A novel role for aminoacyl‐tRNA synthetases in the regulation of polypeptide chain initiation

Pollard, Jeffrey W.; Galpine, Angela R.; Clemens, Michael J.

doi:10.1111/j.1432-1033.1989.tb14793.x

Cited by 30 publications

(15 citation statements)

References 34 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…7C), providing evidence that uncharged tRNA accumulated to the extent that mGcn2 was activated, and consistent with earlier findings (36,46,47). As expected, no change in eIF2␣ phosphorylation was seen in the control cells as a result of the temperature shift.…”

Section: Overexpression Of Rheb But Not Tctp Enhances Mtorc1 Signalsupporting

confidence: 90%

See 1 more Smart Citation

Re-evaluating the Roles of Proposed Modulators of Mammalian Target of Rapamycin Complex 1 (mTORC1) Signaling

Wang

Fonseca

Tang

et al. 2008

Journal of Biological Chemistry

Self Cite

133

View full text Add to dashboard Cite

Signaling through mammalian target of rapamycin complex 1 (mTORC1) is stimulated by amino acids and insulin. Insulin inactivates TSC1/2, the GTPase-activator complex for Rheb, and Rheb⅐GTP activates mTORC1. It is not clear how amino acids regulate mTORC1. FKBP38 (immunophilin FK506-binding protein, 38 kDa), was recently reported to exert a negative effect on mTORC1 function that is relieved by its binding to Rheb⅐GTP. We confirm that Rheb binds wild type FKBP38, but inactive Rheb mutants showed contrasting abilities to bind FKBP38. We were unable to observe any regulation of FKBP38/ mTOR binding by amino acids or insulin. Furthermore, FKBP38 did not inhibit mTORC1 signaling. The translationally controlled tumor protein (TCTP) in Drosophila was recently reported to act as the guanine nucleotide-exchange factor for Rheb. We have studied the role of TCTP in mammalian TORC1 signaling and its control by amino acids. Reducing TCTP levels did not reproducibly affect mTORC1 signaling in amino acidreplete/insulin-stimulated cells. Moreover, overexpressing TCTP did not rescue mTORC1 signaling in amino acid-starved cells. In addition, we were unable to see any stable interaction between TCTP and Rheb or mTORC1. Accumulation of uncharged tRNA has been previously proposed to be involved in the inhibition of mTORC1 signaling during amino acid starvation. To test this hypothesis, we used a Chinese hamster ovary cell line containing a temperature-sensitive mutation in leucyltRNA synthetase. Leucine deprivation markedly inhibited mTORC1 signaling in these cells, but shifting the cells to the nonpermissive temperature for the synthetase did not. These data indicate that uncharged tRNA Leu does not switch off mTORC1 signaling and suggest that mTORC1 is controlled by a distinct pathway that senses the availability of amino acids. Our data also indicate that, in the mammalian cell lines tested here, neither TCTP nor FKBP38 regulates mTORC1 signaling.

show abstract

Section: Overexpression Of Rheb But Not Tctp Enhances Mtorc1 Signalsupporting

confidence: 90%

“…Shifting the cells to the latter temperature mimics the effects of amino acid starvation on protein synthesis (43). The control cells (TR-3) were a single-step temperature revertant of tsH1 and have normal leucyl-tRNA synthetase activity at 39.5°C (35,36). Both TR-3 and tsH1 cells were grown in 5% CO 2 in a humidified incubator at 34°C.…”

Section: Methodsmentioning

confidence: 99%

Re-evaluating the Roles of Proposed Modulators of Mammalian Target of Rapamycin Complex 1 (mTORC1) Signaling

Wang

Fonseca

Tang

et al. 2008

Journal of Biological Chemistry

Self Cite

133

View full text Add to dashboard Cite

show abstract

“…This noncatalytic segment of the kinase is thought to act as a receptor for deacylated tRNAs, and mediate activation of GCN-2 (9). Studies in mammalian cells depleted of amino acids, or treated with histidinol (50), a competitive inhibitor of tRNA His synthetase, or that contain a temperature-sensitive mutant of leucyl tRNA synthetase (51,52), have each also demonstrated increased eIF-2␣ phosphorylation. Although these changes have been attributed to accumulation of uncharged tRNA or altered tRNA aminoacyl synthetase activity, the direct demonstration of an eIF-2␣ kinase activated by amino acid withdrawal is lacking; some data point to a decrease in eIF-2␣ phosphatase induced by amino acid depletion (50).…”

Section: Amino Acid Sufficiency Signals To the Translational Apparatus-mentioning

confidence: 99%

Amino Acid Sufficiency and mTOR Regulate p70 S6 Kinase and eIF-4E BP1 through a Common Effector Mechanism

Hara¹,

Yonezawa²,

Weng³

et al. 1998

Journal of Biological Chemistry

1,247

1,105

View full text Add to dashboard Cite

The present study identifies the operation of a signal tranduction pathway in mammalian cells that provides a checkpoint control, linking amino acid sufficiency to the control of peptide chain initiation. Withdrawal of amino acids from the nutrient medium of CHO-IR cells results in a rapid deactivation of p70 S6 kinase and dephosphorylation of eIF-4E BP1, which become unresponsive to all agonists. Readdition of the amino acid mixture quickly restores the phosphorylation and responsiveness of p70 and eIF-4E BP1 to insulin. Increasing the ambient amino acids to twice that usually employed increases basal p70 activity to the maximal level otherwise attained in the presence of insulin and abrogates further stimulation by insulin. Withdrawal of most individual amino acids also inhibits p70, although with differing potency. Amino acid withdrawal from CHO-IR cells does not significantly alter insulin stimulation of tyrosine phosphorylation, phosphotyrosine-associated phosphatidylinositol 3-kinase activity, c-Akt/protein kinase B activity, or mitogen-activated protein kinase activity. The selective inhibition of p70 and eIF-4E BP1 phosphorylation by amino acid withdrawal resembles the response to rapamycin, which prevents p70 reactivation by amino acids, indicating that mTOR is required for the response to amino acids. A p70 deletion mutant, p70⌬2-46/⌬CT104, that is resistant to inhibition by rapamycin (but sensitive to wortmannin) is also resistant to inhibition by amino acid withdrawal, indicating that amino acid sufficiency and mTOR signal to p70 through a common effector, which could be mTOR itself, or an mTOR-controlled downstream element, such as a protein phosphatase.

show abstract

“…These organized structures include the complexes of aminoacyl-tRNA synthetases described above, the association of aminoacyltRNA synthetases with ribosomes (34-36) and elongation factor (37), and the binding of many protein synthesis components to the cytoskeletal framework of the cell (38)(39)(40)(41). In addition, there is evidence for a functional interaction between aminoacyl-tRNA synthetases and initiation factors (42).…”

Section: Resultsmentioning

confidence: 99%

Existence of two forms of rat liver arginyl-tRNA synthetase suggests channeling of aminoacyl-tRNA for protein synthesis.

Sivaram

Deutscher

1990

Proc. Natl. Acad. Sci. U.S.A.

View full text Add to dashboard Cite

Arginyl-tRNA synthetase (arginine-tRNA ligase, EC 6.1.1.19) is found in extracts of mammalian cells both as a free protein (Mr = 60,000) and as a component (Mr 72,000) of the high molecular weight aminoacyl-tRNA synthetase complex (Mr > 106). Several pieces of evidence indicate that the low molecular weight free form is not a proteolytic degradation product of the complex-bound enzyme but that it preexists in vivo: (i) the endogenous free form differs in size from the active proteolytic fragment generated in vitro, (ii) conditions expected to increase or decrease the amount of proteolysis do not alter the ratio of the two forms of the enzyme, and (iu) the free form contains an NH2-terminal methionine residue. A model is presented that provides a rationale for the existence of two forms of arginyl-tRNA synthetase in cells. In this model the complexed enzyme supplies arginyl-tRNA for protein synthesis, whereas the free enzyme provides arginyltRNA for the N112-terminal arginine modification of proteins by arginyl-tRNA:protein arginyltransferase. This latter process targets certain proteins for removal by the ubiquitindependent protein degradation pathway. The necessity for an additional pool of arginyl-tRNA for the modifcation reaction leads to the conclusion that the arginyl-tRNA destined for protein synthesis (and/or protein modification) is channeled and unavailable for other processes. Other evidence supporting channeling in protein synthesis is discussed.It is becoming increasingly clear that many, if not all, of the macromolecular components of cells are organized into multienzyme complexes or associated with subcellular structures (see ref. 1 for a review). A major consequence of such organization is that it can lead to compartmentalization or channeling of metabolic pathways (i.e., the transfer of metabolites from one enzyme to another without equilibration with the total fluid of the cell). Channeled pathways presumably would be more efficient than free ones by increasing the local substrate concentrations for a given amount of substrate, by

show abstract

A novel role for aminoacyl‐tRNA synthetases in the regulation of polypeptide chain initiation

Cited by 30 publications

References 34 publications

Re-evaluating the Roles of Proposed Modulators of Mammalian Target of Rapamycin Complex 1 (mTORC1) Signaling

Re-evaluating the Roles of Proposed Modulators of Mammalian Target of Rapamycin Complex 1 (mTORC1) Signaling

Amino Acid Sufficiency and mTOR Regulate p70 S6 Kinase and eIF-4E BP1 through a Common Effector Mechanism

Existence of two forms of rat liver arginyl-tRNA synthetase suggests channeling of aminoacyl-tRNA for protein synthesis.

Contact Info

Product

Resources

About