mTOR-dependent Signaling Pathway Research Articles

NRASQ61R mutation drives elevated angiopoietin-2 expression in human endothelial cells and a genetic mouse model.

Angiopoietin-2 (Ang-2) is increased in the blood of patients with kaposiform lymphangiomatosis (KLA) and kaposiform hemangioendothelioma (KHE). While the genetic causes of KHE are not clear, a somatic activating NRASQ61R mutation has been found in the lesions of KLA patients. Our study tested the hypothesis that the NRASQ61R mutation drives elevated Ang-2 expression in endothelial cells. Ang-2 was measured in human endothelial progenitor cells (EPC) expressing NRASQ61R and a genetic mouse model with endothelial targeted NRASQ61R. To determine the signaling pathways driving Ang-2, NRASQ61R EPC were treated with signaling pathway inhibitors. Ang-2 levels were increased in EPC expressing NRASQ61R compared to NRASWT by Western blot analysis of cell lysates and ELISA of the cell culture media. Ang-2 levels were elevated in the blood of NRASQ61R mutant mice. NRASQ61R mutant mice also had reduced platelet counts and splenomegaly with hypervascular lesions, like some KLA patients. mTOR inhibitor rapamycin attenuated Ang-2 expression by NRASQ61R EPC. However, MEK1/2 inhibitor trametinib was more effective blocking increases in Ang-2. Our studies show that the NRASQ61R mutation in endothelial cells induces Ang-2 expression in vitro and in vivo. In cultured human endothelial cells, NRASQ61R drives elevated Ang-2 through MAP kinase and mTOR-dependent signaling pathways.

Transduced Tat-PRAS40 prevents dopaminergic neuronal cell death through ROS inhibition and interaction with 14-3-3σ protein

Proline rich Akt substrate (PRAS40) is a component of mammalian target of rapamycin complex 1 (mTORC1) and activated mTORC1 plays important roles for cellular survival in response to oxidative stress. However, the roles of PRAS40 in dopaminergic neuronal cell death have not yet been examined. Here, we examined the roles of Tat-PRAS40 in MPP+- and MPTP-induced dopaminergic neuronal cell death. Our results showed that Tat-PRAS40 effectively transduced into SH-SY5Y cells and inhibited DNA damage, ROS generation, and apoptotic signaling in MPP+-induced SH-SY5Y cells. Further, these protective mechanisms of Tat-PRAS40 protein display through phosphorylation of Tat-PRAS40, Akt and direct interaction with 14-3-3σ protein, but not via the mTOR-dependent signaling pathway. In a Parkinson’s disease animal model, Tat-PRAS40 transduced into dopaminergic neurons in mouse brain and significantly protected against dopaminergic cell death by phosphorylation of Tat-PRAS40, Akt and interaction with 14-3-3σ protein. In this study, we demonstrated for the first time that Tat-PRAS40 directly protects against dopaminergic neuronal cell death. These results indicate that Tat-PRAS40 may provide a useful therapeutic agent against oxidative stress-induced dopaminergic neuronal cell death, which causes diseases such as PD.

An increase in VGF expression through a rapid, transcription-independent, autofeedback mechanism improves cognitive function

The release of neuropeptides from dense core vesicles (DCVs) modulates neuronal activity and plays a critical role in cognitive function and emotion. The granin family is considered a master regulator of DCV biogenesis and the release of DCV cargo molecules. The expression of the VGF protein (nonacronymic), a secreted neuropeptide precursor that also belongs to the extended granin family, has been previously shown to be induced in the brain by hippocampus-dependent learning, and its downregulation is mechanistically linked to neurodegenerative diseases such as Alzheimer’s disease and other mood disorders. Currently, whether changes in translational efficiency of Vgf and other granin mRNAs may be associated and regulated with learning associated neural activity remains largely unknown. Here, we show that either contextual fear memory training or the administration of TLQP-62, a peptide derived from the C-terminal region of the VGF precursor, acutely increases the translation of VGF and other granin proteins, such as CgB and Scg2, via an mTOR-dependent signaling pathway in the absence of measurable increases in mRNA expression. Luciferase-based reporter assays confirmed that the 3′-untranslated region (3′UTR) of the Vgf mRNA represses VGF translation. Consistently, the truncation of the endogenous Vgf mRNA 3′UTR results in substantial increases in VGF protein expression both in cultured primary neurons and in brain tissues from knock in mice expressing a 3′UTR-truncation mutant encoded by the modified Vgf gene. Importantly, Vgf 3′UTR-truncated mice exhibit enhanced memory performance and reduced anxiety- and depression-like behaviors. Our results therefore reveal a rapid, transcription-independent induction of VGF and other granin proteins after learning that are triggered by the VGF-derived peptide TLQP-62. Our findings suggest that the rapid, positive feedforward increase in the synthesis of granin family proteins might be a general mechanism to replenish DCV cargo molecules that have been released in response to neuronal activation and is crucial for memory function and mood stability.

Molecular Mechanisms of Apoptosis of Glomerular Podocytes in Diabetic Nephropathy

Dysfunctions of glomerular podocytes and triggering of apoptotic processes in them are the main molecular causes of diabetic nephropathy and other kidney diseases. Pathogenetic factors causing these dysfunctions of podocytes are hyperglycemia, increased levels of advanced glycation end-products, oxidative stress, increased activity of inflammatory factors, and endoplasmic reticulum stress. These factors and their combinations result in the triggering of a number of intracellular signaling pathways that cause activation of apoptosis and reduce the survival of podocytes. Among these pathways are: (1) the Wnt/β-catenin pathway, which is activated by the Wnt-proteins when they bind to the complex of Frizzled receptors and LRP co-receptors; (2) the mTOR-dependent signaling pathway, including the mTORC1 and mTORC2 complexes, which are involved in the regulation of autophagy and endoplasmic reticulum stress and are regulated by various stimuli and effectors, in particular, the AMP-activated protein kinase; (3) the Rho/ROCK signaling pathway, including GTPases of the Rho family and Rho-associated protein kinase ROCK1; (4) calcium-dependent signaling pathways triggered by an increase in the concentration of intracellular Ca2+, primarily through the activation of calcium channels of the TRPC family. The review provides a detailed analysis of the current state of knowledge about the molecular mechanisms responsible for the regulation of apoptotic processes in glomerular podocytes and also considers hormonal and other factors that regulate them both under normal conditions and under the conditions of lesions induced by hyperglycemia and diabetic nephropathy.

MTOR Suppresses Macroautophagy During Striatal Postnatal Development and Is Hyperactive in Mouse Models of Autism Spectrum Disorders.

Macroautophagy (hereafter referred to as autophagy) plays a critical role in neuronal function related to development and degeneration. Here, we investigated whether autophagy is developmentally regulated in the striatum, a brain region implicated in neurodevelopmental disease. We demonstrate that autophagic flux is suppressed during striatal postnatal development, reaching adult levels around postnatal day 28 (P28). We also find that mTOR signaling, a key regulator of autophagy, increases during the same developmental period. We further show that mTOR signaling is responsible for suppressing autophagy, via regulation of Beclin-1 and VPS34 activity. Finally, we discover that autophagy is downregulated during late striatal postnatal development (P28) in mice with in utero exposure to valproic acid (VPA), an established mouse model of autism spectrum disorder (ASD). VPA-exposed mice also display deficits in striatal neurotransmission and social behavior. Correction of hyperactive mTOR signaling in VPA-exposed mice restores social behavior. These results demonstrate that neurons coopt metabolic signaling cascades to developmentally regulate autophagy and provide additional evidence that mTOR-dependent signaling pathways represent pathogenic signaling cascades in ASD mouse models that are active during specific postnatal windows.

Ribosomal Protein S6 Hypofunction in Postmortem Human Brain Links mTORC1-Dependent Signaling and Schizophrenia.

The mechanistic target of rapamycin (also known as mammalian target of rapamycin) (mTOR)-dependent signaling pathway plays an important role in protein synthesis, cell growth, and proliferation, and has been linked to the development of the central nervous system. Recent studies suggest that mTOR signaling pathway dysfunction could be involved in the etiopathogenesis of schizophrenia. The main goal of this study was to evaluate the status of mTOR signaling pathway in postmortem prefrontal cortex (PFC) samples of subjects with schizophrenia. For this purpose, we quantified the protein expression and phosphorylation status of the mTOR downstream effector ribosomal protein S6 as well as other pathway interactors such as Akt and GSK3β. Furthermore, we quantified the status of these proteins in the brain cortex of rats chronically treated with the antipsychotics haloperidol, clozapine, or risperidone. We found a striking decrease in the expression of total S6 and in its active phosphorylated form phospho-S6 (Ser235/236) in the brain of subjects with schizophrenia compared to matched controls. The chronic treatment with the antipsychotics haloperidol and clozapine affected both the expression of GSK3β and the activation of Akt [phospho-Akt (Ser473)] in rat brain cortex, while no changes were observed in S6 and phospho-S6 (Ser235/236) protein expression with any antipsychotic treatment. These findings provide further evidence for the involvement of the mTOR-dependent signaling pathway in schizophrenia and suggest that a hypofunctional S6 may have a role in the etiopathogenesis of this disorder.

Soybean isoflavones prevent atrazine-induced neurodegenerative damage by inducing autophagy.

Atrazine (ATR) is a widely used herbicide with documented dopaminergic (DAergic) neurotoxicity that can lead to a Parkinson's disease (PD)-like motor syndrome. However, there have been few studies on preventative interventions. The aim of the present study was to investigate the neuroprotective efficacy of soybean isoflavones (SI) and associated molecular mechanisms in a rat model of ATR-induced DAergic toxicity. Male Sprague-Dawley rats (6 weeks old) received daily intraperitoneal injection of SI (10, 50, or 100mg/kg) or vehicle followed 1h later by oral gavage of ATR (50mg/kg) for 45 consecutive days. Open field and grip-strength tests indicated no differences in motor function among treatment groups. Alternatively, histopathology revealed neuronal damage in the striatum of rats receiving vehicle plus ATR that was ameliorated by SI pretreatment. SI attenuate ATR-induced oxidative stress (indicated by MDA accumulation and GSH depletion) and inflammatory damage (as evidenced by TNF-α and IL-6 elevation) in the substantia nigra. ATR increased expression of the pro-apoptotic factor Bax and reduced expression levels of the DA synthesis enzyme tyrosine hydroxylase (TH) and the anti-apoptotic factor Bcl-2 in the substantia nigra and striatum. All of these effects were reversed by SI pretreatment, suggesting that SI can inhibit ATR-induced apoptosis of DAergic neurons. ATR also inhibited autophagy in the substantial nigra as evidenced by LC3-II and Beclin-1 downregulation and increased expression of p62, whereas SI pretreatment reversed these effects, indicating autophagy induction. Furthermore, ATR increased the expression of mTOR and reduced the expression of phosphorylated S6 (p-S6) and BEX2 in the substantia nigra. Collectively, these findings suggest that SI can prevent ATR-mediated degeneration of DAergic neurons by inducing autophagy through an mTOR-dependent signaling pathway.

Developmental exposure to environmentally relevant concentrations of bifenthrin alters transcription of mTOR and ryanodine receptor-dependent signaling molecules and impairs predator avoidance behavior across early life stages in inland silversides (Menidia beryllina)

Altered transcription of calcium-dependent signaling cascades involving the ryanodine receptor (RyR) and mechanistic target of rapamycin (mTOR) in response to environmental exposures have been described in model vertebrates, including zebrafish, while the relevance for wild fishes remains unknown. To address this knowledge gap, we exposed the euryhaline model species Menidia beryllina (inland silversides) to the insecticide bifenthrin, a known modulator of calcium signaling. The main objectives of this study were to determine: (1) whether exposure of developing silversides to environmentally relevant concentrations of bifenthrin alters their behavior; and (2) whether behavioral changes correlate with altered expression of genes involved in RyR and mTOR-dependent signaling pathways. At six hours post fertilization (hpf), inland silversides were exposed to bifenthrin at 3, 27 and 122 ng/L until 7 days post fertilization (dpf, larvae hatched at 6dpf), followed by a 14-day recovery period in uncontaminated water. Transcriptional responses were measured at 5, 7 and 21 dpf; locomotor behavior following external stimuli and response to an olfactory predator cue were assessed at 7 and 21 dpf. Bifenthrin elicited significant non-monotonic transcriptional responses in the majority of genes examined at 5 dpf and at 21 dpf. Bifenthrin also significantly altered predator avoidance behavior via olfactory mechanisms with main effects identified for animals exposed to 3 and 27 ng/L. Behavioral effects were not detected in response to visual stimuli during acute exposure, but were significant in the predator-cue assessment following the recovery period, suggesting delayed and long-term effects of early developmental exposures to bifenthrin. Our findings demonstrate that at picomolar (pM) concentrations, which are often not represented in ecotoxicological studies, bifenthrin perturbs early development of inland silversides. These developmental impacts are manifested behaviorally at later life stages, specifically as altered patterns of predator avoidance behavior, which have been correlated with population decline. Collectively, these data suggest that bifenthrin may be negatively impacting wild fish populations.

Thyrocyte-specific deletion of insulin and IGF-1 receptors induces papillary thyroid carcinoma-like lesions through EGFR pathway activation.

Insulin and insulin-like growth factor (IGF)-1 signaling in the thyroid are thought to be permissive for the coordinated regulation by thyroid-stimulating hormone (TSH) of thyrocyte proliferation and hormone production. However, the integrated role of insulin receptor (IR) and IGF-1 receptor (IGF-1R) in thyroid development and function has not been explored. Here, we generated thyrocyte-specific IR and IGF-1R double knockout (DTIRKO) mice to precisely evaluate the coordinated functions of these receptors in the thyroid of neonates and adults. Neonatal DTIRKO mice displayed smaller thyroids, paralleling defective folliculogenesis associated with repression of the thyroid-specific transcription factor Foxe1. By contrast, at postnatal day 14, absence of IR and IGF-1R paradoxically induced thyrocyte proliferation, which was mediated by mTOR-dependent signaling pathways. Furthermore, we found elevated production of TSH during the development of follicular hyperplasia at 8 weeks of age. By 50 weeks, all DTIRKO mice developed papillary thyroid carcinoma (PTC)-like lesions that correlated with induction of the ErbB pathway. Taken together, these data define a critical role for IR and IGF-1R in neonatal thyroid folliculogenesis. They also reveal an important reciprocal relationship between IR/IGF-1R and TSH/ErbB signaling in the pathogenesis of thyroid follicular hyperplasia and, possibly, of papillary carcinoma.

Inhibition of Rabies Virus by 1,2,3,4,6-Penta-O-galloyl-β-d-Glucose Involves mTOR-Dependent Autophagy.

The compound 1,2,3,4,6-penta-O-galloyl-β-d-glucose (PGG), a gallotannin present in various plants such as Rhus chinensis Mill and Paeonia suffruticosa, has a broad spectrum of antiviral effects. The present study investigated its potency against infection of mice with rabies virus (RABV). Results demonstrated that PGG strongly inhibited virus titers (50-fold), viral mRNA expression (up to 90%), and protein synthesis in vitro. Importantly, we found that PGG not only suppressed viral adsorption and entry, but also directly inactivated RABV through suppression of autophagy by mediating activation of the mTOR-dependent autophagy signaling pathway. In vivo, PGG (10 mg/kg) alleviated the clinical symptoms and reduced the mortality of infected mice by 27.3%. Collectively, our results indicate that PGG has potent anti-RABV effect, and merits further investigation as an anti-RABV drug.

Midazolam Enhances Mutant Huntingtin Protein Accumulation via Impairment of Autophagic Degradation In Vitro

Background/Aims: Autophagy is a well-known pathway to “clean” the misfolded mutant huntingtin protein (mHtt), which plays a considerable role in polyglutamine diseases. To date, there have been few studies of the choice of anesthetic during surgery in patients with polyglutamine diseases and evaluation of the effects and underlying mechanisms of anesthetics in these patients. Methods: GFP-Htt (Q74)-PC12 cells, which stably express green fluorescent protein-tagged Htt protein containing 74 glutamine repeating units, were used throughout this study. Cells were treated with 15 μM midazolam and 100 mM trehalose (positive control), and the induction of autophagy and autophagic degradation were assessed by detecting changes in autophagy-related proteins and substrates, and cell viability was assessed using the MTT assay. Overexpression of cathepsin D by plasmid transfection was used to restore midazolam-impaired autophagic degradation. Results: Midazolam increased intracellular mHtt levels in a time- and dose-dependent manner. Additionally, enhancing or blocking autophagic flux by trehalose or chloroquine could decrease or increase midazolam-induced mHtt elevation, respectively. Midazolam induced autophagy in the mTOR-dependent signaling pathway, but autophagic degradation was impaired, with a continuous rise in p62 and LC3 II levels and decrease in cathepsin D. However, overexpression of cathepsin D reversed the effects of midazolam. Midazolam led to a 20% decrease in GFP-Htt (Q74)-PC12 cell viability, which could be abrogated by overexpression of cathepsin D. Conclusions: Midazolam increased mHtt levels and decreased Htt (Q74)-PC12 cell viability via impairment of autophagic degradation, which could be restored by overexpression of cathepsin D.

Activation of the mTOR dependent signaling pathway underlies ketamine-induced uropathy.

To investigate the pathogenic role of activation of the mammalian target of the rapamycin (mTOR) in the ketamine induced microvascular injury. Twenty-three patients with ketamine-induced cystitis (KC) and 16 control volunteers were recruited. Bladder tissues were obtained from both groups by cystoscopic biopsies. Phospho-S6 ribosomal protein (p-S6RP), an end product of the mTOR pathway, was stained in the urinary bladder from both groups. Endothelial cells of the urinary bladder (HBdMECs) were examined to investigate the in vitro activation of the mTOR pathway and the co-expression of the endothelial marker (cluster of differentiation 31 [CD31]) and the mesenchymal marker (fibroblast-specific protein 1 [FSP-1]). Expression of p-S6RP increased significantly after ketamine exposure, especially in the vesical microvessels of KC patients. In HBdMECs treated with 100 µM Ketamine, time-dependent activation of the mTOR pathway occurred, with significantly increased levels of the phosphorylated forms of mTOR at 30 min and of S6RP and p70S6 kinase (p70S6K) at 6 h. The increased level of p-S6RP returned to baseline within 2 days after ketamine exposure. The co-expression of CD31 and FSP-1 implied that EndMT was present in HBdMECs at 7 days after ketamine treatment, while TGF-β1 facilitated significant up-regulation of FSP-1 at 1 day after treatment. Furthermore, when the mTOR inhibitor rapamycin was administered with ketamine to the HBdMECs, the expression of FSP-1 decreased significantly. Ketamine induces activation of the mTOR pathway and subsequent mesenchymal phenotypic expression (FSP1) in HBdMECs.

17-DMAG이 마우스 골격근에서 autophagy flux에 미치는 영향

The purpose of this study was to determine if heat shock proteins are involved in autophagy in skeletal muscle. We used the autophagy flux strategy, which is an LC3 II/p62 turnover assay conducted with and without an autophagy inhibitor, to determine whether 17-DMAG (an Hsp90 inhibitor/Hsp72 activator) stimulates autophagy in skeletal muscle. We treated C2C12 cells with 17-DMAG (500 nM) for 24 hr with and without the autophagy inhibitor (Bafilomycin A1, 200 ng/ml), and we injected C57BL/6 mice i.p. with 17-DMAG (10 mg/kg) daily for 7 days with and without colchicine as an autophagy inhibitor (0.4 mg/kg/day, administered on the last 2 days). C2C12 myotubes and tibialis anterior muscles were harvested for analysis of mTOR-dependent autophagy signaling pathway proteins and autophagic marker proteins (p62 and LC3 II) by Western blot analysis. The blots showed that 17-DMAG upregulated hsp72 and decreased Akt protein levels and S6 phosphorylation in C2C12 cells. However, an in vitro autophagic flux assay demonstrated that 17-DMAG did not increase LC3 II and p62 protein concentrations to a greater extent than Bafilomycin A1 treatment alone. Similarly, 17DMAG increased Hsp72 protein levels and decreased the expression of Akt and the phosphorylation of S6 in mouse skeletal muscle. However, unlike the response seen in C2C12 myotubes, the p62 protein levels were significantly decreased in 17-DMAG-treated mouse skeletal muscle (~50%; p<0.05). The LC3 II protein levels in 17-DMAG-treated mice were increased ~2-fold more when degradation was inhibited by colchicine (p<0.01). This suggests that 17-DMAG stimulates basal autophagy in skeletal muscle but is not found in C2C12 myotubes.

Activation of mTOR dependent signaling pathway is a necessary mechanism of antidepressant-like activity of zinc

The rapid antidepressant response to the N-methyl-d-aspartate (NMDA) receptor antagonists is mediated by activation of the mammalian target of the rapamycin (mTOR) signaling pathway, an increase in the synthesis of synaptic proteins and formation of new synapses in the prefrontal cortex (PFC) of rats. Zinc (Zn), which is a potent NMDA receptor antagonist, exerts antidepressant-like effects in screening tests and models of depression. We focused these studies in investigating whether activation of the mTOR signaling pathway is also a necessary mechanism of the antidepressant-like activity of Zn. We observed that a single injection of Zn (5 mg/kg) induced an increase in the phosphorylation of mTOR and p70S6K 30 min and 3 h after Zn treatment at time points when Zn produced also an antidepressant-like effect in the forced swim test (FST). Furthermore, Zn administered 3 h before the decapitation increased the level of brain derived neurotrophic factor (BDNF), GluA1 and synapsin I. An elevated level of GluA1 and synapsin I was still observed 24 h after the Zn treatment, although Zn did not produce any effects in the FST at that time point. We also observed that pretreatment with rapamycin (mTORC1 inhibitor), LY294002 (PI3K inhibitor), H-89 (PKA inhibitor) and GF109203X (PKC inhibitor) blocked the antidepressant-like effect of Zn in FST in rats and blocks Zn-induced activation of mTOR signaling proteins (analyzed 30 min after Zn administration). These studies indicated that the antidepressant-like activity of Zn depends on the activation of mTOR signaling and other signaling pathways related to neuroplasticity, which can indirectly modulate mTOR function.

Cell Surface Area and Membrane Folding in Glioblastoma Cell Lines Differing in PTEN and p53 Status

Glioblastoma multiforme (GBM) is characterized by rapid growth, invasion and resistance to chemo−/radiotherapy. The complex cell surface morphology with abundant membrane folds, microvilli, filopodia and other membrane extensions is believed to contribute to the highly invasive behavior and therapy resistance of GBM cells. The present study addresses the mechanisms leading to the excessive cell membrane area in five GBM lines differing in mutational status for PTEN and p53. In addition to scanning electron microscopy (SEM), the membrane area and folding were quantified by dielectric measurements of membrane capacitance using the single-cell electrorotation (ROT) technique. The osmotic stability and volume regulation of GBM cells were analyzed by video microscopy. The expression of PTEN, p53, mTOR and several other marker proteins involved in cell growth and membrane synthesis were examined by Western blotting. The combined SEM, ROT and osmotic data provided independent lines of evidence for a large variability in membrane area and folding among tested GBM lines. Thus, DK-MG cells (wild type p53 and wild type PTEN) exhibited the lowest degree of membrane folding, probed by the area-specific capacitance C m = 1.9 µF/cm2. In contrast, cell lines carrying mutations in both p53 and PTEN (U373-MG and SNB19) showed the highest C m values of 3.7–4.0 µF/cm2, which corroborate well with their heavily villated cell surface revealed by SEM. Since PTEN and p53 are well-known inhibitors of mTOR, the increased membrane area/folding in mutant GBM lines may be related to the enhanced protein and lipid synthesis due to a deregulation of the mTOR-dependent downstream signaling pathway. Given that membrane folds and extensions are implicated in tumor cell motility and metastasis, the dielectric approach presented here provides a rapid and simple tool for screening the biophysical cell properties in studies on targeting chemo- or radiotherapeutically the migration and invasion of GBM and other tumor types.

Effects of tonic immobility (TI) and corticosterone (CORT) on energy status and protein metabolism in pectoralis major muscle of broiler chickens

Tonic immobility (TI), which can be divided into short (STI) or long (LTI) duration, is a character related to fear. Our previous study has demonstrated LTI phenotype and chronic corticosterone (CORT) administration retarded growth of breast muscle in broiler chickens. In order to investigate the mechanism behind the negative effects of LTI and CORT on growth, the level of mRNA transcription of several key genes linked to energy and protein metabolism was measured in muscle. LTI broilers showed lower levels of ATP, energy charge (EC) (p<0.01), and lower muscle glycogen content (p<0.05) but higher level of ADP (p=0.08) than STI birds. CORT treatment elevated EC level (p<0.05) and reduced liver glycogen content (p<0.05). Real-time PCR results showed that STI chickens had higher mRNA expression of PPAR α (p=0.06) and AMPK α (p=0.09) than LTI. CORT significantly down-regulated α-enolase mRNA expression in breast muscle compared to control (p<0.05). Neither TI nor CORT altered gene expression in Akt/mTOR/p70s6k cascade pathway in muscle (p > 0.05). However, western blot results showed that LTI chickens exhibited higher protein content of total Akt (p=0.05) and phosphorylated Akt (p=0.06) than STI. CORT treatment decreased the total protein content of Akt (p=0.09) and p70s6k (p=0.08). These results suggest that the retardation of muscle growth by LTI and chronic CORT administration parallels a strong alternation in energy status but slight changes of Akt/mTOR/p70s6k cascade, indicating that a decrease in muscle growth induced by LTI and CORT might not be mediated through mTOR-dependent signaling pathways.

Neoplasms-associated autophagy signaling pathways

Autophagy is a cellular catabolic pathway that is essential for survival,differentiation,development and homeostasis.The dual roles of autophagy as a tumor-promoting mechanism and a tumor suppressor mechanism have been elucidated in the recent cancer research.The double function is accomplished by some neoplasms-associated signaling pathways which include mTOR-dependent signaling pathway,Beclin1 network,LKB1-AMPK signaling pathway,p53 and p53-related regulators of autophagy.Thus it can be seen that these signaling pathways function dependently and correlatively as inducing and inhibiting autophagy and play different roles in the process that involves growth and development of neoplasms. Key words: Neoplasms; Autophagy; Signaling pathways

All PI3Kinase signaling is not mTOR: dissecting mTOR-dependent and independent signaling pathways in T cells

The mechanistic target of rapamycin (mTOR) is emerging as playing a central role in regulating T cell activation, differentiation, and function. mTOR integrates diverse signals from the immune microenvironment to shape the outcome of T cell receptor (TCR) antigen recognition. Phosphatidylinositol 3-kinase (PI3K) enzymes are critical mediators of T cell activation through their generation of the second messenger phosphatidylinositol (3,4,5) triphosphate (PIP3). Indeed, PIP3 generation results in the activation of Protein Kinase B (PKB, also known as AKT), a key activator of mTOR. However, recent genetic studies have demonstrated inconsistencies between PI3K disruption and loss of mTOR expression with regard to the regulation of effector and regulatory T cell homeostasis and function. In this review, we focus on how PI3K activation directs mature CD4 T cell activation and effector function by pathways dependent on and independent of mTOR signaling. Importantly, what has become clear is that targeting both mTOR-dependent and mTOR-independent PI3K-induced signaling distally affords the opportunity for more selective regulation of T cell differentiation and function.

Protein synthesis regulation by leucine

In vivo and in vitro studies have demonstrated that high protein diets affect both protein synthesis and regulation of several cellular processes. The role of amino acids as substrate for protein synthesis has been established in the literature. However, the mechanism by which these amino acids modulate transcription and regulate the mRNA translation via mTOR-dependent signaling pathway has yet to be fully determined. It has been verified that mTOR is a protein responsible for activating a cascade of biochemical intracellular events which result in the activation of the protein translation process. Of the aminoacids, leucine is the most effective in stimulating protein synthesis and reducing proteolysis. Therefore, it promotes a positive nitrogen balance, possibly by favoring the activation of this protein. This amino acid also directly and indirectly stimulates the synthesis and secretion of insulin, enhancing its anabolic cellular effects. Therefore, this review aimed to identify the role of leucine in protein synthesis modulation and to discuss the metabolic aspects related to this aminoacid.

Activation of Liver X Receptors Prevents Statin-induced Death of 3T3-L1 Preadipocytes

The biological functions of liver X receptors (LXRs) alpha and beta have primarily been linked to pathways involved in fatty acid and cholesterol homeostasis. Here we report a novel role of LXR activation in protecting cells from statin-induced death. When 3T3-L1 preadipocytes were induced to differentiate by standard isobutylmethylxanthine/dexamethasone/insulin treatment in the presence of statins, they failed to differentiate and underwent massive apoptosis. The simultaneous addition of selective LXR agonists prevented the statin-induced apoptosis. By using mouse embryo fibroblasts from wild-type (LXRalpha+/+/LXRbeta+/+), LXRalpha knock-out mice (LXRalpha(-/-)/LXRbeta+/+), LXRbeta knock-out mice (LXRalpha+/-/LXRbeta(-/-)), and LXR double knock-out mice (LXRalpha(-/-)/LXRbeta(-/-)) as well as 3T3-L1 cells transduced with retroviruses expressing either wild-type LXRalpha or a dominant negative version of LXRalpha, we demonstrate that the response to LXR agonists is LXR-dependent. Interestingly, LXR-mediated rescue of statin-induced apoptosis was not related to up-regulation of genes previously shown to be involved in the antiapoptotic action of LXR. Furthermore, forced expression of Bcl-2 did not prevent statin-induced apoptosis; nor did LXR action depend on protein kinase B, whose activation by insulin was impaired in statin-treated cells. Rather, LXR-dependent rescue of statin-induced apoptosis in 3T3-L1 preadipocytes required NF-kappaB activity, since expression of a dominant negative version of IkappaBalpha prevented LXR agonist-dependent rescue of statin-induced apoptosis. Thus, the results presented in this paper provide novel insight into the action of statins on and LXR-dependent inhibition of apoptosis.