scholarly journals Translational control during cellular senescence

2020 ◽  
Author(s):  
Matthew J. Payea ◽  
Carlos Anerillas ◽  
Ravi Tharakan ◽  
Myriam Gorospe
Keyword(s):  
Translational Control ◽  
Ribosome Biogenesis ◽  
Rrna Processing ◽  
Proliferating Cells ◽  
Cycle Arrest ◽  
Nucleolar Stress ◽  
Specific Proteins ◽  
Inflammatory Proteins ◽  
Secretory Phenotype

Senescence is a state of long-term cell-cycle arrest that arises in cells that have incurred sub-lethal damage. While senescent cells no longer replicate, they remain metabolically active and further develop unique and stable phenotypes that are not present in proliferating cells. On one hand, senescent cells increase in size, maintain an active mTORC1 complex, and produce and secrete a substantial amount of inflammatory proteins as part of the senescence associated secretory phenotype (SASP). On the other hand, these pro-growth phenotypes contrast with the p53-mediated growth arrest typical of senescent cells that is associated with nucleolar stress and an inhibition of rRNA processing and ribosome biogenesis. In sum, translation in senescent cells paradoxically comprises both a global repression of translation triggered by DNA damage and a select increase in the translation of specific proteins, including SASP factors.

scholarly journals Drosophila to Explore Nucleolar Stress

2021 ◽  
Vol 22 (13) ◽  
pp. 6759
Author(s):  
Kathryn R. DeLeo ◽  
Sonu S. Baral ◽  
Alex Houser ◽  
Allison James ◽  
Phelan Sewell ◽  
...  
Keyword(s):  
Ribosome Biogenesis ◽  
Treacher Collins Syndrome ◽  
P Bodies ◽  
Disease States ◽  
Cycle Arrest ◽  
Nucleolar Stress ◽  
Marker Proteins ◽  
Drosophila Larvae ◽  
Disc Cells ◽  
Eye Imaginal Disc

Nucleolar stress occurs when ribosome production or function declines. Nucleolar stress in stem cells or progenitor cells often leads to disease states called ribosomopathies. Drosophila offers a robust system to explore how nucleolar stress causes cell cycle arrest, apoptosis, or autophagy depending on the cell type. We provide an overview of nucleolar stress in Drosophila by depleting nucleolar phosphoprotein of 140 kDa (Nopp140), a ribosome biogenesis factor (RBF) in nucleoli and Cajal bodies (CBs). The depletion of Nopp140 in eye imaginal disc cells generates eye deformities reminiscent of craniofacial deformities associated with the Treacher Collins syndrome (TCS), a human ribosomopathy. We show the activation of c-Jun N-terminal Kinase (JNK) in Drosophila larvae homozygous for a Nopp140 gene deletion. JNK is known to induce the expression of the pro-apoptotic Hid protein and autophagy factors Atg1, Atg18.1, and Atg8a; thus, JNK is a central regulator in Drosophila nucleolar stress. Ribosome abundance declines upon Nopp140 loss, but unusual cytoplasmic granules accumulate that resemble Processing (P) bodies based on marker proteins, Decapping Protein 1 (DCP1) and Maternal expression at 31B (Me31B). Wild type brain neuroblasts (NBs) express copious amounts of endogenous coilin, but coilin levels decline upon nucleolar stress in most NB types relative to the Mushroom body (MB) NBs. MB NBs exhibit resilience against nucleolar stress as they maintain normal coilin, Deadpan, and EdU labeling levels.

scholarly journals Trypanosoma brucei L11 Is Essential to Ribosome Biogenesis and Interacts with the Kinetoplastid-Specific Proteins P34 and P37

mSphere ◽  
2019 ◽  
Vol 4 (4) ◽  
Author(s):  
Daniel Jaremko ◽  
Martin Ciganda ◽  
Linda Christen ◽  
Noreen Williams
Keyword(s):  
Drug Development ◽  
Ribosomal Protein ◽  
Trypanosoma Brucei ◽  
Ribosome Biogenesis ◽  
5S Rrna ◽  
Rrna Processing ◽  
Content Type ◽  
Specific Proteins ◽  
Novel Interactions ◽  
Ribosomal Protein L11

ABSTRACT Eukaryotic ribosome biogenesis is an essential cellular process involving tightly coordinated assembly of multiple rRNA and protein components. Much of our understanding of this pathway has come from studies performed with yeast model systems. These studies have identified critical checkpoints in the maturation of the large ribosomal subunit (LSU/60S), one of which is the proper formation and incorporation of the 5S ribonucleoprotein complex (5S RNP). Research on the 5S RNP has identified a complex containing the four proteins L5, L11, Rpf2, and Rrs1 as well as 5S rRNA. Our laboratory has studied the 5S RNP in Trypanosoma brucei, a eukaryotic parasite, and identified the proteins P34 and P37 as essential, parasite-specific members of this complex. We have additionally identified homologues of L5, Rpf2, Rrs1, and 5S rRNA in T. brucei and characterized their roles in this essential process. In this study, we examined the T. brucei homologue of ribosomal protein L11 as a member of the 5S RNP. We showed that TbL11 is essential and that it is important for proper ribosome subunit formation and 60S rRNA processing. Additionally, we identified TbL11 interactions with TbL5 and TbRpf2, as well as novel interactions with the kinetoplast-specific proteins P34 and P37. These findings expand our understanding of a crucial process outside the context of model yeast organisms and highlight differences in an otherwise highly conserved process that could be used to develop future treatments against T. brucei. IMPORTANCE The human-pathogenic, eukaryotic parasite Trypanosoma brucei causes human and animal African trypanosomiases. Treatments for T. brucei suffer from numerous hurdles, including adverse side effects and developing resistance. Ribosome biogenesis is one critical process for T. brucei survival that could be targeted for new drug development. A critical checkpoint in ribosome biogenesis is formation of the 5S RNP, which we have shown involves the trypanosome-specific proteins P34 and P37 as well as homologues of Rpf2, Rrs1, and L5. We have identified parasite-specific characteristics of these proteins and involvement in key parts of ribosome biogenesis, making them candidates for future drug development. In this work, we characterized the T. brucei homologue of ribosomal protein L11. We show that it is essential for parasite survival and is involved in ribosome biogenesis and rRNA processing. Furthermore, we identified novel interactions with P34 and P37, characteristics that make this protein a potential target for novel chemotherapeutics.

scholarly journals Unique Interactions of the Nuclear Export Receptors TbMex67 and TbMtr2 with Components of the 5S Ribonuclear Particle in Trypanosoma brucei

mSphere ◽  
2019 ◽  
Vol 4 (4) ◽  
Author(s):  
Constance Rink ◽  
Noreen Williams
Keyword(s):  
Trypanosoma Brucei ◽  
Nuclear Export ◽  
Ribosome Biogenesis ◽  
5S Rrna ◽  
Ribosome Assembly ◽  
Rrna Processing ◽  
Ribosomal Subunits ◽  
Content Type ◽  
Final Maturation ◽  
Specific Proteins

ABSTRACT Eukaryotic ribosome biogenesis is a complicated and highly conserved biological process. A critical step in ribosome biogenesis is the translocation of the immature ribosomal subunits from the nucleoplasm, across the nucleopore complex, to the cytoplasm where they undergo final maturation. Many nonribosomal proteins are needed to facilitate export of the ribosomal subunits, and one complex participating in export of the pre-60S in Saccharomyces cerevisiae is the heterodimer Mex67-Mtr2. In Trypanomsoma brucei, the process of ribosome biogenesis differs from the yeast process in key steps and is not yet fully characterized. However, our laboratory has previously identified the trypanosome-specific proteins P34/P37 and has shown that P34/P37 are necessary for the formation of the 5S ribonuclear particle (RNP) and for the nuclear export of the pre-60S subunit. We have also shown that loss of TbMex67 or TbMtr2 leads to aberrant ribosome formation, rRNA processing, and polysome formation in T. brucei. In this study, we characterize the interaction of TbMex67 and TbMtr2 with the components of the 5S RNP (P34/P37, L5 and 5S rRNA) of the 60S subunit. We demonstrate that TbMex67 directly interacts with P34 and L5 proteins as well as 5S rRNA, while TbMtr2 does not. Using protein sequence alignments and structure prediction modeling, we show that TbMex67 lacks the amino acids previously shown to be essential for binding to 5S rRNA in yeast and in general aligns more closely with the human orthologue (NXF1 or TAP). This work suggests that the T. brucei Mex67-Mtr2 binds ribosomal cargo differently from the yeast system. IMPORTANCE Trypanosoma brucei is the causative agent for both African sleeping sickness in humans and nagana in cattle. Ribosome biogenesis in these pathogens requires both conserved and trypanosome-specific proteins to coordinate in a complex pathway. We have previously shown that the trypanosome-specific proteins P34/P37 are essential to the interaction of the TbNmd3-TbXpoI export complex with the 60S ribosomal subunits, allowing their translocation across the nuclear envelope. Our recent studies show that the trypanosome orthologues of the auxiliary export proteins TbMex67-TbMtr2 are required for ribosome assembly, proper rRNA processing, and polysome formation. Here we show that TbMex67-TbMtr2 interact with members of the 60S ribosomal subunit 5S RNP. Although TbMex67 has a unique structure among the Mex67 orthologues and forms unique interactions with the 5S RNP, particularly with trypanosome-specific P34/P37, it performs a conserved function in ribosome assembly. These unique structures and parasite-specific interactions may provide new therapeutic targets against this important parasite.

scholarly journals Loss of Peter Pan (PPAN) Affects Mitochondrial Homeostasis and Autophagic Flux

Cells ◽  
2019 ◽  
Vol 8 (8) ◽  
pp. 894 ◽  
Author(s):  
David P. Dannheisig ◽  
Eileen Beck ◽  
Enrico Calzia ◽  
Paul Walther ◽  
Christian Behrends ◽  
...  
Keyword(s):  
Cellular Response ◽  
Ribosome Biogenesis ◽  
Autophagic Flux ◽  
Inner Mitochondrial Membrane ◽  
Peter Pan ◽  
Atp Production ◽  
Mitochondrial Homeostasis ◽  
Cycle Arrest ◽  
Nucleolar Stress ◽  
Tight Connection

Nucleolar stress is a cellular response to inhibition of ribosome biogenesis or nucleolar disruption leading to cell cycle arrest and/or apoptosis. Emerging evidence points to a tight connection between nucleolar stress and autophagy as a mechanism underlying various diseases such as neurodegeneration and treatment of cancer. Peter Pan (PPAN) functions as a key regulator of ribosome biogenesis. We previously showed that human PPAN localizes to nucleoli and mitochondria and that PPAN knockdown triggers a p53-independent nucleolar stress response culminating in mitochondrial apoptosis. Here, we demonstrate a novel role of PPAN in the regulation of mitochondrial homeostasis and autophagy. Our present study characterizes PPAN as a factor required for maintaining mitochondrial integrity and respiration-coupled ATP production. PPAN interacts with cardiolipin, a lipid of the inner mitochondrial membrane. Down-regulation of PPAN enhances autophagic flux in cancer cells. PPAN knockdown promotes recruitment of the E3-ubiquitin ligase Parkin to damaged mitochondria. Moreover, we provide evidence that PPAN knockdown decreases mitochondrial mass in Parkin-expressing cells. In summary, our study uncovers that PPAN knockdown is linked to mitochondrial damage and stimulates autophagy.

scholarly journals p53 induces a survival transcriptional response after nucleolar stress.

2021 ◽  
pp. mbc.E21-05-0251
Author(s):  
Han Liao ◽  
Anushri Gaur ◽  
Claire Mauvais ◽  
Catherine Denicourt
Keyword(s):  
Cell Cycle ◽  
Cell Cycle Arrest ◽  
Ribosome Biogenesis ◽  
Rrna Synthesis ◽  
Transcriptional Program ◽  
Induce Cell Cycle Arrest ◽  
Cycle Arrest ◽  
Pol I ◽  
Nucleolar Stress ◽  
Metabolic Remodeling

Accumulating evidence indicate that increased ribosome biogenesis is a hallmark of cancer. It is well established that inhibition of any steps of ribosome biogenesis induces a nucleolar stress characterized by p53 activation and subsequent cell cycle arrest and/or cell death. However, cells derived from solid tumors have demonstrated different degree of sensitivity to ribosome biogenesis inhibition, where cytostatic effects rather than apoptosis are observed. The reason for this is not clear and the p53-specific transcriptional program induced after nucleolar stress has not been previously investigated. Here we demonstrate that blocking rRNA synthesis by depletion of essential rRNA processing factors such as LAS1L, PELP1, and NOP2 or by inhibition of RNA Pol I with the specific small molecule inhibitor CX-5461, mainly induce cell cycle arrest accompanied with autophagy in solid tumor-derived cell lines. Using gene expression analysis, we find that p53 orchestrates a transcriptional program involved in promoting metabolic remodeling and autophagy to help cells survive under nucleolar stress. Importantly, our study demonstrates that blocking autophagy significantly sensitizes cancer cells to RNA Pol I inhibition by CX-5461, suggesting that interfering with autophagy should be considered a strategy to heighten the responsiveness of ribosome biogenesis-targeted therapies in p53-positive tumors.

scholarly journals Nucleolar Stress Functions Upstream to Stimulate Expression of Autophagy Regulators

Cancers ◽  
2021 ◽  
Vol 13 (24) ◽  
pp. 6220
Author(s):  
David P. Dannheisig ◽  
Anna Schimansky ◽  
Cornelia Donow ◽  
Astrid S. Pfister
Keyword(s):  
Ribosome Biogenesis ◽  
Autophagic Flux ◽  
Cancer Therapies ◽  
Growth And Survival ◽  
Cycle Arrest ◽  
Pol I ◽  
Nucleolar Stress ◽  
Stress Functions ◽  
Underlying Mechanisms ◽  
Polymerase I

Ribosome biogenesis is essential for protein synthesis, cell growth and survival. The process takes places in nucleoli and is orchestrated by various proteins, among them RNA polymerases I–III as well as ribosome biogenesis factors. Perturbation of ribosome biogenesis activates the nucleolar stress response, which classically triggers cell cycle arrest and apoptosis. Nucleolar stress is utilized in modern anti-cancer therapies, however, also contributes to the development of various pathologies, including cancer. Growing evidence suggests that nucleolar stress stimulates compensatory cascades, for instance bulk autophagy. However, underlying mechanisms are poorly understood. Here we demonstrate that induction of nucleolar stress activates expression of key autophagic regulators such as ATG7 and ATG16L1, essential for generation of autophagosomes. We show that knockdown of the ribosomopathy factor SBDS, or of key ribosome biogenesis factors (PPAN, NPM, PES1) is associated with enhanced levels of ATG7 in cancer cells. The same holds true when interfering with RNA polymerase I function by either pharmacological inhibition (CX-5461) or depletion of the transcription factor UBF-1. Moreover, we demonstrate that RNA pol I inhibition by CX-5461 stimulates autophagic flux. Together, our data establish that nucleolar stress affects transcriptional regulation of autophagy. Given the contribution of both axes in propagation or cure of cancer, our data uncover a connection that might be targeted in future.

scholarly journals Inhibition of the 60S ribosome biogenesis GTPase LSG1 causes endoplasmic reticular disruption and cellular senescence

2018 ◽  
Author(s):  
Asimina Pantazi ◽  
Andrea Quintanilla ◽  
Priya Hari ◽  
Nuria Tarrats ◽  
Eleftheria Parasyraki ◽  
...  
Keyword(s):  
Cellular Senescence ◽  
Ribosome Biogenesis ◽  
Cholesterol Biosynthesis ◽  
Ribosomal Subunit ◽  
Cytokines And Chemokines ◽  
Cycle Arrest ◽  
Therapeutic Uses ◽  
Cholesterol Biosynthesis Pathway ◽  
Er Homeostasis

AbstractCellular senescence is triggered by diverse stimuli and is characterised by long-term growth arrest and secretion of cytokines and chemokines (termed the SASP - senescence-associated secretory phenotype). Senescence can be organismally beneficial as it can prevent the propagation of damaged or mutated clones and stimulate their clearance by immune cells. However, it has recently become clear that senescence also contributes to the pathophysiology of aging through the accumulation of damaged cells within tissues. Here we describe that inhibition of the reaction catalysed by LSG1, a GTPase involved in the biogenesis of the 60S ribosomal subunit, leads to a robust induction of cellular senescence. Perhaps surprisingly, this was not due to ribosome depletion or translational insufficiency, but rather through perturbation of endoplasmic reticulum (ER) homeostasis and a dramatic upregulation of the cholesterol biosynthesis pathway. This cholesterol/ER signature is shared with several other forms of senescence and contributes to the cell cycle arrest in oncogene-induced senescence (OIS). Furthermore, targetting of LSG1 resulted in amplification of the cholesterol/ER signature and restoration of a robust cellular senescence response in transformed cells, suggesting potential therapeutic uses of LSG1 inhibition.

scholarly journals Evidence of p53-Dependent Cross-Talk between Ribosome Biogenesis and the Cell Cycle: Effects of Nucleolar Protein Bop1 on G1/S Transition

2001 ◽  
Vol 21 (13) ◽  
pp. 4246-4255 ◽  
Author(s):  
Dimitri G. Pestov ◽  
Žaklina Strezoska ◽  
Lester F. Lau
Keyword(s):  
Cell Cycle ◽  
Cell Cycle Arrest ◽  
Ribosome Biogenesis ◽  
Dominant Negative ◽  
Nucleolar Protein ◽  
Dominant Negative Mutant ◽  
Dependent Manner ◽  
Rrna Processing ◽  
Restriction Point ◽  
Cycle Arrest

ABSTRACT Bop1 is a novel nucleolar protein involved in rRNA processing and ribosome assembly. We have previously shown that expression of Bop1Δ, an amino-terminally truncated Bop1 that acts as a dominant negative mutant in mouse cells, results in inhibition of 28S and 5.8S rRNA formation and deficiency of newly synthesized 60S ribosomal subunits (Z. Strezoska, D. G. Pestov, and L. F. Lau, Mol. Cell. Biol. 20:5516–5528, 2000). Perturbation of Bop1 activities by Bop1Δ also induces a powerful yet reversible cell cycle arrest in 3T3 fibroblasts. In the present study, we show that asynchronously growing cells are arrested by Bop1Δ in a highly concerted fashion in the G1phase. Kinase activities of the G1-specific Cdk2 and Cdk4 complexes were downregulated in cells expressing Bop1Δ, whereas levels of the Cdk inhibitors p21 and p27 were concomitantly increased. The cells also displayed lack of hyperphosphorylation of retinoblastoma protein (pRb) and decreased expression of cyclin A, indicating their inability to progress through the restriction point. Inactivation of functional p53 abrogated this Bop1Δ-induced cell cycle arrest but did not restore normal rRNA processing. These findings show that deficiencies in ribosome synthesis can be uncoupled from cell cycle arrest and reveal a new role for the p53 pathway as a mediator of the signaling link between ribosome biogenesis and the cell cycle. We propose that aberrant rRNA processing and/or ribosome biogenesis may cause “nucleolar stress,” leading to cell cycle arrest in a p53-dependent manner.

scholarly journals Exosomes are key regulators of non-cell autonomous communication in senescence

2018 ◽  
Author(s):  
Michela Borghesan ◽  
Juan Fafián-Labora ◽  
Paula Carpintero-Fernández ◽  
Pilar Ximenez-Embun ◽  
Hector Peinado ◽  
...  
Keyword(s):  
Extracellular Vesicles ◽  
Cellular Phenotype ◽  
Senescent Phenotype ◽  
Tissue Degeneration ◽  
Cycle Arrest ◽  
Age Related ◽  
Form Part ◽  
Reporter Systems ◽  
Inflammatory Proteins ◽  
Secretory Phenotype

SUMMARYSenescence is a cellular phenotype characterized by an irreversible cell cycle arrest and the secretion of inflammatory proteins, denominated senescence-associated secretory phenotype (SASP). The SASP is important in influencing the behavior of neighboring cells and altering the microenvironment; yet, until now this role has been mainly attributed to soluble factors. Here, we report that extracellular vesicles also alter the environment by transmitting the senescent phenotype to other cells via exosomes (extracellular vesicles of endocytic origin). A combination of functional assays, Cre-/oxP reporter systems, proteomic analysis and RNAi screens confirm that exosomes form part of the senescent secretome and mediate paracrine senescence via the activation of a non-canonical interferon (IFN) pathway. Altogether, we speculate that exosomes could be drivers of tissue degeneration both locally and systemically during aging and age- related disease.

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