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The secretory pathway of protein synthesis and sorting

30/12/2017 · What is the pathway of protein synthesis

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JCI - MNK1 pathway activity maintains protein synthesis …

N2 - It has been shown that SIRT7 regulates rDNA transcription and that reduced SIRT7 levels inhibit tumor growth. This anti-tumor effect could be due to reduced Pol I activity and perturbed ribosome biogenesis. In this study, using pulse labeling with RNA and amino acid analogs, we found that SIRT7 knockdown efficiently suppressed both RNA and protein synthesis. Surprisingly, SIRT7 knockdown preferentially inhibited protein synthesis over rDNA transcription, whereas the levels of both were reduced to similar extents following Pol I knockdown. Using an affinity purification mass spectrometry approach and functional analyses of the resulting SIRT7 interactome, we identified and validated SIRT7 interactions with proteins involved in ribosomal biogenesis. Indeed, SIRT7 co-fractionated with monoribosomes within a sucrose gradient. Using reciprocal isolations, we determined that SIRT7 interacts specifically with mTOR and GTF3C1, a component of the Pol III transcription factor TFIIIC2 complex. Further studies found that SIRT7 knockdown triggered an increase in the levels of LC3B-II, an autophagosome marker, suggesting a link between SIRT7 and the mTOR pathway. Additionally, we provide several lines of evidence that SIRT7 plays a role in modulating Pol III function. Immunoaffinity purification of SIRT7-GFP from a nuclear fraction demonstrated specific SIRT7 interaction with five out of six components of the TFIIIC2 complex, but not with the TFIIIA or TFIIIB complex, the former of which is required for Pol III-dependent transcription of tRNA genes. ChIP assays showed SIRT7 localization to the Pol III targeting genes, and SIRT7 knockdown triggered a reduction in tRNA levels. Taken together, these data suggest that SIRT7 may regulate Pol III transcription through mTOR and the TFIIIC2 complex. We propose that SIRT7 is involved in multiple pathways involved in ribosome biogenesis, and we hypothesize that its down-regulation may contribute to an antitumor effect, partly through the inhibition of protein synthesis.

09/01/2014 · MNK1 pathway activity maintains protein synthesis in ..

New biologic activities of platelets continue to be discovered, indicating that concepts of platelet function in hemostasis, thrombosis, and inflammation require reconsideration as new paradigms evolve. Studies done over 3 decades ago demonstrated that mature circulating platelets have protein synthetic capacity, but it was thought to be low level and inconsequential. In contrast, recent discoveries demonstrate that platelets synthesize protein products with important biologic activities in a rapid and sustained fashion in response to cellular activation. This process, termed signal-dependent translation, uses a constitutive transcriptome and specialized pathways, and can alter platelet phenotype and functions in a fashion that can have clinical relevance. Signal-dependent translation and consequent protein synthesis are examples of a diverse group of posttranscriptural mechanisms in activated platelets that are now being revealed.

Gene expression analysis of protein synthesis pathways …

Signaling Pathways Regulating Protein Synthesis in the …

Using a cell-free system consisting of fractions from homogenates of resting human platelets, Booyse and Rafelson showed that platelet ribosomes are functional and that the lysate system mediated incorporation of radiolabeled amino acids into newly synthesized proteins. In parallel, these investigators and others reported that intact washed human platelets incorporate labeled amino acids into protein products. Rat platelets also incorporate exogenous amino acids into new protein. Puromycin, an inhibitor of translation—but not actinomycin D, an inhibitor of transcription—blocked new protein synthesis by isolated human platelets in these studies.,, This is a classic pattern indicative of posttranscriptional control. Essentially, all of the platelets isolated from normal subjects incorporated radiolabeled amino acids into new protein, demonstrating that this function is not a property of a subset of immature cells. Platelets from splenectomized subjects with idiopathic thrombocytopenic purpura had increased levels of amino acid incorporation into protein, indicating that the physiological state of the subject or the age and maturity of the platelets influence protein synthesis. Extracellular factors were reported to alter protein synthesis by human platelets under some conditions. This provided evidence suggesting that the synthetic mechanisms involved are regulated. Many of these early observations have been corroborated and extended in contemporary studies.,

The initiation step in translation is rate-limiting and begins with interaction of the cap-binding complex of regulatory proteins termed eukaryotic initiation factor 4F to the 5′ cap structure of the mRNA transcript. This is a common and critical event that mediates linearization of the 5′ untranslated region (UTR), ribosomal association, and scanning of the leader sequence under basal and stimulated conditions of protein synthesis in cells of all lineages, although alternative mechanisms are used in a cell- and transcript-selective fashion in such conditions as stress and apoptosis. The cap-binding protein eIF4E, a central component of the eIF4F complex, is abundant in freshly isolated human platelets.,, Platelet activation redistributes eIF4E from the membrane skeleton and cytosol to the cytoskeletal core and facilitates its binding to mRNA transcripts, which are associated with the cytoskeleton and are physically separated from eIF4E under basal conditions. This spatial mechanism of translational control is regulated by engagement of platelet integrins. In platelets and other cells, activity of eIF4E is also regulated by phosphorylation via a p38 mitogen-activated protein (MAP) kinase-catalyzed pathway. Platelets, like other cell types, also have eIF2α,, a critical regulator of binding of the initiator methionyl-tRNA complex to the 40S ribosomal subunit. Thus human platelets have key elements of a translation initiation pathway controlled by eukaryotic initiation factors that are common to a variety of cells. In addition, they have a specialized mechanism of regulation, involving redistribution of eIF4E mediated by cellular activation and integrins.

Signaling Pathways Related to Protein Synthesis and …

Molecular Pathways of Protein Synthesis Inhibition …

Amino acids are classically considered as the building blocks for the synthesis of proteins. Besides this, some of them play a major role in other functions, such as regulation of protein turnover and signal transduction, transport of nitrogen and carbon across the organs, or neurotransmission. The unique characteristics of amino acids are the presence of a free amino group in the α‐carbon and a free carboxyl group. The amino acids differ from each other with respect to their side‐chains. The amino acids are classified into subgroups according to their similarity in carbon skeleton, substituent groups or a common metabolic pathway. The biosynthesis of amino acids involves several biochemical pathways in which amino acids are assembled from other precursors. The biosynthesis of amino acids is distinct from that involving lipids or carbohydrates because it includes the use of nitrogen.

Outline of pathways of synthesis of nonessential amino acids. Modified from Munro HM (ed.) (1969) Evolution of protein metabolism in mammals. In: , vol. 3, pp. 133–182. New York: Academic Press.

Protein synthesis - Others - Signaling Pathways
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  • Overview of the Secretory Pathway - Molecular Cell Biology

    Interferon action: two distinct pathways for inhibition of protein synthesis by double-stranded RNA.

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    Signal-dependent protein synthesis by activated platelets: new pathways to altered phenotype and function.

  • 22/10/1999 · Mechanism of Protein Synthesis

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ribosome and protein synthesis is ..

AB - It has been shown that SIRT7 regulates rDNA transcription and that reduced SIRT7 levels inhibit tumor growth. This anti-tumor effect could be due to reduced Pol I activity and perturbed ribosome biogenesis. In this study, using pulse labeling with RNA and amino acid analogs, we found that SIRT7 knockdown efficiently suppressed both RNA and protein synthesis. Surprisingly, SIRT7 knockdown preferentially inhibited protein synthesis over rDNA transcription, whereas the levels of both were reduced to similar extents following Pol I knockdown. Using an affinity purification mass spectrometry approach and functional analyses of the resulting SIRT7 interactome, we identified and validated SIRT7 interactions with proteins involved in ribosomal biogenesis. Indeed, SIRT7 co-fractionated with monoribosomes within a sucrose gradient. Using reciprocal isolations, we determined that SIRT7 interacts specifically with mTOR and GTF3C1, a component of the Pol III transcription factor TFIIIC2 complex. Further studies found that SIRT7 knockdown triggered an increase in the levels of LC3B-II, an autophagosome marker, suggesting a link between SIRT7 and the mTOR pathway. Additionally, we provide several lines of evidence that SIRT7 plays a role in modulating Pol III function. Immunoaffinity purification of SIRT7-GFP from a nuclear fraction demonstrated specific SIRT7 interaction with five out of six components of the TFIIIC2 complex, but not with the TFIIIA or TFIIIB complex, the former of which is required for Pol III-dependent transcription of tRNA genes. ChIP assays showed SIRT7 localization to the Pol III targeting genes, and SIRT7 knockdown triggered a reduction in tRNA levels. Taken together, these data suggest that SIRT7 may regulate Pol III transcription through mTOR and the TFIIIC2 complex. We propose that SIRT7 is involved in multiple pathways involved in ribosome biogenesis, and we hypothesize that its down-regulation may contribute to an antitumor effect, partly through the inhibition of protein synthesis.

Biological Pathways - Protein Lounge

It has been shown that SIRT7 regulates rDNA transcription and that reduced SIRT7 levels inhibit tumor growth. This anti-tumor effect could be due to reduced Pol I activity and perturbed ribosome biogenesis. In this study, using pulse labeling with RNA and amino acid analogs, we found that SIRT7 knockdown efficiently suppressed both RNA and protein synthesis. Surprisingly, SIRT7 knockdown preferentially inhibited protein synthesis over rDNA transcription, whereas the levels of both were reduced to similar extents following Pol I knockdown. Using an affinity purification mass spectrometry approach and functional analyses of the resulting SIRT7 interactome, we identified and validated SIRT7 interactions with proteins involved in ribosomal biogenesis. Indeed, SIRT7 co-fractionated with monoribosomes within a sucrose gradient. Using reciprocal isolations, we determined that SIRT7 interacts specifically with mTOR and GTF3C1, a component of the Pol III transcription factor TFIIIC2 complex. Further studies found that SIRT7 knockdown triggered an increase in the levels of LC3B-II, an autophagosome marker, suggesting a link between SIRT7 and the mTOR pathway. Additionally, we provide several lines of evidence that SIRT7 plays a role in modulating Pol III function. Immunoaffinity purification of SIRT7-GFP from a nuclear fraction demonstrated specific SIRT7 interaction with five out of six components of the TFIIIC2 complex, but not with the TFIIIA or TFIIIB complex, the former of which is required for Pol III-dependent transcription of tRNA genes. ChIP assays showed SIRT7 localization to the Pol III targeting genes, and SIRT7 knockdown triggered a reduction in tRNA levels. Taken together, these data suggest that SIRT7 may regulate Pol III transcription through mTOR and the TFIIIC2 complex. We propose that SIRT7 is involved in multiple pathways involved in ribosome biogenesis, and we hypothesize that its down-regulation may contribute to an antitumor effect, partly through the inhibition of protein synthesis.

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