TOR signaling

Identification of novel 7-amino-5-methyl-1,6-naphthyridin-2(1H)-one derivatives as potent PI3K/mTOR dual inhibitors

Inhibition of the phosphoinositide 3-kinase (PI3K)/AKT/mammalian target of rapamycin (mTOR) signaling pathway is one of the most intensively studied approaches to cancer therapy. Rational design led to the identification of novel 7-amino-5-methyl-1,6-naphthyridin-2(1H)-one derivatives as potent PI3K/mTOR dual inhibitors. Design, synthesis and structure activity relationship are reported.

Affinity-based target identification for bioactive small molecules

A variety of new approaches of affinity-based target identification for bioactive small molecules are being developed, facilitating drug development and understanding complicated biological processes.

Population pharmacokinetics of sirolimus in pediatric patients with neurofibromatosis type 1

PURPOSE

The narrow therapeutic index and large interpatient variability in sirolimus pharmacokinetics (PK) make therapeutic drug monitoring necessary. Factors responsible for PK variability are not well understood, and published PK studies do not include pediatric patients with neurofibromatosis type 1 (NF1). The objectives of this study were to estimate sirolimus clearance in a cohort of children with NF1 using data collected in a concentration-guided trial, to evaluate the effect of treatment duration on clearance and dose requirements, and to evaluate the association of sirolimus clearance with patient-specific factors, including age, weight, body surface area (BSA), race, and sex.

METHODS

Sirolimus concentration-time data were collected from an ongoing prospective trial in children with NF1. An iterative 2-stage Bayesian method was used for the PK parameter analyses.

RESULTS

Data from 44 patients with NF1 were included in the analyses. Mean age was 8.4 years (SD 4.5, range 3-18), and mean weight was 29.8 kg (SD 16.7, range 12-85.8). Mean sirolimus clearance was 11.8 L/h (SD 4.6, range 2.2-24.1), and the mean dose to obtain a target trough concentration of 10-15 ng/mL was 2.0 mg/m administered twice daily (SD 0.72, range 0.77-3.85). A nonlinear relationship between age and clearance was observed. Total body weight and BSA were strong predictors of sirolimus clearance (r = 0.67 and 0.65, respectively).

CONCLUSIONS

Sirolimus clearance in children with NF1 is comparable with that in pediatric transplant patients. Clearance was most associated with body size parameters (BSA and total body weight) in children with NF1. When normalized for size, an age effect on clearance was observed in the youngest patients, most likely because of the maturational changes in drug absorption and metabolism. A mean dose of 2.0 mg/m twice a day was required for attainment of target trough concentrations of 10-15 ng/mL in children greater than 3 years of age who have NF1. The updated model will allow PK-guided individualized dosing of sirolimus in patients with NF1.

Insulin signaling and the regulation of insect diapause

A rich chapter in the history of insect endocrinology has focused on hormonal control of diapause, especially the major roles played by juvenile hormones (JHs), ecdysteroids, and the neuropeptides that govern JH and ecdysteroid synthesis. More recently, experiments with adult diapause in Drosophila melanogaster and the mosquito Culex pipiens, and pupal diapause in the flesh fly Sarcophaga crassipalpis provide strong evidence that insulin signaling is also an important component of the regulatory pathway leading to the diapause phenotype. Insects produce many different insulin-like peptides (ILPs), and not all are involved in the diapause response; ILP-1 appears to be the one most closely linked to diapause in C. pipiens. Many steps in the pathway leading from perception of daylength (the primary environmental cue used to program diapause) to generation of the diapause phenotype remain unknown, but the role for insulin signaling in mosquito diapause appears to be upstream of JH, as evidenced by the fact that application of exogenous JH can rescue the effects of knocking down expression of ILP-1 or the Insulin Receptor. Fat accumulation, enhancement of stress tolerance, and other features of the diapause phenotype are likely linked to the insulin pathway through the action of a key transcription factor, FOXO. This review highlights many parallels for the role of insulin signaling as a regulator in insect diapause and dauer formation in the nematode Caenorhabditis elegans.

Association of maternal mRNA and phosphorylated EIF4EBP1 variants with the spindle in mouse oocytes: localized translational control supporting female meiosis in mammals

In contrast to other species, localized maternal mRNAs are not believed to be prominent features of mammalian oocytes. We find by cDNA microarray analysis enrichment for maternal mRNAs encoding spindle and other proteins on the mouse oocyte metaphase II (MII) spindle. We also find that the key translational regulator, EIF4EBP1, undergoes a dynamic and complex spatially regulated pattern of phosphorylation at sites that regulate its association with EIF4E and its ability to repress translation. These phosphorylation variants appear at different positions along the spindle at different stages of meiosis. These results indicate that dynamic spatially restricted patterns of EIF4EBP1 phosphorylation may promote localized mRNA translation to support spindle formation, maintenance, function, and other nearby processes. Regulated EIF4EBP1 phosphorylation at the spindle may help coordinate spindle formation with progression through the cell cycle. The discovery that EIF4EBP1 may be part of an overall mechanism that integrates and couples cell cycle progression to mRNA translation and subsequent spindle formation and function may be relevant to understanding mechanisms leading to diminished oocyte quality, and potential means of avoiding such defects. The localization of maternal mRNAs at the spindle is evolutionarily conserved between mammals and other vertebrates and is also seen in mitotic cells, indicating that EIF4EBP1 control of localized mRNA translation is likely key to correct segregation of genetic material across cell types.

Role of follicle-stimulating hormone on biliary cyst growth in autosomal dominant polycystic kidney disease

BACKGROUND

Autosomal dominant polycystic kidney disease (ADPKD) is a common genetic disorder characterized by the progressive development of renal and hepatic cysts. Follicle-stimulating hormone (FSH) has been demonstrated to be a trophic factor for biliary cells in normal rats and experimental cholestasis induced by bile duct ligation (BDL).

AIMS

To assess the effect of FSH on cholangiocyte proliferation during ADPKD using both in vivo and in vitro models.

METHODS

Evaluation of FSH receptor (FSHR), FSH, phospho-extracellular-regulated kinase (pERK) and c-myc expression in liver fragments from normal patients and patients with ADPKD. In vitro, we studied proliferating cell nuclear antigen (PCNA) and cAMP levels in a human immortalized, non-malignant cholangiocyte cell line (H69) and in an immortalized cell line obtained from the epithelium lining the hepatic cysts from the patients with ADPKD (LCDE) with or without transient silencing of the FSH gene.

RESULTS

Follicle-stimulating hormone is linked to the active proliferation of the cystic wall and to the localization of p-ERK and c-myc. This hormone sustains the biliary growth by activation of the cAMP/ERK signalling pathway.

CONCLUSION

These results showed that FSH has an important function in cystic growth acting on the cAMP pathway, demonstrating that it provides a target for medical therapy of hepatic cysts during ADPKD.

Self-reported reproductive health in women with tuberous sclerosis complex

PURPOSE

Little is known about sex-specific manifestations of tuberous sclerosis complex. Inactivating mutations in the TSC1 and TSC2 genes cause tuberous sclerosis complex, and recent evidence points to a crucial role for these genes in maintaining appropriate ovarian function. The main objective of this study was to estimate reproductive dysfunction in a sample of women with tuberous sclerosis complex.

METHODS

We designed a three-part questionnaire that included demographic information, reproductive history, and tuberous sclerosis complex history, and developed strict criteria to assess patterns in menstrual cyclicity; we analyzed 182 responses from female adult members of the Tuberous Sclerosis Alliance.

RESULTS

More than one-third of women in our sample displayed some degree of menstrual irregularity, and their reported miscarriage rate was 41%. More than 4% of women had reproductive histories suggestive of premature ovarian insufficiency, higher than the general population estimate of 1%.

CONCLUSION

Our data reveal an underappreciated aspect of tuberous sclerosis complex in affected women, suggesting that a further exploration of the role the tuberous sclerosis complex genes play in reproductive function is warranted.

Upregulation of Ras homolog enriched in the brain (Rheb) in lipopolysaccharide-induced neuroinflammation

Ras homolog enriched in the brain (Rheb) is a homolog of Ras GTPase that regulates cell growth, proliferation, and cell cycle via mammalian target of rapamycin (mTOR). Recently, it has been confirmed that Rheb activation not only promotes cellular proliferation and differentiation but also enhances cellular apoptosis in response to diverse toxic stimuli. However, the function of Rheb in the central nervous system (CNS) is still with limited understanding. To elaborate whether Rheb was involved in CNS injury, we performed a neuroinflammatory model by lipopolysaccharide (LPS) lateral ventral injection in adult rats. Upregulation of Rheb was observed in the brain cortex by performing western blotting and immunohistochemistry. Double immunofluorescent staining demonstrated that Rheb was mainly in active astrocytes and neurons. PCNA and active caspase-3 were upregulated, and co-labeling with Rheb, which indicated that Rheb might be relevant to astrocytic proliferation and neuronal apoptosis following the inflammatory response by LPS-induced. Furthermore, we also found that the expression profiles of cyclinD1 and CDK4 were parallel with that of Rheb in a time-space dependent manner. Finally, knocking down Rheb by siRNA and treatment with rapamycin or lovastatin showed that not only astrocytic proliferation decreased but also neuronal protection. Based on our data, we suggested that Rheb might play an important role in physiological and pathological functions following neuroinflammation caused by LPS, which might provide a potential target to the treatment of neuroinflammation.

Alternative Pre-mRNA Splicing, Cell Death, and Cancer

Alternative splicing is one of the most powerful mechanisms for generating functionally distinct products from a single genetic loci and for fine-tuning gene activities at the post-transcriptional level. Alternative splicing plays important roles in regulating genes critical for cell death. These cell death genes encode death ligands, cell surface death receptors, intracellular death regulators, signal transduction molecules, and death executor enzymes such as caspases and nucleases. Alternative splicing of these genes often leads to the formation of functionally different products, some of which have antagonistic effects that are either cell death-promoting or cell death-preventing. Differential alternative splicing can affect expression, subcellular distribution, and functional activities of the gene products. Molecular defects in splicing regulation of cell death genes have been associated with cancer development and resistance to treatment. Studies using molecular, biochemical, and systems-based approaches have begun to reveal mechanisms underlying the regulation of alternative splicing of cell death genes. Systematic studies have begun to uncover the multi-level interconnected networks that regulate alternative splicing. A global picture of the complex mechanisms that regulate cell death genes at the pre-mRNA splicing level has thus begun to emerge.

The mechanism of mTOR (mammalian target of rapamycin) in a mouse model of polycystic ovary syndrome (PCOS)

Polycystic ovary syndrome (PCOS) is a common and complex endocrine disorder affecting 5-10% of women in reproductive age that is characterized by hyperandrogenism, oligo- or anovulation and infertility. However the pathophysiology of PCOS still remains unknown. The mammalian target of rapamycin (mTOR) is a central component that regulates various processes including cell growth, proliferation, metabolism, and angiogenesis. mTOR signaling cascade has recently been examined in ovarian follicles where it regulates granulosa cell proliferation and differentiation. mTOR functions as two complexes, mTOR complex 1 and 2. Therefore, we hypothesized that mTORC1 and/or 2 may have important role in proliferation of theca and granulosa cells in PCOS. In the present study, we sought to determine the mTOR signaling pathway in PCOS mouse ovary. We designed 3 groups: Control (C, no treatment), PCOS (P, The injection of DHEA (6 mg/100 g BW in 0.1 ml of sesame oil) (s.c) for 20 consecutive days), Vehicle (V, daily (s.c) sesame oil alone injection). Our results showed that mTORC1 and mTORC2-mediated signaling may play a role in PCOS mouse ovary. These findings provide evidence that mTORC1 and mTORC2 may have responsibility in increased ovarian follicular cell proliferation and growth in PCOS. Consequently, these results suggest that the mTOR signaling pathways (mTORC1 and mTORC 2) may create new clinical strategies to optimize developmental competence of PCOS should target correction of the entire follicle growth, oocyte development process and anovulatory infertility in PCOS.

Anti-myeloma activity of Akt inhibition is linked to the activation status of PI3K/Akt and MEK/ERK pathway

The PI3K/Akt/mTOR signal transduction pathway plays a central role in multiple myeloma (MM) disease progression and development of therapeutic resistance. mTORC1 inhibitors have shown limited efficacy in the clinic, largely attributed to the reactivation of Akt due to rapamycin induced mTORC2 activity. Here, we present promising anti-myeloma activity of MK-2206, a novel allosteric pan-Akt inhibitor, in MM cell lines and patient cells. MK-2206 was able to induce cytotoxicity and inhibit proliferation in all MM cell lines tested, albeit with significant heterogeneity that was highly dependent on basal pAkt levels. MK-2206 was able to inhibit proliferation of MM cells even when cultured with marrow stromal cells or tumor promoting cytokines. The induction of cytotoxicity was due to apoptosis, which at least partially was mediated by caspases. MK-2206 inhibited pAkt and its down-stream targets and up-regulated pErk in MM cells. Using MK-2206 in combination with rapamycin (mTORC1 inhibitor), LY294002 (PI3K inhibitor), or U0126 (MEK1/2 inhibitor), we show that Erk- mediated downstream activation of PI3K/Akt pathway results in resistance to Akt inhibition. These provide the basis for clinical evaluation of MK-2206 alone or in combination in MM and potential use of baseline pAkt and pErk as biomarkers for patient selection.

β-cell metabolic alterations under chronic nutrient overload in rat and human islets

The aim of this study was to assess multifactorial β-cell responses to metabolic perturbations in primary rat and human islets. Treatment of dispersed rat islet cells with elevated glucose and free fatty acids (FFAs, oleate:palmitate = 1:1 v/v) resulted in increases in the size and the number of lipid droplets in β-cells in a time- and concentration-dependent manner. Glucose and FFAs synergistically stimulated the nutrient sensor mammalian target of rapamycin complex 1 (mTORC1). A potent mTORC1 inhibitor, rapamycin (25 nM), significantly reduced triglyceride accumulation in rat islets. Importantly, lipid droplets accumulated only in β-cells but not in α-cells in an mTORC1-dependent manner. Nutrient activation of mTORC1 upregulated the expression of adipose differentiation related protein (ADRP), known to stabilize lipid droplets. Rat islet size and new DNA synthesis also increased under nutrient overload. Insulin secretion into the culture medium increased steadily over a 4-day period without any significant difference between glucose (10 mM) alone and the combination of glucose (10 mM) and FFAs (240 μM). Insulin content and insulin biosynthesis, however, were significantly reduced under the combination of nutrients compared with glucose alone. Elevated nutrients also stimulated lipid droplet formation in human islets in an mTORC1-dependent manner. Unlike rat islets, however, human islets did not increase in size under nutrient overload despite a normal response to nutrients in releasing insulin. The different responses of islet cell growth under nutrient overload appear to impact insulin biosynthesis and storage differently in rat and human islets.

Plasmodium falciparum responds to amino acid starvation by entering into a hibernatory state

The human malaria parasite Plasmodium falciparum is auxotrophic for most amino acids. Its amino acid needs are met largely through the degradation of host erythrocyte hemoglobin; however the parasite must acquire isoleucine exogenously, because this amino acid is not present in adult human hemoglobin. We report that when isoleucine is withdrawn from the culture medium of intraerythrocytic P. falciparum, the parasite slows its metabolism and progresses through its developmental cycle at a reduced rate. Isoleucine-starved parasites remain viable for 72 h and resume rapid growth upon resupplementation. Protein degradation during starvation is important for maintenance of this hibernatory state. Microarray analysis of starved parasites revealed a 60% decrease in the rate of progression through the normal transcriptional program but no other apparent stress response. Plasmodium parasites do not possess a TOR nutrient-sensing pathway and have only a rudimentary amino acid starvation-sensing eukaryotic initiation factor 2α (eIF2α) stress response. Isoleucine deprivation results in GCN2-mediated phosphorylation of eIF2α, but kinase-knockout clones still are able to hibernate and recover, indicating that this pathway does not directly promote survival during isoleucine starvation. We conclude that P. falciparum, in the absence of canonical eukaryotic nutrient stress-response pathways, can cope with an inconsistent bloodstream amino acid supply by hibernating and waiting for more nutrient to be provided.

mTOR is required for asymmetric division through small GTPases in mouse oocytes

Mammalian target of rapamycin (mTOR) is central to the control of cell proliferation, growth, and survival in mammalian cells. Prolonged treatment with rapamycin inhibits mTOR complex 2 (mTORC2) activity, and both the mTORC1-mediated S6K1 and 4E-BP1/eIF4E pathways are essential for TORC2-mediated RhoA, Cdc42, and Rac1 expression during cell motility and F-actin reorganization. The functions of mTOR in the mouse oocyte remain unclear, however. The present study shows that rapamycin affects mTOR expression and cytoskeleton reorganization during meiotic maturation of mouse oocytes. mTOR mRNA was expressed in germinal vesicles (GV) until metaphase I (MI), and increased during metaphase II (MII). Immunostaining showed that mTOR localized around the spindle and in the cytoplasm of oocytes. Treatment of oocytes with rapamycin decreased mTOR at the RNA and protein level, and altered asymmetric division. Formation of the actin cap and the cortical granule-free domain were also disrupted after rapamycin treatment, indicating the failure of spindle migration. Injection of an anti-mTOR antibody yielded results consistent with those obtained for rapamycin treatment, further confirming the involvement of mTOR in oocyte polarity. Furthermore, rapamycin treatment reduced the mRNA expression of small GTPases (RhoA, Cdc42, and Rac1), which are crucial regulatory factors for cytoskeleton reorganization. Taken together, these results suggest that rapamycin inhibits spindle migration and asymmetric division during mouse oocyte maturation via mTOR-mediated small GTPase signaling pathways.

Phase I studies of sirolimus alone or in combination with pharmacokinetic modulators in advanced cancer patients

PURPOSE

Sirolimus is the eponymous inhibitor of the mTOR; however, only its analogs have been approved as cancer therapies. Nevertheless, sirolimus is readily available, has been well studied in organ transplant patients, and shows efficacy in several preclinical cancer models.

EXPERIMENTAL DESIGN

Three simultaneously conducted phase I studies in advanced cancer patients used an adaptive escalation design to find the dose of oral, weekly sirolimus alone or in combination with either ketoconazole or grapefruit juice that achieves similar blood concentrations as its intravenously administered and approved prodrug, temsirolimus. In addition, the effect of sirolimus on inhibition of p70S6 kinase phosphorylation in peripheral T cells was determined.

RESULTS

Collectively, the three studies enrolled 138 subjects. The most commonly observed toxicities were hyperglycemia, hyperlipidemia, and lymphopenia in 52%, 43%, and 41% of subjects, respectively. The target sirolimus area under the concentration curve (AUC) of 3,810 ng-h/mL was achieved at sirolimus doses of 90, 16, and 25 mg in the sirolimus alone, sirolimus plus ketoconazole, and sirolimus plus grapefruit juice studies, respectively. Ketoconazole and grapefruit juice increased sirolimus AUC approximately 500% and 350%, respectively. Inhibition of p70 S6 kinase phosphorylation was observed at all doses of sirolimus and correlated with blood concentrations. One partial response was observed in a patient with epithelioid hemangioendothelioma.

CONCLUSION

Sirolimus can be feasibly administered orally, once weekly with a similar toxicity and pharmacokinetic profile compared with other mTOR inhibitors and warrants further evaluation in studies of its comparative effectiveness relative to recently approved sirolimus analogs.

Folate-conjugated rapamycin slows progression of polycystic kidney disease

Activation of the mammalian target of rapamycin (mTOR) signaling pathway is aberrant in autosomal-dominant polycystic kidney disease (ADPKD). The mTOR inhibitors, such as rapamycin, ameliorate PKD in rodent models, but clinical trials have not shown benefit, possibly as a result of low tissue concentrations of rapamycin at clinically tolerable doses. To overcome this limitation, we synthesized a folate-conjugated form of rapamycin (FC-rapa) that is taken up by folate receptor-mediated endocytosis and cleaved intracellularly to reconstitute the active drug. We found that renal cyst-lining cells highly express the folate receptor in ADPKD and mouse models. In vitro, FC-rapa inhibited mTOR activity in a dose- and folate receptor-dependent manner. Treatment of a PKD mouse model with FC-rapa inhibited mTOR in the target tissue, strongly attenuated proliferation and growth of renal cysts and preserved renal function. Furthermore, FC-rapa inhibited mTOR activity in the kidney but not in other organs. In summary, these results suggest that targeting the kidney using FC-rapa may overcome the significant side effects and lack of renal efficacy observed in clinical trials with mTOR inhibitors in ADPKD.

Mammalian target of rapamycin complex 1 (mTORC1) and 2 (mTORC2) control the dendritic arbor morphology of hippocampal neurons

Dendrites are the main site of information input into neurons. Their development is a multistep process controlled by mammalian target of rapamycin (mTOR) among other proteins. mTOR is a serine/threonine protein kinase that forms two functionally distinct complexes in mammalian cells: mTORC1 and mTORC2. However, the one that contributes to mammalian neuron development remains unknown. This work used short hairpin RNA against Raptor and Rictor, unique components of mTORC1 and mTORC2, respectively, to dissect mTORC involvement in this process. We provide evidence that both mTOR complexes are crucial for the proper dendritic arbor morphology of hippocampal neurons. These two complexes are required for dendritic development both under basal conditions and upon the induction of mTOR-dependent dendritic growth. We also identified Akt as a downstream effector of mTORC2 needed for proper dendritic arbor morphology, the action of which required mTORC1 and p70S6K1.

TORC1 of fission yeast is rapamycin-sensitive

The target of rapamycin (TOR) protein kinase plays central roles in the regulation of cell growth in response to nutritional availability. TOR forms two distinct multiprotein complexes termed TOR complex 1 (TORC1) and TORC2. Typically, only the activity of TORC1 is inhibited by the immunosuppressant rapamycin. Although rapamycin strongly inhibits cell growth of the budding yeast Saccharomyces cerevisiae through inhibition of TORC1, growth of the fission yeast Schizosaccharomyces pombe appears to be resistant to rapamycin. Here, we demonstrate that rapamycin inhibits the kinase activity of S. pombe TORC1 in vitro in a similar manner to TORC1 of other organisms. We furthermore show that incomplete inhibition of TORC1 by rapamycin underlies the apparent rapamycin resistance of S. pombe. In the presence of caffeine, which potentially lowers TORC1 activity, the growth of wild-type S. pombe cells is sensitive to rapamycin in a TORC1-dependent manner. Moreover, treatment of S. pombe cells with rapamycin plus caffeine induces starvation-specific gene expression and autophagy, similarly to cells with reduced TORC1 activity. These results indicate that rapamycin does inhibit TORC1 in S. pombe, but the inhibition is not sufficient to cause a growth defect. These findings establish a universal action of rapamycin on TORC1 inhibition.

mTORC1 signaling and regulation of pancreatic β-cell mass

The capacity of β cells to expand in response to insulin resistance is a critical factor in the development of type 2 diabetes. Proliferation of β cells is a major component for these adaptive responses in animal models. The extracellular signals responsible for β-cell expansion include growth factors, such as insulin, and nutrients, such as glucose and amino acids. AKT activation is one of the important components linking growth signals to the regulation of β-cell expansion. Downstream of AKT, tuberous sclerosis complex 1 and 2 (TSC1/2) and mechanistic target of rapamycin complex 1 (mTORC1) signaling have emerged as prime candidates in this process, because they integrate signals from growth factors and nutrients. Recent studies demonstrate the importance of mTORC1 signaling in β cells. This review will discuss recent advances in the understanding of how this pathway regulates β-cell mass and present data on the role of TSC1 in modulation of β-cell mass. Herein, we also demonstrate that deletion of Tsc1 in pancreatic β cells results in improved glucose tolerance, hyperinsulinemia and expansion of β-cell mass that persists with aging.

Kinase inhibitors in the treatment of immune-mediated disease

Protein kinases are fundamental components of diverse signaling pathways, including immune cells. Their essential functions have made them effective therapeutic targets. Initially, the expectation was that a high degree of selectivity would be critical; however, with time, the use of "multikinase" inhibitors has expanded. Moreover, the spectrum of diseases in which kinase inhibitors are used has also expanded to include not only malignancies but also immune-mediated diseases. At present, thirteen kinase inhibitors have been approved in the United States, all for oncologic indications. However, there are a growing number of molecules, including several Janus kinase inhibitors, that are being tested in clinical trials for autoimmune diseases such as rheumatoid arthritis, psoriasis and inflammatory bowel diseases. It appears likely that this new class of immunomodulatory drugs will have a major impact on the treatment of immune-mediated diseases in the near future.

L-leucine alters pancreatic β-cell differentiation and function via the mTor signaling pathway

Leucine (Leu) is an essential branched-chain amino acid, which activates the mammalian target of rapamycin (mTOR) signaling pathway. The effect of Leu on cell differentiation during embryonic development is unknown. Here, we show that Leu supplementation during pregnancy significantly increased fetal body weight, caused fetal hyperglycemia and hypoinsulinemia, and decreased the relative islet area. We also used rat embryonic pancreatic explant culture for elucidating the mechanism of Leu action on β-cell development. We found that in the presence of Leu, differentiation of pancreatic duodenal homeobox-1-positive progenitor cells into neurogenin3-positive endocrine progenitor cells was inefficient and resulted in decreased β-cell formation. Mechanistically, Leu increases the intracellular levels of hypoxia-inducible factor 1-α, a repressor of endocrine fate in the pancreas, by activating the mTOR complex 1 signaling pathway. Collectively, our findings indicate that Leu supplementation during pregnancy could potentially increase the risk of type 2 diabetes mellitus by inhibiting the differentiation of pancreatic endocrine progenitor cells during a susceptible period of fetal life.

Multiple signal pathways in obesity-associated cancer

Obesity is increasing worldwide and reaches to a large proportion of the population in developed countries. Thus, obesity-associated cancer has become a major health problem. Multiple cancer risk factors in obesity have been identified including insulin/insulin-like growth factor axis, adipokines and cytokines; and multiple intracellular signal pathways have been studied. However, the role of each signal pathway in obesity-associated cancer is controversial. In this review, the recent studies on signal pathways in obesity-associated cancer are summarized and a unified explanation is provided. Multiple risk factors could initially activate phosphoinositide 3-kinase (PI3K/Akt), mitogen-activated protein kinase (MAPK) and signal transducer and activator of transcription 3 (STAT3) pathways. With increased severity of obesity, mammalian target of rapamycin (mTOR), which is down-stream of both PI3K/Akt and MAPK, is highly activated. Activated mTOR in turn inhibits the PI3K/Akt pathway and further activates the STAT3 pathway. This may explain the activation of the PI3K/Akt pathway at the early stage of obesity and its inhibition at the later stage. mTOR inhibition may be used for cancer therapy, but it may be necessary to be combined with the PI3K/Akt inhibitor as decreased mTOR activity will release its feedback inhibition on the PI3K/Akt pathway, which is under the influence of multiple cancer risk factors in obesity. Thus, dual inhibitors of PI3K and mTOR may provide a novel approach.

Identification of cyclohexanone derivatives that act as catalytic inhibitors of topoisomerase I: effects on tamoxifen-resistant MCF-7 cancer cells

Breast cancer is commonly treated with anti-estrogens or aromatase inhibitors, but resistant disease eventually develops and new therapies for such resistance are of great interest. We have previously isolated several tamoxifen-resistant variant sub-lines of the MCF-7 breast cancer cell line and provided evidence that they arose from expansion of pre-existing minor populations. We have searched for therapeutic agents that exhibit selective growth inhibition of the resistant lines and here investigate 2,6-bis(pyridin-3-ylmethylene)-cyclohexanone (RL90) and 2,6-bis(pyridin-4-ylmethylene)-cyclohexanone (RL91). We found that two of the tamoxifen-resistant sub-lines (TamR3 and TamC3) unexpectedly showed increased sensitivity to RL90 and RL91. We utilized growth inhibition assays, flow cytometry and immunoblotting to establish a mechanistic basis for their action. Treated sensitive cells showed S-phase selective DNA damage, as detected by histone H2AX phosphorylation. Cellular responses were similar to those induced by the topoisomerase I poison camptothecin. Although IC(50) values of camptothecin, RL90, RL91 were correlated, studies with purified mammalian topoisomerase I suggested that RL90 and RL91 differed from camptothecin by acting as catalytic topoisomerase I inhibitors. These drugs provide a platform for the further development of DNA damaging drugs that have selective effects on tamoxifen resistant breast cancer cells. The results also raise the question of whether clinical topoisomerase I poisons such as irinotecan and topotecan might be active in the treatment of some types of tamoxifen-resistant cancer.

Involvement of mTOR in CXCL12 mediated T cell signaling and migration

Background

CXCL12 is a pleiotropic chemokine involved in multiple different processes such as immune regulation, inflammatory responses, and cancer development. CXCL12 is also a potent chemokine involved in chemoattraction of T cells to the site of infection or inflammation. Mammalian target of rapamycin (mTOR) is a serine-threonine kinase that modulates different cellular processes, such as metabolism, nutrient sensing, protein translation, and cell growth. The role of mTOR in CXCL12-mediated resting T cell migration has yet to be elucidated.

Methodology/Principal Findings

Rapamycin, an inhibitor of mTOR, significantly inhibits CXCL12 mediated migration of both primary human resting T cells and human T cell leukemia cell line CEM. p70^S6K1, an effector molecule of mTOR signaling pathway, was knocked down by shRNA in CEM cells using a lentiviral gene transfer system. Using p70^S6K1 knock down cells, we demonstrate the role of mTOR signaling in T cell migration both in vitro and in vivo.

Conclusions

Our data demonstrate a new role for mTOR in CXCL12-induced T cell migration, and enrich the current knowledge regarding the clinical use of rapamycin.

mTORC1- and mTORC2-interacting proteins keep their multifunctional partners focused

The mammalian target of rapamycin, best known as mTOR, is a phylogenetically conserved serine/threonine kinase that controls life-defining cellular processes such as growth, metabolism, survival, and migration under the influence of multiple interacting proteins. Historically, the cellular activities blocked by rapamycin in mammalian cells were considered the only events controlled by mTOR. However, this paradigm changed with the discovery of two signaling complexes differentially sensitive to rapamycin, whose catalytic component is mTOR. The one sensitive to rapamycin, known as mTORC1, promotes protein synthesis in response to growth factors and nutrients via the phosphorylation of p70S6K and 4EBP1; while the other, known as mTORC2, promotes cell migration and survival via the activation of Rho GTPases and the phosphorylation of AKT, respectively. Although mTORC2 kinase activity is not inhibited by rapamycin, hours of incubation with this antibiotic can impede the assembly of this signaling complex. The direct mechanism by which mTORC2 leads to cell migration depends on its interaction with P-Rex1, a Rac-specific guanine nucleotide exchange factor, while additional indirect pathways involve the intervention of PKC or AKT, multifunctional ubiquitous serine/threonine kinases that activate effectors of cell migration upon being phosphorylated by mTORC2 in response to chemotactic signals. These mTORC2 effectors are altered in metastatic cancer. Numerous clinical trials are testing mTOR inhibitors as potential antineoplasic drugs. Here, we briefly review the actions of mTOR with emphasis on the controlling role of mTORC1 and mTORC2-interacting proteins and highlight the mechanisms linked to cell migration.

GLUT1 enhances mTOR activity independently of TSC2 and AMPK

Enhanced GLUT1 expression in mesangial cells plays an important role in the development of diabetic nephropathy by stimulating signaling through several pathways resulting in increased glomerular matrix accumulation. Similarly, enhanced mammalian target of rapamycin (mTOR) activation has been implicated in mesangial matrix expansion and glomerular hypertrophy in diabetes. We sought to examine whether enhanced GLUT1 expression increased mTOR activity and, if so, to identify the mechanism. We found that levels of GLUT1 expression and mTOR activation, as evidenced by S6 kinase (S6K) and 4E-BP-1 phosphorylation, changed in tandem in cell lines exposed to elevated levels of extracellular glucose. We then showed that increased GLUT1 expression enhanced S6K phosphorylation by 1.7- to 2.9-fold in cultured mesangial cells and in glomeruli from GLUT1 transgenic mice. Treatment with the mTOR inhibitor, rapamycin, eliminated the GLUT1 effect on S6K phosphorylation. In cells lacking functional tuberous sclerosis complex (TSC) 2, GLUT1 effects on mTOR activity persisted, indicating that GLUT1 effects were not mediated by TSC. Similarly, AMP kinase activity was not altered by enhanced GLUT1 expression. Conversely, enhanced GLUT1 expression led to a 2.4-fold increase in binding of mTOR to its activator, Rheb, and a commensurate 2.1-fold decrease in binding of Rheb to glyceraldehyde 3-phosphate dehydrogenase (GAPDH) consistent with mediation of GLUT1 effects by a metabolic effect on GAPDH. Thus, GLUT1 expression appears to augment mesangial cell growth and matrix protein accumulation via effects on glycolysis and decreased GAPDH interaction with Rheb.

Down-regulation of JAK1 by RNA interference inhibits growth of the lung cancer cell line A549 and interferes with the PI3K/mTOR pathway

PURPOSE

The mammalian Janus kinase (JAK) family plays a critical role in cytokine/growth factor signalling pathways and is associated with human cancers. In this study, we explored the role of JAK1 in the non-small cell lung cancer (NSCLC) cell line A549 and its molecular crosstalk with the phosphatidyl inositol-3-kinase (PI3K)/mammalian target of the rapamycin (mTOR) pathway.

METHODS

One hundred and two NSCLC and 50 normal lung specimens were collected after surgical resection. JAK1 expression and phosphorylation were determined via immunohistochemical staining (IHC) assay. A stable knockdown of JAK1 was performed in A549 cells by RNA interference. Stable cell proliferation, cell cycle, apoptosis, and invasion were characterised in vitro. Tumourigenicity was analysed in vivo. The NSCLC xenograft protein expression of PI3K/mTOR pathway molecules was determined by Western blot assay.

RESULTS

JAK1 expression was higher in NSCLC tissues than in normal lung tissues (P < 0.01). JAK1 knockdown in A549 cells significantly inhibited cell proliferation and invasion while promoting cell arrest at G0/G1 phase (all P < 0.05). The xenograft model showed that JAK1 suppression inhibited tumour growth compared with normal control (P < 0.05). Moreover, JAK1 knockdown inhibited mTOR or P70 ribosomal protein S6 kinase (P70S6K) phosphorylation, but increased glycogen synthase kinase-3α (GSK-3α) and B-cell lymphoma-extra large (Bcl-xl) phosphorylation. Total protein expression and Akt1/2 phosphorylated status remained unchanged.

CONCLUSION

Our study suggests that JAK1 expression and phosphorylation is abnormal in NSCLC tissues. The knockdown of JAK1 significantly inhibits tumourigenicity of the A549 cell line and demonstrates that crosstalk between the JAK1 and PI3K/mTOR pathways is involved.

Perspectives on the role of mTORC2 in B lymphocyte development, immunity and tumorigenesis

Mammalian target of rapamycin complex 2 (mTORC2) is a key downstream mediator of phosphoinositol-3-kinase (PI3K) dependent growth factor signaling. In lymphocytes, mTORC2 has emerged as an important regulator of cell development, homeostasis and immune responses. However, our current understanding of mTORC2 functions and the molecular mechanisms regulating mTORC2 signaling in B and T cells are still largely incomplete. Recent studies have begun to shed light on this important pathway. We have previously reported that mTORC2 mediates growth factor dependent phosphorylation of Akt and facilitates Akt dependent phosphorylation and inactivation of transcription factors FoxO1 and FoxO3a. We have recently explored the functions of mTORC2 in B cells and show that mTORC2 plays a key role in regulating survival and immunoglobulin (Ig) gene recombination of bone marrow B cells through an Akt2-FoxO1 dependent mechanism. Ig recombination is suppressed in proliferating B cells to ensure that DNA double strand breaks are not generated in actively dividing cells. Our results raise the possibility that genetic or pharmacologic inhibition of mTORC2 may promote B cell tumor development as a result of inefficient suppression of Ig recombination in dividing B cells. We also propose a novel strategy to treat cancers based on our recent discovery that mTORC2 regulates Akt protein stability.

Neuroprotective, immunosuppressant and antineoplastic properties of mTOR inhibitors: current and emerging therapeutic options

The acronym mTOR defines a family of serine-threonine protein kinase called mammalian target of rapamycin. The major role of these kinases in the cell is to merge extracellular instructions with information about cellular metabolic resources and to control the rate of anabolic and catabolic processes accordingly. In mammalian cells mTOR is present in two distinct heteromeric protein complexes commonly referred to as mTOR complex 1 (mTORC1) and mTOR complex 2 (mTORC2), involved in the control of a wide variety of cellular processes. It has been recently reported that compounds acting modulating mTOR activity, beside mediating the well recognized processes exploited in the anticancer and immunosuppressant effects, are provided with neuroprotective properties. In fact, mTOR is involved in the mechanism of PI3K/Akt-induced upregulation of glutamate transporter 1, GLT1, that is linked to several neuronal disorders such as stroke, Alzheimer's disease, and amyotrophic lateral sclerosis. Furthermore, in adult brain mTOR is crucial for numerous physiological processes such as synaptic plasticity, learning, memory, and brain control of food uptake. Moreover, the activation of mTOR pathway is involved in neuronal development, dendrite development and spine morphogenesis.

Coordination of Ribosomal Protein and Ribosomal RNA Gene Expression in Response to TOR Signaling

Cells grow in response to nutrients or growth factors, whose presence is detected and communicated by elaborate signaling pathways. Protein kinases play crucial roles in processes such as cell cycle progression and gene expression, and misregulation of such pathways has been correlated with various diseased states. Signals intended to promote cell growth converge on ribosome biogenesis, as the ability to produce cellular proteins is intimately tied to cell growth. Part of the response to growth signals is therefore the coordinate expression of genes encoding ribosomal RNA (rRNA) and ribosomal proteins (RP). A key player in regulating cell growth is the Target of Rapamycin (TOR) kinase, one of the gatekeepers that prevent cell cycle progression from G1 to S under conditions of nutritional stress. TOR is structurally and functionally conserved in all eukaryotes. Under favorable growth conditions, TOR is active and cells maintain a robust rate of ribosome biogenesis, translation initiation and nutrient import. Under stress conditions, TOR signaling is suppressed, leading to cell cycle arrest, while the failure of TOR to respond appropriately to environmental or nutritional signals leads to uncontrolled cell growth. Emerging evidence from Saccharomyces cerevisiae indicates that High Mobility Group (HMGB) proteins, non-sequence-specific chromosomal proteins, participate in mediating responses to growth signals. As HMGB proteins are distinguished by their ability to alter DNA topology, they frequently function in the assembly of higher-order nucleoprotein complexes. We review here recent evidence, which suggests that HMGB proteins may function to coordinate TOR-dependent regulation of rRNA and RP gene expression.

Resveratrol inhibits mTOR signaling by targeting DEPTOR

Resveratrol (RSV, trans-3,4,5-Trihydroxystilbene), a type of polyphenol originally found in red wines, shows a great promise for the treatment of cancer, aging, type 2 diabetes and cardiovascular diseases. Recent studies suggest that suppressing the signaling pathway mediated by mTOR, a well-known energy sensor that integrates various hormonal, nutrient and environmental signals to regulate cell growth, metabolism and survival, could play an important role in mediating the beneficial effect of RSV. The underlying mechanisms by which RSV inhibits mTOR signaling remain elusive, but our recent studies show that RSV inhibits amino acid-stimulated mTOR signaling in C2C12 fibroblasts via a Sirt1- and AMPK-independent mechanism. RSV treatment has no effect on the expression levels of mTOR, raptor and DEPTOR, but greatly promotes the interaction between mTOR and its inhibitor DEPTOR. Our results reveal a novel mechanism by which RSV inhibits mTOR signaling and its function.

Autophagy signaling through reactive oxygen species

Autophagy is a degradative pathway that involves delivery of cytoplasmic components, including proteins, organelles, and invaded microbes to the lysosome for digestion. Autophagy is implicated in the pathology of various human diseases. The association of autophagy to inflammatory bowel diseases is consistent with recent discoveries of its role in immunity. A complex of signaling pathways control the induction of autophagy in different cellular contexts. Reactive oxygen species (ROS) are highly reactive oxygen free radicals or non-radical molecules that are generated by multiple mechanisms in cells, with the nicotinamide adenine dinucleotide phosphate (NADPH) oxidases and mitochondria as major cellular sources. These ROS are important signaling molecules that regulate many signal-transduction pathways and play critical roles in cell survival, death, and immune defenses. ROS were recently shown to activate starvation-induced autophagy, antibacterial autophagy, and autophagic cell death. Current findings implicate ROS in the regulation of autophagy through distinct mechanisms, depending on cell types and stimulation conditions. Conversely, autophagy can also suppress ROS production. Understanding the mechanisms behind ROS-induced autophagy will provide significant therapeutic implications for related diseases.

TOR signaling never gets old: aging, longevity and TORC1 activity

The target of rapamycin (TOR) signal transduction network monitors intra- and extracellular conditions that favor cell growth. Research during the last decade has revealed a modular structure of the TOR signaling network. Each signaling module senses a particular set of signals from the cellular milieu and exerts regulatory control towards TOR activity. The TOR pathway responds to growth factor signals, nutrient availability, and cellular stresses like hypoxia and energy stress. The signaling modules and their molecular components constituting the TOR network are remarkably conserved in both sequence and function across species. In yeast, roundworms, flies, and mice, the TOR pathway has been shown to regulate lifespan. Correspondingly, genetic, dietary or pharmacological manipulation of individual signaling modules as well as TOR activity itself extends lifespan in these model organisms. We discuss the potential impact of manipulating TOR activity for human health and lifespan.

Increased ratio of dietary carbohydrate to protein shifts the focus of metabolic signaling from skeletal muscle to adipose

Background

The Dietary Reference Intakes (DRI) established acceptable macronutrient distribution ranges (AMDR) for carbohydrates and protein, however little is known about differences in glycemic regulations and metabolic signaling across this range. This study examined metabolic outcomes associated with intake of two diets differing in carbohydrate:protein ratios representing the upper and lower ends of the AMDR.

Methods

Adult, male rats were fed either a high carbohydrate (CHO) diet (60% of energy from carbohydrates, 12% protein, 28% fat; n = 30) or a high protein (PRO) diet (35% carbohydrate, 35% protein, 30% fat; n = 30). Rats were meal-fed 3x/d the respective diets for 10 d and then terminated after overnight food deprivation or 30, 60, 90, 120 min post-prandial (PP). Plasma was collected at each of these points to provide a time course for glucose, insulin and C-peptide. Skeletal muscle and adipose tissues were collected at 0, 30 and 90 min for measurements of basal, early and delayed activation of Akt, p70S6K and Erk 1/2. Data were analyzed by two-way ANOVA.

Results

The CHO group produced a consistently elevated response in plasma glucose, insulin and C-peptide following the meal through the 120 min time course. In addition, Akt and Erk 1/2 activation in adipose was much higher than in skeletal muscle. Conversely, the PRO group PP glucose response was minimal and insulin maintained a response similar to a biphasic pattern. Tissue responses for the PRO group were greater for Akt and p70S6K signaling in skeletal muscle compared with adipose.

Conclusion

Taken together these data suggest that altering CHO:PRO ratios within the AMDR produce different glycemic response patterns accompanied by differential metabolic signaling in skeletal muscle and adipose.

Evaluation of the novel protein kinase C inhibitor sotrastaurin as immunosuppressive therapy after renal transplantation

IMPORTANCE OF THE FIELD

The prevalence of acute renal allograft rejection has decreased substantially in past decades due to new and more specific immunosuppressive compounds but improvements in long-term graft function have not been achieved. There is a large need for new immunosuppressive agents that lack toxicity of current agents such as calcineurin inhibitors but show high synergistic efficiency in preventing rejection processes.

AREAS COVERED IN THIS REVIEW

This review summarizes data concerning the pharmacokinetics, pharmacodynamics and clinical efficacy of the new PKC inhibitor sotrastaurin with a focus on renal transplantation. The article contains information that has been presented at international transplant meetings and congresses and that has been published between 2006 and 2010. Additionally, current ongoing trials are described in detail.

WHAT THE READER WILL GAIN

Immunosuppressive regimens after kidney transplantation consist of a combination of several agents in order to minimize drug toxicity. Therefore, the reader is presented with the most up-to-date/current developments in sotrastaurin applications in Phase I and II trials with emphasis on data maintained from studies that combined sotrastaurin with established agents such as mycophenolic acid and tacrolimus.

TAKE HOME MESSAGE

Several trials are ongoing and planned to determine the optimal immunosuppressive regimen to benefit from sotrastaurin's distinct mechanism of action.

Decreased IRS signaling impairs beta-cell cycle progression and survival in transgenic mice overexpressing S6K in beta-cells

OBJECTIVE

The purpose of this study was to evaluate the role of the S6K arm of mammalian target of rapamycin complex 1 (mTORC1) signaling in regulation of β-cell mass and function. Additionally, we aimed to delineate the importance of in vivo S6K activation in the regulation of insulin signaling and the extent to which alteration of insulin receptor substrate (IRS) signaling modulates β-cell mass and function.

RESEARCH DESIGN AND METHODS

The current experiments describe the phenotype of transgenic mice overexpressing a constitutively active form of S6K under the control of the rat insulin promoter.

RESULTS

Activation of S6K signaling in these mice improved insulin secretion in the absence of changes in β-cell mass. The lack of β-cell mass expansion resulted from decreased G(1)-S progression and increased apoptosis. This phenotype was associated with increased p16 and p27 and decreased Cdk2 levels. The changes in cell cycle were accompanied by diminished survival signals because of impaired IRS/Akt signaling.

CONCLUSIONS

This work defines the importance of S6K in regulation of β-cell cycle, cell size, function, and survival. These experiments also demonstrate that in vivo downregulation of IRS signaling by TORC1/S6K induces β-cell insulin resistance, and that this mechanism could explain some of the abnormalities that ultimately result in β-cell failure and diabetes in conditions of nutrient overload.

Altered glucose homeostasis in mice with liver-specific deletion of Src homology phosphatase 2

The Src homology 2 domain-containing protein-tyrosine phosphatase Shp2 has been implicated in a variety of growth factor signaling pathways, but its role in insulin signaling has remained unresolved. In vitro studies suggest that Shp2 is both a negative and positive regulator of insulin signaling, although its physiological function in a number of peripheral insulin-responsive tissues remains unknown. To address the metabolic role of Shp2 in the liver, we generated mice with either chronic or acute hepatic Shp2 deletion using tissue-specific Cre-LoxP and adenoviral Cre approaches, respectively. We then analyzed insulin sensitivity, glucose tolerance, and insulin signaling in liver-specific Shp2-deficient and control mice. Mice with chronic Shp2 deletion exhibited improved insulin sensitivity and increased glucose tolerance compared with controls. Acute Shp2 deletion yielded comparable results, indicating that the observed metabolic effects are directly caused by the lack of Shp2 in the liver. These findings correlated with, and were most likely caused by, direct dephosphorylation of insulin receptor substrate (IRS)1/2 in the liver, accompanied by increased PI3K/Akt signaling. In contrast, insulin-induced ERK activation was dramatically attenuated, yet there was no effect on the putative ERK site on IRS1 (Ser(612)) or on S6 kinase 1 activity. These studies show that Shp2 is a negative regulator of hepatic insulin action, and its deletion enhances the activation of PI3K/Akt pathway downstream of the insulin receptor.

Sin1-mTORC2 suppresses rag and il7r gene expression through Akt2 in B cells

Mammalian target of rapamycin (mTOR) is an important mediator of phosphoinositol-3-kinase (PI3K) signaling. PI3K signaling regulates B cell development, homeostasis, and immune responses. However, the function and molecular mechanism of mTOR-mediated PI3K signaling in B cells has not been fully elucidated. Here we show that Sin1, an essential component of mTOR complex 2 (mTORC2), regulates B cell development. Sin1 deficiency results in increased IL-7 receptor (il7r) and RAG recombinase (rag1 and rag2) gene expression, leading to enhanced pro-B cell survival and augmented V(D)J recombinase activity. We further show that Akt2 specifically mediates the Sin1-mTORC2 dependent suppression of il7r and rag gene expression in B cells by regulating FoxO1 phosphorylation. Finally, we demonstrate that the mTOR inhibitor rapamycin induces rag expression and promotes V(D)J recombination in B cells. Our study reveals that the Sin1/mTORC2-Akt2 signaling axis is a key regulator of FoxO1 transcriptional activity in B cells.

The role of PAS kinase in PASsing the glucose signal

PAS kinase is an evolutionarily conserved nutrient responsive protein kinase that regulates glucose homeostasis. Mammalian PAS kinase is activated by glucose in pancreatic beta cells, and knockout mice are protected from obesity, liver triglyceride accumulation, and insulin resistance when fed a high-fat diet. Yeast PAS kinase is regulated by both carbon source and cell integrity stress and stimulates the partitioning of glucose toward structural carbohydrate biosynthesis. In our current model for PAS kinase regulation, a small molecule metabolite binds the sensory PAS domain and activates the enzyme. Although bona fide PAS kinase substrates are scarce, in vitro substrate searches provide putative targets for exploration.

Rictor phosphorylation on the Thr-1135 site does not require mammalian target of rapamycin complex 2

In animal cells, growth factors coordinate cell proliferation and survival by regulating the phosphoinositide 3-kinase/Akt signaling pathway. Deregulation of this signaling pathway is common in a variety of human cancers. The PI3K-dependent signaling kinase complex defined as mammalian target of rapamycin complex 2 (mTORC2) functions as a regulatory Ser-473 kinase of Akt. We find that activation of mTORC2 by growth factor signaling is linked to the specific phosphorylation of its component rictor on Thr-1135. The phosphorylation of this site is induced by the growth factor stimulation and expression of the oncogenic forms of ras or PI3K. Rictor phosphorylation is sensitive to the inhibition of PI3K, mTOR, or expression of integrin-linked kinase. The substitution of wild-type rictor with its specific phospho-mutants in rictor null mouse embryonic fibroblasts did not alter the growth factor-dependent phosphorylation of Akt, indicating that the rictor Thr-1135 phosphorylation is not critical in the regulation of the mTORC2 kinase activity. We found that this rictor phosphorylation takes place in the mTORC2-deficient cells, suggesting that this modification might play a role in the regulation of not only mTORC2 but also the mTORC2-independent function of rictor.

cAMP-dependent activation of mammalian target of rapamycin (mTOR) in thyroid cells. Implication in mitogenesis and activation of CDK4

How cAMP-dependent protein kinases [protein kinase A (PKA)] transduce the mitogenic stimulus elicited by TSH in thyroid cells to late activation of cyclin D3-cyclin-dependent kinase 4 (CDK4) remains enigmatic. Here we show in PC Cl3 rat thyroid cells that TSH/cAMP, like insulin, activates the mammalian target of rapamycin (mTOR)-raptor complex (mTORC1) leading to phosphorylation of S6K1 and 4E-BP1. mTORC1-dependent S6K1 phosphorylation in response to both insulin and cAMP required amino acids, whereas inhibition of AMP-activated protein kinase and glycogen synthase kinase 3 enhanced insulin but not cAMP effects. Unlike insulin, TSH/cAMP did not activate protein kinase B or induce tuberous sclerosis complex 2 phosphorylation at T1462 and Y1571. However, like insulin, TSH/cAMP produced a stable increase in mTORC1 kinase activity that was associated with augmented 4E-BP1 binding to raptor. This could be caused in part by T246 phosphorylation of PRAS40, which was found as an in vitro substrate of PKA. Both in PC Cl3 cells and primary dog thyrocytes, rapamycin inhibited DNA synthesis and retinoblastoma protein phosphorylation induced by TSH and insulin. Although rapamycin reduced cyclin D3 accumulation, the abundance of cyclin D3-CDK4 complexes was not affected. However, rapamycin inhibited the activity of these complexes by decreasing the TSH and insulin-mediated stimulation of activating T172 phosphorylation of CDK4. We propose that mTORC1 activation by TSH, at least in part through PKA-dependent phosphorylation of PRAS40, crucially contributes to mediate cAMP-dependent mitogenesis by regulating CDK4 T172-phosphorylation.

CCL2 is a negative regulator of AMP-activated protein kinase to sustain mTOR complex-1 activation, survivin expression, and cell survival in human prostate cancer PC3 cells

CCL2 is a cytokine prevalent in the prostate cancer tumor microenvironment. Recently, we reported that CCL2 induces the mammalian target of rapamycin (mTOR) pathway to promote prostate cancer PC3 cell survival; however, the mechanism used by CCL2 to maintain mTOR complex-1 (mTORC1) activation requires clarification. This study demonstrates that upon serum starvation, CCL2 functions as a negative regulator of AMP-activated protein kinase (AMPK) by decreasing phosphorylation at its major regulatory site (Thr(172)) in PC3, DU145, and C4-2B prostate cancer cells. The CCL2-mediated AMPK regulation decreased raptor phosphorylation (Ser(792)) resulting in hyperactivation of mTORC1. D942, a pharmacological activator of AMPK, stunted CCL2-induced mTORC1 activity, survivin expression, and cell survival without significantly affecting Akt activity. CCL2, however, conferred some resistance to the lethal effect of D942 compared with untreated cells. By using Akt-specific inhibitor X, it was shown that Akt inactivation did not cause an increase in AMPK phosphorylation in CCL2-stimulated cells, suggesting that CCL2-mediated negative regulation of AMPK is independent of Akt. Furthermore, bisindolylmaleimide-V, a specific inhibitor of p70(S6K), stunted survivin expression and induced cell death in CCL2-treated PC3. Altogether, these findings suggest that CCL2 hyperactivates mTORC1 through simultaneous regulation of both AMPK and Akt pathways and reveals a new network that promotes prostate cancer: CCL2-AMPK-mTORC1-survivin.

The mTOR kinase determines effector versus memory CD8+ T cell fate by regulating the expression of transcription factors T-bet and Eomesodermin

The mechanisms underpinning integration of instructions that program naive CD8+ T cells for effector and/or memory differentiation are not well understood. Herein, we demonstrate that interleukin-12 (IL-12) enhanced and sustained antigen and costimulatory molecule (B7.1)-induced mTOR kinase activity in naive CD8+ (OT-I) T cells via phosphoinositide 3-kinase and STAT4 transcription factor pathways. Blocking mTOR activity by rapamycin reversed IL-12-induced effector functions because of loss of persistent expression of the transcription factor T-bet. Rapamycin treatment of IL-12-conditioned OT-I cells promoted persistent Eomesodermin expression and produced memory cell precursors that demonstrated enhanced sustenance and antigen-recall responses upon adoptive transfer. The memory cell precursors showed greater tumor efficacy than IL-12-conditioned effector OT-I cells. These results identify mTOR as the central regulator of transcriptional programs that determine effector and/or memory cell fates in CD8+ T cells. Targeting mTOR activity offers new opportunities to regulate CD8+ T cell-mediated immunity.

The late endosome is essential for mTORC1 signaling

Recent work suggests a link between endocytic trafficking and mTORC1 signaling. This paper demonstrates a specific requirement for the integrity of the late endosomal compartment for amino acid and insulin-stimulated mTORC1 signaling to downstream effectors.

The multisubunit mTORC1 complex integrates signals from growth factors and nutrients to regulate protein synthesis, cell growth, and autophagy. To examine how endocytic trafficking might be involved in nutrient regulation of mTORC1, we perturbed specific endocytic trafficking pathways and measured mTORC1 activity using S6K1 as a readout. When early/late endosomal conversion was blocked by either overexpression of constitutively active Rab5 (Rab5CA) or knockdown of the Rab7 GEF hVps39, insulin- and amino acid–stimulated mTORC1/S6K1 activation were inhibited, and mTOR localized to hybrid early/late endosomes. Inhibition of other stages of endocytic trafficking had no effect on mTORC1. Overexpression of Rheb, which activates mTOR independently of mTOR localization, rescued mTORC1 signaling in cells expressing Rab5CA, whereas hyperactivation of endogenous Rheb in TSC2−/− MEFs did not. These data suggest that integrity of late endosomes is essential for amino acid– and insulin-stimulated mTORC1 signaling and that blocking the early/late endosomal conversion prevents mTOR from interacting with Rheb in the late endosomal compartment.

Protein synthesis and the antagonistic pleiotropy hypothesis of aging

Growth and somatic maintenance are thought to be antagonistic piciotropic traits, but the molecular basis for this tradeoff is poorly understood. Here it is proposed that changes in protein synthesis mediate the tradeoffs that take place upon genetic and environmental manipulation in various model systems including yeast, worms, flies and mice. This hypothesis is supported by evidence that inhibition of the TOR (target of rapamycin) pathway and various translation factors that inhibit protein synthesis lead to slowing of growth and development but extend lifespan. Furthermore, dietary restriction (DR) that leads to antagonistic changes in growth and lifespan, also mediates this change by inhibiting protein synthesis. Direct screens to identify genes that extend lifespan from a subset of genes that are essential for growth and development have also uncovered a number of genes involved in protein synthesis. Given the conserved mechanisms of protein synthesis across species, I discuss potential mechanisms that mediate the lifespan extension by inhibition of protein synthesis that are likely to be important for aging and age-related disorders in humans.

Oscillatory flow-induced proliferation of osteoblast-like cells is mediated by alphavbeta3 and beta1 integrins through synergistic interactions of focal adhesion kinase and Shc with phosphatidylinositol 3-kinase and the Akt/mTOR/p70S6K pathway

Interstitial flow in and around bone tissue is oscillatory in nature and affects the mechanical microenvironment for bone cell growth and formation. We investigated the role of oscillatory shear stress (OSS) in modulating the proliferation of human osteoblast-like MG63 cells and its underlying mechanisms. Application of OSS (0.5 +/- 4 dynes/cm(2)) to MG63 cells induced sustained activation of phosphatidylinositol 3-kinase (PI3K)/Akt/mTOR/p70S6K (p70S6 kinase) signaling cascades and hence cell proliferation, which was accompanied by increased expression of cyclins A and D1, cyclin-dependent protein kinases-2, -4, and -6, and bone formation-related genes (c-fos, Egr-1, and Cox-2) and decreased expression of p21(CIP1) and p27(KIP1). OSS-induced activation of PI3K/Akt/mTOR/p70S6K and cell proliferation were inhibited by specific antibodies or small interference RNAs of alpha(v)beta(3) and beta(1) integrins and by dominant-negative mutants of Shc (Shc-SH2) and focal adhesion kinase (FAK) (FAK(F397Y)). Co-immunoprecipitation assay showed that OSS induces sustained increases in association of Shc and FAK with alpha(v)beta(3) and beta(1) integrins and PI3K subunit p85, which were abolished by transfecting the cells with FAK(F397Y) or Shc-SH2. OSS also induced sustained activation of ERK, which was inhibited by the specific PI3K inhibitor LY294002 and was required for OSS-induced activation of mTOR/p70S6K and proliferation in MG63 cells. Our findings provide insights into the mechanisms by which OSS induces osteoblast-like cell proliferation through activation of alpha(v)beta(3) and beta(1) integrins and synergistic interactions of FAK and Shc with PI3K, leading to the modulation of downstream ERK and Akt/mTOR/p70S6K pathways.

4E-BP extends lifespan upon dietary restriction by enhancing mitochondrial activity in Drosophila

Dietary restriction (DR) extends lifespan in multiple species. To examine the mechanisms of lifespan extension upon DR, we assayed genome-wide translational changes in Drosophila. A number of nuclear encoded mitochondrial genes, including those in Complex I and IV of the electron transport chain, showed increased ribosomal loading and enhanced overall activity upon DR. We found that various mitochondrial genes possessed shorter and less structured 5'UTRs, which were important for their enhanced mRNA translation. The translational repressor 4E-BP, the eukaryotic translation initiation factor 4E binding protein, was upregulated upon DR and mediated DR dependent changes in mitochondrial activity and lifespan extension. Inhibition of individual mitochondrial subunits from Complex I and IV diminished the lifespan extension obtained upon DR, reflecting the importance of enhanced mitochondrial function during DR. Our results imply that translational regulation of nuclear-encoded mitochondrial gene expression by 4E-BP plays an important role in lifespan extension upon DR. For a video summary of this article, see the PaperFlick file with the Supplemental Data available online.

Anergic T cells are metabolically anergic

Full T cell activation requires TCR engagement (signal 1) in the context of costimulation (signal 2). Costimulation is required for maximal expression of effector cytokines and prevention of T cell anergy. It has become increasingly clear that another major function of costimulation is to up-regulate the metabolic machinery necessary for T cell function. In this report we demonstrate that anergic T cells are metabolically anergic, in that upon full stimulation (signals 1 plus 2) they fail to up-regulate the machinery necessary to support increased metabolism. These findings suggest that one mechanism responsible for the maintenance of T cell anergy is failure to up-regulate the metabolic machinery. Furthermore, we demonstrate that by blocking leucine, glucose, and energy metabolism, T cell activation is mitigated. Additionally, inhibition of these metabolic pathways during T cell activation leads to anergy in Th1-differentiated cells. Overall, our findings extend the role of T cell metabolism in regulating T cell function.