RESUMEN
Coronaviruses are highly transmissible respiratory viruses that cause symptoms ranging from mild congestion to severe respiratory distress. The recent outbreak of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has underscored the need for new antivirals with broad-acting mechanisms to combat increasing emergence of new variants. Currently, there are only a few antivirals approved for treatment of SARS-CoV-2. Previously, the rocaglate natural product silvestrol and synthetic rocaglates such as CR-1-31b were shown to have antiviral effects by inhibiting eukaryotic translation initiation factor 4A1 (eIF4A) function and virus protein synthesis. In this study, we evaluated amidino-rocaglates (ADRs), a class of synthetic rocaglates with the most potent eIF4A-inhibitory activity to-date, for inhibition of SARS-CoV-2 infection. This class of compounds showed low nanomolar potency against multiple SARS-CoV-2 variants and in multiple cell types, including human lung-derived cells, with strong inhibition of virus over host protein synthesis and low cytotoxicity. The most potent ADRs were also shown to be active against two highly pathogenic and distantly related coronaviruses, SARS-CoV and MERS-CoV. Mechanistically, cells with mutations of eIF4A1, which are known to reduce rocaglate interaction displayed reduced ADR-associated loss of cellular function, consistent with targeting of protein synthesis. Overall, ADRs and derivatives may offer new potential treatments for SARS-CoV-2 with the goal of developing a broad-acting anti-coronavirus agent.
RESUMEN
G-Protein Pathway Suppressor 2 (GPS2) is an inhibitor of non-proteolytic K63 ubiquitination mediated by the E2 ubiquitin-conjugating enzyme Ubc13. Previous studies have associated GPS2-mediated restriction of ubiquitination with the regulation of insulin signaling, inflammatory responses and mitochondria-nuclear communication across different tissues and cell types. However, a detailed understanding of the targets of GPS2/Ubc13 activity is lacking. Here, we have dissected the GPS2-regulated K63 ubiquitome in mouse embryonic fibroblasts and human breast cancer cells, unexpectedly finding an enrichment for proteins involved in RNA binding and translation on the outer mitochondrial membrane. Validation of selected targets of GPS2-mediated regulation, including the RNA-binding protein PABPC1 and translation factors RPS1, RACK1 and eIF3M, revealed a mitochondrial-specific strategy for regulating the translation of nuclear-encoded mitochondrial proteins via non-proteolytic ubiquitination. Removal of GPS2-mediated inhibition, either via genetic deletion or stress-induced nuclear translocation, promotes the import-coupled translation of selected mRNAs leading to the increased expression of an adaptive antioxidant program. In light of GPS2 role in nuclear-mitochondria communication, these findings reveal an exquisite regulatory network for modulating mitochondrial gene expression through spatially coordinated transcription and translation.
Asunto(s)
Mitocondrias , Biosíntesis de Proteínas , Ubiquitinación , Animales , Humanos , Mitocondrias/metabolismo , Ratones , Enzimas Ubiquitina-Conjugadoras/metabolismo , Enzimas Ubiquitina-Conjugadoras/genética , Línea Celular Tumoral , Proteínas Mitocondriales/metabolismo , Proteínas Mitocondriales/genética , Péptidos y Proteínas de Señalización IntracelularRESUMEN
Some chemotherapy drugs modulate the formation of stress granules (SGs), which are RNA-containing cytoplasmic foci contributing to stress response pathways. How SGs mechanistically contribute to pro-survival or pro-apoptotic functions must be better defined. The chemotherapy drug lomustine promotes SG formation by activating the stress-sensing eIF2α kinase HRI (encoded by the EIF2AK1 gene). Here, we applied a DNA microarray-based transcriptome analysis to determine the genes modulated by lomustine-induced stress and suggest roles for SGs in this process. We found that the expression of the pro-apoptotic EGR1 gene was specifically regulated in cells upon lomustine treatment. The appearance of EGR1-encoding mRNA in SGs correlated with a decrease in EGR1 mRNA translation. Specifically, EGR1 mRNA was sequestered to SGs upon lomustine treatment, probably preventing its ribosome translation and consequently limiting the degree of apoptosis. Our data support the model where SGs can selectively sequester specific mRNAs in a stress-specific manner, modulate their availability for translation, and thus determine the fate of a stressed cell.
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Proteína 1 de la Respuesta de Crecimiento Precoz , Lomustina , ARN Mensajero , Humanos , ARN Mensajero/metabolismo , ARN Mensajero/genética , Proteína 1 de la Respuesta de Crecimiento Precoz/metabolismo , Proteína 1 de la Respuesta de Crecimiento Precoz/genética , Lomustina/farmacología , Gránulos de Estrés/metabolismo , Gránulos de Estrés/genética , Apoptosis/efectos de los fármacos , Antineoplásicos Alquilantes/farmacologíaRESUMEN
Emphysema and chronic obstructive pulmonary disease (COPD) most commonly result from the effects of environmental exposures in genetically susceptible individuals. Genome-wide association studies have implicated ADGRG6 in COPD and reduced lung function, and a limited number of studies have examined the role of ADGRG6 in cells representative of the airway. However, the ADGRG6 locus is also associated with DLCO/VA, an indicator of gas exchange efficiency and alveolar function. Here, we sought to evaluate the mechanistic contributions of ADGRG6 to homeostatic function and disease in type 2 alveolar epithelial cells. We applied an inducible CRISPR interference (CRISPRi) human induced pluripotent stem cell (iPSC) platform to explore ADGRG6 function in iPSC-derived AT2s (iAT2s). We demonstrate that ADGRG6 exerts pleiotropic effects on iAT2s including regulation of focal adhesions, cytoskeleton, tight junctions, and proliferation. Moreover, we find that ADGRG6 knockdown in cigarette smoke-exposed iAT2s alters cellular responses to injury, downregulating apical complexes in favor of proliferation. Our work functionally characterizes the COPD GWAS gene ADGRG6 in human alveolar epithelium.
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Células Madre Pluripotentes Inducidas , Enfermedad Pulmonar Obstructiva Crónica , Receptores Acoplados a Proteínas G , Humanos , Células Epiteliales Alveolares/metabolismo , Células Epiteliales/metabolismo , Estudio de Asociación del Genoma Completo , Células Madre Pluripotentes Inducidas/metabolismo , Pulmón/metabolismo , Enfermedad Pulmonar Obstructiva Crónica/genética , Enfermedad Pulmonar Obstructiva Crónica/metabolismo , Receptores Acoplados a Proteínas G/genéticaRESUMEN
The 3' untranslated regions (UTRs) of Ebola virus (EBOV) mRNAs are enriched in their AU content and therefore represent potential targets for RNA binding proteins targeting AU-rich elements (ARE-BPs). ARE-BPs are known to fine-tune RNA turnover and translational activity. We identified putative AREs within EBOV mRNA 3' UTRs and assessed whether they might modulate mRNA stability. Using mammalian and zebrafish embryo reporter assays, we show a conserved, ARE-BP-mediated stabilizing effect and increased reporter activity with the tested EBOV 3' UTRs. When coexpressed with the prototypic ARE-BP tristetraprolin (TTP, ZFP36) that mainly destabilizes its target mRNAs, the EBOV nucleoprotein (NP) 3' UTR resulted in decreased reporter gene activity. Coexpression of NP with TTP led to reduced NP protein expression and diminished EBOV minigenome activity. In conclusion, the enrichment of AU residues in EBOV 3' UTRs makes them possible targets for cellular ARE-BPs, leading to modulation of RNA stability and translational activity.
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Ebolavirus , Fiebre Hemorrágica Ebola , Animales , Regiones no Traducidas 3'/genética , ARN Mensajero/genética , ARN Mensajero/metabolismo , Ebolavirus/genética , Ebolavirus/metabolismo , Fiebre Hemorrágica Ebola/genética , Pez Cebra/metabolismo , Estabilidad del ARN/genética , MamíferosRESUMEN
The telomeric repeat-containing RNA, TERRA, associates with both telomeric DNA and telomeric proteins, often forming RNA:DNA hybrids (R-loops). TERRA is most abundant in cancer cells utilizing the alternative lengthening of telomeres (ALT) pathway for telomere maintenance, suggesting that persistent TERRA R-loops may contribute to activation of the ALT mechanism. Therefore, we sought to identify the enzyme(s) that regulate TERRA metabolism in mammalian cells. Here, we identify that the 5'-3' exoribonuclease XRN2 regulates the stability of TERRA RNA. Moreover, while stabilization of TERRA alone was insufficient to drive ALT, depletion of XRN2 in ALT-positive cells led to a significant increase in TERRA R-loops and exacerbated ALT activity. Together, our findings highlight XRN2 as a key determinant of TERRA metabolism and telomere stability in cancer cells that rely on the ALT pathway.
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ARN Largo no Codificante , ARN Largo no Codificante/genética , ARN Largo no Codificante/metabolismo , Exorribonucleasas/genética , Telómero/genética , Telómero/metabolismo , Homeostasis del Telómero , ADN , ARN/genéticaRESUMEN
Proper defense against microbial infection depends on the controlled activation of the immune system. This is particularly important for the RIG-I-like receptors (RLRs), which recognize viral dsRNA and initiate antiviral innate immune responses with the potential of triggering systemic inflammation and immunopathology. Here, we show that stress granules (SGs), molecular condensates that form in response to various stresses including viral dsRNA, play key roles in the controlled activation of RLR signaling. Without the SG nucleators G3BP1/2 and UBAP2L, dsRNA triggers excessive inflammation and immune-mediated apoptosis. In addition to exogenous dsRNA, host-derived dsRNA generated in response to ADAR1 deficiency is also controlled by SG biology. Intriguingly, SGs can function beyond immune control by suppressing viral replication independently of the RLR pathway. These observations thus highlight the multi-functional nature of SGs as cellular "shock absorbers" that converge on protecting cell homeostasis by dampening both toxic immune response and viral replication.
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ADN Helicasas , ARN Helicasas , Humanos , ADN Helicasas/metabolismo , ARN Helicasas/genética , ARN Helicasas/metabolismo , Proteínas de Unión a Poli-ADP-Ribosa/metabolismo , Gránulos de Estrés , Proteínas con Motivos de Reconocimiento de ARN/metabolismo , Inmunidad Innata , Inflamación/metabolismo , Gránulos Citoplasmáticos/metabolismo , Proteínas Portadoras/metabolismoRESUMEN
Stress-induced tRNA cleavage has been implicated in various cellular processes, where tRNA fragments play diverse regulatory roles. Angiogenin (ANG), a member of the RNase A superfamily, induces cleavage of tRNAs resulting in the formation of tRNA-derived stress-induced RNAs (tiRNAs) that contribute to translational reprogramming aiming at cell survival. In addition to cleaving tRNA anticodon loops, ANG has been shown to cleave 3'-CCA termini of tRNAs in vitro, although it is not known whether this process occurs in cells. It has also been suggested that tiRNAs can be generated independently of ANG, although the role of other stress-induced RNases in tRNA cleavage is poorly understood. Using gene editing and biochemical approaches, we examined the involvement of ANG in stress-induced tRNA cleavage by focusing on its cleavage of CCA-termini as well as anticodon loops. We show that ANG is not responsible for CCA-deactivation under sodium arsenite (SA) treatment in cellulo, and although ANG treatment significantly increases 3'-tiRNA levels in cells, the majority of 3'-tiRNAs retain their 3'-CCA termini. Instead, other RNases can cleave CCA-termini in cells, although with low efficiency. Moreover, in the absence of ANG, other RNases are able to promote the production of tiRNAs in cells. Depletion of RNH1 (an endogenous inhibitor of RNase A superfamily) promotes constitutively-produced tiRNAs and CCA-deactivated tRNAs in cells. Interestingly, SA treatment in RNH1-depleted cells did not increase the amount of tiRNAs or CCA-deactivated tRNAs, suggesting that RNase A superfamily enzymes are largely responsible for SA-induced tRNA cleavage. We show that interplay between stress-induced RNases cause targeting tRNAs in a stress-specific manner in cellulo.
RESUMEN
Platinum-based antineoplastic drugs, such as cisplatin, are commonly used to induce tumor cell death. Cisplatin is believed to induce apoptosis as a result of cisplatin-DNA adducts that inhibit DNA and RNA synthesis. Although idea that DNA damage underlines anti-proliferative effects of cisplatin is dominant in cancer research, there is a poor correlation between the degree of the cell sensitivity to cisplatin and the extent of DNA platination. Here, we examined possible effects of cisplatin on post-transcriptional gene regulation that may contribute to cisplatin-mediated cytotoxicity. We show that cisplatin suppresses formation of stress granules (SGs), pro-survival RNA granules with multiple roles in cellular metabolism. Mechanistically, cisplatin inhibits cellular translation to promote disassembly of polysomes and aggregation of ribosomal subunits. As SGs are in equilibrium with polysomes, cisplatin-induced shift towards ribosomal aggregation suppresses SG formation. Our data uncover previously unknown effects of cisplatin on RNA metabolism.
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Antineoplásicos/farmacología , Cisplatino/farmacología , Gránulos de Ribonucleoproteínas Citoplasmáticas/efectos de los fármacos , Procesamiento Proteico-Postraduccional/efectos de los fármacos , Animales , Línea Celular Tumoral , Células Cultivadas , Gránulos de Ribonucleoproteínas Citoplasmáticas/metabolismo , Humanos , Ratones , Gránulos de Estrés/efectos de los fármacosRESUMEN
The production of ribosomes is an energy-intensive process owing to the intricacy of these massive macromolecular machines. Each human ribosome contains 80 ribosomal proteins and four non-coding RNAs. Accurate assembly requires precise regulation of protein and RNA subunits. In response to stress, the integrated stress response (ISR) rapidly inhibits global translation. How rRNA is coordinately regulated with the rapid inhibition of ribosomal protein synthesis is not known. Here, we show that stress specifically inhibits the first step of rRNA processing. Unprocessed rRNA is stored within the nucleolus, and when stress resolves, it re-enters the ribosome biogenesis pathway. Retention of unprocessed rRNA within the nucleolus aids in the maintenance of this organelle. This response is independent of the ISR or inhibition of cellular translation but is independently regulated. Failure to coordinately control ribosomal protein translation and rRNA production results in nucleolar fragmentation. Our study unveils how the rapid translational shut-off in response to stress coordinates with rRNA synthesis production to maintain nucleolar integrity.
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ARN Ribosómico/metabolismo , Proteínas Ribosómicas/metabolismo , Ribosomas , Células HeLa , Humanos , Biogénesis de Organelos , Procesamiento Postranscripcional del ARN , Ribosomas/genética , Ribosomas/metabolismo , Estrés Fisiológico , Transcripción GenéticaRESUMEN
In the original article [...].
RESUMEN
Cancer cells show significant dysregulation of genes expression, which may favor their survival in the tumor environment. In this study, the cellular vault's components MVP (major vault protein), TEP1 (telomerase-associated protein 1) and vPARP (vault poly(ADP-ribose) polymerase) were transiently or completely inhibited in U2OS cells (human bone osteosarcoma epithelial cells) to evaluate their impact on the cell proliferative and migratory capacity as well as on the development of their resistance to the drug vinorelbine. Comparative analysis of MVP protein expression level in normal colon tissue, primary colorectal tumor, and metastasis showed that the expression of this protein does not increase significantly in the primary tumor, but its expression increases in metastatic cells. Further comparative molecular analysis using the whole transcriptome microarrays for MVP-positive and MVP-negative cells showed that MVP is involved in regulating proliferation and migration of cancer cells. MVP may facilitate metastasis of colon cancer due to its impact on cell migration. Moreover, two vault proteins, MVP and TEP1, contribute the resistance to vinorelbine, while vPARP does not.
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Neoplasias Colorrectales/genética , Metástasis de la Neoplasia/genética , Poli(ADP-Ribosa) Polimerasas/genética , Proteínas de Unión al ARN/genética , Partículas Ribonucleoproteicas en Bóveda/genética , Adulto , Anciano , Movimiento Celular/genética , Proliferación Celular/genética , Neoplasias Colorrectales/patología , Supervivencia sin Enfermedad , Resistencia a Antineoplásicos/genética , Femenino , Regulación Neoplásica de la Expresión Génica/genética , Humanos , Masculino , Persona de Mediana Edad , Metástasis de la Neoplasia/patología , Transcriptoma/genéticaRESUMEN
RNA provides the framework for the assembly of some of the most intricate macromolecular complexes within the cell, including the spliceosome and the mature ribosome. The assembly of these complexes relies on the coordinated association of RNA with hundreds of trans-acting protein factors. While some of these trans-acting factors are RNA-binding proteins (RBPs), others are adaptor proteins, and others still, function as both. Defects in the assembly of these complexes results in a number of human pathologies including neurodegeneration and cancer. Here, we demonstrate that Silencing Defective 2 (SDE2) is both an RNA binding protein and also a trans-acting adaptor protein that functions to regulate RNA splicing and ribosome biogenesis. SDE2 depletion leads to widespread changes in alternative splicing, defects in ribosome biogenesis and ultimately complete loss of cell viability. Our data highlight SDE2 as a previously uncharacterized essential gene required for the assembly and maturation of the complexes that carry out two of the most fundamental processes in mammalian cells.
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Empalme Alternativo/genética , Proteínas de Unión al ADN/genética , Empalme del ARN/genética , Ribosomas/genética , Genes Esenciales/genética , Humanos , Proteínas de Unión al ARN/genética , Empalmosomas/genéticaRESUMEN
Human transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), causative pathogen of the COVID-19 pandemic, exerts a massive health and socioeconomic crisis. The virus infects alveolar epithelial type 2 cells (AT2s), leading to lung injury and impaired gas exchange, but the mechanisms driving infection and pathology are unclear. We performed a quantitative phosphoproteomic survey of induced pluripotent stem cell-derived AT2s (iAT2s) infected with SARS-CoV-2 at air-liquid interface (ALI). Time course analysis revealed rapid remodeling of diverse host systems, including signaling, RNA processing, translation, metabolism, nuclear integrity, protein trafficking, and cytoskeletal-microtubule organization, leading to cell cycle arrest, genotoxic stress, and innate immunity. Comparison to analogous data from transformed cell lines revealed respiratory-specific processes hijacked by SARS-CoV-2, highlighting potential novel therapeutic avenues that were validated by a high hit rate in a targeted small molecule screen in our iAT2 ALI system.
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Células Epiteliales Alveolares/metabolismo , COVID-19/metabolismo , Fosfoproteínas/metabolismo , Proteoma/metabolismo , SARS-CoV-2/metabolismo , Células Epiteliales Alveolares/patología , Células Epiteliales Alveolares/virología , Animales , Antivirales , COVID-19/genética , COVID-19/patología , Chlorocebus aethiops , Efecto Citopatogénico Viral , Citoesqueleto , Evaluación Preclínica de Medicamentos , Humanos , Células Madre Pluripotentes Inducidas/metabolismo , Células Madre Pluripotentes Inducidas/patología , Células Madre Pluripotentes Inducidas/virología , Fosfoproteínas/genética , Transporte de Proteínas , Proteoma/genética , SARS-CoV-2/genética , Transducción de Señal , Células Vero , Tratamiento Farmacológico de COVID-19RESUMEN
Stress granules (SGs) are hypothesized to facilitate TAR DNA-binding protein 43 (TDP-43) cytoplasmic mislocalization and aggregation, which may underly amyotrophic lateral sclerosis pathology. However, much data for this hypothesis is indirect. Additionally, whether P-bodies (PBs; related mRNA-protein granules) affect TDP-43 phenotypes is unclear. Here, we determine that induction of TDP-43 expression in yeast results in the accumulation of SG-like foci that in >90% of cases become the sites where TDP-43 cytoplasmic foci first appear. Later, TDP-43 foci associate less with SGs and more with PBs, though independent TDP-43 foci also accumulate. However, depleting or over-expressing yeast SG and PB proteins reveals no consistent trend between SG or PB assembly and TDP-43 foci formation, toxicity or protein abundance. In human cells, immunostaining endogenous TDP-43 with different TDP-43 antibodies reveals distinct localization and aggregation behaviors. Following acute arsenite stress, all phospho-TDP-43 foci colocalize with SGs. Finally, formation of TDP-43 cytoplasmic foci following low-dose chronic arsenite stress is impaired, but not completely blocked, in G3BP1/2ΔΔ cells. Collectively, our data suggest that SG and PB assembly may facilitate TDP-43 cytoplasmic localization and aggregation but are likely not essential for these events.
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Esclerosis Amiotrófica Lateral/genética , Gránulos Citoplasmáticos/genética , Proteínas de Unión al ADN/genética , Estrés Fisiológico/genética , Esclerosis Amiotrófica Lateral/patología , Citoplasma/genética , Humanos , Agregado de Proteínas/genética , ARN Mensajero/genéticaRESUMEN
Cancer treatments are constantly evolving with new approaches to improve patient outcomes. Despite progresses, too many patients remain refractory to treatment due to either the development of resistance to therapeutic drugs and/or metastasis occurrence. Growing evidence suggests that these two barriers are due to transient survival mechanisms that are similar to those observed during stress response. We review the literature and current available open databases to study the potential role of stress response and, most particularly, the involvement of Stress Granules (proteins) in cancer. We propose that Stress Granule proteins may have prognostic value for patients.
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Tumor interferon (IFN) signaling promotes PD-L1 expression to suppress T cell-mediated immunosurveillance. We identify the IFN-stimulated non-coding RNA 1 (INCR1) as a long noncoding RNA (lncRNA) transcribed from the PD-L1 locus and show that INCR1 controls IFNγ signaling in multiple tumor types. Silencing INCR1 decreases the expression of PD-L1, JAK2, and several other IFNγ-stimulated genes. INCR1 knockdown sensitizes tumor cells to cytotoxic T cell-mediated killing, improving CAR T cell therapy. We discover that PD-L1 and JAK2 transcripts are negatively regulated by binding to HNRNPH1, a nuclear ribonucleoprotein. The primary transcript of INCR1 binds HNRNPH1 to block its inhibitory effects on the neighboring genes PD-L1 and JAK2, enabling their expression. These findings introduce a mechanism of tumor IFNγ signaling regulation mediated by the lncRNA INCR1 and suggest a therapeutic target for cancer immunotherapy.
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Antígeno B7-H1/genética , Interferón gamma/metabolismo , ARN Largo no Codificante/genética , Anciano , Animales , Línea Celular Tumoral , Femenino , Regulación Neoplásica de la Expresión Génica/efectos de los fármacos , Humanos , Inmunoterapia , Inmunoterapia Adoptiva/métodos , Interferón gamma/genética , Interferones/genética , Interferones/metabolismo , Janus Quinasa 2/genética , Janus Quinasa 2/metabolismo , Masculino , Ratones , Ratones Endogámicos NOD , Persona de Mediana Edad , Proteína 2 Ligando de Muerte Celular Programada 1/genética , Factor de Transcripción STAT1/metabolismo , Transducción de Señal/efectos de los fármacos , Linfocitos T CitotóxicosRESUMEN
As cells encounter adverse environmental conditions, such as hypoxia, oxidative stress or nutrient deprivation, they trigger stress response pathways to protect themselves until transient stresses have passed. Inhibition of translation is a key component of such cellular stress responses and mounting evidence has revealed the importance of a class of tRNA-derived small RNAs called tiRNAs in this process. The most potent of these small RNAs are those with the capability of assembling into tetrameric G-quadruplex (G4) structures. However, the mechanism by which these small RNAs inhibit translation has yet to be elucidated. Here we show that eIF4G, the major scaffolding protein in the translation initiation complex, directly binds G4s and this activity is required for tiRNA-mediated translation repression. Targeting of eIF4G results in an impairment of 40S ribosome scanning on mRNAs leading to the formation of eIF2α-independent stress granules. Our data reveals the mechanism by which tiRNAs inhibit translation and demonstrates novel activity for eIF4G in the regulation of translation.
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Factor 4G Eucariótico de Iniciación/metabolismo , G-Cuádruplex , Biosíntesis de Proteínas , ARN de Transferencia/química , ARN de Transferencia/metabolismo , Factor 2 Eucariótico de Iniciación/metabolismo , Factor 4F Eucariótico de Iniciación/química , Factor 4F Eucariótico de Iniciación/metabolismo , Humanos , Iniciación de la Cadena Peptídica Traduccional , Fosfoproteínas/metabolismo , Dominios Proteicos , ARN Mensajero/metabolismo , ARN de Transferencia/genética , Subunidades Ribosómicas Pequeñas de Eucariotas/metabolismoRESUMEN
Ribosomes are perhaps the most critical macromolecular machine as they are tasked with carrying out protein synthesis in cells. They are incredibly complex structures composed of protein components and heavily chemically modified RNAs. The task of assembling mature ribosomes from their component parts consumes a massive amount of energy and requires greater than 200 assembly factors. Among the most critical of these are small nucleolar ribonucleoproteins (snoRNPs). These are small RNAs complexed with diverse sets of proteins. As suggested by their name, they localize to the nucleolus, the site of ribosome biogenesis. There, they facilitate multiple roles in ribosomes biogenesis, such as pseudouridylation and 2'-O-methylation of ribosomal (r)RNA, guiding pre-rRNA processing, and acting as molecular chaperones. Here, we reviewed their activity in promoting the assembly of ribosomes in eukaryotes with regards to chemical modification and pre-rRNA processing.