CRM1 and its ribosome export adaptor NMD3 localize to the nucleolus and affect rRNA synthesis

AbstractTumor cells require nominal increases in protein synthesis in order to maintain high proliferation rates. As such, tumor cells must acquire enhanced ribosome production. How the numerous mutations in tumor cells ultimately achieve this aberrant production is largely unknown. The gene encoding ARF is the most commonly deleted gene in human cancer. ARF plays a significant role in regulating ribosomal RNA synthesis and processing, ribosome export into the cytoplasm, and global protein synthesis. Utilizing ribosome profiling, we show that ARF is a major suppressor of 5′-terminal oligopyrimidine mRNA translation. Genes with increased translational efficiency following loss of ARF include many ribosomal proteins and translation factors. Knockout of p53 largely phenocopies ARF loss, with increased protein synthesis and expression of 5′-TOP encoded proteins. The 5′-TOP regulators eIF4G1 and LARP1 are upregulated in Arf- and p53-null cells.

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Nuclear m6A reader YTHDC1 regulates the scaffold function of LINE1 RNA in mouse ESCs and early embryos

Protein & Cell ◽

10.1007/s13238-021-00837-8 ◽

2021 ◽

Author(s):

Chuan Chen ◽

Wenqiang Liu ◽

Jiayin Guo ◽

Yuanyuan Liu ◽

Xuelian Liu ◽

...

Keyword(s):

Inner Cell Mass ◽

Cell Mass ◽

Embryonic Stem ◽

Rrna Synthesis ◽

Binding Ability ◽

Transcriptome Regulation ◽

Early Embryos ◽

Intrinsic Mechanism ◽

Regulatory Rnas

AbstractN6-methyladenosine (m6A) on chromosome-associated regulatory RNAs (carRNAs), including repeat RNAs, plays important roles in tuning the chromatin state and transcription, but the intrinsic mechanism remains unclear. Here, we report that YTHDC1 plays indispensable roles in the self-renewal and differentiation potency of mouse embryonic stem cells (ESCs), which highly depends on the m6A-binding ability. Ythdc1 is required for sufficient rRNA synthesis and repression of the 2-cell (2C) transcriptional program in ESCs, which recapitulates the transcriptome regulation by the LINE1 scaffold. Detailed analyses revealed that YTHDC1 recognizes m6A on LINE1 RNAs in the nucleus and regulates the formation of the LINE1-NCL partnership and the chromatin recruitment of KAP1. Moreover, the establishment of H3K9me3 on 2C-related retrotransposons is interrupted in Ythdc1-depleted ESCs and inner cell mass (ICM) cells, which consequently increases the transcriptional activities. Our study reveals a role of m6A in regulating the RNA scaffold, providing a new model for the RNA-chromatin cross-talk.

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Harnessing the Nucleolar DNA Damage Response in Cancer Therapy

Genes ◽

10.3390/genes12081156 ◽

2021 ◽

Vol 12 (8) ◽

pp. 1156

Author(s):

Jiachen Xuan ◽

Kezia Gitareja ◽

Natalie Brajanovski ◽

Elaine Sanij

Keyword(s):

Dna Damage ◽

Dna Repair ◽

Cancer Therapy ◽

Dna Damage Response ◽

Rrna Genes ◽

Rrna Synthesis ◽

Pol I ◽

Clinical Investigations ◽

Damage Response ◽

Synthesis And Processing

The nucleoli are subdomains of the nucleus that form around actively transcribed ribosomal RNA (rRNA) genes. They serve as the site of rRNA synthesis and processing, and ribosome assembly. There are 400–600 copies of rRNA genes (rDNA) in human cells and their highly repetitive and transcribed nature poses a challenge for DNA repair and replication machineries. It is only in the last 7 years that the DNA damage response and processes of DNA repair at the rDNA repeats have been recognized to be unique and distinct from the classic response to DNA damage in the nucleoplasm. In the last decade, the nucleolus has also emerged as a central hub for coordinating responses to stress via sequestering tumor suppressors, DNA repair and cell cycle factors until they are required for their functional role in the nucleoplasm. In this review, we focus on features of the rDNA repeats that make them highly vulnerable to DNA damage and the mechanisms by which rDNA damage is repaired. We highlight the molecular consequences of rDNA damage including activation of the nucleolar DNA damage response, which is emerging as a unique response that can be exploited in anti-cancer therapy. In this review, we focus on CX-5461, a novel inhibitor of Pol I transcription that induces the nucleolar DNA damage response and is showing increasing promise in clinical investigations.

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Commuting to Work: Nucleolar Long Non-Coding RNA Control Ribosome Biogenesis from Near and Far

Non-Coding RNA ◽

10.3390/ncrna7030042 ◽

2021 ◽

Vol 7 (3) ◽

pp. 42

Author(s):

Victoria Mamontova ◽

Barbara Trifault ◽

Lea Boten ◽

Kaspar Burger

Keyword(s):

Gene Expression ◽

Rna Polymerase Ii ◽

Ribosome Biogenesis ◽

Intergenic Spacer ◽

Cellular Growth ◽

Rrna Synthesis ◽

Protein Coding ◽

Non Coding Rna ◽

And Function ◽

In Cis

Gene expression is an essential process for cellular growth, proliferation, and differentiation. The transcription of protein-coding genes and non-coding loci depends on RNA polymerases. Interestingly, numerous loci encode long non-coding (lnc)RNA transcripts that are transcribed by RNA polymerase II (RNAPII) and fine-tune the RNA metabolism. The nucleolus is a prime example of how different lncRNA species concomitantly regulate gene expression by facilitating the production and processing of ribosomal (r)RNA for ribosome biogenesis. Here, we summarise the current findings on how RNAPII influences nucleolar structure and function. We describe how RNAPII-dependent lncRNA can both promote nucleolar integrity and inhibit ribosomal (r)RNA synthesis by modulating the availability of rRNA synthesis factors in trans. Surprisingly, some lncRNA transcripts can directly originate from nucleolar loci and function in cis. The nucleolar intergenic spacer (IGS), for example, encodes nucleolar transcripts that counteract spurious rRNA synthesis in unperturbed cells. In response to DNA damage, RNAPII-dependent lncRNA originates directly at broken ribosomal (r)DNA loci and is processed into small ncRNA, possibly to modulate DNA repair. Thus, lncRNA-mediated regulation of nucleolar biology occurs by several modes of action and is more direct than anticipated, pointing to an intimate crosstalk of RNA metabolic events.

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Increased expression of UBF is a critical determinant for rRNA synthesis and hypertrophic growth of cardiac myocytes

The FASEB Journal ◽

10.1096/fj.01-0853fje ◽

2001 ◽

Cited By ~ 4

Author(s):

Y. Brandenburger

Keyword(s):

Cardiac Myocytes ◽

Rrna Synthesis ◽

Critical Determinant ◽

Hypertrophic Growth

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The seven E. coli ribosomal RNA operon upstream regulatory regions differ in structure and transcription factor binding efficiencies

Biological Chemistry ◽

10.1515/bc.2005.062 ◽

2005 ◽

Vol 386 (6) ◽

pp. 523-534 ◽

Cited By ~ 24

Author(s):

Annette Hillebrand ◽

Reinhild Wurm ◽

Artur Menzel ◽

Rolf Wagner

Keyword(s):

Protein Complexes ◽

Rrna Synthesis ◽

Dna Fragments ◽

Promoter Regions ◽

Regulatory Regions ◽

E Coli ◽

Upstream Activating Sequence ◽

Dna Elements ◽

The Individual ◽

Upstream Regulatory Regions

AbstractRibosomal RNAs inE. coliare transcribed from seven operons, which are highly conserved in their organization and sequence. However, the upstream regulatory DNA regions differ considerably, suggesting differences in regulation. We have therefore analyzed the conformation of all seven DNA elements located upstream of the majorE. colirRNA P1 promoters. As judged by temperature-dependent gel electrophoresis with isolated DNA fragments comprising the individual P1 promoters and the complete upstream regulatory regions, all seven rRNA upstream sequences are intrinsically curved. The degree of intrinsic curvature was highest for therrnBandrrnDfragments and less pronounced for therrnAandrrnEoperons. Comparison of the experimentally determined differences in curvature with programs for the prediction of DNA conformation revealed a generally high degree of conformity. Moreover, the analysis showed that the center of curvature is located at about the same position in all fragments. The different upstream regions were analyzed for their capacity to bind the transcription factors FIS and H-NS, which are known as antagonists in the regulation of rRNA synthesis. Gel retardation experiments revealed that both proteins interact with the upstream promoter regions of all seven rDNA fragments, with the affinities of the different DNA fragments for FIS and H-NS and the structure of the resulting complexes deviating considerably. FIS binding was non-cooperative, and at comparable protein concentrations the occupancy of the different DNA fragments varied between two and four binding sites. In contrast, H-NS was shown to bind cooperatively and intermediate states of occupancy could not be resolved for each fragment. The different gel electrophoretic mobilities of the individual DNA/protein complexes indicate variable structures and topologies of the upstream activating sequence regulatory complexes. Our results are highly suggestive of differential regulation of the individual rRNA operons.

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High-resolution autoradiographic localization of DNA-containing sites and RNA synthesis in developing nucleoli of human preimplantation embryos: a new concept of embryonic nucleologenesis

Development ◽

10.1242/dev.101.4.777 ◽

1987 ◽

Vol 101 (4) ◽

pp. 777-791 ◽

Cited By ~ 4

Author(s):

J. Tesarik ◽

V. Kopecny ◽

M. Plachot ◽

J. Mandelbaum

Keyword(s):

Rna Synthesis ◽

Preimplantation Embryos ◽

Synthetic Activity ◽

Rrna Synthesis ◽

Nucleolar Organizer Regions ◽

Careful Study ◽

Matrix Elements ◽

Electron Microscopic Autoradiography ◽

General Validity ◽

Granular Component

Human embryos from the 2-cell to the morula stage, obtained by in vitro fertilization, were incubated with [3H]thymidine or [3H]uridine so as to achieve labelling of all replicating nuclear DNA and the newly synthesized RNA, respectively. The label was localized in different structural components of developing nucleoli using electron microscopic autoradiography. Careful study of the relationship between the structural pattern and nucleic acid distribution made it possible to define four stages of embryonic nucleologenesis. Homogeneous nuclear precursors (i) consist of nucleolar matrix elements appearing as filaments of 3 nm thickness, (ii) do not contain recently replicated DNA and (iii) lack RNA synthetic activity. Penetration of DNA into these bodies is a key event leading to their transformation into heterogeneous nucleolar precursors. In addition to the 3 nm matrix filaments, two types of 5 nm fibrillar components can be recognized in them. The denser type contains DNA and is the site of nucleolar RNA synthesis, while the more loosely arranged 5 nm fibrils are not labelled with [3H]thymidine and apparently represent the newly produced pre-rRNA detached from the transcribing rDNA filament. Compact fibrillogranular nucleoli are characterized by the first appearance of the granular component and reduction of the nontranscribing part of the fibrillar component, both indicating the activation of the machinery for rRNA processing. Finally, the granular component is most evident in reticulated nucleoli, occupying mostly the inner parts of their nucleolonema, while the transcription sites tend to be located at the nucleolar periphery. Our findings advocate a unique concept of embryonic nucleologenesis, different from any other nucleolar event during the cell cycle of differentiated cells. This developmental pattern is characterized by a gradual activation of rRNA synthesis and processing, mediated by progressive association of rDNA and, later on, the newly formed pre-rRNA with pre-existing nucleolar matrix elements that are originally topically separated from nucleolar organizer regions. This model may have a general validity in early animal embryos despite some interspecies variability in the timing of individual steps and resulting structural peculiarities.

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