Inhibition Of mTORC1 Activity Research Articles

Characterisation of autophagy induction by the thiopurine drugs azathioprine, mercaptopurine and thioguanine in THP-1 macrophages.

Activating autophagy may be therapeutically beneficial, and we have previously shown that azathioprine (AZA), an immunomodulatory drug, induces autophagy. Here, we evaluated the induction of autophagy by the thiopurines AZA, mercaptopurine (6-MP) and thioguanine (6-TG) in THP-1 macrophages and investigated the mechanism of action in the context of this cellular process. The cytotoxicity of thiopurines was evaluated using an LDH assay. Induction of endogenous LC3 by thiopurines was evaluated using immunostaining. To confirm autophagy activation by thiopurines, a GFP-RFP-LC3 reporter plasmid was used to monitor the maturation of autophagosomes to autolysosomes. Induction of apoptosis by thiopurines was evaluated using Annexin V/PI staining, and ER stress was assessed via RT‒PCR analysis of XBP1 splicing. To gain insight into the mechanism of action of thiopurines, mTORC1 activity and eIF2α-S51 phosphorylation were evaluated by immunoblotting. Thiopurines were not cytotoxic to cells and induced strong time- and concentration-dependent autophagy. Thiopurines activate autophagy with complete progression through the pathway. Induction of autophagy by thiopurines occurred independently of apoptosis and ER stress. Immunoblotting revealed that AZA inhibited mTORC1 activity, and AZA and 6-TG increased eIF2α-S51 phosphorylation. In contrast, 6-MP had a minor effect on either signalling pathway. Thiopurines are strong inducers of autophagy, and autophagy induction should be considered among the mechanisms responsible for patient response to thiopurines.

MTORC1 activity oscillates throughout the cell cycle, promoting mitotic entry and differentially influencing autophagy induction

Mechanistic Target of Rapamycin Complex 1 (mTORC1) is a master metabolic regulator that is active in nearly all proliferating eukaryotic cells; however, it is unclear whether mTORC1 activity changes throughout the cell cycle. We find that mTORC1 activity oscillates from lowest in mitosis/G1 to highest in S/G2. The interphase oscillation is mediated through the TSC complex but is independent of major known regulatory inputs, including Akt and Mek/Erk signaling. By contrast, suppression of mTORC1 activity in mitosis does not require the TSC complex. mTORC1 has long been known to promote progression through G1. We find that mTORC1 also promotes progression through S and G2 and is important for satisfying the Chk1/Wee1-dependent G2/M checkpoint to allow entry into mitosis. We also find that low mTORC1 activity in G1 sensitizes cells to autophagy induction in response to partial mTORC1 inhibition or reduced nutrient levels. Together, these findings demonstrate that mTORC1 is differentially regulated throughout the cell cycle, with important phase-specific consequences for proliferating cells.

Combined inhibition of KRASG12C and mTORC1 kinase is synergistic in non-small cell lung cancer

Current KRASG12C (OFF) inhibitors that target inactive GDP-bound KRASG12C cause responses in less than half of patients and these responses are not durable. A class of RASG12C (ON) inhibitors that targets active GTP-bound KRASG12C blocks ERK signaling more potently than the inactive-state inhibitors. Sensitivity to either class of agents is strongly correlated with inhibition of mTORC1 activity. We have previously shown that PI3K/mTOR and ERK-signaling pathways converge on key cellular processes and that inhibition of both pathways is required for inhibition of these processes and for significant antitumor activity. We find here that the combination of a KRASG12C inhibitor with a selective mTORC1 kinase inhibitor causes synergistic inhibition of Cyclin D1 expression and cap-dependent translation. Moreover, BIM upregulation by KRASG12C inhibition and inhibition of MCL-1 expression by the mTORC1 inhibitor are both required to induce significant cell death. In vivo, this combination causes deep, durable tumor regressions and is well tolerated. This study suggests that the ERK and PI3K/mTOR pathways each mitigate the effects of inhibition of the other and that combinatorial inhibition is a potential strategy for treating KRASG12C-dependent lung cancer.

Nitidine chloride inhibits mTORC1 signaling through ATF4-mediated Sestrin2 induction and targets IGF2R for lysosomal degradation

AimsNitidine chloride (NC), a natural phytochemical alkaloid derived from Zanthoxylum nitidum (Roxb.) DC, exhibits multiple bioactivities, including antitumor, anti-inflammatory, and other therapeutic effects. However, the primary targets of NC and the mechanism of action (MOA) have not been explicitly defined. MethodsWe explored the effects of NC on mTORC1 signaling by immunoblotting and fluorescence microscopy in wild-type and gene knockout cell lines generated by the CRISPR/Cas9 gene editing technique. We identified IGF2R as a direct target of NC via the drug affinity-responsive target stability (DARTS) method. We investigated the antitumor effects of NC using a mouse melanoma B16 tumor xenograft model. Key findingsNC inhibits mTORC1 activity by targeting amino acid-sensing signaling through activating transcription factor 4 (ATF4)-mediated Sestrin2 induction. NC directly binds to IGF2R and promotes its lysosomal degradation. Moreover, NC displayed potent cytotoxicity against various cancer cells and inhibited B16 tumor xenografts. SignificanceNC inhibits mTORC1 signaling through nutrient sensing and directly targets IGF2R for lysosomal degradation, providing mechanistic insights into the MOA of NC.

Role of vaccinia virus growth factor in stimulating the mTORC1-CAD axis of the de novo pyrimidine pathway under different nutritional cues.

Vaccinia virus (VACV), the prototype poxvirus, actively reprograms host cell metabolism upon infection. However, the nature and molecular mechanisms remain largely elusive. Given the diverse nutritional exposures of cells in different physiological contexts, it is essential to understand how VACV may alter various metabolic pathways in different nutritional conditions. In this study, we established the importance of de novo pyrimidine biosynthesis in VACV infection. We elucidated the significance of vaccinia growth factor (VGF), a viral early protein and a homolog of cellular epidermal growth factor, in enabling VACV to phosphorylate the key enzyme CAD of the de novo pyrimidine pathway at serine 1859, a site known to positively regulate CAD activity. While nutrient-poor conditions typically inhibit mTORC1 activation, VACV activates CAD via mTORC1-S6K1 signaling axis, in conditions where glutamine and asparagine are absent. However, unlike its cellular homolog, epidermal growth factor (EGF), VGF peptide alone in the absence of VACV infection has minimal ability to activate CAD, suggestive of the involvement of other viral factor(s) and differential functions to EGF acquired during poxvirus evolution. Our research provides a foundation for understanding the regulation of a significant metabolic pathway, namely, de novo pyrimidine synthesis during VACV infection, shedding new light on viral regulation under distinct nutritional environments. This study not only has the potential to contribute to the advancement of antiviral treatments but also improve the development of VACV as an oncolytic agent and vaccine vector.

Developing a Tanshinone IIA Memetic by Targeting MIOS to Regulate mTORC1 and Autophagy in Glioblastoma.

Tanshinone IIA (T2A) is a bioactive compound that provides promise in the treatment of glioblastoma multiforme (GBM), with a range of molecular mechanisms including the inhibition of the mechanistic target of rapamycin complex 1 (mTORC1) and the induction of autophagy. Recently, T2A has been demonstrated to function through sestrin 2 (SESN) to inhibit mTORC1 activity, but its possible impact on autophagy through this pathway has not been investigated. Here, the model system Dictyostelium discoideum and GBM cell lines were employed to investigate the cellular role of T2A in regulating SESN to inhibit mTORC1 and activate autophagy through a GATOR2 component MIOS. In D. discoideum, T2A treatment induced autophagy and inhibited mTORC1 activity, with both effects lost upon the ablation of SESN (sesn-) or MIOS (mios-). We further investigated the targeting of MIOS to reproduce this effect of T2A, where computational analysis identified 25 novel compounds predicted to strongly bind the human MIOS protein, with one compound (MIOS inhibitor 3; Mi3) reducing cell proliferation in two GBM cells. Furthermore, Mi3 specificity was demonstrated through the loss of potency in the D. discoideum mios- cells regarding cell proliferation and the induction of autophagy. In GBM cells, Mi3 treatment also reduced mTORC1 activity and induced autophagy. Thus, a potential T2A mimetic showing the inhibition of mTORC1 and induction of autophagy in GBM cells was identified.

Glucose deprivation triggers DCAF1-mediated inactivation of Rheb-mTORC1 and promotes cancer cell survival

Low glucose is a common microenvironment for rapidly growing solid tumors, which has developed multiple approaches to survive under glucose deprivation. However, the specific regulatory mechanism remains largely elusive. In this study, we demonstrate that glucose deprivation, while not amino acid or serum starvation, transactivates the expression of DCAF1. This enhances the K48-linked polyubiquitination and proteasome-dependent degradation of Rheb, inhibits mTORC1 activity, induces autophagy, and facilitates cancer cell survival under glucose deprivation conditions. This study identified DCAF1 as a new cellular glucose sensor and uncovered new insights into mechanism of DCAF1-mediated inactivation of Rheb-mTORC1 pathway for promoting cancer cell survival in response to glucose deprivation.

Regulation of TSC2 lysosome translocation and mitochondrial turnover by TSC2 acetylation status

Sirtuin1 (SIRT1) activity decreases the tuberous sclerosis complex 2 (TSC2) lysine acetylation status, inhibiting the mechanistic target of rapamycin complex 1 (mTORC1) signalling and concomitantly, activating autophagy. This study analyzes the role of TSC2 acetylation levels in its translocation to the lysosome and the mitochondrial turnover in both mouse embryonic fibroblast (MEF) and in mouse insulinoma cells (MIN6) as a model of pancreatic β cells. Resveratrol (RESV), an activator of SIRT1 activity, promotes TSC2 deacetylation and its translocation to the lysosome, inhibiting mTORC1 activity. An improvement in mitochondrial turnover was also observed in cells treated with RESV, associated with an increase in the fissioned mitochondria, positive autophagic and mitophagic fluxes and an enhancement of mitochondrial biogenesis. This study proves that TSC2 in its deacetylated form is essential for regulating mTORC1 signalling and the maintenance of the mitochondrial quality control, which is involved in the homeostasis of pancreatic beta cells and prevents from several metabolic disorders such as Type 2 Diabetes Mellitus.

Mycobacterium tuberculosis produces d-serine under hypoxia to limit CD8+ T cell-dependent immunity in mice

Adaptation to hypoxia is a major challenge for the survival of Mycobacterium tuberculosis (Mtb) in vivo. Interferon (IFN)-γ-producing CD8+ T cells contribute to control of Mtb infection, in part by promoting antimicrobial activities of macrophages. Whether Mtb counters these responses, particularly during hypoxic conditions, remains unknown. Using metabolomic, proteomic and genetic approaches, here we show that Mtb induced Rv0884c (SerC), an Mtb phosphoserine aminotransferase, to produce d-serine. This activity increased Mtb pathogenesis in mice but did not directly affect intramacrophage Mtb survival. Instead, d-serine inhibited IFN-γ production by CD8+ T cells, which indirectly reduced the ability of macrophages to restrict Mtb upon co-culture. Mechanistically, d-serine interacted with WDR24 and inhibited mTORC1 activation in CD8+ T cells. This decreased T-bet expression and reduced IFN-γ production by CD8+ T cells. Our findings suggest an Mtb evasion mechanism where pathogen metabolic adaptation to hypoxia leads to amino acid-dependent suppression of adaptive anti-TB immunity.

Inhibition of mitochondrial folate metabolism drives differentiation through mTORC1 mediated purine sensing

Supporting cell proliferation through nucleotide biosynthesis is an essential requirement for cancer cells. Hence, inhibition of folate-mediated one carbon (1C) metabolism, which is required for nucleotide synthesis, has been successfully exploited in anti-cancer therapy. Here, we reveal that mitochondrial folate metabolism is upregulated in patient-derived leukaemic stem cells (LSCs). We demonstrate that inhibition of mitochondrial 1C metabolism through impairment of de novo purine synthesis has a cytostatic effect on chronic myeloid leukaemia (CML) cells. Consequently, changes in purine nucleotide levels lead to activation of AMPK signalling and suppression of mTORC1 activity. Notably, suppression of mitochondrial 1C metabolism increases expression of erythroid differentiation markers. Moreover, we find that increased differentiation occurs independently of AMPK signalling and can be reversed through reconstitution of purine levels and reactivation of mTORC1. Of clinical relevance, we identify that combination of 1C metabolism inhibition with imatinib, a frontline treatment for CML patients, decreases the number of therapy-resistant CML LSCs in a patient-derived xenograft model. Our results highlight a role for folate metabolism and purine sensing in stem cell fate decisions and leukaemogenesis.

Novel Role of Mitochondrial Folate Metabolism in Cell Fate Decisions and Leukaemogenesis

Folate-mediated one carbon (1C) metabolism sustains proliferation of rapidly dividing cells through its direct contribution to nucleotide biosynthesis. In brief, new 1C units are donated from the amino acid serine (the primary source of 1C units), while folate molecules function as 1C unit carriers. Accordingly, antifolates have been used in the treatment of several malignancies, particularly in the field of haemato-oncology. Chronic myeloid leukaemia (CML) is a clonal myeloproliferative disorder that arises in a single haematopoietic stem cell with the introduction of the BCR::ABL1 oncoprotein. Although it is generally accepted that CML is driven by leukaemic stem cells (LSCs) that are insensitive to standard therapy due to their quiescent/slow-cycling status, the role of folate metabolism in LSCs remains undescribed. Transcriptomic analysis of patient-derived CML LSCs (CD34 +38 -) revealed a significant upregulation of folate metabolism genes, including the mitochondrial hydroxymethyltransferase (SHMT2; p≤0.05), when compared with normal counterparts. Furthermore, CML stem/progenitor (CD34 +) cells displayed a significant increase in the exchange rate of formate (folate intermediate necessary for nucleotide synthesis) compared to the secretome of normal CD34 + cells (p<0.05), suggesting an upregulation of 1C metabolism in therapy resistant CML cells. Following SHMT2 knockout (KO), we observed a strong antiproliferative effect and significantly impaired tumour formation in CML cell line xenograft models (p<0.01), verifying that mitochondrial 1C metabolism is not dispensable for CML cells. Metabolic characterisation using liquid chromatography-mass spectrometry revealed that both genetic and pharmacological inhibition (using the SHMT1/2 inhibitor, SHIN1) of 1C metabolism results in a significant decrease in de novo purine synthesis. Furthermore, we uncovered activation of AMPK signalling and suppression of mTORC1 activity following mitochondrial 1C metabolism inhibition. Notably, formate supplementation or reconstitution of purine levels was sufficient to reverse the effect on AMPK and mTORC1. Phenotypically, SHIN1 treatment induced the expression of erythropoiesis markers CD71 and Glycophorin A in CML cells, including patient derived CD34 + cells. AMPKα1/α2 KO revealed that the increased expression of these markers was independent of AMPK activity. Mechanistically, we discovered that reconstitution of purine levels (adenine) and mTORC1 activity prevented erythroid differentiation following SHMT1/2 inhibition, highlighting that depletion of 1C units drives differentiation of leukaemic cells through mTORC1-mediated purine sensing. Of clinical relevance, combination of SHIN1 with imatinib, a frontline treatment for CML patients, decreased the number of therapy-resistant CML LSCs in a patient-derived xenograft model (p<0.05). Lastly, stable isotope-assisted metabolomics using 13C 315N 1-serine revealed that imatinib reduced labelling into purine nucleotides, but it maintained labelling into glutathione (GSH), the most abundant antioxidant in the cell, and its oxidised derivate (GSSG). Through generation of glycine, folate metabolism directly contributes to the GSH pool. These data suggest that standard therapy does not affect the incorporation of serine into GSH, implying that the synergistic effect with folate metabolism inhibition might be related to impeded antioxidant defence. Overall, our findings highlight a novel role for mitochondrial folate metabolism in stem cell fate decisions and leukaemogenesis. This work is available as a preprint: https://www.biorxiv.org/content/10.1101/2022.12.21.521404v1

Not all kidney cysts are created equal: a distinct renal cystogenic mechanism in tuberous sclerosis complex (TSC).

Tuberous Sclerosis Complex (TSC) is an autosomal dominant genetic disease caused by mutations in either TSC1 or TSC2 genes. Approximately, two million individuals suffer from this disorder worldwide. TSC1 and TSC2 code for the proteins harmartin and tuberin, respectively, which form a complex that regulates the mechanistic target of rapamycin complex 1 (mTORC1) and prevents uncontrollable cell growth. In the kidney, TSC presents with the enlargement of benign tumors (angiomyolipomas) and cysts whose presence eventually causes kidney failure. The factors promoting cyst formation and tumor growth in TSC are poorly understood. Recent studies on kidney cysts in various mouse models of TSC, including mice with principal cell- or pericyte-specific inactivation of TSC1 or TSC2, have identified a unique cystogenic mechanism. These studies demonstrate the development of numerous cortical cysts that are predominantly comprised of hyperproliferating A-intercalated (A-IC) cells that express both TSC1 and TSC2. An analogous cellular phenotype in cystic epithelium is observed in both humans with TSC and in TSC2+/- mice, confirming a similar kidney cystogenesis mechanism in TSC. This cellular phenotype profoundly contrasts with kidney cysts found in Autosomal Dominant Polycystic Kidney Disease (ADPKD), which do not show any notable evidence of A-IC cells participating in the cyst lining or expansion. RNA sequencing (RNA-Seq) and confirmatory expression studies demonstrate robust expression of Forkhead Box I1 (FOXI1) transcription factor and its downstream targets, including apical H+-ATPase and cytoplasmic carbonic anhydrase 2 (CAII), in the cyst epithelia of Tsc1 (or Tsc2) knockout (KO) mice, but not in Polycystic Kidney Disease (Pkd1) mutant mice. Deletion of FOXI1, which is vital to H+-ATPase expression and intercalated (IC) cell viability, completely inhibited mTORC1 activation and abrogated the cyst burden in the kidneys of Tsc1 KO mice. These results unequivocally demonstrate the critical role that FOXI1 and A-IC cells, along with H+-ATPase, play in TSC kidney cystogenesis. This review article will discuss the latest research into the causes of kidney cystogenesis in TSC with a focus on possible therapeutic options for this devastating disease.

Glutamine regulates the cellular proliferation and cell cycle progression by modulating the mTOR mediated protein levels of β-TrCP

ABSTRACT The amino acid glutamine plays an important role in cell growth and proliferation. Reliance on glutamine has long been considered a hallmark of highly proliferating cancer cells. Development of strategies for cancer therapy that primarily target glutamine metabolism has been an active area of research. Glutamine depletion is associated with growth arrest and apoptosis-induced cell death; however, the molecular mechanisms involved in this process are not clearly understood. Here, we show that glutamine depletion activates the energetic stress AMPK pathway and inhibits mTORC1 activity. Furthermore, inhibition of mTORC1 reduces the protein levels of β-TrCP, resulting in aberrant cell cycle progression and reduced proliferation. In agreement with the role of β-TrCP in glutamine metabolism, knockdown of β-TrCP resulted in proliferation and cell cycle defects similar to those observed for glutamine depletion. In summary, our results provide mechanistic insights into the role of glutamine metabolism in regulation of cell growth and proliferation via β-TrCP, uncovering a previously undescribed molecular process involved in glutamine metabolism.

Abstract P3194: Redd1 Is Required For Glucose Metabolism And Insulin Sensitivity In Cardiomyocytes

Type II diabetes (TIID) is characterized by insulin resistance (IR) and doubles a patient’s risk for cardiovascular disease (CVD). The pathogenesis of CVD in patients with TIID, or diabetic cardiomyopathy (DC), is unclear. Regulated in development and DNA damage (REDD)1 is a negative regulator of mammalian target of rapamycin complex (mTORC)1. Notably, deletion of REDD1 leads to systemic IR in mice. REDD1 is, therefore, necessary for insulin sensitivity, however the mechanisms required remain unclear. We hypothesized that REDD1 is required for glucose oxidation and, therefore, insulin sensitivity in cardiomyocytes. To examine the role of REDD1 in cardiomyocyte glucose metabolism and energetics, we cultured wild type (WT) AC16 cardiomyocytes or those with REDD1 deletion with 5.5 mM glucose and examined cellular respiration. The data demonstrate compromised respiration, as indicated by reduced maximal respiratory capacity in REDD1-null versus WT cells (1.5-fold±0.214). Importantly, western blotting confirmed the absence of REDD1 in cells with REDD1 deletion, as well as increased phosphorylation of eukaryotic translation initiation factor 4E-binding protein (p4E-BP)1 (Thr37/46) (1.3-fold±0.085), a direct target of mTORC1. Thus, REDD1 inhibits mTORC1 signaling and enhances glucose-driven respiration in cardiomyocytes. To examine the mechanisms by which REDD1 supports glucose utilization, we examined levels of phosphorylated pyruvate dehydrogenase (pPDH) (Ser293). Our data show that pPDH is increased in REDD1-null cells versus WT controls (1.2-fold±0.054), as well as in hearts from REDD1-deficient mice (1.2-fold±0.013), suggesting reduced glucose oxidation. We also observed enhanced extracellular acidification, an indirect measure of glycolysis, in our REDD1-null cells versus WT controls (1.7-fold±0.136). Pyruvate dehydrogenase kinases (PDKs) phosphorylate PDH. In our REDD1-null cells, we observe a significant increase in PDK4 mRNA versus WT controls (8-fold±0.593), as assessed by qPCR and consistent with the diabetic heart. Together, these data suggest that REDD1 inhibits mTORC1 activity and the expression of PDK4, activating PDH, and glucose oxidation as the mechanism by which cardiomyocytes remain insulin sensitive.

MTORC2 acts as a gatekeeper for mTORC1 deficiency-mediated impairments in ILC3 development.

Group 3 innate lymphoid cells (ILC3s) are mediators of intestinal immunity and barrier function. Recent studies have investigated the role of the mammalian target of rapamycin complex (mTOR) in ILC3s, whereas the mTORC1-related mechanisms and crosstalk between mTORC1 and mTORC2 involved in regulating ILC3 homeostasis remain unknown. In this study, we found that mTORC1 but not mTORC2 was critical in ILC3 development, IL-22 production, and ILC3-mediated intestinal homeostasis. Single-cell RNA sequencing revealed that mTORC1 deficiency led to disruption of ILC3 heterogeneity, showing an increase in differentiation into ILC1-like phenotypes. Mechanistically, mTORC1 deficiency decreased the expression of NFIL3, which is a critical transcription factor responsible for ILC3 development. The activities of both mTORC1 and mTORC2 were increased in wild-type ILC3s after activation by IL-23, whereas inhibition of mTORC1 by Raptor deletion or rapamycin treatment resulted in increased mTORC2 activity. Previous studies have demonstrated that S6K, the main downstream target of mTORC1, can directly phosphorylate Rictor to dampen mTORC2 activity. Our data found that inhibition of mTORC1 activity by rapamycin reduced Rictor phosphorylation in ILC3s. Reversing the increased mTORC2 activity via heterozygous or homozygous knockout of Rictor in Raptor-deleted ILC3s resulted in severe ILC3 loss and complete susceptibility to intestinal infection in mice with mTORC1 deficiency (100% mortality). Thus, mTORC1 acts as a rheostat of ILC3 heterogeneity, and mTORC2 protects ILC3s from severe loss of cellsand immune activity against intestinal infection when mTORC1 activity is diminished.

Downregulation of mTORC1 and Mcl-1 by lipid-oversupply contributes to islet β-cell apoptosis and dysfunction

Pancreatic β-cell apoptosis is a key feature of diabetes and can be induced by chronic exposure to saturated fatty acids (FAs). However, the underlying mechanisms remain poorly understood. We presently evaluated the role of Mcl-1 and mTOR in mice fed with high-fat-diet (HFD) and β-cells exposed to the overloaded palmitic acid (PA). Compared with normal-chow-diet (NCD)-fed mice, HFD group showed impaired glucose tolerance after two months. Along with the diabetes progression, pancreatic islets first became hypertrophic and then atrophic, the ratio of β-cell:α-cell increased in the islets of four months HFD-fed mice while decreased after six months. This process was accompanied by significantly increased β-cell apoptosis and AMPK activity, and decreased Mcl-1 expression and mTOR activity. Consistently, glucose-induced insulin secretion dropped. In terms of mechanism, PA with lipotoxic dose could activate AMPK, which in turn inhibited ERK-stimulated Mcl-1Thr163 phosphorylation. Meanwhile, AMPK blocked Akt activity to release Akt inhibition on GSK3β, followed by GSK3β-initiated Mcl-1Ser159 phosphorylation. The context of Mcl-1 phosphorylation finally led to its degradation by ubiquitination. Also, AMPK inhibited the activity of mTORC1, resulting in a lower level of Mcl-1. Suppression of mTORC1 activity and Mcl-1 expression positively related to β-cell failure. Alteration of Mcl-1 or mTOR expression rendered different tolerance of β-cell to different dose of PA. In conclusion, lipid oversupply-induced dual modulation of mTORC1 and Mcl-1 finally led to β-cell apoptosis and impaired insulin secretion. The study may help further understand the pathogenesis of β-cell dysfunction in case of dyslipidemia, and provide promising therapeutic targets for diabetes.

The TRAF2-p62 axis promotes proliferation and survival of liver cancer by activating mTORC1 pathway

TRAF2 (Tumor necrosis factor receptor-associated factor 2) is a dual function protein, acting as an adaptor protein and a ubiquitin E3 ligase, which plays an essential role in mediating the TNFα-NFκB signal pathway. Dysregulated expression of TRAF2 has been reported in a variety of human cancers. Whether and how TRAF2 regulates the growth of liver cancer cells remains elusive. The goal of this study is to investigate potential dysregulation of TRAF2 and its biological function in liver cancer, and to elucidate the underlying mechanism, leading to validation of TRAF2 as an attractive liver cancer target. Here, we reported TRAF2 is up-regulated in human liver cancer cell lines and tissues, and high TRAF2 expression is associated with a poor prognosis of HCC patients. Proteomics profiling along with Co-immunoprecipitation analysis revealed that p62 is a new substrate of TRAF2, which is subjected to TRAF2-induced polyubiquitination via the K63 linkage at the K420 residue. A strong negative correlation was found between the protein levels of p62 and TRAF2 in human HCC samples. TRAF2 depletion inhibited growth and survival of liver cancer cells both in vitro and in vivo by causing p62 accumulation, which is partially rescued by simultaneous p62 knockdown. Mechanistically, TRAF2-mediated p62 polyubiquitylation activates the mTORC1 by forming the p62-mTORC1-Rag complex, which facilitates the lysosome localization of mTORC1. TRAF2 depletion inhibited mTORC1 activity through the disruption of interaction between p62 and the mTORC1 complex. In conclusion, our study provides the proof-of-concept evidence that TRAF2 is a valid target for liver cancer.

MTORC1-Induced Bone Marrow-Derived Mesenchymal Stem Cell Exhaustion Contributes to the Bone Abnormalities in Klotho-Deficient Mice of Premature Aging.

Stem cell exhaustion is a hallmark of aging. Klotho-deficient mice (kl/kl mice) is a murine model that mimics human aging with significant bone abnormalities. The aim of this study is using kl/kl mice to investigate the functional change of bone marrow-derived mesenchymal stem cells (BMSCs) and explore the underlying mechanism. We found that klotho deficiency leads to bone abnormalities. In addition, kl/kl BMSCs manifested hyperactive proliferation but functionally declined both in vivo and in vitro. Mammalian target of rapamycin complex 1 (mTORC1) activity was higher in freshly isolated kl/kl BMSCs, and autophagy in kl/kl BMSCs was significantly decreased, possibly through mTORC1 activation. Conditional medium containing soluble Klotho protein (sKL) rescued hyperproliferation of kl/kl BMSCs by inhibiting mTORC1 activity and restoring autophagy. Finally, intraperitoneal injection of mTORC1 inhibitor rapamycin restored BMSC quiescence, ameliorated bone phenotype, and increased life span of kl/kl mice in vivo. This research highlights a therapeutic strategy to maintain the homeostasis of adult stem cell pool for healthy bone aging.

Nobiletin is capable of regulating certain anti-cancer pathways in a colon cancer cell line.

Natural remedies have the potential to improve conventional cancer therapies and enhance patient outcomes. Citrus polymethoxyflavone nobiletin has been demonstrated to have anticancer effects on several cancer cell lines. In this study, the anti-cancer activity of nobiletin is investigated on Bax, Bcl-2, HO-1, VEGF, MMP-7, Akt, p70S6K, 4EBP1, tuberin, and hamartin. IC50 doses were 403.6µM, 264µM, and 40µM, respectively, at 24, 48, and 72h. Akt, Bax, Bcl-2, and p70S6K levels decreased at nobiletin concentrations greater than 100, 250, 500, and 1000µM, respectively. Nobiletin decreased HO-1 and VEGF levels at concentrations greater than 100µM. MMP-7 levels interestingly increased at 100µM but decreased at doses greater than 250µM. 4EBP1 levels increased, except from 2000 and 3000µM nobiletin concentrations. Tuberin levels increased at 10, 50, and 3000µM, decreased at 250µM, and remained unchanged at the rest of the concentrations. Nobiletin decreased hamartin levels; however, this decrease was statistically significant only at 10, 100, 250, 500, and 3000µM concentrations. Decreased Akt activity might be interpreted as nobiletin inhibiting mTORC1 activity and subsequently increased 4EBP1 and unchanged or decreased p70S6K protein levels. Akt activity can cause suppression of angiogenesis via decreased VEGF, MMP-7, and HO-1 levels at concentrations greater than 500µM. These results are significant as a nobiletin therapy could prevent colon cancer progression by inhibiting Akt signaling and angiogenesis.

Regulation of skeletal muscle protein synthesis in the preterm pig by intermittent leucine pulses during continuous parenteral feeding.

Extrauterine growth restriction is a common complication of preterm birth. Leucine (Leu) is an agonist for the mechanistic target of rapamycin (mTOR) complex 1 (mTORC1) signaling pathway that regulates translation initiation and protein synthesis in skeletal muscle. Previously, we showed that intermittent intravenous pulses of Leu to neonatal pigs born at term receiving continuous enteral nutrition increases muscle protein synthesis and lean mass accretion. Our objective was to determine the impact of intermittent intravenous pulses of Leu on muscle protein anabolism in preterm neonatal pigs administered continuous parenteral nutrition. Following preterm delivery (on day 105 of 115 gestation), pigs were fitted with umbilical artery and jugular vein catheters and provided continuous parenteral nutrition. Four days after birth, pigs were assigned to receive intermittent Leu (1600 µmol kg-1 h-1 ; n = 8) or alanine (1600 µmol kg-1 h-1 ; n = 8) parenteral pulses every 4 h for 28 h. Anabolic signaling and fractional protein synthesis were determined in skeletal muscle. Leu concentration in the longissimus dorsi and gastrocnemius muscles increased in the leucine (LEU) group compared with the alanine (ALA) group (P < 0.0001). Despite the Leu-induced disruption of the Sestrin2·GATOR2 complex, which inhibits mTORC1 activation, in these muscles (P < 0.01), the abundance of mTOR·RagA and mTOR·RagC was not different. Accordingly, mTORC1-dependent activation of 4EBP1, S6K1, eIF4E·eIF4G, and protein synthesis were not different in any muscle between the LEU and ALA groups. Intermittent pulses of Leu do not enhance muscle protein anabolism in preterm pigs supplied continuous parenteral nutrition.