Sestrins inhibit mTORC1 kinase activation through the GATOR complex

Sestrins in Carcinogenesis-The Firefighters That Sometimes Stoke the Fire

Sestrins (SESN1-3) are a family of stress-responsive proteins that regulate cellular metabolism and redox balance, both of which are frequently disrupted in cancer. As direct targets of stress-responsive transcription factors, including tumour suppressor p53, Sestrins function as leucine-dependent inhibitors of mTORC1 and potent antioxidants. Their downregulation is widely observed across multiple cancers and is associated with increased tumour growth and poor prognosis. Despite their consistent tumour-suppressive effects through mTORC1 inhibition and promotion of p53-dependent apoptosis, Sestrins exhibit a limited role in tumour initiation, which appears to be context-dependent. Their antioxidant activity reduces oxidative damage, thereby protecting against genomic instability and other cancer-promoting events. However, in certain contexts, Sestrins may promote tumour survival and progression by stimulating pro-survival pathways, such as AKT signalling through mTORC2 activation. This review examines the molecular mechanisms underlying these dual functions, with a particular focus on mTOR signalling and oxidative stress. We also discuss Sestrin expression patterns and functional outcomes in various cancer types, including lung, liver, colon, skin, prostate, and follicular lymphomas, highlighting their potential as diagnostic markers and therapeutic targets.

p53-regulated SESN1 and SESN2 regulate cell proliferation and cell death through control of STAT3

Sestrin1 and Sestrin2 (SESN1&2) are evolutionarily conserved, stress-responsive proteins that regulate cell growth and viability. The primary target of Sestrins is the mTORC1 protein kinase, an activator of anabolic processes and an autophagy inhibitor. Our previous studies showed that inactivating SESN1&2 in lung adenocarcinoma A549 cells accelerates cell proliferation and confers resistance to cell death without affecting mTORC1 activity, suggesting that SESN1&2 modulate cellular processes via mTORC1-independent mechanisms. This work describes a new mechanism through which SESN1&2 regulate cell proliferation and death by suppressing the STAT3 transcription factor. Normally activated in response to stress and inflammation, STAT3 is frequently overactivated in human cancers. This overactivation promotes the expression of pro-proliferative and anti-apoptotic genes that drive carcinogenesis. We demonstrate that SESN1&2 inactivation stimulates STAT3 by downregulating the PTPRD phosphatase, a protein responsible for STAT3 dephosphorylation. Our study demonstrates that SESN1&2 deficiency may cause STAT3 activation and facilitate carcinogenesis and drug resistance, making SESN1&2 reactivation a potential cancer treatment strategy.

Animal amino acid sensor - A review

Cell growth and metabolism necessitate the involvement of amino acids, which are sensed and integrated by the mammalian target of rapamycin complex 1 (mTORC1). However, the molecular mechanisms underlying amino acid sensing remain poorly understood. Research indicates that amino acids are detected by specific sensors, with the signals being relayed to mTORC1 indirectly. This paper reviews the structures and biological functions of the amino acid sensors identified thus far. Additionally, it evaluates the potential role these sensors play in the developmental changes of the livestock production.

Sestrin2 Attenuates Myocardial Endoplasmic Reticulum Stress and Cardiac Dysfunction During Ischemia/Reperfusion Injury

BACKGROUND

Sesn2 (Sestrin2) is a stress-induced protein that provides protective effects during myocardial ischemia and reperfusion (I/R) injury, while endoplasmic reticulum (ER) stress may be a pivotal mediator of I/R injury. The goal of this study was to determine whether Sesn2-mTOR (mammalian target of rapamycin) signaling regulates ER stress during myocardial I/R.

METHODS AND RESULTS

In vivo cardiac I/R was induced by ligation and subsequent release of the left anterior descending coronary artery in wild-type (WT) and cardiac-specific Sesn2 knockout (Sesn2cKO) mice. At 6 hours and 24 hours after reperfusion, cardiac function was evaluated, and heart samples were collected for analysis. I/R induced cardiac ER stress and upregulated Sesn2 mRNA and protein levels. Inhibiting ER stress with 4-phenylbutyric acid reduced infarct size by 37.5%, improved cardiac systolic function, and mitigated myocardial cell apoptosis post-I/R. Hearts from Sesn2cKO mice displayed increased susceptibility to ER stress during I/R compared with WT. Notably, cardiac mTOR signaling was further increased in Sesn2cKO hearts compared with WT hearts during I/R. In mice with cardiac Sesn2 deficiency, compared with WT, ER lumen was significantly expanded after tunicamycin-induced ER stress, as assessed by transmission electron microscopy. Additionally, pharmacological inhibition of mTOR signaling with rapamycin improved cardiac function after tunicamycin treatment and significantly attenuated the unfolded protein response and apoptosis in WT and Sesn2cKO mice.

CONCLUSIONS

Sesn2 attenuates cardiac ER stress post-I/R injury via regulation of mTOR signaling. Thus, modulation of the mTOR pathway by Sesn2 could be a critical factor for maintaining cardiac ER homeostasis control during myocardial I/R injury.

Double-Edge Effects of Leucine on Cancer Cells

Leucine is an essential amino acid that cannot be produced endogenously in the human body and therefore needs to be obtained from dietary sources. Leucine plays a pivotal role in stimulating muscle protein synthesis, along with isoleucine and valine, as the group of branched-chain amino acids, making them one of the most popular dietary supplements for athletes and gym-goers. The individual effects of leucine, however, have not been fully clarified, as most of the studies so far have focused on the grouped effects of branched-chain amino acids. In recent years, leucine and its metabolites have been shown to stimulate muscle protein synthesis mainly via the mammalian target of the rapamycin complex 1 signaling pathway, thereby improving muscle atrophy in cancer cachexia. Interestingly, cancer research suggests that leucine may have either anti-cancer or pro-tumorigenic effects. In the current manuscript, we aim to review leucine's roles in muscle protein synthesis, tumor suppression, and tumor progression, specifically summarizing the molecular mechanisms of leucine's action. The role of leucine is controversial in hepatocellular carcinoma, whereas its pro-tumorigenic effects have been demonstrated in breast and pancreatic cancers. In summary, leucine being used as nutritional supplement for athletes needs more attention, as its pro-oncogenic effects may have been identified by recent studies. Anti-cancer or pro-tumorigenic effects of leucine in various cancers should be further investigated to achieve clear conclusions.

Nutrient sensing of mTORC1 signaling in cancer and aging

The mechanistic target of rapamycin complex 1 (mTORC1) is indispensable for preserving cellular and organismal homeostasis by balancing the anabolic and catabolic processes in response to various environmental cues, such as nutrients, growth factors, energy status, oxygen levels, and stress. Dysregulation of mTORC1 signaling is associated with the progression of many types of human disorders including cancer, age-related diseases, neurodegenerative disorders, and metabolic diseases. The way mTORC1 senses various upstream signals and converts them into specific downstream responses remains a crucial question with significant impacts for our perception of the related physiological and pathological process. In this review, we discuss the recent molecular and functional insights into the nutrient sensing of the mTORC1 signaling pathway, along with the emerging role of deregulating nutrient-mTORC1 signaling in cancer and age-related disorders.

Spatial and functional separation of mTORC1 signalling in response to different amino acid sources

Amino acid (AA) availability is a robust determinant of cell growth through controlling mechanistic/mammalian target of rapamycin complex 1 (mTORC1) activity. According to the predominant model in the field, AA sufficiency drives the recruitment and activation of mTORC1 on the lysosomal surface by the heterodimeric Rag GTPases, from where it coordinates the majority of cellular processes. Importantly, however, the teleonomy of the proposed lysosomal regulation of mTORC1 and where mTORC1 acts on its effector proteins remain enigmatic. Here, by using multiple pharmacological and genetic means to perturb the lysosomal AA-sensing and protein recycling machineries, we describe the spatial separation of mTORC1 regulation and downstream functions in mammalian cells, with lysosomal and non-lysosomal mTORC1 phosphorylating distinct substrates in response to different AA sources. Moreover, we reveal that a fraction of mTOR localizes at lysosomes owing to basal lysosomal proteolysis that locally supplies new AAs, even in cells grown in the presence of extracellular nutrients, whereas cytoplasmic mTORC1 is regulated by exogenous AAs. Overall, our study substantially expands our knowledge about the topology of mTORC1 regulation by AAs and hints at the existence of distinct, Rag- and lysosome-independent mechanisms that control its activity at other subcellular locations. Given the importance of mTORC1 signalling and AA sensing for human ageing and disease, our findings will probably pave the way towards the identification of function-specific mTORC1 regulators and thus highlight more effective targets for drug discovery against conditions with dysregulated mTORC1 activity in the future.

Unveiling GATOR2 Function: Novel Insights from Drosophila Research

The multiprotein Target of Rapamycin (TOR) Complex 1 (TORC1) is a serine/threonine kinase that stimulates anabolic metabolism and suppresses catabolism. Deregulation of TORC1 is implicated in various human pathologies, including cancer, epilepsy, and neurodegenerative disorders. The Gap Activity Towards Rags (GATOR) complex contains two subcomplexes: GATOR1, which inhibits TORC1 activity; and GATOR2, which counteracts GATOR1s function. Structural and biochemical studies have elucidated how GATOR1 regulates TORC1 activity by acting as a GTPase activating protein for Rag GTPase. However, while cryogenic electron microscopy has determined that the structure of the multi-protein GATOR2 complex is conserved from yeast to humans, how GATOR2 inhibits GATOR1 remains unclear. Here, we describe recent whole-animal studies in Drosophila that have yielded novel insights into GATOR2 function, including identifying a novel role for the GATOR2 subunit WDR59, redefining the core proteins sufficient for GATOR2 activity, and defining a TORC1-independent role for GATOR2 in the regulation of the lysosomal autophagic endomembrane system. Additionally, the recent characterization of a novel methionine receptor in Drosophila that acts through the GATOR2 complex suggests an attractive model for the evolution of species-specific nutrient sensors. Research on GATOR2 function in Drosophila highlights how whole-animal genetic models can be used to dissect intracellular signaling pathways to identify tissue-specific functions and functional redundancies that may be missed in studies confined to rapidly proliferating cell lines.

Effects of gallic acid and physical training on liver damage, force, and anxiety in obese mice: Hepatic modulation of Sestrin 2 (SESN2) and PGC-α expression

Obesity and overweight are multifactorial diseases affecting more than one-third of the world's population. Physical inactivity contributes to a positive energy balance and the onset of obesity. Exercise combined with a balanced diet is an effective non-pharmacological strategy to improve obesity-related disorders. Gallic acid (GA), is a natural endogenous polyphenol found in a variety of fruits, vegetables, and wines, with beneficial effects on energetic homeostasis. The present study aims to investigate the effects of exercise training on obese mice supplemented with GA. Animal experimentation was performed with male Swiss mice divided into five groups: ST (standard control), HFD (obese control), HFD + GA (GA supplement), HFD + Trained (training), and HFD + GA + Trained (GA and training). The groups are treated for eight weeks with 200 mg/kg/body weight of the feed compound and, if applicable, physical training. The main findings of the present study show that GA supplementation improves liver fat, body weight, adiposity, and plasma insulin levels. In addition, animals treated with the GA and a physical training program demonstrate reduced levels of anxiety. Gene expression analyses show that Sesn2 is activated via PGC-1α independent of the GATOR2 protein, which is activated by GA in the context of physical activity. These data are corroborated by molecular docking analysis, demonstrating the interaction of GA with GATOR2. The present study contributes to understanding the metabolic effects of GA and physical training and demonstrates a new hepatic mechanism of action via Sestrin 2 and PGC-1α.

Locked in Structure: Sestrin and GATOR-A Billion-Year Marriage

Sestrins are a conserved family of stress-responsive proteins that play a crucial role in cellular metabolism, stress response, and ageing. Vertebrates have three Sestrin genes (SESN1, SESN2, and SESN3), while invertebrates encode only one. Initially identified as antioxidant proteins that regulate cell viability, Sestrins are now recognised as crucial inhibitors of the mechanistic target of rapamycin complex 1 kinase (mTORC1), a central regulator of anabolism, cell growth, and autophagy. Sestrins suppress mTORC1 through an inhibitory interaction with the GATOR2 protein complex, which, in concert with GATOR1, signals to inhibit the lysosomal docking of mTORC1. A leucine-binding pocket (LBP) is found in most vertebrate Sestrins, and when bound with leucine, Sestrins do not bind GATOR2, prompting mTORC1 activation. This review examines the evolutionary conservation of Sestrins and their functional motifs, focusing on their origins and development. We highlight that the most conserved regions of Sestrins are those involved in GATOR2 binding, and while analogues of Sestrins exist in prokaryotes, the unique feature of eukaryotic Sestrins is their structural presentation of GATOR2-binding motifs.

Nitidine chloride inhibits mTORC1 signaling through ATF4-mediated Sestrin2 induction and targets IGF2R for lysosomal degradation

AIMS

Nitidine chloride (NC), a natural phytochemical alkaloid derived from Zanthoxylum nitidum (Roxb.) DC, exhibits multiple bioactivities, including antitumor, anti-inflammatory, and other therapeutic effects. However, the primary targets of NC and the mechanism of action (MOA) have not been explicitly defined.

METHODS

We explored the effects of NC on mTORC1 signaling by immunoblotting and fluorescence microscopy in wild-type and gene knockout cell lines generated by the CRISPR/Cas9 gene editing technique. We identified IGF2R as a direct target of NC via the drug affinity-responsive target stability (DARTS) method. We investigated the antitumor effects of NC using a mouse melanoma B16 tumor xenograft model.

KEY FINDINGS

NC inhibits mTORC1 activity by targeting amino acid-sensing signaling through activating transcription factor 4 (ATF4)-mediated Sestrin2 induction. NC directly binds to IGF2R and promotes its lysosomal degradation. Moreover, NC displayed potent cytotoxicity against various cancer cells and inhibited B16 tumor xenografts.

SIGNIFICANCE

NC inhibits mTORC1 signaling through nutrient sensing and directly targets IGF2R for lysosomal degradation, providing mechanistic insights into the MOA of NC.

mTOR in metabolic homeostasis and disease

The ability to maintain cellular metabolic homeostasis is critical to life, in which mTOR plays an important role. This kinase integrates upstream nutrient signals and performs essential functions in physiology and metabolism by increasing metabolism and suppressing autophagy. Thus, dysregulation of mTOR activity leads to diseases, especially metabolic diseases such as cancer, type 2 diabetes and neurological disorders. Therefore, inhibition of overactivated mTOR becomes a rational approach to treat a variety of metabolic diseases. In this review, we discuss how mTOR responds to upstream signals and how mTOR regulates metabolic processes, including protein, nucleic acid, and lipid metabolism. Furthermore, we discuss the possible causes and consequences of dysregulated mTOR signaling activity, and summarize relevant applications, such as inhibition of mTOR activity to treat these diseases. This review will advance our comprehensive knowledge of the association between mTOR and metabolic homeostasis, which has significant ramifications for human health.

mTORC1 Signaling Inhibition Modulates Mitochondrial Function in Frataxin Deficiency

Lysosomes regulate mitochondrial function through multiple mechanisms including the master regulator, mechanistic Target of Rapamycin Complex 1 (mTORC1) protein kinase, which is activated at the lysosomal membrane by nutrient, growth factor and energy signals. mTORC1 promotes mitochondrial protein composition changes, respiratory capacity, and dynamics, though the full range of mitochondrial-regulating functions of this protein kinase remain undetermined. We find that acute chemical modulation of mTORC1 signaling decreased mitochondrial oxygen consumption, increased mitochondrial membrane potential and reduced susceptibility to stress-induced mitophagy. In cellular models of Friedreich's Ataxia (FA), where loss of the Frataxin (FXN) protein suppresses Fe-S cluster synthesis and mitochondrial respiration, the changes induced by mTORC1 inhibitors lead to improved cell survival. Proteomic-based profiling uncover compositional changes that could underlie mTORC1-dependent modulation of FXN-deficient mitochondria. These studies highlight mTORC1 signaling as a regulator of mitochondrial composition and function, prompting further evaluation of this pathway in the context of mitochondrial disease.

Interventions of sestrin proteins: Insights to clinical therapy

Sestrin proteins, conserved family proteins which mainly induced by ROS, DNA damage, inflammation, and other injuries. Growing evidences proved sestrin proteins exert protective functions in cardiovascular diseases, chronic degenerative osteoarthritis, musculoskeletal diseases, aging and others, sestrin proteins exhibit an anti-inflammatory response, improving metabolism and other valuable character. However, there is no comprehensive and detailed summary and literature research on the intervention methods of sestrin proteins at present. As the advance of research during last several years, exercise training and other interventions are considered to be the potential methods to up-regulate expression level of protein. In view of the physiological function of this protein, a review of the main studies on regulating the expression level of this protein can provide a novel approach for the clinical treatment and scientific research. In present study, all related researches about interventions and potential mechanisms were reviewed and the mainstream methodologies were described.

Developing a Tanshinone IIA Memetic by Targeting MIOS to Regulate mTORC1 and Autophagy in Glioblastoma

Tanshinone IIA (T2A) is a bioactive compound that provides promise in the treatment of glioblastoma multiforme (GBM), with a range of molecular mechanisms including the inhibition of the mechanistic target of rapamycin complex 1 (mTORC1) and the induction of autophagy. Recently, T2A has been demonstrated to function through sestrin 2 (SESN) to inhibit mTORC1 activity, but its possible impact on autophagy through this pathway has not been investigated. Here, the model system Dictyostelium discoideum and GBM cell lines were employed to investigate the cellular role of T2A in regulating SESN to inhibit mTORC1 and activate autophagy through a GATOR2 component MIOS. In D. discoideum, T2A treatment induced autophagy and inhibited mTORC1 activity, with both effects lost upon the ablation of SESN (sesn-) or MIOS (mios-). We further investigated the targeting of MIOS to reproduce this effect of T2A, where computational analysis identified 25 novel compounds predicted to strongly bind the human MIOS protein, with one compound (MIOS inhibitor 3; Mi3) reducing cell proliferation in two GBM cells. Furthermore, Mi3 specificity was demonstrated through the loss of potency in the D. discoideum mios- cells regarding cell proliferation and the induction of autophagy. In GBM cells, Mi3 treatment also reduced mTORC1 activity and induced autophagy. Thus, a potential T2A mimetic showing the inhibition of mTORC1 and induction of autophagy in GBM cells was identified.

COPII cage assembly factor Sec13 integrates information flow regulating endomembrane function in response to human variation

How information flow is coordinated for managing transit of 1/3 of the genome through endomembrane pathways by the coat complex II (COPII) system in response to human variation remains an enigma. By examining the interactome of the COPII cage-assembly component Sec13, we show that it is simultaneously associated with multiple protein complexes that facilitate different features of a continuous program of chromatin organization, transcription, translation, trafficking, and degradation steps that are differentially sensitive to Sec13 levels. For the trafficking step, and unlike other COPII components, reduction of Sec13 expression decreased the ubiquitination and degradation of wild-type (WT) and F508del variant cargo protein cystic fibrosis transmembrane conductance regulator (CFTR) leading to a striking increase in fold stability suggesting that the events differentiating export from degradation are critically dependent on COPII cage assembly at the ER Golgi intermediate compartment (ERGIC) associated recycling and degradation step linked to COPI exchange. Given Sec13's multiple roles in protein complex assemblies that change in response to its expression, we suggest that Sec13 serves as an unanticipated master regulator coordinating information flow from the genome to the proteome to facilitate spatial covariant features initiating and maintaining design and function of membrane architecture in response to human variation.

SESN2-Mediated AKT/GSK-3β/NRF2 Activation to Ameliorate Adriamycin Cardiotoxicity in High-Fat Diet-Induced Obese Mice

Aims: Obese patients are highly sensitive to adriamycin (ADR)-induced cardiotoxicity. However, the potential mechanism of superimposed toxicity remains to be elucidated. Sestrin 2 (SESN2), a potential antioxidant, could attenuate stress-induced cardiomyopathy; therefore, this study aims to explore whether SESN2 enhances cardiac resistance to ADR-induced oxidative damage in high-fat diet (HFD)-induced obese mice. Results: The results revealed that obesity decreased SESN2 expression in ADR-exposed heart. And, HFD mice may predispose to ADR-induced cardiotoxicity, which was probably associated with inhibiting protein kinase B (AKT), glycogen synthase kinase-3 beta (GSK-3β) phosphorylation and subsequently blocking nuclear localization of nuclear factor erythroid-2 related factor 2 (NRF2), ultimately resulting in cardiac oxidative damage. However, these destructive cascades and cardiac oxidative damage effects induced by HFD/sodium palmitate combined with ADR were blocked by overexpression of SESN2. Moreover, the antioxidant effect of SESN2 could be largely abolished by sh-Nrf2 or wortmannin. And sulforaphane, an NRF2 agonist, could remarkably reverse cardiac pathological and functional abnormalities caused by ADR in obese mice. Innovation and Conclusion: This study demonstrated that SESN2 might be a promising therapeutic target for improving anthracycline-related cardiotoxicity in obesity by upregulating activity of NRF2 via AKT/GSK-3β/Src family tyrosine kinase signaling pathway. Antioxid. Redox Signal. 40, 598-615.

New insights into GATOR2-dependent interactions and its conformational changes in amino acid sensing

Eukaryotic cells coordinate growth under different environmental conditions via mechanistic target of rapamycin complex 1 (mTORC1). In the amino-acid-sensing signalling pathway, the GATOR2 complex, containing five evolutionarily conserved subunits (WDR59, Mios, WDR24, Seh1L and Sec13), is required to regulate mTORC1 activity by interacting with upstream CASTOR1 (arginine sensor) and Sestrin2 (leucine sensor and downstream GATOR1 complex). GATOR2 complex utilizes β-propellers to engage with CASTOR1, Sestrin2 and GATOR1, removal of these β-propellers results in substantial loss of mTORC1 capacity. However, structural information regarding the interface between amino acid sensors and GATOR2 remains elusive. With the recent progress of the AI-based tool AlphaFold2 (AF2) for protein structure prediction, structural models were predicted for Sentrin2-WDR24-Seh1L and CASTOR1-Mios β-propeller. Furthermore, the effectiveness of relevant residues within the interface was examined using biochemical experiments combined with molecular dynamics (MD) simulations. Notably, fluorescence resonance energy transfer (FRET) analysis detected the structural transition of GATOR2 in response to amino acid signals, and the deletion of Mios β-propeller severely impeded that change at distinct arginine levels. These findings provide structural perspectives on the association between GATOR2 and amino acid sensors and can facilitate future research on structure determination and function.

Role of sestrins in metabolic and aging-related diseases

Sestrins are a type of highly conserved stress-inducing protein that has antioxidant and mTORC1 inhibitory functions. Metabolic dysfunction and aging are the main risk factors for development of human diseases, such as diabetes, neurodegenerative diseases, and cancer. Sestrins have important roles in regulating glucose and lipid metabolism, anti-tumor functions, and aging by inhibiting the reactive oxygen species and mechanistic target of rapamycin complex 1 pathways. In this review, the structure and biological functions of sestrins are summarized, and how sestrins are activated and contribute to regulation of the downstream signal pathways of metabolic and aging-related diseases are discussed in detail with the goal of providing new ideas and therapeutic targets for the treatment of related diseases.

Epigenetic regulation of autophagy-related genes: Implications for neurodevelopmental disorders

Macroautophagy/autophagy is an evolutionarily highly conserved catabolic process that is important for the clearance of cytosolic contents to maintain cellular homeostasis and survival. Recent findings point toward a critical role for autophagy in brain function, not only by preserving neuronal health, but especially by controlling different aspects of neuronal development and functioning. In line with this, mutations in autophagy-related genes are linked to various key characteristics and symptoms of neurodevelopmental disorders (NDDs), including autism, micro-/macrocephaly, and epilepsy. However, the group of NDDs caused by mutations in autophagy-related genes is relatively small. A significant proportion of NDDs are associated with mutations in genes encoding epigenetic regulatory proteins that modulate gene expression, so-called chromatinopathies. Intriguingly, several of the NDD-linked chromatinopathy genes have been shown to regulate autophagy-related genes, albeit in non-neuronal contexts. From these studies it becomes evident that tight transcriptional regulation of autophagy-related genes is crucial to control autophagic activity. This opens the exciting possibility that aberrant autophagic regulation might underly nervous system impairments in NDDs with disturbed epigenetic regulation. We here summarize NDD-related chromatinopathy genes that are known to regulate transcriptional regulation of autophagy-related genes. Thereby, we want to highlight autophagy as a candidate key hub mechanism in NDD-related chromatinopathies.Abbreviations: ADNP: activity dependent neuroprotector homeobox; ASD: autism spectrum disorder; ATG: AutTophaGy related; CpG: cytosine-guanine dinucleotide; DNMT: DNA methyltransferase; EHMT: euchromatic histone lysine methyltransferase; EP300: E1A binding protein p300; EZH2: enhancer of zeste 2 polycomb repressive complex 2 subunit; H3K4me3: histone 3 lysine 4 trimethylation; H3K9me1/2/3: histone 3 lysine 9 mono-, di-, or trimethylation; H3K27me2/3: histone 3 lysine 27 di-, or trimethylation; hiPSCs: human induced pluripotent stem cells; HSP: hereditary spastic paraplegia; ID: intellectual disability; KANSL1: KAT8 regulatory NSL complex subunit 1; KAT8: lysine acetyltransferase 8; KDM1A/LSD1: lysine demethylase 1A; MAP1LC3B: microtubule associated protein 1 light chain 3 beta; MTOR: mechanistic target of rapamycin kinase; MTORC1: mechanistic target of rapamycin complex 1; NDD: neurodevelopmental disorder; PHF8: PHD finger protein 8; PHF8-XLID: PHF8-X linked intellectual disability syndrome; PTM: post-translational modification; SESN2: sestrin 2; YY1: YY1 transcription factor; YY1AP1: YY1 associated protein 1.

Structures and Functions of the Human GATOR1 Complex

Eukaryotic cells coordinate available nutrients with their growth through the mechanistic target of rapamycin complex 1 (mTORC1) pathway, in which numerous evolutionarily conserved protein complexes survey and transmit nutrient inputs toward mTORC1. mTORC1 integrates these inputs and activates downstream anabolic or catabolic programs that are in tune with cellular needs, effectively maintaining metabolic homeostasis. The GAP activity toward Rags-1 (GATOR1) protein complex is a critical negative regulator of the mTORC1 pathway and, in the absence of amino acid inputs, is activated to turn off mTORC1 signaling. GATOR1-mediated inhibition of mTORC1 signaling is tightly regulated by an ensemble of protein complexes that antagonize or promote its activity in response to the cellular nutrient environment. Structural, biochemical, and biophysical studies of the GATOR1 complex and its interactors have advanced our understanding of how it regulates cellular metabolism when amino acids are limited. Here, we review the current research with a focus on GATOR1 structure, its enzymatic mechanism, and the growing group of proteins that regulate its activity. Finally, we discuss the implication of GATOR1 dysregulation in physiology and human diseases.

Advances in the regulatory mechanisms of mTOR in necroptosis

The mammalian target of rapamycin (mTOR), an evolutionarily highly conserved serine/threonine protein kinase, plays a prominent role in controlling gene expression, metabolism, and cell death. Programmed cell death (PCD) is indispensable for maintaining homeostasis by removing senescent, defective, or malignant cells. Necroptosis, a type of PCD, relies on the interplay between receptor-interacting serine-threonine kinases (RIPKs) and the membrane perforation by mixed lineage kinase domain-like protein (MLKL), which is distinguished from apoptosis. With the development of necroptosis-regulating mechanisms, the importance of mTOR in the complex network of intersecting signaling pathways that govern the process has become more evident. mTOR is directly responsible for the regulation of RIPKs. Autophagy is an indirect mechanism by which mTOR regulates the removal and interaction of RIPKs. Another necroptosis trigger is reactive oxygen species (ROS) produced by oxidative stress; mTOR regulates necroptosis by exploiting ROS. Considering the intricacy of the signal network, it is reasonable to assume that mTOR exerts a bifacial effect on necroptosis. However, additional research is necessary to elucidate the underlying mechanisms. In this review, we summarized the mechanisms underlying mTOR activation and necroptosis and highlighted the signaling pathway through which mTOR regulates necroptosis. The development of therapeutic targets for various diseases has been greatly advanced by the expanding knowledge of how mTOR regulates necroptosis.

Status of Research on Sestrin2 and Prospects for its Application in Therapeutic Strategies Targeting Myocardial Aging

Cardiac aging is accompanied by changes in the heart at the cellular and molecular levels, leading to alterations in cardiac structure and function. Given today's increasingly aging population, the decline in cardiac function caused by cardiac aging has a significant impact on quality of life. Antiaging therapies to slow the aging process and attenuate changes in cardiac structure and function have become an important research topic. Treatment with drugs, including metformin, spermidine, rapamycin, resveratrol, astaxanthin, Huolisu oral liquid, and sulforaphane, has been demonstrated be effective in delaying cardiac aging by stimulating autophagy, delaying ventricular remodeling, and reducing oxidative stress and the inflammatory response. Furthermore, caloric restriction has been shown to play an important role in delaying aging of the heart. Many studies in cardiac aging and cardiac aging-related models have demonstrated that Sestrin2 has antioxidant and anti-inflammatory effects, stimulates autophagy, delays aging, regulates mitochondrial function, and inhibits myocardial remodeling by regulation of relevant signaling pathways. Therefore, Sestrin2 is likely to become an important target for antimyocardial aging therapy.

The post-translational regulation of transcription factor EB (TFEB) in health and disease

Transcription factor EB (TFEB) is a basic helix-loop-helix leucine zipper transcription factor that acts as a master regulator of lysosomal biogenesis, lysosomal exocytosis, and macro-autophagy. TFEB contributes to a wide range of physiological functions, including mitochondrial biogenesis and innate and adaptive immunity. As such, TFEB is an essential component of cellular adaptation to stressors, ranging from nutrient deprivation to pathogenic invasion. The activity of TFEB depends on its subcellular localisation, turnover, and DNA-binding capacity, all of which are regulated at the post-translational level. Pathological states are characterised by a specific set of stressors, which elicit post-translational modifications that promote gain or loss of TFEB function in the affected tissue. In turn, the resulting increase or decrease in survival of the tissue in which TFEB is more or less active, respectively, may either benefit or harm the organism as a whole. In this way, the post-translational modifications of TFEB account for its otherwise paradoxical protective and deleterious effects on organismal fitness in diseases ranging from neurodegeneration to cancer. In this review, we describe how the intracellular environment characteristic of different diseases alters the post-translational modification profile of TFEB, enabling cellular adaptation to a particular pathological state.

Multifaceted role of mTOR (mammalian target of rapamycin) signaling pathway in human health and disease

The mammalian target of rapamycin (mTOR) is a protein kinase that controls cellular metabolism, catabolism, immune responses, autophagy, survival, proliferation, and migration, to maintain cellular homeostasis. The mTOR signaling cascade consists of two distinct multi-subunit complexes named mTOR complex 1/2 (mTORC1/2). mTOR catalyzes the phosphorylation of several critical proteins like AKT, protein kinase C, insulin growth factor receptor (IGF-1R), 4E binding protein 1 (4E-BP1), ribosomal protein S6 kinase (S6K), transcription factor EB (TFEB), sterol-responsive element-binding proteins (SREBPs), Lipin-1, and Unc-51-like autophagy-activating kinases. mTOR signaling plays a central role in regulating translation, lipid synthesis, nucleotide synthesis, biogenesis of lysosomes, nutrient sensing, and growth factor signaling. The emerging pieces of evidence have revealed that the constitutive activation of the mTOR pathway due to mutations/amplification/deletion in either mTOR and its complexes (mTORC1 and mTORC2) or upstream targets is responsible for aging, neurological diseases, and human malignancies. Here, we provide the detailed structure of mTOR, its complexes, and the comprehensive role of upstream regulators, as well as downstream effectors of mTOR signaling cascades in the metabolism, biogenesis of biomolecules, immune responses, and autophagy. Additionally, we summarize the potential of long noncoding RNAs (lncRNAs) as an important modulator of mTOR signaling. Importantly, we have highlighted the potential of mTOR signaling in aging, neurological disorders, human cancers, cancer stem cells, and drug resistance. Here, we discuss the developments for the therapeutic targeting of mTOR signaling with improved anticancer efficacy for the benefit of cancer patients in clinics.

Regulation of nucleo-cytosolic 26S proteasome translocation by aromatic amino acids via mTOR is essential for cell survival under stress

The proteasome is responsible for removal of ubiquitinated proteins. Although several aspects of its regulation (e.g., assembly, composition, and post-translational modifications) have been unraveled, studying its adaptive compartmentalization in response to stress is just starting to emerge. We found that following amino acid starvation, the proteasome is translocated from its large nuclear pool to the cytoplasm-a response regulated by newly identified mTOR-agonistic amino acids-Tyr, Trp, and Phe (YWF). YWF relay their signal upstream of mTOR through Sestrin3 by disrupting its interaction with the GATOR2 complex. The triad activates mTOR toward its downstream substrates p62 and transcription factor EB (TFEB), affecting both proteasomal and autophagic activities. Proteasome translocation stimulates cytosolic proteolysis which replenishes amino acids, thus enabling cell survival. In contrast, nuclear sequestration of the proteasome following mTOR activation by YWF inhibits this proteolytic adaptive mechanism, leading to cell death, which establishes this newly identified pathway as a key stress-coping mechanism.

Amino acids contribute to adaptive thermogenesis. New insights into the mechanisms of action of recent drugs for metabolic disorders are emerging

Adaptive thermogenesis is the heat production by muscle contractions (shivering thermogenesis) or brown adipose tissue (BAT) and beige fat (non-shivering thermogenesis) in response to external stimuli, including cold exposure. BAT and beige fat communicate with peripheral organs and the brain through a variegate secretory and absorption processes - controlling adipokines, microRNAs, extracellular vesicles, and metabolites - and have received much attention as potential therapeutic targets for managing obesity-related disorders. The sympathetic nervous system and norepinephrine-releasing adipose tissue macrophages (ATM) activate uncoupling protein 1 (UCP1), expressed explicitly in brown and beige adipocytes, dissolving the electrochemical gradient and uncoupling tricarboxylic acid cycle and the electron transport chain from ATP production. Mounting evidence has attracted attention to the multiple effects of dietary and endogenously synthesised amino acids in BAT thermogenesis and metabolic phenotype in animals and humans. However, the mechanisms implicated in these processes have yet to be conclusively characterized. In the present review article, we aim to define the principal investigation areas in this context, including intestinal microbiota constitution, adipose autophagy modulation, and secretome and metabolic fluxes control, which lead to increased brown/beige thermogenesis. Finally, also based on our recent epicardial adipose tissue results, we summarise the evidence supporting the notion that the new dual and triple agonists of glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP), and glucagon (GCG) receptor - with never before seen weight loss and insulin-sensitizing efficacy - promote thermogenic-like amino acid profiles in BAT with robust heat production and likely trigger sympathetic activation and adaptive thermogenesis by controlling amino acid metabolism and ATM expansion in BAT and beige fat.

An update on the bridging factors connecting autophagy and Nrf2 antioxidant pathway

Macroautophagy/autophagy is a lysosome-dependent catabolic pathway for the degradation of intracellular proteins and organelles. Autophagy dysfunction is related to many diseases, including lysosomal storage diseases, cancer, neurodegenerative diseases, cardiomyopathy, and chronic metabolic diseases, in which increased reactive oxygen species (ROS) levels are also observed. ROS can randomly oxidize proteins, lipids, and DNA, causing oxidative stress and damage. Cells have developed various antioxidant pathways to reduce excessive ROS and maintain redox homeostasis. Treatment targeting only one aspect of diseases with autophagy dysfunction and oxidative stress shows very limited effects. Herein, identifying the bridging factors that can regulate both autophagy and antioxidant pathways is beneficial for dual-target therapies. This review intends to provide insights into the current identified bridging factors that connect autophagy and Nrf2 antioxidant pathway, as well as their tight interconnection with each other. These factors could be potential dual-purpose targets for the treatment of diseases implicated in both autophagy dysfunction and oxidative stress.

Effects of Leucine Ingestion and Contraction on the Sestrin/GATOR2 Pathway and mTORC1 Activation in Rat Fast-Twitch muscle

BACKGROUND

Leucine activates the mechanistic/mammalian target of rapamycin complex 1 (mTORC1) in mammalian skeletal muscle. Recent studies have shown that Sestrin, a leucine sensor, might play a role in this process. However, it remains unknown whether Sestrin dissociates from GATOR2 in a dose- and time-dependent manner and whether an acute bout of muscle contraction augments this dissociation.

OBJECTIVE

This study aimed to examine the effects of leucine ingestion and muscle contraction on the interaction between Sestrin1/2 and GATOR2 and on mTORC1 activation.

METHODS

Male Wistar rats were randomly assigned to control (C), leucine 3 (L3), or leucine 10 (L10) groups. Intact gastrocnemius muscles were subjected to 30 repetitive unilateral contractions. The L3 and L10 groups were then orally administered 3 and 10 mmol/kg body weight of L-leucine 2 h after the end of the contractions, respectively. Blood and muscle samples were collected 30, 60, or 120 min after the administration.

RESULTS

The blood and muscle leucine concentrations increased in a dose-dependent manner. The ratio of phosphorylated ribosomal protein S6 kinase (S6K) to total S6K (which indicates mTORC1 signaling activation) was markedly increased by muscle contraction and increased in a dose-dependent manner only in rested muscle. Leucine ingestion but not muscle contraction increased Sestrin1 dissociation from GATOR2 and Sestrin2 association with GATOR2. A negative relationship was observed between the blood and muscle leucine concentrations and the Sestrin1 association with GATOR2.

CONCLUSIONS

The results suggest that Sestrin1, but not Sestrin2, regulates leucine-related mTORC1 activation via its dissociation from GATOR2 and that acute exercise-induced mTORC1 activation involves pathways other than the leucine-related Sestrin1/GATOR2 pathway.

A coordinated multiorgan metabolic response contributes to human mitochondrial myopathy

Mitochondrial diseases are a heterogeneous group of monogenic disorders that result from impaired oxidative phosphorylation (OXPHOS). As neuromuscular tissues are highly energy-dependent, mitochondrial diseases often affect skeletal muscle. Although genetic and bioenergetic causes of OXPHOS impairment in human mitochondrial myopathies are well established, there is a limited understanding of metabolic drivers of muscle degeneration. This knowledge gap contributes to the lack of effective treatments for these disorders. Here, we discovered fundamental muscle metabolic remodeling mechanisms shared by mitochondrial disease patients and a mouse model of mitochondrial myopathy. This metabolic remodeling is triggered by a starvation-like response that evokes accelerated oxidation of amino acids through a truncated Krebs cycle. While initially adaptive, this response evolves in an integrated multiorgan catabolic signaling, lipid store mobilization, and intramuscular lipid accumulation. We show that this multiorgan feed-forward metabolic response involves leptin and glucocorticoid signaling. This study elucidates systemic metabolic dyshomeostasis mechanisms that underlie human mitochondrial myopathies and identifies potential new targets for metabolic intervention.

Role of mammalian target of rapamycin (mTOR) signalling in oncogenesis

The signalling system known as mammalian target of rapamycin (mTOR) is believed to be required for several biological activities involving cell proliferation. The serine-threonine kinase identified as mTOR recognises PI3K-AKT stress signals. It is well established in the scientific literature that the deregulation of the mTOR pathway plays a crucial role in cancer growth and advancement. This review focuses on the normal functions of mTOR as well as its abnormal roles in cancer development.

mTOR in programmed cell death and its therapeutic implications

Mechanistic target of rapamycin (mTOR), a highly conserved serine/threonine kinase, is involved in cellular metabolism, protein synthesis, and cell death. Programmed cell death (PCD) assists in eliminating aging, damaged, or neoplastic cells, and is indispensable for sustaining normal growth, fighting pathogenic microorganisms, and maintaining body homeostasis. mTOR has crucial functions in the intricate signaling pathway network of multiple forms of PCD. mTOR can inhibit autophagy, which is part of PCD regulation. Cell survival is affected by mTOR through autophagy to control reactive oxygen species production and the degradation of pertinent proteins. Additionally, mTOR can regulate PCD in an autophagy-independent manner by affecting the expression levels of related genes and phosphorylating proteins. Therefore, mTOR acts through both autophagy-dependent and -independent pathways to regulate PCD. It is conceivable that mTOR exerts bidirectional regulation of PCD, such as ferroptosis, according to the complexity of signaling pathway networks, but the underlying mechanisms have not been fully explained. This review summarizes the recent advances in understanding mTOR-mediated regulatory mechanisms in PCD. Rigorous investigations into PCD-related signaling pathways have provided prospective therapeutic targets that may be clinically beneficial for treating various diseases.

Muscular Sestrins: Roles in Exercise Physiology and Stress Resistance

Sestrins are a family of stress-inducible proteins that are critical for stress adaptation and the maintenance of metabolic homeostasis. High expression of Sestrins is observed in skeletal and cardiac muscle tissues, suggesting their significance in the physiological homeostasis of these organs. Furthermore, expression of Sestrins is dynamically controlled in the tissues, based on the level of physical activity and the presence or absence of stress insults. Genetic studies in model organisms have shown that muscular Sestrin expression is critical for metabolic homeostasis, exercise adaptation, stress resistance, and repair and may mediate the beneficial effects of some available therapeutics. The current minireview summarizes and discusses recent findings that shed light on the role of Sestrins in regulating muscle physiology and homeostasis.

Glucose-Induced Activation of mTORC1 is Associated with Hexokinase2 Binding to Sestrins in HEK293T Cells

BACKGROUND

Sestrins (SESN1-3) act as proximal sensors in leucine-induced activation of the protein kinase mechanistic target of rapamycin (mTOR) in complex 1 (mTORC1), a key regulator of cell growth and metabolism.

OBJECTIVE

In the present study, the hypothesis that SESNs also mediate glucose-induced activation of mTORC1 was tested.

METHODS

Rats underwent overnight fasting, and in the morning, either saline or a glucose solution (4 g⋅kg-1 BW/10 mL⋅kg-1) was administered by oral gavage; mTORC1 activation in the tibialis anterior muscle was assessed. To further assess the mechanism through which glucose promotes mTORC1 activation, wild-type (WT) HEK293T and HEK293T cells lacking either all 3 SESNs (SESNTKO) or hexokinase 2 (HK2KO) were deprived of glucose, followed by glucose addback, and mTORC1 activation was assessed. In addition, glucose-induced changes in the association of the SESNs with components of the GAP activity toward the Rags (GATOR2) complex and with hexokinase 2 (HK2) were assessed by co-immunoprecipitation. One- and two-way ANOVA with Tukey post hoc comparisons were used.

RESULTS

Glucose administration to fasted rats promoted mTORC1 activation. Similarly, glucose readdition (GluAB) to the medium of glucose-deprived WT cells also promoted mTORC1 activation. By contrast, SESNTKO cells demonstrated attenuated mTORC1 activation following GluAB compared with WT cells. Interestingly, HK2 associated with all 3 SESNs in a glucose-dependent manner, i.e., HK2 abundance in SESN immunoprecipitates was high in cells deprived of glucose and decreased in response to GluAB. Moreover, similar to SESNTKO cells, the sensitivity of mTORC1 to GluAB was attenuated in HK2KO cells compared with WT cells.

CONCLUSIONS

The results of this study demonstrate that the SESNs and HK2 play important roles in glucose-induced mTORC1 activation in HEK293T cells. However, unlike leucine-induced mTORC1 activation, the effect was independent of the changes in SESN-GATOR2 interaction, and instead, it was associated with alterations in the association of SESNs with HK2.

Sertoli cell adaptation to glucose deprivation: Potential role of AMPK in the regulation of lipid metabolism

Sertoli cells (SCs) provide an adequate environment for germ cell development. SCs possess unique features that meet germ cells' metabolic demands: they produce lactate from glucose, which is delivered as energy substrate to germ cells. SCs store fatty acids (FAs) as triacylglycerols (TAGs) in lipid droplets (LDs) and can oxidize FAs to sustain their own energetic demands. They also produce ketone bodies from FAs. It has been shown that exposure of SCs to metabolic stresses, such as glucose deprivation, triggers specific adaptive responses that sustain cell survival and preserve lactate supply to germ cells. The aim of the present study was to investigate whether there are modifications in rat SCs lipid metabolism, including LD content, FA oxidation, and ketone bodies production, as part of their adaptive response to glucose deprivation. The present study was performed in 20-day-old rat SCs cultures. We determined LD content by Oil Red O staining, FA oxidation by measuring the release of ³ H₂ O from [³ H] palmitate, TAGs and 3-hydroxybutyrate levels by spectrophotometric methods, and mRNA levels by RT-qPCR. Results show that the absence of glucose in SC culture medium entails: (1) a decrease in LD content and TAGs levels that is accompanied by decreased perilipin 1 mRNA levels, (2) an increase in FA oxidation that is in part mediated by AMP kinase (AMPK) activation and (3) a decrease in 3-hydroxybutyrate production. Additionally, we studied whether sestrins (SESN1, 2 and 3), proteins involved in the cellular response to stress, are regulated in glucose deprivation conditions. We show that there is an increase in SESN2 mRNA levels in deprived conditions. In conclusion, glucose deprivation affects SC lipid metabolism promoting FA mobilization from LDs to be used as energy source.

Influence of mTOR-regulated anabolic pathways on equine skeletal muscle health

Skeletal muscle is a highly dynamic organ that is essential for locomotion as well as endocrine regulation in all populations of horses. However, despite the importance of adequate muscle development and maintenance, the mechanisms underlying protein anabolism in horses on different diets, exercise programs, and at different life stages remain obscure. Mechanistic target of rapamycin (mTOR) is a key component of the protein synthesis pathway and is regulated by biological factors such as insulin and amino acid availability. Providing a diet ample in vital amino acids, such as leucine and glutamine, is essential in activating sensory pathways that recruit mTOR to the lysosome and assist in the translation of important downstream targets. When the diet is well balanced, mitochondrial biogenesis and protein synthesis are activated in response to increased exercise bouts in the performing athlete. It is important to note that the mTOR kinase pathways are multi-faceted and very complex, with several binding partners and targets that lead to specific functions in protein turnover of the cell, and ultimately, the capacity to maintain or grow muscle mass. Further, these pathways are likely altered across the lifespan, with an emphasis of growth in young horses while decreases in musculature with aged horses appears to be attributable to degradation or other regulators of protein synthesis rather than alterations in the mTOR pathway. Previous work has begun to pinpoint ways in which the mTOR pathway is influenced by diet, exercise, and age; however, future research is warranted to quantify the functional outcomes related to changes in mTOR. Promisingly, this could provide direction on appropriate management techniques to support skeletal muscle growth and maximize athletic potential in differing equine populations.

Sestrin2 as a Protective Shield against Cardiovascular Disease

A timely and adequate response to stress is inherently present in each cell and is important for maintaining the proper functioning of the cell in changing intracellular and extracellular environments. Disruptions in the functioning or coordination of defense mechanisms against cellular stress can reduce the tolerance of cells to stress and lead to the development of various pathologies. Aging also reduces the effectiveness of these defense mechanisms and results in the accumulation of cellular lesions leading to senescence or death of the cells. Endothelial cells and cardiomyocytes are particularly exposed to changing environments. Pathologies related to metabolism and dynamics of caloric intake, hemodynamics, and oxygenation, such as diabetes, hypertension, and atherosclerosis, can overwhelm endothelial cells and cardiomyocytes with cellular stress to produce cardiovascular disease. The ability to cope with stress depends on the expression of endogenous stress-inducible molecules. Sestrin2 (SESN2) is an evolutionary conserved stress-inducible cytoprotective protein whose expression is increased in response to and defend against different types of cellular stress. SESN2 fights back the stress by increasing the supply of antioxidants, temporarily holding the stressful anabolic reactions, and increasing autophagy while maintaining the growth factor and insulin signaling. If the stress and the damage are beyond repair, SESN2 can serve as a safety valve to signal apoptosis. The expression of SESN2 decreases with age and its levels are associated with cardiovascular disease and many age-related pathologies. Maintaining sufficient levels or activity of SESN2 can in principle prevent the cardiovascular system from aging and disease.

GATOR2-dependent mTORC1 activity is a therapeutic vulnerability in FOXO1 fusion-positive rhabdomyosarcoma

Oncogenic FOXO1 gene fusions drive a subset of rhabdomyosarcoma (RMS) with poor survival; to date, these cancer drivers are therapeutically intractable. To identify new therapies for this disease, we undertook an isogenic CRISPR-interference screen to define PAX3-FOXO1-specific genetic dependencies and identified genes in the GATOR2 complex. GATOR2 loss in RMS abrogated aa-induced lysosomal localization of mTORC1 and consequent downstream signaling, slowing G1-S cell cycle transition. In vivo suppression of GATOR2 impaired the growth of tumor xenografts and favored the outgrowth of cells lacking PAX3-FOXO1. Loss of a subset of GATOR2 members can be compensated by direct genetic activation of mTORC1. RAS mutations are also sufficient to decouple mTORC1 activation from GATOR2, and indeed, fusion-negative RMS harboring such mutations exhibit aa-independent mTORC1 activity. A bisteric, mTORC1-selective small molecule induced tumor regressions in fusion-positive patient-derived tumor xenografts. These findings highlight a vulnerability in FOXO1 fusion-positive RMS and provide rationale for the clinical evaluation of bisteric mTORC1 inhibitors, currently in phase I testing, to treat this disease. Isogenic genetic screens can, thus, identify potentially exploitable vulnerabilities in fusion-driven pediatric cancers that otherwise remain mostly undruggable.

Non-canonical mTORC1 signaling at the lysosome

The mechanistic target of rapamycin complex 1 (mTORC1) signaling hub integrates multiple environmental cues to modulate cell growth and metabolism. Over the past decade considerable knowledge has been gained on the mechanisms modulating mTORC1 lysosomal recruitment and activation. However, whether and how mTORC1 is able to elicit selective responses to diverse signals has remained elusive until recently. We discuss emerging evidence for a 'non-canonical' mTORC1 signaling pathway that controls the function of microphthalmia/transcription factor E (MiT-TFE) transcription factors, key regulators of cell metabolism. This signaling pathway is mediated by a specific mechanism of substrate recruitment, and responds to stimuli that appear to converge on the lysosomal surface. We discuss the relevance of this pathway in physiological and disease conditions.

Cryo-EM structure of the SEA complex

The SEA complex (SEAC) is a growth regulator that acts as a GTPase-activating protein (GAP) towards Gtr1, a Rag GTPase that relays nutrient status to the Target of Rapamycin Complex 1 (TORC1) in yeast1. Functionally, the SEAC has been divided into two subcomplexes: SEACIT, which has GAP activity and inhibits TORC1, and SEACAT, which regulates SEACIT2. This system is conserved in mammals: the GATOR complex, consisting of GATOR1 (SEACIT) and GATOR2 (SEACAT), transmits amino acid3 and glucose4 signals to mTORC1. Despite its importance, the structure of SEAC/GATOR, and thus molecular understanding of its function, is lacking. Here, we solve the cryo-EM structure of the native eight-subunit SEAC. The SEAC has a modular structure in which a COPII-like cage corresponding to SEACAT binds two flexible wings, which correspond to SEACIT. The wings are tethered to the core via Sea3, which forms part of both modules. The GAP mechanism of GATOR1 is conserved in SEACIT, and GAP activity is unaffected by SEACAT in vitro. In vivo, the wings are essential for recruitment of the SEAC to the vacuole, primarily via the EGO complex. Our results indicate that rather than being a direct inhibitor of SEACIT, SEACAT acts as a scaffold for the binding of TORC1 regulators.

Non-genomic activation of the AKT-mTOR pathway by the mitochondrial stress response in thyroid cancer

Cancer progression is associated with metabolic reprogramming and causes significant intracellular stress; however, the mechanisms that link cellular stress and growth signalling are not fully understood. Here, we identified a mechanism that couples the mitochondrial stress response (MSR) with tumour progression. We demonstrated that the MSR is activated in a significant proportion of human thyroid cancers via the upregulation of heat shock protein D family members and the mitokine, growth differentiation factor 15. Our study also revealed that MSR triggered AKT/S6K signalling by activating mTORC2 via activating transcription factor 4/sestrin 2 activation whilst promoting leucine transporter and nutrient-induced mTORC1 activation. Importantly, we found that an increase in ^mtDNA played an essential role in MSR-induced mTOR activation and that crosstalk between MYC and MSR potentiated mTOR activation. Together, these findings suggest that the MSR could be a predictive marker for aggressive human thyroid cancer as well as a useful therapeutic target.

Autophagy induction promoted by m6A reader YTHDF3 through translation upregulation of FOXO3 mRNA

Autophagy is crucial for maintaining cellular energy homeostasis and for cells to adapt to nutrient deficiency, and nutrient sensors regulating autophagy have been reported previously. However, the role of eiptranscriptomic modifications such as m⁶A in the regulation of starvation-induced autophagy is unclear. Here, we show that the m⁶A reader YTHDF3 is essential for autophagy induction. m⁶A modification is up-regulated to promote autophagosome formation and lysosomal degradation upon nutrient deficiency. METTL3 depletion leads to a loss of functional m⁶A modification and inhibits YTHDF3-mediated autophagy flux. YTHDF3 promotes autophagy by recognizing m⁶A modification sites around the stop codon of FOXO3 mRNA. YTHDF3 also recruits eIF3a and eIF4B to facilitate FOXO3 translation, subsequently initiating autophagy. Overall, our study demonstrates that the epitranscriptome regulator YTHDF3 functions as a nutrient responder, providing a glimpse into the post-transcriptional RNA modifications that regulate metabolic homeostasis.

Role of mechanistic target of rapamycin in autophagy and alcohol-associated liver disease

Mechanistic target of rapamycin (mTOR) is a serine-threonine kinase and a cellular sensor for nutrient and energy status, which is critical in regulating cell metabolism and growth by governing the anabolic (protein and lipid synthesis) and catabolic process (autophagy). Alcohol-associated liver disease (ALD) is a major chronic liver disease worldwide that carries a huge financial burden. The spectrum of the pathogenesis of ALD includes steatosis, fibrosis, inflammation, ductular reaction, and eventual hepatocellular carcinoma, which is closely associated with metabolic changes that are regulated by mTOR. In this review, we summarized recent progress of alcohol consumption on the changes of mTORC1 and mTORC2 activity, the potential mechanisms and possible impact of the mTORC1 changes on autophagy in ALD. We also discussed the potential beneficial effects and limitations of targeting mTORC1 against ALD.

Milk Exosomal microRNAs: Postnatal Promoters of β Cell Proliferation but Potential Inducers of β Cell De-Differentiation in Adult Life

Pancreatic β cell expansion and functional maturation during the birth-to-weaning period is driven by epigenetic programs primarily triggered by growth factors, hormones, and nutrients provided by human milk. As shown recently, exosomes derived from various origins interact with β cells. This review elucidates the potential role of milk-derived exosomes (MEX) and their microRNAs (miRs) on pancreatic β cell programming during the postnatal period of lactation as well as during continuous cow milk exposure of adult humans to bovine MEX. Mechanistic evidence suggests that MEX miRs stimulate mTORC1/c-MYC-dependent postnatal β cell proliferation and glycolysis, but attenuate β cell differentiation, mitochondrial function, and insulin synthesis and secretion. MEX miR content is negatively affected by maternal obesity, gestational diabetes, psychological stress, caesarean delivery, and is completely absent in infant formula. Weaning-related disappearance of MEX miRs may be the critical event switching β cells from proliferation to TGF-β/AMPK-mediated cell differentiation, whereas continued exposure of adult humans to bovine MEX miRs via intake of pasteurized cow milk may reverse β cell differentiation, promoting β cell de-differentiation. Whereas MEX miR signaling supports postnatal β cell proliferation (diabetes prevention), persistent bovine MEX exposure after the lactation period may de-differentiate β cells back to the postnatal phenotype (diabetes induction).

Serum Sestrin2 Was Lower in Septic Shock Patients with Cardiomyopathy

Background

To determine the clinical significance of variations in serum sestrin2 protein levels in the development of septic cardiomyopathy in septic shock patients.

Methods

The serum sestrin2 concentrations of each sample were determined using ELISA in a total of 67 control persons and 188 patients with septic shock. Furthermore, using transthoracic echocardiography, septic shock patients were split into two groups based on whether or not cardiomyopathy had developed, and the differences in each index between the two groups were analyzed. We looked at the relationship between serum sestrin2 levels, norepinephrine dosage, and NTproBNP levels. The influencing variables for the prediction of septic cardiomyopathy linked with the development of septic cardiomyopathy and clinical prognosis in septic cardiomyopathy were determined using multivariate binary logistic regression.

Results

Assessment of left ventricular systolic function by measurement of LVEF revealed that 61/188 (32.4%) of the 188 patients with septic shock included in the research satisfied the diagnostic criteria for septic cardiomyopathy. (1) Sestrin2 protein levels showed a significant difference between septic shock and healthy controls (p < 0.01). (2) Compared to the group without septic cardiomyopathy, the group with combined septic cardiomyopathy had lower serum sestrin2 protein levels (p < 0.05), lower systolic blood pressure (p < 0.05), and higher plasma NTproBNP levels (p < 0.01) and used greater norepinephrine dosages (p < 0.01). The levels of serum sestrin2 protein revealed a little negative relationship with NTproBNP and norepinephrine dose. However, a binary logistic regression analysis revealed that none of these factors was an independent predictor of septic shock. (3) Age, lactate level, SOFA score, positive bacteremia, and sestrin2 protein were shown to be substantial discrepancies in clinical outcomes in patients with septic cardiomyopathy, becoming variables that impact clinical outcomes. Positive bacteremia (p = 0.031, OR = 5.084), SOFA score (p = 0.021, OR = 1.304), and sestrin2 protein (p =  0.039, OR = 0.897) were revealed to have independent influences in predicting clinical mortality outcome in septic cardiomyopathy using multivariate binary logistic regression.

Conclusion

High serum sestrin2 levels clearly distinguish septic shock patients from healthy controls, whereas low serum sestrin2 levels are related with cardiac dysfunction to some extent but are not an independent influence factor for septic cardiomyopathy. Low serum sestrin2 levels were shown to be useful in predicting clinical outcome in patients with septic cardiomyopathy.

Molecular Mechanism of Tanshinone against Prostate Cancer

Prostate cancer (PCa) is the most common malignant tumor of the male urinary system in Europe and America. According to the data in the World Cancer Report 2020, the incidence rate of PCa ranks second in the prevalence of male malignant tumors and varies worldwide between regions and population groups. Although early PCa can achieve good therapeutic results after surgical treatment, due to advanced PCa, it can adapt and tolerate androgen castration-related drugs through a variety of mechanisms. For this reason, it is often difficult to achieve effective therapeutic results in the treatment of advanced PCa. Tanshinone is a new fat-soluble phenanthraquinone compound derived from Salvia miltiorrhiza that can play a therapeutic role in different cancers, including PCa. Several studies have shown that Tanshinone can target various molecular pathways of PCa, including the signal transducer and activator of transcription 3 (STAT3) pathway, androgen receptor (AR) pathway, phosphatidylinositol-3-kinase (PI3K)/protein kinase B (Akt)/mammalian target of rapamycin (mTOR) pathway, and mitogen-activated protein kinase (MAPK) pathway, which will affect the release of pro-inflammatory cytokines and affect cell proliferation, apoptosis, tumor metabolism, genomic stability, and tumor drug resistance. Thus, the occurrence and development of PCa cells are inhibited. In this review, we summarized the in vivo and in vitro evidence of Tanshinone against prostate cancer and discussed the effect of Tanshinone on nuclear factor kappa-B (NF-κB), AR, and mTOR. At the same time, we conducted a network pharmacology analysis on the four main components of Tanshinone to further screen the possible targets of Tanshinone against prostate cancer and provide ideas for future research.