Roles of the mammalian target of rapamycin, mTOR, in controlling ribosome biogenesis and protein synthesis

2012 ◽  
Vol 40 (1) ◽  
pp. 168-172 ◽  
Author(s):  
Valentina Iadevaia ◽  
Yilin Huo ◽  
Ze Zhang ◽  
Leonard J. Foster ◽  
Christopher G. Proud

mTORC1 (mammalian target of rapamycin complex 1) is controlled by diverse signals (e.g. hormones, growth factors, nutrients and cellular energy status) and regulates a range of processes including anabolic metabolism, cell growth and cell division. We have studied the impact of inhibiting mTOR on protein synthesis in human cells. Partial inhibition of mTORC1 by rapamycin has only a limited impact on protein synthesis, but inhibiting mTOR kinase activity causes much greater inhibition of protein synthesis. Using a pulsed stable-isotope-labelling technique, we show that the rapamycin and mTOR (mammalian target of rapamycin) kinase inhibitors have differential effects on the synthesis of specific proteins. In particular, the synthesis of proteins encoded by mRNAs that have a 5′-terminal pyrimidine tract is strongly inhibited by mTOR kinase inhibitors. Many of these mRNAs encode ribosomal proteins. mTORC1 also promotes the synthesis of rRNA, although the mechanisms involved remain to be clarified. We found that mTORC1 also regulates the processing of the precursors of rRNA. mTORC1 thus co-ordinates several steps in ribosome biogenesis.

2012 ◽  
Vol 444 (1) ◽  
pp. 141-151 ◽  
Author(s):  
Yilin Huo ◽  
Valentina Iadevaia ◽  
Zhong Yao ◽  
Isabelle Kelly ◽  
Sabina Cosulich ◽  
...  

mTORC1 [mTOR (mammalian target of rapamycin) complex 1] regulates diverse cell functions. mTORC1 controls the phosphorylation of several proteins involved in mRNA translation and the translation of specific mRNAs, including those containing a 5′-TOP (5′-terminal oligopyrimidine). To date, most of the proteins encoded by known 5′-TOP mRNAs are proteins involved in mRNA translation, such as ribosomal proteins and elongation factors. Rapamycin inhibits some mTORC1 functions, whereas mTOR-KIs (mTOR kinase inhibitors) interfere with all of them. mTOR-KIs inhibit overall protein synthesis more strongly than rapamycin. To study the effects of rapamycin or mTOR-KIs on synthesis of specific proteins, we applied pSILAC [pulsed SILAC (stable isotope-labelling with amino acids in cell culture)]. Our results reveal, first, that mTOR-KIs and rapamycin differentially affect the synthesis of many proteins. Secondly, mTOR-KIs inhibit the synthesis of proteins encoded by 5′-TOP mRNAs much more strongly than rapamycin does, revealing that these mRNAs are controlled by rapamycin-insensitive outputs from mTOR. Thirdly, the synthesis of certain other proteins shows a similar pattern of inhibition. Some of them appear to be encoded by ‘novel’ 5′-TOP mRNAs; they include proteins which, like known 5′-TOP mRNA-encoded proteins, are involved in protein synthesis, whereas others are enzymes involved in intermediary or anabolic metabolism. These results indicate that mTOR signalling may promote diverse biosynthetic processes through the translational up-regulation of specific mRNAs. Lastly, a SILAC-based approach revealed that, although rapamycin and mTOR-KIs have little effect on general protein stability, they stabilize proteins encoded by 5′-TOP mRNAs.


2011 ◽  
Vol 39 (2) ◽  
pp. 446-450 ◽  
Author(s):  
Yilin Huo ◽  
Valentina Iadevaia ◽  
Christopher G. Proud

mTOR (mammalian target of rapamycin) forms two distinct types of complex, mTORC (mTOR complex) 1 and 2. Rapamycin inhibits some of the functions of mTORC1, whereas newly developed mTOR kinase inhibitors interfere with the actions of both types of complex. We have explored the effects of rapamycin and mTOR kinase inhibitors on general protein synthesis and, using a new stable isotope-labelling method, the synthesis of specific proteins. In HeLa cells, rapamycin only had a modest effect on total protein synthesis, whereas mTOR kinase inhibitors decreased protein synthesis by approx. 30%. This does not seem to be due to the ability of mTOR kinase inhibitors to block the binding of eIFs (eukaryotic initiation factors) eIF4G and eIF4E. Analysis of the effects of the inhibitors on the synthesis of specific proteins showed a spectrum of behaviours. As expected, synthesis of proteins encoded by mRNAs that contain a 5′-TOP (5′-terminal oligopyrimidine tract) was impaired by rapamycin, but more strongly by mTOR kinase inhibition. Several proteins not known to be encoded by 5′-TOP mRNAs also showed similar behaviour. Synthesis of proteins encoded by ‘non-TOP’ mRNAs was less inhibited by mTOR kinase inhibitors and especially by rapamycin. The implications of our findings are discussed.


2010 ◽  
Vol 21 (12) ◽  
pp. 1922-1936 ◽  
Author(s):  
Quira Zeidan ◽  
Zihao Wang ◽  
Antonio De Maio ◽  
Gerald W. Hart

Protein synthesis is globally regulated through posttranslational modifications of initiation and elongation factors. Recent high-throughput studies have identified translation factors and ribosomal proteins (RPs) as substrates for the O-GlcNAc modification. Here we determine the extent and abundance of O-GlcNAcylated proteins in translational preparations. O-GlcNAc is present on many proteins that form active polysomes. We identify twenty O-GlcNAcylated core RPs, of which eight are newly reported. We map sites of O-GlcNAc modification on four RPs (L6, L29, L32, and L36). RPS6, a component of the mammalian target of rapamycin (mTOR) signaling pathway, follows different dynamics of O-GlcNAcylation than nutrient-induced phosphorylation. We also show that both O-GlcNAc cycling enzymes OGT and OGAse strongly associate with cytosolic ribosomes. Immunofluorescence experiments demonstrate that OGAse is present uniformly throughout the nucleus, whereas OGT is excluded from the nucleolus. Moreover, nucleolar stress only alters OGAse nuclear staining, but not OGT staining. Lastly, adenovirus-mediated overexpression of OGT, but not of OGAse or GFP control, causes an accumulation of 60S subunits and 80S monosomes. Our results not only establish that O-GlcNAcylation extensively modifies RPs, but also suggest that O-GlcNAc play important roles in regulating translation and ribosome biogenesis.


2015 ◽  
Vol 58 (14) ◽  
pp. 5599-5608 ◽  
Author(s):  
Deborah S. Mortensen ◽  
Sophie M. Perrin-Ninkovic ◽  
Graziella Shevlin ◽  
Jan Elsner ◽  
Jingjing Zhao ◽  
...  

2013 ◽  
Vol 56 (7) ◽  
pp. 3090-3101 ◽  
Author(s):  
Anthony A. Estrada ◽  
Daniel G. Shore ◽  
Elizabeth Blackwood ◽  
Yung-Hsiang Chen ◽  
Gauri Deshmukh ◽  
...  

2013 ◽  
Vol 97 (2) ◽  
pp. 286-294 ◽  
Author(s):  
Moïse Coëffier ◽  
Sophie Claeyssens ◽  
Christine Bôle-Feysot ◽  
Charlène Guérin ◽  
Brigitte Maurer ◽  
...  

2020 ◽  
Vol 44 (7-8) ◽  
pp. 393-402
Author(s):  
Minhang Xin ◽  
Hui-Yan Wang ◽  
Hao Zhang ◽  
Ying Shen ◽  
San-Qi Zhang

Twenty-five novel 2,4,6-trisubstituted triazines were synthesized and biologically evaluated. Most of the compounds synthesized showed good antiproliferative activity against HCT-116 and MCF-7. Compounds B18 and B19 showed the best antiproliferative activity. Further study showed B18 and B19 inhibited four phosphoinositide 3-kinase isoforms and mammalian target of rapamycin with good potency. These results demonstrate that 2,4,6-trisubstituted triazines are potentially useful phosphoinositide 3-kinase inhibitors for the development of new anticancer drugs.


Endocrinology ◽  
2009 ◽  
Vol 150 (8) ◽  
pp. 3637-3644 ◽  
Author(s):  
Geyang Xu ◽  
Yin Li ◽  
Wenjiao An ◽  
Shenduo Li ◽  
Youfei Guan ◽  
...  

Ghrelin, a gastric hormone, provides a hunger signal to the central nervous system to stimulate food intake. Mammalian target of rapamycin (mTOR) is an intracellular fuel sensor critical for cellular energy homeostasis. Here we showed the reciprocal relationship of gastric mTOR signaling and ghrelin during changes in energy status. mTOR activity was down-regulated, whereas gastric preproghrelin and circulating ghrelin were increased by fasting. In db/db mice, gastric mTOR signaling was enhanced, whereas gastric preproghrelin and circulating ghrelin were decreased. Inhibition of the gastric mTOR signaling by rapamycin stimulated the expression of gastric preproghrelin and ghrelin mRNA and increased plasma ghrelin in both wild-type and db/db mice. Activation of the gastric mTOR signaling by l-leucine decreased the expression of gastric preproghrelin and the level of plasma ghrelin. Overexpression of mTOR attenuated ghrelin promoter activity, whereas inhibition of mTOR activity by overexpression of TSC1 or TSC2 increased its activity. Ghrelin receptor antagonist d-Lys-3-GH-releasing peptide-6 abolished the rapamycin-induced increment in food intake despite that plasma ghrelin remained elevated. mTOR is therefore a gastric fuel sensor whose activity is linked to the regulation of energy intake through ghrelin.


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