scholarly journals Role of mTOR signaling in intestinal cell migration

2006 ◽  
Vol 291 (3) ◽  
pp. G510-G517 ◽  
Author(s):  
J. Marc Rhoads ◽  
Xiaomei Niu ◽  
Jack Odle ◽  
Lee M. Graves
Keyword(s):  
Amino Acids ◽  
Protein Synthesis ◽  
Cell Migration ◽  
Mammalian Target Of Rapamycin ◽  
Cell Types ◽  
Intestinal Cell ◽  
Resting Cells ◽  
Initial Event ◽  
Intracellular Ca ◽  
Intestinal Repair

An early signaling event activated by amino acids and growth factors in many cell types is the phosphorylation of the mammalian target of rapamycin (mTOR; FRAP), which is functionally linked to ribosomal protein s6 kinase (p70s6k), a kinase that plays a critical regulatory role in the translation of mRNAs and protein synthesis. We previously showed that intestinal cell migration, the initial event in epithelial restitution, is enhanced by l-arginine (ARG). In this study, we used amino acids as prototypic activators of mTOR and ARG, IGF-1, or serum as recognized stimulators of intestinal cell migration. We found that 1) protein synthesis is required for intestinal cell migration, 2) mTOR/p70s6k pathway inhibitors (rapamycin, wortmannin, and intracellular Ca2+ chelation) inhibit cell migration, 3) ARG activates migration and mTOR/p70s6k (but not ERK-2) in migrating enterocytes, and 4) immunocytochemistry reveals abundant p70s6k staining in cytoplasm, whereas phospho-p70s6k is virtually all intranuclear in resting cells but redistributes to the periphery on activation by ARG. We conclude that mTOR/p70s6k signaling is essential to intestinal cell migration, is activated by ARG, involves both nuclear and cytoplasmic events, and may play a role in intestinal repair.

Le transport de la phénylalanine et de la tyrosine chez Brevibacterium linens : spécificité et incorporation dans les protéines

1984 ◽  
Vol 30 (4) ◽  
pp. 430-438 ◽  
Author(s):  
P. Boyaval ◽  
Evelyne Moreira ◽  
M. J. Desmazeaud
Keyword(s):  
Amino Acids ◽  
Protein Synthesis ◽  
Cellular Protein ◽  
Cellular Proteins ◽  
Resting Cells ◽  
Brevibacterium Linens ◽  
Competitive Inhibitors ◽  
High Concentrations ◽  
Cellular Protein Synthesis

The specificity of phenylalanine and tyrosine carriers was investigated using actively metabolizing cells of Brevibacterium linens. The cellular protein synthesis of resting cells was very weakly inhibited, even with high concentrations of chloramphenicol or tetracycline. The nonaromatic amino acids were weak inhibitors for these carriers, while fluorinated analogues of phenylalanine and tyrosine were very potent competitive inhibitors. In practice these analogues cannot be used to replace amino acids to evaluate transport without incorporation because they are incorporated in cellular proteins.

scholarly journals mTOR inhibition activates overall protein degradation by the ubiquitin proteasome system as well as by autophagy

2015 ◽  
Vol 112 (52) ◽  
pp. 15790-15797 ◽  
Author(s):  
Jinghui Zhao ◽  
Bo Zhai ◽  
Steven P. Gygi ◽  
Alfred Lewis Goldberg
Keyword(s):  
Amino Acids ◽  
Protein Synthesis ◽  
Protein Degradation ◽  
Mammalian Cells ◽  
Cholesterol Biosynthesis ◽  
Mammalian Target Of Rapamycin ◽  
Ubiquitin Proteasome System ◽  
Mtor Inhibition ◽  
Protein Ubiquitination ◽  
Ubiquitin Proteasome

Growth factors and nutrients enhance protein synthesis and suppress overall protein degradation by activating the protein kinase mammalian target of rapamycin (mTOR). Conversely, nutrient or serum deprivation inhibits mTOR and stimulates protein breakdown by inducing autophagy, which provides the starved cells with amino acids for protein synthesis and energy production. However, it is unclear whether proteolysis by the ubiquitin proteasome system (UPS), which catalyzes most protein degradation in mammalian cells, also increases when mTOR activity decreases. Here we show that inhibiting mTOR with rapamycin or Torin1 rapidly increases the degradation of long-lived cell proteins, but not short-lived ones, by stimulating proteolysis by proteasomes, in addition to autophagy. This enhanced proteasomal degradation required protein ubiquitination, and within 30 min after mTOR inhibition, the cellular content of K48-linked ubiquitinated proteins increased without any change in proteasome content or activity. This rapid increase in UPS-mediated proteolysis continued for many hours and resulted primarily from inhibition of mTORC1 (not mTORC2), but did not require new protein synthesis or key mTOR targets: S6Ks, 4E-BPs, or Ulks. These findings do not support the recent report that mTORC1 inhibition reduces proteolysis by suppressing proteasome expression [Zhang Y, et al. (2014) Nature 513(7518):440–443]. Several growth-related proteins were identified that were ubiquitinated and degraded more rapidly after mTOR inhibition, including HMG-CoA synthase, whose enhanced degradation probably limits cholesterol biosynthesis upon insulin deficiency. Thus, mTOR inhibition coordinately activates the UPS and autophagy, which provide essential amino acids and, together with the enhanced ubiquitination of anabolic proteins, help slow growth.

scholarly journals Codon optimality in cancer

Oncogene ◽  
2021 ◽  
Author(s):  
Sarah L. Gillen ◽  
Joseph A. Waldron ◽  
Martin Bushell
Keyword(s):  
Amino Acids ◽  
Protein Synthesis ◽  
Cell Fate ◽  
Supply And Demand ◽  
Cell Types ◽  
Coding Region ◽  
Translation Elongation ◽  
Cell Fate Decisions ◽  
Codon Preference ◽  
Different Cell Types

AbstractA key characteristic of cancer cells is their increased proliferative capacity, which requires elevated levels of protein synthesis. The process of protein synthesis involves the translation of codons within the mRNA coding sequence into a string of amino acids to form a polypeptide chain. As most amino acids are encoded by multiple codons, the nucleotide sequence of a coding region can vary dramatically without altering the polypeptide sequence of the encoded protein. Although mutations that do not alter the final amino acid sequence are often thought of as silent/synonymous, these can still have dramatic effects on protein output. Because each codon has a distinct translation elongation rate and can differentially impact mRNA stability, each codon has a different degree of ‘optimality’ for protein synthesis. Recent data demonstrates that the codon preference of a transcriptome matches the abundance of tRNAs within the cell and that this supply and demand between tRNAs and mRNAs varies between different cell types. The largest observed distinction is between mRNAs encoding proteins associated with proliferation or differentiation. Nevertheless, precisely how codon optimality and tRNA expression levels regulate cell fate decisions and their role in malignancy is not fully understood. This review describes the current mechanistic understanding on codon optimality, its role in malignancy and discusses the potential to target codon optimality therapeutically in the context of cancer.

The mTOR Pathway in the Control of Protein Synthesis

Physiology ◽  
2006 ◽  
Vol 21 (5) ◽  
pp. 362-369 ◽  
Author(s):  
Xuemin Wang ◽  
Christopher G. Proud
Keyword(s):  
Amino Acids ◽  
Protein Synthesis ◽  
Growth Factors ◽  
Mammalian Target Of Rapamycin ◽  
Mtor Pathway ◽  
Target Of Rapamycin ◽  
Cell Physiology ◽  
Elongation Factors ◽  
Energy Deficiency

Signaling through mammalian target of rapamycin (mTOR) is activated by amino acids, insulin, and growth factors, and impaired by nutrient or energy deficiency. mTOR plays key roles in cell physiology. mTOR regulates numerous components involved in protein synthesis, including initiation and elongation factors, and the biogenesis of ribosomes themselves.

scholarly journals Distinct Modes of Balancing Glomerular Cell Proteostasis in Mucolipidosis Type II and III Prevent Proteinuria

2020 ◽  
Vol 31 (8) ◽  
pp. 1796-1814 ◽  
Author(s):  
Wiebke Sachs ◽  
Marlies Sachs ◽  
Elke Krüger ◽  
Stephanie Zielinski ◽  
Oliver Kretz ◽  
...  
Keyword(s):  
Protein Synthesis ◽  
Lysosomal Enzymes ◽  
Mammalian Target Of Rapamycin ◽  
Early Death ◽  
Protein Translation ◽  
Cell Types ◽  
Lysosomal Storage ◽  
Compensatory Mechanisms ◽  
Glomerular Cell ◽  
Lysosomal Dysfunction

BackgroundThe mechanisms balancing proteostasis in glomerular cells are unknown. Mucolipidosis (ML) II and III are rare lysosomal storage disorders associated with mutations of the Golgi-resident GlcNAc-1-phosphotransferase, which generates mannose 6-phosphate residues on lysosomal enzymes. Without this modification, lysosomal enzymes are missorted to the extracellular space, which results in lysosomal dysfunction of many cell types. Patients with MLII present with severe skeletal abnormalities, multisystemic symptoms, and early death; the clinical course in MLIII is less progressive. Despite dysfunction of a major degradative pathway, renal and glomerular involvement is rarely reported, suggesting organ-specific compensatory mechanisms.MethodsMLII mice were generated and compared with an established MLIII model to investigate the balance of protein synthesis and degradation, which reflects glomerular integrity. Proteinuria was assessed in patients. High-resolution confocal microscopy and functional assays identified proteins to deduce compensatory modes of balancing proteostasis.ResultsPatients with MLII but not MLIII exhibited microalbuminuria. MLII mice showed lysosomal enzyme missorting and several skeletal alterations, indicating that they are a useful model. In glomeruli, both MLII and MLIII mice exhibited reduced levels of lysosomal enzymes and enlarged lysosomes with abnormal storage material. Nevertheless, neither model had detectable morphologic or functional glomerular alterations. The models rebalance proteostasis in two ways: MLII mice downregulate protein translation and increase the integrated stress response, whereas MLIII mice upregulate the proteasome system in their glomeruli. Both MLII and MLIII downregulate the protein complex mTORC1 (mammalian target of rapamycin complex 1) signaling, which decreases protein synthesis.ConclusionsSevere lysosomal dysfunction leads to microalbuminuria in some patients with mucolipidosis. Mouse models indicate distinct compensatory pathways that balance proteostasis in MLII and MLIII.

scholarly journals Mechanisms involved in the nutritional regulation of mRNA translation: features of the avian model

2006 ◽  
Vol 19 (1) ◽  
pp. 104-116 ◽  
Author(s):  
Sophie Tesseraud ◽  
Mourad Abbas ◽  
Sophie Duchene ◽  
Karine Bigot ◽  
Pascal Vaudin ◽  
...  
Keyword(s):  
Amino Acids ◽  
Protein Synthesis ◽  
Amino Acid ◽  
Muscle Growth ◽  
Mammalian Target Of Rapamycin ◽  
Mrna Translation ◽  
Initiation Factor ◽  
Nutritional Regulation ◽  
Translational Repressor

Abstract:Insulin and amino acids are key factors in regulating protein synthesis. The mechanisms of their action have been widely studied for several years. The insulin signal is mediated by the activation of intracellular kinases such as phosphatidylinositol–3'kinase and the mammalian target of rapamycin (mTOR), affecting the phosphorylation of some major effectors involved in the regulation of translation initiation, i.e. p70 S6 kinase (p70S6K) and the translational repressor eukaryotic initiation factor 4E binding protein (4E-BP1). The amino acid–induced signalling cascade also originates from mTOR and promotes p70S6K and 4E–BP1 activation. However, the mechanisms of regulation are complex and little understood, especially in vivo. Elucidating these mechanisms is important for both fundamental physiology and nutritional applications, i.e. better control of the use of nutrients and optimisation of dietary amino acid supplies in various physiological and physiopathological situations. In comparative physiology, the chicken is an interesting model to gain better understanding of the nutritional regulation of mRNA translation because of the very high rates of muscle growth and protein synthesis, and the unusual features compared with mammals. In the present review we provide an overview of the roles of insulin and amino acids as regulators of protein synthesis in both mammals and avian species.

Exercise- and nutrient-controlled mechanisms involved in maintenance of the musculoskeletal mass

2007 ◽  
Vol 35 (5) ◽  
pp. 1302-1305 ◽  
Author(s):  
M.J. Rennie
Keyword(s):  
Amino Acids ◽  
Protein Synthesis ◽  
Protein Turnover ◽  
Muscle Protein ◽  
Muscle Protein Synthesis ◽  
Mammalian Target Of Rapamycin ◽  
Inhibitory Effect ◽  
Bone Collagen ◽  
Disuse Atrophy ◽  
Protein Breakdown

The mechanisms of maintenance of the protein mass of muscle and associated connective tissue and bone are becoming more accessible as a result of the use of a combination of well-established techniques for measurement of protein turnover and measurement of protein expression and phosphorylation state of signalling molecules involved in anabolic and catabolic responses. Amino acids, hormones and physical activity appear to be the major short-term physiological regulators of muscle mass, mainly through their actions on protein synthesis and breakdown, on a time scale of minutes to hours, with duration of changes in gene expression up to weeks. Amino acids are the main components in the diet regulating protein turnover, having marked effects in stimulating muscle protein synthesis and with almost no effect on muscle protein breakdown. Branched-chain amino acids, and in particular leucine, simulate protein synthesis via signalling pathways involving mTOR (mammalian target of rapamycin) in a dose–response manner. Insulin has little effect on protein synthesis in human muscle, but it has a marked inhibitory effect on protein breakdown. The amino acid simulation of anabolism is not dependent on the presence of insulin, IGF-1 (insulin-like growth factor-1) or growth hormone. Exercise not only stimulates protein synthesis in muscle, but also in tendon; and disuse atrophy is accompanied by marked decreases of both muscle and tendon collagen protein synthesis. Bone collagen synthesis appears to be nutritionally regulated by the availability of amino acids, but not lipid or glucose.

scholarly journals Rapid heparin-sensitive Ca2+ release following Ca2+-ATPase inhibition in intact HL-60 granulocytes. Evidence for Ins(1,4,5)P3-dependent Ca2+ cycling across the membrane of Ca2+ stores

1994 ◽  
Vol 302 (1) ◽  
pp. 155-162 ◽  
Author(s):  
C J Favre ◽  
D P Lew ◽  
K H Krause
Keyword(s):  
Osmotic Shock ◽  
Cell Types ◽  
Underlying Mechanism ◽  
Resting Cells ◽  
Atpase Inhibitor ◽  
Intact Cells ◽  
Permeabilized Cells ◽  
Partial Activation ◽  
Intracellular Ca ◽  
Atpase Inhibition

In many cell types, emptying of intracellular Ca2+ stores after application of inhibitors of the intracellular Ca(2+)-ATPase (e.g. thapsigargin) is astonishingly rapid. It was the aim of this study to elucidate the underlying mechanism. We first compared thapsigargin-induced emptying of intracellular Ca2+ stores in intact and homogenized HL-60 granulocytes. Thapsigargin-induced Ca2+ release was rapid in intact cells (33.9 +/- 4.9% of store content/min), but it was slow in permeabilized or homogenized cells (7.7 +/- 3.9 and 12 +/- 3.8% of store content/min respectively). To study whether the Ins(1,4,5)P3 receptor might be involved in thapsigargin-induced Ca2+ release, we tested the effect of heparin, a competitive Ins(1,4,5)P3 antagonist. In homogenized and permeabilized preparations, heparin did not interfere with thapsigargin-induced Ca2+ release. In contrast, when introduced into intact cells by an endocytosis/osmotic-shock procedure, heparin, but not the inactive de-N-sulphated heparin, decreased the rate of Ca2+ release by approx. 70%. Heparin inhibited Ca2+ release in response to the Ins(1,4,5)P3-generating receptor agonist N-formylmethionyl-leucyl-phenylalanine (f-MLP) (50 nM) and to thapsigargin (50 nM) at comparable concentrations. Heparin inhibition was competitive for f-MLP-induced, but not for thapsigargin-induced, Ca2+ release. In permeabilized cells, the addition of low Ins(1,4,5)P3 concentrations before thapsigargin increased the rate of thapsigargin-induced Ca2+ release 4-fold. Taken together, our results suggest that the rapid Ca(2+)-ATPase-inhibitor-induced Ca2+ release is due to a partial activation of the Ins(1,4,5)P3 receptor in resting cells. This implies Ca2+ cycling across the membrane of Ins(1,4,5)P3-sensitive Ca2+ stores in resting cells.

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