptin signaling in lean individuals is essential for early intervention and prevention of metabolic disorders. Leptin receptor antagonists block the binding of leptin to its receptors, potentially reducing its effects and used in cases where excessive leptin activity might be harmful.

MATERIALS AND METHODS

In this work, we blocked the central actions of leptin in lean male adult Wistar rat by chronically administering intracerebroventricularly the superactive leptin receptor antagonist (SLA) (D23L/L39A/D40A/F41A) and investigated its impact on the hypothalamic proteome using label-free sequential window acquisition of all theoretical fragment ion spectra mass spectrometry (SWATH-MS) for quantitative proteomics.

KEY FINDINGS

Our results show an accumulation of proteins involved in mRNA processing, mRNA stability, and translation in the hypothalamus of SLA-treated rats. Conversely, hypothalamic leptin signaling deficiency reduces the representation of proteins implicated in energy metabolism, neural circuitry, and neurotransmitter release.

SIGNIFICANCE

The alterations in the adult rat hypothalamic proteome contribute to dysregulate appetite, metabolism, and energy balance, which are key factors in the development and progression of obesity and related metabolic disorders. Additionally, using bioinformatic analysis, we identified a series of transcription factors that are potentially involved in the upstream regulatory mechanisms responsible for the observed signature.

Leishmania Ribosomal Protein (RP) paralogous genes compensate each other's expression maintaining protein native levels

In the protozoan parasite Leishmania, most genes encoding for ribosomal proteins (RPs) are present as two or more copies in the genome. However, their untranslated regions (UTRs) are predominantly divergent and might be associated with a distinct regulation of the expression of paralogous genes. Herein, we investigated the expression profiles of two RPs (S16 and L13a) encoded by duplicated genes in Leishmania major. The genes encoding for the S16 protein possess identical coding sequences (CDSs) and divergent UTRs, whereas the CDSs of L13a diverge by two amino acids and by their UTRs. Using CRISPR/Cas9 genome editing, we generated knockout (Δ) and endogenously tagged transfectants for each paralog of L13a and S16 genes. Combining tagged and Δ cell lines we found evidence of differential expression of both RPS16 and RPL13a isoforms throughout parasite development, with one isoform consistently more abundant than its respective copy. In addition, compensatory expression was observed for each paralog upon deletion of the corresponding isoform, suggesting functional conservation between these proteins. This differential expression pattern relates to post-translational processes, given compensation occurs at the level of the protein, with no alterations detected at transcript level. Ribosomal profiles for RPL13a indicate a standard behavior for these paralogues suggestive of interaction with heavy RNA-protein complexes, as already reported for other RPs in trypanosomatids. We identified paralog-specific bound to their 3'UTRs which may be influential in regulating paralog expression. In support, we identified conserved cis-elements within the 3'UTRs of RPS16 and RPL13a; cis-elements exclusive to the UTR of the more abundant paralog or to the less abundant ones were identified.

Pan-cellular organelles and suborganelles-from common functions to cellular diversity?

Cell diversification is at the base of increasing multicellular organism complexity in phylogeny achieved during ontogeny. However, there are also functions common to all cells, such as cell division, cell migration, translation, endocytosis, exocytosis, etc. Here we revisit the organelles involved in such common functions, reviewing recent evidence of unexpected differences of proteins at these organelles. For instance, centrosomes or mitochondria differ significantly in their protein composition in different, sometimes closely related, cell types. This has relevance for development and disease. Particularly striking is the high amount and diversity of RNA-binding proteins at these and other organelles, which brings us to review the evidence for RNA at different organelles and suborganelles. We include a discussion about (sub)organelles involved in translation, such as the nucleolus and ribosomes, for which unexpected cell type-specific diversity has also been reported. We propose here that the heterogeneity of these organelles and compartments represents a novel mechanism for regulating cell diversity. One reason is that protein functions can be multiplied by their different contributions in distinct organelles, as also exemplified by proteins with moonlighting function. The specialized organelles still perform pan-cellular functions but in a cell type-specific mode, as discussed here for centrosomes, mitochondria, vesicles, and other organelles. These can serve as regulatory hubs for the storage and transport of specific and functionally important regulators. In this way, they can control cell differentiation, plasticity, and survival. We further include examples highlighting the relevance for disease and propose to examine organelles in many more cell types for their possible differences with functional relevance.

Host-like RNA Elements Regulate Virus Translation

Viruses are obligate, intracellular parasites that co-opt host cell machineries for propagation. Critical among these machineries are those that translate RNA into protein and their mechanisms of control. Most regulatory mechanisms effectuate their activity by targeting sequence or structural features at the RNA termini, i.e., at the 5' or 3' ends, including the untranslated regions (UTRs). Translation of most eukaryotic mRNAs is initiated by 5' cap-dependent scanning. In contrast, many viruses initiate translation at internal RNA regions at internal ribosome entry sites (IRESs). Eukaryotic mRNAs often contain upstream open reading frames (uORFs) that permit condition-dependent control of downstream major ORFs. To offset genome compression and increase coding capacity, some viruses take advantage of out-of-frame overlapping uORFs (oORFs). Lacking the essential machinery of protein synthesis, for example, ribosomes and other translation factors, all viruses utilize the host apparatus to generate virus protein. In addition, some viruses exhibit RNA elements that bind host regulatory factors that are not essential components of the translation machinery. SARS-CoV-2 is a paradigm example of a virus taking advantage of multiple features of eukaryotic host translation control: the virus mimics the established human GAIT regulatory element and co-opts four host aminoacyl tRNA synthetases to form a stimulatory binding complex. Utilizing discontinuous transcription, the elements are present and identical in all SARS-CoV-2 subgenomic RNAs (and the genomic RNA). Thus, the virus exhibits a post-transcriptional regulon that improves upon analogous eukaryotic regulons, in which a family of functionally related mRNA targets contain elements that are structurally similar but lacking sequence identity. This "thrifty" virus strategy can be exploited against the virus since targeting the element can suppress the expression of all subgenomic RNAs as well as the genomic RNA. Other 3' end viral elements include 3'-cap-independent translation elements (3'-CITEs) and 3'-tRNA-like structures. Elucidation of virus translation control elements, their binding proteins, and their mechanisms can lead to novel therapeutic approaches to reduce virus replication and pathogenicity.

Myc Dysregulation in Activated Macrophages Initiates Iron-Mediated Lipid Peroxidation that Fuels Type I Interferon and Compromises TB Resistance

A quarter of human population is infected with Mycobacterium tuberculosis, but less than 10% of those infected develop clinical, mostly pulmonary, TB. To dissect mechanisms of susceptibility in immunocompetent individuals, we developed a genetically defined sst1-susceptible mouse model that uniquely reproduces a defining feature of human TB: development of necrotic lung lesions after infection with virulent Mtb. In this study, we explored the connectivity of the sst1-regulated pathways during prolonged macrophage activation with TNF. We determined that the aberrant response of the sst1-susceptible macrophages to TNF was primarily driven by conflicting Myc and antioxidant response pathways that resulted in a coordinated failure to properly sequester intracellular iron and activate ferroptosis inhibitor enzymes. Consequently, iron-mediated lipid peroxidation fueled IFNβ superinduction and sustained the Type I Interferon (IFN-I) pathway hyperactivity that locked the sst1-susceptible macrophages in a state of unresolving stress and compromised their resistance to Mtb. The accumulation of the aberrantly activated, stressed, macrophages within granuloma microenvironment led to the local failure of anti-tuberculosis immunity and tissue necrosis. Our findings suggest a novel link between metabolic dysregulation in macrophages and susceptibility to TB, offering insights into potential therapeutic targets aimed at modulating macrophage function and improving TB control.

Translation regulation in response to stress

Cell stresses occur in a wide variety of settings: in disease, during industrial processes, and as part of normal day-to-day rhythms. Adaptation to these stresses requires cells to alter their proteome. Cells modify the proteins they synthesize to aid proteome adaptation. Changes in both mRNA transcription and translation contribute to altered protein synthesis. Here, we discuss the changes in translational mechanisms that occur following the onset of stress, and the impact these have on stress adaptation.

Loss of function of ribosomal protein L13a blocks blastocyst formation and reveals a potential nuclear role in gene expression

Ribosomal proteins play diverse roles in development and disease. Most ribosomal proteins have canonical roles in protein synthesis, while some exhibit extra-ribosomal functions. Previous studies in our laboratory revealed that ribosomal protein L13a (RPL13a) is involved in the translational silencing of a cohort of inflammatory proteins in myeloid cells. This prompted us to investigate the role of RPL13a in embryonic development. Here we report that RPL13a is required for early development in mice. Crosses between Rpl13a+/- mice resulted in no Rpl13a-/- offspring. Closer examination revealed that Rpl13a-/- embryos were arrested at the morula stage during preimplantation development. RNA sequencing analysis of Rpl13a-/- morulae revealed widespread alterations in gene expression, including but not limited to several genes encoding proteins involved in the inflammatory response, embryogenesis, oocyte maturation, stemness, and pluripotency. Ex vivo analysis revealed that RPL13a was localized to the cytoplasm and nucleus between the two-cell and morula stages. RNAi-mediated depletion of RPL13a phenocopied Rpl13a-/- embryos and knockdown embryos exhibited increased expression of IL-7 and IL-17 and decreased expression of the lineage specifier genes Sox2, Pou5f1, and Cdx2. Lastly, a protein-protein interaction assay revealed that RPL13a is associated with chromatin, suggesting an extra ribosomal function in transcription. In summary, our data demonstrate that RPL13a is essential for the completion of preimplantation embryo development. The mechanistic basis of the absence of RPL13a-mediated embryonic lethality will be addressed in the future through follow-up studies on ribosome biogenesis, global protein synthesis, and identification of RPL13a target genes using chromatin immunoprecipitation and RNA-immunoprecipitation-based sequencing.

Ribosomal dysregulation: A conserved pathophysiological mechanism in human depression and mouse chronic stress

The underlying biological mechanisms that contribute to the heterogeneity of major depressive disorder (MDD) presentation remain poorly understood, highlighting the need for a conceptual framework that can explain this variability and bridge the gap between animal models and clinical endpoints. Here, we hypothesize that comparative analysis of molecular data from different experimental systems of chronic stress, and MDD has the potential to provide insight into these mechanisms and address this gap. Thus, we compared transcriptomic profiles of brain tissue from postmortem MDD subjects and from mice exposed to chronic variable stress (CVS) to identify orthologous genes. Ribosomal protein genes (RPGs) were down-regulated, and associated ribosomal protein (RP) pseudogenes were up-regulated in both conditions. A seeded gene co-expression analysis using altered RPGs common between the MDD and CVS groups revealed that down-regulated RPGs homeostatically regulated the synaptic changes in both groups through a RP-pseudogene-driven mechanism. In vitro analysis demonstrated that the RPG dysregulation was a glucocorticoid-driven endocrine response to stress. In silico analysis further demonstrated that the dysregulation was reversed during remission from MDD and selectively responded to ketamine but not to imipramine. This study provides the first evidence that ribosomal dysregulation during stress is a conserved phenotype in human MDD and chronic stress-exposed mouse. Our results establish a foundation for the hypothesis that stress-induced alterations in RPGs and, consequently, ribosomes contribute to the synaptic dysregulation underlying MDD and chronic stress-related mood disorders. We discuss the role of ribosomal heterogeneity in the variable presentations of depression and other mood disorders.

Post-transcriptional regulation of myeloid cell-mediated inflammatory responses

Myeloid cells, particularly macrophages, act as the frontline responders to infectious agents and initiate inflammation. While the molecular mechanisms driving inflammatory responses have primarily focused on pattern recognition by myeloid cells and subsequent transcriptional events, it is crucial to note that post-transcriptional regulation plays a pivotal role in this process. In addition to the transcriptional regulation of innate immune responses, additional layers of intricate network of post-transcriptional mechanisms critically determine the quantity and duration of key inflammatory products and thus the outcome of immune responses. A multitude of mechanisms governing post-transcriptional regulation in innate immunity have been uncovered, encompassing RNA alternative splicing, mRNA stability, and translational regulation. This review encapsulates the current insights into the post-transcriptional regulation of inflammatory genes within myeloid cells, with particular emphasis on translational regulation during inflammation. While acknowledging the advancements, we also shed light on the existing gaps in immunological research pertaining to post-transcriptional levels and propose perspectives that controlling post-transcriptional process may serve as potential targets for therapeutic interventions in inflammatory diseases.

GSK3α Regulates Temporally Dynamic Changes in Ribosomal Proteins upon Amino Acid Starvation in Cancer Cells

Amino acid availability is crucial for cancer cells' survivability. Leukemia and colorectal cancer cells have been shown to resist asparagine depletion by utilizing GSK3-dependent proteasomal degradation, termed the Wnt-dependent stabilization of proteins (Wnt/STOP), to replenish their amino acid pool. The inhibition of GSK3α halts the sourcing of amino acids, which subsequently leads to cancer cell vulnerability toward asparaginase therapy. However, resistance toward GSK3α-mediated protein breakdown can occur, whose underlying mechanism is poorly understood. Here, we set out to define the mechanisms driving dependence toward this degradation machinery upon asparagine starvation in cancer cells. We show the independence of known stress response pathways including the integrated stress response mediated with GCN2. Additionally, we demonstrate the independence of changes in cell cycle progression and expression levels of the asparagine-synthesizing enzyme ASNS. Instead, RNA sequencing revealed that GSK3α inhibition and asparagine starvation leads to the temporally dynamic downregulation of distinct ribosomal proteins, which have been shown to display anti-proliferative functions. Using a CRISPR/Cas9 viability screen, we demonstrate that the downregulation of these specific ribosomal proteins can rescue cell death upon GSK3α inhibition and asparagine starvation. Thus, our findings suggest the vital role of the previously unrecognized regulation of ribosomal proteins in bridging GSK3α activity and tolerance of asparagine starvation.

An overview of anti-SARS-CoV-2 and anti-inflammatory potential of baicalein and its metabolite baicalin: Insights into molecular mechanisms

The current Coronavirus Disease 2019 (COVID-19) pandemic, caused by the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), is highly contagious infection that breaks the healthcare systems of several countries worldwide. Till to date, no effective antiviral drugs against COVID-19 infection have reached the market, and some repurposed drugs and vaccines are prescribed for the treatment and prevention of this disease. The currently prescribed COVID-19 vaccines are less effective against the newly emergent variants of concern of SARS-CoV-2 due to several mutations in viral spike protein and obviously there is an urgency to develop new antiviral drugs against this disease. In this review article, we systematically discussed the anti-SARS-CoV-2 and anti-inflammatory efficacy of two flavonoids, baicalein and its 7-O-glucuronide, baicalin, isolated from Scutellaria baicalensis, Oroxylum indicum, and other plants as well as their pharmacokinetics and oral bioavailability, for development of safe and effective drugs for COVID-19 treatment. Both baicalein and baicalin target the activities of viral S-, 3CL-, PL-, RdRp- and nsp13-proteins, and host mitochondrial OXPHOS for suppression of viral infection. Moreover, these compounds prevent sepsis-related inflammation and organ injury by modulation of host innate immune responses. Several nanoformulated and inclusion complexes of baicalein and baicalin have been reported to increase oral bioavailability, but their safety and efficacy in SARS-CoV-2-infected transgenic animals are not yet evaluated. Future studies on these compounds are required for use in clinical trials of COVID-19 patients.

The human antigen R as an actionable super-hub within the network of cancer cell persistency and plasticity

In this perspective article, a clinically inspired phenotype-driven experimental approach is put forward to address the challenge of the adaptive response of solid cancers to small-molecule targeted therapies. A list of conditions is derived, including an experimental quantitative assessment of cell plasticity and an information theory-based detection of in vivo dependencies, for the discovery of post-transcriptional druggable mechanisms capable of preventing at multiple levels the emergence of plastic dedifferentiated slow-proliferating cells. The approach is illustrated by the author's own work in the example case of the adaptive response of BRAFV600-melanoma to BRAF inhibition. A bench-to-bedside and back to bench effort leads to a therapeutic strategy in which the inhibition of the baseline activity of the interferon-γ-activated inhibitor of translation (GAIT) complex, incriminated in the expression insufficiency of the RNA-binding protein HuR in a minority of cells, results in the suppression of the plastic, intermittently slow-proliferating cells involved in the adaptive response. A similar approach is recommended for the validation of other classes of mechanisms that we seek to modulate to overcome this complex challenge of modern cancer therapy.

A viral pan-end RNA element and host complex define a SARS-CoV-2 regulon

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of COVID-19, generates multiple protein-coding, subgenomic RNAs (sgRNAs) from a longer genomic RNA, all bearing identical termini with poorly understood roles in regulating viral gene expression. Insulin and interferon-gamma, two host-derived, stress-related agents, and virus spike protein, induce binding of glutamyl-prolyl-tRNA synthetase (EPRS1), within an unconventional, tetra-aminoacyl-tRNA synthetase complex, to the sgRNA 3'-end thereby enhancing sgRNA expression. We identify an EPRS1-binding sarbecoviral pan-end activating RNA (SPEAR) element in the 3'-end of viral RNAs driving agonist-induction. Translation of another co-terminal 3'-end feature, ORF10, is necessary for SPEAR-mediated induction, independent of Orf10 protein expression. The SPEAR element enhances viral programmed ribosomal frameshifting, thereby expanding its functionality. By co-opting noncanonical activities of a family of essential host proteins, the virus establishes a post-transcriptional regulon stimulating global viral RNA translation. A SPEAR-targeting strategy markedly reduces SARS-CoV-2 titer, suggesting a pan-sarbecoviral therapeutic modality.

Specialized Ribosomes in Health and Disease

Ribosomal heterogeneity exists within cells and between different cell types, at specific developmental stages, and occurs in response to environmental stimuli. Mounting evidence supports the existence of specialized ribosomes, or specific changes to the ribosome that regulate the translation of a specific group of transcripts. These alterations have been shown to affect the affinity of ribosomes for certain mRNAs or change the cotranslational folding of nascent polypeptides at the exit tunnel. The identification of specialized ribosomes requires evidence of the incorporation of different ribosomal proteins or of modifications to rRNA and/or protein that lead(s) to physiologically relevant changes in translation. In this review, we summarize ribosomal heterogeneity and specialization in mammals and discuss their relevance to several human diseases.

Mutation at the Site of Hydroxylation in the Ribosomal Protein uL15 (RPL27a) Causes Specific Changes in the Repertoire of mRNAs Translated in Mammalian Cells

Ribosomal protein uL15 (RPL27a) carries a specific modification, hydroxylation, at the His39 residue, which neighbors the CCA terminus of the E-site-bound tRNA at the mammalian ribosome. Under hypoxia, the level of hydroxylation of this protein decreases. We transiently transfected HEK293T cells with constructs expressing wild-type uL15 or mutated uL15 (His39Ala) incapable of hydroxylation, and demonstrated that ribosomes containing both proteins are competent in translation. By applying RNA-seq to the total cellular and polysome-associated mRNAs, we identified differentially expressed genes (DEGs) in cells containing exogenous uL15 or its mutant form. Analyzing mRNA features of up- and down-regulated DEGs, we found an increase in the level of more abundant mRNAs and shorter CDSs in cells with uL15 mutant for both translated and total cellular mRNAs. The level of longer and rarer mRNAs, on the contrary, decreased. Our data show how ribosome heterogeneity can change the composition of the translatome and transcriptome, depending on the properties of the translated mRNAs.

Antinociceptive Activity of Vanilloids in Caenorhabditis elegans is Mediated by the Desensitization of the TRPV Channel OCR-2 and Specific Signal Transduction Pathways

Vanilloids, including capsaicin and eugenol, are ligands of transient receptor potential channel vanilloid subfamily member 1 (TRPV1). Prolonged treatment with vanilloids triggered the desensitization of TRPV1, leading to analgesic or antinociceptive effects. Caenorhabditis elegans (C. elegans) is a model organism expressing vanilloid receptor orthologs (e.g., OSM-9 and OCR-2) that are associated with behavioral and physiological processes, including sensory transduction. We have shown that capsaicin and eugenol hamper the nocifensive response to noxious heat in C. elegans. The objective of this study was to perform proteomics to identify proteins and pathways responsible for the induced phenotype and to identify capsaicin and eugenol targets using a thermal proteome profiling (TPP) strategy. The results indicated hierarchical differences following Reactome Pathway enrichment analyses between capsaicin- and eugenol-treated nematodes. However, both treated groups were associated mainly with signal transduction pathways, energy generation, biosynthesis and structural processes. Wnt signaling, a specific signal transduction pathway, is involved following treatment with both molecules. Wnt signaling pathway is noticeably associated with pain. The TPP results show that capsaicin and eugenol target OCR-2 but not OSM-9. Further protein-protein interaction (PPI) analyses showed other targets associated with enzymatic catalysis and calcium ion binding activity. The resulting data help to better understand the broad-spectrum pharmacological activity of vanilloids.

Proteome diversification by mRNA translation in cancer

mRNA translation is a highly conserved and tightly controlled mechanism for protein synthesis and is well known to be altered by oncogenes to promote cancer development. This distorted mRNA translation is accompanied by the vulnerability of cancer to inhibitors of key mRNA translation components. Novel studies also suggest that these alternations could be utilized for immunotherapy. Ribosome heterogeneity and alternative responses to nutrient shortages, which aid cancer growth and spread, are proposed to elicit aberrant protein production but may also result in previously unidentified therapeutic targets, such as the presentation of cancer-specific peptides at the surface of cancer cells (neoepitopes). This review will assess the driving forces in tRNA and ribosome function that underlie proteome diversification due to alterations in mRNA translation in cancer cells.

RNA-Binding Proteins as Epigenetic Regulators of Brain Functions and Their Involvement in Neurodegeneration

A central aspect of nervous system development and function is the post-transcriptional regulation of mRNA fate, which implies time- and site-dependent translation, in response to cues originating from cell-to-cell crosstalk. Such events are fundamental for the establishment of brain cell asymmetry, as well as of long-lasting modifications of synapses (long-term potentiation: LTP), responsible for learning, memory, and higher cognitive functions. Post-transcriptional regulation is in turn dependent on RNA-binding proteins that, by recognizing and binding brief RNA sequences, base modifications, or secondary/tertiary structures, are able to control maturation, localization, stability, and translation of the transcripts. Notably, most RBPs contain intrinsically disordered regions (IDRs) that are thought to be involved in the formation of membrane-less structures, probably due to liquid-liquid phase separation (LLPS). Such structures are evidenced as a variety of granules that contain proteins and different classes of RNAs. The other side of the peculiar properties of IDRs is, however, that, under altered cellular conditions, they are also prone to form aggregates, as observed in neurodegeneration. Interestingly, RBPs, as part of both normal and aggregated complexes, are also able to enter extracellular vesicles (EVs), and in doing so, they can also reach cells other than those that produced them.

Proteomic study on the lymphocytes from pregnant Wistar rat females treated with immunosuppressive regimen

Kidney transplantation remains the therapeutic option for patients with end-stage kidney disease. Current immunosuppressive regimens are efficient in combating acute kidney rejection. However, insights into chronic kidney allograft injury remains limited. Simultaneously, pregnancy is more common after kidney transplantation than during dialysis treatment. Due to ethical issues, comprehensive studies on the impact of immunosuppressive regimens on pregnancy are challenging. The study aimed to investigate the proteomic status of lymphocytes obtained from pregnant female rats under immunosuppressive treatment. The experiment involved a group of 10 female, pregnant Wistar rats, five of which were treated with tacrolimus, mofetil mycophenolate, and glucocorticosteroids; five were used as control. The lymphocytes were obtained and analyzed with mass spectrometry. Measurements were processed by a database search in the ProteinPilot software with a cutoff of 1% false discovery rate. The outcomes were verified statistically by a t-test (p value < 0.05) regarding proteins up- and downregulation. A total of 2082 proteins were identified in all experiments. Eight hundred five proteins were quantified in an absolute manner in a data-independent acquisition-total protein approach analysis. Ninety-five proteins were recognized as present at different concentrations in analyzed groups and were annotated to intracellular pathways. The proteins involved in nonsense-mediated decay and L13a-mediated translational silencing of ceruloplasmin expression were recognized as downregulated. The set of proteins clinically identified as acute phase proteins was upregulated. Despite the blockade of adaptive cellular immunity, the lymphocytes in the analyzed group reveal sustained proinflammatory status with decreased ability to regulate translation. This potentially affects pregnancy and immunity.

Condensin I and condensin II proteins form a LINE-1 dependent super condensin complex and cooperate to repress LINE-1

Condensin I and condensin II are multi-subunit complexes that are known for their individual roles in genome organization and preventing genomic instability. However, interactions between condensin I and condensin II subunits and cooperative roles for condensin I and condensin II, outside of their genome organizing functions, have not been reported. We previously discovered that condensin II cooperates with Gamma Interferon Activated Inhibitor of Translation (GAIT) proteins to associate with Long INterspersed Element-1 (LINE-1 or L1) RNA and repress L1 protein expression and the retrotransposition of engineered L1 retrotransposition in cultured human cells. Here, we report that the L1 3'UTR is required for condensin II and GAIT association with L1 RNA, and deletion of the L1 RNA 3'UTR results in increased L1 protein expression and retrotransposition. Interestingly, like condensin II, we report that condensin I also binds GAIT proteins, associates with the L1 RNA 3'UTR, and represses L1 retrotransposition. We provide evidence that the condensin I protein, NCAPD2, is required for condensin II and GAIT protein association with L1 RNA. Furthermore, condensin I and condensin II subunits interact to form a L1-dependent super condensin complex (SCC) which is located primarily within the cytoplasm of both transformed and primary epithelial cells. These data suggest that increases in L1 expression in epithelial cells promote cytoplasmic condensin protein associations that facilitate a feedback loop in which condensins may cooperate to mediate L1 repression.

Moonlighting translation factors: multifunctionality drives diverse gene regulation

Translation factors have traditionally been viewed as proteins that drive ribosome function and ensure accurate mRNA translation. Recent discoveries have highlighted that these factors can also moonlight in gene regulation, but through functions distinct from their canonical roles in protein synthesis. Notably, the additional functions that translation factors encode are diverse, ranging from transcriptional control and extracellular signaling to RNA binding, and are highly regulated in response to external cues and the intrinsic cellular state. Thus, this multifunctionality of translation factors provides an additional mechanism for exquisite control of gene expression.

Strategy for Microscale Extraction and Proteome Profiling of Peripheral Blood Mononuclear Cells

Peripheral blood mononuclear cells (PBMCs) play vital roles in physiological and pathological processes and represent a rich source for disease monitoring. Typical molecular profiling on PBMCs involves the sorting of cell subsets and thus requires a large volume of peripheral blood (PB), which impedes the clinical practicability of omics tools in PBMC measurements. It would be clinically invaluable to develop a convenient approach for preparing PBMCs from small volumes of PB and for deep proteome profiling of PBMCs. To this end, here, we designed an apparatus (PBMC-mCap) for microscale enrichment and proteome analysis of PBMCs, which pushed the needed PB volume from the normal 2 mL or higher to 100 μL or lower, comparable to the volume of a drop of finger blood. A PBMC-specific mass spectra library containing 8869 proteins and 121,956 peptides was further built, which, in combination with the optimized data-independent acquisition strategy, helped to identify 6000 and 6500 proteins from PBMCs with 100 μL and 1 mL of PB as initial materials, respectively. Further application of the strategy for PBMC proteomes revealed a steady difference between gender (male vs female) and upon stimulus (COVID-19 vaccination). For the latter, we observed differentially expressed genes and pathways involving the activation of immune cells, including the NF-κB pathway, inflammation response, and antiviral response. Our strategy for the proteome analysis of microscale PBMCs may provide a convenient clinical toolkit for disease diagnosis and healthy state monitoring.

Baicalin Induces a Potent Innate Immune Response to Inhibit Respiratory Syncytial Virus Replication via Regulating Viral Non-Structural 1 and Matrix RNA

Respiratory syncytial virus (RSV) infection is the most frequent cause of hospitalization in pediatric patients. Current systemic treatment and vaccines are not curative and re-infection is often associated with a more drastic incidence of the disease. Baicalin is a flavonoid isolated from Scutellaria baicalensis with potent anti-viral characteristics, namely against RSV. However, its precise mechanism of action remains unclear. Here, using in vitro methods and an in vivo murine model of RSV infection, we showed that baicalin inhibits RSV replication induces translational upregulation of type I interferons (IFNs), IFN-α and IFN-β, and reverses epithelial thickening in lung tissues. Moreover, baicalin inhibits transcription of the RSV non-structural proteins NS1 and NS2. Molecular docking and surface plasmon resonance-based affinity analysis showed that baicalin also binds to the α3 helix of the NS1 protein with an affinity constant of 1.119 × 10⁻⁵ M. Polysome profiling showed that baicalin inhibits translation of the RSV matrix protein (M) RNA. Baicalin mediates increased release of the ribosomal protein L13a from the large ribosomal subunit, where the extra ribosomal subunit L13a inhibits M RNA translation. These results comprehensively establish the multiple mechanisms by which baicalin induces a potent innate immune response against RSV infection.

Identifying ribosome heterogeneity using ribosome profiling

Recent studies have revealed multiple mechanisms that can lead to heterogeneity in ribosomal composition. This heterogeneity can lead to preferential translation of specific panels of mRNAs, and is defined in large part by the ribosomal protein (RP) content, amongst other things. However, it is currently unknown to what extent ribosomal composition is heterogeneous across tissues, which is compounded by a lack of tools available to study it. Here we present dripARF, a method for detecting differential RP incorporation into the ribosome using Ribosome Profiling (Ribo-seq) data. We combine the 'waste' rRNA fragment data generated in Ribo-seq with the known 3D structure of the human ribosome to predict differences in the composition of ribosomes in the material being studied. We have validated this approach using publicly available data, and have revealed a potential role for eS25/RPS25 in development. Our results indicate that ribosome heterogeneity can be detected in Ribo-seq data, providing a new method to study this phenomenon. Furthermore, with dripARF, previously published Ribo-seq data provides a wealth of new information, allowing the identification of RPs of interest in many disease and normal contexts. dripARF is available as part of the ARF R package and can be accessed through https://github.com/fallerlab/ARF.

METTL18-mediated histidine methylation of RPL3 modulates translation elongation for proteostasis maintenance

Protein methylation occurs predominantly on lysine and arginine residues, but histidine also serves as a methylation substrate. However, a limited number of enzymes responsible for this modification have been reported. Moreover, the biological role of histidine methylation has remained poorly understood to date. Here, we report that human METTL18 is a histidine methyltransferase for the ribosomal protein RPL3 and that the modification specifically slows ribosome traversal on Tyr codons, allowing the proper folding of synthesized proteins. By performing an in vitro methylation assay with a methyl donor analog and quantitative mass spectrometry, we found that His245 of RPL3 is methylated at the τ-N position by METTL18. Structural comparison of the modified and unmodified ribosomes showed stoichiometric modification and suggested a role in translation reactions. Indeed, genome-wide ribosome profiling and an in vitro translation assay revealed that translation elongation at Tyr codons was suppressed by RPL3 methylation. Because the slower elongation provides enough time for nascent protein folding, RPL3 methylation protects cells from the cellular aggregation of Tyr-rich proteins. Our results reveal histidine methylation as an example of a ribosome modification that ensures proteome integrity in cells.

Proteomic analysis of the ATP synthase interactome in notothenioids highlights a pathway that inhibits ceruloplasmin production

Antarctic notothenioids have unique adaptations that allow them to thrive in sub-zero Antarctic waters. Within the suborder Notothenioidei, species of the family Channichthyidae (icefish) lack haemoglobin and in some instances myoglobin too. In studies of mitochondrial function of notothenioids, few have focussed specifically on ATP synthase. In this study, we find that the icefish Champsocephalus gunnari has a significantly higher level of ATP synthase subunit α expression than in red-blooded Notothenia rossii, but a much smaller interactome than the other species. We characterise the interactome of ATP synthase subunit a in two red-blooded species Trematomus bernacchii, N. rossii, and in the icefish Chionodraco rastrospinosus, and C. gunnari and find that in comparison with the other species, reactome enrichment for C. gunnari lacks chaperonin-mediated protein folding, and fewer oxidative-stress-associated proteins are present in the identified interactome of C. gunnari. Reactome enrichment analysis also identifies a transcript-specific translational silencing pathway for the iron oxidase protein ceruloplasmin, which has previously been reported in studies of icefish as distinct from other red-blooded fish and vertebrates in its activity and RNA transcript expression. Ceruloplasmin protein expression is detected by Western blot in the liver of T. bernacchii, but not in N. rossii, C. rastrospinosus, and C. gunnari. We suggest that the translation of ceruloplasmin transcripts is silenced by the identified pathway in icefish notothenioids, which is indicative of altered iron metabolism and Fe(II) detoxification.

Aminoacyl-tRNA synthetases of the multi-tRNA synthetase complex and their role in tumorigenesis

In mammalian cells, 20 aminoacyl-tRNA synthetases (AARS) catalyze the ligation of amino acids to their cognate tRNAs to generate aminoacylated-tRNAs. In higher eukaryotes, 9 of the 20 AARSs, along with 3 auxiliary proteins, join to form the cytoplasmic multi-tRNA synthetase complex (MSC). The complex is absent in prokaryotes, but evolutionary expansion of MSC constituents, primarily by addition of novel interacting domains, facilitates formation of subcomplexes that join to establish the holo-MSC. In some cases, environmental cues direct the release of constituents from the MSC which enables the execution of non-canonical, i.e., "moonlighting", functions distinct from their essential activities in protein translation. These activities are generally beneficial, but can also be deleterious to the cell. Elucidation of the non-canonical activities of several AARSs residing in the MSC suggest they are potential therapeutic targets for cancer, as well as metabolic and neurologic diseases. Here, we describe the role of MSC-resident AARSs in cancer progression, and the factors that regulate their release from the MSC. Also, we highlight recent developments in therapeutic modalities that target MSC AARSs for cancer prevention and treatment.

Receptors for Respiratory Syncytial Virus Infection and Host Factors Regulating the Life Cycle of Respiratory Syncytial Virus

Respiratory syncytial virus (RSV) is a common cause of lower respiratory tract infections and responsible for a large proportion of mortality in children and the elderly. There are no licensed vaccines available to date. Prophylaxis and therapeutic RSV-specific antibodies are limited to populations at high risk owing to high cost and uncertain clinical value. Receptors and host factors are two determinants important for virus entry and establishment of infection in vivo. The identification and understanding of viral receptors and host factors can help us to gain insight into the pathogenesis of RSV infection. Herein, we reviewed receptors and host factors that have been reported thus far. RSV could bind to CX3C chemokine receptor 1 and heparan sulfate proteoglycans via the G protein, and to nucleolin, insulin-like growth factor-1 receptor, epidermal growth factor, and intercellular adhesion molecule-1 via the F protein. Seven host restriction factors and 13 host factors essential for RSV infection were reviewed. We characterized the functions and their roles in the life cycle of RSV, trying to provide an update on the information of RSV-related receptors and host factors.

Shaping the Innate Immune Response Through Post-Transcriptional Regulation of Gene Expression Mediated by RNA-Binding Proteins

Innate immunity is the frontline of defense against infections and tissue damage. It is a fast and semi-specific response involving a myriad of processes essential for protecting the organism. These reactions promote the clearance of danger by activating, among others, an inflammatory response, the complement cascade and by recruiting the adaptive immunity. Any disequilibrium in this functional balance can lead to either inflammation-mediated tissue damage or defense inefficiency. A dynamic and coordinated gene expression program lies at the heart of the innate immune response. This expression program varies depending on the cell-type and the specific danger signal encountered by the cell and involves multiple layers of regulation. While these are achieved mainly via transcriptional control of gene expression, numerous post-transcriptional regulatory pathways involving RNA-binding proteins (RBPs) and other effectors play a critical role in its fine-tuning. Alternative splicing, translational control and mRNA stability have been shown to be tightly regulated during the innate immune response and participate in modulating gene expression in a global or gene specific manner. More recently, microRNAs assisting RBPs and post-transcriptional modification of RNA bases are also emerging as essential players of the innate immune process. In this review, we highlight the numerous roles played by specific RNA-binding effectors in mediating post-transcriptional control of gene expression to shape innate immunity.

Identification of a novel native peptide derived from 60S ribosomal protein L23a that translationally regulates p53 to reduce myocardial ischemia-reperfusion

Myocardial ischemia-reperfusion (I/R) is a severe disease，but its underlying mechanism is not fully elucidated and no effective clinical treatment is available. Utilizing intracellular peptidomics, we identified a novel native peptide PDRL23A (Peptide Derived from RPL23A), that is intimately related to hypoxic stress. We further show that PDRL23A effectively alleviates hypoxia-induced cardiomyocyte injury in vitro, along with improvements in mitochondrial function and redox homeostasis, including ROS accumulation, oxidative phosphorylation, and mitochondrial membrane potential. Strikingly, the in vivo results indicate that, short-term pretreatment with PDRL23A could effectively inhibit I/R-induced cardiomyocyte death, myocardial fibrosis and decreased cardiac function. Interestingly, PDRL23A was found to interact with 60 S ribosomal protein L26 (RPL26), hampering RPL26-governed p53 translation, and resulting in a reduction in the level of p53 protein, which in turn reduced p53-mediated apoptosis under hypoxic conditions. Collectively, a native peptide, PDRL23A, which translationally regulates p53 to protect against myocardial I/R injury, has been identified for the first time. Our findings provide insight into the adaptive mechanisms of hypoxia and present a potential new treatment for myocardial I/R.

Phosphorylation of ribosomal protein S6 differentially affects mRNA translation based on ORF length

Phosphorylation of Ribosomal Protein S6 (RPS6) was the first post-translational modification of the ribosome to be identified and is a commonly-used readout for mTORC1 activity. Although the cellular and organismal functions of RPS6 phosphorylation are known, the molecular consequences of RPS6 phosphorylation on translation are less well understood. Here we use selective ribosome footprinting to analyze the location of ribosomes containing phosphorylated RPS6 on endogenous mRNAs in cells. We find that RPS6 becomes progressively dephosphorylated on ribosomes as they translate an mRNA. As a consequence, average RPS6 phosphorylation is higher on mRNAs with short coding sequences (CDSs) compared to mRNAs with long CDSs. We test whether RPS6 phosphorylation differentially affects mRNA translation based on CDS length by genetic removal of RPS6 phosphorylation. We find that RPS6 phosphorylation promotes translation of mRNAs with short CDSs more strongly than mRNAs with long CDSs. Interestingly, RPS6 phosphorylation does not promote translation of mRNAs with 5′ TOP motifs despite their short CDS lengths, suggesting they are translated via a different mode. In sum this provides a dynamic view of RPS6 phosphorylation on ribosomes as they translate mRNAs and the functional consequence on translation.

The Dynamic Regulation of mRNA Translation and Ribosome Biogenesis During Germ Cell Development and Reproductive Aging

The regulation of mRNA translation, both globally and at the level of individual transcripts, plays a central role in the development and function of germ cells across species. Genetic studies using flies, worms, zebrafish and mice have highlighted the importance of specific RNA binding proteins in driving various aspects of germ cell formation and function. Many of these mRNA binding proteins, including Pumilio, Nanos, Vasa and Dazl have been conserved through evolution, specifically mark germ cells, and carry out similar functions across species. These proteins typically influence mRNA translation by binding to specific elements within the 3′ untranslated region (UTR) of target messages. Emerging evidence indicates that the global regulation of mRNA translation also plays an important role in germ cell development. For example, ribosome biogenesis is often regulated in a stage specific manner during gametogenesis. Moreover, oocytes need to produce and store a sufficient number of ribosomes to support the development of the early embryo until the initiation of zygotic transcription. Accumulating evidence indicates that disruption of mRNA translation regulatory mechanisms likely contributes to infertility and reproductive aging in humans. These findings highlight the importance of gaining further insights into the mechanisms that control mRNA translation within germ cells. Future work in this area will likely have important impacts beyond germ cell biology.

A structurally conserved RNA element within SARS-CoV-2 ORF1a RNA and S mRNA regulates translation in response to viral S protein-induced signaling in human lung cells

The positive-sense, single-stranded RNA genome SARS-CoV-2 harbors functionally important cis-acting elements governing critical aspects of viral gene expression. However, insights on how these elements sense various signals from the host cell and regulate viral protein synthesis are lacking. Here, we identified two novel cis-regulatory elements in SARS-CoV-2 ORF1a and S RNAs and describe their role in translational control of SARS-CoV-2. These elements are sequence-unrelated but form conserved hairpin structures (validated by NMR) resembling Gamma Activated Inhibitor of Translation (GAIT) elements that are found in a cohort of human mRNAs directing translational suppression in myeloid cells in response to IFN-γ. Our studies show that treatment of human lung cells with receptor-binding S1 subunit, S protein pseudotyped lentivirus, and S protein-containing virus-like particles triggers a signaling pathway involving DAP-kinase1 that leads to phosphorylation and release of the ribosomal protein L13a from the large ribosomal subunit. Released L13a forms a Virus Activated Inhibitor of Translation (VAIT) complex that binds to ORF1a and S VAIT elements, causing translational silencing. Translational silencing requires extracellular S protein (and its interaction with host ACE2 receptor), but not its intracellular synthesis. RNA-protein interaction analyses and in vitro translation experiments showed that GAIT and VAIT elements do not compete with each other, highlighting differences between the two pathways. Sequence alignments of SARS-CoV-2 genomes showed a high level of conservation of VAIT elements, suggesting their functional importance. This VAIT-mediated translational control mechanism of SARS-CoV-2 may provide novel targets for small molecule intervention and/or facilitate development of more effective mRNA vaccines. Importance Specific RNA elements in the genomes of RNA viruses play important roles in host-virus interaction. For SARS-CoV-2, the mechanistic insights on how these RNA elements could sense the signals from the host cell are lacking. Here we report a novel relationship between the GAIT-like SARS-CoV-2 RNA element (called VAITs) and the signal generated from the host cell. We show that for SARS-CoV-2, the interaction of spike protein with ACE2 not only serves the purpose for viral entry into the host cell, but also transduces signals that culminate into the phosphorylation and the release of L13a from the large ribosomal subunit. We also show that this event leads to the translational arrest of ORF1a and S mRNAs in a manner dependent on the structure of the RNA elements. Translational control of viral mRNA by a host-cell generated signal triggered by viral protein is a new paradigm in the host-virus relationship.

Ogfod1 deletion increases cardiac beta-alanine levels and protects mice against ischemia-reperfusion injury

AIMS

Prolyl hydroxylation is a post-translational modification that regulates protein stability, turnover, and activity. The proteins that catalyze prolyl hydroxylation belong to the 2-oxoglutarate- and iron-dependent oxygenase family of proteins. 2-oxoglutarate- and iron-dependent oxygenase domain-containing protein 1 (Ogfod1), which hydroxylates a proline in ribosomal protein s23 is a newly-described member of this family. The aims of this study were to investigate roles for Ogfod1 in the heart, and in the heart's response to stress.

METHODS AND RESULTS

We isolated hearts from wild type (WT) and Ogfod1 knockout (KO) mice and performed quantitative proteomics using Tandem Mass Tag labelling coupled to Liquid Chromatography and tandem Mass Spectrometry (LC-MS/MS) to identify protein changes. Ingenuity Pathway Analysis identified "Urate Biosynthesis/Inosine 5'-phosphate Degradation" and "Purine Nucleotides Degradation II (Aerobic)" as the most significantly-enriched pathways. We performed metabolomics analysis and found that both purine and pyrimidine pathways were altered with the purine nucleotide inosine 5'-monophosphate (IMP) showing a 3.5-fold enrichment in KO hearts (P = 0.011) and the pyrimidine catabolism product beta-alanine showing a 1.7-fold enrichment in KO hearts (P = 0.014). As changes in these pathways have been shown to contribute to cardioprotection, we subjected isolated perfused hearts to ischemia and reperfusion (I/R). KO hearts showed a 41.4% decrease in infarct size and a 34% improvement in cardiac function compared to WT hearts. This protection was also evident in an in vivo I/R model. Additionally, our data show that treating isolated perfused WT hearts with carnosine, a metabolite of beta-alanine, improved protection in the context of I/R injury, whereas treating KO hearts with carnosine had no impact on recovery of function or infarct size.

CONCLUSIONS

Taken together, these data show that Ogfod1 deletion alters the myocardial proteome and metabolome to confer protection against I/R injury.

TRANSLATIONAL PERSPECTIVE

Heart disease is the leading cause of death in the US. In characterizing the cardiovascular effects of deleting the prolyl hydroxylase Ogfod1 and investigating its role in disease pathology, we found that deleting Ogfod1 protected hearts against ex vivo and in vivo I/R injury. Ogfod1-KO hearts showed significant metabolomic and proteomic changes that supported altered purine and pyrimidine nucleotide synthesis and turnover. Beta-alanine, a precursor of the anti-oxidant carnosine and a product of pyrimidine degradation, accumulated in KO hearts to help confer cardioprotection. Altogether, these data suggest a role for Ogfod1 downregulation as a therapeutic strategy for heart disease.

Ribosome-Induced Cellular Multipotency, an Emerging Avenue in Cell Fate Reversal

The ribosome, which is present in all three domains of life, plays a well-established, critical role in the translation process by decoding messenger RNA into protein. Ribosomal proteins, in contrast, appear to play non-translational roles in growth, differentiation, and disease. We recently discovered that ribosomes are involved in reverting cellular potency to a multipotent state. Ribosomal incorporation (the uptake of free ribosome by living cells) can direct the fate of both somatic and cancer cells into multipotency, allowing them to switch cell lineage. During this process, both types of cells experienced cell-cycle arrest and cellular stress while remaining multipotent. This review provides a molecular perspective on current insights into ribosome-induced multipotency and sheds light on how a common stress-associated mechanism may be involved. We also discuss the impact of this phenomenon on cancer cell reprogramming and its potential in cancer therapy.

Inflammation and tumor progression: signaling pathways and targeted intervention

Cancer development and its response to therapy are regulated by inflammation, which either promotes or suppresses tumor progression, potentially displaying opposing effects on therapeutic outcomes. Chronic inflammation facilitates tumor progression and treatment resistance, whereas induction of acute inflammatory reactions often stimulates the maturation of dendritic cells (DCs) and antigen presentation, leading to anti-tumor immune responses. In addition, multiple signaling pathways, such as nuclear factor kappa B (NF-kB), Janus kinase/signal transducers and activators of transcription (JAK-STAT), toll-like receptor (TLR) pathways, cGAS/STING, and mitogen-activated protein kinase (MAPK); inflammatory factors, including cytokines (e.g., interleukin (IL), interferon (IFN), and tumor necrosis factor (TNF)-α), chemokines (e.g., C-C motif chemokine ligands (CCLs) and C-X-C motif chemokine ligands (CXCLs)), growth factors (e.g., vascular endothelial growth factor (VEGF), transforming growth factor (TGF)-β), and inflammasome; as well as inflammatory metabolites including prostaglandins, leukotrienes, thromboxane, and specialized proresolving mediators (SPM), have been identified as pivotal regulators of the initiation and resolution of inflammation. Nowadays, local irradiation, recombinant cytokines, neutralizing antibodies, small-molecule inhibitors, DC vaccines, oncolytic viruses, TLR agonists, and SPM have been developed to specifically modulate inflammation in cancer therapy, with some of these factors already undergoing clinical trials. Herein, we discuss the initiation and resolution of inflammation, the crosstalk between tumor development and inflammatory processes. We also highlight potential targets for harnessing inflammation in the treatment of cancer.

Mouse aging cell atlas analysis reveals global and cell type-specific aging signatures

Aging is associated with complex molecular and cellular processes that are poorly understood. Here we leveraged the Tabula Muris Senis single-cell RNA-seq data set to systematically characterize gene expression changes during aging across diverse cell types in the mouse. We identified aging-dependent genes in 76 tissue-cell types from 23 tissues and characterized both shared and tissue-cell-specific aging behaviors. We found that the aging-related genes shared by multiple tissue-cell types also change their expression congruently in the same direction during aging in most tissue-cell types, suggesting a coordinated global aging behavior at the organismal level. Scoring cells based on these shared aging genes allowed us to contrast the aging status of different tissues and cell types from a transcriptomic perspective. In addition, we identified genes that exhibit age-related expression changes specific to each functional category of tissue-cell types. Altogether, our analyses provide one of the most comprehensive and systematic characterizations of the molecular signatures of aging across diverse tissue-cell types in a mammalian system.

Panel of suitable reference genes and its gender differences of fetal rat liver under physiological conditions and exposure to dexamethasone during pregnancy

The panel of suitable reference genes in the fetal liver have not been reported. In this study, five commonly used reference genes (GAPDH, β-actin, Rn18 s, Rpl13a, and Rps29) were firstly selected as candidates. Bestkeeper, GeNorm, and NormFinder software were then used to screen out the panel of suitable reference genes of male and female fetal rat liver under physiological and prenatal dexamethasone exposure (PDE) conditions. Finally, we verified the reliability of the screened panel of reference genes by standardizing sterol regulatory element binding protein 1c (SREBP1c) expression with different reference genes. The results showed that GAPDH + Rn18 s and GAPDH + Rpl13a were respectively the panel of suitable reference genes in male and female rat fetal liver under the physiological model, while Rn18 s + Rps29 and GAPDH + Rn18 s were respectively under the PDE model. The results showed that different reference genes affected the statistical results of SREBP1c expression, and the screened panel of suitable reference genes under the PDE model had smaller intragroup differences, when compared with other reference genes under physiological and PDE models. In conclusion, we screened and determined that the panel of suitable reference genes were GAPDH + Rn18 s and Rn18 s + Rps29 in the male rat fetal liver under physiological and PDE models, while they were GAPDH + Rpl13a and GAPDH + Rn18 s in the females, and confirmed that the selection of the panel of suitable reference genes in the fetal liver had gender differences and pathological model specificity.

The role of RNA-binding and ribosomal proteins as specific RNA translation regulators in cellular differentiation and carcinogenesis

Tight control of mRNA expression is required for cell differentiation; imbalanced regulation may lead to developmental disorders and cancer. The activity of the translational machinery (including ribosomes and translation factors) regulates the rate (slow or fast) of translation of encoded proteins, and the quality of these proteins highly depends on which mRNAs are available for translation. Specific RNA-binding and ribosomal proteins seem to play a key role in controlling gene expression to determine the differentiation fate of the cell. This demonstrates the important role of RNA-binding proteins, specific ribosome-binding proteins and microRNAs as key molecules in controlling the specific proteins required for the differentiation or dedifferentiation of cells. This delicate balance between specific proteins (in terms of quality and availability) and post-translational modifications occurring in the cytoplasm is crucial for cell differentiation, dedifferentiation and oncogenic potential. In this review, we report how defects in the regulation of mRNA translation can be dependent on specific proteins and can induce an imbalance between differentiation and dedifferentiation in cell fate determination.

A cyclin-dependent kinase, CDK11/p58, represses cap-dependent translation during mitosis

During mitosis, translation of most mRNAs is strongly repressed; none of the several explanatory hypotheses suggested can fully explain the molecular basis of this phenomenon. Here we report that cyclin-dependent CDK11/p58-a serine/threonine kinase abundantly expressed during M phase-represses overall translation by phosphorylating a subunit (eIF3F) of the translation factor eIF3 complex that is essential for translation initiation of most mRNAs. Ectopic expression of CDK11/p58 strongly repressed cap-dependent translation, and knockdown of CDK11/p58 nullified the translational repression during M phase. We identified the phosphorylation sites in eIF3F responsible for M phase-specific translational repression by CDK11/p58. Alanine substitutions of CDK11/p58 target sites in eIF3F nullified its effects on cell cycle-dependent translational regulation. The mechanism of translational regulation by the M phase-specific kinase, CDK11/p58, has deep evolutionary roots considering the conservation of CDK11 and its target sites on eIF3F from C. elegans to humans.

Regulation of ribosomal protein genes: An ordered anarchy

Ribosomal protein genes are among the most highly expressed genes in most cell types. Their products are generally essential for ribosome synthesis, which is the cornerstone for cell growth and proliferation. Many cellular resources are dedicated to producing ribosomal proteins and thus this process needs to be regulated in ways that carefully balance the supply of nascent ribosomal proteins with the demand for new ribosomes. Ribosomal protein genes have classically been viewed as a uniform interconnected regulon regulated in eukaryotic cells by target of rapamycin and protein kinase A pathway in response to changes in growth conditions and/or cellular status. However, recent literature depicts a more complex picture in which the amount of ribosomal proteins produced varies between genes in response to two overlapping regulatory circuits. The first includes the classical general ribosome‐producing program and the second is a gene‐specific feature responsible for fine‐tuning the amount of ribosomal proteins produced from each individual ribosomal gene. Unlike the general pathway that is mainly controlled at the level of transcription and translation, this specific regulation of ribosomal protein genes is largely achieved through changes in pre‐mRNA splicing efficiency and mRNA stability. By combining general and specific regulation, the cell can coordinate ribosome production, while allowing functional specialization and diversity. Here we review the many ways ribosomal protein genes are regulated, with special focus on the emerging role of posttranscriptional regulatory events in fine‐tuning the expression of ribosomal protein genes and its role in controlling the potential variation in ribosome functions.

This article is categorized under:

Translation > Ribosome Biogenesis

Translation > Ribosome Structure/Function

Translation > Translation Regulation

RNA-binding proteins balance brain function in health and disease

Posttranscriptional gene expression including splicing, RNA transport, translation, and RNA decay provides an important regulatory layer in many if not all molecular pathways. Research in the last decades has positioned RNA-binding proteins (RBPs) right in the center of posttranscriptional gene regulation. Here, we propose interdependent networks of RBPs to regulate complex pathways within the central nervous system (CNS). These are involved in multiple aspects of neuronal development and functioning, including higher cognition. Therefore, it is not sufficient to unravel the individual contribution of a single RBP and its consequences but rather to study and understand the tight interplay between different RBPs. In this review, we summarize recent findings in the field of RBP biology and discuss the complex interplay between different RBPs. Second, we emphasize the underlying dynamics within an RBP network and how this might regulate key processes such as neurogenesis, synaptic transmission, and synaptic plasticity. Importantly, we envision that dysfunction of specific RBPs could lead to perturbation within the RBP network. This would have direct and indirect (compensatory) effects in mRNA binding and translational control leading to global changes in cellular expression programs in general and in synaptic plasticity in particular. Therefore, we focus on RBP dysfunction and how this might cause neuropsychiatric and neurodegenerative disorders. Based on recent findings, we propose that alterations in the entire regulatory RBP network might account for phenotypic dysfunctions observed in complex diseases including neurodegeneration, epilepsy, and autism spectrum disorders.

Novel Insights into Beta 2 Adrenergic Receptor Function in the rd10 Model of Retinitis Pigmentosa

Background: In retinitis pigmentosa (RP), inherited rod death is followed by cone loss and blindness. Why cones die is still a matter of consideration. Here, we investigate the pathogenic role of the sympathetic transmission in the rd10 mouse model of RP. Methods: Retinal levels of beta adrenergic receptor (BAR) 2 and norepinephrine (NE) were measured. After administration of the BAR1/2 blocker propranolol or the hypoxia-inducible factor (HIF)-1 activator dimethyloxalylglycine (DMOG), retinal levels of HIF-1α, BAR2 or proteins involved in BAR2 desensitization were also measured. In DMOG treated mice, expression and localization of BAR2, inflammatory markers and cone arrestin were determined. Finally, rd10 mice were subjected to electroretinogram (ERG) analysis to assess rod and cone function. Results: In the rd10 retina, BAR2 overexpression and NE accumulation were found, with BAR2 immunoreactivity localized to Müller cells. BAR2 overexpression was likely due to desensitization defects. Upregulated levels of BAR2 were drastically reduced by propranolol that also restored desensitization defects. Due to the low level of HIF-1 consequent to the hyperoxic environment in the rd10 retina, we hypothesized a link between HIF-1 and BAR2. HIF-1α stabilization with DMOG resulted in i. increased HIF-1α accumulation, ii. decreased BAR2 levels, iii. restored desensitization processes, iv. reduced expression of inflammatory markers and v. increased cone survival without improved retinal function. Conclusions: Our results support a pathogenic role of the sympathetic system in RP that might help to understand why rd10 mice show a positive response to BAR blockers.

Phosphorylation of the N-terminal domain of ribosomal P-stalk protein uL10 governs its association with the ribosome

The uL10 protein is the main constituent of the ribosomal P-stalk, anchoring the whole stalk to the ribosome through interactions with rRNA. The P-stalk is the core of the GTPase-associated center (GAC), a critical element for ribosome biogenesis and ribosome translational activity. All P-stalk proteins (uL10, P1, and P2) undergo phosphorylation within their C termini. Here, we show that uL10 has multiple phosphorylation sites, mapped also within the N-terminal rRNA-binding domain. Our results reveal that the introduction of a negative charge within the N terminus of uL10 impairs its association with the ribosome. These findings demonstrate that uL10 N-terminal phosphorylation has regulatory potential governing the uL10 interaction with the ribosome and may control the activity of GAC.

Moonlighting Proteins in the Fuzzy Logic of Cellular Metabolism

The numerous interconnected biochemical pathways that make up the metabolism of a living cell comprise a fuzzy logic system because of its high level of complexity and our inability to fully understand, predict, and model the many activities, how they interact, and their regulation. Each cell contains thousands of proteins with changing levels of expression, levels of activity, and patterns of interactions. Adding more layers of complexity is the number of proteins that have multiple functions. Moonlighting proteins include a wide variety of proteins where two or more functions are performed by one polypeptide chain. In this article, we discuss examples of proteins with variable functions that contribute to the fuzziness of cellular metabolism.

Aminoacyl-tRNA synthetases in cell signaling

Aminoacyl-tRNA synthetases (ARSs) are a family of essential "housekeeping" enzymes ubiquitous in the three major domains of life. ARSs uniquely connect the essential minimal units of both major oligomer classes-the 3-nucleotide codons of oligonucleotides and the amino acids of proteins. They catalyze the esterification of amino acids to the 3'-end of cognate transfer RNAs (tRNAs) bearing the correct anticodon triplet to ensure accurate transfer of information from mRNA to protein according to the genetic code. As an essential translation factor responsible for the first biochemical reaction in protein biosynthesis, ARSs control protein production by catalyzing aminoacylation, and by editing of mischarged aminoacyl-tRNAs to maintain translational fidelity. In addition to their primary enzymatic activities, many ARSs have noncanonical functions unrelated to their catalytic activity in protein synthesis. Among the ARSs with "moonlighting" activities, several, including GluProRS (or EPRS), LeuRS, LysRS, SerRS, TyrRS, and TrpRS, exhibit cell signaling-related activities that sense environmental signals, regulate gene expression, and modulate cellular functions. ARS signaling functions generally depend on catalytically-inactive, appended domains not present in ancient enzyme forms, and are activated by stimulus-dependent post-translational modification. Activation often results in cellular re-localization and gain of new interacting partners. The newly formed ARS-bearing complexes conduct a host of signal transduction functions, including immune response, mTORC1 pathway signaling, and fibrogenic and angiogenic signaling, among others. Because noncanonical functions of ARSs in signal transduction are uncoupled from canonical aminoacylation functions, function-specific inhibitors can be developed, thus providing promising opportunities and therapeutic targets for treatment of human disease.

Ribosome heterogeneity in stem cells and development

Translation control is critical to regulate protein expression. By directly adjusting protein levels, cells can quickly respond to dynamic transitions during stem cell differentiation and embryonic development. Ribosomes are multisubunit cellular assemblies that mediate translation. Previously seen as invariant machines with the same composition of components in all conditions, recent studies indicate that ribosomes are heterogeneous and that different ribosome types can preferentially translate specific subsets of mRNAs. Such heterogeneity and specialized translation functions are very important in stem cells and development, as they allow cells to quickly respond to stimuli through direct changes of protein abundance. In this review, we discuss ribosome heterogeneity that arises from multiple features of rRNAs, including rRNA variants and rRNA modifications, and ribosomal proteins, including their stoichiometry, compositions, paralogues, and posttranslational modifications. We also discuss alterations of ribosome-associated proteins (RAPs), with a particular focus on their consequent specialized translational control in stem cells and development.

Post-transcriptional regulation of C-C motif chemokine ligand 2 expression by ribosomal protein L22 during LPS-mediated inflammation

Monocyte infiltration to the site of pathogenic invasion is critical for inflammatory response and host defence. However, this process demands precise regulation as uncontrolled migration of monocytes to the site delays resolution of inflammation and ultimately promotes chronic inflammation. C-C motif chemokine ligand 2 (CCL2) plays a key role in monocyte migration, and hence, its expression should be tightly regulated. Here, we report a post-transcriptional regulation of CCL2 involving the large ribosomal subunit protein L22 (RPL22) in LPS-activated, differentiated THP-1 cells. Early events following LPS treatment include transcriptional upregulation of RPL22 and its nuclear accumulation. The protein binds to the first 20 nt sequence of the 5'UTR of ccl2 mRNA. Simultaneous nuclear translocation of up-frameshift-1 protein and its interaction with RPL22 results in cytoplasmic degradation of the ccl2 mRNA at a later stage. Removal of RPL22 from cells results in increased expression of CCL2 in response to LPS causing disproportionate migration of monocytes. We propose that post-transcriptional regulation of CCL2 by RPL22 fine-tunes monocyte infiltration during a pathogenic insult and maintains homeostasis of the immune response critical to resolution of inflammation. DATABASES: Microarray data are available in NCBI GEO database (Accession No GSE126525).

High-fat diet-induced GAIT element-mediated translational silencing of mRNAs encoding inflammatory proteins in macrophage protects against atherosclerosis

Previously, we identified a mechanism of inflammation control directed by ribosomal protein L13a and "GAIT" (Gamma Activated Inhibitor of Translation) elements in target mRNAs and showed that its elimination in myeloid cell-specific L13a knockout mice (L13a KO) increased atherosclerosis susceptibility and severity. Here, we investigated the mechanistic basis of this endogenous defense against atherosclerosis. We compared molecular and cellular aspects of atherosclerosis in high-fat diet (HFD)-fed L13a KO and intact (control) mice. HFD treatment of control mice induced release of L13a from 60S ribosome, formation of RNA-binding complex, and subsequent GAIT element-mediated translational silencing. Atherosclerotic plaques from HFD-treated KO mice showed increased infiltration of M1 type inflammatory macrophages. Macrophages from KO mice showed increased phagocytic activity and elevated expression of LDL receptor and pro-inflammatory mediators. NanoString analysis of the plaques from KO mice showed upregulation of a number of mRNAs encoding inflammatory proteins. Bioinformatics analysis suggests the presence of the potential GAIT elements in the 3'UTRs of several of these mRNAs. Macrophage induces L13a/GAIT-dependent translational silencing of inflammatory genes in response to HFD as an endogenous defense against atherosclerosis in ApoE^-/- model.