Dataset Information

Rheb-TOR signaling promotes protein synthesis, but not glucose or amino acid import, in Drosophila.

ABSTRACT:

Background

The Ras-related GTPase, Rheb, regulates the growth of animal cells. Genetic and biochemical tests place Rheb upstream of the target of rapamycin (TOR) protein kinase, and downstream of the tuberous sclerosis complex (TSC1/TSC2) and the insulin-signaling pathway. TOR activity is regulated by nutritional cues, suggesting that Rheb might either control, or respond to, nutrient availability.

Results

We show that Rheb and TOR do not promote the import of glucose, bulk amino acids, or arginine in Drosophila S2 cells, but that both gene products are important regulators of ribosome biogenesis, protein synthesis, and cell size. S2 cell size, protein synthesis, and glucose import were largely insensitive to manipulations of insulin signaling components, suggesting that cellular energy levels and TOR activity can be maintained through insulin/PI3K-independent mechanisms in S2 cell culture. In vivo in Drosophila larvae, however, we found that insulin signaling can regulate protein synthesis, and thus may affect TOR activity.

Conclusion

Rheb-TOR signaling controls S2 cell growth by promoting ribosome production and protein synthesis, but apparently not by direct effects on the import of amino acids or glucose. The effect of insulin signaling upon TOR activity varies according to cellular type and context.

SUBMITTER: Hall DJ

PROVIDER: S-EPMC1847425 | biostudies-literature | 2007 Mar

REPOSITORIES: biostudies-literature

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Publications

Rheb-TOR signaling promotes protein synthesis, but not glucose or amino acid import, in Drosophila.

Hall Dayna J DJ Grewal Savraj S SS de la Cruz Aida Flor A AF Edgar Bruce A BA

BMC biology 20070319

<h4>Background</h4>The Ras-related GTPase, Rheb, regulates the growth of animal cells. Genetic and biochemical tests place Rheb upstream of the target of rapamycin (TOR) protein kinase, and downstream of the tuberous sclerosis complex (TSC1/TSC2) and the insulin-signaling pathway. TOR activity is regulated by nutritional cues, suggesting that Rheb might either control, or respond to, nutrient availability.<h4>Results</h4>We show that Rheb and TOR do not promote the import of glucose, bulk amino ...[more]

PMID: 17371599

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Project description:We show that the sensitivity of tsc mutant cells to rapamycin is mediated by TORC1 and can be suppressed by overexpression of the 2-oxoglutarate-Fe(II) dependent oxygenase, Isp7. We show that Isp7 is a novel regulator of amino acids uptake that acts via regulation of gene expression, both upstream and downstream of TOR signaling. suppressed by overexpression of the putative 2-oxoglutarate-Fe(II) dependent oxygenase, Isp7. We show that Isp7 is a novel master regulator of amino acids uptake that acts via regulation of gene expression, both upstream and downstream of TOR signaling. TOR proteins reside in two distinct complexes, TOR complex 1 and 2 (TORC1 and TORC2) that are central for the regulation of cellular growth, proliferation and survival. TOR is also the target for the immunosuppressive and anti-cancer drug rapamycin. In Schizosaccharaomyces pombe, disruption of the TSC complex, mutations in which can lead to the Tuberous Sclerosis syndrome in humans, results in a rapamycin sensitive phenotype under poor nitrogen conditions. We show here that the sensitivity to rapamycin is mediated via inhibition of TORC1 and suppressed by overexpression of isp7+, a member of the family of 2-oxoglutarate-Fe(II) dependent oxygenases. The transcript level of isp7+ is negatively regulated by TORC1 but positively regulated by TORC2. Yet, we find extensive similarity between the transcriptome of cells disrupted for isp7+ and cells mutated in the catalytic subunit of TORC1. Moreover, Isp7 regulates amino acid permease expression similarly to TORC1 and in contrast to TORC2. Overexpression of isp7+ induces TORC1-dependent phosphorylation of ribosomal protein Rps6, while inhibiting TORC2-dependent phosphorylation and activation of the AGC-like kinase Gad8. Taken together, our findings suggest a central role for Isp7 in amino acid homeostasis and the presence of isp7+-dependent regulatory loops that affect both TORC1 and TORC2. 6 Samples (arrays) were performed. We generated pairwise comparison between DISP7 and WT, using Partek Genomics Suite. Genes with pâ¤5%[FDR] and a fold-change difference of â¥2\1.5 or <-2\-1.5 were selected.

Project description:Postexercise protein ingestion can elevate rates of myofibrillar protein synthesis (MyoPS), mTORC1 activity, and mTOR translocation/protein-protein interactions. However, it is unclear if leucine-enriched essential amino acids (LEAA) can similarly facilitate intracellular mTOR trafficking in humans after exercise. The purpose of this study was to determine the effect of postexercise LEAA (4 g total EAAs, 1.6 g leucine) on acute MyoPS and mTORC1 translocation and signaling. Recreationally active men performed lower-body resistance exercise (5 × 8-10 leg press and leg extension) to volitional failure. Following exercise participants consumed LEAA (n = 8) or an isocaloric carbohydrate drink (PLA; n = 10). MyoPS was measured over 1.5-4 h of recovery by oral pulse of l-[ring-2H5]-phenylalanine. Phosphorylation of proteins in the mTORC1 pathway were analyzed via immunoblotting and mTORC1-LAMP2/WGA/Rheb colocalization via immunofluorescence microscopy. There was no difference in MyoPS between groups (LEAA = 0.098 ± 0.01%/h; PL = 0.090 ± 0.01%/h; P > 0.05). Exercise increased (P < 0.05) rpS6Ser240/244(LEAA = 35.3-fold; PLA = 20.6-fold), mTORSer2448(LEAA = 1.8-fold; PLA = 1.2-fold) and 4EBP1Thr37/46(LEAA = 1.5-fold; PLA = 1.4-fold) phosphorylation irrespective of nutrition (P > 0.05). LAT1 and SNAT2 protein expression were not affected by exercise or nutrient ingestion. mTOR-LAMP2 colocalization was greater in LEAA preexercise and decreased following exercise and supplement ingestion (P < 0.05), yet was unchanged in PLA. mTOR-WGA (cell periphery marker) and mTOR-Rheb colocalization was greater in LEAA compared with PLA irrespective of time-point (P < 0.05). In conclusion, the postexercise consumption of 4 g of LEAA maintains mTOR in peripheral regions of muscle fibers, in closer proximity to its direct activator Rheb, during prolonged recovery independent of differences in MyoPS or mTORC1 signaling compared with PLA ingestion. This intracellular localization of mTOR may serve to "prime" the kinase for future anabolic stimuli.NEW & NOTEWORTHY This is the first study to investigate whether postexercise leucine-enriched amino acid (LEAA) ingestion elevates mTORC1 translocation and protein-protein interactions in human skeletal muscle. Here, we observed that although LEAA ingestion did not further elevate postexercise MyoPS or mTORC1 signaling compared with placebo, mTORC1 peripheral location and interaction with Rheb were maintained. This may serve to "prime" mTORC1 for subsequent anabolic stimuli.

Dataset Information

Rheb-TOR signaling promotes protein synthesis, but not glucose or amino acid import, in Drosophila.

Background

Results

Conclusion

Publications

Rheb-TOR signaling promotes protein synthesis, but not glucose or amino acid import, in Drosophila.

Similar Datasets

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