Activation of mTORC2 by Association with the Ribosome

Targeting mTOR in Acute Lymphoblastic Leukemia

Acute Lymphoblastic Leukemia (ALL) is an aggressive hematologic disorder and constitutes approximately 25% of cancer diagnoses among children and teenagers. Pediatric patients have a favourable prognosis, with 5-years overall survival rates near 90%, while adult ALL still correlates with poorer survival. However, during the past few decades, the therapeutic outcome of adult ALL was significantly ameliorated, mainly due to intensive pediatric-based protocols of chemotherapy. Mammalian (or mechanistic) target of rapamycin (mTOR) is a conserved serine/threonine kinase belonging to the phosphatidylinositol 3-kinase (PI3K)-related kinase family (PIKK) and resides in two distinct signalling complexes named mTORC1, involved in mRNA translation and protein synthesis and mTORC2 that controls cell survival and migration. Moreover, both complexes are remarkably involved in metabolism regulation. Growing evidence reports that mTOR dysregulation is related to metastatic potential, cell proliferation and angiogenesis and given that PI3K/Akt/mTOR network activation is often associated with poor prognosis and chemoresistance in ALL, there is a constant need to discover novel inhibitors for ALL treatment. Here, the current knowledge of mTOR signalling and the development of anti-mTOR compounds are documented, reporting the most relevant results from both preclinical and clinical studies in ALL that have contributed significantly into their efficacy or failure.

Rapamycin regulates cholesterol biosynthesis and cytoplasmic ribosomal proteins in hippocampus and temporal lobe of APP/PS1 mouse

As an inhibitor of the immune system and a longevity drug, rapamycin has been suggested as a treatment for Alzheimer's disease, although the underlying mechanisms remain to be clarified. To elucidate the mechanisms, we performed a high-throughput quantitative proteomics analysis and bioinformatics analysis of the changes in the proteome profiles of hippocampus and temporal lobe of wild-type mice, APP/PS1 mice and rapamycin-treated APP/PS1 mice (ProteomeXchange: PXD009540). Morris Water Maze tests were used to evaluate the effectiveness of rapamycin in APP/PS1 treatment and Western blot analysis was used to verify the proteomics data. The results of Morris Water Maze tests indicated that rapamycin improved the spatial learning and memory abilities of APP/PS1 mice. Proteome analysis identified 100 significantly changed (SC) proteins in hippocampus and 260 in temporal lobe in APP/PS1 mice. Among these, 57 proteins in hippocampus and 167 proteins in temporal lobe were rescued by rapamycin. STRING analysis indicated relatively more complicated protein interactions of AD-related rapamycin rescued proteins in temporal lobe. Pathway analysis showed that SC proteins in APP/PS1 mice were mainly enriched in cholesterol biosynthesis pathway and cytoplasmic ribosomal proteins. After rapamycin treatment, the expression of most proteins in these signaling pathways were reversed. Overall, our findings demonstrate that rapamycin may be an potential strategy which can effectively delays the progression of AD.

mTOR Signaling pathway as a master regulator of memory CD8+ T-cells, Th17, and NK cells development and their functional properties

The mammalian target of rapamycin (mTOR) is a member of the evolutionary phosphatidylinositol kinase-related kinases (PIKKs). mTOR plays a pivotal role in the regulation of diverse aspects of cellular physiology such as body metabolism, cell growth, protein synthesis, cell size, autophagy, and cell differentiation. Immunologically, mTOR has a fundamental part in controlling and shaping diverse functions of innate and adaptive immune cells, in particular, T-cell subsets differentiation, survival, and metabolic reprogramming to ultimately regulate the fate of diverse immune cell types. Researchers report that rapamycin, a selective mTOR inhibitor, and immunosuppressive agent, has surprising immunostimulatory effects on inducing both quantitative and qualitative aspects of virus-specific memory CD8⁺ T-cells differentiation and homeostasis in a T-cell-intrinsic manner. The mTOR signaling pathway also plays a critical role in dictating the outcome of regulatory T cells (Treg), T helper 17 (Th17) cells, and natural killer (NK) cells proliferation and maturation, as well as the effector functions and cytotoxic properties of NK cells. Manipulation of mTOR activity is a critical therapeutic approach for pharmacological agents that seek to inhibit mTOR. This approach should enhance specific memory CD8 ⁺ T-cells responses and induce fully functional effector properties of NK cells to provoke their antitumor and antiviral activities.

Rapamycin in ischemic stroke: Old drug, new tricks?

The significant morbidity that accompanies stroke makes it one of the world's most devastating neurological disorders. Currently, proven effective therapies have been limited to thrombolysis and thrombectomy. The window for the administration of these therapies is narrow, hampered by the necessity of rapidly imaging patients. A therapy that could extend this window by protecting neurons may improve outcome. Endogenous neuroprotection has been shown to be, in part, due to changes in mTOR signalling pathways and the instigation of productive autophagy. Inducing this effect pharmacologically could improve clinical outcomes. One such therapy already in use in transplant medicine is the mTOR inhibitor rapamycin. Recent evidence suggests that rapamycin is neuroprotective, not only via neuronal autophagy but also through its broader effects on other cells of the neurovascular unit. This review highlights the potential use of rapamycin as a multimodal therapy, acting on the blood-brain barrier, cerebral blood flow and inflammation, as well as directly on neurons. There is significant potential in applying this old drug in new ways to improve functional outcomes for patients after stroke.

Lysosome: The metabolic signaling hub

For the past five decades, the lysosome has been characterized as an unglamorous cellular recycling center. This notion has undergone a radical shift in the last 10 years, with new research revealing that this organelle serves as a major hub for metabolic signaling pathways. The discovery that master growth regulators, including the protein kinase mTOR (mechanistic target of rapamycin), make their home at the lysosomal surface has generated intense interest in the lysosome's key role in nutrient sensing and cellular homeostasis. The transcriptional networks required for lysosomal maintenance and function are just being unraveled and their connection to lysosome-based signaling pathways revealed. The catabolic and anabolic pathways that converge on the lysosome connect this organelle with multiple facets of cellular function; when these pathways are deregulated they underlie multiple human diseases, and promote cellular and organismal aging. Thus, understanding how lysosome-based signaling pathways function will not only illuminate the fascinating biology of this organelle but will also be critical in unlocking its therapeutic potentials.

mTOR signalling and cellular metabolism are mutual determinants in cancer

Oncogenic signalling and metabolic alterations are interrelated in cancer cells. mTOR, which is frequently activated in cancer, controls cell growth and metabolism. mTOR signalling regulates amino acid, glucose, nucleotide, fatty acid and lipid metabolism. Conversely, metabolic inputs, such as amino acids, activate mTOR. In this Review, we discuss how mTOR signalling rewires cancer cell metabolism and delineate how changes in metabolism, in turn, sustain mTOR signalling and tumorigenicity. Several drugs are being developed to perturb cancer cell metabolism. However, their efficacy as stand-alone therapies, similar to mTOR inhibitors, is limited. Here, we discuss how the interdependence of mTOR signalling and metabolism can be exploited for cancer therapy.

Translation Stress Regulates Ribosome Synthesis and Cell Proliferation

Ribosome and protein synthesis are major metabolic events that control cellular growth and proliferation. Impairment in ribosome biogenesis pathways and mRNA translation is associated with pathologies such as cancer and developmental disorders. Processes that control global protein synthesis are tightly regulated at different levels by numerous factors and linked with multiple cellular signaling pathways. Several of these merge on the growth promoting factor c-Myc, which induces ribosome biogenesis by stimulating Pol I, Pol II, and Pol III transcription. However, how cells sense and respond to mRNA translation stress is not well understood. It was more recently shown that mRNA translation stress activates c-Myc, through a specific induction of E2F1 synthesis via a PI3Kδ-dependent pathway. This review focuses on how this novel feedback pathway stimulates cellular growth and proliferation pathways to synchronize protein synthesis with ribosome biogenesis. It also describes for the first time the oncogenic activity of the mRNA, and not the encoded protein.

Akt2 causes TGFβ-induced deptor downregulation facilitating mTOR to drive podocyte hypertrophy and matrix protein expression

TGFβ promotes podocyte hypertrophy and expression of matrix proteins in fibrotic kidney diseases such as diabetic nephropathy. Both mTORC1 and mTORC2 are hyperactive in response to TGFβ in various renal diseases. Deptor is a component of mTOR complexes and a constitutive inhibitor of their activities. We identified that deptor downregulation by TGFβ maintains hyperactive mTOR in podocytes. To unravel the mechanism, we found that TGFβ -initiated noncanonical signaling controls deptor inhibition. Pharmacological inhibitor of PI 3 kinase, Ly 294002 and pan Akt kinase inhibitor MK 2206 prevented the TGFβ induced downregulation of deptor, resulting in suppression of both mTORC1 and mTORC2 activities. However, specific isoform of Akt involved in this process is not known. We identified Akt2 as predominant isoform expressed in kidney cortex, glomeruli and podocytes. TGFβ time-dependently increased the activating phosphorylation of Akt2. Expression of dominant negative PI 3 kinase and its signaling inhibitor PTEN blocked Akt2 phosphorylation by TGFβ. Inhibition of Akt2 using a phospho-deficient mutant that inactivates its kinase activity, as well as siRNA against the kinase markedly diminished TGFβ -mediated deptor suppression, its association with mTOR and activation of mTORC1 and mTORC2. Importantly, inhibition of Akt2 blocked TGFβ -induced podocyte hypertrophy and expression of the matrix protein fibronectin. This inhibition was reversed by the downregulation of deptor. Interestingly, we detected increased phosphorylation of Akt2 concomitant with TGFβ expression in the kidneys of diabetic rats. Thus, our data identify previously unrecognized Akt2 kinase as a driver of TGFβ induced deptor downregulation and sustained mTORC1 and mTORC2 activation. Furthermore, we provide the first evidence that deptor downstream of Akt2 contributes to podocyte hypertrophy and matrix protein expression found in glomerulosclerosis in different renal diseases.

Identification of MΦ specific POTEE expression: Its role in mTORC2 activation via protein-protein interaction in TAMs

POTE is known as cancer antigen, expressed in many cancers, along with very few normal tissues like prostate, ovary, testes and embryo. Till date, POTEE identified as majorly expressed POTE paralog. Functionally, POTEF regulates TLR signaling which play important role in innate immunity provided clue about expression of POTE in immune cells. We have chosen three Thp1monocytes, Jurkat T1 and MΦ cells as a model. Here, first time we report expression of POTEE in immune cells specifically only in MΦ but not in monocytes or T-cells. In addition, expression level remains unaltered in MΦ subtypes M1 and M2 and MΦ subjected to various stresses, except MΦs treated with Hyp-CM where MΦs acquires properties of TAMs. In TAMs, POTEE was involved differential protein-protein interaction with mTOR, RICTOR, and Rad51 indicating its biological role in cell invasion through mTORC2 activation. siRNA mediated knockdown of POTEE suggests its importance in cell survival of MΦs as well as TAMs.

HIV-1 Nef-POTEE; A novel interaction modulates macrophage dissemination via mTORC2 signaling pathway

AIMS

Human immunodeficiency virus -1 [HIV-1] Nef, localizes in different cellular compartments and modulates several cellular pathways. Nef promotes virus pathogenicity through alteration in cell surface receptor expression, apoptosis, protein trafficking etc. Nef regulates viral pathogenesis through interaction with different host proteins. Thus, molecular mechanisms of pathogenesis could be deciphered by identifying novel Nef interacting proteins.

MAIN METHODS

HIV-1 Nef interacting proteins were identified by pull down assay and MALDI-TOF analysis. The interaction was further validated through mammalian two hybrid assay. Functional role of this interaction was identified by immunoprecipitation assay, cell invasion and cell migration studies. Fold Change in mRNA levels of CD163, CD206, CCL17 and CCL18 was analyzed using qPCR.

KEY FINDINGS

In current study, C. elegans protein ACT4C and its human homolog POTEE was identified to be interacting with Nef. This interaction activates mTORC2 complex, which in-turn activates AKT and PKC-α. The activation of mTORC2 complex was found to be initiated by the interaction of Nef, mTORC2, Rictor to POTEE. The cellular phenotype and functions affected by Nef-POTEE interaction resulted in significant increase in cell invasion and migration of macrophages (MΦ).

SIGNIFICANCE

MΦ is primary target of HIV-1 infection where HIV-1 replicates and polarizes immunosuppressive M2 phenotype. Combine effect of M2 phenotype and Viral-host protein interactions compromise the MΦ associated physiological functions. Infected MΦ dissemination into other system also leads to HIV-1 induced malignancies. Therefore, targeting POTEE-Nef interaction can lead to formulating better therapeutic strategy against HIV-1.

Weighing In on mTOR Complex 2 Signaling: The Expanding Role in Cell Metabolism

In all eukaryotes, the mechanistic target of rapamycin (mTOR) signaling emerges as a master regulator of homeostasis, which integrates environmental inputs, including nutrients, energy, and growth factors, to regulate many fundamental cellular processes such as cell growth and metabolism. mTOR signaling functions through two structurally and functionally distinct complexes, mTOR complex 1 (mTORC1) and mTOR complex 2 (mTORC2), which correspond to two major branches of signal output. While mTORC1 is well characterized for its structure, regulation, and function in the last decade, information of mTORC2 signaling is only rapidly expanding in recent years, from structural biology, signaling network, to functional impact. Here we review the recent advances in many aspects of the mTORC2 signaling, with particular focus on its involvement in the control of cell metabolism and its physiological implications in metabolic diseases and aging.

Therapeutic Use of mTOR Inhibitors in Renal Diseases: Advances, Drawbacks, and Challenges

The mammalian (or mechanistic) target of rapamycin (mTOR) pathway has a key role in the regulation of a variety of biological processes pivotal for cellular life, aging, and death. Impaired activity of mTOR complexes (mTORC1/mTORC2), particularly mTORC1 overactivation, has been implicated in a plethora of age-related disorders, including human renal diseases. Since the discovery of rapamycin (or sirolimus), more than four decades ago, advances in our understanding of how mTOR participates in renal physiological and pathological mechanisms have grown exponentially, due to both preclinical studies in animal models with genetic modification of some mTOR components as well as due to evidence coming from the clinical experience. The main clinical indication of rapamycin is as immunosuppressive therapy for the prevention of allograft rejection, namely, in renal transplantation. However, considering the central participation of mTOR in the pathogenesis of other renal disorders, the use of rapamycin and its analogs meanwhile developed (rapalogues) everolimus and temsirolimus has been viewed as a promising pharmacological strategy. This article critically reviews the use of mTOR inhibitors in renal diseases. Firstly, we briefly overview the mTOR components and signaling as well as the pharmacological armamentarium targeting the mTOR pathway currently available or in the research and development stages. Thereafter, we revisit the mTOR pathway in renal physiology to conclude with the advances, drawbacks, and challenges regarding the use of mTOR inhibitors, in a translational perspective, in four classes of renal diseases: kidney transplantation, polycystic kidney diseases, renal carcinomas, and diabetic nephropathy.

mTOR Regulation of Glycolytic Metabolism in T Cells

T cell activation, differentiation and effector function is intrinsically linked to the regulation of metabolic pathways. Evidence has shown that inflammatory T cell responses are dependent upon the adoption of aerobic glycolytic metabolism. Furthermore, activation and regulation of the mechanistic target of rapamycin signaling pathway serves a key determinant of T cell metabolism, with subsequent effects on T cell effector responses. In this mini-review, we discuss the mechanisms underpinning the function of the Warburg effect in T cell responses and the role of mTOR in these processes.

ETV7 is an essential component of a rapamycin-insensitive mTOR complex in cancer

The mechanistic target of rapamycin (mTOR) serine/threonine kinase, a critical regulator of cell proliferation, is frequently deregulated in human cancer. Although rapamycin inhibits the two canonical mTOR complexes, mTORC1 and mTORC2, it often shows minimal benefit as an anticancer drug. This is caused by rapamycin resistance of many different tumors, and we show that a third mTOR complex, mTORC3, contributes to this resistance. The ETS (E26 transformation-specific) transcription factor ETV7 interacts with mTOR in the cytoplasm and assembles mTORC3, which is independent of ETV7's transcriptional activity. This complex exhibits bimodal mTORC1/2 activity but is devoid of crucial mTORC1/2 components. Many human cancers activate mTORC3 at considerable frequency, and tumor cell lines that lose mTORC3 expression become rapamycin-sensitive. We show mTORC3's tumorigenicity in a rhabdomyosarcoma mouse model in which transgenic ETV7 expression accelerates tumor onset and promotes tumor penetrance. Discovery of mTORC3 represents an mTOR paradigm shift and identifies a novel target for anticancer drug development.

Biological Aspects of mTOR in Leukemia

The mammalian target of rapamycin (mTOR) is a central processor of intra- and extracellular signals, regulating many fundamental cellular processes such as metabolism, growth, proliferation, and survival. Strong evidences have indicated that mTOR dysregulation is deeply implicated in leukemogenesis. This has led to growing interest in the development of modulators of its activity for leukemia treatment. This review intends to provide an outline of the principal biological and molecular functions of mTOR. We summarize the current understanding of how mTOR interacts with microRNAs, with components of cell metabolism, and with controllers of apoptotic machinery. Lastly, from a clinical/translational perspective, we recapitulate the therapeutic results in leukemia, obtained by using mTOR inhibitors as single agents and in combination with other compounds.

Coordination of Necessary and Permissive Signals by PTEN Inhibition for CNS Axon Regeneration

In the nearly 10 years since PTEN was identified as a prominent intrinsic inhibitor of CNS axon regeneration, the PTEN negatively regulated PI3K-AKT-mTOR pathway has been intensively explored in diverse models of axon injury and diseases and its mechanism for axon regeneration is becoming clearer. It is therefore timely to summarize current knowledge and discuss future directions of translational regenerative research for neural injury and neurodegenerative diseases. Using mouse optic nerve crush as an in vivo retinal ganglion cell axon injury model, we have conducted an extensive molecular dissection of the PI3K-AKT pathway to illuminate the cross-regulating mechanisms in axon regeneration. AKT is the nodal point that coordinates both positive and negative signals to regulate adult CNS axon regeneration through two parallel pathways, activating mTORC1 and inhibiting GSK3ββ. Activation of mTORC1 or its effector S6K1 alone can only slightly promote axon regeneration, whereas blocking mTORC1 significantly prevent axon regeneration, suggesting the necessary role of mTORC1 in axon regeneration. However, mTORC1/S6K1-mediated feedback inhibition prevents potent AKT activation, which suggests a key permissive signal from an unidentified AKT-independent pathway is required for stimulating the neuron-intrinsic growth machinery. Future studies into this complex neuron-intrinsic balancing mechanism involving necessary and permissive signals for axon regeneration is likely to lead eventually to safe and effective regenerative strategies for CNS repair.

Cross Talk Networks of Mammalian Target of Rapamycin Signaling With the Ubiquitin Proteasome System and Their Clinical Implications in Multiple Myeloma

Multiple myeloma (MM) is the second most common hematological malignancy and results from the clonal amplification of plasma cells. Despite recent advances in treatment, MM remains incurable with a median survival time of only 5-6years, thus necessitating further insights into MM biology and exploitation of novel therapeutic approaches. Both the ubiquitin proteasome system (UPS) and the PI3K/Akt/mTOR signaling pathways have been implicated in the pathogenesis, and treatment of MM and different lines of evidence suggest a close cross talk between these central cell-regulatory signaling networks. In this review, we outline the interplay between the UPS and mTOR pathways and discuss their implications for the pathophysiology and therapy of MM.

mTORC Inhibitors as Broad-Spectrum Therapeutics for Age-Related Diseases

Chronological age represents the greatest risk factor for many life-threatening diseases, including neurodegeneration, cancer, and cardiovascular disease; ageing also increases susceptibility to infectious disease. Current efforts to tackle individual diseases may have little impact on the overall healthspan of older individuals, who would still be vulnerable to other age-related pathologies. However, recent progress in ageing research has highlighted the accumulation of senescent cells with chronological age as a probable underlying cause of pathological ageing. Cellular senescence is an essentially irreversible proliferation arrest mechanism that has important roles in development, wound healing, and preventing cancer, but it may limit tissue function and cause widespread inflammation with age. The serine/threonine kinase mTOR (mechanistic target of rapamycin) is a regulatory nexus that is heavily implicated in both ageing and senescence. Excitingly, a growing body of research has highlighted rapamycin and other mTOR inhibitors as promising treatments for a broad spectrum of age-related pathologies, including neurodegeneration, cancer, immunosenescence, osteoporosis, rheumatoid arthritis, age-related blindness, diabetic nephropathy, muscular dystrophy, and cardiovascular disease. In this review, we assess the use of mTOR inhibitors to treat age-related pathologies, discuss possible molecular mechanisms of action where evidence is available, and consider strategies to minimize undesirable side effects. We also emphasize the urgent need for reliable, non-invasive biomarkers of senescence and biological ageing to better monitor the efficacy of any healthy ageing therapy.

Extracellular vesicles direct migration by synthesizing and releasing chemotactic signals

Chemotactic signals are relayed to neighboring cells through the secretion of additional chemoattractants. We previously showed in Dictyostelium discoideum that the adenylyl cyclase A, which synthesizes the chemoattractant cyclic adenosine monophosphate (cAMP), is present in the intraluminal vesicles of multivesicular bodies (MVBs) that coalesce at the back of cells. Using ultrastructural reconstructions, we now show that ACA-containing MVBs release their contents to attract neighboring cells. We show that the released vesicles are capable of directing migration and streaming and are central to chemotactic signal relay. We demonstrate that the released vesicles not only contain cAMP but also can actively synthesize and release cAMP to promote chemotaxis. Through proteomic, pharmacological, and genetic approaches, we determined that the vesicular cAMP is released via the ABCC8 transporter. Together, our findings show that extracellular vesicles released by Ddiscoideum cells are functional entities that mediate signal relay during chemotaxis and streaming.

mTOR and Tumor Cachexia

Cancer cachexia affects most patients with advanced forms of cancers. It is mainly characterized by weight loss, due to muscle and adipose mass depletion. As cachexia is associated with increased morbidity and mortality in cancer patients, identifying the underlying mechanisms leading to cachexia is essential in order to design novel therapeutic strategies. The mechanistic target of rapamycin (mTOR) is a major intracellular signalling intermediary that participates in cell growth by upregulating anabolic processes such as protein and lipid synthesis. Accordingly, emerging evidence suggests that mTOR and mTOR inhibitors influence cancer cachexia. Here, we review the role of mTOR in cellular processes involved in cancer cachexia and highlight the studies supporting the contribution of mTOR in cancer cachexia.

Role of microRNAs in the main molecular pathways of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the most common primary liver malignant neoplasia. HCC is characterized by a poor prognosis. The need to find new molecular markers for its diagnosis and prognosis has led to a progressive increase in the number of scientific studies on this topic. MicroRNAs (miRNAs) are small non-coding RNA that play a role in almost all main cellular pathways. miRNAs are involved in the regulation of expression of the major tumor-related genes in carcinogenesis, acting as oncogenes or tumor suppressor genes. The aim of this review was to identify papers published in 2017 investigating the role of miRNAs in HCC tumorigenesis. miRNAs were classified according to their role in the main molecular pathways involved in HCC tumorigenesis: (1) mTOR; (2) Wnt; (3) JAK/STAT; (4) apoptosis; and (5) MAPK. The role of miRNAs in prognosis/response prediction was taken into consideration. Bearing in mind that the analysis of miRNAs in serum and other body fluids would be crucial for clinical management, the role of circulating miRNAs in HCC patients was also investigated. The most represented miRNA-regulated pathway in HCC is mTOR, but apoptosis, Wnt, JAK/STAT or MAPK pathways are also influenced by miRNA expression levels. These miRNAs could thus be used in clinical practice as diagnostic, prognostic or therapeutic targets for HCC treatment.

Glutaminolysis Promotes Collagen Translation and Stability via α-Ketoglutarate-mediated mTOR Activation and Proline Hydroxylation

Glutaminolysis is the metabolic process of glutamine, aberration of which has been implicated in several pathogeneses. Although we and others recently found a diversity of metabolic dysregulation in organ fibrosis, it is unknown if glutaminolysis regulates the profibrotic activities of myofibroblasts, the primary effector in this pathology. In this study, we found that lung myofibroblasts demonstrated significantly augmented glutaminolysis that was mediated by elevated glutaminase 1 (Gls1). Inhibition of glutaminolysis by specific Gls1 inhibitors CB-839 and BPTES as well as Gls1 siRNA blunted the expression of collagens but not that of fibronectin, elastin, or myofibroblastic marker smooth muscle actin-α. We found that glutaminolysis enhanced collagen translation and stability, which were mediated by glutaminolysis-dependent mTOR complex 1 activation and collagen proline hydroxylation, respectively. Furthermore, we found that the amount of the glutaminolytic end product α-ketoglutarate (α-KG) was increased in myofibroblasts. Similar to glutaminolysis, α-KG activated mTOR complex 1 and promoted the expression of collagens but not of fibronectin, elastin, or smooth muscle actin-α. α-KG also remarkably inhibited collagen degradation in fibroblasts. Taken together, our studies identified a previously unrecognized mechanism by which a major metabolic program regulates the exuberant production of collagens in myofibroblasts and suggest that glutaminolysis is a novel therapeutic target for treating organ fibrosis, including idiopathic pulmonary fibrosis.

mTOR Inhibitor Therapy and Metabolic Consequences: Where Do We Stand?

mTOR (mechanistic target of rapamycin) protein kinase acts as a central integrator of nutrient signaling pathways. Besides the immunosuppressive role after solid organ transplantations or in the treatment of some cancers, another promising role of mTOR inhibitor as an antiaging therapeutic has emerged in the recent years. Acute or intermittent rapamycin treatment has some resemblance to calorie restriction in metabolic effects such as an increased insulin sensitivity. However, the chronic inhibition of mTOR by macrolide rapamycin or other rapalogs has been associated with glucose intolerance and insulin resistance and may even provoke type II diabetes. These metabolic adverse effects limit the use of mTOR inhibitors. Metformin is a widely used drug for the treatment of type 2 diabetes which activates AMP-activated protein kinase (AMPK), acting as calorie restriction mimetic. In addition to the glucose-lowering effect resulting from the decreased hepatic glucose production and increased glucose utilization, metformin induces fatty acid oxidations. Here, we review the recent advances in our understanding of the metabolic consequences regarding glucose metabolism induced by mTOR inhibitors and compare them to the metabolic profile provoked by metformin use. We further suggest metformin use concurrent with rapalogs in order to pharmacologically address the impaired glucose metabolism and prevent the development of new-onset diabetes mellitus after solid organ transplantations induced by the chronic rapalog treatment.

mTORC2 in the dorsomedial striatum of mice contributes to alcohol-dependent F-Actin polymerization, structural modifications, and consumption

Actin is highly enriched at dendritic spines, and actin remodeling plays an essential role in structural plasticity. The mammalian target of rapamycin complex 2 (mTORC2) is a regulator of actin polymerization. Here, we report that alcohol consumption increases F-actin content in the dorsomedial striatum (DMS) of mice, thereby altering dendritic spine morphology in a mechanism that requires mTORC2. Specifically, we found that excessive alcohol consumption increases mTORC2 activity in the DMS, and that knockdown of Rictor, an essential component of mTORC2 signaling, reduces actin polymerization, and attenuates the alcohol-dependent alterations in spine head size and the number of mushroom spines. Finally, we show that knockdown of Rictor in the DMS reduces alcohol consumption, whereas intra-DMS infusion of the mTORC2 activator, A-443654, increases alcohol intake. Together, these results suggest that mTORC2 in the DMS facilitates the formation of F-actin, which in turn induces changes in spine structure to promote and/or maintain excessive alcohol intake.

Signaling Pathways Involved in the Regulation of mRNA Translation

Translation is a key step in the regulation of gene expression and one of the most energy-consuming processes in the cell. In response to various stimuli, multiple signaling pathways converge on the translational machinery to regulate its function. To date, the roles of phosphoinositide 3-kinase (PI3K)/AKT and the mitogen-activated protein kinase (MAPK) pathways in the regulation of translation are among the best understood. Both pathways engage the mechanistic target of rapamycin (mTOR) to regulate a variety of components of the translational machinery. While these pathways regulate protein synthesis in homeostasis, their dysregulation results in aberrant translation leading to human diseases, including diabetes, neurological disorders, and cancer. Here we review the roles of the PI3K/AKT and MAPK pathways in the regulation of mRNA translation. We also highlight additional signaling mechanisms that have recently emerged as regulators of the translational apparatus.

Who does TORC2 talk to?

The target of rapamycin (TOR) is a protein kinase that, by forming complexes with partner proteins, governs diverse cellular signalling networks to regulate a wide range of processes. TOR thus plays central roles in maintaining normal cellular functions and, when dysregulated, in diverse diseases. TOR forms two distinct types of multiprotein complexes (TOR complexes 1 and 2, TORC1 and TORC2). TORC1 and TORC2 differ in their composition, their control and their substrates, so that they play quite distinct roles in cellular physiology. Much effort has been focused on deciphering the detailed regulatory links within the TOR pathways and the structure and control of TOR complexes. In this review, we summarize recent advances in understanding mammalian (m) TORC2, its structure, its regulation, and its substrates, which link TORC2 signalling to the control of cell functions. It is now clear that TORC2 regulates several aspects of cell metabolism, including lipogenesis and glucose transport. It also regulates gene transcription, the cytoskeleton, and the activity of a subset of other protein kinases.

The Kinase Complex mTOR Complex 2 Promotes the Follicular Migration and Functional Maturation of Differentiated Follicular Helper CD4+ T Cells During Viral Infection

Follicular helper CD4⁺ T (T_FH) cells are critical for optimal B-cell-mediated humoral immunity by initiating, fueling, and sustaining germinal center reactions. The differentiation of T_FH cells relies on multiple intrinsic and extrinsic factors; however, the details by which these factors are integrated to coordinate T_FH differentiation are largely unknown. In this study, using a mouse model of acute lymphocytic choriomeningitis virus (LCMV) viral infection, we demonstrate that mTOR complex 2 (mTORC2) kinase integrates TCR signaling and ICOS-mediated co-stimulation to promote late differentiation and functional maturation of virus-specific T_FH cells. Specifically, mTORC2 functions to maintain T_FH lineage specifications, including phenotypes, migratory characteristics, and functional properties. Thus, our results highlight the importance of mTORC2 in guarding T_FH phenotypic and functional maturation.

Effect of Nutrition on Statural Growth

In children, proper growth and development are often regarded as a surrogate marker for good health. A complex system controls the initiation, rate, and cessation of growth, and thus gives a wonderful example of the interactions between genetics, epigenetics, and environmental factors (especially stress and nutrition). Malnutrition is considered a leading cause of growth attenuation in children. This review summarizes our current knowledge regarding the mechanisms linking nutrition and skeletal growth, including systemic factors, such as insulin, growth hormone, insulin-like growth factor-1, fibroblast growth factor-21, etc., and local mechanisms, including mTOR, miRNAs, and epigenetics. Studying the molecular mechanisms regulating skeletal growth may lead to the establishment of better nutritional and therapeutic regimens for more effective linear growth in children with malnutrition and growth abnormalities. 
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A Boolean network of the crosstalk between IGF and Wnt signaling in aging satellite cells

Aging is a complex biological process, which determines the life span of an organism. Insulin-like growth factor (IGF) and Wnt signaling pathways govern the process of aging. Both pathways share common downstream targets that allow competitive crosstalk between these branches. Of note, a shift from IGF to Wnt signaling has been observed during aging of satellite cells. Biological regulatory networks necessary to recreate aging have not yet been discovered. Here, we established a mathematical in silico model that robustly recapitulates the crosstalk between IGF and Wnt signaling. Strikingly, it predicts critical nodes following a shift from IGF to Wnt signaling. These findings indicate that this shift might cause age-related diseases.

mTOR at the Transmitting and Receiving Ends in Tumor Immunity

Cancer is a complex disease and a leading cause of death worldwide. Immunity is critical for cancer control. Cancer cells exhibit high mutational rates and therefore altered self or neo-antigens, eliciting an immune response to promote tumor eradication. Failure to mount a proper immune response leads to cancer progression. mTOR signaling controls cellular metabolism, immune cell differentiation, and effector function. Deregulated mTOR signaling in cancer cells modulates the tumor microenvironment, thereby affecting tumor immunity and possibly promoting carcinogenesis.

Sirolimus and metformin synergistically inhibit hepatocellular carcinoma cell proliferation and improve long-term survival in patients with HCC related to hepatitis B virus induced cirrhosis after liver transplantation

Immunosuppressive agents used postoperatively after liver transplantation (LT) for hepatocellular carcinoma (HCC) favor recurrence and metastasis. Therefore, new effective immunosuppressants are needed. This retrospective study assessed combined sirolimus and metformin on survival of HCC patients after LT. In 2001-2013, 133 HCC patients with LT were divided into four groups: sirolimus and metformin combination (Sir+Met), sirolimus monotherapy (Sir), other immunosuppressants in diabetes mellitus (DM) patients without metformin (No Sir with DM), and other immunosuppressants in patients without DM (No Sir without DM). Kaplan-Meier and Log-rank tests were used to assess survival. Cell proliferation and tumor xenograft assays were performed to disclose the mechanisms underlying the sirolimus and metformin effects. The Sir+Met group showed significantly prolonged survival compared to the other groups. The most significant cytotoxicity was seen in the Sir+Met group, with significantly decreased levels of phosphorylated PI3K, AKT, AMPK, mTOR, 4EBP1 and S6K, compared with the other groups. In agreement, Sir+Met had the highest suppressive effect on tumor growth among all groups (P<0.01). In summary, Sir+Met treatment significantly prolonged survival, likely by suppressing cell proliferation. Therefore, this combination could represent a potential routine-regimen for patients post LT.

Endoplasmic Reticulum-Mitochondrial Contactology: Structure and Signaling Functions

Interorganellar contacts are increasingly recognized as central to the control of cellular behavior. These contacts, which typically involve a small fraction of the endomembrane surface, are local communication hubs that resemble synapses. We propose the term contactology to denote the analysis of interorganellar contacts. Endoplasmic reticulum (ER) contacts with mitochondria were recognized several decades ago; major roles in ion and lipid transfer, signaling, and membrane dynamics have been established, while others continue to emerge. The functional diversity of ER-mitochondrial (ER-mito) contacts is mirrored in their structural heterogeneity, with subspecialization likely supported by multiple, different linker-forming protein structures. The nanoscale size of the contacts has made studying their structure, function, and dynamics difficult. This review focuses on the structure of the ER-mito contacts, methods for studying them, and the roles of contacts in Ca²⁺ and reactive oxygen species (ROS) signaling.

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.

The Role of the Mammalian Target of Rapamycin (mTOR) in Pulmonary Fibrosis

The phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT)/mammalian target of rapamycin (mTOR)-dependent pathway is one of the most integral pathways linked to cell metabolism, proliferation, differentiation, and survival. This pathway is dysregulated in a variety of diseases, including neoplasia, immune-mediated diseases, and fibroproliferative diseases such as pulmonary fibrosis. The mTOR kinase is frequently referred to as the master regulator of this pathway. Alterations in mTOR signaling are closely associated with dysregulation of autophagy, inflammation, and cell growth and survival, leading to the development of lung fibrosis. Inhibitors of mTOR have been widely studied in cancer therapy, as they may sensitize cancer cells to radiation therapy. Studies also suggest that mTOR inhibitors are promising modulators of fibroproliferative diseases such as idiopathic pulmonary fibrosis (IPF) and radiation-induced pulmonary fibrosis (RIPF). Therefore, mTOR represents an attractive and unique therapeutic target in pulmonary fibrosis. In this review, we discuss the pathological role of mTOR kinase in pulmonary fibrosis and examine how mTOR inhibitors may mitigate fibrotic progression.

PIM1 destabilization activates a p53-dependent response to ribosomal stress in cancer cells

Defects in ribosome biogenesis triggers a stress response (ribosomal stress) that can lead to growth arrest and apoptosis. Signaling pathways activated by ribosomal stress are specifically involved in the pathological mechanism of a group of disorders defined as ribosomopathies. However, more generally, the quality control of ribosome synthesis is part of the regulatory circuits that control cell metabolism. A number of studies identified tumor suppressor p53 as a central player in ribosomal stress. We have previously reported that the kinase PIM1 plays a role as a sensor for ribosome deficiency. In this report we address the relationship between PIM1 and p53 in cancer cell lines after depletion of a ribosomal protein. We identified a novel signaling pathway that includes the kinase AKT and the ubiquitin ligase MDM2. In fact, our results indicate that the lower level of PIM1, induced by ribosomal stress, causes inactivation of AKT, inhibition of MDM2 and a consequent p53 stabilization. Therefore, we propose that activation of p53 in response to ribosomal stress, is dependent on the pathway PIM1-AKT-MDM2. In addition, we report evidence that PIM1 level may be relevant to assess the sensitivity of cancer cells to chemotherapeutic drugs that induce ribosomal stress.

mTORC2 (Rictor) in Alzheimer's Disease and Reversal of Amyloid-β Expression-Induced Insulin Resistance and Toxicity in Rat Primary Cortical Neurons

Mammalian target of rapamycin complex 1 (mTORC1), a nutrient sensor and central controller of cell growth and proliferation, is altered in various models of Alzheimer's disease (AD). Even less studied or understood in AD is mammalian target of rapamycin complex 2 (mTORC2) that influences cellular metabolism, in part through the regulations of Akt/PKB and SGK. Dysregulation of insulin/PI3K/Akt signaling is another important feature of AD pathogenesis. We found that both total mTORC1 and C2 protein levels and individual C1 and C2 enzymatic activities were decreased in human AD brain samples. In two rodent AD models, mTORC1 and C2 activities were also decreased. In a neuronal culture model of AD characterized by accumulation of cellular amyloid-β (Aβ)42, mTORC1 activity was reduced. Autophagic vesicles and markers were correspondingly increased and new protein synthesis was inhibited, consistent with mTORC1 hypofunction. Interestingly, mTORC2 activity in neural culture seemed resistant to the effects of intracellular amyloid. In various cell lines, Aβ expression provoked insulin resistance, characterized by inhibition of stimulated Akt phosphorylation, and an increase in negative mTORC1 regular, p-AMPK, itself a nutrient sensor. Rapamycin decreased phospho-mTOR and to lesser degree p-Rictor. This further suppression of mTORC1 activity protected cells from Aβ-induced toxicity and insulin resistance. More striking, Rictor over-expression fully reversed the Aβ-effects on primary neuronal cultures. Finally, using in vitro assay, Rictor protein addition completely overcame oligomeric Aβ-induced inhibition of the PDK-Akt activation step. We conclude that striking a new balance by restoring mTORC2 abundance and/or inhibition of mTORC1 has therapeutic potential in AD.

Rictor/TORC2 mediates gut-to-brain signaling in the regulation of phenotypic plasticity in C. elegans

Animals integrate external cues with information about internal conditions such as metabolic state to execute the appropriate behavioral and developmental decisions. Information about food quality and quantity is assessed by the intestine and transmitted to modulate neuronal functions via mechanisms that are not fully understood. The conserved Target of Rapamycin complex 2 (TORC2) controls multiple processes in response to cellular stressors and growth factors. Here we show that TORC2 coordinates larval development and adult behaviors in response to environmental cues and feeding state in the bacterivorous nematode C. elegans. During development, pheromone, bacterial food, and temperature regulate expression of the daf-7 TGF-β and daf-28 insulin-like peptide in sensory neurons to promote a binary decision between reproductive growth and entry into the alternate dauer larval stage. We find that TORC2 acts in the intestine to regulate neuronal expression of both daf-7 and daf-28, which together reflect bacterial-diet dependent feeding status, thus providing a mechanism for integration of food signals with external cues in the regulation of neuroendocrine gene expression. In the adult, TORC2 similarly acts in the intestine to modulate food-regulated foraging behaviors via a PDF-2/PDFR-1 neuropeptide signaling-dependent pathway. We also demonstrate that genetic variation affects food-dependent larval and adult phenotypes, and identify quantitative trait loci (QTL) associated with these traits. Together, these results suggest that TORC2 acts as a hub for communication of feeding state information from the gut to the brain, thereby contributing to modulation of neuronal function by internal state.

Decision-making in all animals, including humans, involves weighing available information about the external environment as well as the animals’ internal conditions. Information about the environment is obtained via the sensory nervous system, whereas internal state can be assessed via cues such as levels of hormones or nutrients. How multiple external and internal inputs are processed in the nervous system to drive behavior or development is not fully understood. In this study, we examine how the nematode C. elegans integrates dietary information received by the gut with environmental signals to alter nervous system function. We have found that a signaling complex, called TORC2, acts in the gut to relay nutrition signals to alter hormonal signaling by the nervous system in C. elegans. Altered neuronal signaling in turn affects a food-dependent binary developmental decision in larvae, as well as food-dependent foraging behaviors in adults. Our results provide a mechanism by which animals prioritize specific signals such as feeding status to appropriately alter their development and/or behavior.

mTOR signaling in skeletal development and disease

The mammalian/mechanistic target of rapamycin (mTOR) is a serine/threonine protein kinase that integrates inputs from nutrients and growth factors to control many fundamental cellular processes through two distinct protein complexes mTORC1 and mTORC2. Recent mouse genetic studies have established that mTOR pathways play important roles in regulating multiple aspects of skeletal development and homeostasis. In addition, mTORC1 has emerged as a common effector mediating the bone anabolic effect of Igf1, Wnt and Bmp. Dysregulation of mTORC1 could contribute to various skeletal diseases including osteoarthritis and osteoporosis. Here we review the current understanding of mTOR signaling in skeletal development and bone homeostasis, as well as in the maintenance of articular cartilage. We speculate that targeting mTOR signaling may be a valuable approach for treating skeletal diseases.

Drugs directed at a key cellular signaling pathway could prove useful for treating skeletal diseases. Jianquan Chen from Soochow University in Suzhou, China, and Fanxin Long from Washington University School of Medicine in St. Louis, Missouri, USA, provide an overview of how proteins involved in the mechanistic target of rapamycin (mTOR) signaling pathway sense and integrate a range of environmental cues to regulate bone and cartilage development. In particular, they review the differing roles of the two distinct mTOR-containing protein complexes, mTORC1 and mTORC2. Both seem to mediate bone formation and resorption but in different ways, with implications for how best to treat osteoarthritis, osteoporosis, and other degenerative skeletal diseases. The authors suggest that more specific mTOR inhibitors with minimal side effects are needed to help stimulate bone growth in these diseases.

mTOR Pathways in Cancer and Autophagy

TOR (target of rapamycin), an evolutionarily-conserved serine/threonine kinase, acts as a central regulator of cell growth, proliferation and survival in response to nutritional status, growth factor, and stress signals. It plays a crucial role in coordinating the balance between cell growth and cell death, depending on cellular conditions and needs. As such, TOR has been identified as a key modulator of autophagy for more than a decade, and several deregulations of this pathway have been implicated in a variety of pathological disorders, including cancer. At the molecular level, autophagy regulates several survival or death signaling pathways that may decide the fate of cancer cells; however, the relationship between autophagy pathways and cancer are still nascent. In this review, we discuss the recent cellular signaling pathways regulated by TOR, their interconnections to autophagy, and the clinical implications of TOR inhibitors in cancer.

Nutrient Sensing, Signaling and Ageing: The Role of IGF-1 and mTOR in Ageing and Age-Related Disease

Nutrient signaling through insulin/IGF-1 was the first pathway demonstrated to regulate ageing and age-related disease in model organisms. Pharmacological or dietary interventions targeting nutrient signaling pathways have been shown to robustly attenuate ageing in many organisms. Caloric restriction, the most widely studied longevity promoting intervention, works through multiple nutrient signaling pathways, while inhibition of mTOR through treatment with rapamycin reproducibly delays ageing and disease through specific inhibition of the mTOR complexes. Although the benefits of reduced insulin/IGF-1 in lifespan and health are well documented in model organisms, defining the precise role of the IGF-1 in human ageing and age-related disease has proven more difficult. Association studies provide some insight but also reveal paradoxes. Low serum IGF-1 predicts longevity, but IGF-1 decreases with age and IGF-1 therapy benefits some of age-related pathologies. Circulating IGF-1 has been associated both positively and negatively with risk of age-related diseases in humans, and in some cases both activation and inhibition of IGF-1 signaling have provided benefit in animal models of the same diseases. Interventions designed modulate the nutrient sensing signaling pathways positively or negatively are already available for clinical use, highlighting the need for a clear understanding of the role of nutrient signaling in ageing and age-related disease. This chapter examines data from model organisms and human genetic association studies, with a special emphasis on IGF-1 and mTOR, and discusses potential models for resolving the paradoxes surrounding IGF-1 data.

Targeting the intracellular signaling "STOP" and "GO" pathways for the treatment of alcohol use disorders

In recent years, research has identified the molecular and neural substrates underlying the transition of moderate "social" consumption of alcohol to the characteristic alcohol use disorder (AUD) phenotypes including excessive and compulsive alcohol use which we define in the review as the GO signaling pathways. In addition, growing evidence points to the existence of molecular mechanisms that keep alcohol consumption in check and that confer resilience for the development of AUD which we define herein as the STOP signaling pathways. In this review, we focus on examples of the GO and the STOP intracellular signaling pathways and discuss our current knowledge of how manipulations of these pathways may be used for the treatment of AUD.

Culture degeneration in conidia of Beauveria bassiana and virulence determinants by proteomics

The quality of Beauveria bassiana conidia directly affects the virulence against insects. In this study, continuous subculturing of B. bassiana on both rice grains and potato dextrose agar (PDA) resulted in 55 and 49 % conidial yield reduction after 12 passages and 68 and 60 % virulence reduction after 20 and 12 passages at four d post-inoculation, respectively. The passage through Tenebrio molitor and Spodoptera exigua restored the virulence of rice and PDA subcultures, respectively. To explore the molecular mechanisms underlying the conidial quality and the decline of virulence after multiple subculturing, we investigated the conidial proteomic changes. Successive subculturing markedly increased the protein levels in oxidative stress response, autophagy, amino acid homeostasis, and apoptosis, but decreased the protein levels in DNA repair, ribosome biogenesis, energy metabolism, and virulence. The nitro blue tetrazolium assay verified that the late subculture's colony and conidia had a higher oxidative stress level than the early subculture. A 2A-type protein phosphatase and a Pleckstrin homology domain protein Slm1, effector proteins of the target of rapamycin (TOR) complex 1 and 2, respectively, were dramatically increased in the late subculture. These results suggest that TOR signalling might be associated with ageing in B. bassiana late subculture, in turn affecting its physiological characteristics and virulence.

The atypical protein kinase RIOK3 contributes to glioma cell proliferation/survival, migration/invasion and the AKT/mTOR signaling pathway

The RIO (right open reading frame) protein kinases include RIOK1, RIOK2 and RIOK3. Emerging evidence has suggested an important role of RIO kinases in cancer cell proliferation, apoptosis, migration and invasion. However, the expression profile and specific roles of RIOK3 are largely unknown during glioma progression. In the current study, quantitative real-time PCR, Western blot, and immunohistochemical analysis showed that RIOK3 was upregulated in glioma tissues. Available database analysis revealed that higher levels of RIOK3 were associated with poorer survival outcome in glioma patients. Flow cytometry, CCK8 and EdU assays showed that downregulation of RIOK3 arrested cell cycle progression and inhibited glioma cell proliferation. Wound healing, transwell and gelatin zymography assays revealed that silencing RIOK3 decreased glioma cell migration and invasion. Furthermore, the downregulation of RIOK3 significantly decreased the activity of AKT/mTOR signaling and induced apoptosis in glioma cells. Overexpression of RIOK3 showed the opposite effects on glioma cell proliferation, migration, invasion and the AKT/mTOR pathway. These results indicate that high RIOK3 levels in gliomas appear to contribute to the growth and expansion of this cancer, and may thus serve as a novel therapeutic target.

TOR-mediated regulation of metabolism in aging

Cellular metabolism is regulated by the mTOR kinase, a key component of the molecular nutrient sensor pathway that plays a central role in cellular survival and aging. The mTOR pathway promotes protein and lipid synthesis and inhibits autophagy, a process known for its contribution to longevity in several model organisms. The nutrient‐sensing pathway is regulated at the lysosomal membrane by a number of proteins for which deficiency triggers widespread aging phenotypes in tested animal models. In response to environmental cues, this recently discovered lysosomal nutrient‐sensing complex regulates autophagy transcriptionally through conserved factors, such as the transcription factors TFEB and FOXO, associated with lifespan extension. This key metabolic pathway strongly depends on nucleocytoplasmic compartmentalization, a cellular phenomenon gradually lost during aging. In this review, we discuss the current progress in understanding the contribution of mTOR‐regulating factors to autophagy and longevity. Furthermore, we review research on the regulation of metabolism conducted in multiple aging models, including Caenorhabditis elegans, Drosophila and mouse, and human iPSCs. We suggest that conserved molecular pathways have the strongest potential for the development of new avenues for treatment of age‐related diseases.

Dysregulation of mRNA translation and energy metabolism in cancer

Dysregulated mRNA translation and aberrant energy metabolism are frequent in cancer. Considering that mRNA translation is an energy demanding process, cancer cells must produce sufficient ATP to meet energy demand of hyperactive translational machinery. In recent years, the mammalian/mechanistic target of rapamycin (mTOR) emerged as a central regulatory node which coordinates energy consumption by the translation apparatus and ATP production in mitochondria. Aberrant mTOR signaling underpins the vast majority of cancers whereby increased mTOR activity is thought to be a major determinant of both malignant translatomes and metabolomes. Nonetheless, the role of mTOR and other related signaling nodes (e.g. AMPK) in orchestrating protein synthesis and cancer energetics is only recently being unraveled. In this review, we discuss recent findings that provide insights into the molecular underpinnings of coordination of translational and metabolic programs of cancer cells, and potential strategies to translate these findings into clinical treatments.

The Role of Mammalian Target of Rapamycin (mTOR) in Insulin Signaling

The mammalian target of rapamycin (mTOR) is a serine/threonine kinase that controls a wide spectrum of cellular processes, including cell growth, differentiation, and metabolism. mTOR forms two distinct multiprotein complexes known as mTOR complex 1 (mTORC1) and mTOR complex 2 (mTORC2), which are characterized by the presence of raptor and rictor, respectively. mTOR controls insulin signaling by regulating several downstream components such as growth factor receptor-bound protein 10 (Grb10), insulin receptor substrate (IRS-1), F-box/WD repeat-containing protein 8 (Fbw8), and insulin like growth factor 1 receptor/insulin receptor (IGF-IR/IR). In addition, mTORC1 and mTORC2 regulate each other through a feedback loop to control cell growth. This review outlines the current understanding of mTOR regulation in insulin signaling in the context of whole body metabolism.

mTORC2/AKT/HSF1/HuR constitute a feed-forward loop regulating Rictor expression and tumor growth in glioblastoma

Overexpression of Rictor has been demonstrated to result in increased mTORC2 nucleation and activity leading to tumor growth and increased invasive characteristics in glioblastoma multiforme (GBM). However the mechanisms regulating Rictor expression in these tumors is not clearly understood. In this report, we demonstrate that Rictor is regulated at the level of mRNA translation via HSF1-induced HuR activity. HuR is shown to directly bind the 3′ UTR of the Rictor transcript and enhance translational efficiency. Moreover, we demonstrate that mTORC2/AKT signaling activates HSF1 resulting in a feed-forward cascade in which continued mTORC2 activity is able to drive Rictor expression. RNAi-mediated blockade of AKT, HSF1 or HuR is sufficient to downregulate Rictor and inhibit GBM growth and invasive characteristics in vitro and suppresses xenograft growth in mice. Modulation of AKT or HSF1 activity via the ectopic expression of mutant alleles support the ability of AKT to activate HSF1 and demonstrate continued HSF1/HuR/Rictor signaling in the context of AKT knockdown. We further show that constitutive overexpression of HuR is able to maintain Rictor expression under conditions of AKT or HSF1 loss. The expression of these components is also examined in patient GBM samples and correlative associations between the relative expression of these factors support the presence of these signaling relationships in GBM. These data support a role for a feed-forward loop mechanism by which mTORC2 activity stimulates Rictor translational efficiency via an AKT/HSF1/HuR signaling cascade resulting in enhanced mTORC2 activity in these tumors.

Analysis of cell cycle parameters during the transition from unhindered growth to ribosomal and translational stress conditions

Abrogation of ribosome synthesis (ribosomal stress) leads to cell cycle arrest. However, the immediate cell response to cessation of ribosome formation and the transition from normal cell proliferation to cell cycle arrest have not been characterized. Furthermore, there are conflicting conclusions about whether cells are arrested in G2/M or G1, and whether the cause is dismantling ribosomal assembly per se, or the ensuing decreased number of translating ribosomes. To address these questions, we have compared the time kinetics of key cell cycle parameters after inhibiting ribosome formation or function in Saccharomyces cerevisiae. Within one-to-two hours of repressing genes for individual ribosomal proteins or Translation Elongation factor 3, configurations of spindles, spindle pole bodies began changing. Actin began depolarizing within 4 hours. Thus the loss of ribosome formation and function is sensed immediately. After several hours no spindles or mitotic actin rings were visible, but membrane ingression was completed in most cells and Ace2 was localized to daughter cell nuclei demonstrating that the G1 stage was reached. Thus cell division was completed without the help of a contractile actin ring. Moreover, cell wall material held mother and daughter cells together resulting in delayed cell separation, suggesting that expression or function of daughter gluconases and chitinases is inhibited. Moreover, cell development changes in very similar ways in response to inhibition of ribosome formation and function, compatible with the notion that decreased translation capacity contributes to arresting the cell cycle after abrogation of ribosome biogenesis. Potential implications for the mechanisms of diseases caused by mutations in ribosomal genes (ribosomopathies) are discussed.

Target of rapamycin FATC domain as a general membrane anchor: The FKBP-12 like domain of FKBP38 as a case study

Increased efforts have been undertaken to better understand the formation of signaling complexes at cellular membranes. Since the preparation of proteins containing a transmembrane domain or a prenylation motif is generally challenging an alternative membrane anchoring unit that is easy to attach, water-soluble and binds to different membrane mimetics would find broad application. The 33-residue long FATC domain of yeast TOR1 (y1fatc) fulfills these criteria and binds to neutral and negatively charged micelles, bicelles, and liposomes. As a case study, we fused it to the FKBP506-binding region of the protein FKBP38 (FKBP38-BD) and used ¹ H-¹⁵ N NMR spectroscopy to characterize localization of the chimeric protein to micelles, bicelles, and liposomes. Based on these and published data for y1fatc, its use as a C-terminally attachable membrane anchor for other proteins is compatible with a wide range of buffer conditions (pH circa 6-8.5, NaCl 0 to >150 mM, presence of reducing agents, different salts such as MgCl₂ and CaCl₂ ). The high water-solubility of y1fatc enables its use for titration experiments against a membrane-localized interaction partner of the fused target protein. Results from studies with peptides corresponding to the C-terminal 17-11 residues of the 33-residue long domain by 1D ¹ H NMR and CD spectroscopy indicate that they still can interact with membrane mimetics. Thus, they may be used as membrane anchors if the full y1fatc sequence is disturbing or if a chemically synthesized y1fatc peptide shall be attached by native chemical ligation, for example, unlabeled peptide to ¹⁵ N-labeled target protein for NMR studies.