Regulation of mTORC1 by PI3K signaling

Milk's Role as an Epigenetic Regulator in Health and Disease

It is the intention of this review to characterize milk's role as an epigenetic regulator in health and disease. Based on translational research, we identify milk as a major epigenetic modulator of gene expression of the milk recipient. Milk is presented as an epigenetic "doping system" of mammalian development. Milk exosome-derived micro-ribonucleic acids (miRNAs) that target DNA methyltransferases are implicated to play the key role in the upregulation of developmental genes such as FTO, INS, and IGF1. In contrast to miRNA-deficient infant formula, breastfeeding via physiological miRNA transfer provides the appropriate signals for adequate epigenetic programming of the newborn infant. Whereas breastfeeding is restricted to the lactation period, continued consumption of cow's milk results in persistent epigenetic upregulation of genes critically involved in the development of diseases of civilization such as diabesity, neurodegeneration, and cancer. We hypothesize that the same miRNAs that epigenetically increase lactation, upregulate gene expression of the milk recipient via milk-derived miRNAs. It is of critical concern that persistent consumption of pasteurized cow's milk contaminates the human food chain with bovine miRNAs, that are identical to their human analogs. Commercial interest to enhance dairy lactation performance may further increase the epigenetic miRNA burden for the milk consumer.

PRAS40 alleviates neurotoxic prion peptide-induced apoptosis via mTOR-AKT signaling

AIMS

The proline-rich Akt substrate of 40-kDa (PRAS40) protein is a direct inhibitor of mTORC1 and an interactive linker between the Akt and mTOR pathways. The mammalian target of rapamycin (mTOR) is considered to be a central regulator of cell growth and metabolism. Several investigations have demonstrated that abnormal mTOR activity may contribute to the pathogenesis of several neurodegenerative disorders and lead to cognitive deficits.

METHODS

Here, we used the PrP peptide 106-126 (PrP^106-126 ) in a cell model of prion diseases (also known as transmissible spongiform encephalopathies, TSEs) to investigate the mechanisms of mTOR-mediated cell death in prion diseases.

RESULTS

We have shown that, upon stress caused by PrP^106-126 , the mTOR pathway activates and contributes to cellular apoptosis. Moreover, we demonstrated that PRAS40 down-regulates mTOR hyperactivity under stress conditions and alleviates neurotoxic prion peptide-induced apoptosis. The effect of PRAS40 on apoptosis is likely due to an mTOR/Akt signaling.

CONCLUSION

PRAS40 inhibits mTORC1 hyperactivation and plays a key role in protecting cells against neurotoxic prion peptide-induced apoptosis. Thus, PRAS40 is a potential therapeutic target for prion disease.

Predicting the Behavior of Perivascular Epithelioid Cell Tumors of the Uterine Corpus

Perivascular epithelioid cell tumors (PEComas) are rare neoplasms that share phenotypic features with angiomyolipomas, clear cell sugar tumors, and lymphangioleiomyomatosis. They presumably represent the neoplastic counterpart of a yet-unidentified perivascular epithelioid cell that expresses smooth muscle and melanocytic immunomarkers. The uterus is the second most common site of origin for perivascular epithelioid cell tumors, after the retroperitoneum. Although most uterine perivascular epithelioid cell tumors are clinically benign and can be cured by a complete surgical excision, there is a subset characterized by both local and distant dissemination. Unfortunately, no single histopathologic or immunohistochemical parameter can accurately predict the clinical behavior of these tumors, which is why the 2012 World Health Organization classification of tumors of the female reproductive organs suggests the use of several criteria to predict the risk of aggressive clinical behavior. Here we review those perivascular epithelioid cell tumors of the uterine corpus with aggressive clinical behavior reported in the literature, and we discuss their most relevant clinical and histopathologic features.

Promotion Effects of miR-375 on the Osteogenic Differentiation of Human Adipose-Derived Mesenchymal Stem Cells

MicroRNA plays an important role in bone tissue engineering; however, its role and function in osteogenic differentiation warrant further investigation. In this study, we demonstrated that miR-375 was upregulated during the osteogenic differentiation of human adipose-derived mesenchymal stem cells (hASCs). Overexpression of miR-375 significantly enhanced hASCs osteogenesis both in vitro and in vivo, while knockdown of miR-375 inhibited the osteogenic differentiation of hASCs. Mechanistically, microarray analysis revealed DEPTOR as a target of miR-375 in hASCs. Knockdown of DEPTOR accelerated the osteogenic differentiation of hASCs by inhibiting AKT signaling, which mimics miR-375 overexpression. Furthermore, we confirmed that miR-375 regulated osteogenesis by targeting YAP1, and that YAP1 reversely bound to miR-375 promoter to inhibit miR-375 expression. Taken together, our results suggested that miR-375 promoted the osteogenic differentiation of hASCs via the YAP1/DEPTOR/AKT regulatory network, indicating that miR-375-targeted therapy might be a valuable approach to promote bone regeneration.

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miR-375 promotes osteogenic differentiation of hASCs in vitro and in vivo

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miR-375 inhibits AKT signaling by directly targeting DEPTOR

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YAP1 and miR-375 form a negative feedback loop to regulate hASCs osteogenesis

mTOR function and therapeutic targeting in breast cancer

The mTOR pathway was discovered in the late 1970s after the compound and natural inhibitor of mTOR, rapamycin was isolated from the bacterium Streptomyces hygroscopicus. mTOR is serine/threonine kinase belonging to the phosphoinositide 3-kinase related kinase (PIKK) family. It forms two distinct complexes; mTORC1 and mTORC2. mTORC1 has a key role in regulating protein synthesis and autophagy whilst mTORC2 is involved in regulating kinases of the AGC family. mTOR signaling is often over active in multiple cancer types including breast cancer. This can involve mutations in mTOR itself but more commonly, in breast cancer, this is related to an increase in activity of ErbB family receptors or alterations and mutations of PI3K signaling. Rapamycin and its analogues (rapalogues) bind to the intercellular receptor FKBP12, and then predominantly inhibit mTORC1 signaling via an allosteric mechanism. Research has shown that inhibition of mTOR is a useful strategy in tackling cancers, with it acting to slow tumor growth and limit the spread of a cancer. Rapalogues have now made their way into the clinic with the rapalogue everolimus (RAD-001/Afinitor) approved for use in conjunction with exemestane, in post-menopausal breast cancer patients with advanced disease who are HER-2 negative (normal expression), hormone receptor positive and whose prior treatment with non-steroidal aromatase inhibitors has failed. Testing across multiple trials has proven that everolimus and other rapalogues are a viable way of treating certain types of cancer. However, rapalogues have shown some drawbacks both in research and clinically, with their use often activating feedback pathways that counter their usefulness. As such, new types of inhibitors are being explored that work via different mechanisms, including inhibitors that are ATP competitive with mTOR and which act to perturb signaling from both mTOR complexes.

Targeting autophagy as a strategy for drug discovery and therapeutic modulation

Autophagy is a self-protective mechanism of living cells or organisms under various stress conditions. Studies of human genetics and pathophysiology have implicated that alterations in autophagy affect the context of cellular homeostasis and disease-associated phenotypes. The molecular components of autophagy are currently being explored as new pharmacologic targets for drug development and therapeutic intervention of various diseases. Drugs that restore the normal autophagic pathways have the potential for effectively treating human disorders that depend on aberrations of autophagy. Here, we review the role of autophagy and its alterations in the pathogenesis of diverse diseases, and drug discovery strategies for modulating autophagy for therapeutic benefits as well as possible safety concerns and caveats associated with such approaches.

Inhibition of CYFIP2 promotes gastric cancer cell proliferation and chemoresistance to 5-fluorouracil through activation of the Akt signaling pathway

Gastric cancer is a common gastrointestinal malignancy that accounts for a notable proportion of cancer-associated mortalities worldwide. Cytoplasmic fragile X mental retardation 1-interacting protein 2 (CYFIP2) is a novel p53-mediated pro-apoptotic protein whose expression is decreased in gastric cancer. However, whether decreased expression of CYFIP2 contributes to gastric carcinogenesis remains unclear. In order to mimic in vivo gastric tumor CYFIP2 expression levels, the present study used short hairpin RNA targeting CYFIP2 mRNA to silence CYFIP2 expression in MGC803 and SGC7901 gastric cancer cells. Gastric cancer cells with constitutively decreased CYFIP2 expression levels were successfully established. It was observed that CYFIP2 knockdown promoted proliferation and colony formation, and inhibited apoptosis in these cells. Furthermore, 5-fluorouracil (5-FU)-induced apoptosis was decreased following inhibition of CYFIP2 expression. In SGC7901 cells, protein expression of active caspase-3 and cleaved poly (ADP-ribose) polymerase was increased following treatment with 5-FU, while phosphorylated Akt serine/threonine kinase 1 (Akt) levels were decreased. These 5-FU-induced effects were reduced following CYFIP2 knockdown. In addition, inhibition of the Akt signaling pathway using the Akt inhibitor LY294002 restored CYFIP2-knockdown SGC7901 cell chemosensitivity to 5-FU. The results of the present study demonstrate that decreased CYFIP2 expression is associated with increased gastric tumor growth in vitro and that CYFIP2 knockdown-induced activation of the Akt pro-survival signaling pathway confers resistance to 5-FU-based chemotherapy in gastric cancer cells. Therefore, combined treatment with an Akt inhibitor and chemotherapeutic drugs may improve the efficacy of gastric cancer therapy in patients with low CYFIP2 expression.

The dual specificity PI3K/mTOR inhibitor PKI-587 displays efficacy against T-cell acute lymphoblastic leukemia (T-ALL)

Although significant improvements have been made in the treatment of acute lymphoblastic leukemia (ALL), there is a substantial subset of high-risk T-cell ALL (T-ALL) patients with relatively poor prognosis. Like in other leukemia types, alterations of the PI3K/mTOR pathway are predominant in ALL which is also responsible for treatment failure and relapse. In this study, we show that relapsed T-ALL patients display an enrichment of the PI3K/mTOR pathway. Using a panel of inhibitors targeting multiple components of the PI3K/mTOR pathway, we observed that the dual-specific PI3K/mTOR inhibitor PKI-587 was the most selective inhibitor for T-ALL cells dependent on the PI3K/mTOR pathway. Furthermore, we observed that PKI-587 blocked proliferation and colony formation of T-ALL cell lines. Additionally, PKI-587 selectively abrogated PI3K/mTOR signaling without affecting MAPK signaling both in in vitro and in vivo. Inhibition of the PI3K/mTOR pathway using PKI-587 delayed tumor progression, reduced tumor load and enhanced the survival rate in immune-deficient mouse xenograft models without inducing weight loss in the inhibitor treated mice. This preclinical study shows beneficial effects of PKI-587 on T-ALL that warrants further investigation in the clinical setting.

Disruption of the vacuolar-type H+-ATPase complex in liver causes MTORC1-independent accumulation of autophagic vacuoles and lysosomes

The vacuolar-type H⁺-translocating ATPase (v-H⁺-ATPase) has been implicated in the amino acid-dependent activation of the mechanistic target of rapamycin complex 1 (MTORC1), an important regulator of macroautophagy. To reveal the mechanistic links between the v-H⁺-ATPase and MTORC1, we destablilized v-H⁺-ATPase complexes in mouse liver cells by induced deletion of the essential chaperone ATP6AP2. ATP6AP2-mutants are characterized by massive accumulation of endocytic and autophagic vacuoles in hepatocytes. This cellular phenotype was not caused by a block in endocytic maturation or an impaired acidification. However, the degradation of LC3-II in the knockout hepatocytes appeared to be reduced. When v-H⁺-ATPase levels were decreased, we observed lysosome association of MTOR and normal signaling of MTORC1 despite an increase in autophagic marker proteins. To better understand why MTORC1 can be active when v-H⁺-ATPase is depleted, the activation of MTORC1 was analyzed in ATP6AP2-deficient fibroblasts. In these cells, very little amino acid-elicited activation of MTORC1 was observed. In contrast, insulin did induce MTORC1 activation, which still required intracellular amino acid stores. These results suggest that in vivo the regulation of macroautophagy depends not only on v-H⁺-ATPase-mediated regulation of MTORC1.

Nutrient sensing and TOR signaling in yeast and mammals

Coordinating cell growth with nutrient availability is critical for cell survival. The evolutionarily conserved TOR (target of rapamycin) controls cell growth in response to nutrients, in particular amino acids. As a central controller of cell growth, mTOR (mammalian TOR) is implicated in several disorders, including cancer, obesity, and diabetes. Here, we review how nutrient availability is sensed and transduced to TOR in budding yeast and mammals. A better understanding of how nutrient availability is transduced to TOR may allow novel strategies in the treatment for mTOR-related diseases.

Kinetic Modeling and Analysis of the Akt/Mechanistic Target of Rapamycin Complex 1 (mTORC1) Signaling Axis Reveals Cooperative, Feedforward Regulation

Mechanistic target of rapamycin complex 1 (mTORC1) controls biosynthesis and has been implicated in uncontrolled cell growth in cancer. Although many details of mTORC1 regulation are well understood, a systems-level, predictive framework synthesizing those details is currently lacking. We constructed various mathematical models of mTORC1 activation mediated by Akt and aligned the model outputs to kinetic data acquired for growth factor-stimulated cells. A model based on a putative feedforward loop orchestrated by Akt consistently predicted how the pathway was altered by depletion of key regulatory proteins. Analysis of the successful model also elucidates two dynamical motifs: neutralization of a negative regulator, which characterizes how Akt indirectly activates mTORC1, and seesaw enzyme regulation, which describes how activated and inhibited states of mTORC1 are controlled in concert to produce a nonlinear, ultrasensitive response. Such insights lend quantitative understanding of signaling networks and their precise manipulation in various contexts.

Evaluating the mTOR Pathway in Physiological and Pharmacological Settings

Mammalian/mechanistic target of rapamycin (mTOR) is an evolutionarily conserved genuine protein kinase, which phosphorylates serine/threonine in response to growth factors and nutrients. It functions as a catalytic core in two distinct multiprotein complexes: mTOR complex 1 (mTORC1) and mTOR complex 2 (mTORC2). mTORC1 promotes cell growth and proliferation by positively regulating translation, transcription, and lipid biosynthesis in response to growth factors and amino acids, whereas it inhibits autophagy, an essential degradation and recycling pathway. mTORC2 regulates cell survival and cytoskeleton organization. Mechanistic insights into the function and regulation of mTOR complexes have been provided in various experimental settings and monitoring mTOR activity has been a most valuable way to judge whether levels of environmental cues such nutrients and growth factors can satisfy cellular needs for cell growth, proliferation, and autophagic response. Here, we describe useful methods to access mTOR activity in different experimental settings.

Gene-environment interactions in development and disease

Developmental geneticists continue to make substantial jumps in our understanding of the genetic pathways that regulate development. This understanding stems predominantly from analyses of genetically tractable model organisms developing in laboratory environments. This environment is vastly different from that in which human development occurs. As such, most causes of developmental defects in humans are thought to involve multifactorial gene-gene and gene-environment interactions. In this review, we discuss how gene-environment interactions with environmental teratogens may predispose embryos to structural malformations. We elaborate on the growing number of gene-ethanol interactions that might underlie susceptibility to fetal alcohol spectrum disorders. WIREs Dev Biol 2017, 6:e247. doi: 10.1002/wdev.247 For further resources related to this article, please visit the WIREs website.

Identification of DEP domain-containing proteins by a machine learning method and experimental analysis of their expression in human HCC tissues

The Dishevelled/EGL-10/Pleckstrin (DEP) domain-containing (DEPDC) proteins have seven members. However, whether this superfamily can be distinguished from other proteins based only on the amino acid sequences, remains unknown. Here, we describe a computational method to segregate DEPDCs and non-DEPDCs. First, we examined the Pfam numbers of the known DEPDCs and used the longest sequences for each Pfam to construct a phylogenetic tree. Subsequently, we extracted 188-dimensional (188D) and 20D features of DEPDCs and non-DEPDCs and classified them with random forest classifier. We also mined the motifs of human DEPDCs to find the related domains. Finally, we designed experimental verification methods of human DEPDC expression at the mRNA level in hepatocellular carcinoma (HCC) and adjacent normal tissues. The phylogenetic analysis showed that the DEPDCs superfamily can be divided into three clusters. Moreover, the 188D and 20D features can both be used to effectively distinguish the two protein types. Motif analysis revealed that the DEP and RhoGAP domain was common in human DEPDCs, human HCC and the adjacent tissues that widely expressed DEPDCs. However, their regulation was not identical. In conclusion, we successfully constructed a binary classifier for DEPDCs and experimentally verified their expression in human HCC tissues.

Mitochondria and Cancer

Mitochondria are bioenergetic, biosynthetic, and signaling organelles that are integral in stress sensing to allow for cellular adaptation to the environment. Therefore, it is not surprising that mitochondria are important mediators of tumorigenesis, as this process requires flexibility to adapt to cellular and environmental alterations in addition to cancer treatments. Multiple aspects of mitochondrial biology beyond bioenergetics support transformation, including mitochondrial biogenesis and turnover, fission and fusion dynamics, cell death susceptibility, oxidative stress regulation, metabolism, and signaling. Thus, understanding mechanisms of mitochondrial function during tumorigenesis will be critical for the next generation of cancer therapeutics.

Intestinal Epithelial-Specific mTORC1 Activation Enhances Intestinal Adaptation After Small Bowel Resection

BACKGROUND & AIMS

Intestinal adaptation is a compensatory response to the massive loss of small intestine after surgical resection. We investigated the role of intestinal epithelial cell-specific mammalian target of rapamycin complex 1 (i-mTORC1) in intestinal adaptation after massive small bowel resection (SBR).

METHODS

We performed 50% proximal SBR on mice to study adaptation. To manipulate i-mTORC1 activity, Villin-Cre^ER transgenic mice were crossed with tuberous sclerosis complex (TSC)1^flox/flox or Raptor^flox/flox mice to inducibly activate or inactivate i-mTORC1 activity with tamoxifen. Western blot was used to confirm the activity of mTORC1. Crypt depth and villus height were measured to score adaptation. Immunohistochemistry was used to investigate differentiation and rates of crypt proliferation.

RESULTS

After SBR, mice treated with systemic rapamycin showed diminished structural adaptation, blunted crypt cell proliferation, and significant body weight loss. Activating i-mTORC1 via TSC1 deletion induced larger hyperproliferative crypts and disorganized Paneth cells without a significant change in villus height. After SBR, ablating TSC1 in intestinal epithelium induced a robust villus growth with much stronger crypt cell proliferation, but similar body weight recovery. Acute inactivation of i-mTORC1 through deletion of Raptor did not change crypt cell proliferation or mucosa structure, but significantly reduced lysozyme/matrix metalloproteinase-7-positive Paneth cell and goblet cell numbers, with increased enteroendocrine cells. Surprisingly, ablation of intestinal epithelial cell-specific Raptor after SBR did not affect adaptation or crypt proliferation, but dramatically reduced body weight recovery after surgery.

CONCLUSIONS

Systemic, but not intestinal-specific, mTORC1 is important for normal adaptation responses to SBR. Although not required, forced enterocyte mTORC1 signaling after resection causes an enhanced adaptive response.

Tracking the Activity of mTORC1 in Living Cells Using Genetically Encoded FRET-based Biosensor TORCAR

Mechanistic target of rapamycin complex 1 (mTORC1) is a highly conserved serine/threonine protein kinase that responds to multiple distinct signals (e.g., growth factors, amino acids, stress, and energy level) and coordinates cell growth and proliferation. The underlying molecular mechanisms by which these stimuli regulate the activity of mTORC1 are still not fully understood. The spatial compartmentalization of mTORC1 signaling has been suggested as an important mechanism for mTORC1 to achieve the signal specificity and efficiency. To examine the spatial regulation of the activity of mTORC1 in live cells, we describe a protocol using a newly developed molecular tool, a genetically encoded fluorescence resonance energy transfer (FRET)-based mTORC1 activity reporter, TORCAR. When expressed in the cell, TORCAR acts as a surrogate substrate of mTORC1, and exhibits a change in FRET in response to phosphorylation by mTORC1. Genetically targeting TORCAR to specific subcellular locations further allows for the characterization of spatial compartmentalized mTORC1 signaling. © 2016 by John Wiley & Sons, Inc.

New developments in the genetics and pathogenesis of tumours in tuberous sclerosis complex

In just the past 5 years, dramatic changes have occurred in the clinical management of tuberous sclerosis complex (TSC). Detailed knowledge about the role of the TSC proteins in regulating the activity of the mammalian target of rapamycin complex 1 (mTORC1) underlies this paradigm-shifting progress. Advances continue to be made in understanding the genetic pathogenesis of the different tumours that occur in TSC, including pivotal discoveries using next-generation sequencing (NGS). For example, the pathogenesis of angiofibromas is now known to involve UV-induced mutations, and the pathogenesis of multifocal renal cell carcinoma (RCC) in TSC is now known to result from distinct second-hit mutations. In parallel, the pathological features of TSC-associated tumours, including TSC-associated renal cell carcinoma, continue to be defined, despite the fact that TSC was first described 180 years ago. Here, we review recent discoveries related to the pathological features and genetic pathogenesis of TSC-associated tumours. Copyright © 2016 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

A systems study reveals concurrent activation of AMPK and mTOR by amino acids

Amino acids (aa) are not only building blocks for proteins, but also signalling molecules, with the mammalian target of rapamycin complex 1 (mTORC1) acting as a key mediator. However, little is known about whether aa, independently of mTORC1, activate other kinases of the mTOR signalling network. To delineate aa-stimulated mTOR network dynamics, we here combine a computational–experimental approach with text mining-enhanced quantitative proteomics. We report that AMP-activated protein kinase (AMPK), phosphatidylinositide 3-kinase (PI3K) and mTOR complex 2 (mTORC2) are acutely activated by aa-readdition in an mTORC1-independent manner. AMPK activation by aa is mediated by Ca²⁺/calmodulin-dependent protein kinase kinase β (CaMKKβ). In response, AMPK impinges on the autophagy regulators Unc-51-like kinase-1 (ULK1) and c-Jun. AMPK is widely recognized as an mTORC1 antagonist that is activated by starvation. We find that aa acutely activate AMPK concurrently with mTOR. We show that AMPK under aa sufficiency acts to sustain autophagy. This may be required to maintain protein homoeostasis and deliver metabolite intermediates for biosynthetic processes.

mTORC1 is known to mediate the signalling activity of amino acids. Here, the authors combine modelling with experiments and find that amino acids acutely stimulate mTORC2, IRS/PI3K and AMPK, independently of mTORC1. AMPK activation through CaMKKβ sustains autophagy under non-starvation conditions.

Rac1-Mediated DNA Damage and Inflammation Promote Nf2 Tumorigenesis but Also Limit Cell-Cycle Progression

Merlin encoded by the Nf2 gene is a bona fide tumor suppressor that has been implicated in regulation of both the Hippo-Yap and Rac1-Pak1 pathways. Using genetically engineered murine liver models, we show that co-deletion of Rac1 with Nf2 blocks tumor initiation but paradoxically exacerbates hepatomegaly induced by Nf2 loss, which can be suppressed either by treatment with pro-oxidants or by co-deletion of Yap. Our results suggest that while Yap acts as the central driver of proliferation during Nf2 tumorigenesis, Rac1 primarily functions as an inflammation switch by inducing reactive oxygen species that, on one hand, induce nuclear factor κB signaling and expression of inflammatory cytokines, and on the other activate p53 checkpoint and senescence programs dampening the cyclin D1-pRb-E2F1 pathway. Interestingly, senescence markers are associated with benign NF2 tumors but not with malignant NF2 mutant mesotheliomas, suggesting that senescence may underlie the benign nature of most NF2 tumors.

Bone muscle crosstalk targets muscle regeneration pathway regulated by core circadian transcriptional repressors DEC1 and DEC2

Deletion of proprotein convertase Mbtps1 in bone osteocytes leads to a significant postnatal increase in skeletal muscle size and contractile function, while causing only a 25% increase in stiffness in long bones. Concerns about leakiness in skeletal muscle were discounted since Cre recombinase expression does not account for our findings, and, Mbtps1 protein and mRNA is not deleted. Interestingly, the response of normal skeletal muscle to exercise and the regenerative response of skeletal muscle to the deletion of Mbtps1 in bone share some key regulatory features including a preference for slow twitch muscle fibers. In addition, transcriptional regulators PPAR, PGC-1α, LXR, and repressors DEC1 and DEC2 all occupy central positions within these two pathways. We hypothesize that the age-dependent muscle phenotype in Dmp1-Cre Mbtps1 cKO mice is due to bone→muscle crosstalk. Many of the myogenic genes altered in this larger and functionally improved muscle are regulated by circadian core transcriptional repressors DEC1 and DEC2, and furthermore, display a temporal coordination with Dec1 and Dec2 expression consistent with a regulatory co-dependency. These considerations lead us to propose that Dmp1-Cre Mbtps1 cKO osteocytes activate myogenesis by increased release of an activator of muscle PPAR-gamma, for example, PGE₂ or sphingosine-1-P, or, by diminished release of an inhibitor of LXR, for example, long-chain polyunsaturated fatty acids. We hope that further investigation of these interacting pathways in the Dmp1-Cre Mbtps1 cKO model will lead to clinically translatable findings applicable to age-related sarcopenia and other muscle wasting syndromes.

Tumor Metabolism, the Ketogenic Diet and β-Hydroxybutyrate: Novel Approaches to Adjuvant Brain Tumor Therapy

Malignant brain tumors are devastating despite aggressive treatments such as surgical resection, chemotherapy and radiation therapy. The average life expectancy of patients with newly diagnosed glioblastoma is approximately ~18 months. It is clear that increased survival of brain tumor patients requires the design of new therapeutic modalities, especially those that enhance currently available treatments and/or limit tumor growth. One novel therapeutic arena is the metabolic dysregulation that results in an increased need for glucose in tumor cells. This phenomenon suggests that a reduction in tumor growth could be achieved by decreasing glucose availability, which can be accomplished through pharmacological means or through the use of a high-fat, low-carbohydrate ketogenic diet (KD). The KD, as the name implies, also provides increased blood ketones to support the energy needs of normal tissues. Preclinical work from a number of laboratories has shown that the KD does indeed reduce tumor growth in vivo. In addition, the KD has been shown to reduce angiogenesis, inflammation, peri-tumoral edema, migration and invasion. Furthermore, this diet can enhance the activity of radiation and chemotherapy in a mouse model of glioma, thus increasing survival. Additional studies in vitro have indicated that increasing ketones such as β-hydroxybutyrate (βHB) in the absence of glucose reduction can also inhibit cell growth and potentiate the effects of chemotherapy and radiation. Thus, while we are only beginning to understand the pluripotent mechanisms through which the KD affects tumor growth and response to conventional therapies, the emerging data provide strong support for the use of a KD in the treatment of malignant gliomas. This has led to a limited number of clinical trials investigating the use of a KD in patients with primary and recurrent glioma.

mTOR Signaling Confers Resistance to Targeted Cancer Drugs

Cancer is a complex disease and a leading cause of death worldwide. Extensive research over decades has led to the development of therapies that target cancer-specific signaling pathways. However, the clinical benefits of such drugs are at best transient due to tumors displaying intrinsic or adaptive resistance. The underlying compensatory pathways that allow cancer cells to circumvent a drug blockade are poorly understood. We review here recent studies suggesting that mammalian TOR (mTOR) signaling is a major compensatory pathway conferring resistance to many cancer drugs. mTOR-mediated resistance can be cell-autonomous or non-cell-autonomous. These findings suggest that mTOR signaling should be monitored routinely in tumors and that an mTOR inhibitor should be considered as a co-therapy.

Targeting mTOR signaling by polyphenols: A new therapeutic target for ageing

Current ageing research is aimed not only at the promotion of longevity, but also at improving ‎health span‎ through the‎ discovery and development‎ of new therapeutic strategies‎‏‎ by investigating ‎molecular and ‎cellular ‎pathways involved in cellular senescence.‎ Understanding the mechanism of action ‎of ‎polyphenolic compounds targeting mTOR (mechanistic target of rapamycin) and related pathways opens up new directions ‎‎to revolutionize ways to slow down the ‎onset and development of age-dependent degeneration. Herein, we will ‎discuss the mechanisms by which polyphenols can delay the‎ molecular ‎pathogenesis of ageing via manipulation or more specifically inhibition of mTOR-signaling pathways. We will also discuss the implications of polyphenols in targeting mTOR and its related ‎pathways‎‎ on ‎health life span extension and longevity.‎.

Regulation of mTORC1 by lysosomal calcium and calmodulin

Blockade of lysosomal calcium release due to lysosomal lipid accumulation has been shown to inhibit mTORC1 signaling. However, the mechanism by which lysosomal calcium regulates mTORC1 has remained undefined. Herein we report that proper lysosomal calcium release through the calcium channel TRPML1 is required for mTORC1 activation. TRPML1 depletion inhibits mTORC1 activity, while overexpression or pharmacologic activation of TRPML1 has the opposite effect. Lysosomal calcium activates mTORC1 by inducing association of calmodulin (CaM) with mTOR. Blocking the interaction between mTOR and CaM by antagonists of CaM significantly inhibits mTORC1 activity. Moreover, CaM is capable of stimulating the kinase activity of mTORC1 in a calcium-dependent manner in vitro. These results reveal that mTOR is a new type of CaM-dependent kinase, and TRPML1, lysosomal calcium and CaM play essential regulatory roles in the mTORC1 signaling pathway.

mTORC2 activation is regulated by the urokinase receptor (uPAR) in bladder cancer

Mammalian target of rapamycin complex 2 (mTORC2) has been identified as a major regulator of bladder cancer cell migration and invasion. Upstream pathways that mediate mTORC2 activation remain poorly defined. Urokinase-type plasminogen activator receptor (uPAR) is a GPI-anchored membrane protein and known activator of cell-signaling. We identified increased uPAR expression in 94% of invasive human bladder cancers and in 54-71% of non-invasive bladder cancers, depending on grade. Normal urothelium was uPAR-immunonegative. Analysis of publicly available datasets identified uPAR gene amplification or mRNA upregulation in a subset of bladder cancer patients with reduced overall survival. Using biochemical approaches, we showed that uPAR activates mTORC2 in bladder cancer cells. Highly invasive bladder cancer cell lines, including T24, J82 and UM-UC-3 cells, showed increased uPAR mRNA expression and protein levels compared with the less aggressive cell lines, UROtsa and RT4. uPAR gene-silencing significantly reduced phosphorylation of Serine-473 in Akt, an mTORC2 target. uPAR gene-silencing also reduced bladder cancer cell migration and Matrigel invasion. S473 phosphorylation was observed by immunohistochemistry in human bladder cancers only when the tumors expressed high levels of uPAR. S473 phosphorylation was not controlled by uPAR in bladder cancer cell lines that are PTEN-negative; however, this result probably did not reflect altered mTORC2 regulation. Instead, PTEN deficiency de-repressed alternative kinases that phosphorylate S473. Our results suggest that uPAR and mTORC2 are components of a single cell-signaling pathway. Targeting uPAR or mTORC2 may be beneficial in patients with bladder cancer.

Critical Functions of the Lysosome in Cancer Biology

Lysosomes (or lytic bodies) were so named because they contain high levels of hydrolytic enzymes. Lysosome function and dysfunction have been found to play important roles in human disease, including cancer; however, the ways in which lysosomes contribute to tumorigenesis and cancer progression are still being uncovered. Beyond serving as a cellular recycling center, recent evidence suggests that the lysosome is involved in energy homeostasis, generating building blocks for cell growth, mitogenic signaling, priming tissues for angiogenesis and metastasis formation, and activating transcriptional programs. This review examines emerging knowledge of how lysosomal processes contribute to the hallmarks of cancer and highlights vulnerabilities that might be exploited for cancer therapy.

Macrophage Apoptosis and Efferocytosis in the Pathogenesis of Atherosclerosis

Macrophage apoptosis and the ability of macrophages to clean up dead cells, a process called efferocytosis, are crucial determinants of atherosclerosis lesion progression and plaque stability. Environmental stressors initiate endoplasmic reticulum (ER) stress and activate the unfolded protein response (UPR). Unresolved ER stress with activation of the UPR initiates apoptosis. Macrophages are resistant to apoptotic stimuli, because of activity of the PI3K/Akt pathway. Macrophages express 3 Akt isoforms, Akt1, Akt2 and Akt3, which are products of distinct but homologous genes. Akt displays isoform-specific effects on atherogenesis, which vary with different vascular cell types. Loss of macrophage Akt2 promotes the anti-inflammatory M2 phenotype and reduces atherosclerosis. However, Akt isoforms are redundant with regard to apoptosis. c-Jun NH₂-terminal kinase (JNK) is a pro-apoptotic effector of the UPR, and the JNK1 isoform opposes anti-apoptotic Akt signaling. Loss of JNK1 in hematopoietic cells protects macrophages from apoptosis and accelerates early atherosclerosis. IκB kinase α (IKKα, a member of the serine/threonine protein kinase family) plays an important role in mTORC2-mediated Akt signaling in macrophages, and IKKα deficiency reduces macrophage survival and suppresses early atherosclerosis. Efferocytosis involves the interaction of receptors, bridging molecules, and apoptotic cell ligands. Scavenger receptor class B type I is a critical mediator of macrophage efferocytosis via the Src/PI3K/Rac1 pathway in atherosclerosis. Agonists that resolve inflammation offer promising therapeutic potential to promote efferocytosis and prevent atherosclerotic clinical events. (Circ J 2016; 80: 2259-2268).

Recent advances in targeting mTOR signaling pathway using small molecule inhibitors

Targeted-based cancer therapy (TBCT) or personalized medicine is one of the main treatment modalities for cancer that has been developed to decrease the undesirable effects of chemotherapy. Targeted therapy inhibits the growth of tumor cells by interrupting with particular molecules required for tumorigenesis and proliferation of tumor cells rather than interfering with dividing normal cells. Therefore, targeted therapies are anticipated to be more efficient than former tumor treatment agents with minimal side effects on non-tumor cells. Small molecule inhibitors (SMIs) are currently one of the most investigated anti-tumor agents of TBCT. These small organic agents target several vital molecules involved in cell biological processes and induce target cells apoptosis and necrosis. Mechanistic (mammalian) target of rapamycin (mTOR) complexes (mTORC1/2) control different intracellular processes, including growth, proliferation, angiogenesis and metabolism. Signaling pathways, in which mTOR complexes are involved in are usually dysregulated in various tumors and have been shown to be ideal targets for SMIs. Currently, different mTOR-SMIs are in the clinic for the treatment of cancer patients, and several others are in preclinical or clinical settings. In this review, we summarize recent advances in developing different mTOR inhibitors, which are currently in preclinical and clinical investigations or have been approved for cancer treatment.

Array-CGH diagnosis in ovarian failure: identification of new molecular actors for ovarian physiology

Background

Ovarian failure (OF) is considered premature if it occurs before the age of 40.

This study investigates the genetic aetiology underlying OF in women under the age of 40 years.

Methods

We conducted an experimental prospective study performing all genome microarrays in 60 patients younger than 40 years presenting an OF revealed by a decrease of circulating Anti-Müllerian Hormone (AMH) and leading to an oocyte donation program.

Results

We identified nine significant copy number variations (CNVs) including candidate genes potentially implicated in reproductive function. These genes are principally involved in cell division and chromosome segregation (SYCE1, CLASP1, CENP-A, CDC16), in ciliary development and/or function (RSPH1, KIF24), are linked with known gonadal genes or expressed in female genital tract (CSMD1, SEMA6D, KIAA1324).

Conclusions

Our data strengthen the idea that microarrays should be used in combination with karyotype for aetiological assessment of patients with OF. This analysis may have a therapeutic impact as the identification of new molecular actors for gonadal development or ovarian physiology is useful for the prediction of an ovarian reserve decline and makes possible preventive fertility preservation.

Mechanistic target of rapamycin complex 1 is an essential mediator of metabolic and mitogenic effects of fibroblast growth factor 19 in hepatoma cells

Fibroblast growth factor 19 (FGF19) is an important postprandial enterokine which regulates liver metabolism and hepatocyte proliferation. However, the precise mechanism by which FGF19 regulates these cellular effects is poorly understood. Given that mechanistic target of rapamycin complex 1 (mTORC1) regulates numerous postprandial adaptations, we investigated the potential role of mTORC1 in FGF19 action. We found that FGF19 activated mTORC1 in HepG2 and HuH7 human hepatoma cells, differentiated 3T3-L1 adipocytes and mouse liver. FGF19 activates the mTORC1-p70S6K and extracellular signal-regulated kinase (Erk)-p90RSK pathways independently to regulate S6 in an additive manner in hepatoma cells, but it uses mTORC1 as the primary pathway to regulate S6 in 3T3-L1 adipocytes. Thus, mTORC1 is a novel mediator of FGF19 signaling, which can act in parallel with Erk or function as the primary pathway to regulate S6. The FGF19-induced mTORC1 pathway requires amino acids for efficient signaling; thus, involvement of mTORC1 confers amino acid sensitivity to FGF19 signaling. Although Akt and Erk are known to activate mTORC1, we found that FGF19 signals to mTORC1 through a third recently identified mTORC1 regulator, Ras-like (Ral) protein. Pharmacological or genetic inhibition of RalA or RalB abolished FGF19-induced mTORC1 activation, demonstrating that Ral proteins are required for FGF19 to activate mTORC1. FGF19 induced metabolic gene expression, fatty acid oxidation, cell growth, and proliferation in HepG2 cells; and these effects were abolished by mTORC1 inhibition, demonstrating an essential role of mTORC1 in FGF19 action.

CONCLUSION

mTORC1 is a novel and essential mediator of FGF19 action on metabolic and mitogenic programs; thus, the involvement of mTORC1 in FGF19 signaling is an important factor to consider when targeting the pathway for cancer or diabetes therapy. (Hepatology 2016;64:1289-1301).

PI3K signaling in Leishmania infections

PI3K signaling plays a role in the host response to Leishmania infections. At the cellular level PI3K signaling is engaged by the parasite to control several cellular processes, which ensures parasite persistence. At the systemic level, there is evidence that recruitment of regulatory cells into lesions is impaired in the absence of robust PI3K signaling. In this mini-review the more recent studies that investigated the roles of PI3K signaling in Leishmania infections are discussed.

Perspective: The Potential Role of Essential Amino Acids and the Mechanistic Target of Rapamycin Complex 1 (mTORC1) Pathway in the Pathogenesis of Child Stunting

Stunting is the best summary measure of chronic malnutrition in children. Approximately one-quarter of children under age 5 worldwide are stunted. Lipid-based or micronutrient supplementation has little to no impact in reducing stunting, which suggests that other critical dietary nutrients are missing. A dietary pattern of poor-quality protein is associated with stunting. Stunted children have significantly lower circulating essential amino acids than do nonstunted children. Inadequate dietary intakes of essential amino acids could adversely affect growth, because amino acids are required for synthesis of proteins. The master growth regulation pathway, the mechanistic target of rapamycin complex 1 (mTORC1) pathway, is exquisitely sensitive to amino acid availability. mTORC1 integrates cues such as nutrients, growth factors, oxygen, and energy to regulate growth of bone, skeletal muscle, nervous system, gastrointestinal tract, hematopoietic cells, immune effector cells, organ size, and whole-body energy balance. mTORC1 represses protein and lipid synthesis and cell and organismal growth when amino acids are deficient. Over the past 4 decades, the main paradigm for child nutrition in developing countries has been micronutrient malnutrition, with relatively less attention paid to protein. In this Perspective, we present the view that essential amino acids and the mTORC1 pathway play a key role in child growth. The current assumption that total dietary protein intake is adequate for growth among most children in developing countries needs re-evaluation.

BEZ235: When Promising Science Meets Clinical Reality

An article in a recent issue of The Oncologist reports the results of a phase I clinical trial of BEZ235 in patients with advanced renal cell carcinoma. The study was terminated early due to toxicity and a lack of clinical efficacy. The rapid and concise publication of this type of clinical result is necessary for effective collaboration and, ultimately, better outcomes for cancer patients.

The ERK1/2 and mTORC1 Signaling Pathways Are Involved in the Muscarinic Acetylcholine Receptor-Mediated Proliferation of SNU-407 Colon Cancer Cells

Muscarinic acetylcholine receptors (mAChRs) regulate diverse cellular functions, including cell growth and proliferation, via multiple signaling pathways. Previously, we showed that mAChRs stimulate the MEK1/2-ERK1/2-RSK pathway in SNU-407 colon cancer cells and subsequently promote cell proliferation. In this study, we provide evidence that the PI3K-Akt-mTORC1-S6K1 pathway is activated by mAChRs in SNU-407 cells and that this pathway is associated with protein biosynthesis and cell proliferation. When the cells were treated with the cholinergic agonist carbachol, Akt was activated in a dose- and time-dependent fashion. This carbachol effect was almost completely blocked by the PI3K inhibitor LY294002, implying that PI3K is responsible for the Akt activation. S6K1, a major downstream target of mTORC1, was also activated by carbachol in a temporal profile similar to that of the Akt activation. This carbachol-stimulated S6K1 activation was abrogated by LY294002 or the mTORC1 inhibitor rapamycin, supporting the notion that mAChRs mediate S6K1 activation via the PI3K-Akt-mTORC1 pathway. We observed that global protein biosynthesis, monitored by puromycin incorporation, was strongly increased by carbachol in an atropine-sensitive manner. Inhibition experiments indicated that the ERK1/2 and mTORC1 signaling pathways may be involved in carbachol-stimulated global protein biosynthesis. We also found that treating SNU-407 cells with LY294002 or rapamycin significantly suppressed carbachol-stimulated cell proliferation. In the presence of the MEK1/2 inhibitor U0126, cell proliferation was further reduced by rapamycin treatment. Our data thus suggest that both the MEK1/2-ERK1/2 and mTORC1 pathways play important roles in mAChR-mediated cell proliferation in SNU-407 colon cancer cells. J. Cell. Biochem. 117: 2854-2863, 2016. © 2016 Wiley Periodicals, Inc.

Tumor mutational analysis of GOG248, a phase II study of temsirolimus or temsirolimus and alternating megestrol acetate and tamoxifen for advanced endometrial cancer (EC): An NRG Oncology/Gynecologic Oncology Group study

OBJECTIVE

Rapamycin analogs have reproducible but modest efficacy in endometrial cancer (EC). Identification of molecular biomarkers that predict benefit could guide clinical development.

METHODS

Fixed primary tissue and whole blood were collected prospectively from patients enrolled on GOG 248. DNA was isolated from macro-dissected tumors and blood; next-generation sequence analysis was performed on a panel of cancer related genes. Associations between clinical outcomes [response rate (RR) 20%; progression-free survival (PFS) median 4.9months] and mutations (PTEN, PIK3CA, PIK3R1, KRAS, CTNNB1, AKT1, TSC1, TSC2, NF1, FBXW7) were explored.

RESULTS

Sequencing data was obtained from tumors of 55 of the 73 enrolled pts. Mutation rates were consistent with published reports: mutations in PTEN (45%), PIK3CA (29%), PIK3R1 (24%), K-RAS (16%), CTNNB1 (18%) were common and mutations in AKT1 (4%), TSC1 (2%), TSC2 (2%), NF1 (9%) and FBXW7 (4%) were less common. Increased PFS (HR 0.16; 95% CI 0.01-0.78) and RR (response difference 0.83; 95% CI 0.03-0.99) were noted for AKT1 mutation. An increase in PFS (HR 0.46; 95% CI 0.20-0.97) but not RR (response difference 0.00, 95% CI -0.34-0.34) was identified for CTNNB1 mutation. Both patients with TSC mutations had an objective response. There were no statistically significant associations between mutations in PIK3CA, PTEN, PIK3R1, or KRAS and PFS or RR.

CONCLUSIONS

Mutations in AKT1, TSC1 and TSC2 are rare, but may predict clinical benefit from temsirolimus. CTNNB1 mutations were associated with longer PFS on temsirolimus.

Structure of the Tuberous Sclerosis Complex 2 (TSC2) N Terminus Provides Insight into Complex Assembly and Tuberous Sclerosis Pathogenesis

Tuberous sclerosis complex (TSC) is caused by mutations in the TSC1 and TSC2 tumor suppressor genes. The gene products hamartin and tuberin form the TSC complex that acts as GTPase-activating protein for Rheb and negatively regulates the mammalian target of rapamycin complex 1 (mTORC1). Tuberin contains a RapGAP homology domain responsible for inactivation of Rheb, but functions of other protein domains remain elusive. Here we show that the TSC2 N terminus interacts with the TSC1 C terminus to mediate complex formation. The structure of the TSC2 N-terminal domain from Chaetomium thermophilum and a homology model of the human tuberin N terminus are presented. We characterize the molecular requirements for TSC1-TSC2 interactions and analyze pathological point mutations in tuberin. Many mutations are structural and produce improperly folded protein, explaining their effect in pathology, but we identify one point mutant that abrogates complex formation without affecting protein structure. We provide the first structural information on TSC2/tuberin with novel insight into the molecular function.

Decreased Whole-Body Fat Mass Produced by Chronic Alcohol Consumption is Associated with Activation of S6K1-Mediated Protein Synthesis and Increased Autophagy in Epididymal White Adipose Tissue

BACKGROUND

Chronic alcohol consumption leads to a loss of white adipose tissue (WAT) but the underlying mechanisms for this lipodystrophy are not fully elucidated. This study tested the hypothesis that the reduction in WAT mass in chronic alcohol-fed mice is associated with a decreased protein synthesis specifically related to impaired function of mammalian target of rapamycin (mTOR).

METHODS

Adult male mice were provided an alcohol-containing liquid diet for 24 weeks or an isonitrogenous isocaloric control diet. In vivo protein synthesis was determined at this time and thereafter epididymal WAT (eWAT) was excised for analysis of signal transduction pathways central to controling protein synthesis and degradation.

RESULTS

While chronic alcohol feeding decreased whole-body and eWAT mass, this was associated with a discordant increase in protein synthesis in eWAT. This increase was not associated with a change in mTOR, 4E-BP1, Akt, or PRAS40 phosphorylation. Instead, a selective increase in phosphorylation of S6K1 and its downstream substrates, S6 and eIF4B was detected in alcohol-fed mice. Alcohol also increased eEF2K phosphorylation and decreased eEF2 phosphorylation consistent with increased translation elongation. Alcohol increased Atg12-5, LC3B-I and -II, and ULK1 S555 phosphorylation, suggesting increased autophagy, while markers of apoptosis (cleaved caspase-3 and -9, and PARP) were unchanged. Lipolytic enzymes (ATGL and HSL phosphorylation) were increased and lipogenic regulators (PPARγ and C/EBPα) were decreased in eWAT by alcohol. Although alcohol increased TNF-α, IL-6, and IL-1β mRNA, no change in key components of the NLRP3 inflammasome (NLRP3, ACS, and cleaved caspase-1) was detected suggesting alcohol did not increase pyroptosis. Plasma insulin did not differ between groups.

CONCLUSIONS

These results demonstrate that the alcohol-induced decrease in whole-body fat mass resulted in part from activation of autophagy in eWAT as protein synthesis was increased and mediated by the specific increase in the activity of S6K1.

WT1 is involved in the Akt-JNK pathway dependent autophagy through directly regulating Gas1 expression in human osteosarcoma cells

Macroautophagy (herein termed autophagy) works as a protective mechanism in tumorigenesis and development under metabolic stress condition. Multitudes of genes have been found involved in this process during past decades. In the present study, we report that Wilm's tumor suppressor1 (WT1) is involved in autophagy in osteosarcoma (OS) cells. WT1, a transcription factor with multitude of target genes, expresses in a majority of cancer types. Though wide-ranging effect of WT1 is now well documented, the function of WT1 in tumors remains poorly defined. In this chapter, it is found that high expression of WT1 positively correlates with active autophagy in human osteosarcoma cells. And further study on cell signaling pathway illustrates that Akt/JNK pathway acts as a positive regulator of autophagy induced by WT1. Here, we present evidence that WT1 modulates Akt/JNK signaling pathway mediated autophagy by controlling the expression of growth arrest-specific 1 (Gas1). We show that WT1 is required for Gas1 transcription in osteosarcoma cells. And Gas1 is upregulated followed WT1 overexpression in a time-dependent manner. Loss of Gas1 results in a reduction of WT1-induced autophagy.

Novel drugs that target the metabolic reprogramming in renal cell cancer

Molecular profiling studies of tumor tissue from patients with clear cell renal cell cancer (ccRCC) have revealed extensive metabolic reprogramming in this disease. Associations were found between metabolic reprogramming, histopathologic Fuhrman grade, and overall survival of patients. Large-scale genomics, proteomics, and metabolomic analyses have been performed to identify the molecular players in this process. Genes involved in glycolysis, the pentose phosphate pathway, glutamine metabolism, and lipogenesis were found to be upregulated in renal cell cancer (RCC) specimens as compared to normal tissue. Preclinical research indicates that mutations in VHL, FBP1, and the PI3K-AKT-mTOR pathway drives aerobic glycolysis through transcriptional activation of the hypoxia-inducible factors (HIF). Mechanistic studies revealed glutamine as an important source for de novo fatty acid synthesis through reductive carboxylation. Amplification of MYC drives reductive carboxylation. In this review, we present a detailed overview of the metabolic changes in RCC in conjunction with potential novel therapeutics. We discuss preclinical studies that have investigated targeted agents that interfere with various aspects of tumor cell metabolism and emphasize their impact specifically on glycolysis, lipogenesis, and tumor growth. Furthermore, we describe a number of phase 1 and 2 clinical trials that have been conducted with these agents.

Sustained activation of mTORC1 in macrophages increases AMPKα-dependent autophagy to maintain cellular homeostasis

Background

The mechanistic target of rapamycin complex 1 (mTORC1) is a well-conserved serine/threonine protein kinase that controls autophagy as well as many other processes such as protein synthesis, cell growth, and metabolism. The activity of mTORC1 is stringently and negatively controlled by the tuberous sclerosis proteins 1 and 2 complex (TSC1/2).

Results

In contrast to the previous studies using Tsc1 knockout mouse embryonic fibroblasts (MEF) cells, we demonstrated evidence that TSC1 deficient macrophages exhibited enhanced basal and mycobacterial infection-induced autophagy via AMPKα-dependent phosphorylation of ULK1 (Ser555). These effects were concomitant with constitutive activation of mTORC1 and can be reversed by addition of amino acids or rapamycin, and by the knockdown of the regulatory-associated protein of mTOR, Raptor. In addition, increased autophagy in TSC1 deficient macrophages resulted in suppression of inflammation during mycobacterial infection, which was reversed upon amino acid treatment of the TSC1 deficient macrophages. We further demonstrated that TSC1 conditional knockout mice infected with Mycobacterium tuberculosis, the causative agent of tuberculosis, resulted in less bacterial burden and a comparable level of inflammation when compared to wild type mice.

Conclusions

Our data revealed that sustained activation of mTORC1 due to defects in TSC1 promotes AMPKα-dependent autophagic flux to maintain cellular homeostasis.

Bidirectional Synaptic Structural Plasticity after Chronic Cocaine Administration Occurs through Rap1 Small GTPase Signaling

Dendritic spines are the sites of most excitatory synapses in the CNS, and opposing alterations in the synaptic structure of medium spiny neurons (MSNs) of the nucleus accumbens (NAc), a primary brain reward region, are seen at early versus late time points after cocaine administration. Here we investigate the time-dependent molecular and biochemical processes that regulate this bidirectional synaptic structural plasticity of NAc MSNs and associated changes in cocaine reward in response to chronic cocaine exposure. Our findings reveal key roles for the bidirectional synaptic expression of the Rap1b small GTPase and an associated local synaptic protein translation network in this process. The transcriptional mechanisms and pathway-specific inputs to NAc that regulate Rap1b expression are also characterized. Collectively, these findings provide a precise mechanism by which nuclear to synaptic interactions induce "metaplasticity" in NAc MSNs, and we reveal the specific effects of this plasticity on reward behavior in a brain circuit-specific manner.

Relation Between Cellular Senescence and Liver Diseases

Cellular senescence refers to a process that cellular proliferation and differentiation modulated by the multiple stimulating factors gradually decline. Aging cells present the irreversible stop of proliferation and differentiation and change in secretory function because the cell cycle of aging cells is steadily blocked at some point. It has have been shown that cellular senescence plays an important role in the occurrence and development of liver diseases. In this paper, we review the advances in relations between cellular senescence and liver diseases.

Tuberous sclerosis complex

Tuberous sclerosis complex (TSC) is an autosomal dominant disorder that affects multiple organ systems and is caused by loss-of-function mutations in one of two genes: TSC1 or TSC2. The disorder can affect both adults and children. First described in depth by Bourneville in 1880, it is now estimated that nearly 2 million people are affected by the disease worldwide. The clinical features of TSC are distinctive and can vary widely between individuals, even within one family. Major features of the disease include tumours of the brain, skin, heart, lungs and kidneys, seizures and TSC-associated neuropsychiatric disorders, which can include autism spectrum disorder and cognitive disability. TSC1 (also known as hamartin) and TSC2 (also known as tuberin) form the TSC protein complex that acts as an inhibitor of the mechanistic target of rapamycin (mTOR) signalling pathway, which in turn plays a pivotal part in regulating cell growth, proliferation, autophagy and protein and lipid synthesis. Remarkable progress in basic and translational research, in addition to several randomized controlled trials worldwide, has led to regulatory approval of the use of mTOR inhibitors for the treatment of renal angiomyolipomas, brain subependymal giant cell astrocytomas and pulmonary lymphangioleiomyomatosis, but further research is needed to establish full indications of therapeutic treatment. In this Primer, we review the state-of-the-art knowledge in the TSC field, including the molecular and cellular basis of the disease, medical management, major knowledge gaps and ongoing research towards a cure.

Molecular targets of metformin antitumor action

Epidemiological studies have shown that metformin, a first line therapeutic agent for diabetes mellitus, reduced the risk of developing various malignancies. Several preclinical studies established some possible mechanisms of its anticancer effects. The primary effect of metformin action is a decrease in cell energy status, which activates AMP-activated kinase (AMPK), a cellular metabolic sensor. This event is followed by a decrease in serum concentrations of insulin and insulin growth factor I (IGF-I), the potent mitogens for cancer cells. In addition to the indirect mode of action, metformin may exhibit direct inhibitory effect on cancer cells by targeting mammalian target of rapamycin (mTOR) signaling and anabolic processes. This review gathers information on mechanisms of metformin antitumor activity, with special attention given to the impact of this antidiabetic drug on insulin/PI3K/mTOR and AMPK signaling. Furthermore, the factors required for this novel activity of metformin are discussed.

Emerging role of mTOR in the response to cancer therapeutics

The movement toward precision medicine with targeted therapeutics for cancer treatment has been hindered by both innate and acquired resistance. Understanding the molecular wiring and plasticity of oncogenic signaling networks is essential to the development of therapeutic strategies to avoid or overcome resistance. The mechanistic target of rapamycin (mTOR) complex 1 (mTORC1) represents a highly integrated signaling node that is dysregulated in the majority of human cancers. Several studies have revealed that sustained mTORC1 inhibition is essential to avoid resistance to targeted therapeutics against the driving oncogenic pathway in a given cancer. Here we discuss the role of mTORC1 in dictating the response of tumors to targeted therapeutics and review recent examples from lung cancer, breast cancer, and melanoma.

The Genetics of Fetal Alcohol Spectrum Disorders

The term "fetal alcohol spectrum disorders" (FASD) defines the full range of ethanol (EtOH)-induced birth defects. Numerous variables influence the phenotypic outcomes of embryonic EtOH exposure. Among these variables, genetics appears to play an important role, yet our understanding of the genetic predisposition to FASD is still in its infancy. We review the current literature that relates to the genetics of FASD susceptibility and gene-EtOH interactions. Where possible, we comment on potential mechanisms of reported gene-EtOH interactions. Early indications of genetic sensitivity to FASD came from human and animal studies using twins or inbred strains, respectively. These analyses prompted searches for susceptibility loci involved in EtOH metabolism and analyses of candidate loci, based on phenotypes observed in FASD. More recently, genetic screens in animal models have provided an additional insight into the genetics of FASD. Understanding FASD requires that we understand the many factors influencing phenotypic outcome following embryonic EtOH exposure. We are gaining ground on understanding some of the genetics behind FASD, yet much work remains to be carried out. Coordinated analyses using human patients and animal models are likely to be highly fruitful in uncovering the genetics behind FASD.

Interleukin-6 influences stress-signalling by reducing the expression of the mTOR-inhibitor REDD1 in a STAT3-dependent manner

Interleukin 6 (IL-6) is a pleiotropic cytokine and a strong activator of Mammalian Target of Rapamycin (mTOR). In contrast, mTOR activity is negatively regulated by Regulated in Development and DNA Damage Responses 1 (REDD1). Expression of REDD1 is induced by cellular stressors such as glucocorticoids and DNA damaging agents. We show that the expression of basal as well as stress-induced REDD1 is reduced by IL-6. The reduction of REDD1 expression by IL-6 is independent of proteasomal or caspase-mediated degradation of REDD1 protein. Instead, induction of REDD1 mRNA is reduced by IL-6. The regulation of REDD1 expression by IL-6 is independent of Phosphatidylinositide-3-Kinase (PI3K) and Mitogen-Activated Protein Kinase (MAPK) signalling but depends on the expression and activation of Signal Transducer and Activator of Transcription 3 (STAT3). Furthermore, the reduction of basal REDD1 expression by IL-6 correlates with IL-6-induced activation of mTOR signalling. Inhibition of STAT3 activation blocks IL-6-induced mTOR activation. In summary, we present a novel STAT3-dependent mechanism of both IL-6-induced activation of mTOR and IL-6-dependent reversion of stress-induced inhibition of mTOR activity.