Lysosomal Regulation of mTORC1 by Amino Acids in Mammalian Cells

Plant-based proteins: clinical and technological importance

Healthy and sustainable diets have seen a surge in popularity in recent years, driven by a desire to consume foods that not only help health but also have a favorable influence on the environment, such as plant-based proteins. This has created controversy because plant-based proteins may not always contain all the amino acids required by the organism. However, protein extraction methods have been developed due to technological advancements to boost their nutritional worth. Furthermore, certain chemicals, such as bioactive peptides, have been identified and linked to favorable health effects. As a result, the current analysis focuses on the primary plant-based protein sources, their chemical composition, and the molecular mechanism activated by the amino acid types of present. It also discusses plant protein extraction techniques, bioactive substances derived from these sources, product development using plant protein, and the therapeutic benefits of these plant-based proteins in clinical research.

Exploring the Integrated Role of miRNAs and lncRNAs in Regulating the Transcriptional Response to Amino Acids and Insulin-like Growth Factor 1 in Gilthead Sea Bream (Sparus aurata) Myoblasts

In this study, gilthead sea bream (Sparus aurata) fast muscle myoblasts were stimulated with two pro-growth treatments, amino acids (AA) and insulin-like growth factor 1 (Igf-1), to analyze the transcriptional response of mRNAs, microRNAs (miRNAs) and long non-coding RNAs (lncRNAs) and to explore their possible regulatory network using bioinformatic approaches. AA had a higher impact on transcription (1795 mRNAs changed) compared to Igf-1 (385 mRNAs changed). Both treatments stimulated the transcription of mRNAs related to muscle differentiation (GO:0042692) and sarcomere (GO:0030017), while AA strongly stimulated DNA replication and cell division (GO:0007049). Both pro-growth treatments altered the transcription of over 100 miRNAs, including muscle-specific miRNAs (myomiRs), such as miR-133a/b, miR-206, miR-499, miR-1, and miR-27a. Among 111 detected lncRNAs (>1 FPKM), only 30 were significantly changed by AA and 11 by Igf-1. Eight lncRNAs exhibited strong negative correlations with several mRNAs, suggesting a possible regulation, while 30 lncRNAs showed strong correlations and interactions with several miRNAs, suggesting a role as sponges. This work is the first step in the identification of the ncRNAs network controlling muscle development and growth in gilthead sea bream, pointing out potential regulatory mechanisms in response to pro-growth signals.

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.

Growth or death? Control of cell destiny by mTOR and autophagy pathways

One of the central regulators of cell growth, proliferation, and metabolism is the mammalian target of rapamycin, mTOR, which exists in two structurally and functionally different complexes: mTORC1 and mTORC2; unlike m TORC2, mTORC1 is activated in response to the sufficiency of nutrients and is inhibited by rapamycin. mTOR complexes have critical roles not only in protein synthesis, gene transcription regulation, proliferation, tumor metabolism, but also in the regulation of the programmed cell death mechanisms such as autophagy and apoptosis. Autophagy is a conserved catabolic mechanism in which damaged molecules are recycled in response to nutrient starvation. Emerging evidence indicates that the mTOR signaling pathway is frequently activated in tumors. In addition, dysregulation of autophagy was associated with the development of a variety of human diseases, such as cancer and aging. Since mTOR can inhibit the induction of the autophagic process from the early stages of autophagosome formation to the late stage of lysosome degradation, the use of mTOR inhibitors to regulate autophagy could be considered a potential therapeutic option. The present review sheds light on the mTOR and autophagy signaling pathways and the mechanisms of regulation of mTOR-autophagy.

A Novel Tri-Hydroxy-Methylated Chalcone Isolated from Chromolaena tacotana with Anti-Cancer Potential Targeting Pro-Survival Proteins

Chromolaena tacotana (Klatt) R. M. King and H. Rob (Ch. tacotana) contains bioactive flavonoids that may have antioxidant and/or anti-cancer properties. This study investigated the potential anti-cancer properties of a newly identified chalcone isolated from the inflorescences of the plant Chromolaena tacotana (Klatt) R. M. King and H. Rob (Ch. tacotana). The chalcone structure was determined using HPLC/MS (QTOF), UV, and NMR spectroscopy. The compound cytotoxicity and selectivity were evaluated on prostate, cervical, and breast cancer cell lines using the MTT assay. Apoptosis and autophagy induction were assessed through flow cytometry by detecting annexin V/7-AAD, active Casp3/7, and LC3B proteins. These results were supported by Western blot analysis. Mitochondrial effects on membrane potential, as well as levels of pro- and anti-apoptotic proteins were analyzed using flow cytometry, fluorescent microscopy, and Western blot analysis specifically on a triple-negative breast cancer (TNBC) cell line. Furthermore, molecular docking (MD) and molecular dynamics (MD) simulations were performed to evaluate the interaction between the compounds and pro-survival proteins. The compound identified as 2',3,4-trihydroxy-4',6'-dimethoxy chalcone inhibited the cancer cell line proliferation and induced apoptosis and autophagy. MDA-MB-231, a TNBC cell line, exhibited the highest sensitivity to the compound with good selectivity. This activity was associated with the regulation of mitochondrial membrane potential, activation of the pro-apoptotic proteins, and reduction of anti-apoptotic proteins, thereby triggering the intrinsic apoptotic pathway. The chalcone consistently interacted with anti-apoptotic proteins, particularly the Bcl-2 protein, throughout the simulation period. However, there was a noticeable conformational shift observed with the negative autophagy regulator mTOR protein. Future studies should focus on the molecular mechanisms underlying the anti-cancer potential of the new chalcone and other flavonoids from Ch. tacotana, particularly against predominant cancer cell types.

A Toxoplasma gondii putative arginine transporter localizes to the plant-like vacuolar compartment and controls parasite extracellular survival and stage differentiation

Toxoplasma gondii is a protozoan parasite that infects a broad spectrum of hosts and can colonize many organs and cell types. The ability to reside within a wide range of different niches requires substantial adaptability to diverse microenvironments. Very little is known about how this parasite senses various milieus and adapts its metabolism to survive, replicate during the acute stage, and then differentiate to the chronic stage. Most eukaryotes, from yeast to mammals, rely on a nutrient sensing machinery involving the TORC complex as master regulator of cell growth and cell cycle progression. The lysosome functions as a signaling hub where TORC complex assembles and is activated by transceptors, which both sense and transport amino acids, including the arginine transceptor SLC38A9. While most of the TORC components are lost in T. gondii , indicating the evolution of a distinct nutrient sensing mechanism, the parasite's lysosomal plant-like vacuolar compartment (PLVAC) may still serve as a sensory platform for controlling parasite growth and differentiation. Using SLC38A9 to query the T. gondii proteome, we identified four putative amino acid transporters, termed TgAAT1-4, that structurally resemble the SLC38A9 arginine transceptor. Assessing their expression and sub-cellular localization, we found that one of them, TgAAT1, localized to the PLVAC and is necessary for normal parasite extracellular survival and bradyzoite differentiation. Moreover, we show that TgAAT1 is involved in the PLVAC efflux of arginine, an amino acid playing a key role in T. gondii differentiation, further supporting the hypothesis that TgAAT1 might play a role in nutrient sensing.

IMPORTANCE

T. gondii is a highly successful parasite infecting a broad range of warm-blood organisms including about one third of all humans. Although Toxoplasma infections rarely result in symptomatic disease in individuals with a healthy immune system, the incredibly high number of persons infected along with the risk of severe infection in immunocompromised patients and the potential link of chronic infection to mental disorders make this infection a significant public health concern. As a result, there is a pressing need for new treatment approaches that are both effective and well-tolerated. The limitations in understanding how Toxoplasma gondii manages its metabolism to adapt to changing environments and triggers its transformation into bradyzoites have hindered the discovery of vulnerabilities in its metabolic pathways or nutrient acquisition mechanisms to identify new therapeutic targets. In this work, we have shown that the lysosome-like organelle PLVAC, acting through the putative arginine transporter TgAAT1, plays a pivotal role in regulating the parasite's extracellular survival and differentiation into bradyzoites.

Review: Nutritional regulation of muscle growth in neonatal swine

Despite advances in the nutritional support of low birth weight and early-weaned piglets, most experience reduced extrauterine growth performance. To further optimize nutritional support and develop targeted intervention strategies, the mechanisms that regulate the anabolic response to nutrition must be fully understood. Knowledge gained in these studies represents a valuable intersection of agriculture and biomedical research, as low birth weight and early-weaned piglets face many of the same morbidities as preterm and low birth weight infants, including extrauterine growth faltering and reduced lean growth. While the reasons for poor growth performance are multifaceted, recent studies have increased our understanding of the role of nutrition in the regulation of skeletal muscle growth in the piglet. The purpose of this review is to summarize the published literature surrounding advances in the current understanding of the anabolic signaling that occurs after a meal and how this response is developmentally regulated in the neonatal pig. It will focus on the regulation of protein synthesis, and especially the upstream and downstream effectors surrounding the master protein kinase, mechanistic target of rapamycin complex 1 (mTORC1) that controls translation initiation. It also will examine the regulatory pathways associated with the postprandial anabolic agents, insulin and specific amino acids, that are upstream of mTORC1 and lead to its activation. Lastly, the integration of upstream signaling cascades by mTORC1 leading to the activation of translation initiation factors that regulate protein synthesis will be discussed. This review concludes that anabolic signaling cascades are stimulated by both insulin and amino acids, especially leucine, through separate pathways upstream of mTORC1, and that these stimulatory pathways result in mTORC1 activation and subsequent activation of downstream effectors that regulate translation initiation Additionally, it is concluded that this anabolic response is unique to the skeletal muscle of the neonate, resulting from increased sensitivity to the rise in both insulin and amino acid after a meal. However, this response is dampened in skeletal muscle of the low birth weight pig, indicative of anabolic resistance. Elucidation of the pathways and regulatory mechanisms surrounding protein synthesis and lean growth allow for the development of potential targeted therapeutics and intervention strategies both in livestock production and neonatal care.

Muscle Protein Synthesis with a Hybrid Dairy and Plant-Based Protein Blend (P4) Is Equal to Whey Protein in a Murine Ageing Model after Fasting

P4, a specific combination of dairy proteins (whey and casein) and plant-based protein isolates (pea and soy), has been shown to provide a more balanced amino acid (AA) profile than its single constituent proteins; however, less is known about how this translates to muscle protein synthesis (MPS). The aim of this study was to investigate the effect of P4 compared to whey or casein against fasted control on MPS. C57BL/6J mice, aged 25 months, were fasted overnight, followed by oral gavage of either whey, P4, casein, or water as a fasted control. Thirty minutes after ingestion, puromycin (0.04 µmol∙g^-1 bodyweight) was subcutaneously injected; 30-min thereafter, mice were sacrificed. MPS was measured by the SUnSET method, and signalling proteins were determined in the left-tibialis anterior (TA) muscle by the WES technique. AA composition was determined in plasma and right-TA muscle. Dried blood spots (DBS) were analysed for postprandial AA dynamics at 10, 20, 45, 60 min. MPS was 1.6-fold increased with whey (p = 0.006) and 1.5-fold with P4 compared to fasted (p = 0.008), while no change was seen with casein. This was confirmed by a significant increase of phosphorylated/total ratio of 4E-BP1 for both whey (p = 0.012) and P4 (p = 0.001). No changes were observed in p70S6K and mTOR phosphorylation/total ratio with whey or P4. Intramuscular leucine levels were lower for P4 (0.71 µmol∙g dry weight^-1) compared to whey (0.97 µmol∙g dry weight^-1) (p = 0.0007). Ten minutes postprandial, DBS showed significantly increased blood AA levels of BCAAs, histidine, lysine, threonine, arginine, and tyrosine for P4 versus fasted. In conclusion, a hybrid mix of dairy and plant-based proteins (P4) resulted in a MPS response that was similar to whey protein in aged mice after fasting. This suggests that other anabolic triggers beyond leucine or the well-balanced amino acid profile and bioavailability of the blend benefit stimulation of MPS.

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.

The Biology of Lysosomes: From Order to Disorder

Since its discovery in 1955, the understanding of the lysosome has continuously increased. Once considered a mere waste removal system, the lysosome is now recognised as a highly crucial cellular component for signalling and energy metabolism. This notable evolution raises the need for a summarized review of the lysosome's biology. As such, throughout this article, we will be compiling the current knowledge regarding the lysosome's biogenesis and functions. The comprehension of this organelle's inner mechanisms is crucial to perceive how its impairment can give rise to lysosomal disease (LD). In this review, we highlight some examples of LD fine-tuned mechanisms that are already established, as well as others, which are still under investigation. Even though the understanding of the lysosome and its pathologies has expanded through the years, some of its intrinsic molecular aspects remain unknown. In order to illustrate the complexity of the lysosomal diseases we provide a few examples that have challenged the established single gene-single genetic disorder model. As such, we believe there is a strong need for further investigation of the exact abnormalities in the pathological pathways in lysosomal disease.

The role of the mTOR pathway in diabetic retinopathy

The retina, the part of the eye, translates the light signal into an electric current that can be sent to the brain as visual information. To achieve this, the retina requires fine-tuned vascularization for its energy supply. Diabetic retinopathy (DR) causes alterations in the eye vascularization that reduce the oxygen supply with consequent retinal neurodegeneration. During DR, the mammalian target of rapamycin (mTOR) pathway seems to coordinate retinal neurodegeneration with multiple anabolic and catabolic processes, such as autophagy, oxidative stress, cell death, and the release of pro-inflammatory cytokines, which are closely related to chronic hyperglycemia. This review outlines the normal anatomy of the retina and how hyperglycemia can be involved in the neurodegeneration underlying this disease through over activation or inhibition of the mTOR pathway.

Drosophila as a Model Organism to Study Basic Mechanisms of Longevity

The spatio-temporal regulation of gene expression determines the fate and function of various cells and tissues and, as a consequence, the correct development and functioning of complex organisms. Certain mechanisms of gene activity regulation provide adequate cell responses to changes in environmental factors. Aside from gene expression disorders that lead to various pathologies, alterations of expression of particular genes were shown to significantly decrease or increase the lifespan in a wide range of organisms from yeast to human. Drosophila fruit fly is an ideal model system to explore mechanisms of longevity and aging due to low cost, easy handling and maintenance, large number of progeny per adult, short life cycle and lifespan, relatively low number of paralogous genes, high evolutionary conservation of epigenetic mechanisms and signalling pathways, and availability of a wide range of tools to modulate gene expression in vivo. Here, we focus on the organization of the evolutionarily conserved signaling pathways whose components significantly influence the aging process and on the interconnections of these pathways with gene expression regulation.

A virulence factor as a therapeutic: the probiotic Enterococcus faecium SF68 arginine deiminase inhibits innate immune signaling pathways

The probiotic bacterial strain Enterococcus faecium SF68 has been shown to alleviate symptoms of intestinal inflammation in human clinical trials and animal feed supplementation studies. To identify factors involved in immunomodulatory effects on host cells, E. faecium SF68 and other commensal and clinical Enterococcus isolates were screened using intestinal epithelial cell lines harboring reporter fusions for NF-κB and JNK(AP-1) activation to determine the responses of host cell innate immune signaling pathways when challenged with bacterial protein and cell components. Cell-free, whole-cell lysates of E. faecium SF68 showed a reversible, inhibitory effect on both NF-κB and JNK(AP-1) signaling pathway activation in intestinal epithelial cells and abrogated the response to bacterial and other Toll-like receptor (TLR) ligands. The inhibitory effect was species-specific, and was not observed for E. avium, E. gallinarum, or E. casseliflavus. Screening of protein fractions of E. faecium SF68 lysates yielded an active fraction containing a prominent protein identified as arginine deiminase (ADI). The E. faecium SF68 arcA gene encoding arginine deiminase was cloned and introduced into E. avium where it conferred the same NF-_κB inhibitory effects on intestinal epithelial cells as seen for E. faecium SF68. Our results indicate that the arginine deiminase of E. faecium SF68 is responsible for inhibition of host cell NF-κB and JNK(AP-1) pathway activation, and is likely to be responsible for the anti-inflammatory and immunomodulatory effects observed in prior clinical human and animal trials. The implications for the use of this probiotic strain for preventive and therapeutic purposes are discussed.

PP2A-dependent TFEB activation is blocked by PIKfyve-induced mTORC1 activity

Transcriptional factor EB (TFEB) is a master regulator of genes required for autophagy and lysosomal function. The nuclear localization of TFEB is blocked by the mechanistic target of rapamycin complex 1 (mTORC1)-dependent phosphorylation of TFEB at multiple sites including Ser-211. Here we show that inhibition of PIKfyve, which produces phosphatidylinositol 3,5-bisphosphate on endosomes and lysosomes, causes a loss of Ser-211 phosphorylation and concomitant nuclear localization of TFEB. We found that while mTORC1 activity toward S6K1, as well as other major mTORC1 substrates, is not impaired, PIKfyve inhibition specifically impedes the interaction of TFEB with mTORC1. This suggests that mTORC1 activity on TFEB is selectively inhibited due to loss of mTORC1 access to TFEB. In addition, we found that TFEB activation during inhibition of PIKfyve relies on the ability of protein phosphatase 2A (PP2A) but not calcineurin/PPP3 to dephosphorylate TFEB Ser-211. Thus when PIKfyve is inhibited, PP2A is dominant over mTORC1 for control of TFEB phosphorylation at Ser-S211. Together these findings suggest that mTORC1 and PP2A have opposing roles on TFEB via phosphorylation and dephosphorylation of Ser-211, respectively, and further that PIKfyve inhibits TFEB activity by facilitating mTORC1-dependent phosphorylation of TFEB.

A new insight into cell biological and biochemical changes through aging

After several years of extensive research, the main cause of aging is yet elusive. There are some theories about aging, such as stem cell aging, senescent cells accumulation, and neuro-endocrine theories. None of them is able to explain all changes that happen in cells and body through aging. By finding out the main cause of aging, it will be much easier to control, prevent and even reverse the aging process. Our cells, regardless of their replicative capacity, get old through aging and they have almost the same epigenetic age. Different cell signaling pathways contribute to aging. The most important one is mTORC1 that becomes hyperactive in cells that undergo aging. Other significant changes with age are lysosome accumulation, impaired autophagy, and mitophagy. Immune system undergoes gradual changes through aging including a shift from lymphoid to myeloid lineage production as well as increased IL-6 and TNF-α which lead to age-related weight loss and meta-inflammation. Additionally, our endocrine system also experiences some changes that should be taken into consideration when looking for the main cause of aging in the human body. In this review, we planned to summarize some of the changes that happen in cells and the body through aging.

Regulation of mTORC1 by amino acids in mammalian cells: A general picture of recent advances

The mechanistic target of rapamycin complex 1 (mTORC1) integrates various types of signal inputs, such as energy, growth factors, and amino acids to regulate cell growth and proliferation mainly through the 2 direct downstream targets, eukaryotic translation initiation factor 4E-binding protein 1 (4EBP1) and ribosomal protein S6 kinase 1 (S6K1). Most of the signal arms upstream of mTORC1 including energy status, stress signals, and growth factors converge on the tuberous sclerosis complex (TSC) - Ras homologue enriched in brain (Rheb) axis. Amino acids, however, are distinct from other signals and modulate mTORC1 using a unique pathway. In recent years, the transmission mechanism of amino acid signals upstream of mTORC1 has been gradually elucidated, and some sensors or signal transmission pathways for individual amino acids have also been discovered. With the help of these findings, we propose a general picture of recent advances, which demonstrates that various amino acids from lysosomes, cytoplasm, and Golgi are sensed by their respective sensors. These signals converge on mTORC1 and form a huge and complicated signal network with multiple synergies, antagonisms, and feedback mechanisms.

MYC Rules: Leading Glutamine Metabolism toward a Distinct Cancer Cell Phenotype

Simple Summary

In the last decade, metabolic reprogramming has emerged as a driving characteristic of cancer cells. The MYC oncogene, a transcription factor, has become of growing interest as a fundamental driver of differential cancer cell metabolism. Furthermore, the non-essential amino acid glutamine is deemed to be an important nutrient for cancer cells. In fact, glutamine can integrate into a wide variety of metabolic pathways, from energy metabolism to nucleotide synthesis. This review offers a comprehensive and specific overview of recent discoveries in the regulation of MYC oncogene activation on glutamine metabolism in cancer cells.

Abstract

Metabolic reprogramming and deregulated cellular energetics are hallmarks of cancer. The aberrant metabolism of cancer cells is thought to be the product of differential oncogene activation and tumor suppressor gene inactivation. MYC is one of the most important oncogenic drivers, its activation being reported in a variety of cancer types and sub-types, among which are the most prevalent and aggressive of all malignancies. This review aims to offer a comprehensive overview and highlight the importance of the c-Myc transcription factor on the regulation of metabolic pathways, in particular that of glutamine and glutaminolysis. Glutamine can be extensively metabolized into a variety of substrates and be integrated in a complex metabolic network inside the cell, from energy metabolism to nucleotide and non-essential amino acid synthesis. Together, understanding metabolic reprogramming and its underlying genetic makeup, such as MYC activation, allows for a better understanding of the cancer cell phenotype and thus of the potential vulnerabilities of cancers from a metabolic standpoint.

Cross-Interplay between Osmolytes and mTOR in Alzheimer's Disease Pathogenesis

Alzheimer's disease, categorized by the piling of amyloid-β (Aβ), hyperphosphorylated tau, PHFs, NFTs and mTOR hyperactivity, is a neurodegenerative disorder, affecting people across the globe. Osmolytes are known for osmoprotectants and play a pivotal role in protein folding, function and protein stability, thus, preventing proteins aggregation, and counteracting effects of denaturing solutes on proteins. Osmolytes (viz., sorbitol, inositol, and betaine) perform a pivotal function of maintaining homeostasis during hyperosmotic stress. The selective advantage of utilising osmolytes over inorganic ions by cells is in maintaining cell volume without compromising cell function, which is important for organs such as the brain. Osmolytes have been documented not only as neuroprotectors but they also seem to act as neurodegenerators. Betaine, sucrose and trehalose supplementation has been seen to induce autophagy thereby inhibiting the accumulation of Aβ. In contrast, sucrose has also been associated with mTOR hyperactivity, a hallmark of AD pathology. The neuroprotective action of taurine is revealed when taurine supplementation is seen to inhibit neural damage, apoptosis and oxidative damage. Inositol stereoisomers (viz., scyllo-inositol and myo-inositol) have also been seen to inhibit Aβ production and plaque formation in the brain, inhibiting AD pathogenesis. However, TMAO affects the aging process adversely by deregulating the mTOR signalling pathway and then kindling cognitive dysfunction via degradation of chemical synapses and synaptic plasticity. Thus, it can be concluded that osmolytes may act as a probable therapeutic approach for neurodevelopmental disorders. Here, we have reviewed and focussed upon the impact of osmolytes on mTOR signalling pathway and thereby its role in AD pathogenesis.

Cardamonin inhibits cell proliferation by caspase-mediated cleavage of Raptor

The antiproliferative effect of cardamonin on mTORC1 is related with downregulation of Raptor. We investigated the mechanism that cardamonin decreases Raptor expression through caspase-mediated protein degradation. SKOV3 cells and HeLa cells were pretreated with caspase inhibitor z-VAD-fmk for 30 min and then exposed to different doses of cardamonin and cisplatin, respectively. We analyzed the gene expression of caspases based on TCGA and GTEx gene expression data in serous cystadenocarcinoma and normal tissues, monitored caspase activity by caspase colorimetric assay kit, detected expression of mTORC1-associated proteins and apoptosis-associated proteins by western blotting, and finally detected cell viability by methyl thiazolyl tetrazolium (MTT) assay. A different expression of caspases except caspase-1 was found between serous cystadenocarcinoma and normal tissues. Raptor was cleaved when caspases were activated by cisplatin and caspase-6/caspase-8 was activated by cardamonin in SKOV3 cells. We further used a monoclonal antibody recognizing the N-terminal part of Raptor to find that Raptor was cleaved into a smaller fragment of about 70 kDa by cardamonin and was rescued by z-VAD-fmk treatment. As a result of Raptor cleavage, mTORC1 activity was decreased and cell viability was inhibited, while cell apoptosis was induced in SKOV3 cells. Notably, similar results are only observed in HeLa cells with a high dose of cardamonin. We concluded that caspase-mediated cleavage of Raptor might be an important mechanism in that cardamonin regulated Raptor and mTORC1 activity.

Dietary Protein and Amino Acid Deficiency Inhibit Pancreatic Digestive Enzyme mRNA Translation by Multiple Mechanisms

BACKGROUND & AIMS

Chronic amino acid (AA) deficiency, as in kwashiorkor, reduces the size of the pancreas through an effect on mammalian target of rapamycin complex 1 (mTORC1). Because of the physiological importance of AAs and their role as a substrate, a stimulant of mTORC1, and protein synthesis, we studied the effect of acute protein and AA deficiency on the response to feeding.

METHODS

ICR/CD-1 mice were fasted overnight and refed for 2 hours with 4 different isocaloric diets: control (20% Prot); Protein-free (0% Prot); control (AA-based diet), and a leucine-free (No Leu). Protein synthesis, polysomal profiling, and the activation of several protein translation factors were analyzed in pancreas samples.

RESULTS

All diets stimulated the Protein Kinase-B (Akt)/mTORC1 pathway, increasing the phosphorylation of the kinase Akt, the ribosomal protein S6 (S6) and the formation of the eukaryotic initiation factor 4F (eIF4F) complex. Total protein synthesis and polysome formation were inhibited in the 0% Prot and No Leu groups to a similar extent, compared with the 20% Prot group. The 0% Prot diet partially reduced the Akt/mTORC1 pathway and the activity of the guanine nucleotide exchange factor eIF2B, without affecting eIF2α phosphorylation. The No Leu diet increased the phosphorylation of eIF2α and general control nonderepressible 2, and also inhibited eIF2B activity, without affecting mTORC1. Essential and nonessential AA levels in plasma and pancreas indicated a complex regulation of their cellular transport mechanisms and their specific effect on the synthesis of digestive enzymes.

CONCLUSIONS

These studies show that dietary AAs are important regulators of postprandial digestive enzyme synthesis, and their deficiency could induce pancreatic insufficiency and malnutrition.

Genes expression profiling of alveolar macrophages exposed to non-functionalized, anionic and cationic multi-walled carbon nanotubes shows three different mechanisms of toxicity

Functionalized multi-walled carbon nanotubes (MWCNT) have become the focus of increased research interest, particularly in their application as tools in different areas, such as the biomedical field. Despite the benefits associated with functionalization of MWCNT, particularly in overcoming issues relating to solubility, several studies have demonstrated that these functionalized nanoparticles display different toxicity profiles. For this study, we aim to compare NR8383 cells responses to three well-characterized MWCNT with varying functional groups. This study employed cytotoxicity assays, transcriptomics and proteomics to assess their toxicity using NR8383 rat alveolar macrophages as an in vitro model. The study findings indicated that all MWCNT altered ribosomal protein translation, cytoskeleton arrangement and induced pro-inflammatory response. Only functionalized MWCNT alter mTOR signaling pathway in conjunction with increased Lamtor gene expression. Furthermore, the type of functionalization was also important, with cationic MWCNT activating the transcription factor EB and inducing autophagy while the anionic MWCNT altering eukaryotic translation initiation factor 4 (EIF4) and phosphoprotein 70 ribosomal protein S6 kinase (p70S6K) signaling pathway as well as upregulation Tlr2 gene expression. This study proposes that MWCNT toxicity mechanisms are functionalization dependent and provides evidence that inflammatory response is a key event of carbon nanotubes toxicity.

Current perspectives on targeting PIM kinases to overcome mechanisms of drug resistance and immune evasion in cancer

PIM kinases are a class of serine/threonine kinases that play a role in several of the hallmarks of cancer including cell cycle progression, metabolism, inflammation and immune evasion. Their constitutively active nature and unique catalytic structure has led them to be an attractive anticancer target through the use of small molecule inhibitors. This review highlights the enhanced activity of PIM kinases in cancer that can be driven by hypoxia in the tumour microenvironment and the important role that aberrant PIM kinase activity plays in resistance mechanisms to chemotherapy, radiotherapy, anti-angiogenic therapies and targeted therapies. We highlight an interaction of PIM kinases with numerous major oncogenic players, including but not limited to, stabilisation of p53, synergism with c-Myc, and notable parallel signalling with PI3K/Akt. We provide a comprehensive overview of PIM kinase's role as an escape mechanism to targeted therapies including PI3K/mTOR inhibitors, MET inhibitors, anti-HER2/EGFR treatments and the immunosuppressant rapamycin, providing a rationale for co-targeting treatment strategies for a more durable patient response. The current status of PIM kinase inhibitors and their use as a combination therapy with other targeted agents, in addition to the development of novel multi-molecularly targeted single therapeutic agents containing a PIM kinase targeting moiety are discussed.

The Effects of Calorie Restriction on Autophagy: Role on Aging Intervention

Autophagy is an important housekeeping process that maintains a proper cellular homeostasis under normal physiologic and/or pathologic conditions. It is responsible for the disposal and recycling of metabolic macromolecules and damaged organelles through broad lysosomal degradation processes. Under stress conditions, including nutrient deficiency, autophagy is substantially activated to maintain proper cell function and promote cell survival. Altered autophagy processes have been reported in various aging studies, and a dysregulated autophagy is associated with various age-associated diseases. Calorie restriction (CR) is regarded as the gold standard for many aging intervention methods. Although it is clear that CR has diverse effects in counteracting aging process, the exact mechanisms by which it modulates those processes are still controversial. Recent advances in CR research have suggested that the activation of autophagy is linked to the observed beneficial anti-aging effects. Evidence showed that CR induced a robust autophagy response in various metabolic tissues, and that the inhibition of autophagy attenuated the anti-aging effects of CR. The mechanisms by which CR modulates the complex process of autophagy have been investigated in depth. In this review, several major advances related to CR’s anti-aging mechanisms and anti-aging mimetics will be discussed, focusing on the modification of the autophagy response.

Functions and Implications of Autophagy in Colon Cancer

Autophagy is an essential function to breakdown cellular proteins and organelles to recycle for new nutrient building blocks. In colorectal cancer, the importance of autophagy is becoming widely recognized as it demonstrates both pro- and anti-tumorigenic functions. In colon cancer, cell autonomous and non-autonomous roles for autophagy are essential in growth and progression. However, the mechanisms downstream of autophagy (to reduce or enhance tumor growth) are not well known. Additionally, the signals that activate and coordinate autophagy for tumor cell growth and survival are not clear. Here, we highlight the context- and cargo-dependent role of autophagy in proliferation, cell death, and cargo breakdown.

mTOR hyperactivity mediates lysosomal dysfunction in Gaucher's disease iPSC-neuronal cells

Bi-allelic GBA1 mutations cause Gaucher's disease (GD), the most common lysosomal storage disorder. Neuronopathic manifestations in GD include neurodegeneration, which can be severe and rapidly progressive. GBA1 mutations are also the most frequent genetic risk factors for Parkinson's disease. Dysfunction of the autophagy-lysosomal pathway represents a key pathogenic event in GBA1-associated neurodegeneration. Using an induced pluripotent stem cell (iPSC) model of GD, we previously demonstrated that lysosomal alterations in GD neurons are linked to dysfunction of the transcription factor EB (TFEB). TFEB controls the coordinated expression of autophagy and lysosomal genes and is negatively regulated by the mammalian target of rapamycin complex 1 (mTORC1). To further investigate the mechanism of autophagy-lysosomal pathway dysfunction in neuronopathic GD, we examined mTORC1 kinase activity in GD iPSC neuronal progenitors and differentiated neurons. We found that mTORC1 is hyperactive in GD cells as evidenced by increased phosphorylation of its downstream protein substrates. We also found that pharmacological inhibition of glucosylceramide synthase enzyme reversed mTORC1 hyperactivation, suggesting that increased mTORC1 activity is mediated by the abnormal accumulation of glycosphingolipids in the mutant cells. Treatment with the mTOR inhibitor Torin1 upregulated lysosomal biogenesis and enhanced autophagic clearance in GD neurons, confirming that lysosomal dysfunction is mediated by mTOR hyperactivation. Further analysis demonstrated that increased TFEB phosphorylation by mTORC1 results in decreased TFEB stability in GD cells. Our study uncovers a new mechanism contributing to autophagy-lysosomal pathway dysfunction in GD, and identifies the mTOR complex as a potential therapeutic target for treatment of GBA1-associated neurodegeneration.

Identification of a factor controlling lysosomal homeostasis using a novel lysosomal trafficking probe

Lysosomes are largely responsible for significant degradation of intracellular and extracellular proteins via the secretory pathway, autophagy, and endocytosis. Therefore, dysregulation of lysosomal homeostasis influences diverse cellular functions. However, a straightforward and quantitative method to measure the integrity of the lysosomal pathway has not been developed. Here, we report the plasmid-based lysosomal-METRIQ (MEasurement of protein Transporting integrity by RatIo Quantification) probe that enables simple quantification of lysosomal integrity by lysosomal green and cytosolic red fluorescent proteins using a flow cytometer. In cultured cells, the lysosomal-METRIQ probe detected not only suppression of the lysosomal pathway but also upregulation of lysosomal activity such as lysosomal biogenesis. To identify factors involved in lysosomal homeostasis, we carried out compound screening and found that the cyclin-dependent kinase (CDK) inhibitors kenpaullone and purvalanol A induce synthesis of cathepsin D and an increase in the number of lysosomes. Subsequent studies revealed that CDK5 maintains lysosomal homeostasis independently of cell cycle arrest. Our results suggest that the lysosomal-METRIQ probe is an effective and efficient tool for measuring lysosomal activity in mammalian cells.

Physical decline and survival in the elderly are affected by the genetic variability of amino acid transporter genes

Amino acid (AA) availability is a rate-limiting factor in the regulation of muscle protein metabolism and, consequently, a risk factor for age-related decline in muscle performance. AA transporters are emerging as sensors of AA availability and activators of mTORC1 signalling, acting as transceptors. Here, we evaluated the association of 58 single nucleotide polymorphisms (SNPs) in 10 selected AA transporter genes with parameters of physical performance (Hand Grip, Activity of Daily Living, Walking time). By analysing a sample of 475 subjects aged 50-89 years, we found significant associations with SLC7A5/LAT1, SLC7A8/LAT2, SLC36A1/PAT1, SLC38A2/SNAT2, SLC3A2/CD98, SLC38A7/SNAT7 genes. Further investigation of the SNPs in a cross-sectional study including 290 subjects aged 90-107 years revealed associations of SLC3A2/CD98, SLC38A2/SNAT2, SLC38A3/SNAT3, SLC38A9/SNAT9 variability with longevity. Finally, a longitudinal study examining the survival rate over 10 years showed age-dependent complexity due to possible antagonistic pleiotropic effects for a SNP in SLC38A9/SNAT9, conferring a survival advantage before 90 years of age and a disadvantage later, probably due to the remodelling of AA metabolism. On the whole, our findings support the hypothesis that AA transporters may impact on the age-related physical decline and survival at old age in a complex way, likely through a mechanism involving mTORC1 signalling.

Metabolic regulation through the endosomal system

The endosomal system plays an essential role in cell homeostasis by controlling cellular signaling, nutrient sensing, cell polarity and cell migration. However, its place in the regulation of tissue, organ and whole body physiology is less well understood. Recent studies have revealed an important role for the endosomal system in regulating glucose and lipid homeostasis, with implications for metabolic disorders such as type 2 diabetes, hypercholesterolemia and non-alcoholic fatty liver disease. By taking insights from in vitro studies of endocytosis and exploring their effects on metabolism, we can begin to connect the fields of endosomal transport and metabolic homeostasis. In this review, we explore current understanding of how the endosomal system influences the systemic regulation of glucose and lipid metabolism in mice and humans. We highlight exciting new insights that help translate findings from single cells to a wider physiological level and open up new directions for endosomal research.

Physiological responses of the abalone Haliotis discus hannai to daily and seasonal temperature variations

Organisms inhabiting tidal mixing-front zones in shallow temperate seas are subjected to large semidiurnal temperature fluctuations in summer. The ability to optimize energy acquisition to this episodic thermal oscillation may determine the survival, growth and development of these ectotherms. We compared the physiological and molecular responses of Haliotis discus hannai cultivated in suspended cages to fluctuating or stable temperature conditions. Several physiological indicators (respiration, excretion rates and O:N) were measured in both conditions, and alterations in the proteome during thermal fluctuations were assessed. No summer mortality was observed in abalone cultivated in fluctuating temperatures compared with that at stable high temperatures. Metabolic rates increased sharply during stable warm summer conditions and fluctuated in accordance with short-term temperature fluctuations (20–26 °C). Ammonia excretion rates during acute responses were comparable in both conditions. When abalone were exposed to fluctuating temperatures, enzyme activities were downregulated and structure-related protein expression was upregulated compared with that at an acclimation temperature (26 °C), highlighting that exposure to low temperatures during fluctuations alters molecular processes. Our results reveal that modulation of physiological traits and protein expression during semidiurnal thermal fluctuations may buffer abalone from the lethal consequences of extreme temperatures in summer.

Blockage of glutamine-dependent anaplerosis affects mTORC1/2 activity and ultimately leads to cellular senescence-like response

The purpose of study was to explore the role of glutamine-dependent anaplerosis in cell fate determination (proliferation and senescence) and the potential associated mechanism by employing a pharmacological inhibitor of glutamine-dependent anaplerosis, amino-oxyacetate (AOA). Using the WI38 normal human embryonic fibroblast cell line, we found that exposure to AOA induced mTORC1 inactivation−mTORC2 activation (within day 1), cell cycle arrest (day 2–6) and cellular senescence (day 4–6). These AOA effects were blocked by concomitantly providing anaplerotic factors [α-ketoglutarate (αKG), pyruvate or oxaloacetate], and not affected by ROS scavenger N-acetyl-cysteine (NAC). Moreover, AOA-induced cellular senescence in WI38 cells is associated with elevated protein levels of p53, p21^CIP1 and p16^INK4A and decreased Rb protein level, which was blocked by αKG supplementation. In p16^INK4A-deficient U2OS human osteosarcoma cells and p16^INK4A-knockdown WI38 cells, AOA exposure also induced similar effects on cell proliferation, and protein level of P-Rb-S807/811 and Rb. Interestingly, no AOA induction of cellular senescence was observed in U2OS cells, yet was still seen in p16^INK4A-knockdown WI38 cells accompanied by the presence of p16 antibody-reactive p12. In summary, we disclose that glutamine-dependent anaplerosis is essential to cell growth and closely associated with mTORC1 activation and mTORC2 inactivation, and impedes cellular senescence particularly associated with p16^INK4A.

Summary: Glutamine-dependent anaplerosis is essential to cell growth and closely associated with mTORC1 activation and mTORC2 inactivation, and impedes cellular senescence particularly associated with p16^INK4A.

Phosphorylated mTORC1 represses autophagic-related mRNA translation in neurons exposed to ischemia-reperfusion injury

OBJECTIVES

The sequential reactivation of mechanistic target of rapamycin (mTOR) inhibited autophagic flux in neurons exposed to oxygen-glucose deprivation/reperfusion (OGD/R), which was characterized by reduction of autophagosome formation and restriction of autolysosome degradation. However, its detailed molecular mechanism was still unknown. In this study, we further explore the existing form of mTOR and its suppression on the transcriptional levels of related mRNA from neurons exposed to ischemia-reperfusion injury.

METHODS

The OGD/R or middle cerebral artery occlusion/reperfusion (MCAO/R)-treated neurons was used to simulate ischemia/reperfusion injury . Autophagy flux was monitored by means of microtubule-associated protein 1 light chain 3 (LC3) and p62. The reactivation of mTOR was determined by phosphorylation of ribosomal protein S6 kinase 1 (S6K1). Then the inhibitors of mTOR were used to confirm its existence form. Finally, the mRNA transcription levels were analyzed to observe the negative regulation of mTOR.

RESULTS

The sequential phosphorylation of mTOR contributed to the neuronal autophagy flux blocking. mTOR was re-phosphorylated and existed as mTOR complex 1 (mTORC1), which was supported by phosphorylation of S6K1 at Thr 389 in neurons. In addition, the phosphorylation of S6K1 was decreased roughly by applying mTORC1 inhibitors, rapamycin and torin 1. However, the administration of mTORC1/2 inhibitor PP242 could recover the phosphorylation of S6K1, which suggested that mTORC2 was involved in the regulation of mTORC1 activity. In paralleling with reactivation of mTORC1, related mRNA transcription was repressed in neurons under ischemia-reperfusion exposure in vivo and in vitro. The mRNA expression levels of LC3, Stx17, Vamp8, Snap29, Lamp2a, and Lamp2b were decreased in neurons after reperfusion, comparing with ischemia-treated neurons.

CONCLUSIONS

The reactivated mTORC1 could suppress the transcription levels of related mRNA, such as LC3, Stx17, Vamp8, Snap29, Lamp2a, and Lamp2b. The research will expand the horizons that mTOR would negatively regulate autophagy at transcription and post-translation levels in neurons suffering ischemia-reperfusion injury.

Live Tracking of Inter-organ Communication by Endogenous Exosomes In Vivo

Extracellular vesicles (EVs) are released by most cell types but providing evidence for their physiological relevance remains challenging due to a lack of appropriate model organisms. Here, we developed an in vivo model to study EV function by expressing CD63-pHluorin in zebrafish embryos. A combination of imaging methods and proteomic analysis allowed us to study biogenesis, composition, transfer, uptake, and fate of individual endogenous EVs. We identified a subpopulation of EVs with exosome features, released in a syntenin-dependent manner from the yolk syncytial layer into the blood circulation. These exosomes are captured, endocytosed, and degraded by patrolling macrophages and endothelial cells in the caudal vein plexus (CVP) in a scavenger receptor- and dynamin-dependent manner. Interference with exosome biogenesis affected CVP growth, suggesting a role in trophic support. Altogether, our work represents a system for studying endogenous EV function in vivo with high spatiotemporal accuracy, demonstrating functional inter-organ communication by exosomes.

mTOR Complex 1 Implicated in Aphid/Buchnera Host/Symbiont Integration

Obligate nutritional endosymbioses are arguably the most intimate of all interspecific associations. While many insect nutritional endosymbioses are well studied, a full picture of how two disparate organisms, a bacterial endosymbiont and a eukaryotic host, are integrated is still lacking. The mTOR pathway is known to integrate nutritional conditions with cell growth and survival in eukaryotes. Characterization and localization of amino acid transporters in aphids suggest the mTOR pathway as a point of integration between an aphid host and its amino acid-provisioning endosymbiont Buchnera aphidicola. The mTOR pathway is unannotated in aphids and unstudied in any nutritional endosymbiosis. We annotated mTOR pathway genes in two aphid species, Acyrthosiphon pisum and Myzus persicae, using both BLASTp searches and Hidden Markov Models. Using previously collected RNAseq data we constructed new reference transcriptomes for bacteriocyte, gut, and whole insect tissue for three lines of M. persicae. Annotation of the mTOR pathway identified homologs of all known invertebrate mTOR genes in both aphid species with some duplications. Differential expression analysis showed that genes specific to the amino acid-sensitive mTOR Complex 1 were more highly expressed in bacteriocytes than genes specific to the amino acid-insensitive mTOR Complex 2. Almost all mTOR genes involved in sensing amino acids showed higher expression in bacteriocytes than in whole insect tissue. When compared to gut, the putative glutamine/arginine sensing transporter ACYPI000333, an ortholog of SLC38A9, showed 6.5 times higher expression in bacteriocytes. Our results suggest that the mTOR pathway may be functionally important in mediating integration of Buchnera into aphid growth and reproduction.

Nutrient sensing, growth and senescence

Cell growth is dictated by a wide range of mitogenic signals, the amplitude and relative contribution of which vary throughout development, differentiation and in a tissue-specific manner. The ability to sense and appropriately respond to changes in mitogens is fundamental to control cell growth, and reduced responsiveness of nutrient sensing pathways is widely associated with human disease and ageing. Cellular senescence is an important tumour suppressor mechanism that is characterised by an irreversible exit from the cell cycle in response to replicative exhaustion or excessive DNA damage. Despite the fact that senescent cells can no longer divide, they remain metabolically active and display a range of pro-growth phenotypes that are supported in part by the mTORC1-autophagy signalling axis. As our understanding of the basic mechanisms of controlling mTORC1-autophagy activity and cell growth continues to expand, we are able to explore how changes in nutrient sensing contribute to the acquisition and maintenance of cellular senescence. Furthermore, while the protective effect of senescence to limit cellular transformation is clear, more recently, the age-related accumulation of these pro-inflammatory senescent cells has been shown to contribute to a decline in organismal fitness. We will further discuss whether dysregulation of nutrient sensing pathways can be targeted to promote senescent cell death which would have important implications for healthy ageing.

Fluorescent Proteins for Investigating Biological Events in Acidic Environments

The interior lumen of acidic organelles (e.g., endosomes, secretory granules, lysosomes and plant vacuoles) is an important platform for modification, transport and degradation of biomolecules as well as signal transduction, which remains challenging to investigate using conventional fluorescent proteins (FPs). Due to the highly acidic luminal environment (pH ~ 4.5⁻6.0), most FPs and related sensors are apt to lose their fluorescence. To address the need to image in acidic environments, several research groups have developed acid-tolerant FPs in a wide color range. Furthermore, the engineering of pH insensitive sensors, and their concomitant use with pH sensitive sensors for the purpose of pH-calibration has enabled characterization of the role of luminal ions. In this short review, we summarize the recent development of acid-tolerant FPs and related functional sensors and discuss the future prospects for this field.

mTORC1 and Nutrient Homeostasis: The Central Role of the Lysosome

The mechanistic target of rapamycin complex 1 (mTORC1) coordinates cellular growth and metabolism with environmental inputs to ensure that cells grow only under favourable conditions. When active, mTORC1 stimulates biosynthetic pathways including protein, lipid and nucleotide synthesis and inhibits cellular catabolism through repression of the autophagic pathway, thereby promoting cell growth and proliferation. The recruitment of mTORC1 to the lysosomal surface has been shown to be essential for its activation. This finding has significantly enhanced our knowledge of mTORC1 regulation and has focused the attention of the field on the lysosome as a signalling hub which coordinates several homeostatic pathways. The intriguing localisation of mTORC1 to the cellular organelle that plays a crucial role in catabolism enables mTORC1 to feedback to autophagy and lysosomal biogenesis, thus leading mTORC1 to enact precise spatial and temporal control of cell growth. This review will cover the signalling interactions which take place on the surface of lysosomes and the cross-talk which exists between mTORC1 activity and lysosomal function.

Drug discovery targeting the mTOR pathway

Mechanistic target of rapamycin (mTOR) is the kinase subunit of two structurally and functionally distinct large multiprotein complexes, referred to as mTOR complex 1 (mTORC1) and mTORC2. mTORC1 and mTORC2 play key physiological roles as they control anabolic and catabolic processes in response to external cues in a variety of tissues and organs. However, mTORC1 and mTORC2 activities are deregulated in widespread human diseases, including cancer. Cancer cells take advantage of mTOR oncogenic signaling to drive their proliferation, survival, metabolic transformation, and metastatic potential. Therefore, mTOR lends itself very well as a therapeutic target for innovative cancer treatment. mTOR was initially identified as the target of the antibiotic rapamycin that displayed remarkable antitumor activity in vitro Promising preclinical studies using rapamycin and its derivatives (rapalogs) demonstrated efficacy in many human cancer types, hence supporting the launch of numerous clinical trials aimed to evaluate the real effectiveness of mTOR-targeted therapies. However, rapamycin and rapalogs have shown very limited activity in most clinical contexts, also when combined with other drugs. Thus, novel classes of mTOR inhibitors with a stronger antineoplastic potency have been developed. Nevertheless, emerging clinical data suggest that also these novel mTOR-targeting drugs may have a weak antitumor activity. Here, we summarize the current status of available mTOR inhibitors and highlight the most relevant results from both preclinical and clinical studies that have provided valuable insights into both their efficacy and failure.

PIM Kinases and Their Relevance to the PI3K/AKT/mTOR Pathway in the Regulation of Ovarian Cancer

Ovarian cancer is a medical term that includes a number of tumors with different molecular biology, phenotypes, tumor progression, etiology, and even different diagnosis. Some specific treatments are required to address this heterogeneity of ovarian cancer, thus molecular characterization may provide an important tool for this purpose. On a molecular level, proviral-integration site for Moloney-murine leukemia virus (PIM) kinases are over expressed in ovarian cancer and play a vital role in the regulation of different proteins responsible for this tumorigenesis. Likewise, the phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT)/mammalian target of rapamycin (mTOR) pathway is also a central regulator of the ovarian cancer. Interestingly, recent research has linked the PIM kinases to the PI3K/AKT/mTOR pathway in several types of cancers, but their connection in ovarian cancer has not been studied yet. Once the exact relationship of PIM kinases with the PI3K/AKT/mTOR pathway is acquired in ovarian cancer, it will hopefully provide effective treatments on a molecular level. This review mainly focuses on the role of PIM kinases in ovarian cancer and their interactions with proteins involved in its progression. In addition, this review suggests a connection between the PIM kinases and the PI3K/AKT/mTOR pathway and their parallel mechanism in the regulation of ovarian cancer.

Autophagy: 'Self-Eating' Your Way to Longevity

Ageing is the gradual decline in biological function both at the cellular and organismal level. One of the key characteristics of cellular ageing is the accumulation of damaged proteins and organelles which, in turn, can cause cellular toxicity and death. Autophagy is an evolutionarily conserved process that is responsible for the sequestration of damaged or surplus cytoplasmic components which are then delivered to the lysosome for degradation. This house-keeping mechanism is essential to maintain cellular homeostasis and survival, particularly during stress. A decline or loss of sensitivity/responsiveness of autophagy is intimately linked with an accelerated rate of ageing as well as many age-related diseases including neurodegeneration, cancer and metabolic disease where damage accumulation exceeds damage removal. This chapter summarises current knowledge regarding the relationship between autophagy and ageing and outlines some strategies that can be implemented to promote the anti-ageing effects of autophagy to improve human health and lifespan.

Targeting autophagy in liver cancer

Autophagy is a catabolic cellular process conserved in animals. It is characterized by the main role of recycling all the non-functional products of the cells. Once, autophagy players detect non-functioning sub-cellular organelles and proteins, they start the so-called nucleation process. The organelles will be surrounded by a double membrane vesicle mainly constituted by endoplasmic reticulum (ER) membrane and autophagy proteins, e.g., MAP1LC3B, Beclin-1, VPS34, Unc-51 like autophagy activating kinase (ULK1) and ubiquitination-related proteins. Then the autophagic membrane will go through an elongation phase involving additional autophagy players. Once the autophagic vesicle is complete, the sub-cellular organelles will be isolated from the rest of the cytosol and driven to the final fusion with lysosomes. Here, the digestion process will end. Alteration and or impairment of autophagy have been shown to be correlated with development of diseases affecting the central nervous system, e.g., Alzheimer and other neurodegenerative diseases. Nonetheless, autophagy defect is responsible for tumorigenesis in blood and solid malignancies, in particular liver cancer. Malignancies of the liver are determined by several genetics and epigenetics mechanisms triggering the up-regulation of survival mechanisms and resistance to cell death. Furthermore, liver cancer could result from pathologic conditions like cirrhosis and fibrosis related to virus infection, aflatoxin, alcohol consumption and high fat diet together with insulin resistance. The role exerted by autophagy in the pathogenesis of the liver and tumor development has been evidenced in recent years. The alteration of autophagy assumes a fundamental role for liver tumorigenesis determining an accumulation of non-functional proteins and organelles that trigger oxidative stress leading to genotoxic stress and gene alterations. Furthermore, the absence of this degradation mechanism could prompt the cells to alter their metabolic status and turn into malignant cells. Interestingly, the heterozygous loss of function of Beclin-1 is able to trigger liver tumorigenesis or even the simple accumulation of proteins caused by the block of the final autolysosome fusion and degradation process is responsible for liver cancer development. This review highlights the importance of targeting the autophagy process in liver cancer in order to restore its function and to promote autophagy-mediated cell demise.

Evolutionary Conservation of the Components in the TOR Signaling Pathways

Target of rapamycin (TOR) is an evolutionarily conserved protein kinase that controls multiple cellular processes upon various intracellular and extracellular stimuli. Since its first discovery, extensive studies have been conducted both in yeast and animal species including humans. Those studies have revealed that TOR forms two structurally and physiologically distinct protein complexes; TOR complex 1 (TORC1) is ubiquitous among eukaryotes including animals, yeast, protozoa, and plants, while TOR complex 2 (TORC2) is conserved in diverse eukaryotic species other than plants. The studies have also identified two crucial regulators of mammalian TORC1 (mTORC1), Ras homolog enriched in brain (RHEB) and RAG GTPases. Of these, RAG regulates TORC1 in yeast as well and is conserved among eukaryotes with the green algae and land plants as apparent exceptions. RHEB is present in various eukaryotes but sporadically missing in multiple taxa. RHEB, in the budding yeast Saccharomyces cerevisiae, appears to be extremely divergent with concomitant loss of its function as a TORC1 regulator. In this review, we summarize the evolutionarily conserved functions of the key regulatory subunits of TORC1 and TORC2, namely RAPTOR, RICTOR, and SIN1. We also delve into the evolutionary conservation of RHEB and RAG and discuss the conserved roles of these GTPases in regulating TORC1.

Leucine-induced localization of Leucyl-tRNA synthetase in lysosome membrane

Leucyl-tRNA synthetase (LRS) plays major roles in providing leucine-tRNA and activating mechanistic target of rapamycin complex 1 (mTORC1) through intracellular leucine sensing. mTORC1 activated by amino acids affects the influence on physiology functions including cell proliferation, protein synthesis and autophagy in various organisms. Biochemical results demonstrating leucine sensing have been published, but visual results are lacking. Therefore, we observed the location of LRS with and without leucine using stimulated emission depletion (STED) microscopy one of the super-resolution microscopy and transmission electron microscopy (TEM). This revealed that LRS was translocated to the lysosome on addition of leucine. The translocation was inhibited by treatment with compound BC-LI-0186, disrupting the interaction between RagD and LRS. Immuno-TEM revealed a clear decrease in LRS translocation to the lysosome on addition of the inhibitor. This direct visualization of leucine sensing and LRS translocation to the lysosome was related to mTORC1 activation. To study the relationship between mTORC1 activation and LRS translocation, we monitored the change in autophagy for each condition using TEM and CLSM. The results showed a decrease in autophagy on addition of leucine, demonstrating crosstalk between leucine sensing, LRS translocation, RagD interaction, and mTORC1 activation.