Hallmarks of ribosomopathies

Associations of Serum Per- and Polyfluoroalkyl Substances with Genotoxic Biomarkers: New Insights from Cross-Sectional and In Vivo Evidence

The effects of perfluoroalkyl and polyfluoroalkyl substances (PFAS) on genomic stability remain unclear. Here, a cross-sectional study was conducted to establish the associations of PFAS with genotoxic biomarkers. We recruited a cohort of 453 residents in 2021 in Zhejiang, China. Thirty PFAS in serum were quantified, alongside seven indicators of genomic stability [five rDNA copy numbers (rDNA-CN), mitochondrial DNA copy numbers (mtDNA-CN), and relative telomere length (RTL)] in whole blood. Results showed that PFUnDA, perfluorohexanesulfonic acid (PFHxS), perfluorooctanesulfonic acid (PFOS), 6:2 Cl-PFESA, and PFO5DoDA were positively correlated with rDNA-CN, while PFHpA, PFOA, and PFMOAA showed inverse associations. PFO4DA and PFO5DoDA were positively correlated with mtDNA-CN. PFOA, HFPO-TA, and PFMOAA were negatively associated with the RTL, while perfluorononanoic acid, PFHxS, PFOS, and 6:2 Cl-PFESA showed positive associations. Nonlinear exposure-response relationships were also observed between PFAS and genotoxic biomarkers using restricted cubic spline models. Furthermore, PFAS mixtures were positively associated with mtDNA-CN, with PFO5DoDA showing the highest contribution by the quantile-based g-computation model. In vivo studies further confirmed that PFO5DoDA increased mtDNA-CN in male mice in a dose-dependent manner. This study provides novel evidence that PFAS disrupt genomic stability, with effects varying by functional groups and fluoroalkyl(ether) chain lengths.

EMG1 methyltransferase activity affects ribosome occupancy at KSHV uORFs

Viruses lack their own translational machinery and rely exclusively on the host cell for synthesis of viral proteins. Viruses have evolved diverse mechanisms to redirect the host cell translation apparatus to favor viral transcripts. A unique mechanism employed by Kaposi's sarcoma-associated herpesvirus (KSHV) involves manipulation of cellular ribosome composition, producing virus-induced specialized ribosomes. These ribosomes scan through KSHV upstream open reading frames (uORFs) in late lytic genes, allowing efficient translation of downstream main KSHV ORFs. Here, we highlight the enhanced association of the ribosomal biogenesis factor EMG1 with precursor-40S ribosome complexes during KSHV lytic replication. Depletion of EMG1 results in significantly reduced expression of viral proteins and progression through the lytic cascade, culminating in a dramatic reduction of infectious virus production. We further demonstrate that the methyltransferase activity of EMG1 is required for effective regulation of translation of KSHV uORFs in late lytic genes.

A tripartite cell-free translation system to study mammalian translation

Genetic manipulation of cellular systems often leads to the adaptation of gene expression programs, rendering detailed mechanistic insights challenging to isolate and elucidate. The proteome constitutes the ultimate manifestation of gene expression programs with multiple layers of regulation to ensure faithful execution. While current high-throughput techniques to investigate regulation at the level of translation, such as Ribo-Seq and nascent proteomics, can capture nuanced changes in the translational landscape, they suffer from potential confounding factors imposed by adaptation of the cellular states. Cell-free translation systems have been used to elucidate molecular mechanisms for decades, but experimental setups have rigid composition and often rely on non-human model systems and artificially designed mRNA constructs. Here we detail a tripartite cell-free translation system based on the separation of mRNAs, ribosomes and ribosome-depleted cytoplasmic lysate from human cells, allowing for flexible reconstitution of translation reactions, which can be performed in 1-4 days. In this setup, cellular parts such as the cytoplasmic lysate can be kept constant, while ribosome complexes or mRNA can be varied or subjected to treatments or vice versa. We detail how complete mRNA populations can be used as input with subsequent detection of nascent peptides using autoradiography or mass spectrometry. We utilize this protocol to resolve which aspects of the translational machinery are selectively affected by environmental and cellular stress conditions that trigger ribosome stalling and collisions, which have been unresolvable until now.

CAPRIN2 RNA-binding protein contributes to balance erythroid production: Implications in the fine-tuning of proteostasis during erythropoiesis

Erythropoiesis is a process that requires tight control of gene transcription, mRNA stability, and protein synthesis and degradation. These regulatory layers adapt dynamically to developmental needs and physiological stresses, ensuring precise control of erythroid production. Ribosomopathies, such as Diamond-Blackfan anemia (DBA), are characterized by defects in ribosome function. Zooming in on erythroid precursors, ribosomopathies lead to dysregulated translation of mRNAs encoding specific and essential erythropoietic genes, including master transcription factors such as GATA1. This causes defective maturation and increased apoptosis of erythroid progenitors, and consequently, anemia. Beyond ribosomal proteins, RNA-binding proteins have been put forward as an additional and targeted checkpoint regulating cellular proteostasis. CAPRIN2, which is present in neurons and erythroid cells, is one such RNA-binding protein, involved in RNA translation regulation and its levels rise during terminal erythroid differentiation. Overexpression of CAPRIN2 in Chinese hamster ovary (CHO) cells causes reduced growth, cell cycle arrest, and apoptosis. Here, we demonstrate that GATA1 potentially regulates Caprin2 transcription, and that Caprin2 loss boosts erythroid production and maturation during gestation and adulthood, a phenomenon that is enhanced in situations of stress erythropoiesis. Our results provide new insight into the role of CAPRIN2 in erythropoiesis. We hypothesize that it regulates the translation of key mRNAs during erythropoiesis. We propose that CAPRIN2 is involved in the balance of erythroid production and that its manipulation may control erythroid production, offering a potential and promising approach to manage altered erythropoiesis.

Protection of the genome and the central exome by peripheral non-coding DNA against DNA damage in health, ageing and age-related diseases

DNA in eukaryotic genomes is under constant assault from both exogenous and endogenous sources, leading to DNA damage, which is considered a major molecular driver of ageing. Fortunately, the genome and the central exome are safeguarded against these attacks by abundant peripheral non-coding DNA. Non-coding DNA codes for small non-coding RNAs that inactivate foreign nucleic acids in the cytoplasm and physically blocks these attacks in the nucleus. Damage to non-coding DNA produced during such blockage is removed in the form of extrachromosomal circular DNA (eccDNA) through nucleic pore complexes. Consequently, non-coding DNA serves as a line of defence for the exome against DNA damage. The total amount of non-coding DNA/heterochromatin declines with age, resulting in a decrease in both physical blockage and eccDNA exclusion, and thus an increase in the accumulation of DNA damage in the nucleus during ageing and in age-related diseases. Here, we summarize recent evidence supporting a protective role of non-coding DNA in healthy and pathological states and argue that DNA damage is the proximate cause of ageing and age-related genetic diseases. Strategies aimed at strengthening the protective role of non-coding DNA/heterochromatin could potentially offer better systematic protection for the dynamic genome and the exome against diverse assaults, reduce the burden of DNA damage to the exome, and thus slow ageing, counteract age-related genetic diseases and promote a healthier life for individuals.

Specialized ribosomes: integrating new insights and current challenges

Variation in the composition of different ribosomes, termed ribosome heterogeneity, is a now well established phenomenon. However, the functional implications of this heterogeneity on the regulation of protein synthesis are only now beginning to be revealed. While there are numerous examples of heterogeneous ribosomes, there are comparatively few bona fide specialized ribosomes described. Specialization requires that compositionally distinct ribosomes, through their subtly altered structure, have a functional consequence to the translational output. Even for those examples of ribosome specialization that have been characterized, the precise mechanistic details of how changes in protein and rRNA composition enable the ribosome to regulate translation are still missing. Here, we suggest looking at the evolution of specialization across the tree of life may help reveal central principles of translation regulation. We consider functional and structural studies that have provided insight into the potential mechanisms through which ribosome heterogeneity could affect translation, including through mRNA and open reading frame selectivity, elongation dynamics and post-translational folding. Further, we highlight some of the challenges that must be addressed to show specialization and review the contribution of various models. Several studies are discussed, including recent studies that show how structural insight is starting to shed light on the molecular details of specialization. Finally, we discuss the future of ribosome specialization studies, where advances in technology will likely enable the next wave of research questions. Recent work has helped provide a more comprehensive understanding of how ribosome heterogeneity affects translational control.This article is part of the discussion meeting issue 'Ribosome diversity and its impact on protein synthesis, development and disease'.

Ribosomes: from conserved origin to functional/medical mobility and heterogeneity

Ribosomes, the molecular machines that translate the genetic code from mRNA into proteins in all living cells, are highly structurally conserved across all domains of life and hence are believed to have evolved from a structurally unified pocket. Initially perceived as uniform cellular factories for protein synthesis, currently, ribosomes have emerged as more complex entities. Structural, medical and biochemical studies, including ours, have revealed significant variability in their compositions across tissues, species, functions and developmental stages, highlighting their multifunctional potential. Moreover, the diversity of ribosomes, their components and their associated biological factors challenge the traditional perception of uniform interactions under various conditions, including stress, and expose their mobility and heterogeneity. Evidence for their functional diversity can be seen even in modifications of ribosomal genes, where minor changes may play critical roles under stress or may lead to diseases called ribosomopathies, including Diamond-Blackfan anaemia, some types of cancer and Alzheimer's disease. Thus, through in-depth structural explorations, we improve the understanding of the mechanisms regulating protein biosynthesis in response to various environmental stressors. These findings should potentially reshape the perceptions of the various ribosomal roles.This article is part of the discussion meeting issue 'Ribosome diversity and its impact on protein synthesis, development and disease'.

Impacts of ribosomal RNA sequence variation on gene expression and phenotype

Since the framing of the Central Dogma, it has been speculated that physically distinct ribosomes within cells may influence gene expression and cellular physiology. While heterogeneity in ribosome composition has been reported in bacteria, protozoans, fungi, zebrafish, mice and humans, its functional implications remain actively debated. Here, we review recent evidence demonstrating that expression of conserved variant ribosomal DNA (rDNA) alleles in bacteria, mice and humans renders their actively translating ribosome pool intrinsically heterogeneous at the level of ribosomal RNA (rRNA). In this context, we discuss reports that nutrient limitation-induced stress in Escherichia coli leads to changes in variant rRNA allele expression, programmatically altering transcription and cellular phenotype. We highlight that cells expressing ribosomes from distinct operons exhibit distinct drug sensitivities, which can be recapitulated in vitro and potentially rationalized by subtle perturbations in ribosome structure or in their dynamic properties. Finally, we discuss evidence that differential expression of variant rDNA alleles results in different populations of ribosome subtypes within mammalian tissues. These findings motivate further research into the impacts of rRNA heterogeneities on ribosomal function and predict that strategies targeting distinct ribosome subtypes may hold therapeutic potential.This article is part of the discussion meeting issue 'Ribosome diversity and its impact on protein synthesis, development and disease'.

Ribosome specialization by cancer-associated ribosomal protein mutations: progress made and open questions

Congenital mutations in ribosomal proteins (RPs) cause Diamond-Blackfan anaemia (DBA) syndrome. Whereas DBA patients suffer from anaemia and disease symptoms owing to a lack of cell proliferation (hypo-proliferation) early in life, they have a significantly elevated risk of developing cancer (a disease of hyper-proliferation) at a later age. The association between ribosome defects and cancer is further underscored by animal models in which heterozygous RP loss promotes tumourigenesis, as well as by a variety of somatic RP mutations that have been described in haematological and solid malignancies. As discussed in this article, we have gained deeper insight into molecular mechanisms by which RP mutations can be associated with hypo- followed by hyper-proliferation phenotypes. Factors such as oxidative stress and DNA damage, onco-ribosome specialization with hyper-translation of oncogenes and altered extra-ribosomal functions seem essential. However, many questions still remain and more research is needed to explore to what extent different cancer-associated RP mutations can structurally and functionally specialize ribosomes into onco-ribosomes, and what opportunities this can provide to develop innovative cancer therapies.This article is part of the discussion meeting issue 'Ribosome diversity and its impact on protein synthesis, development and disease'.

The zebrafish (Danio rerio) snoRNAome

Small nucleolar RNAs (snoRNAs) are one of the most abundant and evolutionary ancient group of functional non-coding RNAs. They were originally described as guides of post-transcriptional rRNA modifications, but emerging evidence suggests that snoRNAs fulfil an impressive variety of cellular functions. To reveal the true complexity of snoRNA-dependent functions, we need to catalogue first the complete repertoire of snoRNAs in a given cellular context. While the systematic mapping and characterization of "snoRNAomes" for some species have been described recently, this has not been done hitherto for the zebrafish (Danio rerio). Using size-fractionated RNA sequencing data from adult zebrafish tissues, we created an interactive "snoRNAome" database for this species. Our custom-designed analysis pipeline allowed us to identify with high-confidence 67 previously unannotated snoRNAs in the zebrafish genome, resulting in the most complete set of snoRNAs to date in this species. Reanalyzing multiple previously published datasets, we also provide evidence for the dynamic expression of some snoRNAs during the early stages of zebrafish development and tissue-specific expression patterns for others in adults. To facilitate further investigations into the functions of snoRNAs in zebrafish, we created a novel interactive database, snoDanio, which can be used to explore small RNA expression from transcriptomic data.

A role for the kinetochore protein, NUF2, in ribosome biogenesis

Ribosome biogenesis (RB) is an intricate and evolutionarily conserved process that takes place mainly in the nucleolus and is required for eukaryotic cells to maintain homeostasis, grow in size, and divide. Our laboratory has identified the NUF2 protein, part of the mitotic kinetochore, in a genome-wide siRNA screen for proteins required for making ribosomes in MCF10A human breast epithelial cells. After rigorous validation and using several biochemical and cell-based assays, we find a role for NUF2 in pre-rRNA transcription, the primary and rate-limiting step of RB. siRNA depletion of other components of the NUF2 kinetochore sub-complex, NDC80, SPC24, and SPC25, also reduce pre-rRNA transcription. Interestingly, essential protein components for pre-rRNA transcription, including the largest subunit of RNA polymerase I, POLR1A, are reduced upon siRNA depletion of NUF2 and its protein partners. Their reduced levels are a likely mechanism for the decrease in pre-rRNA transcription. siRNA depletion of NUF2 and NDC80 also cause increased TP53 and CDKN1A (p21) mRNA levels, which can be restored by codepletion of RPL5, indicating activation of the nucleolar stress pathway (NSP). These results reveal a new connection between proteins with a known role in mitosis to the function of the nucleolus in RB during interphase.

The 40S ribosomal subunit recycling complex modulates mitochondrial dynamics and endoplasmic reticulum - mitochondria tethering at mitochondrial fission/fusion hotspots

The 40S ribosomal subunit recycling pathway is an integral link in the cellular quality control network, occurring after translational errors have been corrected by the ribosome-associated quality control (RQC) machinery. Despite our understanding of its role, the impact of translation quality control on cellular metabolism remains poorly understood. Here, we reveal a conserved role of the 40S ribosomal subunit recycling (USP10-G3BP1) complex in regulating mitochondrial dynamics and function. The complex binds to fission-fusion proteins located at mitochondrial hotspots, regulating the functional assembly of endoplasmic reticulum-mitochondria contact sites (ERMCSs). Furthermore, it alters the activity of mTORC1/2 pathways, suggesting a link between quality control and energy fluctuations. Effective communication is essential for resolving proteostasis-related stresses. Our study illustrates that the USP10-G3BP1 complex acts as a hub that interacts with various pathways to adapt to environmental stimuli promptly. It advances our molecular understanding of RQC regulation and helps explain the pathogenesis of human proteostasis and mitochondrial dysfunction diseases.

Autonomous ribosome biogenesis in vitro

Ribosome biogenesis is pivotal in the self-replication of life. In Escherichia coli, three ribosomal RNAs and 54 ribosomal proteins are synthesized and subjected to cooperative hierarchical assembly facilitated by numerous accessory factors. Realizing ribosome biogenesis in vitro is a critical milestone for understanding the self-replication of life and creating artificial cells. Despite its importance, this goal has not yet been achieved owing to its complexity. In this study, we report the successful realization of ribosome biogenesis in vitro. Specifically, we developed a highly specific and sensitive reporter assay for the detection of nascent ribosomes. The reporter assay allowed for combinatorial and iterative exploration of reaction conditions for ribosome biogenesis, leading to the simultaneous, autonomous synthesis of both small and large subunits of ribosomes in vitro through transcription, translation, processing, and assembly in a single reaction space. Our achievement represents a crucial advancement toward revealing the fundamental principles underlying the self-replication of life and creating artificial cells.

Visualizing the modification landscape of the human 60S ribosomal subunit at close to atomic resolution

Chemical modifications of ribosomal RNAs (rRNAs) and proteins expand their topological repertoire, and together with the plethora of bound ligands, fine-tune ribosomal function. Detailed knowledge of this natural composition provides important insights into ribosome genesis and function and clarifies some aspects of ribosomopathies. The discovery of new structural properties and functional aspects of ribosomes has gone hand in hand with cryo-electron microscopy (cryo-EM) and its technological development. In line with the ability to visualize atomic details - a prerequisite for identifying chemical modifications and ligands in cryo-EM maps - in this work we present the structure of the 60S ribosomal subunit from HeLa cells at the very high global resolution of 1.78 Å. We identified 113 rRNA modifications and four protein modifications including uL2-Hisβ-ox216, which stabilizes the local structure near the peptidyl transferase centre via an extended hydrogen-bonding network. We can differentiate metal ions Mg2+ and K+, polyamines spermine, spermidine and putrescine and identify thousands of water molecules binding to the 60S subunit. Approaching atomic resolution cryo-EM has become a powerful tool to examine fine details of macromolecular structures that will expand our knowledge about translation and other biological processes in the future and assess the variability of the chemical space due to differences between species/tissues or varying physicochemical environment.

Insulin signaling regulates R2 retrotransposon expression to orchestrate transgenerational rDNA copy number maintenance

Preserving a large number of essential yet highly unstable ribosomal DNA (rDNA) repeats is critical for the germline to perpetuate the genome through generations. Spontaneous rDNA loss must be countered by rDNA copy number (CN) expansion. Germline rDNA CN expansion is best understood in Drosophila melanogaster, which relies on unequal sister chromatid exchange (USCE) initiated by DNA breaks at rDNA. The rDNA-specific retrotransposon R2 responsible for USCE-inducing DNA breaks is typically expressed only when rDNA CN is low to minimize the danger of DNA breaks; however, the underlying mechanism of R2 regulation remains unclear. Here we identify the insulin receptor (InR) as a major repressor of R2 expression, limiting unnecessary R2 activity. Through single-cell RNA sequencing, we find that male germline stem cells (GSCs), the major cell type that undergoes rDNA CN expansion, have reduced InR expression when rDNA CN is low. Reduced InR activity in turn leads to R2 expression and CN expansion. We further find that dietary manipulation alters R2 expression and rDNA CN expansion activity. This work reveals that the insulin pathway integrates rDNA CN surveying with environmental sensing, revealing a potential mechanism by which diet exerts heritable changes to genomic content.

Research Progress of Ribosomal Proteins in Reproductive Development

Ribosomal proteins constitute the principal components of ribosomes, and their functions span a wide spectrum. Recent investigations have unveiled their involvement in oocyte and embryo development, playing a pivotal role in reproductive development. Numerous pieces of evidence indicate that ribosomal proteins participate in the regulation of various cellular activities, including nucleolar stress, oxidative stress, cell proliferation and autophagy. Despite these findings, the precise mechanisms through which ribosomal proteins influence reproductive development via these cellular activities remain elusive. Therefore, elucidating the mechanisms of action is essential for a comprehensive understanding of the role and function of ribosomal proteins in reproductive development. This paper systematically reviews the progress in research on nucleolar stress, oxidative stress, cell proliferation and autophagy concerning ribosomal proteins during reproductive development. Furthermore, we explore the potential of ribosomal proteins as diagnostic markers for various diseases. Additionally, we propose the development of drugs and therapies targeting ribosomal proteins, underscoring the potential for novel medical interventions in the context of reproductive health.

The Interplay Between the MYC Oncogene and Ribosomal Proteins in Osteosarcoma Onset and Progression: Potential Mechanisms and Indication of Candidate Therapeutic Targets

High-grade osteosarcoma (OS) is the most common primary bone tumor mainly affecting children and young adults. First-line treatment consists of neo-adjuvant chemotherapy with doxorubicin, cisplatin, and methotrexate and surgery. The mean long-term survival rate for localized disease at diagnosis is 65-70%, dropping down to 20% when metastases are present at diagnosis. Therefore, curing OS is a clinical challenge, particularly for patients that do not respond to standard treatments. MYC has frequently been reported to be involved in the pathogenesis of OS and its high expression may be associated with drug resistance and patients' worse prognosis. Moreover, MYC is a master regulator of ribosomal proteins (RPs) synthesis and ribosome biogenesis (RiBi), which is often up-regulated in human tumors. In recent years, RPs have been recognized not only for their traditional role in ribosome assembly but also for their extra-ribosomal functions, many of which are linked to the onset and progression of cancer. In this review we focus on the role and possible interplay of MYC and RPs expression in association with drug resistance and worse prognosis in OS and discuss therapeutic options that target de-regulated MYC, RiBi, or RPs, which are already clinically available or under evaluation in clinical trials.

WDR68 stimulates cellular proliferation via activating ribosome biogenesis in 293T cells

WDR68, a conserved WD40 repeat-containing protein, interacts with E1A and is involved in the E1A-induced cell proliferation and oncogenic transformation, but the intrinsic molecular mechanisms of this process remain to be elucidated. Here, we demonstrate that WDR68 promotes the proliferation of 293T cells by interacting with a series of ribosome biogenesis-regulating proteins. Gene Set Enrichment Analysis (GSEA) of RNA-seq data also revealed that the ribosome biogenesis-associated gene signatures could be the most significantly enriched in the WDR68 expression groups. In accordance, 293T cells are more sensitive to the ribosome biogenesis inhibitors than 293 cells. Taken together, our results indicated that WDR68 could promote cell proliferation through the activation of ribosome biogenesis in the 293T cell context. This provides new insights into the understanding of the function of WDR68 and the molecular characterisation of 293T tool cells.

Decoding ribosome complexity: role of ribosomal proteins in cancer and disease

The ribosome is a remarkably complex machinery, at the interface with diverse cellular functions and processes. Evolutionarily conserved, yet intricately regulated, ribosomes play pivotal roles in decoding genetic information into the synthesis of proteins and in the generation of biomass critical for cellular physiological functions. Recent insights have revealed the existence of ribosome heterogeneity at multiple levels. Such heterogeneity extends to cancer, where aberrant ribosome biogenesis and function contribute to oncogenesis. This led to the emergence of the concept of 'onco-ribosomes', specific ribosomal variants with altered structural dynamics, contributing to cancer initiation and progression. Ribosomal proteins (RPs) are involved in many of these alterations, acting as critical factors for the translational reprogramming of cancer cells. In this review article, we highlight the roles of RPs in ribosome biogenesis, how mutations in RPs and their paralogues reshape the translational landscape, driving clonal evolution and therapeutic resistance. Furthermore, we present recent evidence providing new insights into post-translational modifications of RPs, such as ubiquitylation, UFMylation and phosphorylation, and how they regulate ribosome recycling, translational fidelity and cellular stress responses. Understanding the intricate interplay between ribosome complexity, heterogeneity and RP-mediated regulatory mechanisms in pathology offers profound insights into cancer biology and unveils novel therapeutic avenues targeting the translational machinery in cancer.

The Beak of Eukaryotic Ribosomes: Life, Work and Miracles

Ribosomes are not totally globular machines. Instead, they comprise prominent structural protrusions and a myriad of tentacle-like projections, which are frequently made up of ribosomal RNA expansion segments and N- or C-terminal extensions of ribosomal proteins. This is more evident in higher eukaryotic ribosomes. One of the most characteristic protrusions, present in small ribosomal subunits in all three domains of life, is the so-called beak, which is relevant for the function and regulation of the ribosome's activities. During evolution, the beak has transitioned from an all ribosomal RNA structure (helix h33 in 16S rRNA) in bacteria, to an arrangement formed by three ribosomal proteins, eS10, eS12 and eS31, and a smaller h33 ribosomal RNA in eukaryotes. In this review, we describe the different structural and functional properties of the eukaryotic beak. We discuss the state-of-the-art concerning its composition and functional significance, including other processes apparently not related to translation, and the dynamics of its assembly in yeast and human cells. Moreover, we outline the current view about the relevance of the beak's components in human diseases, especially in ribosomopathies and cancer.

The Paradox of Ribosomal Insufficiency Coupled with Increased Cancer: Shifting the Perspective from the Cancer Cell to the Microenvironment

Ribosomopathies are defined as inherited diseases in which ribosomal factors are mutated. In general, they present multiorgan symptoms. In spite of the fact that in cellular models, ribosomal insufficiency leads to a reduced rate of oncogenic transformation, patients affected by ribosomopathies present a paradoxical increase in cancer incidence. Several hypotheses that explain this paradox have been formulated, mostly on the assumption that altered ribosomes in a stem cell induce compensatory changes that lead to a cancer cell. For instance, the lack of a specific ribosomal protein can lead to the generation of an abnormal ribosome, an oncoribosome, that itself leads to altered translation and increased tumorigenesis. Alternatively, the presence of ribosomal stress may induce compensatory proliferation that in turns selects the loss of tumor suppressors such as p53. However, modern views on cancer have shifted the focus from the cancer cell to the tumor microenvironment. In particular, it is evident that human lymphocytes are able to eliminate mutant cells and contribute to the maintenance of cancer-free tissues. Indeed, many tumors develop in conditions of reduced immune surveillance. In this review, we summarize the current evidence and attempt to explain cancer and ribosomopathies from the perspective of the microenvironment.

Ribosomal DNA copy number variation associates with hematological profiles and renal function in the UK Biobank

The phenotypic impact of genetic variation of repetitive features in the human genome is currently understudied. One such feature is the multi-copy 47S ribosomal DNA (rDNA) that codes for rRNA components of the ribosome. Here, we present an analysis of rDNA copy number (CN) variation in the UK Biobank (UKB). From the first release of UKB whole-genome sequencing (WGS) data, a discovery analysis in White British individuals reveals that rDNA CN associates with altered counts of specific blood cell subtypes, such as neutrophils, and with the estimated glomerular filtration rate, a marker of kidney function. Similar trends are observed in other ancestries. A range of analyses argue against reverse causality or common confounder effects, and all core results replicate in the second UKB WGS release. Our work demonstrates that rDNA CN is a genetic influence on trait variance in humans.

The impact of ribosome biogenesis in cancer: from proliferation to metastasis

The dysregulation of ribosome biogenesis is a hallmark of cancer, facilitating the adaptation to altered translational demands essential for various aspects of tumor progression. This review explores the intricate interplay between ribosome biogenesis and cancer development, highlighting dynamic regulation orchestrated by key oncogenic signaling pathways. Recent studies reveal the multifaceted roles of ribosomes, extending beyond protein factories to include regulatory functions in mRNA translation. Dysregulated ribosome biogenesis not only hampers precise control of global protein production and proliferation but also influences processes such as the maintenance of stem cell-like properties and epithelial-mesenchymal transition, contributing to cancer progression. Interference with ribosome biogenesis, notably through RNA Pol I inhibition, elicits a stress response marked by nucleolar integrity loss, and subsequent G1-cell cycle arrest or cell death. These findings suggest that cancer cells may rely on heightened RNA Pol I transcription, rendering ribosomal RNA synthesis a potential therapeutic vulnerability. The review further explores targeting ribosome biogenesis vulnerabilities as a promising strategy to disrupt global ribosome production, presenting therapeutic opportunities for cancer treatment.

Identification of genes related to ribosomal proteins in colorectal cancer: exploring their potential as biomarkers, prognostic indicators, and therapeutic targets

BACKGROUND

Colorectal cancer (CRC) ranks as the third most commonly diagnosed cancer in both females and males, underscoring the need for the identification of effective biomarkers.

METHODS AND RESULTS

We assessed the expression levels of ribosomal proteins (RPs) at both mRNA and protein levels. Subsequently, leveraging the STRING database, we constructed a protein-protein interaction network and identified hub genes. The co-expression network of differentially expressed genes associated with CRC and their target hub RPs was constructed using the weighted gene co-expression network analysis algorithm. Gene ontology and molecular signatures database were conducted to gain insights into the biological roles of genes associated with the identified module. To confirm the results, the expression level of the candidate genes in the CRC samples compared to the adjacent healthy was evaluated by the RT-qPCR method. Our findings indicated that the genes related to RPs were predominantly enriched in biological processes associated with Myc Targets, Oxidative Phosphorylation, and cell proliferation. Also, results demonstrated that elevated levels of GRWD1, MCM5, IMP4, and RABEPK that related to RPs were associated with poor prognostic outcomes for CRC patients. Notably, IMP4 and RABEPK exhibited higher diagnostic value. Moreover, the expression of IMP4 and RABEPK showed a significant association with drug resistance using cancer cell line encyclopedia and genomics of drug sensitivity in cancer databases. Also, the results showed that the expression level of IMP4 and RABEPK in cancerous samples was significantly higher compared to the adjacent healthy ones.

CONCLUSION

The general results of this study have shown that many genes related to RPs are increased in cancer and could be associated with the death rate of patients. We also highlighted the therapeutic and prognostic potentials of RPs genes in CRC.

Mechanisms of Translation-coupled Quality Control

Stalling of ribosomes engaged in protein synthesis can lead to significant defects in the function of newly synthesized proteins and thereby impair protein homeostasis. Consequently, partially synthesized polypeptides resulting from translation stalling are recognized and eliminated by several quality control mechanisms. First, if translation elongation reactions are halted prematurely, a quality control mechanism called ribosome-associated quality control (RQC) initiates the ubiquitination of the nascent polypeptide chain and subsequent proteasomal degradation. Additionally, when ribosomes with defective codon recognition or peptide-bond formation stall during translation, a quality control mechanism known as non-functional ribosomal RNA decay (NRD) leads to the degradation of malfunctioning ribosomes. In both of these quality control mechanisms, E3 ubiquitin ligases selectively recognize ribosomes in distinct translation-stalling states and ubiquitinate specific ribosomal proteins. Significant efforts have been devoted to characterize E3 ubiquitin ligase sensing of ribosome 'collision' or 'stalling' and subsequent ribosome is rescued. This article provides an overview of our current understanding of the molecular mechanisms and physiological functions of ribosome dynamics control and quality control of abnormal translation.

Subverting the Canon: Novel Cancer-Promoting Functions and Mechanisms for snoRNAs

Small nucleolar RNAs (snoRNAs) constitute a class of intron-derived non-coding RNAs ranging from 60 to 300 nucleotides. Canonically localized in the nucleolus, snoRNAs play a pivotal role in RNA modifications and pre-ribosomal RNA processing. Based on the types of modifications they involve, such as methylation and pseudouridylation, they are classified into two main families-box C/D and H/ACA snoRNAs. Recent investigations have revealed the unconventional synthesis and biogenesis strategies of snoRNAs, indicating their more profound roles in pathogenesis than previously envisioned. This review consolidates recent discoveries surrounding snoRNAs and provides insights into their mechanistic roles in cancer. It explores the intricate interactions of snoRNAs within signaling pathways and speculates on potential therapeutic solutions emerging from snoRNA research. In addition, it presents recent findings on the long non-coding small nucleolar RNA host gene (lncSNHG), a subset of long non-coding RNAs (lncRNAs), which are the transcripts of parental SNHGs that generate snoRNA. The nucleolus, the functional epicenter of snoRNAs, is also discussed. Through a deconstruction of the pathways driving snoRNA-induced oncogenesis, this review aims to serve as a roadmap to guide future research in the nuanced field of snoRNA-cancer interactions and inspire potential snoRNA-related cancer therapies.

A common cellular response to broad splicing perturbations is characterized by metabolic transcript downregulation driven by the Mdm2-p53 axis

Disruptions in core cellular processes elicit stress responses that drive cell-state changes leading to organismal phenotypes. Perturbations in the splicing machinery cause widespread mis-splicing, resulting in p53-dependent cell-state changes that give rise to cell-type-specific phenotypes and disease. However, a unified framework for how cells respond to splicing perturbations, and how this response manifests itself in nuanced disease phenotypes, has yet to be established. Here, we show that a p53-stabilizing Mdm2 alternative splicing event and the resulting widespread downregulation of metabolic transcripts are common events that arise in response to various splicing perturbations in both cellular and organismal models. Together, our results classify a common cellular response to splicing perturbations, put forth a new mechanism behind the cell-type-specific phenotypes that arise when splicing is broadly disrupted, and lend insight into the pleiotropic nature of the effects of p53 stabilization in disease.

Mutations of ribosomal protein genes induce overexpression of catalase in Saccharomyces cerevisiae

Ribosome assembly defects result in ribosomopathies, primarily caused by inadequate protein synthesis and induced oxidative stress. This study aimed to investigate the link between deleting one ribosomal protein gene (RPG) paralog and oxidative stress response. Our results indicated that RPG mutants exhibited higher oxidant sensitivity than the wild type (WT). The concentrations of H2O2 were increased in the RPG mutants. Catalase and superoxide dismutase (SOD) activities were generally higher at the stationary phase, with catalase showing particularly elevated activity in the RPG mutants. While both catalase genes, CTT1 and CTA1, consistently exhibited higher transcription in RPG mutants, Ctt1 primarily contributed to the increased catalase activity. Stress-response transcription factors Msn2, Msn4, and Hog1 played a role in regulating these processes. Previous studies have demonstrated that H2O2 can cleave 25S rRNA via the Fenton reaction, enhancing ribosomes' ability to translate mRNAs associated with oxidative stress-related genes. The cleavage of 25S rRNA was consistently more pronounced, and the translation efficiency of CTT1 and CTA1 mRNAs was altered in RPG mutants. Our results provide evidence that the mutations in RPGs increase H2O2 levels in vivo and elevate catalase expression through both transcriptional and translational controls.

BRIX1 promotes ribosome synthesis and enhances glycolysis by selected translation of GLUT1 in colorectal cancer

BACKGROUND

Ribosome biogenesis protein BRX1 homolog (BRIX1) is critically required for the synthesis of the 60S ribosome subunit. However, the role and mechanism of BRIX1 in colorectal cancer (CRC) remain unclear.

METHODS

Kyoto Encyclopedia of Gene and Genome pathway and Gene Ontology analyses were used for bioinformatics analysis. The rRNA levels were detected in CRC tissues and cells. Nascent RNA synthesis was detected via cellular immunofluorescence. The correlation was analyzed between patient Positron Emission Tomography-Computed Tomography (PET-CT) values and their BRIX1 expression. The extracellular acidification rate (ECAR) and oxygen consumption rate were determined via live metabolic analyses. Polysome fractions were collected for BRIX1 mRNA used in translation. The orthotopic model and Cell Counting Kit-8 (CCK8) assay were used to assess BRIX1 function in CRC.

RESULTS

BRIX1 is a core protein involved in ribosome-related pathway changes in CRC. Gene Ontology analysis showed that BRIX1 was primarily enriched in ribosome assembly and ribosome biogenesis pathways. In fresh CRC tissue, rRNA levels (5S, 5.8S, 18S and 28S) were higher in the BRIX1 high-expression group than in the BRIX1 low-expression group. Similarly, BRIX1 knockdown significantly decreased rRNA levels for 5S, 5.8S, 18S and 28S in CRC cells, whereas overexpression of BRIX1 significantly increased these levels. In addition, BRIX1 knockdown inhibited nascent RNA synthesis in CRC cells. In clinical data analysis, BRIX1 expression was related to the glucose uptake in PET-CT. BRIX1 knockdown significantly decreased the ECAR value, glucose uptake and lactic acid production in CRC cells, whereas BRIX1 overexpression significantly increased these. Furthermore, BRIX1 knockdown significantly decreased the protein expression of GLUT1, whereas BRIX1 overexpression significantly increased this; however, expression of BRIX1 mRNA was unaffected in either case. Blocking glycolysis by si-GLUT1 or galactose reversed BRIX1 promotion of glycolysis and cell proliferation in CRC cells.

NOC1 is a direct MYC target, and its protein interactome dissects its activity in controlling nucleolar function

The nucleolus is a subnuclear compartment critical in ribosome biogenesis and cellular stress responses. These mechanisms are governed by a complex interplay of proteins, including NOC1, a member of the NOC family of nucleolar proteins responsible for controlling rRNA processing and ribosomal maturation. This study reveals a novel relationship between NOC1 and MYC transcription factor, known for its crucial role in controlling ribosomal biogenesis, cell growth, and proliferation. Here, we demonstrate that NOC1 functions as a direct target of MYC, as it is transcriptionally induced through a functional MYC-binding E-box sequence in the NOC1 promoter region. Furthermore, protein interactome analysis reveals that NOC1-complex includes the nucleolar proteins NOC2 and NOC3 and other nucleolar components such as Nucleostemin1 Ns1 transporters of ribosomal subunits and components involved in rRNA processing and maturation. In response to MYC, NOC1 expression and localization within the nucleolus significantly increase, suggesting a direct functional link between MYC activity and NOC1 function. Notably, NOC1 over-expression leads to the formation of large nuclear granules and enlarged nucleoli, which co-localize with nucleolar fibrillarin and Ns1. Additionally, we demonstrate that NOC1 expression is necessary for Ns1 nucleolar localization, suggesting a role for NOC1 in maintaining nucleolar structure. Finally, the co-expression of NOC1 and MYC enhances nucleolus size and maintains their co-localization, outlining another aspect of the cooperation between NOC1 and MYC in nucleolar dynamics. This study also reveals an enrichment with NOC1 with few proteins involved in RNA processing, modification, and splicing. Moreover, proteins such as Ythdc1, Flacc, and splenito are known to mediate N6-methyladenosine (m6A) methylation of mRNAs in nuclear export, revealing NOC1's potential involvement in coordinating RNA splicing and nuclear mRNA export. In summary, we uncovered novel roles for NOC1 in nucleolar homeostasis and established its direct connection with MYC in the network governing nucleolar structure and function. These findings also highlight NOC1's interaction with proteins relevant to specific RNA functions, suggesting a broader role in addition to its control of nucleolar homeostasis and providing new insight that can be further investigated.

Downregulation of ribosomal RNA (rRNA) genes in human head and neck squamous cell carcinoma (HNSCC) cells correlates with rDNA promoter hypermethylation

Eukaryotes carry hundreds of ribosomal RNA (rRNA) genes as tandem arrays, which generate rRNA for protein synthesis. Humans carry ∼ 400 rRNA gene copies and their expression is epigenetically regulated. Dysregulation of rRNA synthesis and ribosome biogenesis are characteristic features of cancers. Targeting aberrant rRNA expression for cancer therapy is being explored. Head and neck squamous cell carcinoma (HNSCC) is among the most prevalent cancers globally. Using quantitative PCR and bisulfite sequencing, we show that rRNA genes are downregulated and their promoters are hypermethylated in HNSCC cell lines. These findings may have relevance for prognosis and diagnosis of HNSCC.

The Link of mRNA and rRNA Transcription by PUF60/FIR through TFIIH/P62 as a Novel Therapeutic Target for Cancer

The interaction between mRNA and ribosomal RNA (rRNA) transcription in cancer remains unclear. RNAP I and II possess a common N-terminal tail (NTT), RNA polymerase subunit RPB6, which interacts with P62 of transcription factor (TF) IIH, and is a common target for the link between mRNA and rRNA transcription. The mRNAs and rRNAs affected by FUBP1-interacting repressor (FIR) were assessed via RNA sequencing and qRT-PCR analysis. An FIR, a c-myc transcriptional repressor, and its splicing form FIRΔexon2 were examined to interact with P62. Protein interaction was investigated via isothermal titration calorimetry measurements. FIR was found to contain a highly conserved region homologous to RPB6 that interacts with P62. FIRΔexon2 competed with FIR for P62 binding and coactivated transcription of mRNAs and rRNAs. Low-molecular-weight chemical compounds that bind to FIR and FIRΔexon2 were screened for cancer treatment. A low-molecular-weight chemical, BK697, which interacts with FIRΔexon2, inhibited tumor cell growth with rRNA suppression. In this study, a novel coactivation pathway for cancer-related mRNA and rRNA transcription through TFIIH/P62 by FIRΔexon2 was proposed. Direct evidence in X-ray crystallography is required in further studies to show the conformational difference between FIR and FIRΔexon2 that affects the P62-RBP6 interaction.

A highly efficient human cell-free translation system

Cell-free protein synthesis (CFPS) systems enable easy in vitro expression of proteins with many scientific, industrial, and therapeutic applications. Here we present an optimized, highly efficient human cell-free translation system that bypasses many limitations of currently used in vitro systems. This CFPS system is based on extracts from human HEK293T cells engineered to endogenously express GADD34 and K3L proteins, which suppress phosphorylation of translation initiation factor eIF2α. Overexpression of GADD34 and K3L proteins in human cells before cell lysate preparation significantly simplifies lysate preparation. We find that expression of the GADD34 and K3L accessory proteins before cell lysis maintains low levels of phosphorylation of eIF2α in the extracts. During in vitro translation reactions, eIF2α phosphorylation increases moderately in a GCN2-dependent fashion that can be inhibited by GCN2 kinase inhibitors. This new CFPS system should be useful for exploring human translation mechanisms in more physiological conditions outside the cell.

Ribosomal DNA Copy Number Variation is Coupled with DNA Methylation Changes at the 45S rDNA Locus

The human ribosomal DNA (rDNA) copy number (CN) has been challenging to analyse, and its sequence has been excluded from reference genomes due to its highly repetitive nature. The 45S rDNA locus encodes essential components of the cell, nevertheless rDNA displays high inter-individual CN variation that could influence human health and disease. CN alterations in rDNA have been hypothesized as a possible factor in autism spectrum disorders (ASD) and were shown to be altered in Schizophrenia patients. We tested whether whole-genome bisulphite sequencing can be used to simultaneously quantify rDNA CN and measure DNA methylation at the 45S rDNA locus. Using this approach, we observed high inter-individual variation in rDNA CN, and limited intra-individual copy differences in several post-mortem tissues. Furthermore, we did not observe any significant alterations in rDNA CN or DNA methylation in Autism Spectrum Disorder (ASD) brains in 16 ASD vs 11 control samples. Similarly, no difference was detected when comparing neurons form 28 Schizophrenia (Scz) patients vs 25 controls or oligodendrocytes from 22 Scz samples vs 20 controls. However, our analysis revealed a strong positive correlation between CN and DNA methylation at the 45S rDNA locus in multiple tissues. This was observed in brain and confirmed in small intestine, adipose tissue, and gastric tissue. This should shed light on a possible dosage compensation mechanism that silences additional rDNA copies to ensure homoeostatic regulation of ribosome biogenesis.

Clinical, genetic and structural delineation of RPL13-related spondyloepimetaphyseal dysplasia suggest extra-ribosomal functions of eL13

Spondyloepimetaphyseal dysplasia with severe short stature, RPL13-related (SEMD-RPL13), MIM#618728), is a rare autosomal dominant disorder characterized by short stature and skeletal changes such as mild spondylar and epimetaphyseal dysplasia affecting primarily the lower limbs. The genetic cause was first reported in 2019 by Le Caignec et al., and six disease-causing variants in the gene coding for a ribosomal protein, RPL13 (NM_000977.3) have been identified to date. This study presents clinical and radiographic data from 12 affected individuals aged 2-64 years from seven unrelated families, showing highly variable manifestations. The affected individuals showed a range from mild to severe short stature, retaining the same radiographic pattern of spondylar- and epi-metaphyseal dysplasia, but with varying severity of the hip and knee deformities. Two new missense variants, c.548 G>A, p.(Arg183His) and c.569 G>T, p.(Arg190Leu), and a previously known splice variant c.477+1G>A were identified, confirming mutational clustering in a highly specific RNA binding motif. Structural analysis and interpretation of the variants' impact on the protein suggests that disruption of extra-ribosomal functions of the protein through binding of mRNA may play a role in the skeletal phenotype of SEMD-RPL13. In addition, we present gonadal and somatic mosaicism for the condition.

A single pseudouridine on rRNA regulates ribosome structure and function in the mammalian parasite Trypanosoma brucei

Trypanosomes are protozoan parasites that cycle between insect and mammalian hosts and are the causative agent of sleeping sickness. Here, we describe the changes of pseudouridine (Ψ) modification on rRNA in the two life stages of the parasite using four different genome-wide approaches. CRISPR-Cas9 knock-outs of all four snoRNAs guiding Ψ on helix 69 (H69) of the large rRNA subunit were lethal. A single knock-out of a snoRNA guiding Ψ530 on H69 altered the composition of the 80S monosome. These changes specifically affected the translation of only a subset of proteins. This study correlates a single site Ψ modification with changes in ribosomal protein stoichiometry, supported by a high-resolution cryo-EM structure. We propose that alteration in rRNA modifications could generate ribosomes preferentially translating state-beneficial proteins.

The role of dysregulated mRNA translation machinery in cancer pathogenesis and therapeutic value of ribosome-inactivating proteins

Dysregulated protein synthesis is a hallmark of tumors. mRNA translation reprogramming contributes to tumorigenesis, which is fueled by abnormalities in ribosome formation, tRNA abundance and modification, and translation factors. Not only malignant cells but also stromal cells within tumor microenvironment can undergo transformation toward tumorigenic phenotypes during translational reprogramming. Ribosome-inactivating proteins (RIPs) have garnered interests for their ability to selectively inhibit protein synthesis and suppress tumor growth. This review summarizes the role of dysregulated translation machinery in tumor development and explores the potential of RIPs in cancer treatment.

Microfluidics-free single-cell genomics with templated emulsification

Current single-cell RNA-sequencing approaches have limitations that stem from the microfluidic devices or fluid handling steps required for sample processing. We develop a method that does not require specialized microfluidic devices, expertise or hardware. Our approach is based on particle-templated emulsification, which allows single-cell encapsulation and barcoding of cDNA in uniform droplet emulsions with only a vortexer. Particle-templated instant partition sequencing (PIP-seq) accommodates a wide range of emulsification formats, including microwell plates and large-volume conical tubes, enabling thousands of samples or millions of cells to be processed in minutes. We demonstrate that PIP-seq produces high-purity transcriptomes in mouse-human mixing studies, is compatible with multiomics measurements and can accurately characterize cell types in human breast tissue compared to a commercial microfluidic platform. Single-cell transcriptional profiling of mixed phenotype acute leukemia using PIP-seq reveals the emergence of heterogeneity within chemotherapy-resistant cell subsets that were hidden by standard immunophenotyping. PIP-seq is a simple, flexible and scalable next-generation workflow that extends single-cell sequencing to new applications.

A single-cell transcriptomic atlas characterizes age-related changes of murine cranial stem cell niches

The craniofacial bones provide structural support for the skull and accommodate the vulnerable brain tissue with a protective cavity. The bone tissue undergoes constant turnover, which relies on skeletal stem cells (SSCs) and/or mesenchymal stem cells (MSCs) and their niches. SSCs/MSCs and their perivascular niche within the bone marrow are well characterized in long bones. As for cranial bones, besides bone marrow, the suture mesenchyme has been identified as a unique niche for SSCs/MSCs of craniofacial bones. However, a comprehensive study of the two different cranial stem cell niches at single-cell resolution is still lacking. In addition, during the progression of aging, age-associated changes in cranial stem cell niches and resident cells remain uncovered. In this study, we investigated age-related changes in cranial stem cell niches via single-cell RNA sequencing (scRNA-seq). The transcriptomic profiles and cellular compositions have been delineated, indicating alterations of the cranial bone marrow microenvironment influenced by inflammaging. Moreover, we identified a senescent mesenchymal cell subcluster and several age-related immune cell subclusters by reclustering and pseudotime trajectory analysis, which might be closely linked to inflammaging. Finally, differentially expressed genes (DEGs) and cell-cell communications were analyzed during aging, revealing potential regulatory factors. Overall, this work highlights the age-related changes in cranial stem cell niches, which deepens the current understanding of cranial bone and suture biology and may provide therapeutic targets for antiaging and regenerative medicine.

Regulation and function of R-loops at repetitive elements

R-loops are atypical, three-stranded nucleic acid structures that contain a stretch of RNA:DNA hybrids and an unpaired, single stranded DNA loop. R-loops are physiological relevant and can act as regulators of gene expression, chromatin structure, DNA damage repair and DNA replication. However, unscheduled and persistent R-loops are mutagenic and can mediate replication-transcription conflicts, leading to DNA damage and genome instability if left unchecked. Detailed transcriptome analysis unveiled that 85% of the human genome, including repetitive regions, hold transcriptional activity. This anticipates that R-loops management plays a central role for the regulation and integrity of genomes. This function is expected to have a particular relevance for repetitive sequences that make up to 75% of the human genome. Here, we review the impact of R-loops on the function and stability of repetitive regions such as centromeres, telomeres, rDNA arrays, transposable elements and triplet repeat expansions and discuss their relevance for associated pathological conditions.

Telomere biology and ribosome biogenesis: structural and functional interconnections

Telomeres are nucleoprotein structures that play a pivotal role in the protection and maintenance of eukaryotic chromosomes. Telomeres and the enzyme telomerase, which replenishes telomeric DNA lost during replication, are important factors necessary to ensure continued cell proliferation. Cell proliferation is also dependent on proper and efficient protein synthesis, which is carried out by ribosomes. Mutations in genes involved in either ribosome biogenesis or telomere biology result in cellular abnormalities and can cause human genetic diseases, defined as ribosomopathies and telomeropathies, respectively. Interestingly, recent discoveries indicate that many of the ribosome assembly and rRNA maturation factors have additional noncanonical functions in telomere biology. Similarly, several key proteins and enzymes involved in telomere biology, including telomerase, have unexpected roles in rRNA transcription and maturation. These observations point to an intriguing cross-talk mechanism potentially explaining the multiple pleiotropic symptoms of mutations in many causal genes identified in various telomeropathy and ribosomopathy diseases. In this review, we provide a brief summary of eukaryotic telomere and rDNA loci structures, highlight several universal features of rRNA and telomerase biogenesis, evaluate intriguing interconnections between telomere biology and ribosome assembly, and conclude with an assessment of overlapping features of human diseases of telomeropathies and ribosomopathies.

Fetal anemia and elevated hepcidin in a mouse model of fetal alcohol spectrum disorder

INTRODUCTION

Prenatal alcohol exposure (PAE) impairs offspring growth and cognition, and this is worsened by concurrent iron deficiency. Alcohol disrupts fetal iron metabolism and produces functional iron deficiency, even when maternal iron status is adequate. We used a mouse model of moderate PAE to investigate the mechanisms underlying this dysregulated iron status.

METHODS

C57BL/6J female mice received 3 g/kg alcohol daily from embryonic day (E) 8.5-17.5 and were assessed at E17.5.

RESULTS

Alcohol reduced fetal hemoglobin, hematocrit, and red blood cell counts, despite elevated erythropoietin production. Alcohol suppressed maternal hepcidin expression and the upstream iron-sensing BMP/SMAD pathway, consistent with its effects in the nonpregnant state. In contrast, alcohol elevated fetal hepcidin, although this was not accompanied by an upregulation of the BMP/SMAD or proinflammatory IL-6/STAT3 pathways. Fetal expression of hepatic genes contributing to hemoglobin synthesis and iron metabolism were unaffected by alcohol, whereas those affecting ribosome biogenesis were suppressed, suggesting a novel candidate effector for this fetal anemia.

CONCLUSION

These data confirm and extend prior observations that PAE disrupts maternal and fetal iron metabolism and impairs the fetus's ability to regulate iron status. We propose this dysregulation increases gestational iron needs and represents a conserved response to PAE.

IMPACT

Prenatal alcohol exposure causes a functional iron deficiency in a model that also impairs cognition in later life. Prenatal alcohol exposure causes fetal anemia. This fetal anemia is accompanied by elevated hepcidin and erythropoietin. Findings are consistent with prior observations that prenatal alcohol exposure increases maternal-fetal iron requirements during pregnancy.

Principles of human pre-60S biogenesis

During the early stages of human large ribosomal subunit (60S) biogenesis, an ensemble of assembly factors establishes and fine-tunes the essential RNA functional centers of pre-60S particles by an unknown mechanism. Here, we report a series of cryo-electron microscopy structures of human nucleolar and nuclear pre-60S assembly intermediates at resolutions of 2.5 to 3.2 angstroms. These structures show how protein interaction hubs tether assembly factor complexes to nucleolar particles and how guanosine triphosphatases and adenosine triphosphatase couple irreversible nucleotide hydrolysis steps to the installation of functional centers. Nuclear stages highlight how a conserved RNA-processing complex, the rixosome, couples large-scale RNA conformational changes with pre-ribosomal RNA processing by the RNA degradation machinery. Our ensemble of human pre-60S particles provides a rich foundation with which to elucidate the molecular principles of ribosome formation.

Inhibition of MYC translation through targeting of the newly identified PHB-eIF4F complex as a therapeutic strategy in CLL

Dysregulation of messenger RNA (mRNA) translation, including preferential translation of mRNA with complex 5' untranslated regions such as the MYC oncogene, is recognized as an important mechanism in cancer. Here, we show that both human and murine chronic lymphocytic leukemia (CLL) cells display a high translation rate, which is inhibited by the synthetic flavagline FL3, a prohibitin (PHB)-binding drug. A multiomics analysis performed in samples from patients with CLL and cell lines treated with FL3 revealed the decreased translation of the MYC oncogene and of proteins involved in cell cycle and metabolism. Furthermore, inhibiting translation induced a proliferation arrest and a rewiring of MYC-driven metabolism. Interestingly, contrary to other models, the RAS-RAF-(PHBs)-MAPK pathway is neither impaired by FL3 nor implicated in translation regulation in CLL cells. Here, we rather show that PHBs are directly associated with the eukaryotic initiation factor (eIF)4F translation complex and are targeted by FL3. Knockdown of PHBs resembled FL3 treatment. Importantly, inhibition of translation controlled CLL development in vivo, either alone or combined with immunotherapy. Finally, high expression of translation initiation-related genes and PHBs genes correlated with poor survival and unfavorable clinical parameters in patients with CLL. Overall, we demonstrated that translation inhibition is a valuable strategy to control CLL development by blocking the translation of several oncogenic pathways including MYC. We also unraveled a new and direct role of PHBs in translation initiation, thus creating new therapeutic opportunities for patients with CLL.

Human PBMC scRNA-seq-based aging clocks reveal ribosome to inflammation balance as a single-cell aging hallmark and super longevity

Quantifying aging rate is important for evaluating age-associated decline and mortality. A blood single-cell RNA sequencing dataset for seven supercentenarians (SCs) was recently generated. Here, we generate a reference 28-sample aging cohort to compute a single-cell level aging clock and to determine the biological age of SCs. Our clock model placed the SCs at a blood biological age to between 80.43 and 102.67 years. Compared to the model-expected aging trajectory, SCs display increased naive CD8⁺ T cells, decreased cytotoxic CD8⁺ T cells, memory CD4⁺ T cells, and megakaryocytes. As the most prominent molecular hallmarks at the single-cell level, SCs contain more cells and cell types with high ribosome level, which is associated with and, according to Bayesian network inference, contributes to a low inflammation state and slow aging of SCs. Inhibiting ribosomal activity or translation in monocytes validates such translation against inflammation balance revealed by our single-cell aging clock.

The multi-functional Smc5/6 complex in genome protection and disease

Structural maintenance of chromosomes (SMC) complexes are ubiquitous genome regulators with a wide range of functions. Among the three types of SMC complexes in eukaryotes, cohesin and condensin fold the genome into different domains and structures, while Smc5/6 plays direct roles in promoting chromosomal replication and repair and in restraining pathogenic viral extra-chromosomal DNA. The importance of Smc5/6 for growth, genotoxin resistance and host defense across species is highlighted by its involvement in disease prevention in plants and animals. Accelerated progress in recent years, including structural and single-molecule studies, has begun to provide greater insights into the mechanisms underlying Smc5/6 functions. Here we integrate a broad range of recent studies on Smc5/6 to identify emerging features of this unique SMC complex and to explain its diverse cellular functions and roles in disease pathogenesis. We also highlight many key areas requiring further investigation for achieving coherent views of Smc5/6-driven mechanisms.

Juvenile-onset multifocal atrial arrhythmias, atrial standstill and compound heterozygosity of genetic variants in TAF1A: sentinel event for evolving dilated cardiomyopathy-a case report

Background

Juvenile onset of extensive atrial electromechanical failure, including atrial standstill, is a rare disease entity that may precede ventricular cardiomyopathy. Genetic variants associated with early-onset atrioventricular (AV) cardiomyopathy are increasingly recognized.

Case summary

A 16-year-old patient presented with atrial brady- and tachyarrhythmias and concomitant impaired atrial electromechanical function (atrial standstill). The atrial phenotype preceded the development of a predominantly right-sided AV dilated cardiomyopathy with pronounced myocardial fibrosis. A His-bundle pacemaker was installed for high-degree AV conduction block and sinus arrest. Using familial-based whole-exome sequencing, a missense mutation and a copy number variant deletion (compound heterozygosity) of the TAF1A gene (involved in ribosomal RNA synthesis) were identified.

Discussion

Juvenile onset of severe atrial electromechanical failure with atrial arrhythmias should prompt deep pheno- and genotyping and calls for vigilance for downstream cardiomyopathic deterioration.

A highly efficient human cell-free translation system

Cell-free protein synthesis (CFPS) systems enable easy in vitro expression of proteins with many scientific, industrial, and therapeutic applications. Here we present an optimized, highly efficient human cell-free translation system that bypasses many limitations of currently used in vitro systems. This CFPS system is based on extracts from human HEK293T cells engineered to endogenously express GADD34 and K3L proteins, which suppress phosphorylation of translation initiation factor eIF2α. Overexpression of GADD34 and K3L proteins in human cells significantly simplifies cell lysate preparation. The new CFPS system improves the translation of 5' cap-dependent mRNAs as well as those that use internal ribosome entry site (IRES) mediated translation initiation. We find that expression of the GADD34 and K3L accessory proteins before cell lysis maintains low levels of phosphorylation of eIF2α in the extracts. During in vitro translation reactions, eIF2α phosphorylation increases moderately in a GCN2-dependent fashion that can be inhibited by GCN2 kinase inhibitors. We also find evidence for activation of regulatory pathways related to eukaryotic elongation factor 2 (eEF2) phosphorylation and ribosome quality control in the extracts. This new CFPS system should be useful for exploring human translation mechanisms in more physiological conditions outside the cell.

Expression of RNA polymerase I catalytic core is influenced by RPA12

RNA Polymerase I (Pol I) has recently been recognized as a cancer therapeutic target. The activity of this enzyme is essential for ribosome biogenesis and is universally activated in cancers. The enzymatic activity of this multi-subunit complex resides in its catalytic core composed of RPA194, RPA135, and RPA12, a subunit with functions in RNA cleavage, transcription initiation and elongation. Here we explore whether RPA12 influences the regulation of RPA194 in human cancer cells. We use a specific small-molecule Pol I inhibitor BMH-21 that inhibits transcription initiation, elongation and ultimately activates the degradation of Pol I catalytic subunit RPA194. We show that silencing RPA12 causes alterations in the expression and localization of Pol I subunits RPA194 and RPA135. Furthermore, we find that despite these alterations not only does the Pol I core complex between RPA194 and RPA135 remain intact upon RPA12 knockdown, but the transcription of Pol I and its engagement with chromatin remain unaffected. The BMH-21-mediated degradation of RPA194 was independent of RPA12 suggesting that RPA12 affects the basal expression, but not the drug-inducible turnover of RPA194. These studies add to knowledge defining regulatory factors for the expression of this Pol I catalytic subunit.

Inhalable mixture of polycyclic aromatic hydrocarbons and metals, DNA oxidative stress and nasal ribosomal DNA copy number amplification: Direct and indirect effect analyses among population

The ribosomal DNA (rDNA) plays a crucial role in maintaining genome stability. So far, alterations of rDNA from airborne pollutants exposure remain unclear. Nasal epithelial cells are the earliest respiratory barrier, which has an accessible surrogate for evaluating respiratory impairment. We developed a mixture-centered biomarkers study integrated epidemiological and biological evidence among 768 subjects, a mixture of polycyclic aromatic hydrocarbons (PAHs) and metals. We identified the mixed exposure of PAHs and metals by environmental and biological monitoring, selected urinary 8-hydroxy-2'-deoxyguanosine as DNA oxidative stress marker, and measured their rDNA copy number (rDNA CN) in nasal epithelial cells. We performed linear regression, adaptive elastic net regression, BKMR, and mediation analyses to assess the direct and indirect effects. We found a 10% elevation in urinary 1-hydroxypyrene was correlated with a separate 0.31% and 0.82% amplification of nasal 5S and 45S rDNA CN, respectively (all P < 0.05). A 10% increment of urine nickel was associated with a separate 0.37% and 1.18% elevation of nasal 5S and 45S rDNA CN, respectively (all P < 0.05). BKMR results also confirmed our findings of PAHs and nickel. Our findings suggested that DNA oxidative stress might trigger rDNA instability induced by inhaled PAHs and metals.