Signalling by amino acid nutrients

Lysine crotonylation regulates leucine-deprivation-induced autophagy by a 14-3-3ε-PPM1B axis

Lysine crotonylation as a protein post-translational modification regulates diverse cellular processes and functions. However, the role of crotonylation in nutrient signaling pathways remains unclear. Here, we find a positive correlation between global crotonylation levels and leucine-deprivation-induced autophagy. Crotonylome profiling identifies many crotonylated proteins regulated by leucine deprivation. Bioinformatics analysis dominates 14-3-3 proteins in leucine-mediated crotonylome. Expression of 14-3-3ε crotonylation-deficient mutant significantly inhibits leucine-deprivation-induced autophagy. Molecular dynamics analysis shows that crotonylation increases molecular instability and disrupts the 14-3-3ε amphipathic pocket through which 14-3-3ε interacts with binding partners. Leucine-deprivation-induced 14-3-3ε crotonylation leads to the release of protein phosphatase 1B (PPM1B) from 14-3-3ε interaction. Active PPM1B dephosphorylates ULK1 and subsequently initiates autophagy. We further find that 14-3-3ε crotonylation is regulated by HDAC7. Taken together, our findings demonstrate that the 14-3-3ε-PPM1B axis regulated by crotonylation may play a vital role in leucine-deprivation-induced autophagy.

IDO inhibits a tryptophan sufficiency signal that stimulates mTOR: A novel IDO effector pathway targeted by D-1-methyl-tryptophan

Tryptophan catabolism by indoleamine 2,3-dioxygenase (IDO) alters inflammation and favors T-cell tolerance in cancer, but the underlying molecular mechanisms remain poorly understood. The integrated stress response kinase GCN2, a sensor of uncharged tRNA that is activated by amino acid deprivation, is recognized as an important effector of the IDO pathway. However, in a mouse model of inflammatory carcinogenesis, ablation of Gcn2 did not promote resistance against tumor development like the absence of IDO does, implying the existence of additional cancer-relevant pathways that operate downstream of IDO. Addressing this gap in knowledge, we report that the IDO-mediated catabolism of tryptophan also inhibits the immunoregulatory kinases mTOR and PKC-Θ, along with the induction of autophagy. These effects were relieved specifically by tryptophan but also by the experimental agent 1-methyl-D-tryptophan (D-1MT, also known as NLG8189), the latter of which reversed the inhibitory signals generated by IDO with higher potency. Taken together, our results implicate mTOR and PKC-Θ in IDO-mediated immunosuppressive signaling, and they provide timely insights into the unique mechanism of action of D-1MT as compared with traditional biochemical inhibitors of IDO. These findings are important translationally, because they suggest broader clinical uses for D-1MT against cancers that overexpress any tryptophan catabolic enzyme (IDO, IDO2 or TDO). Moreover, they define mTOR and PKC-Θ as candidate pharmacodynamic markers for D-1MT responses in patients recruited to ongoing phase IB/II cancer trials, addressing a current clinical need.

Baicalein suppresses growth of non-small cell lung carcinoma by targeting MAP4K3

Exploring key genes associated with non-small cell lung carcinoma (NSCLC) may lead to targeted therapies for NSCLC patients. The protein kinase MAP4K3 has been established as an important modulator of cell growth and autophagy in mammals. Herein, we investigated the somatic mutations and the expression pattern of MAP4K3 detected in NSCLC patients based on the TCGA database. Abnormal MAP4K3 expression and its somatic mutations are associated with the carcinogenesis and thereby becoming an attractive therapeutic target. Baicalein, a natural product, was determined to be the first-reported MAP4K3 binding ligand with its KD values of 6.47 μM measured by microscale thermophoresis. Subsequent in silico docking and mutation studies demonstrated that baicalein directly binds to MAP4K3, presumably to the substrate-binding pocket of this kinase domain, causing inactivity of MAP4K3. We further showed that baicalein could induce degradation of MAP4K3 through decreasing its stability and promoting the ubiquitin proteasome pathway. Degradation of MAP4K3 could cause dissociation of the transcription factor EB and 14-3-3 complex, enhance rapid transport of TFEB to the nucleus and trigger TFEB-dependent autophagy, resulting in lung cancer cells proliferation arrest. Knockdown of MAP4K3 expression by siRNA was sufficient to mimic baicalein-induced autophagy. Ectopic expression of the MAP4K3 protein resulted in significant resistance to baicalein-induced autophagy. Baicalein exhibited good tumor growth inhibition in a nude mouse model for human H1299 xenografts, which might be tightly related to its binding to MAP4K3 and degradation of MAP4K3. Our data provide novel mechanistic insights of baicalein/ MAP4K3/ mTORC1/ TFEB axis in regulating baicalein-induced autophagy in NSCLC, suggesting potential therapies for treatment of NSCLC.

Astragalus polysaccharide combined with 10-hydroxycamptothecin inhibits metastasis in non-small cell lung carcinoma cell lines via the MAP4K3/mTOR signaling pathway

Non‑small cell lung carcinoma (NSCLC) is a life‑threatening malignancy. The level of the cell growth regulator mitogen‑activated protein kinase kinase kinase kinase 3 (MAP4K3) has been shown to be correlated with a high risk of NSCLC recurrence and poor recurrence‑free survival rate. The present study examined the effects of Astragalus polysaccharide (APS) and 10‑hydroxycamptothecin (HCPT), which are associated with marked suppression and dephosphorylation of the MAP4K3/mammalian target of rapamycin (mTOR) signaling pathway, in the H1299 NSCLC cell line. APS and HCPT decreased H1299 cell viability, induced apoptosis and altered the cell cycle stages, as evaluated using an 3‑(4,5‑dimethylthiazol‑2‑yl)‑2,5‑diphenyltetrazolium bromide assay and flow cytometric analysis. Furthermore, APS increased the expression of apoptosis‑associated genes B‑cell lymphoma 2 (Bcl‑2) and Bcl‑2‑associated X protein (BAX), of proteases cysteine‑aspartic acid protease (caspase)‑3 and ‑9, and of cytochrome c. HCPT promoted autophagy in H1299 cells, with concomitant suppression of the expression of MAP4K3 and downregulation of mTOR signaling. Notably, combination treatment with the two agents reduced the migration and invasion of H1299 cells compared with the single treatments. It was also demonstrated that the overexpression of MAP4K3 promoted the migration and invasion of H1299 cells, and that the kinase activity was essential to this. These findings suggested that MAP4K3 may be an attractive target for the treatment of NSCLC.

Ceramide inhibits PKCθ by regulating its phosphorylation and translocation to lipid rafts in Jurkat cells

Protein kinase C theta (PKCθ) is a novel, calcium-independent member of the PKC family of kinases that was identified as a central player in T cell signaling and proliferation. Upon T cell activation by antigen-presenting cells, PKCθ gets phosphorylated and activated prior to its translocation to the immunological synapse where it couples with downstream effectors. PKCθ may be regulated by ceramide, a crucial sphingolipid that is known to promote differentiation, growth arrest, and apoptosis. To further investigate the mechanism, we stimulated human Jurkat T cells with either PMA or anti-CD3/anti-CD28 antibodies following induction of ceramide accumulation by adding exogenous ceramide, bacterial sphingomyelinase, or Fas ligation. Our results suggest that ceramide regulates the PKCθ pathway through preventing its critical threonine 538 (Thr538) phosphorylation and subsequent activation, thereby inhibiting the kinase's translocation to lipid rafts. Moreover, this inhibition is not likely to be a generic effect of ceramide on membrane reorganization. Other lipids, namely dihydroceramide, palmitate, and sphingosine, did not produce similar effects on PKCθ. Addition of the phosphatase inhibitors okadaic acid and calyculin A reversed the inhibition exerted by ceramide, and this suggests involvement of a ceramide-activated protein phosphatase. Such previously undescribed mechanism of regulation of PKCθ raises the possibility that ceramide, or one of its derivatives, and may prove valuable in novel therapeutic approaches for disorders involving autoimmunity or excessive inflammation-where PKCθ plays a critical role.

L-arginine affects the IVM of cattle cumulus-oocyte complexes

Nitric oxide (NO) is identified as a signaling molecule involved in many cellular or physiological functions, including meiotic maturation of cattle oocytes. This study aimed to evaluate the effect of supplementation of culture medium with the L-arginine (L-arg, NO synthesis precursor) in nuclear maturation of oocytes, concentrations of nitrate/nitrite, progesterone (P₄), and 17β-estradiol (E₂) in the culture medium; and the cyclic guanosine monophosphate (cGMP) and cyclic adenosine monophosphate (cAMP) intracellular concentrations in the cumulus-oocyte complexes (COCs) during the first hours of maturation in the presence of hemisections (HSs) of the follicular wall (control -ve). The addition of 5.0-mM L-arg increased (P < 0.05) the percentage of oocytes at the germinal vesicle breakdown stage after 7 hours of cultivation compared with control -ve. All concentrations of L-arg (2.5, 5.0, and 10.0 mM) increased the percentage of oocytes that reached the metaphase I (MI) at 15 hours (P < 0.05) but do not affect the progression from MI to metaphase II (P > 0.05) at 22 hours. All concentrations of L-arg tested increased (P < 0.05) the percentage of cumulus cells with plasma membrane integrity at 22 hours of cultivation. L-arginine did not change (P > 0.05) the nitrate/nitrite, P₄, and E₂ concentrations in relation to control -ve at any of the times tested. In immature COCs, immediately after being removed from the follicles (0 hours), the intracellular concentration of cGMP in the control -ve and treatment with 5-mM L-arg progressively decreased (P < 0.05) after the first hour of cultivation; however, COCs treated with 5.0-mM L-arg had higher concentrations of cGMP at 1 hour of cultivation (P < 0.05). The cAMP concentration of COCs supplemented or not with 5.0-mM L-arg progressively increased until 3 hours of cultivation and at, 6 hours, decreased (P < 0.05). The results show, in using this system, that (1) the mechanisms that give the oocyte the ability to restart the meiosis until MI after adding 5.0-mM L-arg do not involve changes in the concentration of nitrate/nitrite, P₄, and E₂ in the culture medium and (2) L-arg acts on a pathway that involves changing the cGMP concentration but does not involve changing cAMP concentration. More studies are needed to assess whether the observed effects of L-arg during IVM using this system are via NO or not and what the role is in increasing the viability of cumulus cells in the resumption and progression of meiosis until MI.

The crucial role of l-arginine in macrophage activation: What you need to know about it

Nowadays, it is well recognized that amino acids are powerful molecules responsible for regulatory control over fundamental cellular processes. However, our understanding of the signaling cascades involved in amino acid sensing in organisms, as well as signal initiation, is largely limited. This is also the case of semi-essential amino acid l-arginine, which has multiple metabolic fates, and it is considered as one of the most versatile amino acids. Recently, some new and important facts have been published considering the role of l-arginine in the regulation of inflammatory processes in several human and mouse models, mediated also via the regulation of macrophage activation. Therefore, this mini review focuses on the actual summarization of information about (i) l-arginine bioavailability in organism, (ii) l-arginine-dependent regulation of nitric oxide synthase expression and nitric oxide production, and importantly (iii) its role in the activation of intracellular signaling pathways and G-protein-coupled receptors in macrophages.

Effects of physiologic concentrations of l-lysine on in vitro replication of feline herpesvirus 1

OBJECTIVE

To evaluate the effects of various concentrations of l-lysine on in vitro replication of feline herpesvirus 1 (FHV-1).

SAMPLE

Cultures of Crandell-Rees feline kidney (CRFK) cells.

PROCEDURES

CRFK cells were inoculated with FHV-1 and maintained in media with 20 combinations of l-arginine and l-lysine concentrations. Changes in cell viability were monitored by continuous measurement of electrical impedance of cultured cells and by observation of viral cytopathic effects. Viral load was determined by use of quantitative PCR assay in supernatants obtained from infected cultures at specified time points.

RESULTS

Increases in l-lysine concentration had no effect on the kinetics of cell death in FHV-1-infected cultures. There was also no significant effect (r(2) < 0.1) on viral DNA load for l-arginine concentrations ≥ 12 μg/mL There was a significant effect of increases in l-lysine concentration on viral DNA load in media supplemented with 6 μg of l-arginine/mL (mean ± SD slope, -4,641 ± 1,626 units; adjusted r(2) = 0.45). However, the difference between the lowest (1 × 10(6.28) copies/μL) and highest (1 × 10(6.86) copies/μL) FHV-1 DNA load in these media was < 1 logarithm.

CONCLUSIONS AND CLINICAL RELEVANCE

The difference in FHV-1 DNA load was unlikely to be biologically important. Various l-lysine concentrations did not inhibit in vitro replication of FHV-1 at l-arginine concentrations sufficient to maintain cell growth. This conclusion was consistent with results of other studies in which investigators have not detected a consistently beneficial effect when l-lysine is administered to FHV-1-infected cats.

Interference of peritoneal dialysis fluids with cell cycle mechanisms

INTRODUCTION

Peritoneal dialysis fluids (PDF) differ with respect to osmotic and buffer compound, and pH and glucose degradation products (GDP) content. The impact on peritoneal membrane integrity is still insufficiently described. We assessed global genomic effects of PDF in primary human peritoneal mesothelial cells (PMC) by whole genome analyses, quantitative real-time polymerase chain reaction (RT-PCR) and functional measurements.

METHODS

PMC isolated from omentum of non-uremic patients were incubated with conventional single chamber PDF (CPDF), lactate- (LPDF), bicarbonate- (BPDF) and bicarbonate/lactate-buffered double-chamber PDF (BLPDF), icodextrin (IPDF) and amino acid PDF (APDF), diluted 1:1 with medium. Affymetrix GeneChip U133Plus2.0 (Affymetrix, CA, USA) and quantitative RT-PCR were applied; cell viability was assessed by proliferation assays.

RESULTS

The number of differentially expressed genes compared to medium was 464 with APDF, 208 with CPDF, 169 with IPDF, 71 with LPDF, 45 with BPDF and 42 with BLPDF. Out of these genes 74%, 73%, 79%, 72%, 47% and 57% were downregulated. Gene Ontology (GO) term annotations mainly revealed associations with cell cycle (p = 10(-35)), cell division, mitosis, and DNA replication. One hundred and eighteen out of 249 probe sets detecting genes involved in cell cycle/division were suppressed, with APDF-treated PMC being affected the most regarding absolute number and degree, followed by CPDF and IPDF. Bicarbonate-containing PDF and BLPDF-treated PMC were affected the least. Quantitative RT-PCR measurements confirmed microarray findings for key cell cycle genes (CDK1/CCNB1/CCNE2/AURKA/KIF11/KIF14). Suppression was lowest for BPDF and BLPDF, they upregulated CCNE2 and SMC4. All PDF upregulated 3 out of 4 assessed cell cycle repressors (p53/BAX/p21). Cell viability scores confirmed gene expression results, being 79% of medium for LPDF, 101% for BLPDF, 51% for CPDF and 23% for IPDF. Amino acid-containing PDF (84%) incubated cells were as viable as BPDF (86%).

CONCLUSION

In conclusion, PD solutions substantially differ with regard to their gene regulating profile and impact on vital functions of PMC, i.e. on cells known to be essential for peritoneal membrane homeostasis.

Arginine, leucine, and glutamine stimulate proliferation of porcine trophectoderm cells through the MTOR-RPS6K-RPS6-EIF4EBP1 signal transduction pathway

During the peri-implantation and early placentation periods in pigs, conceptuses (embryo and its extra-embryonic membranes) undergo dramatic morphological changes and differentiation that require the exchange of nutrients (histotroph) and gasses across the trophectoderm and a true epitheliochorial placenta. Of these nutrients, arginine (Arg), leucine (Leu), and glutamine (Gln) are essential components of histotroph; however, little is known about changes in their total amounts in the uterine lumen of cyclic and pregnant gilts and their effects on cell signaling cascades. Therefore, we determined quantities of Arg, Leu, and Gln in uterine luminal fluids and found that total recoverable amounts of these amino acids increased in pregnant but not cyclic gilts between Days 12 and 15 after onset of estrus. We hypothesized that Arg, Leu, and Gln have differential effects on hypertrophy, hyperplasia, and differentiated functions of trophectoderm cells that are critical to conceptus development. Primary porcine trophectoderm (pTr) cells treated with either Arg, Leu, or Gln had increased abundance of phosphorylated RPS6K, RPS6, and EIF4EBP1 compared to basal levels, and this effect was maintained for up to 120 min. When pTr cells were treated with Arg, Leu, and Gln, low levels of pRPS6K and pEIF4EBP1 were detected in the cytosol, but the abundance of nuclear pRPS6K increased. Immunofluorescence analyses revealed abundant amounts of pRPS6 protein in the cytoplasm of pTr cells treated with Arg, Leu, and Gln. These amino acids also increased proliferation of pTr cells. Furthermore, when Arg, Leu, and Gln were combined with siRNAs for either MTOR, RPTOR, or RICTOR, effects of those amino acids on proliferation of pTr cells were significantly inhibited. Collectively, these results indicate that Arg, Leu, and Gln act coordinately to stimulate proliferation of pTr cells through activation of the MTOR-RPS6K-RPS6-EIF4EBP1 signal transduction pathway.

Select nutrients, progesterone, and interferon tau affect conceptus metabolism and development

Interferon tau (IFNT), a novel multifunctional type I interferon secreted by trophectoderm, is the pregnancy recognition signal in ruminants that also has antiviral, antiproliferative, and immunomodulatory bioactivities. IFNT, with progesterone, affects availability of the metabolic substrate in the uterine lumen by inducing expression of genes for transport of select nutrients into the uterine lumen that activate mammalian target of rapamycin (mTOR) cell signaling responsible for proliferation, migration, and protein synthesis by conceptus trophectoderm. As an immunomodulatory protein, IFNT induces an anti-inflammatory state affecting metabolic events that decrease adiposity and glutamine:fructose-6-phosphate amidotransferase 1 activity, while increasing insulin sensitivity, nitric oxide production by endothelial cells, and brown adipose tissue in rats. This short review focuses on effects of IFNT and progesterone affecting transport of select nutrients into the uterine lumen to stimulate mTOR cell signaling required for conceptus development, as well as effects of IFNT on the immune system and adiposity in rats with respect to its potential therapeutic value in reducing obesity.

Mechanistic mammalian target of rapamycin (MTOR) cell signaling: effects of select nutrients and secreted phosphoprotein 1 on development of mammalian conceptuses

Morphological differentiation of uterine glands in mammals is a postnatal event vulnerable to adverse effects of endocrine disruptors. Exposure of ewe lambs to a progestin from birth to postnatal day 56 prevents development of uterine glands and, as adults, the ewes are unable to exhibit estrous cycles or maintain pregnancy. Uterine epithelia secrete proteins and transport nutrients into the uterine lumen necessary for conceptus development, pregnancy recognition signaling and implantation, including arginine and secreted phosphoprotein 1 (SPP1). Arginine can be metabolized to nitric oxide and to polyamines or act directly to activate MTOR cell signaling to stimulate proliferation, migration, and mRNA translation in trophectoderm cells. SPP1 binds αvβ3 and α5β1 integrins and induces focal adhesion assembly, adhesion and migration of conceptus trophectoderm cells during implantation. Thus, arginine and SPP1 mediate growth, migration, cytoskeletal remodeling and adhesion of trophectoderm essential for pregnancy recognition signaling and implantation.

Uterine histotroph and conceptus development: select nutrients and secreted phosphoprotein 1 affect mechanistic target of rapamycin cell signaling in ewes

Interferon tau (IFNT), the pregnancy recognition signal in ruminants, abrogates the uterine luteolytic mechanism to ensure maintenance of function for the corpora lutea to produce progesterone (P4). IFNT also suppresses expression of classical IFN-stimulated genes by uterine lumenal epithelium (LE) and superficial glandular (sGE) epithelium but, acting in concert with progesterone, affects expression of a multitude of genes critical to growth and development of the conceptus. The LE and sGE secrete proteins and transport nutrients into the uterine lumen necessary for conceptus development, pregnancy recognition signaling, and implantation. Secretions include arginine and secreted phosphoprotein 1 (SPP1). Arginine can be metabolized to nitric oxide and to polyamines or act directly to activate the mechanistic target of rapamycin cell signaling pathway to stimulate proliferation, migration, and mRNA translation in trophectoderm cells. SPP1 binds alphavbeta3 and alpha5beta1 integrins to induce focal adhesion assembly, adhesion, and migration of conceptus trophectoderm cells during implantation. Thus, arginine and SPP1 mediate growth, migration, cytoskeletal remodeling, and adhesion of trophectoderm essential for pregnancy recognition signaling and implantation. This minireview focuses on components of histotroph that affect conceptus development in the ewe.

mTOR Signalling in Health and Disease

The TOR (target of rapamycin) proteins are found in all eukaryotes. TOR has a protein kinase domain, as well as other domains through which it interacts with partner proteins to form at least two types of multiprotein complex, TORC1 and TORC2 (TOR complexes 1 and 2). Rapamycin, an antibiotic and immunosuppressant, inhibits functions of TORC1. Use of this drug has revealed roles for TORC1 and its mammalian counterpart, mTORC1, in promoting many anabolic processes. mTORC1 signalling is activated by growth factors and nutrients. It is highly active in many cancers and plays a role in tumorigenesis and in other diseases. Much less is known so far about the functions and regulation of (m)TORC2. The goal of this meeting was to bring together researchers studying the roles of mTORC1/2 in normal cell and animal physiology in diverse systems, as well as scientists exploring the therapeutic value of inhibiting mTOR (mammalian TOR) signalling.