Site-specific methylation of 18S ribosomal RNA by SNORD42A is required for acute myeloid leukemia cell proliferation

SNORD88B-mediated WRN nucleolar trafficking drives self-renewal in liver cancer initiating cells and hepatocarcinogenesis

Whether small nucleolar RNAs (snoRNAs) are involved in the regulation of liver cancer stem cells (CSCs) self-renewal and serve as therapeutic targets remains largely unclear. Here we show that a functional snoRNA (SNORD88B) is robustly expressed in Hepatocellular carcinoma (HCC) tumors and liver CSCs. SNORD88B deficiency abolishes the self-renewal of liver CSCs and hepatocarcinogenesis. Mechanistically, SNORD88B anchors WRN in the nucleolus, promoting XRCC5 interacts with STK4 promoter to suppress its transcription, leading to inactivation of Hippo signaling. Moreover, low expression of STK4 and high expression of XRCC5 are positively correlated with HCC poor prognosis. Additionally, snord88b knockout suppresses mouse liver tumorigenesis. Notably, co-administration of SNORD88B antisense oligonucleotides (ASOs) with MST1 agonist adapalene (ADA) exert synergistic antitumor effects and increase overall murine survival. Our findings delineate that SNORD88B drives self-renewal of liver CSCs and accelerates HCC tumorigenesis via non-canonical mechanism, providing potential targets for liver cancer therapy by eliminating liver CSCs.

The landscape of RNA-chromatin interaction reveals small non-coding RNAs as essential mediators of leukemia maintenance

RNA constitutes a large fraction of chromatin. Spatial distribution and functional relevance of most of RNA-chromatin interactions remain unknown. We established a landscape analysis of RNA-chromatin interactions in human acute myeloid leukemia (AML). In total more than 50 million interactions were captured in an AML cell line. Protein-coding mRNAs and long non-coding RNAs exhibited a substantial number of interactions with chromatin in cis suggesting transcriptional activity. In contrast, small nucleolar RNAs (snoRNAs) and small nuclear RNAs (snRNAs) associated with chromatin predominantly in trans suggesting chromatin specific functions. Of note, snoRNA-chromatin interaction was associated with chromatin modifications and occurred independently of the classical snoRNA-RNP complex. Two C/D box snoRNAs, namely SNORD118 and SNORD3A, displayed high frequency of trans-association with chromatin. The transcription of SNORD118 and SNORD3A was increased upon leukemia transformation and enriched in leukemia stem cells, but decreased during myeloid differentiation. Suppression of SNORD118 and SNORD3A impaired leukemia cell proliferation and colony forming capacity in AML cell lines and primary patient samples. Notably, this effect was leukemia specific with less impact on healthy CD34+ hematopoietic stem and progenitor cells. These findings highlight the functional importance of chromatin-associated RNAs overall and in particular of SNORD118 and SNORD3A in maintaining leukemia propagation.

Role of RNA modifications in blood development and regeneration

Blood development and regeneration require rapid turnover of cells, and ribonucleic acid (RNA) modifications play a key role in it via regulating stemness and cell fate regulation. RNA modifications affect gene activity via posttranscriptional and translation-mediated mechanisms. Diverse molecular players involved in RNA-modification processes are abundantly expressed by hematopoietic stem cells and lineages. Close to 150 RNA chemical modifications have been reported, but only N6-methyl adenosine (m6A), inosine (I), pseudouridine (Ψ), and m1A-a handful-have been studied in-cell fate regulation. The role of RNA modification in blood diseases and disorders is an emerging field and offers potential for therapeutic interventions. Knowledge of RNA-modification and enzymatic activities could be used to design therapies in the future. Here, we summarized the recent advances in RNA modification and the epitranscriptome field and discussed their regulation of blood development and regeneration.

Phase separation-competent FBL promotes early pre-rRNA processing and translation in acute myeloid leukaemia

RNA-binding proteins (RBPs) are pivotal in acute myeloid leukaemia (AML), a lethal disease. Although specific phase separation-competent RBPs are recognized in AML, the effect of their condensate formation on AML leukaemogenesis, and the therapeutic potential of inhibition of phase separation are underexplored. In our in vivo CRISPR RBP screen, fibrillarin (FBL) emerges as a crucial nucleolar protein that regulates AML cell survival, primarily through its phase separation domains rather than methyltransferase or acetylation domains. These phase separation domains, with specific features, coordinately drive nucleoli formation and early processing of pre-rRNA (including efflux, cleavage and methylation), eventually enhancing the translation of oncogenes such as MYC. Targeting the phase separation capability of FBL with CGX-635 leads to elimination of AML cells, suggesting an additional mechanism of action for CGX-635 that complements its established therapeutic effects. We highlight the potential of PS modulation of critical proteins as a possible therapeutic strategy for AML.

Non‐m6A RNA modifications in haematological malignancies

Dysregulated RNA modifications, stemming from the aberrant expression and/or malfunction of RNA modification regulators operating through various pathways, play pivotal roles in driving the progression of haematological malignancies. Among RNA modifications, N6-methyladenosine (m6A) RNA modification, the most abundant internal mRNA modification, stands out as the most extensively studied modification. This prominence underscores the crucial role of the layer of epitranscriptomic regulation in controlling haematopoietic cell fate and therefore the development of haematological malignancies. Additionally, other RNA modifications (non-m6A RNA modifications) have gained increasing attention for their essential roles in haematological malignancies. Although the roles of the m6A modification machinery in haematopoietic malignancies have been well reviewed thus far, such reviews are lacking for non-m6A RNA modifications. In this review, we mainly focus on the roles and implications of non-m6A RNA modifications, including N4-acetylcytidine, pseudouridylation, 5-methylcytosine, adenosine to inosine editing, 2'-O-methylation, N1-methyladenosine and N7-methylguanosine in haematopoietic malignancies. We summarise the regulatory enzymes and cellular functions of non-m6A RNA modifications, followed by the discussions of the recent studies on the biological roles and underlying mechanisms of non-m6A RNA modifications in haematological malignancies. We also highlight the potential of therapeutically targeting dysregulated non-m6A modifiers in blood cancer.

Exploring the role of ribosomal RNA modifications in cancer

Recent advances have highlighted the significant roles of post-transcriptional modifications in rRNA in various cancers. Evidence suggests that dysregulation of rRNA modifications acts as a common denominator in cancer development, with alterations in these modifications conferring competitive advantages to cancer cells. Specifically, rRNA modifications modulate protein synthesis and favor the specialized translation of oncogenic programs, thereby contributing to the formation of a protumorigenic proteome in cancer cells. These findings reveal a novel regulatory layer mediated by changes in the deposition of rRNA chemical modifications. Moreover, inhibition of these modifications in vitro and in preclinical studies demonstrates potential therapeutic applications. The recurrence of altered rRNA modification patterns across different types of cancer underscores their importance in cancer progression, proposing them as potential biomarkers and novel therapeutic targets. This review will highlight the latest insights into how post-transcriptional rRNA modifications contribute to cancer progression and summarize the main developments and ongoing challenges in this research area.

Decoding the ribosome's hidden language: rRNA modifications as key players in cancer dynamics and targeted therapies

Ribosomal RNA (rRNA) modifications, essential components of ribosome structure and function, significantly impact cellular proteomics and cancer biology. These chemical modifications transcend structural roles, critically shaping ribosome functionality and influencing cellular protein profiles. In this review, the mechanisms by which rRNA modifications regulate both rRNA functions and broader cellular physiological processes are critically discussed. Importantly, by altering the translational output, rRNA modifications can shift the cellular equilibrium towards oncogenesis, thus playing a key role in cancer development and progression. Moreover, a special focus is placed on the functions of mitochondrial rRNA modifications and their aberrant expression in cancer, an area with profound implications yet largely uncharted. Dysregulation in these modifications can lead to metabolic dysfunction and apoptosis resistance, hallmark traits of cancer cells. Furthermore, the current challenges and future perspectives in targeting rRNA modifications are highlighted as a therapeutic approach for cancer treatment. In conclusion, rRNA modifications represent a frontier in cancer research, offering novel insights and therapeutic possibilities. Understanding and harnessing these modifications can pave the way for breakthroughs in cancer treatment, potentially transforming the approach to combating this complex disease.

CRISPR screens in mechanism and target discovery for AML

CRISPR-based screens have discovered novel functional genes involving in diverse tumor biology and elucidated the mechanisms of the cancer pathological states. Recently, with its randomness and unbiasedness, CRISPR screens have been used to discover effector genes with previously unknown roles for AML. Those novel targets are related to AML survival resembled cellular pathways mediating epigenetics, synthetic lethality, transcriptional regulation, mitochondrial and energy metabolism. Other genes that are crucial for pharmaceutical targeting and drug resistance have also been identified. With the rapid development of novel strategies, such as barcodes and multiplexed mosaic CRISPR perturbation, more potential therapeutic targets and mechanism in AML will be discovered. In this review, we present an overview of recent progresses in the development of CRISPR-based screens for the mechanism and target identification in AML and discuss the challenges and possible solutions in this rapidly growing field.

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.

How snoRNAs can contribute to cancer at multiple levels

snoRNAs are a class of non-coding RNAs known to guide site specifically RNA modifications such as 2'-O-methylation and pseudouridylation. Recent results regarding snoRNA alterations in cancer has been made available and suggest their potential evaluation as diagnostic and prognostic biomarkers. A large part of these data, however, was not consistently confirmed and failed to provide mechanistic insights on the contribution of altered snoRNA expression to the neoplastic process. Here, we aim to critically review the available literature on snoRNA in cancer focusing on the studies elucidating the functional consequences of their deregulation. Beyond the canonical guide function in RNA processing and modification we also considered additional roles in which snoRNA, in various forms and through different modalities, are involved and that have been recently reported.

Diamond-Blackfan anemia, the archetype of ribosomopathy: How distinct is it from the other constitutional ribosomopathies?

Diamond-Blackfan anemia (DBA) was the first ribosomopathy described in humans. DBA is a congenital hypoplastic anemia, characterized by macrocytic aregenerative anemia, manifesting by differentiation blockage between the BFU-e/CFU-e developmental erythroid progenitor stages. In 50 % of the DBA cases, various malformations are noted. Strikingly, for a hematological disease with a relative erythroid tropism, DBA is due to ribosomal haploinsufficiency in 24 different ribosomal protein (RP) genes. A few other genes have been described in DBA-like disorders, but they do not fit into the classical DBA phenotype (Sankaran et al., 2012; van Dooijeweert et al., 2022; Toki et al., 2018; Kim et al., 2017 [1-4]). Haploinsufficiency in a RP gene leads to defective ribosomal RNA (rRNA) maturation, which is a hallmark of DBA. However, the mechanistic understandings of the erythroid tropism defect in DBA are still to be fully defined. Erythroid defect in DBA has been recently been linked in a non-exclusive manner to a number of mechanisms that include: 1) a defect in translation, in particular for the GATA1 erythroid gene; 2) a deficit of HSP70, the GATA1 chaperone, and 3) free heme toxicity. In addition, p53 activation in response to ribosomal stress is involved in DBA pathophysiology. The DBA phenotype may thus result from the combined contributions of various actors, which may explain the heterogenous phenotypes observed in DBA patients, even within the same family.

RNA modifications in physiology and disease: towards clinical applications

The ability of chemical modifications of single nucleotides to alter the electrostatic charge, hydrophobic surface and base pairing of RNA molecules is exploited for the clinical use of stable artificial RNAs such as mRNA vaccines and synthetic small RNA molecules - to increase or decrease the expression of therapeutic proteins. Furthermore, naturally occurring biochemical modifications of nucleotides regulate RNA metabolism and function to modulate crucial cellular processes. Studies showing the mechanisms by which RNA modifications regulate basic cell functions in higher organisms have led to greater understanding of how aberrant RNA modification profiles can cause disease in humans. Together, these basic science discoveries have unravelled the molecular and cellular functions of RNA modifications, have provided new prospects for therapeutic manipulation and have led to a range of innovative clinical approaches.

Intron Editing Reveals SNORD-Dependent Maturation of the Small Nucleolar RNA Host Gene GAS5 in Human Cells

The GAS5 gene encodes a long non-coding RNA (lncRNA) and intron-located small nucleolar RNAs (snoRNAs). Its structure, splice variants, and diverse functions in mammalian cells have been thoroughly investigated. However, there are still no data on a successful knockout of GAS5 in human cells, with most of the loss-of-function experiments utilizing standard techniques to produce knockdowns. By using CRISPR/Cas9 to introduce double-strand breaks in the terminal intronic box C/D snoRNA genes (SNORDs), we created monoclonal cell lines carrying continuous deletions in one of the GAS5 alleles. The levels of GAS5-encoded box C/D snoRNAs and lncRNA GAS5 were assessed, and the formation of the novel splice variants was analyzed. To comprehensively evaluate the influence of specific SNORD mutations, human cell lines with individual mutations in SNORD74 and SNORD81 were obtained. Specific mutations in SNORD74 led to the downregulation of all GAS5-encoded SNORDs and GAS5 lncRNA. Further analysis revealed that SNORD74 contains a specific regulatory element modulating the maturation of the GAS5 precursor transcript. The results demonstrate that the maturation of GAS5 occurs through the m6A-associated pathway in a SNORD-dependent manner, which is a quite intriguing epitranscriptomic mechanism.

BRD9 determines the cell fate of hematopoietic stem cells by regulating chromatin state

ATP-dependent chromatin remodeling SWI/SNF complexes exist in three subcomplexes: canonical BAF (cBAF), polybromo BAF (PBAF), and a newly described non-canonical BAF (ncBAF). While cBAF and PBAF regulate fates of multiple cell types, roles for ncBAF in hematopoietic stem cells (HSCs) have not been investigated. Motivated by recent discovery of disrupted expression of BRD9, an essential component of ncBAF, in multiple cancers, including clonal hematopoietic disorders, we evaluate here the role of BRD9 in normal and malignant HSCs. BRD9 loss enhances chromatin accessibility, promoting myeloid lineage skewing while impairing B cell development. BRD9 significantly colocalizes with CTCF, whose chromatin recruitment is augmented by BRD9 loss, leading to altered chromatin state and expression of myeloid-related genes within intact topologically associating domains. These data uncover ncBAF as critical for cell fate specification in HSCs via three-dimensional regulation of gene expression and illuminate roles for ncBAF in normal and malignant hematopoiesis.

An integrated workflow for quantitative analysis of the newly synthesized proteome

The analysis of proteins that are newly synthesized upon a cellular perturbation can provide detailed insight into the proteomic response that is elicited by specific cues. This can be investigated by pulse-labeling of cells with clickable and stable-isotope-coded amino acids for the enrichment and mass spectrometric characterization of newly synthesized proteins (NSPs), however convoluted protocols prohibit their routine application. Here we report the optimization of multiple steps in sample preparation, mass spectrometry and data analysis, and we integrate them into a semi-automated workflow for the quantitative analysis of the newly synthesized proteome (QuaNPA). Reduced input requirements and data-independent acquisition (DIA) enable the analysis of triple-SILAC-labeled NSP samples, with enhanced throughput while featuring high quantitative accuracy. We apply QuaNPA to investigate the time-resolved cellular response to interferon-gamma (IFNg), observing rapid induction of targets 2 h after IFNg treatment. QuaNPA provides a powerful approach for large-scale investigation of NSPs to gain insight into complex cellular processes.

Non-Coding RNAs in Human Cancer and Other Diseases: Overview of the Diagnostic Potential

Non-coding RNAs (ncRNAs) are abundant single-stranded RNA molecules in human cells, involved in various cellular processes ranging from DNA replication and mRNA translation regulation to genome stability defense. MicroRNAs are multifunctional ncRNA molecules of 18-24 nt in length, involved in gene silencing through base-pair complementary binding to target mRNA transcripts. piwi-interacting RNAs are an animal-specific class of small ncRNAs sized 26-31 nt, responsible for the defense of genome stability via the epigenetic and post-transcriptional silencing of transposable elements. Long non-coding RNAs are ncRNA molecules defined as transcripts of more than 200 nucleotides, their function depending on localization, and varying from the regulation of cell differentiation and development to the regulation of telomere-specific heterochromatin modifications. The current review provides recent data on the several forms of small and long non-coding RNA's potential to act as diagnostic, prognostic or therapeutic target for various human diseases.

A prognostic signature based on snoRNA predicts the overall survival of lower-grade glioma patients

Introduction

Small nucleolar RNAs (snoRNAs) are a group of non-coding RNAs enriched in the nucleus which direct post-transcriptional modifications of rRNAs, snRNAs and other molecules. Recent studies have suggested that snoRNAs have a significant role in tumor oncogenesis and can be served as prognostic markers for predicting the overall survival of tumor patients.

Methods

We screened 122 survival-related snoRNAs from public databases and eventually selected 7 snoRNAs that were most relevant to the prognosis of lower-grade glioma (LGG) patients for the establishment of the 7-snoRNA prognostic signature. Further, we combined clinical characteristics related to the prognosis of glioma patients and the 7-snoRNA prognostic signature to construct a nomogram.

Results

The prognostic model displayed greater predictive power in both validation set and stratification analysis. Results of enrichment analysis revealed that these snoRNAs mainly participated in the post-transcriptional process such as RNA splicing, metabolism and modifications. In addition, 7-snoRNA prognostic signature were positively correlated with immune scores and expression levels of multiple immune checkpoint molecules, which can be used as potential biomarkers for immunotherapy prediction. From the results of bioinformatics analysis, we inferred that SNORD88C has a major role in the development of glioma, and then performed in vitro experiments to validate it. The results revealed that SNORD88C could promote the proliferation, invasion and migration of glioma cells.

Discussion

We established a 7-snoRNA prognostic signature and nomogram that can be applied to evaluate the survival of LGG patients with good sensitivity and specificity. In addition, SNORD88C could promote the proliferation, migration and invasion of glioma cells and is involved in a variety of biological processes related to DNA and RNA.

Depletion of SNORA33 Abolishes ψ of 28S-U4966 and Affects the Ribosome Translational Apparatus

Eukaryotic ribosomes are complex molecular nanomachines translating genetic information from mRNAs into proteins. There is natural heterogeneity in ribosome composition. The pseudouridylation (ψ) of ribosomal RNAs (rRNAs) is one of the key sources of ribosome heterogeneity. Nevertheless, the functional consequences of ψ-based ribosome heterogeneity and its relevance for human disease are yet to be understood. Using HydraPsiSeq and a chronic disease model of non-osteoarthritic primary human articular chondrocytes exposed to osteoarthritic synovial fluid, we demonstrated that the disease microenvironment is capable of instigating site-specific changes in rRNA ψ profiles. To investigate one of the identified differential rRNA ψ sites (28S-ψ4966), we generated SNORA22 and SNORA33 KO SW1353 cell pools using LentiCRISPRv2/Cas9 and evaluated the ribosome translational capacity by 35S-Met/Cys incorporation, assessed the mode of translation initiation and ribosomal fidelity using dual luciferase reporters, and assessed cellular and ribosomal proteomes by LC-MS/MS. We uncovered that the depletion of SNORA33, but not SNORA22, reduced 28S-ψ4966 levels. The resulting loss of 28S-ψ4966 affected ribosomal protein composition and function and led to specific changes in the cellular proteome. Overall, our pioneering findings demonstrate that cells dynamically respond to disease-relevant changes in their environment by altering their rRNA pseudouridylation profiles, with consequences for ribosome function and the cellular proteome relevant to human disease.

RNA modifications in cancer

Currently, more than 170 modifications have been identified on RNA. Among these RNA modifications, various methylations account for two-thirds of total cases and exist on almost all RNAs. Roles of RNA modifications in cancer are garnering increasing interest. The research on m6A RNA methylation in cancer is in full swing at present. However, there are still many other popular RNA modifications involved in the regulation of gene expression post-transcriptionally besides m6A RNA methylation. In this review, we focus on several important RNA modifications including m1A, m5C, m7G, 2'-O-Me, Ψ and A-to-I editing in cancer, which will provide a new perspective on tumourigenesis by peeking into the complex regulatory network of epigenetic RNA modifications, transcript processing, and protein translation.

SNORD6 promotes cervical cancer progression by accelerating E6-mediated p53 degradation

Small nucleolar RNAs (snoRNAs) are a class of non-coding RNAs widely distributed in eukaryotic nucleoli. In recent years, studies have revealed that snoRNAs can also participate in the occurrence and development of malignant tumors through different pathways. Cervical cancer is one of the most common malignant tumors of the female reproductive system, and the high-risk HPV virus infection is its main pathogenic mechanism. However, the outcomes in different patients with malignant tumors vary, indicating that other factors might affect the pathogenic process of cervical cancer. In this study, we screened the poor prognosis indicator SNORD6 from the TCGA database to find the snoRNA that affects the disease outcome during the pathogenesis of cervical cancer. We discovered that SNORD6 expression in cervical cancer tissues was higher than that in normal cervical tissues. Cell phenotype experiments revealed that the knockdown of SNORD6 retarded cell proliferation and plate clone formation. Furthermore, G1-S phase cell cycle arrest was induced, DNA synthesis was decreased, cell migration and invasion were reduced, while the level of apoptosis increased, whereas the opposite results were obtained after SNORD6 overexpression. Moreover, after intratumoral injection of ASO-SNORD6, the tumor growth rate slowed down, and the tumor volume decreased compared with the control group. In the mechanism study, we found that SNORD6 concurrently acted as a binding "hub" to promote the formation of the tumor suppressor protein p53 degradation complex E6-E6AP-p53. This reaction enhanced the ubiquitination and degradation of p53, thus influenced the regulation of p53 activities in the cell cycle and apoptosis. This study preliminarily clarified the biological role and specific mechanism of SNORD6 in the occurrence of cervical cancer, broadening the basic theoretical research of ovarian cancer and may provide a new perspective on the diagnosis and treatment of cervical cancer.

Small Nucleolar (Sno)RNA: Therapy Lays in Translation

The ribosome is one of the largest complexes in the cell. Adding to its complexity are more than 200 RNA modification sites present on ribosomal RNAs (rRNAs) in a single human ribosome. These modifications occur in functionally important regions of the rRNA molecule, and they are vital for ribosome function and proper gene expression. Until recent technological advancements, the study of rRNA modifications and their profiles has been extremely laborious, leaving many questions unanswered. Small nucleolar RNAs (snoRNAs) are non-coding RNAs that facilitate and dictate the specificity of rRNA modification deposition, making them an attractive target for ribosome modulation. Here, we propose that through the mapping of rRNA modification profiles, we can identify cell-specific modifications with high therapeutic potential. We also describe the challenges of achieving the targeting specificity needed to implement snoRNAs as therapeutic targets in cancers.

snoRNAs in hematopoiesis and blood malignancies: A comprehensive review

Small nucleolar RNAs (snoRNAs) are noncoding RNA molecules of highly variable size, usually ranging from 60 to 150 nucleotides. They are classified into H/ACA box snoRNAs, C/D box snoRNAs, and scaRNAs. Their functional profile includes biogenesis of ribosomes, processing of rRNAs, 2'-O-methylation and pseudouridylation of RNAs, alternative splicing and processing of mRNAs and the generation of small RNA molecules like miRNA. The snoRNAs have been observed to have an important role in hematopoiesis and malignant hematopoietic conditions including leukemia, lymphoma, and multiple myeloma. Blood malignancies arise in immune system cells or the bone marrow due to chromosome abnormalities. It has been estimated that annually over 1.25 million cases of blood cancer occur worldwide. The snoRNAs often show a differential expression profile in blood malignancies. Recent reports associate the abnormal expression of snoRNAs with the inhibition of apoptosis, uncontrolled cell proliferation, angiogenesis, and metastasis. This implies that targeting snoRNAs could be a potential way to treat hematologic malignancies. In this review, we describe the various functions of snoRNAs, their role in hematopoiesis, and the consequences of their dysregulation in blood malignancies. We also evaluate the potential of the dysregulated snoRNAs as biomarkers and therapeutic targets for blood malignancies.

Cryo-EM reconstruction of the human 40S ribosomal subunit at 2.15 Å resolution

The chemical modification of ribosomal RNA and proteins is critical for ribosome assembly, for protein synthesis and may drive ribosome specialisation in development and disease. However, the inability to accurately visualise these modifications has limited mechanistic understanding of the role of these modifications in ribosome function. Here we report the 2.15 Å resolution cryo-EM reconstruction of the human 40S ribosomal subunit. We directly visualise post-transcriptional modifications within the 18S rRNA and four post-translational modifications of ribosomal proteins. Additionally, we interpret the solvation shells in the core regions of the 40S ribosomal subunit and reveal how potassium and magnesium ions establish both universally conserved and eukaryote-specific coordination to promote the stabilisation and folding of key ribosomal elements. This work provides unprecedented structural details for the human 40S ribosomal subunit that will serve as an important reference for unravelling the functional role of ribosomal RNA modifications.

Ribosomal RNA-based epitranscriptomic regulation of chondrocyte translation and proteome in osteoarthritis

OBJECTIVE

Osteoarthritis-related cartilage extracellular matrix remodeling is dependent on changes in chondrocyte protein expression. Yet, the role of ribosomes in chondrocyte translation regulation is unknown. In this exploratory study, we investigated ribosomal RNA (rRNA) epitranscriptomic-based ribosome heterogeneity in human articular chondrocytes and its relevance for osteoarthritis.

METHODS

Sequencing-based rRNA 2'-O-methylation profiling analysis (RiboMethSeq) was performed on non-OA primary human articular chondrocytes (n = 5) exposed for 14 days to osteoarthritic synovial fluid (14 donors, pooled, 20% v/v). The SW1353 SNORD71 KO cell pool was generated using LentiCRISPRv2/Cas9. The mode of translation initiation and fidelity were determined by dual-luciferase reporters. The cellular proteome was analyzed by LC-MS/MS and collagen type I protein expression was evaluated by immunoblotting. Loading of COL1A1 mRNA into polysomes was determined by sucrose gradient ultracentrifugation and fractionation.

RESULTS

We discovered that osteoarthritic synovial fluid instigates site-specific changes in the rRNA 2'-O-me profile of primary human articular chondrocytes. We identified five sites with differential 2'-O-me levels. The 2'-O-me status of 5.8S-U14 (one of identified differential 2'-O-me sites; decreased by 7.7%, 95% CI [0.9-14.5%]) was targeted by depleting the level of its guide snoRNA SNORD71 (50% decrease, 95% CI [33-64%]). This resulted in an altered ribosome translation modus (e.g., CrPV IRES, FC 3, 95% CI [2.2-4.1]) and promoted translation of COL1A1 mRNA which led to increased levels of COL1A1 protein (FC 1.7, 95% CI [1.3-2.0]).

CONCLUSIONS

Our data identify a novel concept suggesting that articular chondrocytes employ rRNA epitranscriptomic mechanisms in osteoarthritis development.

A Dynamic rRNA Ribomethylome Drives Stemness in Acute Myeloid Leukemia

The development and regulation of malignant self-renewal remain unresolved issues. Here, we provide biochemical, genetic, and functional evidence that dynamics in ribosomal RNA (rRNA) 2'-O-methylation regulate leukemia stem cell (LSC) activity in vivo. A comprehensive analysis of the rRNA 2'-O-methylation landscape of 94 patients with acute myeloid leukemia (AML) revealed dynamic 2'-O-methylation specifically at exterior sites of ribosomes. The rRNA 2'-O-methylation pattern is closely associated with AML development stage and LSC gene expression signature. Forced expression of the 2'-O-methyltransferase fibrillarin (FBL) induced an AML stem cell phenotype and enabled engraftment of non-LSC leukemia cells in NSG mice. Enhanced 2'-O-methylation redirected the ribosome translation program toward amino acid transporter mRNAs enriched in optimal codons and subsequently increased intracellular amino acid levels. Methylation at the single site 18S-guanosine 1447 was instrumental for LSC activity. Collectively, our work demonstrates that dynamic 2'-O-methylation at specific sites on rRNAs shifts translational preferences and controls AML LSC self-renewal.

SIGNIFICANCE

We establish the complete rRNA 2'-O-methylation landscape in human AML. Plasticity of rRNA 2'-O-methylation shifts protein translation toward an LSC phenotype. This dynamic process constitutes a novel concept of how cancers reprogram cell fate and function. This article is highlighted in the In This Issue feature, p. 247.

The Promising Role of Non-Coding RNAs as Biomarkers and Therapeutic Targets for Leukemia

Early-stage leukemia identification is crucial for effective disease management and leads to an improvement in the survival of leukemia patients. Approaches based on cutting-edge biomarkers with excellent accuracy in body liquids provide patients with the possibility of early diagnosis with high sensitivity and specificity. Non-coding RNAs have recently received a great deal of interest as possible biomarkers in leukemia due to their participation in crucial oncogenic processes such as proliferation, differentiation, invasion, apoptosis, and their availability in body fluids. Recent studies have revealed a strong correlation between leukemia and the deregulated non-coding RNAs. On this basis, these RNAs are also great therapeutic targets. Based on these advantages, we tried to review the role of non-coding RNAs in leukemia. Here, the significance of several non-coding RNA types in leukemia is highlighted, and their potential roles as diagnostic, prognostic, and therapeutic targets are covered.

Genetic and epigenetic defects of the RNA modification machinery in cancer

Cancer was initially considered to be an exclusively genetic disease, but an interplay of dysregulated genetic and epigenetic mechanisms is now known to contribute to the cancer phenotype. More recently, chemical modifications of RNA molecules - the so-called epitranscriptome - have been found to regulate various aspects of RNA function and homeostasis. Specific enzymes, known as RNA-modifying proteins (RMPs), are responsible for depositing, removing, and reading chemical modifications in RNA. Intensive investigations in the epitranscriptomic field in recent years, in conjunction with great technological advances, have revealed the critical role of RNA modifications in regulating numerous cellular pathways. Furthermore, growing evidence has revealed that RNA modification machinery is often altered in human cancers, highlighting the enormous potential of RMPs as pharmacological targets or diagnostic markers.

C/D box small nucleolar RNA SNORD104 promotes endometrial cancer by regulating the 2'-O-methylation of PARP1

BACKGROUND

Small nucleolar RNAs (snoRNAs) are dysregulated in many cancers, although their exact role in tumor genesis and progression remains unclear.

METHODS

The expression profiles of snoRNAs in endometrial cancer (EC) tissues were analyzed using data from The Cancer Genome Atlas, and SNORD104 was identified as an upregulated snoRNA in EC. The tumorigenic role of SNORD104 in EC was established in CCK8, colony formation, EdU, apoptosis, Transwell, and in vivo xenograft experiments. The molecular mechanisms of SNORD104 were analyzed by RNA immunoprecipitation (RIP), Nm-seq, RTL-P assay, RNA stability assay, qRT-PCR, and western blotting.

RESULTS

Antisense oligonucleotide (ASO)-mediated knockdown of SNORD104 in Ishikawa cells significantly inhibited their proliferation, colony formation ability, migration, and invasion in vitro and increased apoptosis. On the other hand, overexpression of SNORD104 promoted EC growth in vivo and in vitro. RIP assay showed that SNORD104 binds to the 2'-O-methyltransferase fibrillarin (FBL), and according to the results of Nm-seq and RTL-P assay, SNORD104 upregulated PARP1 (encoding poly (ADP-ribose) polymerase 1) 2'-O-methylation. The binding of FBL to PARP1 mRNA was also verified by RIP assay. Furthermore, SNORD104 expression was positively correlated with PARP1 expression in EC tissues. In the presence of actinomycin D, SNORD104 increased the stability of PARP1 mRNA and promoted its nuclear localization. Finally, silencing FBL or PARP1 in the HEC1B cells overexpressing SNORD104 inhibited their proliferative and clonal capacities and increased apoptosis rates.

CONCLUSIONS

SNORD104 enhances PARP1 mRNA stability and translation in the EC cells by upregulating 2'-O-methylation and promotes tumor growth.

The snoRNA-like lncRNA LNC-SNO49AB drives leukemia by activating the RNA-editing enzyme ADAR1

Long noncoding RNAs (lncRNAs) are usually 5' capped and 3' polyadenylated, similar to most typical mRNAs. However, recent studies revealed a type of snoRNA-related lncRNA with unique structures, leading to questions on how they are processed and how they work. Here, we identify a novel snoRNA-related lncRNA named LNC-SNO49AB containing two C/D box snoRNA sequences, SNORD49A and SNORD49B; and show that LNC-SNO49AB represents an unreported type of lncRNA with a 5'-end m7G and a 3'-end snoRNA structure. LNC-SNO49AB was found highly expressed in leukemia patient samples, and silencing LNC-SNO49AB dramatically suppressed leukemia progression in vitro and in vivo. Subcellular location indicated that the LNC-SNO49AB is mainly located in nucleolus and interacted with the nucleolar protein fibrillarin. However, we found that LNC-SNO49AB does not play a role in 2'-O-methylation regulation, a classical function of snoRNA; instead, its snoRNA structure affected the lncRNA stability. We further demonstrated that LNC-SNO49AB could directly bind to the adenosine deaminase acting on RNA 1(ADAR1) and promoted its homodimerization followed by a high RNA A-to-I editing activity. Transcriptome profiling shows that LNC-SNO49AB and ADAR1 knockdown respectively share very similar patterns of RNA modification change in downstream signaling pathways, especially in cell cycle pathways. These findings suggest a previously unknown class of snoRNA-related lncRNAs, which function via a manner in nucleolus independently on snoRNA-guide rRNA modification. This is the first report that a lncRNA regulates genome-wide RNA A-to-I editing by enhancing ADAR1 dimerization to facilitate hematopoietic malignancy, suggesting that LNC-SNO49AB may be a novel target in therapy directed to leukemia.

Integrative analysis of a novel 5 methylated snoRNA genes prognostic signature in patients with glioma

Aim: To explore the prognostic value of methylated snoRNA genes in glioma and construct a prognostic risk signature. Materials & methods: We retrieved clinical information and 450K methylation data from The Cancer Genome Atlas and obtained five methylated snoRNA genes. Then we established a risk signature and verified the effect of SNORA71B on glioma cells with functional assays. Results: A risk signature containing five methylated snoRNA genes was constructed and demonstrated to be an independent predictor of glioma prognosis. Silencing SNORA71B restrained the proliferation, migration and invasion of glioma cells and reduced the expression of mesenchymal and cell cycle marker proteins. Conclusion: This study constructed a methylated snoRNA gene risk signature, which may provide a reference for glioma patients' prognosis assessment.

Small but strong: Pivotal roles and potential applications of snoRNAs in hematopoietic malignancies

Small nucleolar RNAs (snoRNAs) belong to a family of noncoding RNAs that are 60-300 nucleotides in length, and they are classified into two classes according to their structure and function: C/D box snoRNAs, playing an essential role in 2’-O-methylation modification on ribosomal RNA; H/ACA box snoRNAs, involved in the pseudouridylation of rRNA. SnoRNAs with unclear functions, no predictable targets, and unusual subcellular locations are called orphan snoRNAs. Recent studies have revealed abnormal expression and demonstrated the pivotal roles of snoRNAs and their host genes in various types of hematological malignancies. This review discusses recent discoveries concerning snoRNAs in a variety of hematological malignancies, including multiple myeloma, lymphoma and leukemia, and sheds light on the application of snoRNAs as diagnostic and prognostic markers as well as therapeutic targets of hematological malignancies in the future.

Ribosome Biogenesis: A Central Player in Cancer Metastasis and Therapeutic Resistance

Ribosomes are a complex ensemble of rRNA and ribosomal proteins that function as mRNA translation machines. Ribosome biogenesis is a multistep process that begins in the nucleolus and concludes in the cytoplasm. The process is tightly controlled by multiple checkpoint and surveillance pathways. Perturbations in these checkpoints and pathways can lead to hyperactivation of ribosome biogenesis. Emerging evidence suggests that cancer cells harbor a specialized class of ribosomes (onco-ribosomes) that facilitates the oncogenic translation program, modulates cellular functions, and promotes metabolic rewiring. Mutations in ribosomal proteins, rRNA processing, and ribosome assembly factors result in ribosomopathies that are associated with an increased risk of developing malignancies. Recent studies have linked mutations in ribosomal proteins and aberrant ribosomes with poor prognosis, highlighting ribosome-targeted therapy as a promising approach for treating patients with cancer. Here, we summarize various aspects of dysregulation of ribosome biogenesis and the impact of resultant onco-ribosomes on malignant tumor behavior, therapeutic resistance, and clinical outcome. Ribosome biogenesis is a promising therapeutic target, and understanding the important determinants of this process will allow for improved and perhaps selective therapeutic strategies to target ribosome biosynthesis.

Targeted Degradation of mRNA Decapping Enzyme DcpS by a VHL-Recruiting PROTAC

The RNA decapping scavenger protein, DcpS, has recently been identified as a dependency in acute myeloid leukemia (AML). The potent DcpS inhibitor RG3039 attenuates AML cell viability, and shRNA knockdown of DcpS is also antiproliferative. Importantly, DcpS was found to be non-essential in normal human hematopoietic cells, which opens a therapeutic window for AML treatment by DcpS modulation. Considering this strong DcpS dependence in AML cell lines, we explored PROTAC-mediated degradation as an alternative strategy to modulate DcpS activity. Herein, we report the development of JCS-1, a PROTAC exhibiting effective degradation of DcpS at nanomolar concentrations. JCS-1 non-covalently binds DcpS with a RG3039-based warhead and recruits the E3 ligase VHL, which induces potent, rapid, and sustained DcpS degradation in several AML cell lines. JCS-1 serves as a chemical biology tool to interrogate DcpS degradation and associated changes in RNA processes in different cellular contexts, which may be an attractive strategy for the treatment of AML and other DcpS-dependent genetic disorders.

snoRNAs: functions and mechanisms in biological processes, and roles in tumor pathophysiology

Small nucleolar RNAs (snoRNAs), a type of non-coding RNA, are widely present in the nucleoli of eukaryotic cells and play an important role in rRNA modification. With the recent increase in research on snoRNAs, new evidence has emerged indicating that snoRNAs also participate in tRNA and mRNA modification. Studies suggest that numerous snoRNAs, including tumor-promoting and tumor-suppressing snoRNAs, are not only dysregulated in tumors but also show associations with clinical prognosis. In this review, we summarize the reported functions of snoRNAs and the possible mechanisms underlying their role in tumorigenesis and cancer development to guide the snoRNA-based clinical diagnosis and treatment of cancer in the future.

Non-coding small nucleolar RNA SNORD17 promotes the progression of hepatocellular carcinoma through a positive feedback loop upon p53 inactivation

Recent evidence suggests that small nucleolar RNAs (snoRNAs) are involved in the progression of various cancers, but their precise roles in hepatocellular carcinoma (HCC) remain largely unclear. Here, we report that SNORD17 promotes the progression of HCC through a positive feedback loop with p53. HCC-related microarray datasets from the Gene Expression Omnibus (GEO) database and clinical HCC samples were used to identify clinically relevant snoRNAs in HCC. SNORD17 was found upregulated in HCC tissues compared with normal liver tissues, and the higher expression of SNORD17 predicted poor outcomes in patients with HCC, especially in those with wild-type p53. SNORD17 promoted the growth and tumorigenicity of HCC cells in vitro and in vivo by inhibiting p53-mediated cell cycle arrest and apoptosis. Mechanistically, SNORD17 anchored nucleophosmin 1 (NPM1) and MYB binding protein 1a (MYBBP1A) in the nucleolus by binding them simultaneously. Loss of SNORD17 promoted the translocation of NPM1 and MYBBP1A into the nucleoplasm, leading to NPM1/MDM2-mediated stability and MYBBP1A/p300-mediated activation of p53. Interestingly, p300-mediated acetylation of p53 inhibited SNORD17 expression by binding to the promoter of SNORD17 in turn, forming a positive feedback loop between SNORD17 and p53. Administration of SNORD17 antisense oligonucleotides (ASOs) significantly suppressed the growth of xenograft tumors in mice. In summary, this study suggests that SNORD17 drives cancer progression by constitutively inhibiting p53 signaling in HCC and may represent a potential therapeutic target for HCC.

Targeting SNORA38B attenuates tumorigenesis and sensitizes immune checkpoint blockade in non-small cell lung cancer by remodeling the tumor microenvironment via regulation of GAB2/AKT/mTOR signaling pathway

BACKGROUND

Non-coding RNAs (ncRNAs), including small nucleolar RNAs (snoRNAs), are widely involved in the physiological and pathological processes of human beings. While up to date, although considerable progress has been achieved in ncRNA-related pathogenesis of non-small cell lung cancer (NSCLC), the underlying mechanisms and biological significance of snoRNAs in NSCLC still need to be further clarified.

METHODS

Quantitative real-time polymerase chain reaction or RNAscope was performed to verify the expression of Small Nucleolar RNA, H/ACA Box 38B (SNORA38B) in NSCLC cell lines or clinical samples. BALB/c nude mice xenograft model or C57BL/6J mice syngeneic tumor model were estimated to detect the effects of SNORA38B in tumor growth or tumor immune microenvironment in vivo. Cytometry by time of flight, enzyme-linked immunosorbent assay and flow cytometry assay were conducted to clarify the effects and mechanisms of SNORA38B-mediated tumor immunosuppressive microenvironment. The binding activity between SNORA38B and E2F transcription factor 1(E2F1) was detected by RNA immunoprecipitation and RNA pull-down assays. Then, bioinformatics analysis and chromatin immunoprecipitation were utilized to demonstrate the regulation of GRB2-associated-binding protein 2 (GAB2) by E2F1. Moreover, the combinatorial treatment of SNORA38B locked nucleic acid (LNA) and immune checkpoint blockade (ICB) was used to treat murine Lewis lung carcinoma-derived tumor burden C57BL/6J mice to clarify the effectiveness of targeting SNORA38B in NSCLC immunotherapy.

RESULTS

SNORA38B was found highly expressed in NSCLC tissues and cell lines, and associated with worse prognosis. Further results showed that SNORA38B functioned as an oncogene via facilitating cell proliferation, migration, invasion, and inhibiting cell apoptosis in vitro and promoting tumorigenesis of NSCLC cells in vivo. SNORA38B could also recruit the CD4+FOXP3+ regulatory T cells by triggering tumor cells to secrete interleukin 10, which in turn reduced the infiltration of CD3+CD8+ T cells in NSCLC tumor microenvironment (TME), favoring tumor progression and poorer immune efficacy. Mechanistically, SNORA38B mainly distributed in the nucleus, and promoted NSCLC progression by regulating GAB2 transcription to activate protein kinase B (AKT)/mammalian target of rapamycin (mTOR) pathway through directly binding with E2F1. Moreover, we found that SNORA38B LNAs were able to ameliorate CD3+CD8+ T cell infiltration in TME, which sensitized NSCLC to the treatment of ICB.

CONCLUSIONS

In conclusion, our data demonstrated that SNORA38B functioned as an oncogene in NSCLC both in vitro and in vivo at least in part by regulating the GAB2/AKT/mTOR pathway via directly binding to E2F1. SNORA38B could also sensitize NSCLC to immunotherapy, which may be a critical therapeutic target for NSCLC.

The Potential Role of Small Nucleolar RNAs in Cancers – An Evidence Map

Purpose

Cancer seriously endangers human health in every country of the world. New evidence shows that small nucleolar RNAs play important roles in tumorigenesis. Herein, we created this evidence map to systematically assess the impact of dysregulated snoRNAs on cancers.

Methods

We searched four databases to February 2022 using the keywords, “carcinoma”, “neoplasms”, “tumor”, “cancer”, “snoRNA”, and “small nucleolar rna”. The research data were independently screened by two reviewers. Bubble plot, mind map, heatmap were used to depict the relationship between snoRNAs and cancers.

Results

In total, 102 studies met the inclusion criteria and were analyzed in this evidence map. In this study, we found that dysregulated snoRNAs were statistically associated with the clinicopathological characteristics of cancer patients, and affected tumor cell phenotypes. Abnormally expressed snoRNAs were associated with poor survival in cancer patients. Current research confirmed that snoRNAs have good diagnostic efficiency for cancers. snoRNAs could modulate biological processes and signaling pathways of different cancer cells by altering rRNA, regulating mRNA, and recruiting protein factors.

Conclusion

Taken all together, ectopic snoRNAs may serve as new biomarkers for clinical assessment, diagnostic, prognostic prediction of cancer patients, and provide a potential therapeutic strategy for cancer treatment. This article provided a visual analysis of existing evidence on snoRNAs and cancers, which can offer useful information for different researchers interested in snoRNAs.

Chromatin-associated orphan snoRNA regulates DNA damage-mediated differentiation via a non-canonical complex

Small nucleolar RNAs (snoRNAs) are commonly acknowledged as a class of homogeneous non-coding RNAs that guide ribosomal RNA modifications. However, snoRNAs referred to as orphans have largely unknown functions. Here, we systematically profile chromatin-associated snoRNAs (casnoRNAs) in mammalian cells and identify a subgroup of orphan casnoRNAs responding to DNA damage stress, among which SNORA73 shows the most marked reduction in chromatin enrichment. Downregulated SNORA73 maintains cancer genome stability and differentiation block in hematopoietic malignancy. Mechanistically, casnoRNA the 5' end non-canonical structure of SNORA73 is critical for its function and binding to poly (ADP-ribose) polymerase 1 (PARP1). SNORA73 inhibits PARP1 auto-PARylation to affect cancer genome stability by forming a small nucleolar ribonucleoprotein (snoRNP) with PARP1 and canonical H/ACA proteins DKC1/NHP2. Our findings reveal the role of an orphan snoRNA serving as casnoRNA and highlights a link between non-canonical structure of snoRNA and their functional diversity.

Epitranscriptomic modifications in acute myeloid leukemia: m6A and 2'-O-methylation as targets for novel therapeutic strategies

Modifications of RNA commonly occur in all species. Multiple enzymes are involved as writers, erasers and readers of these modifications. Many RNA modifications or the respective enzymes are associated with human disease and especially cancer. Currently, the mechanisms how RNA modifications impact on a large number of intracellular processes are emerging and knowledge about the pathogenetic role of RNA modifications increases. In Acute Myeloid Leukemia (AML), the N6-methyladenosine (m6A) modification has emerged as an important modulator of leukemogenesis. The writer proteins METTL3 and METTL14 are both involved in AML pathogenesis and might be suitable therapeutic targets. Recently, close links between 2'-O-methylation (2'-O-me) of ribosomal RNA and leukemogenesis were discovered. The AML1-ETO oncofusion protein which specifically occurs in a subset of AML was found to depend on induction of snoRNAs and 2'-O-me for leukemogenesis. Also, NPM1, an important tumor suppressor in AML, was associated with altered snoRNAs and 2'-O-me. These findings point toward novel pathogenetic mechanisms and potential therapeutic interventions. The current knowledge and the implications are the topic of this review.

The role of OncoSnoRNAs and Ribosomal RNA 2'-O-methylation in Cancer

Ribosomes are essential nanomachines responsible for all protein production in cells. Ribosome biogenesis and function are energy costly processes, they are tightly regulated to match cellular needs. In cancer, major pathways that control ribosome biogenesis and function are often deregulated to ensure cell survival and to accommodate the continuous proliferation of tumour cells. Ribosomal RNAs (rRNAs) are abundantly modified with 2'-O-methylation (Nm, ribomethylation) being one of the most common modifications. In eukaryotic ribosomes, ribomethylation is performed by the methyltransferase Fibrillarin guided by box C/D small nucleolar RNAs (snoRNAs). Accumulating evidences indicate that snoRNA expression and ribosome methylation profiles are altered in cancer. Here we review our current knowledge on differential snoRNA expression and rRNA 2ʹ-O methylation in the context of human malignancies, and discuss the consequences and opportunities for cancer diagnostics, prognostics, and therapeutics.

Germline DDX41 mutations cause ineffective hematopoiesis and myelodysplasia

DDX41 mutations are the most common germline alterations in adult myelodysplastic syndromes (MDSs). The majority of affected individuals harbor germline monoallelic frameshift DDX41 mutations and subsequently acquire somatic mutations in their other DDX41 allele, typically missense R525H. Hematopoietic progenitor cells (HPCs) with biallelic frameshift and R525H mutations undergo cell cycle arrest and apoptosis, causing bone marrow failure in mice. Mechanistically, DDX41 is essential for small nucleolar RNA (snoRNA) processing, ribosome assembly, and protein synthesis. Although monoallelic DDX41 mutations do not affect hematopoiesis in young mice, a subset of aged mice develops features of MDS. Biallelic mutations in DDX41 are observed at a low frequency in non-dominant hematopoietic stem cell clones in bone marrow (BM) from individuals with MDS. Mice chimeric for monoallelic DDX41 mutant BM cells and a minor population of biallelic mutant BM cells develop hematopoietic defects at a younger age, suggesting that biallelic DDX41 mutant cells are disease modifying in the context of monoallelic DDX41 mutant BM.

Small but Mighty-The Emerging Role of snoRNAs in Hematological Malignancies

Over recent years, the long known class of small nucleolar RNAs (snoRNAs) have gained interest among the scientific community, especially in the clinical context. The main molecular role of this interesting family of non-coding RNAs is to serve as scaffolding RNAs to mediate site-specific RNA modification of ribosomal RNAs (rRNAs) and small nuclear RNAs (snRNAs). With the development of new sequencing techniques and sophisticated analysis pipelines, new members of the snoRNA family were identified and global expression patterns in disease backgrounds could be determined. We will herein shed light on the current research progress in snoRNA biology and their clinical role by influencing disease outcome in hematological diseases. Astonishingly, in recent studies snoRNAs emerged as potent biomarkers in a variety of these clinical setups, which is also highlighted by the frequent deregulation of snoRNA levels in the hema-oncological context. However, research is only starting to reveal how snoRNAs might influence cellular functions and the connected disease hallmarks in hematological malignancies.

Small nucleolar RNA is potential as a novel player in leukemogenesis and clinical application

Lack of clarity of the mechanisms that underlie leukemogenesis obstructs the diagnosis, prognosis, and treatment of leukemia. Research has found that small nuclear RNA (snoRNA) plays an essential role in leukemia. These small non-coding RNAs are involved in ribosome biogenesis, including the 2′-O-methylation and pseudouridylation of precursor ribosomal RNA (pre-rRNA), and pre-rRNA splicing. Recently, many snoRNAs were found to be orphans that have no predictable RNA modification targets, but these RNAs have always been found to be located in different subcellular organelles, and they play diverse roles. Using high-throughput technology, snoRNA expression profiles have been revealed in leukemia, and some of the deregulated snoRNAs may regulate the cell cycle, differentiation, proliferation, and apoptosis in leukemic cells and confer drug resistance during leukemia treatment. In this review, we discuss the expression profiles and functions of snoRNAs, particularly orphan snoRNAs, in leukemia. It is possible that the dysregulated snoRNAs are promising diagnosis and prognosis markers for leukemia, which may serve as potential therapeutic targets in leukemia treatment.

Constitutive and variable 2'-O-methylation (Nm) in human ribosomal RNA

Epitranscriptomic modifications of stable RNAs are dynamically regulated and specific profiles of 2ʹ-O-methylation in rRNA have been associated with distinct cancer types. However, these observations pointed out the existence of at least two distinct groups: a rather large group with constitutive rRNA Nm residues exhibiting a stable level of methylation and a more restricted set of variable modifications, giving rise to the concept of ‘specialized ribosomes’. These heterogeneous ribosomes can modulate their translational properties and be key regulatory players, depending on the physiological state of the cell. However, these conclusions were drawn from a limited set of explored human cell lines or tissues, mostly related to cancer cells of the same type. Here, we report a comprehensive analysis of human rRNA Nm modification variability observed for >15 human cell lines grown in different media and conditions. Our data demonstrate that human Nm sites can be classified into four groups, depending on their observed variability. About ⅓ of rRNA 2ʹ-O-methylations are almost invariably modified at the same level in all tested samples (stable modifications), the second group of relatively invariant modifications (another ½ of the total) showing a slightly higher variance (low variable group) and two variable groups, showing an important heterogeneity. Mapping of these four classes on the human ribosome 3D structure shows that stably modified positions are preferentially located in the important ribosome functional sites, while variable and highly variable residues are mostly distributed to the ribosome periphery. Possible relationships of such stable and variable modifications to the ribosome functions are discussed.

The high-performance technology CRISPR/Cas9 improves knowledge and management of acute myeloid leukemia

Knowledge on acute myeloid leukemia pathogenesis and treatment has progressed recently, but not enough to provide ideal management. Improving the prognosis of acute myeloid leukemia patients depends on advances in molecular biology for the detection of new therapeutic targets and the production of effective drugs. The CRISPR/Cas9 technology allows gene insertions and deletions and it is the first step in investigating the function of their encoded proteins. Thus, new experimental models have been developed and progress has been made in understanding protein metabolism, antitumor activity, leukemic cell maintenance, differentiation, growth, apoptosis, and self-renewal, the combined pathogenetic mechanisms involved in leukemogenesis. The CRISPR/Cas9 system is used to understand drug resistance and find solutions to overcome it. The therapeutic progress achieved using the CRISPR/Cas9 system is remarkable. FST gene removal inhibited acute myeloid leukemia cell growth. Lysine acetyltransferase gene deletion contributed to decreased proliferation rate, increased apoptosis, and favored differentiation of acute myelid leukemia cells carrying MLL-X gene fusions. The removal of CD38 gene from NK cells decreased NK fratricidal cells contributing to increased efficacy of new CD38 CAR-NK cells to target leukemic blasts. BCL2 knockout has synergistic effects with FLT3 inhibitors. Exportin 1 knockout is synergistic with midostaurin treatment in acute myeloid leukemia with FLT3-ITD mutation. Using the results of CRISPR/Cas9 libraries and technology application will allow us to get closer to achieving the goal of curing acute myeloid leukemia in the coming decades.

2'O-Ribose Methylation of Ribosomal RNAs: Natural Diversity in Living Organisms, Biological Processes, and Diseases

Recent findings suggest that ribosomes, the translational machineries, can display a distinct composition depending on physio-pathological contexts. Thanks to outstanding technological breakthroughs, many studies have reported that variations of rRNA modifications, and more particularly the most abundant rRNA chemical modification, the rRNA 2'O-ribose methylation (2'Ome), intrinsically occur in many organisms. In the last 5 years, accumulating reports have illustrated that rRNA 2'Ome varies in human cell lines but also in living organisms (yeast, plant, zebrafish, mouse, human) during development and diseases. These rRNA 2'Ome variations occur either within a single cell line, organ, or patient's sample (i.e., intra-variability) or between at least two biological conditions (i.e., inter-variability). Thus, the ribosomes can tolerate the absence of 2'Ome at some specific positions. These observations question whether variations in rRNA 2'Ome could provide ribosomes with particular translational regulatory activities and functional specializations. Here, we compile recent studies supporting the heterogeneity of ribosome composition at rRNA 2'Ome level and provide an overview of the natural diversity in rRNA 2'Ome that has been reported up to now throughout the kingdom of life. Moreover, we discuss the little evidence that suggests that variations of rRNA 2'Ome can effectively impact the ribosome activity and contribute to the etiology of some human diseases.

Regulation of Ribosome Function by RNA Modifications in Hematopoietic Development and Leukemia: It Is Not Only a Matter of m6A

Growth and maturation of hematopoietic stem cells (HSCs) are largely controlled at both transcriptional and post-transcriptional levels. In particular, hematopoietic development requires a tight control of protein synthesis. Furthermore, translational deregulation strongly contributes to hematopoietic malignancies. Researchers have recently identified a new layer of gene expression regulation that consists of chemical modification of RNA species, which led to the birth of the epitranscriptomics field. RNA modifications provide an additional level of control in hematopoietic development by acting as post-transcriptional regulators of lineage-specific genetic programs. Other reviews have already described the important role of the N⁶-methylation of adenosine (m⁶A) within mRNA species in regulating hematopoietic differentiation and diseases. The aim of this review is to summarize the current status of the role of RNA modifications in the regulation of ribosome function, beyond m⁶A. In particular, we discuss the importance of RNA modifications in tRNA and rRNA molecules. By balancing translational rate and fidelity, they play an important role in regulating normal and malignant hematopoietic development.

RNA Epigenetics: Fine-Tuning Chromatin Plasticity and Transcriptional Regulation, and the Implications in Human Diseases

Chromatin structure plays an essential role in eukaryotic gene expression and cell identity. Traditionally, DNA and histone modifications have been the focus of chromatin regulation; however, recent molecular and imaging studies have revealed an intimate connection between RNA epigenetics and chromatin structure. Accumulating evidence suggests that RNA serves as the interplay between chromatin and the transcription and splicing machineries within the cell. Additionally, epigenetic modifications of nascent RNAs fine-tune these interactions to regulate gene expression at the co- and post-transcriptional levels in normal cell development and human diseases. This review will provide an overview of recent advances in the emerging field of RNA epigenetics, specifically the role of RNA modifications and RNA modifying proteins in chromatin remodeling, transcription activation and RNA processing, as well as translational implications in human diseases.