Recurrent point mutations in ribosomal proteins (RPs) RPL10 and RPS15 are found in T-cell acute lymphoblastic leukemia (T-ALL) and chronic lymphocytic leukemia (CLL), respectively. Furthermore, deletions of RPL5, RPL11, and RPL22 are frequent in hematologic diseases such as Diamond Blackfan Anemia, T-ALL, multiple myeloma, and in a variety of solid tumors. Yet, the role of these RP defects in dysregulation of the ribosomal translation function remains poorly understood. We engineered an isogenic RiboCancer cell line library modeling the most recurrent RP defects in blood and solid cancers and characterized it by a multi-omics translatome analysis (proteome, Ribo-seq, and total RNA-seq) as well as RiboMethSeq. Within this RiboCancer panel, CLL-associated Rps15 mutations induced the strongest alterations in mRNA translation, affecting up to 10% of expressed genes. Cryo-electron microscopy revealed that these mutations destabilize the Rps15 C-terminus and affect the translation elongation cycle dynamics by deregulating accommodation of aminoacylated tRNAs at the ribosomal A-site. This accommodation defect showed specificity for 11 codons, explaining the reduced translation efficiency of genes with high presence of these codons in Rps15-mutant cells. Notably, these genes were enriched for epigenetic and transcriptional regulators such as transcription factor Runx3, resulting in downregulation of Runx3 target genes involved in immune regulation. By developing and characterizing a unique RiboCancer cell line panel, we mapped translational rewiring driven by the most frequent somatic RP mutations. We provide unprecedented mechanistic insights into translation defects induced by CLL-associated Rps15 mutations, and reveal an intriguing translation-based rewiring of transcription in CLL.

Acute myeloid leukemia (AML) persistence and relapse are sustained by leukemia-propagating cells, yet the molecular programs supporting their expansion during disease evolution remain incompletely understood. Using serial patient-derived xenotransplantation, we establish a longitudinal model in which leukemia-initiating capacity progressively increases. Integrated single-cell transcriptomics and multi-omics profiling reveal a predominantly non-genetic trajectory that follows a conserved pattern across models and is associated with coordinated changes across epigenetic, transcriptional, and proteomic layers. Ribosome profiling and rRNA 2'-O-methylation analyses further support a stage-specific increase in translational activity with ribosome remodeling in advanced xenografts. A pharmacological screen of 3,247 compounds uncovers a limited set of vulnerabilities that consistently emerge during disease progression, including CRBN-dependent degradation of GSPT1 (CC-885) and IAP antagonism (AZD5582). In vivo validation shows that both agents markedly reduce leukemic burden, impair leukemia propagation, and enhance cytarabine activity in patient-derived xenograft (PDX) models. Together, these findings show that leukemic propagation is driven by a non-genetic remodeling program, providing a framework to prioritize and test stage-specific therapeutic strategies in AML.

The ribosome, long considered an invariant actor of gene expression, recently emerged as a contributor to translational control through chemical modifications of ribosomal RNAs (rRNAs). These modifications are guided by small nucleolar RNAs (snoRNAs), which direct modifying enzymes to specific rRNA positions. Here, we report that lung adenocarcinoma (LUAD) cells that are resistant to tyrosine kinase inhibitors (TKIs) reshape both their translational program and rRNA 2’O-ribose methylation (2’Ome) profiles. EML4-ALK-positive LUAD cells that are resistant to crizotinib (ALK inhibitor) exhibit reduced global protein synthesis and a change in selective translation of mRNAs, encoding proteins previously linked to resistance. These cells show concomitant reduction in SNORD104 and 2’Ome at its associated 28S_Cm1327 position. Functional studies reveal that SNORD104 depletion abolishes 2’Ome at 28S_Cm1327 without affecting basal translation or cell viability, but enhances both under crizotinib exposure. Moreover, SNORD104 knockdown attenuates caspase activation and PARP cleavage during treatment, supporting reduced cell death. Altogether, our findings support a role for snoRNA-guided rRNA modification as a novel non-genomic mechanism in early adaptive responses to crizotinib therapy in LUAD.

Proteins normally localized in the intracellular compartments of healthy cells have been observed at the surface of cancer cells, despite lacking a transmembrane domain or secretion signals. This unexpected localization likely reflects yet-unknown functions and presents a unique opportunity to develop cancer cell-specific antibody- or peptide-based therapeutic strategies. While ribosomal proteins (RPs) are primarily involved in translation, several display moonlighting functions in the cytoplasm and nucleus. In this study, we uncover an extracellular form of the ribosomal protein L21 (eL21) in triple-negative breast cancer (TNBC) cells. Using complementary approaches and a broad set of antibodies, we demonstrate that eL21 localizes to the surface of cancer cells. Remarkably, we show that anti-eL21 antibodies trigger a potent, rapid and dose-dependent anti-proliferative effect, including TNBC cell cycle arrest and apoptosis. These findings identify eL21 as a novel ribosomal protein with extra-ribosomal functions at the cancer cell surface and highlight its potential as a therapeutic target in TNBC.

Deletions and point mutations targeting ribosomal proteins (RPs) have been identified in cancer. Yet, their role in translational dysregulation remains poorly understood. We performed an integrated genome-wide translatome analysis (proteome, Ribo-seq and total RNA-seq) as well as RiboMethSeq on an isogenic cell line library modeling the most recurrent RP defects in cancer (Rpl5+/−, Rpl11+/−, Rpl22+/−, Rpl22−/−, Rpl10 R98S, Rps15 P131S and Rps15 H137Y). RP knock-out had minimal effects on translation, whereas RP point mutations induced a significant number of translation efficiency changes, affecting up to 10% of expressed genes in Rps15 mutants associated with Chronic Lymphocytic Leukemia (CLL). Cryo-electron microscopy and biochemical analyses revealed that the Rps15 mutations destabilize the C-terminal Rps15 domain, affecting the translation elongation cycle dynamics, and deregulating accommodation of aminoacylated tRNAs at the ribosomal A-site. Using Ribo-seq and translation reporter assays, we show that this accommodation defect shows codon specificity, explaining the reduced translation efficiency of genes enriched for these codons in Rps15 mutant cells, such as histones. Notably, genes with reduced translation efficiency in Rps15 mutated cells were enriched for transcriptional regulators such as transcription factor Runx3, resulting in downregulation of Runx3 target genes involved in immune regulation. Altogether, this study provides a comparative map of the translational rewiring driven by the most frequent somatic RP mutations. We provide unprecedented mechanistic insights in the translation defects induced by CLL-associated Rps15 mutations, and reveal an unappreciated cross-talk between translational and transcriptional dysregulation in these RP mutant cells. ![Figure][1] ### Competing Interest Statement The authors have declared no competing interest. European Research Council, https://ror.org/0472cxd90, 334946 FWO, G092620, 1S49817N Stichting tegen Kanker, https://ror.org/01h3dr788, F/2024/2554 iBOF, iBOF/23/014 European Hematology Association Institut National du Cancer, https://ror.org/03m8vkq32, PLBIO-2020-091 La Ligue Contre le Cancer French National Research Agency, ANR-10-INBS-08, ANR-24-INBS-0015, ANR-10-INBS-04 [1]: pending:yes

Neuroblastoma is a heterogeneous malignant pediatric tumor, the prognosis of which depends on patient age and disease stage. Current treatment strategies rely on four key diagnostic criteria: age, histological stage, genomic profile, and MYCN gene status. The oncogenic activity of MYC depends on ribosome biogenesis, which is hyperactivated in cancer cells to support their high proliferative capacity, and which may thus represent a vulnerability in neuroblastoma and constitute a therapeutic target. Here, using the well-established IMR-32 cell line along with a previously established panel of patient-derived neuroblastoma cell lines with varying MYCN status, we show that RNA polymerase I inhibition following exposure to CX-5461 and BMH-21 suppressed cell proliferation at nanomolar concentrations and induced ribosomal stress, leading to the activation of apoptosis and the p21 pathway. Furthermore, analysis of expression of ribosome biogenesis factors using publicly available datasets and RT-qPCR data from an in-house neuroblastoma cohort, we identified FBL as a marker of poor prognosis in neuroblastoma. Consistently, FBL knockdown reduced neuroblastoma cell proliferation, supporting its relevance as a therapeutic target. In conclusion, our study reinforces the therapeutic potential of ribosome biogenesis inhibition in neuroblastoma and expands the list of potential targets to include rRNA maturation factors. These findings highlight the relevance of targeting ribosome biogenesis as a novel approach for neuroblastoma treatment.

The epithelial-mesenchymal transition (EMT) is a dynamic transdifferentiation of epithelial cells into mesenchymal cells. EMT programs exhibit great diversity, based primarily on the distinct impact of molecular activities of the EMT transcription factors. Using a panel of cancer cell lines and a series of 71 triple-negative primary breast tumors, we report that the EMT transcription factor ZEB1 modulates site-specific chemical modifications of ribosomal RNA (rRNA). Overexpression of ZEB1 and ZEB2, but not TWIST1, decreased the level of 2 '-O-ribose methylation (2 ' Ome) of 28S rRNA at position Um2402. ZEB1 overexpression specifically reduced the expression of the corresponding C/D box small nucleolar RNAs (snoRNAs) SNORD143/144, which guide the rRNA 2 ' Ome complex at the 28S_Um2402 site. During ZEB1-induced EMT induction/reversion, the levels of both 2 ' Ome at 28S_Um2402 and SNORD143/144 were dynamically comodulated. Taken together, these data demonstrate that 2 ' Ome rRNA epitranscriptomics is a novel marker of ZEB1-induced EMT.

The epithelial-mesenchymal transition (EMT) is a dynamic transdifferentiation of epithelial cells into mesenchymal cells. EMT programs exhibit great diversity, based primarily on the distinct impact of molecular activities of the EMT transcription factors. Using a panel of cancer cell lines and a series of 71 triple-negative primary breast tumors, we report that the EMT transcription factor ZEB1 modulates site-specific chemical modifications of ribosomal RNA (rRNA). Overexpression of ZEB1 and ZEB2, but not TWIST1, decreased the level of 2'-O-ribose methylation (2'Ome) of 28S rRNA at position Um2402. ZEB1 overexpression specifically reduced the expression of the corresponding C/D box small nucleolar RNAs (snoRNAs) SNORD143/144, which guide the rRNA 2'Ome complex at the 28S_Um2402 site. During ZEB1-induced EMT induction/reversion, the levels of both 2'Ome at 28S_Um2402 and SNORD143/144 were dynamically comodulated. Taken together, these data demonstrate that 2'Ome rRNA epitranscriptomics is a novel marker of ZEB1-induced EMT.

BACKGROUND: Triple-negative breast cancer (TNBC) remains one of the most challenging breast cancer subtypes to treat due to the lack of effective therapeutic options. Ribosome biogenesis has recently emerged as a promising therapeutic target across various cancers. Despite the current targeting of ribosome biogenesis through RNA polymerase I (RNA Pol I) inhibition, we speculated that other factors essential for ribosome assembly, such as ribosomal RNA (rRNA) maturation factors, may also represent therapeutic targets in TNBC. METHODS: Ribosome biogenesis was evaluated in each breast cancer subtype using expression level of ribosome biogenesis factors from the UCSC XENA database. The sensitivity of TNBC cell to inhibition of ribosome biogenesis was evaluated on the TNBC cell lines MDA-MB-231 and BT-20, either using RNA Pol I inhibitors CX-5461 or BMH-21 or by knocking-down Fibrillarin (FBL) gene using an shRNA approach. Tumor cell growth and survival was monitored both in vitro and as xenografted tumors. RESULTS: We demonstrate that ribosome biogenesis-related genes are significantly overexpressed in TNBC compared to other breast cancer subtypes, highlighting its potential role in TNBC progression. Accordingly, we show that RNA Pol I inhibition exerts potent anti-proliferative effects in pre-clinical models of TNBC, both in vitro and in vivo. However, the DNA-damaging activity of RNA Pol I inhibitors raises safety concerns, highlighting the need for alternative strategies to inhibit ribosome biogenesis. To this end, we show that targeting a downstream rRNA maturation step, specifically pre-rRNA cleavage, by inhibiting the maturation factor Fibrillarin, also inhibits tumor growth in TNBC models. Notably, ribosome biogenesis inhibition, through either RNA Pol I or Fibrillarin targeting, induces cell cycle arrest without triggering significant cell death. CONCLUSION: These findings establish ribosome biogenesis as a therapeutic vulnerability in TNBC and identify rRNA maturation, and Fibrillarin in particular, as novel targets for potential therapeutic intervention.

All routine clinical treatments for colorectal cancer include 5-fluorouracil (5-FU), which cannot counteract recurrence and metastases formation. As the pyrimidine analog 5-FU can impact multiple pathways including both DNA and RNA metabolism, studying its mode of actions could lead to improved therapies. Using a dedicated reporter system for lineage-tracing and deep translatome profiling we demonstrate that 5-FU causes some colorectal cancer cells to tolerate the drug, due to a durable translational reprogramming that sustains cell plasticity. This period of drug tolerance coincides with specific translational activation of genes coding for proteins with major pro-tumoral functions. We unravel a major unexpected translational overexpression of the pro-inflammatory and pro-tumoral IL-8 cytokine, alongside other anti-apoptotic, senescence-associated secretory phenotype and cancer-related senescence phenotype genes. Given the adverse prognostic implications of elevated IL-8 levels across various cancers, our findings suggest IL-8 targeting could counteract 5-FU resistance. ### Competing Interest Statement The authors have declared no competing interest.

Neuroblastoma (NB) is the most common pediatric tumor and is currently treated by several types of therapies including chemotherapies, such as bortezomib treatment. However, resistance to bortezomib is frequently observed by mechanisms that remain to be deciphered. Bortezomib treatment leads to caspase activation and aggresome formation. Using models of patients-derived NB cell lines with different levels of sensitivity to bortezomib, we show that the activated form of caspase 3 accumulates within aggresomes of NB resistant cells leading to an impairment of bortezomib-induced apoptosis and increased cell survival. Our findings unveil a new mechanism of resistance to chemotherapy based on an altered subcellular distribution of the executioner caspase 3. This mechanism could explain the resistance developed in NB patients treated with bortezomib, emphasizing the potential of drugs targeting aggresomes.

Regulation of mRNA translation is a crucial step in controlling gene expression in stressed cells, impacting many pathologies, including heart ischemia. In recent years, ribosome heterogeneity has emerged as a key control mechanism driving the translation of subsets of mRNAs. In this study, we investigated variations in ribosome composition in human cardiomyocytes subjected to endoplasmic reticulum stress induced by tunicamycin treatment. Our findings demonstrate that this stress inhibits global translation in cardiomyocytes while activating internal ribosome entry site (IRES)-dependent translation. Analysis of translating ribosome composition in stressed and unstressed cardiomyocytes was conducted using mass spectrometry. We observed no significant changes in ribosomal protein composition, but several mitochondrial ribosomal proteins (MRPs) were identified in cytosolic polysomes, showing drastic variations between stressed and unstressed cells. The most notable increase in polysomes of stressed cells was observed in MRPS15. Its interaction with ribosomal proteins was confirmed by proximity ligation assay (PLA) and immunoprecipitation, suggesting its intrinsic role as a ribosomal component during stress. Knock-down or overexpression experiments of MRPS15 revealed its role as an activator of IRES-dependent translation. Furthermore, polysome profiling after immunoprecipitation with anti-MRPS15 antibody revealed that the “MRPS15 ribosome” is specialized in translating mRNAs involved in the unfolded protein response.

Epithelial-mesenchymal transition (EMT) involves profound changes in cell morphology, driven by transcriptional and epigenetic reprogramming. However, evidence suggests that translation and ribosome composition also play key roles in establishing pathophysiological phenotypes. Using genome-wide analyses, we reported significant rearrangement of the translational landscape and machinery during EMT. Specifically, a cell line overexpressing the EMT transcription factor ZEB1 displayed alterations in translational reprogramming and fidelity. Furthermore, using riboproteomics, we unveiled an increased level of the ribosomal protein RPL36A in mesenchymal ribosomes, indicating precise tuning of ribosome composition. Remarkably, RPL36A overexpression alone was sufficient to trigger the acquisition of mesenchymal features, including a switch in the molecular pattern, cell morphology, and behavior, demonstrating its pivotal role in EMT. These findings underline the importance of translational reprogramming and fine-tuning of ribosome composition in EMT.

Differentially expressed genes in Xenograted T-ALL shSYNCRIP-SNHG5 versus ShCtrl

Background High-grade adult-type diffuse gliomas (HGGs) constitute a heterogeneous group of aggressive tumors that are mostly incurable. Recent advances highlighting the contribution of ribosomes to cancer development have offered new clinical perspectives. Here, we uncovered that isocitrate dehydrogenase (IDH)wt and IDHmut HGGs display distinct alterations of ribosome biology, in terms of rRNA epitranscriptomics and ribosome biogenesis, which could constitute novel hallmarks that can be exploited for the management of these pathologies. Methods We analyzed (1) the ribosomal RNA 2’O-ribose methylation (rRNA 2’Ome) using RiboMethSeq and in-house developed bioinformatics tools (https://github.com/RibosomeCRCL/ribomethseq-nfandrRMSAnalyzer) on 3 independent cohorts compiling 71 HGGs (IDHwt n = 30, IDHmut n = 41) and 9 non-neoplastic samples, (2) the expression of ribosome biogenesis factors using medium throughput RT-qPCR as a readout of ribosome biogenesis, and (3) the sensitivity of 5 HGG cell lines to RNA Pol I inhibitors (CX5461, BMH-21). Results Unsupervised analysis demonstrated that HGGs could be distinguished based on their rRNA 2’Ome epitranscriptomic profile, with IDHwt glioblastomas displaying the most significant alterations of rRNA 2’Ome at specific sites. In contrast, IDHmut HGGs are largely characterized by an overexpression of ribosome biogenesis factors compared to non-neoplastic tissues or IDHwt glioblastomas. Finally, IDHmut HGG-derived spheroids display higher cytotoxicity to CX5461 than IDHwt glioblastoma, while all HGG spheroids display a similar cytotoxicity to BMH-21. Conclusions In HGGs, IDH mutational status is associated with specific alterations of the ribosome biology and with distinct sensitivities to RNA Pol I inhibitors.

Differentially Expressed Proteins Deleted versus non-deleted clones

Abstract snoDB is an interactive database of human small nucleolar RNAs (snoRNAs) that includes up-to-date information on snoRNA features, genomic location, conservation, host gene, snoRNA–RNA targets and snoRNA abundance and provides links to other resources. In the second edition of this database (snoDB 2.0), we added an entirely new section on ribosomal RNA (rRNA) chemical modifications guided by snoRNAs with easy navigation between the different rRNA versions used in the literature and experimentally measured levels of modification. We also included new layers of information, including snoRNA motifs, secondary structure prediction, snoRNA–protein interactions, copy annotations and low structure bias expression data in a wide panel of tissues and cell lines to bolster functional probing of snoRNA biology. Version 2.0 features updated identifiers, more links to external resources and duplicate entry resolution. As a result, snoDB 2.0, which is freely available at https://bioinfo-scottgroup.med.usherbrooke.ca/snoDB/, represents a one-stop shop for snoRNA features, rRNA modification targets, functional impact and potential regulators.

Nutrient availability is a key determinant of tumor cell behavior. While nutrient-rich conditions favor proliferation and tumor growth, scarcity, and particularly glutamine starvation, promotes cell dedifferentiation and chemoresistance. Here, linking ribosome biogenesis plasticity with tumor cell fate, we uncover that the amino acid sensor GCN2 represses the expression of the precursor of ribosomal RNA, 47S, under metabolic stress. We show that blockade of GCN2 triggers cell death by an irremediable nucleolar stress and subsequent TP53-mediated apoptosis in patient-derived models of colon adenocarcinoma (COAD). In nutrient-rich conditions, GCN2 activity supports cell proliferation through the transcription stimulation of 47S rRNA, independently of the canonical ISR axis. However, impairment of GCN2 activity prevents nuclear translocation of the methionyl tRNA synthetase (MetRS) underlying the generation of a nucleolar stress, mTORC1 inhibition and autophagy induction. Inhibition of the GCN2-MetRS axis drastically improves the cytotoxicity of RNA pol I inhibitors, including the first-line chemotherapy oxaliplatin, on patient-derived COAD tumoroids. Our data thus reveal that GCN2 differentially controls the ribosome biogenesis according the nutritional context. Furthermore, pharmacological co-inhibition of the two GCN2 branches and the RNA pol I activity may represent a valuable strategy for elimination of proliferative and metabolically-stressed COAD cell.