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AMPK-dependent phosphorylation of TIF-IA at S635 down-regulates Pol I transcription. (A) Overexpression of a dominant-negative mutant of AMPK (DN) counteracts repression of Pol I transcription under glucoserestriction. (Upper) HEK293T cells expressing HA-AMPK/WT or HA-AMPK/DN were cultured for 6 h in the presence (white bars) or absence (gray bars) of glucose. Left bars represent values from mock-transfected cells. Pre-rRNA levels were determined by RT-qPCR and normalized to-actin mRNA. (Lower) The immunoblot shows equal expression levels of HA-AMPK/WT and HAAMPK/DN. (B) Overexpression of TIF-IAS635A prevents down-regulation of Pol I transcription upon glucose-deprivation. HEK293T cells were transfected with the rDNA reporter pHrP 2-BH alone () or were cotransfected with expression plasmids encoding Fl-TIF-IA (TIF-IA) or Fl-TIF-IAS635A (S635A). Cells were cultured in glucose-rich medium (white bars) or glucose-free-medium for 6 h before harvesting (gray bars). The graph represents the level of reporter transcripts normalized to-actin mRNA as determined by RT-qPCR in three independent experiments. (C) TIF-IAS635A rescues rRNA synthesis in glucosedeprived cells. Mock-infected NIH 3T3 cells and cells stably expressing Fl-TIF-IA or Fl-TIF-IAS635A were cultured for 12 h in the presence or absence of glucose. After pulse-labeling with FUrd, nascent RNA was visualized by indirect immunofluorescence with-BrU antibodies.
Source publication
AMP-activated protein kinase (AMPK) senses changes in the intracellular AMP/ATP ratio, switching off energy-consuming processes and switching on catabolic pathways in response to energy depletion. Here, we show that AMPK down-regulates rRNA synthesis under glucose restriction by phosphorylating the RNA polymerase I (Pol I)-associated transcription...
Similar publications
Most transcripts in growing cells are ribosomal RNA precursors (pre-rRNA). Here, we show that in mammals, aberrant pre-rRNA transcripts generated by RNA polymerase I (Pol I) are polyadenylated and accumulate markedly after treatment with low concentrations of actinomycin D (ActD), which blocks the synthesis of full-length rRNA. The poly(A) polymera...
Citations
... Second, the mTORC1 pathway receives input from growth factors, hormones, mechanical loading, and nutrients to balance protein synthesis through multiple mechanisms based on cellular energy levels (Hoppe et al. 2009). This contributes to ribosome biogenesis by forming the preinitiation complex (PIC) that marks the initiation of rRNA transcription, as well as through regulation of ribosomal protein translation (Figueiredo and McCarthy 2019;Walden 2019). ...
... Third, high glucose was shown to lead to chromatin remodelling independent of UBF and mTORC1, which in turn promotes rRNA transcription in cell cultures (Zhai et al. 2012). Together, these mechanistic observations underscore a potential role for glucose in muscle ribosome biogenesis and function in human skeletal muscle, acting in concert with RT to potentiate transcription of ribosomal RNA and increasing translational capacity (Hillier et al. 2000;Hoppe et al. 2009;Zhai et al. 2012;Tanaka and Tsuneoka 2018). ...
... Zhai et al. 2012;Kim et al. 2013;Tanaka et al. 2015). Despite previously reported upregulation in PIC assembly due to high-glucose mediated mTORC1, ERK1/2 and PIH1 or low-glucose mediated AMPK and SIRT1 activation (Hoppe et al. 2009;Mariappan et al. 2011;Zhai et al. 2012;Kim et al. 2013;Tanaka et al. 2015), the present study displayed no signs of such effects of glucose vs. placebo conditions. Importantly, previous studies investigated high vs. low glucose conditions (Mariappan et al. 2011), or high glucose vs. glucose starvation (Hoppe et al. 2009;Tanaka et al. 2015), while the present study aimed to compare the high glucose condition to a placebo condition (stevia), with a matched daily macronutrient and energy intake. ...
Purpose
Resistance training-induced skeletal muscle hypertrophy seems to depend on ribosome biogenesis and content. High glucose treatment may augment ribosome biogenesis through potentiating resistance training-induced adaptations. This was investigated with total RNA and ribosomal RNA abundances as main outcomes, with relevant transcriptional/translational regulators (c-Myc/UBF/rpS6) as a secondary outcome.
Methods
Sixteen healthy, moderately trained individuals [male/female, n = 9/7; age, 24.1 (3.3)] participated in a within-participant crossover trial with unilateral resistance training (leg press and knee extension, 3 sets of 10 repetitions maximum) and pre- and post-exercise ingestion of either glucose (3 × 30 g, 90 g total) or placebo supplements (Stevia rebaudiana, 3 × 0.3 g, 0.9 g total), together with protein (2 × 25 g, 50 g total), on alternating days for 12 days. Six morning resistance exercise sessions were conducted per condition, and the sessions were performed in an otherwise fasted state. Micro-biopsies were sampled from m. vastus lateralis before and after the intervention.
Results
Glucose ingestion did not have beneficial effects on resistance training-induced increases of ribosomal content (mean difference 7.6% [− 7.2, 24.9], p = 0.34; ribosomal RNA, 47S/18S/28S/5.8S/5S, range 7.6–37.9%, p = 0.40–0.98) or levels of relevant transcriptional or translational regulators (c-MYK/UBF/rpS6, p = 0.094–0.292). Of note, both baseline and trained state data of total RNA showed a linear relationship with UBF; a ∼14% increase in total RNA corresponded to 1 SD unit increase in UBF (p = 0.003).
Conclusion
Glucose ingestion before and after resistance training sessions did not augment ribosomal RNA accumulation during twelve days of heavy-load resistance training in moderately trained young adults.
... To link Pol I activity to cellular nutrient states, IIS, mTOR, and AMPK pathways target the essential Pol I transcription initiation factor 1A (TIF-1A, also known as TIF-IA or RRN3), which is conserved from yeast to human 9 . TIF-1A is inactivated by AMPK-mediated phosphorylation but requires IIS and mTORdependent phosphorylations to recruit Pol I to the rDNA promoter [10][11][12] . Thus, pre-rRNA synthesis and TIF-1A activity are likely to connect nutrient-sensing signaling and longevity regulation. ...
Ribosome biogenesis is initiated by RNA polymerase I (Pol I)-mediated synthesis of pre-ribosomal RNA (pre-rRNA). Pol I activity was previously linked to longevity, but the underlying mechanisms were not studied beyond effects on nucleolar structure and protein translation. Here we use multi-omics and functional tests to show that curtailment of Pol I activity remodels the lipidome and preserves mitochondrial function to promote longevity in Caenorhabditis elegans. Reduced pre-rRNA synthesis improves energy homeostasis and metabolic plasticity also in human primary cells. Conversely, the enhancement of pre-rRNA synthesis boosts growth and neuromuscular performance of young nematodes at the cost of accelerated metabolic decline, mitochondrial stress and premature aging. Moreover, restriction of Pol I activity extends lifespan more potently than direct repression of protein synthesis, and confers geroprotection even when initiated late in life, showcasing this intervention as an effective longevity and metabolic health treatment not limited by aging.
... For example, inhibition of the target of rapamycin (TOR) and insulin/insulin-like growth factor signaling (IIS) pathways, which extends lifespan, downregulates rDNA transcription through the regulation of different RPI and RPIII transcription factors (19). Similarly, the adenosine monophosphate (AMP)-activated protein kinase signaling pathway receives inputs from the cellular energy status, and its activation-required for lifespan extension by CR or metformin treatment-represses rDNA transcription (21). ...
Aging is a multifactorial process characterized by an age-related decline in organismal fitness. This deterioration is the major risk factor for chronic diseases such as cardiovascular pathologies, neurodegeneration, or cancer, and it represents one of the main challenges of modern society. Therefore, understanding why and how we age would be a fundamental pillar to design strategies to promote a healthy aging. In the last decades, the study of the molecular bases of disease has been revolutionized by the discovery of different types of noncoding RNAs (ncRNAs) with regulatory potential. In this work, we will review the implication of ncRNAs in aging, with the aim to provide a first approach to the different aging-associated ncRNAs, their mechanism of action, and their potential relevance as therapeutic targets and disease biomarkers.
... Transcriptional down regulation in differentiated tissues reduces E met and also might extend the chronological life span of differentiated cells, as suggested in S. cerevisiae [45], that thus need a lower turn-over rate which is compatible with the reduced differentiation rate. The dropdown in 18s rRNA expression level is consistent with several studies reporting that amino acid/glucose starvation reduces rDNA transcription in yeast and mammal cells [46,47]. Being rRNA the most abundant transcript of the cell, also a small reduction in its transcriptional rate allows for high energy saving. ...
Starvation resistance is a life‐saving mechanism for many organisms facing food availability fluctuation in the natural environment. Different strategies have been episodically identified for some model organisms, the first of which was the ability to suppress metabolic rate. Among the identified strategies, the ability of planarians to shrink their body under fasting conditions and revert the process after feeding (the growth–degrowth process) represents a fascinating mechanism to face long periods of fasting. The growth–degrowth process is strictly related to the capability of planarians to continuously maintain tissue homeostasis and body proportions even in challenging conditions, thanks to the presence of a population of pluripotent stem cells. Here, we take advantage of several previous studies describing the growth–degrowth process and of recent progress in the understanding of planarian homeostasis mechanisms, to identify tissue‐selective transcriptional downregulation as a driving strategy for the development of a thrifty phenotype, and the p53 transcription factor as a player in adjusting tissue homeostasis in accordance with food availability.
... AMP-activated protein kinase (AMPK) is another critical cellular energy sensor that regulates diverse metabolic processes under stress and can also have an effect on RiBi (Hardie, 2011;Hardie et al., 2012). Specifically, when activated by an increase in the AMP/ATP ratio, such as in times of energy shortage, AMPK can phosphorylate a single serine residue (Ser-635) on the RNA polymerase I-associated transcription factor TIF-IA, thereby inhibiting its binding to SL-1 and preventing the assembly of the TF complex (Hoppe et al., 2009). ...
Diverse acute and chronic injuries induce damage responses in the gastrointestinal (GI) system, and numerous cell types in the gastrointestinal tract demonstrate remarkable resilience, adaptability, and regenerative capacity in response to stress. Metaplasias, such as columnar and secretory cell metaplasia, are well-known adaptations that these cells make, the majority of which are epidemiologically associated with an elevated cancer risk. On a number of fronts, it is now being investigated how cells respond to injury at the tissue level, where diverse cell types that differ in proliferation capacity and differentiation state cooperate and compete with one another to participate in regeneration. In addition, the cascades or series of molecular responses that cells show are just beginning to be understood. Notably, the ribosome, a ribonucleoprotein complex that is essential for translation on the endoplasmic reticulum (ER) and in the cytoplasm, is recognized as the central organelle during this process. The highly regulated management of ribosomes as key translational machinery, and their platform, rough endoplasmic reticulum, are not only essential for maintaining differentiated cell identity, but also for achieving successful cell regeneration after injury. This review will cover in depth how ribosomes, the endoplasmic reticulum, and translation are regulated and managed in response to injury (e.g., paligenosis), as well as why this is essential for the proper adaptation of a cell to stress. For this, we will first discuss how multiple gastrointestinal organs respond to stress through metaplasia. Next, we will cover how ribosomes are generated, maintained, and degraded, in addition to the factors that govern translation. Finally, we will investigate how ribosomes and translation machinery are dynamically regulated in response to injury. Our increased understanding of this overlooked cell fate decision mechanism will facilitate the discovery of novel therapeutic targets for gastrointestinal tract tumors, focusing on ribosomes and translation machinery.
... AMPK can directly and indirectly inactivate mTORC1 by phosphorylation (Hardie, 2008), which thus potentially impair rDNA transcription and ribosome biogenesis (Kusnadi et al., 2015). AMPK could also prevent Pol I-mediated rDNA transcription by inhibiting the interaction between TIF-1A and Pol I complex with the rDNA promoter, which blunts PIC assembly (Hoppe et al., 2009). ...
Age-related loss of skeletal muscle mass leads to a reduction of strength. It is likely due to an inadequate stimulation of muscle protein synthesis (MPS) in response to anabolic stimuli, such as mechanical load. Ribosome biogenesis is a major determinant of translational capacity and is essential for the control of muscle mass. This mini-review aims to put forth the hypothesis that ribosome biogenesis is impaired by aging in response to mechanical load, which could contribute to the age-related anabolic resistance and progressive muscle atrophy. Recent animal studies indicate that aging impedes muscle hypertrophic response to mechanical overload. This is associated with an impaired transcription of ribosomal DNA (rDNA) by RNA polymerase I (Pol I), a limited increase in total RNA concentration, a blunted activation of AKT/mTOR pathway, and an increased phosphorylation of AMPK. In contrast, an age-mediated impairment of ribosome biogenesis is unlikely in response to electrical stimulations. In human, the hypertrophic response to resistance exercise training is diminished with age. This is accompanied by a deficit in long-term MPS and an absence of increased total RNA concentration. The results addressing the acute response to resistance exercise suggest an impaired Pol I-mediated rDNA transcription and attenuated activation/expression of several upstream regulators of ribosome biogenesis in muscles from aged individuals. Altogether, emerging evidence indicates that impaired ribosome biogenesis could partly explain age-related anabolic resistance to mechanical load, which may ultimately contribute to progressive muscle atrophy. Future research should develop more advanced molecular tools to provide in-depth analysis of muscle ribosome biogenesis.
... In contrast, under conditions of cell stress, JNK phosphorylates RRN3, which diminishes the interaction of RRN3 with Pol I and SL-1 and downregulates Pol I transcription [90]. Energy deficits and a high AMP/ATP ratio activate AMPK, which phosphorylates and inactivates RRN3 and causes the demethylation of the rDNA promoter by KDM2A [91,92]. ...
... These activities of ARF augment its major effect to bind to and inhibit NPM and MDM2 [174]. Cellular energy sensor AMPK has been reported to phosphorylate RRN3 and prevent its interaction with SL-1 in energy-starved cells, and alternatively, to reduce transcription by increasing the promoter methylation by KDM2A [91,92]. MYBBP1A, a nucleolar protein and tumor suppressor, also attenuates Pol I transcription and rRNA processing [175]. ...
RNA polymerase I is a highly processive enzyme with fast initiation and elongation rates. The structure of Pol I, with its in-built RNA cleavage ability and incorporation of subunits homologous to transcription factors, enables it to quickly and efficiently synthesize the enormous amount of rRNA required for ribosome biogenesis. Each step of Pol I transcription is carefully controlled. However, cancers have highjacked these control points to switch the enzyme, and its transcription, on permanently. While this provides an exceptional benefit to cancer cells, it also creates a potential cancer therapeutic vulnerability. We review the current research on the regulation of Pol I transcription, and we discuss chemical biology efforts to develop new targeted agents against this process. Lastly, we highlight challenges that have arisen from the introduction of agents with promiscuous mechanisms of action and provide examples of agents with specificity and selectivity against Pol I.
... The expression and posttranscriptional modification of these proteins are tightly regulated by signaling pathways involved in cell proliferation, mitogenic growth, nutrient and energy sensing, as well as stress responses. For instance, TIF-IA is phosphorylated on Ser635 residue by AMPK following energy deprivation, and on Thr 200 residue by JNK2 following oxidative stress (45,46). Both modifications cause the dissociation between SL1 and TIF-IA, consequently leading to the disruption of rRNA transcription. ...
Studies in the past decades have uncovered an emerging role of the nucleolus in stress response and human disease progression. The disruption of ribosome biogenesis in the nucleolus causes aberrant nucleolar architecture and function, termed nucleolar stress, to initiate stress-responsive pathways via nucleolar release sequestration of various proteins. While data obtained from both clinical and basic investigations have faithfully demonstrated an involvement of nucleolar stress in the pathogenesis of cardiomyopathy, much remains unclear regarding its precise role in the progression of cardiac diseases. On the one hand, the initiation of nucleolar stress following acute myocardial damage leads to the upregulation of various cardioprotective nucleolar proteins, including nucleostemin (NS), nucleophosmin (NPM) and nucleolin (NCL). As a result, nucleolar stress plays an important role in facilitating the survival and repair of cardiomyocytes. On the other hand, abnormalities in nucleolar architecture and function are correlated with the deterioration of cardiac diseases. Notably, the cardiomyocytes of advanced ischemic and dilated cardiomyopathy display impaired silver-stained nucleolar organiser regions (AgNORs) and enlarged nucleoli, resembling the characteristics of tissue aging. Collectively, nucleolar abnormalities are critically involved in the development of cardiac diseases.
... Ribosome biogenesis is an energy-intensive process and needs to be coordinated with an adequate energy status. Nutrient deprivation may cause rapid phosphorylation of TIF-IA at S635 residue by AMPK, leading to the inactivation of TIF-IA and the shutdown of rRNA transcription [44]. Likewise, mTOR-mediated TIF-IA phosphorylation at its N-terminal residues also couples nutrient availability to the adaptive increase of rRNA synthesis [27,45]. ...
... While the direct evidence linking nucleolar stress to metabolic disorders remains scarce, an influence of nutrient availability on nucleolar activity has been well-established. Nutrient-sensing pathways, such as AMPK and mTOR, have been implicated in the regulation of rRNA synthesis and nucleolar homeostasis [27,44]. Intriguingly, studies indicated a role of snoRNAs in mediating metabolic stress and lipotoxicity [175,176]. ...
Besides the canonical function in ribosome biogenesis, there have been significant recent advances towards the fascinating roles of the nucleolus in stress response, cell destiny decision and disease progression. Nucleolar stress, an emerging concept describing aberrant nucleolar structure and function as a result of impaired rRNA synthesis and ribosome biogenesis under stress conditions, has been linked to a variety of signaling transductions, including but not limited to Mdm2-p53, NF-κB and HIF-1α pathways. Studies have uncovered that nucleolus is a stress sensor and signaling hub when cells encounter various stress conditions, such as nutrient deprivation, DNA damage and oxidative and thermal stress. Consequently, nucleolar stress plays a pivotal role in the determination of cell fate, such as apoptosis, senescence, autophagy and differentiation, in response to stress-induced damage. Nucleolar homeostasis has been involved in the pathogenesis of various chronic diseases, particularly tumorigenesis, neurodegenerative diseases and metabolic disorders. Mechanistic insights have revealed the indispensable role of nucleolus-initiated signaling in the progression of these diseases. Accordingly, the intervention of nucleolar stress may pave the path for developing novel therapies against these diseases. In this review, we systemically summarize recent findings linking the nucleolus to stress responses, signaling transduction and cell-fate decision, set the spotlight on the mechanisms by which nucleolar stress drives disease progression, and highlight the merit of the intervening nucleolus in disease treatment.
... AMPK inhibits cap-dependent translation during both initiation and elongation steps in protein biosynthesis [28]. AMPK downregulates ribosomal RNA synthesis by inducing the inhibitory phosphorylation of transcription initiation factor 1A [29,30]. A recent study suggested that AMPK stimulates cap-independent and IRES-dependent translation of Hif-1α during energy stress to activate the expression of genes important for cell survival [31]. ...
5′-adenosine monophosphate (AMP)-activated protein kinase (AMPK) is an enzyme that regulates cellular energy homeostasis, glucose, fatty acid uptake, and oxidation at low cellular ATP levels. AMPK plays an important role in several molecular mechanisms and physiological conditions. It has been shown that AMPK can be dysregulated in different chronic diseases, such as inflammation, diabetes, obesity, and cancer. Due to its fundamental role in physiological and pathological cellular processes, AMPK is considered one of the most important targets for treating different diseases. Over decades, different AMPK targeting compounds have been discovered, starting from those that activate AMPK indirectly by altering intracellular AMP:ATP ratio to compounds that activate AMPK directly by binding to its activation sites. However, indirect altering of intracellular AMP:ATP ratio influences different cellular processes and induces side effects. Direct AMPK activators showed more promising results in eliminating side effects as well as the possibility to engineer drugs for specific AMPK isoforms activation. In this review, we discuss AMPK targeting drugs, especially concentrating on those compounds that activate AMPK by mimicking AMP. These compounds are poorly described in the literature and still, a lot of questions remain unanswered about the exact mechanism of AMP regulation. Future investigation of the mechanism of AMP binding will make it possible to develop new compounds that, in combination with others, can activate AMPK in a synergistic manner.
