Rapamycin selectively inhibits interleukin-2 activation of p70 S6 kinase

Impact of varied immunosuppressive agents and posttransplant diabetes mellitus on prognosis among diverse transplant recipients (Experimental studies)

The success of solid organ transplantation (SOT) and the use of immunosuppressive agents offer hope to patients with end-stage diseases. However, the impact of posttransplant diabetes mellitus (PTDM) on SOT patients has become increasingly evident. In our study, we utilized the Scientific Registry of Transplant Recipients (SRTR) database to investigate the association between PTDM and patient survival in various types of organ transplantations, including liver, kidney, intestinal, heart, lung, and combined heart-lung transplantations (all P<0.001). Our findings revealed a negative effect of PTDM on the survival of these patients. Furthermore, we examined the effects of both generic and innovator immunosuppressive agents on the development of PTDM and the overall survival of different SOT populations. Interestingly, the results were inconsistent, indicating that the impact of these agents may vary depending on the specific type of transplantation and patient population. Overall, our study provides a comprehensive and systematic assessment of the effects of different immunosuppressive agents on prognosis, as well as the impact of PTDM on the survival of patients undergoing various types of SOT. These findings emphasize the need for further research and highlight the importance of optimizing immunosuppressive regimens and managing PTDM in SOT patients to improve their long-term outcomes.

NKG2D receptor signaling shapes T cell thymic education

The role of natural killer group 2D (NKG2D) in peripheral T cells as a costimulatory receptor is well established. However, its contribution to T cell thymic education and functional imprint is unknown. Here, we report significant changes in development, receptor signaling, transcriptional program, and function in T cells from mice lacking NKG2D signaling. In C57BL/6 (B6) and OT-I mice, we found that NKG2D deficiency results in Vβ chain usage changes and stagnation of the double-positive stage in thymic T cell development. We found that the expression of CD5 and CD45 in thymocytes from NKG2D deficient mice were reduced, indicating a direct influence of NKG2D on the strength of T cell receptor (TCR) signaling during the developmental stage of T cells. Depicting the functional consequences of NKG2D, peripheral OT-I NKG2D-deficient cells were unresponsive to ovalbumin peptide stimulation. Paradoxically, while αCD3/CD28 agonist antibodies led to phenotypic T cell activation, their ability to produce cytokines remained severely compromised. We found that OT-I NKG2D-deficient cells activate STAT5 in response to interleukin-15 but were unable to phosphorylate ERK or S6 upon TCR engagement, underpinning a defect in TCR signaling. Finally, we showed that NKG2D is expressed in mouse and human thymic T cells at the double-negative stage, suggesting an evolutionarily conserved function during T cell development. The data presented in this study indicate that NKG2D impacts thymic T cell development at a fundamental level by reducing the TCR threshold and affecting the functional imprint of the thymic progeny. In summary, understanding the impact of NKG2D on thymic T cell development and TCR signaling contributes to our knowledge of immune system regulation, immune dysregulation, and the design of immunotherapies.

Protective Role of Ethanol Extract of Cibotium barometz (Cibotium Rhizome) against Dexamethasone-Induced Muscle Atrophy in C2C12 Myotubes

Sarcopenia is a progressive muscle disease characterized by the loss of skeletal muscle mass, strength, function, and physical performance. Since the disease code was assigned, attention has been focused on natural products that can protect against muscle atrophy. Cibotium barometz (Cibotium Rhizome) has been used as an herbal medicine for the treatment of bone or joint diseases in Asian countries. However, no studies have identified the mechanism of action of Cibotium Rhizome on muscle atrophy related to sarcopenia at the site of myotubes. The aim of this study was to investigate the improvement effect of the ethanol extract of Cibotium Rhizome (ECR) on dexamethasone-induced muscle atrophy in an in vitro cell model, i.e., the C2C12 myotubes. High-performance liquid chromatography was performed to examine the phytochemicals in ECR. Seven peaks in the ECR were identified, corresponding to the following compounds: protocatechuic acid, (+)-catechin hydrate, p-coumaric acid, ellagic acid, chlorogenic acid, caffeic acid, and ferulic acid. In atrophy-like conditions induced by 100 μM dexamethasone for 24 h in C2C12, ECR increased the expression of the myosin heavy chain, p-Akt, the p-mammalian target of rapamycin (mTOR), p-p70S6K, and repressed the expression of regulated in development and DNA damage responses 1 (REDD1), kruppel-like factor 15 (KLF 15), muscle atrophy F-box, and muscle-specific RING finger protein-1 in C2C12. In addition, ECR alleviated dexamethasone-induced muscle atrophy by repressing REDD1 and KLF15 transcription in C2C12 myotubes, indicating the need for further studies to provide a scientific basis for the development of useful therapeutic agents using ECR to alleviate the effects of skeletal muscle atrophy or sarcopenia.

Signaling Pathways Leading to mTOR Activation Downstream Cytokine Receptors in Lymphocytes in Health and Disease

CD8+ T cells and Natural Killer (NK) cells are cytotoxic lymphocytes important in the response to intracellular pathogens and cancer. Their activity depends on the integration of a large set of intracellular and environmental cues, including antigenic signals, cytokine stimulation and nutrient availability. This integration is achieved by signaling hubs, such as the mechanistic target of rapamycin (mTOR). mTOR is a conserved protein kinase that controls cellular growth and metabolism in eukaryotic cells and, therefore, is essential for lymphocyte development and maturation. However, our current understanding of mTOR signaling comes mostly from studies performed in transformed cell lines, which constitute a poor model for comprehending metabolic pathway regulation. Therefore, it is only quite recently that the regulation of mTOR in primary cells has been assessed. Here, we review the signaling pathways leading to mTOR activation in CD8+ T and NK cells, focusing on activation by cytokines. We also discuss how this knowledge can contribute to immunotherapy development, particularly for cancer treatment.

Hypoxia-inducible factor-1 alpha expression is induced by IL-2 via the PI3K/mTOR pathway in hypoxic NK cells and supports effector functions in NKL cells and ex vivo expanded NK cells

Natural killer (NK) cells are cytotoxic innate lymphocytes that are specialized to kill tumor cells. NK cells are responsive to the primary cytokine IL-2 in the tumor microenvironment (TME), to activate its effector functions against tumors. Despite their inherent ability to kill tumor cells, dysfunctional NK cells observed within advanced solid tumors are associated with poor patient survival. Hypoxia in the TME is a major contributor to immune evasion in solid tumors that could contribute to impaired NK cell function. HIF-1α is a nodal regulator of hypoxia in driving the adaptive cellular responses to changes in oxygen concentrations. Whether HIF-1α is expressed in hypoxic NK cells in the context of IL-2 and whether its expression regulates NK cell effector function are unclear. Here, we report that freshly isolated NK cells from human peripheral blood in hypoxia could not stabilize HIF-1α protein coincident with impaired anti-tumor cytotoxicity. However, ex vivo expansion of these cells restored HIF-1α levels in hypoxia to promote antitumor cytotoxic functions. Similarly, the human NK cell line NKL expressed HIF-1α upon IL-2 stimulation in hypoxia and exhibited improved anti-tumor cytotoxicity and IFN-γ secretion. We found that ex vivo expanded human NK cells and NKL cells required the concerted activation of PI3K/mTOR pathway initiated by IL-2 signaling in combination with hypoxia for HIF-1α stabilization. These findings highlight that HIF-1α stabilization in hypoxia maximizes NK cell effector function and raises the prospect of NK cells as ideal therapeutic candidates for solid tumors.

Current status of xenotransplantation research and the strategies for preventing xenograft rejection

Transplantation is often the last resort for end-stage organ failures, e.g., kidney, liver, heart, lung, and pancreas. The shortage of donor organs is the main limiting factor for successful transplantation in humans. Except living donations, other alternatives are needed, e.g., xenotransplantation of pig organs. However, immune rejection remains the major challenge to overcome in xenotransplantation. There are three different xenogeneic types of rejections, based on the responses and mechanisms involved. It includes hyperacute rejection (HAR), delayed xenograft rejection (DXR) and chronic rejection. DXR, sometimes involves acute humoral xenograft rejection (AHR) and cellular xenograft rejection (CXR), which cannot be strictly distinguished from each other in pathological process. In this review, we comprehensively discussed the mechanism of these immunological rejections and summarized the strategies for preventing them, such as generation of gene knock out donors by different genome editing tools and the use of immunosuppressive regimens. We also addressed organ-specific barriers and challenges needed to pave the way for clinical xenotransplantation. Taken together, this information will benefit the current immunological research in the field of xenotransplantation.

mTOR Inhibitors Induce Erythropoietin Resistance in Renal Transplant Recipients

Aim

To elucidate the role of mTOR inhibitors on iron, hepcidin and erythropoietin-mediated regulation of hemopoiesis in stable renal transplant recipients (RTR).

Background

Impaired hemopoiesis is common following renal transplantation managed using mTOR inhibitors. The mechanisms responsible are uncertain but include direct effects on iron, hepcidin or erythropoietin-mediated hemopoiesis.

Methods

We conducted a single center prospective case-control study of 26 adult RTR with stable allograft function. RTR received stable mTOR dosing (cases, 11/26 [42%]) or stable tacrolimus dosing (controls, 15/26 [58%]). Baseline demographics, full blood count, renal function, iron studies, hepcidin-25, Interleukin-6 (IL-6) and erythropoietin (EPO) levels were determined.

Results

There were no differences in age, gender or allograft function. Mean daily sirolimus dose for cases was 1.72 mg, with mean trough level of 8.46 ng/mL. Mean daily tacrolimus dose for controls was 4.3 mg, with mean trough level of 5.8 ng/mL. There were no differences in mean hemoglobin (143 vs. 147 g/L; p = 0.59), MCV (88 vs. 90 fL; p = 0.35), serum ferritin (150 vs. 85.7 μg/L; p = 0.06), transferrin saturation (26 vs. 23.3%; p = 0.46), IL-6 (11 vs. 7.02 pg/ml; p = 0.14) or hepcidin-25 (3.62 vs. 3.26 nM; p = 0.76) between the groups. EPO levels were significantly higher in the group receiving mTOR therapy (16.8 vs. 8.49 IU/L; p = 0.028). On logistic regression analysis EPO level was the only variable that had a significant impact providing an odds ratio of 0.84 (95%CI 0.66–0.98). The area under the receiver operator characteristic curve (ROC) for the analysis was 0.77 (95%CI 0.54–0.94) with p = 0.04.

Conclusion: Higher levels of EPO in the absence of deranged iron biochemistry or hepcidin-25 levels suggest that EPO resistance rather than impaired iron metabolism may contribute to the impaired hemopoiesis previously demonstrated in RTR on mTOR therapy.

Systemic Efficacy of Sirolimus via the ERBB Signaling Pathway in Breast Cancer

Rapamycin, also known as sirolimus, inhibits the mTOR pathway in complex diseases such as cancer, and its downstream targets are ribosomal S6 kinases (RPS6K). Sirolimus is involved in regulating cell growth and cell survival through roles such as the mediation of epidermal growth factor signaling. However, the systemic efficacy of sirolimus in pathway regulation is unclear. The purpose of this study is to determine systemic drug efficacy using computational methods and drug-induced datasets. We suggest a computational method using gene expression datasets induced by sirolimus and an inverse algorithm that simultaneously identifies parameters referring to gene–gene interactions. We downloaded two sirolimus-induced microarray gene expression datasets and used a computational method to obtain the most enriched pathway, then adopted an inverse algorithm to discover the gene–gene interactions of that pathway. In the results, RPS6KB1 was a target gene of sirolimus and was associated with genes in the pathway. The common gene interactions from two datasets were a hub gene, RPS6KB1, and 10 related genes (AKT3, CBLC, MAP2K7, NRG1/2, PAK3, PIK3CD/G, PRKCG, and SHC3) in the epidermal growth factor (ERBB) signaling pathway.

Safety Profile of Rapamycin Perfluorocarbon Nanoparticles for Preventing Cisplatin-Induced Kidney Injury

Cancer treatment-induced toxicities may restrict maximal effective dosing for treatment and cancer survivors' quality of life. It is critical to develop novel strategies that mitigate treatment-induced toxicity without affecting the efficacy of anti-cancer therapies. Rapamycin is a macrolide with anti-cancer properties, but its clinical application has been hindered, partly by unfavorable bioavailability, pharmacokinetics, and side effects. As a result, significant efforts have been undertaken to develop a variety of nano-delivery systems for the effective and safe administration of rapamycin. While the efficacy of nanostructures carrying rapamycin has been studied intensively, the pharmacokinetics, biodistribution, and safety remain to be investigated. In this study, we demonstrate the potential for rapamycin perfluorocarbon (PFC) nanoparticles to mitigate cisplatin-induced acute kidney injury with a single preventative dose. Evaluations of pharmacokinetics and biodistribution suggest that the PFC nanoparticle delivery system improves rapamycin pharmacokinetics. The safety of rapamycin PFC nanoparticles was shown both in vitro and in vivo. After a single dose, no disturbance was observed in blood tests or cardiac functional evaluations. Repeated dosing of rapamycin PFC nanoparticles did not affect overall spleen T cell proliferation and responses to stimulation, although it significantly decreased the number of Foxp3+CD4+ T cells and NK1.1+ cells were observed.

Taraxasterol mitigates Con A-induced hepatitis in mice by suppressing interleukin-2 expression and its signaling in T lymphocytes

Discovery of anti-inflammatory drugs that can suppress T lymphocyte activation and proliferation by inhibiting TCR/CD3 and IL-2/IL-2R signaling is still needed in clinic, though rapamycin and other related reagents have made great success. Taraxasterol (TAS) is an active ingredient of dandelion, an anti-inflammatory medicinal herb with low in vivo toxicity that has long been used in China. Yet the action mechanism of TAS on lymphocytes remains elusive. The anti-inflammatory effects of TAS were evaluated in C57BL/6 mouse primary lymphocytes stimulated with concanavalin A (Con A) in vitro and in mouse model of Con A-induced acute hepatitis in vivo. Our results showed that TAS significantly suppressed Con A-induced acute hepatitis in a mouse model, reducing the hepatic necrosis areas, the release of aminotransferases, and the production of IL-2 and other inflammatory cytokines. Supporting this, in vitro study also showed that TAS reduced the production of IL-2 and the expression of IL-2 receptor subunit α (CD25) upon the stimulation of Con A, which was likely mediated by suppressing NF-κB activation. The downstream pathways of IL-2/IL-2R signaling, including the activation of PI3K/PDK1/mTOR, STAT3 and STAT5, were also suppressed by TAS. Consistently, Con A-induced T cell proliferation was also inhibited by TAS in vitro. Our data indicate that TAS can suppress both T lymphocyte activation and cell proliferation by down-regulating IL-2 expression and its signaling pathway thereby ameliorating Con A-induced acute hepatitis, highlighting TAS as a potential drug candidate for treating inflammatory diseases including autoimmune hepatitis.

Regulation of electrogenic Na+ /HCO3 - cotransporter 1 (NBCe1) function and its dependence on m-TOR mediated phosphorylation of Ser245

Astrocytes are pivotal responders to alterations of extracellular pH, primarily by regulation of their principal acid-base transporter, the membrane-bound electrogenic Na⁺ /bicarbonate cotransporter 1 (NBCe1). Here, we describe amammalian target of rapamycin (mTOR)-dependent and NBCe1-mediated astroglial response to extracellular acidosis. Using primary mouse cortical astrocytes, we investigated the effect of long-term extracellular metabolic acidosis on regulation of NBCe1 and elucidated the underlying molecular mechanisms by immunoblotting, biotinylation of surface proteins, intracellular H⁺ recording using the H⁺ -sensitive dye 2',7'-bis-(carboxyethyl)-5-(and-6)-carboxyfluorescein, and phosphoproteomic analysis. The results showed significant increase of NBCe1-mediated recovery of intracellular pH from acidification in WT astrocytes, but not in cortical astrocytes from NBCe1-deficient mice. Acidosis-induced upregulation of NBCe1 activity was prevented following inhibition of mTOR signaling by rapamycin. Yet, during acidosis or following exposure of astrocytes to rapamycin, surface protein abundance of NBCe1 remained -unchanged. Mutational analysis in HeLa cells suggested that NBCe1 activity was dependent on phosphorylation state of Ser²⁴⁵ , a residue conserved in all NBCe1 variants. Moreover, phosphorylation state of Ser²⁴⁵ is regulated by mTOR and is inversely correlated with NBCe1 transport activity. Our results identify pSer²⁴⁵ as a novel regulator of NBCe1 functional expression. We propose that context-dependent and mTOR-mediated multisite phosphorylation of serine residues of NBCe1 is likely to be a potent mechanism contributing to the response of astrocytes to acid/base challenges during pathophysiological conditions.

A prion accelerates proliferation at the expense of lifespan

In fluctuating environments, switching between different growth strategies, such as those affecting cell size and proliferation, can be advantageous to an organism. Trade-offs arise, however. Mechanisms that aberrantly increase cell size or proliferation-such as mutations or chemicals that interfere with growth regulatory pathways-can also shorten lifespan. Here we report a natural example of how the interplay between growth and lifespan can be epigenetically controlled. We find that a highly conserved RNA-modifying enzyme, the pseudouridine synthase Pus4/TruB, can act as a prion, endowing yeast with greater proliferation rates at the cost of a shortened lifespan. Cells harboring the prion grow larger and exhibit altered protein synthesis. This epigenetic state, [BIG+] (better in growth), allows cells to heritably yet reversibly alter their translational program, leading to the differential synthesis of dozens of proteins, including many that regulate proliferation and aging. Our data reveal a new role for prion-based control of an RNA-modifying enzyme in driving heritable epigenetic states that transform cell growth and survival.

Overview of therapeutic drug monitoring of immunosuppressive drugs: Analytical and clinical practices

Immunosuppressant drugs (ISDs) play a key role in short-term patient survival together with very low acute allograft rejection rates in transplant recipients. Due to the narrow therapeutic index and large inter-patient pharmacokinetic variability of ISDs, therapeutic drug monitoring (TDM) is needed to dose adjustment for each patient (personalized medicine approach) to avoid treatment failure or side effects of the therapy. To achieve this, TDM needs to be done effectively. However, it would not be possible without the proper clinical practice and analytical tools. The purpose of this review is to provide a guide to establish reliable TDM, followed by a critical overview of the current analytical methods and clinical practices for the TDM of ISDs, and to discuss some of the main practical aspects of the TDM.

Natural products as drugs and tools for influencing core processes of eukaryotic mRNA translation

Eukaryotic protein synthesis is the highly conserved, complex mechanism of translating genetic information into proteins. Although this process is essential for cellular homoeostasis, dysregulations are associated with cellular malfunctions and diseases including cancer and diabetes. In the challenging and ongoing search for adequate treatment possibilities, natural products represent excellent research tools and drug leads for new interactions with the translational machinery and for influencing mRNA translation. In this review, bacterial-, marine- and plant-derived natural compounds that interact with different steps of mRNA translation, comprising ribosomal assembly, translation initiation and elongation, are highlighted. Thereby, the exact binding and interacting partners are unveiled in order to accurately understand the mode of action of each natural product. The pharmacological relevance of these compounds is furthermore assessed by evaluating the observed biological activities in the light of translational inhibition and by enlightening potential obstacles and undesired side-effects, e.g. in clinical trials. As many of the natural products presented here possess the potential to serve as drug leads for synthetic derivatives, structural motifs, which are indispensable for both mode of action and biological activities, are discussed. Evaluating the natural products emphasises the strong diversity of their points of attack. Especially the fact that selected binding partners can be set in direct relation to different diseases emphasises the indispensability of natural products in the field of drug development. Discovery of new, unique and unusual interacting partners again renders them promising tools for future research in the field of eukaryotic mRNA translation.

Cell cycle dependence on the mevalonate pathway: Role of cholesterol and non-sterol isoprenoids

The mevalonate pathway is responsible for the synthesis of isoprenoids, including sterols and other metabolites that are essential for diverse biological functions. Cholesterol, the main sterol in mammals, and non-sterol isoprenoids are in high demand by rapidly dividing cells. As evidence of its importance, many cell signaling pathways converge on the mevalonate pathway and these include those involved in proliferation, tumor-promotion, and tumor-suppression. As well as being a fundamental building block of cell membranes, cholesterol plays a key role in maintaining their lipid organization and biophysical properties, and it is crucial for the function of proteins located in the plasma membrane. Importantly, cholesterol and other mevalonate derivatives are essential for cell cycle progression, and their deficiency blocks different steps in the cycle. Furthermore, the accumulation of non-isoprenoid mevalonate derivatives can cause DNA replication stress. Identification of the mechanisms underlying the effects of cholesterol and other mevalonate derivatives on cell cycle progression may be useful in the search for new inhibitors, or the repurposing of preexisting cholesterol biosynthesis inhibitors to target cancer cell division. In this review, we discuss the dependence of cell division on an active mevalonate pathway and the role of different mevalonate derivatives in cell cycle progression.

Bacteria as a treasure house of secondary metabolites with anticancer potential

Cancer stands in the frontline among leading killers worldwide and the annual mortality rate is expected to reach 16.4 million by 2040. Humans suffer from about 200 different types of cancers and many of them have a small number of approved therapeutic agents. Moreover, several types of major cancers are diagnosed at advanced stages as a result of which the existing therapies have limited efficacy against them and contribute to a dismal prognosis. Therefore, it is essential to develop novel potent anticancer agents to counteract cancer-driven lethality. Natural sources such as bacteria, plants, fungi, and marine microorganisms have been serving as an inexhaustible source of anticancer agents. Notably, over 13,000 natural compounds endowed with different pharmacological properties have been isolated from different bacterial sources. In the present article, we have discussed about the importance of natural products, with special emphasis on bacterial metabolites for cancer therapy. Subsequently, we have comprehensively discussed the various sources, mechanisms of action, toxicity issues, and off-target effects of clinically used anticancer drugs (such as actinomycin D, bleomycin, carfilzomib, doxorubicin, ixabepilone, mitomycin C, pentostatin, rapalogs, and romidepsin) that have been derived from different bacteria. Furthermore, we have also discussed some of the major secondary metabolites (antimycins, chartreusin, elsamicins, geldanamycin, monensin, plicamycin, prodigiosin, rebeccamycin, salinomycin, and salinosporamide) that are currently in the clinical trials or which have demonstrated potent anticancer activity in preclinical models. Besides, we have elaborated on the application of metagenomics in drug discovery and briefly described about anticancer agents (bryostatin 1 and ET-743) identified through the metagenomics approach.

Duloxetine suppresses BMP-4-induced release of osteoprotegerin via inhibition of the SMAD signaling pathway in osteoblasts

Duloxetine, a selective serotonin-norepinephrine reuptake inhibitor, is currently recommended for the treatment of chronic painful disorders such as fibromyalgia, chronic musculoskeletal pain, and diabetic peripheral neuropathy. We previously demonstrated that bone morphogenetic protein-4 (BMP-4) stimulates osteoprotegerin (OPG) production in osteoblast-like MC3T3-E1 cells, and that p70 S6 kinase positively regulates OPG synthesis. The present study aimed to investigate the effect of duloxetine on BMP-4-stimulated OPG synthesis in these cells. Duloxetine dose-dependently suppressed OPG release stimulated by BMP-4. Fluvoxamine, a selective serotonin reuptake inhibitor (SSRI), reduced BMP-4-stimulated OPG release, whereas a selective and specific norepinephrine reuptake inhibitor, reboxetine, failed to affect OPG release. In addition, another SSRI sertraline also inhibited BMP-4-stimulated OPG release. On the other hand, siRNA of SMAD1 reduced the OPG release stimulated by BMP-4, indicating the involvement of the SMAD1/5/8 pathway in OPG release. Rapamycin inhibited BMP-4-stimulated p70 S6 kinase phosphorylation, and compound C suppressed the SMAD1/5/8 phosphorylation stimulated by BMP-4. Duloxetine did not affect BMP-4-induced phosphorylation of p70 S6 kinase but suppressed SMAD1/5/8 phosphorylation. Both fluvoxamine and sertraline also inhibited BMP-4-elicited phosphorylation of SMAD1/5/8. These results strongly suggest that duloxetine suppresses BMP-4-stimulated OPG release via inhibition of the Smad1/5/8 signaling pathway in osteoblasts.

Regulation and metabolic functions of mTORC1 and mTORC2

Cells metabolize nutrients for biosynthetic and bioenergetic needs to fuel growth and proliferation. The uptake of nutrients from the environment and their intracellular metabolism is a highly controlled process that involves cross talk between growth signaling and metabolic pathways. Despite constant fluctuations in nutrient availability and environmental signals, normal cells restore metabolic homeostasis to maintain cellular functions and prevent disease. A central signaling molecule that integrates growth with metabolism is the mechanistic target of rapamycin (mTOR). mTOR is a protein kinase that responds to levels of nutrients and growth signals. mTOR forms two protein complexes, mTORC1, which is sensitive to rapamycin, and mTORC2, which is not directly inhibited by this drug. Rapamycin has facilitated the discovery of the various functions of mTORC1 in metabolism. Genetic models that disrupt either mTORC1 or mTORC2 have expanded our knowledge of their cellular, tissue, as well as systemic functions in metabolism. Nevertheless, our knowledge of the regulation and functions of mTORC2, particularly in metabolism, has lagged behind. Since mTOR is an important target for cancer, aging, and other metabolism-related pathologies, understanding the distinct and overlapping regulation and functions of the two mTOR complexes is vital for the development of more effective therapeutic strategies. This review discusses the key discoveries and recent findings on the regulation and metabolic functions of the mTOR complexes. We highlight findings from cancer models but also discuss other examples of the mTOR-mediated metabolic reprogramming occurring in stem and immune cells, type 2 diabetes/obesity, neurodegenerative disorders, and aging.

Wheat Germination Is Dependent on Plant Target of Rapamycin Signaling

Germination is a process of seed sprouting that facilitates embryo growth. The breakdown of reserved starch in the endosperm into simple sugars is essential for seed germination and subsequent seedling growth. At the early stage of germination, gibberellic acid (GA) activates transcription factor GAMYB to promote de novo synthesis of isoforms of α-amylase in the aleurone layer and scutellar epithelium of the embryo. Here, we demonstrate that wheat germination is regulated by plant target of rapamycin (TOR) signaling. TOR is a central component of the essential-nutrient–dependent pathway controlling cell growth in all eukaryotes. It is known that rapamycin, a highly specific allosteric inhibitor of TOR, is effective in yeast and animal cells but ineffective in most of higher plants likely owing to structural differences in ubiquitous rapamycin receptor FKBP12. The action of rapamycin on wheat growth has not been studied. Our data show that rapamycin inhibits germination of wheat seeds and of their isolated embryos in a dose-dependent manner. The involvement of Triticum aestivum TOR (TaTOR) in wheat germination was consistent with the suppression of wheat embryo growth by specific inhibitors of the TOR kinase: pp242 or torin1. Rapamycin or torin1 interfered with GA function in germination because of a potent inhibitory effect on α-amylase and GAMYB gene expression. The TOR inhibitors selectively targeted the GA-dependent gene expression, whereas expression of the abscisic acid-dependent ABI5 gene was not affected by either rapamycin or torin1. To determine whether the TaTOR kinase activation takes place during wheat germination, we examined phosphorylation of a ribosomal protein, T. aestivum S6 kinase 1 (TaS6K1; a substrate of TOR). The phosphorylation of serine 467 (S467) in a hydrophobic motif on TaS6K1 was induced in a process of germination triggered by GA. Moreover, the germination-induced phosphorylation of TaS6K1 on S467 was dependent on TaTOR and was inhibited by rapamycin or torin1. Besides, a gibberellin biosynthesis inhibitor (paclobutrazol; PBZ) blocked not only α-amylase gene expression but also TaS6K1 phosphorylation in wheat embryos. Thus, a hormonal action of GA turns on the synthesis of α-amylase in wheat germination via activation of the TaTOR–S6K1 signaling pathway.

Transcriptional Regulation of NK Cell Development by mTOR Complexes

The mechanistic target of Rapamycin (mTOR) is essential for multiple cellular processes. The unique roles of mTOR complex 1 (mTORC1) or mTOR2 in regulating immune functions are emerging. NK cells are the major lymphocyte subset of innate immunity, and their development and effector functions require metabolic reprogramming. Recent studies demonstrate that in NK cells, conditionally disrupting the formation of mTORC1 or mTOR complex 2 (mTORC2) alters their development significantly. Transcriptomic profiling of NK cells at the single-cell level demonstrates that mTORC1 was critical for the early developmental progression, while mTORC2 regulated the terminal maturation. In this review, we summarize the essential roles of mTOR complexes in NK development and functions.

Immunosuppressive Agents and Infectious Risk in Transplantation: Managing the "Net State of Immunosuppression"

Successful solid organ transplantation reflects meticulous attention to the details of immunosuppression, balancing risks for graft rejection against risks for infection. The 'net state of immune suppression' is a conceptual framework of all factors contributing to infectious risk. Assays which measure immune function in the immunosuppressed transplant recipient relative to infectious risk and allograft function are lacking. The best measures of integrated immune function may be quantitative viral loads to assess the individual's ability to control latent viral infections. Few studies address adjustment of immunosuppression during active infections. Thus, confronted with infection in solid organ recipients, the management of immunosuppression is based largely on clinical experience. This review examines known measures of immune function and the immunologic effects of common immunosuppressive drugs and available studies reporting modification of drug regimens for specific infections. These data provide a conceptual framework for the management of immunosuppression during infection in organ recipients.

Low-Dose Interleukin-2 Combined With Rapamycin Led to an Expansion of CD4+CD25+FOXP3+ Regulatory T Cells and Prolonged Human Islet Allograft Survival in Humanized Mice

Islet transplantation is an emerging therapy for type 1 diabetes and hypoglycemic unawareness. However, a key challenge for islet transplantation is cellular rejection and the requirement for long-term immunosuppression. In this study, we established a diabetic humanized NOD-scidIL2Rγ^null (NSG) mouse model of T-cell-mediated human islet allograft rejection and developed a therapeutic regimen of low-dose recombinant human interleukin-2 (IL-2) combined with low-dose rapamycin to prolong graft survival. NSG mice that had received renal subcapsular human islet allografts and were transfused with 1 × 10⁷ of human spleen mononuclear cells reconstituted human CD45⁺ cells that were predominantly CD3⁺ T cells and rejected their grafts with a median survival time of 27 days. IL-2 alone (0.3 × 10⁶ IU/m² or 1 × 10⁶ IU/m²) or rapamycin alone (0.5-1 mg/kg) for 3 weeks did not prolong survival. However, the combination of rapamycin with IL-2 for 3 weeks significantly prolonged human islet allograft survival. Graft survival was associated with expansion of CD4⁺CD25⁺FOXP3⁺ regulatory T cells (Tregs) and enhanced transforming growth factor-β production by CD4⁺ T cells. CD8⁺ T cells showed reduced interferon-γ production and reduced expression of perforin-1. The combination of IL-2 and rapamycin has the potential to inhibit human islet allograft rejection by expanding CD4⁺FOXP3⁺ Tregs in vivo and suppressing effector cell function and could be the basis of effective tolerance-based regimens.

Transcription and Translation Inhibitors in Cancer Treatment

Transcription and translation are fundamental cellular processes that govern the protein production of cells. These processes are generally up regulated in cancer cells, to maintain the enhanced metabolism and proliferative state of these cells. As such cancerous cells can be susceptible to transcription and translation inhibitors. There are numerous druggable proteins involved in transcription and translation which make lucrative targets for cancer drug development. In addition to proteins, recent years have shown that the "undruggable" transcription factors and RNA molecules can also be targeted to hamper the transcription or translation in cancer. In this review, we summarize the properties and function of the transcription and translation inhibitors that have been tested and developed, focusing on the advances of the last 5 years. To complement this, we also discuss some of the recent advances in targeting oncogenes tightly controlling transcription including transcription factors and KRAS. In addition to natural and synthetic compounds, we review DNA and RNA based approaches to develop cancer drugs. Finally, we conclude with the outlook to the future of the development of transcription and translation inhibitors.

TAK1 mediates convergence of cellular signals for death and survival

TGF-β activated kinase 1, a MAPK kinase kinase family serine threonine kinase has been implicated in regulating diverse range of cellular processes that include embryonic development, differentiation, autophagy, apoptosis and cell survival. TAK1 along with its binding partners TAB1, TAB2 and TAB3 displays a complex pattern of regulation that includes serious crosstalk with major signaling pathways including the C-Jun N-terminal kinase (JNK), p38 MAPK, and I-kappa B kinase complex (IKK) involved in establishing cellular commitments for death and survival. This review also highlights how TAK1 orchestrates regulation of energy homeostasis via AMPK and its emerging role in influencing mTORC1 pathway to regulate death or survival in tandem.

Distinct Roles of mTOR Targets S6K1 and S6K2 in Breast Cancer

The mechanistic target of rapamycin (mTOR) is a master regulator of protein translation, metabolism, cell growth and proliferation. It forms two complexes, mTOR complex 1 (mTORC1) and 2 (mTORC2). mTORC1 is frequently deregulated in many cancers, including breast cancer, and is an important target for cancer therapy. The immunosuppressant drug rapamycin and its analogs that inhibit mTOR are currently being evaluated for their potential as anti-cancer agents, albeit with limited efficacy. mTORC1 mediates its function via its downstream targets 40S ribosomal S6 kinases (S6K) and eukaryotic translation initiation factor 4E (eIF4E)-binding protein 1 (4E-BP1). There are two homologs of S6K: S6K1 and S6K2. Most of the earlier studies focused on S6K1 rather than S6K2. Because of their high degree of structural homology, it was generally believed that they behave similarly. Recent studies suggest that while they may share some functions, they may also exhibit distinct or even opposite functions. Both homologs have been implicated in breast cancer, although how they contribute to breast cancer may differ. The purpose of this review article is to compare and contrast the expression, structure, regulation and function of these two S6K homologs in breast cancer.

Sirolimus and mTOR Inhibitors: A Review of Side Effects and Specific Management in Solid Organ Transplantation. Drug Saf. 2019;42:813-825. [PMID: 30868436 DOI: 10.1007/s40264-019-00810-9]

Inhibitors of mechanistic target of rapamycin (mTOR inhibitors) are used as antiproliferative immunosuppressive drugs and have many clinical applications in various drug combinations. Experience in transplantation studies has been gained regarding the side effect profile of these drugs and the potential benefits and limitations compared with other immunosuppressive agents. This article reviews the adverse effects of mTOR inhibitors in solid organ transplantation, with special attention given to mechanisms hypothesized to cause adverse events and their management strategies.

High urea induces depression and LTP impairment through mTOR signalling suppression caused by carbamylation

BACKGROUND

Urea, the end product of protein metabolism, has been considered to have negligible toxicity for a long time. Our previous study showed a depression phenotype in urea transporter (UT) B knockout mice, which suggests that abnormal urea metabolism may cause depression. The purpose of this study was to determine if urea accumulation in brain is a key factor causing depression using clinical data and animal models.

METHODS

A meta-analysis was used to identify the relationship between depression and chronic diseases. Functional Magnetic Resonance Imaging (fMRI) brain scans and common biochemical indexes were compared between the patients and healthy controls. We used behavioural tests, electrophysiology, and molecular profiling techniques to investigate the functional role and molecular basis in mouse models.

FINDINGS

After performing a meta-analysis, we targeted the relevance between chronic kidney disease (CKD) and depression. In a CKD mouse model and a patient cohort, depression was induced by impairing the medial prefrontal cortex. The enlarged cohort suggested that urea was responsible for depression. In mice, urea was sufficient to induce depression, interrupt long-term potentiation (LTP) and cause loss of synapses in several models. The mTORC1-S6K pathway inhibition was necessary for the effect of urea. Lastly, we identified that the hydrolysate of urea, cyanate, was also involved in this pathophysiology.

INTERPRETATION

These data indicate that urea accumulation in brain is an independent factor causing depression, bypassing the psychosocial stress. Urea or cyanate carbamylates mTOR to inhibit the mTORC1-S6K dependent dendritic protein synthesis, inducing impairment of synaptic plasticity in mPFC and depression-like behaviour. CKD patients may be able to attenuate depression only by strict management of blood urea.

Signaling and Function of Interleukin-2 in T Lymphocytes

The discovery of interleukin-2 (IL-2) changed the molecular understanding of how the immune system is controlled. IL-2 is a pleiotropic cytokine, and dissecting the signaling pathways that allow IL-2 to control the differentiation and homeostasis of both pro- and anti-inflammatory T cells is fundamental to determining the molecular details of immune regulation. The IL-2 receptor couples to JAK tyrosine kinases and activates the STAT5 transcription factors. However, IL-2 does much more than control transcriptional programs; it is a key regulator of T cell metabolic programs. The development of global phosphoproteomic approaches has expanded the understanding of IL-2 signaling further, revealing the diversity of phosphoproteins that may be influenced by IL-2 in T cells. However, it is increasingly clear that within each T cell subset, IL-2 will signal within a framework of other signal transduction networks that together will shape the transcriptional and metabolic programs that determine T cell fate.

mTOR as a central hub of nutrient signalling and cell growth

The highly conserved protein kinase mechanistic target of rapamycin (mTOR; originally known as mammalian target of rapamycin) is a central cell growth regulator connecting cellular metabolism and growth with a wide range of environmental inputs as part of mTOR complex 1 (mTORC1) and mTORC2. In this Review, we introduce the landmark discoveries in the mTOR field, starting from the isolation of rapamycin to the molecular characterizations of key components of the mTORC signalling network with an emphasis on amino acid sensing, and discuss the perspectives of mTORC inhibitors in therapeutic applications.

Perspectives of RAS and RHEB GTPase Signaling Pathways in Regenerating Brain Neurons

Cellular activation of RAS GTPases into the GTP-binding “ON” state is a key switch for regulating brain functions. Molecular protein structural elements of rat sarcoma (RAS) and RAS homolog protein enriched in brain (RHEB) GTPases involved in this switch are discussed including their subcellular membrane localization for triggering specific signaling pathways resulting in regulation of synaptic connectivity, axonal growth, differentiation, migration, cytoskeletal dynamics, neural protection, and apoptosis. A beneficial role of neuronal H-RAS activity is suggested from cellular and animal models of neurodegenerative diseases. Recent experiments on optogenetic regulation offer insights into the spatiotemporal aspects controlling RAS/mitogen activated protein kinase (MAPK) or phosphoinositide-3 kinase (PI3K) pathways. As optogenetic manipulation of cellular signaling in deep brain regions critically requires penetration of light through large distances of absorbing tissue, we discuss magnetic guidance of re-growing axons as a complementary approach. In Parkinson’s disease, dopaminergic neuronal cell bodies degenerate in the substantia nigra. Current human trials of stem cell-derived dopaminergic neurons must take into account the inability of neuronal axons navigating over a large distance from the grafted site into striatal target regions. Grafting dopaminergic precursor neurons directly into the degenerating substantia nigra is discussed as a novel concept aiming to guide axonal growth by activating GTPase signaling through protein-functionalized intracellular magnetic nanoparticles responding to external magnets.

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 Role of the Mammalian Target of Rapamycin (mTOR) in Pulmonary Fibrosis.Int J Mol Sci. 2018;19. [PMID: 29518028 DOI: 10.3390/ijms19030778]

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.

Development of a novel inducer of protein–protein interactions based on aplyronine A

An aplyronine A–swinholide A hybrid, consisting of the macrolactone part of aplyronine A and the side chain part of swinholide A, was designed, synthesized, and evaluated for biological activities.

MNK Controls mTORC1:Substrate Association through Regulation of TELO2 Binding with mTORC1

The mechanistic target of rapamycin (mTOR) integrates numerous stimuli and coordinates the adaptive response of many cellular processes. To accomplish this, mTOR associates with distinct co-factors that determine its signaling output. While many of these co-factors are known, in many cases their function and regulation remain opaque. The MAPK-interacting kinase (MNK) contributes to rapamycin resistance in cancer cells. Here, we demonstrate that MNK sustains mTORC1 activity following rapamycin treatment and contributes to mTORC1 signaling following T cell activation and growth stimuli in cancer cells. We determine that MNK engages with mTORC1, promotes mTORC1 association with the phosphatidyl inositol 3' kinase-related kinase (PIKK) stabilizer, TELO2, and facilitates mTORC1:substrate binding. Moreover, our data suggest that DEPTOR, the endogenous inhibitor of mTOR, opposes mTORC1:substrate association by preventing TELO2:mTORC1 binding. Thus, MNK orchestrates counterbalancing forces that regulate mTORC1 enzymatic activity.

Twenty-five years of mTOR: Uncovering the link from nutrients to growth

In my PNAS Inaugural Article, I describe the development of the mTOR field, starting with efforts to understand the mechanism of action of the drug rapamycin, which ∼25 y ago led to the discovery of the mTOR protein kinase. I focus on insights that we have contributed and on work that has been particularly influential to me, as well as provide some personal reflections and stories. We now appreciate that, as part of two distinct complexes, mTORC1 and mTORC2, mTOR is the major regulator of growth (mass accumulation) in animals and is the key link between the availability of nutrients in the environment and the control of most anabolic and catabolic processes. Nutrients signal to mTORC1 through the lysosome-associated Rag GTPases and their many regulators and associated cytosolic and lysosomal nutrient sensors. mTOR signaling is deregulated in common diseases, like cancer and epilepsy, and mTORC1 is a well-validated modulator of aging in multiple model organisms. There is significant excitement around using mTORC1 inhibitors to treat cancer and neurological disease and, potentially, to improve healthspan and lifespan.

Targeting MYC Dependence by Metabolic Inhibitors in Cancer

MYC is a critical growth regulatory gene that is commonly overexpressed in a wide range of cancers. Therapeutic targeting of MYC transcriptional activity has long been a goal, but it has been difficult to achieve with drugs that directly block its DNA-binding ability. Additional approaches that exploit oncogene addiction are promising strategies against MYC-driven cancers. Also, drugs that target metabolic regulatory pathways and enzymes have potential for indirectly reducing MYC levels. Glucose metabolism and oxidative phosphorylation, which can be targeted by multiple agents, promote cell growth and MYC expression. Likewise, modulation of the signaling pathways and protein synthesis regulated by adenosine monophosphate-activated protein kinase (AMPK) and mechanistic target of rapamycin (mTOR) can also be an effective route for suppressing MYC translation. Furthermore, recent data suggest that metabolism of nucleotides, fatty acids and glutamine are exploited to alter MYC levels. Combination therapies offer potential new approaches to overcome metabolic plasticity caused by single agents. Although potential toxicities must be carefully controlled, new inhibitors currently being tested in clinical trials offer significant promise. Therefore, as both a downstream target of metabolism and an upstream regulator, MYC is a prominent central regulator of cancer metabolism. Exploiting metabolic vulnerabilities of MYC-driven cancers is an emerging research area with translational potential.

Second-generation total synthesis of aplyronine A featuring Ni/Cr-mediated coupling reactions

Second-generation total synthesis of aplyronine A, a potent antitumor marine macrolide, was achieved using Ni/Cr-mediated coupling reactions as key steps.

The interplay between cell signalling and the mevalonate pathway in cancer

The mevalonate (MVA) pathway is an essential metabolic pathway that uses acetyl-CoA to produce sterols and isoprenoids that are integral to tumour growth and progression. In recent years, many oncogenic signalling pathways have been shown to increase the activity and/or the expression of MVA pathway enzymes. This Review summarizes recent advances and discusses unique opportunities for immediately targeting this metabolic vulnerability in cancer with agents that have been approved for other therapeutic uses, such as the statin family of drugs, to improve outcomes for cancer patients.

Biosynthesis, regulation, and engineering of a linear polyketide tautomycetin: a novel immunosuppressant in Streptomyces sp. CK4412

Tautomycetin (TMC) is a natural product with a linear structure that includes an ester bond connecting a dialkylmaleic moiety to a type I polyketide chain. Although TMC was originally identified as an antifungal antibiotic in the late 1980s, follow-up studies revealed its novel immunosuppressant activity. Specifically, TMC exhibited a mechanistically unique immunosuppressant activity about 100 times higher than that of cyclosporine A, a widely used immunosuppressant drug. Interestingly, a structurally close relative, tautomycin (TTM), was reported to not possess TMC-like immunosuppressant activity, suggesting that a distinctive polyketide moiety of TMC plays a critical role in immunosuppressant activity. Cloning and engineering of a TMC polyketide biosynthetic gene cluster generated several derivatives showing different biological activities. TMC was also found to be biosynthesized as a linear structure without forming a lactone ring, unlike the most polyketide-based compounds, implying the presence of a unique polyketide thioesterase in the cluster. Although TMC biosynthesis was limited due to its tight regulation by two pathway-specific regulatory genes located in the cluster, its production was significantly stimulated through homologous and heterologous expression of its entire biosynthetic gene cluster using a Streptomyces artificial chromosome vector system. In this mini-review, we summarize recent advances in the biosynthesis, regulation, and pathway engineering of a linear polyketide, TMC, in Streptomyces sp. CK4412.

Context-Specific Function of S6K2 in Th Cell Differentiation

The mammalian target of rapamycin (mTOR) is essential for Th cell proliferation and effector differentiation, making the mTOR signaling network an attractive immunomodulatory target for autoimmune-related diseases. Although direct targeting of mTOR complex-1 (mTORC1) with rapamycin can provide clinical benefit, targeting downstream enzymes has the potential to offer more selective immunosuppression. In this study, we evaluated p70 ribosomal protein S6 Kinase 2 (S6K2), a downstream effector of mTORC1, for its role in T cell function and autoimmunity. S6K2 is a direct substrate of mTORC1, with a potential role in Th17 differentiation suggested by biochemical studies. Using a genetic approach with S6K2 knockout mice, we found that S6K2 loss reduces Th17 skewing and increases regulatory T cell differentiation in vitro when cultured in RPMI 1640 media. However, S6K2 was dispensable for Th17 differentiation in IMDM. In an in vivo experimental autoimmune encephalomyelitis model in which rapamycin suppresses disease, S6K2 knockout mice did not exhibit differences in clinical score or Th17 differentiation. These results suggest that S6K2 is dispensable for Th17-driven autoimmunity and highlight how distinct experimental conditions can produce significantly different results in T cell differentiation.

Mitochondrial stress induces cellular senescence in an mTORC1-dependent manner

Although mitochondrial stress is a key determinant of cellular homeostasis, the intracellular mechanisms by which this stress is communicated to the nucleus and its impact on cell fate decisions are not well defined. In this study, we report that activation of mTORC1 signaling triggered by mitochondrial-generated reactive oxygen species (ROS) results in activation of the senescence program. We show that exposure of human fibroblasts to nucleoside analogs commonly used in antiretroviral therapies, and known to induce mitochondrial dysfunction, increases mitochondrial ROS and leads to a rise in intracellular ROS concomitant with activation of mTORC1. In this setting, it appears that mTORC1 activates senescence through HDM2 phosphorylation, facilitating a p53-mediated response. Inhibition of mTORC1 by rapamycin decreases HDM2 phosphorylation and blocks activation of the senescence program in human cells. In addition, decreasing mitochondrial ROS directly blocks mTORC1 signaling and prevents the onset of senescence. Consistent with these results, both total and mitochondrial-specific ROS increased in cells undergoing replicative senescence along with ribosomal p70 phosphorylation. The results reveal a novel link between mitochondrial dysfunction, mTORC1 signaling, and the senescence program.

The 4E-BP-eIF4E axis promotes rapamycin-sensitive growth and proliferation in lymphocytes

Rapamycin has been used as a clinical immunosuppressant for many years; however, the molecular basis for its selective effects on lymphocytes remains unclear. We investigated the role of two canonical effectors of the mammalian target of rapamycin (mTOR): ribosomal S6 kinases (S6Ks) and eukaryotic initiation factor 4E (eIF4E)-binding proteins (4E-BPs). S6Ks are thought to regulate cell growth (increase in cell size), and 4E-BPs are thought to control proliferation (increase in cell number), with mTORC1 signaling serving to integrate these processes. However, we found that the 4E-BP-eIF4E signaling axis controlled both the growth and proliferation of lymphocytes, processes for which the S6Ks were dispensable. Furthermore, rapamycin disrupted eIF4E function selectively in lymphocytes, which was due to the increased abundance of 4E-BP2 relative to that of 4E-BP1 in these cells and the greater sensitivity of 4E-BP2 to rapamycin. Together, our findings suggest that the 4E-BP-eIF4E axis is uniquely rapamycin-sensitive in lymphocytes and that this axis promotes clonal expansion of these cells by coordinating growth and proliferation.

Caffeic acid phenethyl ester induced cell cycle arrest and growth inhibition in androgen-independent prostate cancer cells via regulation of Skp2, p53, p21Cip1 and p27Kip1

Prostate cancer (PCa) patients receiving the androgen ablation therapy ultimately develop recurrent castration-resistant prostate cancer (CRPC) within 1–3 years. Treatment with caffeic acid phenethyl ester (CAPE) suppressed cell survival and proliferation via induction of G1 or G2/M cell cycle arrest in LNCaP 104-R1, DU-145, 22Rv1, and C4–2 CRPC cells. CAPE treatment also inhibited soft agar colony formation and retarded nude mice xenograft growth of LNCaP 104-R1 cells. We identified that CAPE treatment significantly reduced protein abundance of Skp2, Cdk2, Cdk4, Cdk7, Rb, phospho-Rb S807/811, cyclin A, cyclin D1, cyclin H, E2F1, c-Myc, SGK, phospho-p70S6kinase T421/S424, phospho-mTOR Ser2481, phospho-GSK3α Ser21, but induced p21^Cip1, p27^Kip1, ATF4, cyclin E, p53, TRIB3, phospho-p53 (Ser6, Ser33, Ser46, Ser392), phospho-p38 MAPK Thr180/Tyr182, Chk1, Chk2, phospho-ATM S1981, phospho-ATR S428, and phospho-p90RSK Ser380. CAPE treatment decreased Skp2 and Akt1 protein expression in LNCaP 104-R1 tumors as compared to control group. Overexpression of Skp2, or siRNA knockdown of p21^Cip1, p27^Kip1, or p53 blocked suppressive effect of CAPE treatment. Co-treatment of CAPE with PI3K inhibitor LY294002 or Bcl-2 inhibitor ABT737 showed synergistic suppressive effects. Our finding suggested that CAPE treatment induced cell cycle arrest and growth inhibition in CRPC cells via regulation of Skp2, p53, p21^Cip1, and p27^Kip1.