Next Generation Sequencing Facilitates Quantitative Analysis of the Role of Ddx21 in hematopoietic stem cells [RNA-seq]
Ontology highlight
ABSTRACT:
ORGANISM(S): Mus musculus
PROVIDER: GSE312007 | GEO | 2026/03/20
REPOSITORIES: GEO
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Project description:PARP inhibitors (PARPi) prevent cancer cell growth by inducing synthetic lethality with DNA repair defects (e.g., in BRCA1/2 mutant cells). We have identified an alternate pathway for PARPi-mediated growth control in BRCA1/2-intact breast cancer cells involving rDNA transcription and ribosome biogenesis. PARP-1 binds to snoRNAs, which stimulate PARP-1 catalytic activity in the nucleolus independent of DNA damage. Activated PARP-1 ADP-ribosylates DDX21, an RNA helicase that localizes to nucleoli and promotes rDNA transcription when ADP-ribosylated. Treatment with PARPi or mutation of the ADP-ribosylation sites reduce DDX21 nucleolar localization, rDNA transcription, ribosome biogenesis, protein translation, and cell growth. The salient features of this pathway are evident in xenografts in mice and human breast cancer patient samples. Elevated levels of PARP-1 and nucleolar DDX21 are associated with cancer-related outcomes. Our studies provide a mechanistic rationale for efficacy of PARPi in cancer cells lacking defects in DNA repair whose growth is inhibited by PARPi.
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Project description:DEAD-box RNA helicases are vital for the regulation of various aspects of the RNA life cycle, but the molecular underpinnings of their involvement, particularly in mammalian cells, remain poorly understood. Here we show that the DEAD-box RNA helicase DDX21 can sense transcriptional status of both RNA Pol I and Pol II to control transcriptional and post-transcriptional steps of ribosome biogenesis in human cells. We demonstrate that DDX21 widely associates with Pol I- and Pol II-transcribed genes and with diverse species of protein-coding and noncoding RNAs. Although broad, these molecular interactions, both at the chromatin and at the RNA level, exhibit a remarkable specificity for the ribosomal pathway. In the nucleolus, DDX21 occupies the transcribed rDNA locus, directly contacts both rRNA and snoRNAs and, as a functional component of the snoRNA ribonucleoprotein (snoRNP) complex, promotes modification of rRNA. In the nucleoplasm, DDX21 is incorporated into the 7SK snRNP complex, which facilitates DDX21 association with promoters of Pol II-transcribed genes encoding ribosomal proteins and snoRNAs. Promoter-bound DDX21 facilitates the release of P-TEFb from the 7SK snRNP, enhancing productive Pol II elongation. Altogether, we present a unifying mechanism for the coordinated regulation of ribosomal genes across nuclear compartments, and provide first evidence implicating a mammalian RNA helicase in RNA modification and Pol II elongation control. Examination of DDX21 chromatin association and DDX21 RNA interacting partners in HEK293 cells
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Project description:Myriad of craniofacial disorders are caused by heterozygous mutations in general regulators of housekeeping cellular functions such as ribosome biogenesis. While it is understood that many of these highly tissue-specific malformations are a consequence of defects in cranial neural crest cells (cNCCs), an embryonic cell group that gives rise to most of the facial structures during embryogenesis, the mechanism underlying cell type-selectivity of these effects remains largely unknown. Here we show that DDX21, a DEAD-box RNA helicase involved in control of both RNA polymerase (Pol) I and Pol II dependent transcriptional arms of ribosome biogenesis, is a key mediator of the nucleolar stress response. Using an in vitro model of Treacher Collins Syndrome (TCS), a craniofacial disorder caused by heterozygous mutations in components of the Pol I transcriptional machinery, we demonstrate that perturbations in ribosomal RNA (rRNA) transcription induce DDX21-mediated surveillance mechanism in cNCCs, leading to DDX21 relocalization from the nucleolus to the nucleoplasm, its eviction from Pol I and Pol II chromatin targets and inhibition of rRNA processing. Importantly, these effects are cell type-selective, cell-autonomous and involve activation of the p53 pathway. We further show that cNCCs are characterized by the inherently high reservoir of p53 mRNA and sensitivity to p53-mediated apoptosis. Remarkably, preventing the loss of DDX21 from nucleolus and chromatin can rescue both the sensitivity to apoptosis and TCS-associated craniofacial phenotypes in vivo. This mechanism is not restricted to TCS, as gene function perturbations linked to other ribosomopathies with craniofacial manifestations also lead to the activation of DDX21 surveillance. Lastly, we provide evidence that inhibition of rRNA synthesis leads to rDNA damage, and furthermore, that rDNA damage is sufficient to activate DDX21 surveillance and elicits tissue-selective and dosage-dependent effects on craniofacial development in vivo.
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Project description:The nucleolus is a dynamic structure where ribosome subunits are produced. Indeed, nucleoli respond to any change in cellular homeostasis by altering the rate of ribosome biogenesis, thus working as a stress sensor. Consequently, imbalances in ribosome biogenesis promotes changes in morphology and function and can evoke a nucleolar stress and DNA damage responses. These changes in nucleolar architecture and composition, culminating in impaired ribosome biogenesis, prompt the emergence of the nucleolar stress, which manifests as a contributing factor in aging and cancer. Here, we illuminate the pivotal role that the RNA binding protein Hnrnpk plays in orchestrating nucleolar dynamics and sustaining ribosome function. As a ribonucleoprotein, Hnrnpk governs the chaperoning of nascent transcripts to facilitate their processing and subsequent nuclear export for ribosomal integration. When overexpressed, Hnrnpk induces disruptive alterations in nucleolar structure, resulting in stress-like phenotypes; such as unbalances of molecular components, accumulation and delocalization of nucleolin, and decrease expression and occupation of fibrillarin. Consequentially, these aberrations in nucleolar equilibrium engenders a disruption in ribosome biogenesis and concomitantly halts the protein translation machinery. Nucleolin (Ncl) haploinsufficiency is correlated with enlarged nucleoli, increased ribosome components, heightened translational rates translation and a concomitant decrease in lifespan. Thus, an Hnrnpk overexpression-dependent surge of Ncl levels stemming may instigate a decline in nucleolar integrity and perturbations in ribosome biogenesis—an event intimately associated with ribosomopathies and the ensuing syndrome of bone marrow failure syndrome. Intersting, the aging process shares a number of common biological hallmarks with bone marrow failure. Again, alterations in Hnrnpk expression, specifically overexpression triggers nucleolar stress, driving cell cycle arrest and senescence of the cells. Our investigations demonstrate that p53, c-Myc and Ncl haploinsufficiency rescue these Hnrnpk-mediated phenotypes. Collectively, the data begin to decipher novel signaling pathway involved in nucleolar stress - ribosome stress – and p53 driven cell cycle arrest that governs this process. Together, these findings support the idea that nucleolar disturbances contribute to ribosome impairment, thus catalyzing the genesis of hematopoietic anomalies and aging process. Significantly, this study elucidates Hnrnpk as a previously unrecognized master regulator within these intricate ribosomal mechanisms; providing a novel window to view the orchestration of nucleolar integrity, ribosome function, and cellular senescence.
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Project description:The nucleolus is a membraneless organelle responsible for ribosome biogenesis, perinuclear heterochromatin formation, and genome stability regulation. However, how cell fate decision occurs, including early embryonic development, ESC differentiation, and tumorigenesis, remains poorly understood at the nucleolar level. It has been observed that large nucleoli and rDNA hyperactivity are common in pluripotent stem cells and tumor cells, while the nucleolus shrinks and rDNA transcriptional activity decrease during lineage commitment. iPSCs nucleolar size and rDNA transcriptional activity are greater than that before reprogramming. It remains unclear how and when the differentiated cell nucleoli convert to the stem cell nucleoli during iPSC reprogramming.In this study, we found that nucleolar remodeling, manifested as enlarged nucleolus, activation of rDNA transcription, enhanced activity of nucleolar organizing regions (NORs), and conversion of reticular nucleolar ultrastructure into low-granular, is an early and stage-specific event that occurs during iPSCs reprogramming. Our study highlights the importance of rDNA transcriptional activity in the early stages of iPSC reprogramming, which is crucial for nucleolar remodeling and regaining stemness. Interfering rDNA transcription hinders nucleolar remodeling, which has disastrous consequences for chromatin remodeling in early stage of iPSC reprogramming and iPSCs establishment. Moreover, our results revealed a nucleolar regulation on chromatin accessibility during iPSC reprogramming and identified some candidate genes (Mybl2, Bard1 and other chromosome related genes) that might be associated with iPSC reprogramming, which may apply to nucleolar remodeling in other cell fated decision.
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2014-11-17 | GSE56802 | GEO
Project description:The nucleolus is the membraneless organelle in the nucleus mainly responsible for ribosome biogenesis. It is also an excellent stress sensor and any changes on its architecture or composition leads to nucleolar stress deriving in cell cycle arrest and interruption of ribosomal activity. However, nucleolar stress sustained is also a contributing factor to pathologies like aging and cancer, highlighting the importance of its homeostasis in the cells. In this study, we identified and described the pivotal role of the RNA-binding protein Hnrnpk in the ribosome biogenesis and nucleolar dynamics. We developed an in vitro model of Hnrnpk overexpression with CRISPR-Cas9/SAM and an in vivo mouse model of Hnrnpk ubiquitous overexpression. We found that this overexpression disrupted translation and caused alterations in the nucleolar structure, resulting in nucleolar stress with alterations in the levels and localization of the nucleolar components fibrillarin and nucleolin, as well as impaired ribosome biogenesis. These aberrations trigger cell cycle arrest and cell senescence, and the phenotype could be rescued with haploinsufficiency of p53, suggesting that it is a consequence of a p53-dependant nucleolar stress mechanism. Finally, in our mouse model, Hnrnpk overexpression led to an aging phenotype with bone marrow failure and reduced lifespan, similar to a ribosomopathy-like phenotype. Together, our findings identify Hnrnpk as a novel master regulator of ribosome biogenesis and nucleolar homeostasis through p53, providing a new view of the orchestration of nucleolar integrity, ribosome function and cellular senescence.
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