Browsing by Subject "Protein Biosynthesis"
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Item Multiple Gq-Coupled Receptors Converge on a Common Protein Synthesis-Dependent Long Term Depression That Is Affected in Fragile X Syndrome(2007-12-18) Volk, Lenora Joanne; Huber, Kimberly M.Activation of Gq-coupled group I metabotropic glutamate receptors (mGluR1, mGluR5) induces long-term synaptic depression (LTD) that requires rapid, dendritic protein synthesis. The significance of protein synthesis-dependent mGluR LTD to cognitive function is highlighted by the recent finding that mGluR-dependent LTD is enhanced and protein synthesis-independent in the mouse model of fragile X syndrome mental retardation (FXS, Fmr1 KO mice). In fact, group I mGluR antagonism ameliorates some symptoms of FXS in model organisms. However, disagreement exists in the literature as to the specific roles of mGluR1 and mGluR5 in LTD. Using pharmacological and genetic manipulations, I find that mGluR1 or mGluR5 activation is sufficient to induce LTD. In contrast, I see a selective role for persistent mGluR1 activity in expression of LTD induced with the group I mGluR agonist, DHPG. These data demonstrate a novel role for mGluR1 in induction and expression of LTD at hippocampal Schaffer collateral-CA1 synapses and confirm a role for mGluR5 in induction of LTD at this synapse. LTD induced synaptically with paired-pulse low frequency stimulation (PP-LFS) is Gq- and protein synthesis-dependent and shares common signaling and expression mechanisms with DHPG-induced LTD. However, I find that PP-LFS LTD persists in the presence of group 1 mGluR antagonists and in mGluR1 or mGluR5 knockout mice. These data led to the hypothesis that Gq-coupled receptors other than mGluRs are activated by PP-LFS to induce LTD, and LTD mediated by these receptors should share similar signaling and expression mechanisms with mGluR LTD. A previous study shows that muscarinic acetylcholine receptors (mAChRs) activate protein synthesis in hippocampal CA1 dendrites. Data presented here demonstrate that PP-LFS activates both Gq-coupled mAChRs and mGluRs to induce LTD. Pharmacological activation of mAChRs induces LTD that requires rapid protein synthesis and activation of ERK and mTOR translational activation pathways. New proteins maintain mAChR-dependent LTD through a persistent decrease in surface AMPA receptors. In addition, mAChR LTD is enhanced and protein synthesis-independent in Fmr1 knock-out mice. These data reveal that multiple Gq-coupled receptors converge on a common protein synthesis-dependent LTD mechanism that is aberrant in FXS. These findings suggest novel therapeutic strategies for FXS in the form of mAChR antagonists.Item [News](1978-04-27) Land, ChrisItem Regulation of Liver Metabolism by Fibroblast Growth Factor 19(2012-07-20) Kir, Serkan; Mangelsdorf, David J.; Kliewer, Steven A.Fibroblast Growth Factor (FGF) 19 is a postprandial enterokine up-regulated by bile acid receptor FXR upon bile acid uptake into the ileum. FGF19 inhibits hepatic bile acid synthesis through transcriptional repression of cholesterol 7 alpha-hydroxylase (CYP7A1) via a mechanism involving nuclear receptor Small Heterodimer Partner (SHP). Here, I show that two other nuclear receptors, Hepatocyte Nuclear Factor 4 alpha (HNF4 alpha) and Liver Receptor Homolog-1 (LRH-1), enable SHP binding to the Cyp7a1 promoter and therefore are important for negative feedback regulation of Cyp7a1. HNF4 alpha and LRH-1 are also crucial activators of Cyp7a1 transcription. They maintain active transcription histone marks on the Cyp7a1 promoter, whereas FGF19 down-regulates these marks in a SHP-dependent way. Secondly, I show that the MEK/ERK signaling pathway is an integral regulator of bile acid metabolism. ERK activity is necessary to maintain hepatic Shp and Cyp7a1 transcription at their physiologic levels. Inhibition of this pathway causes loss of Shp transcription by disrupting HNF4 alpha and LRH-1 binding to the Shp promoter. Independent from the effects on Shp, MEK/ERK inhibition induces Cyp7a1 transcription. Unexpectedly, the MEK/ERK pathway is not required for repression of Cyp7a1 by FGF19. Although this pathway is activated by FGF19 in livers of Fgf receptor 4 (Fgfr4)-deficient mice probably via other FGFRs, Cyp7a1 repression is largely impaired. Thus, I propose that a signaling mechanism uniquely regulated by FGFR4 must be responsible for FGF19-dependent repression of bile acid synthesis. In addition to its roles in bile acid metabolism, I also show that FGF19 stimulates hepatic protein and glycogen synthesis, but does not induce lipogenesis. The effects of FGF19 are independent of the activity of either insulin or the protein kinase Akt, and instead are mediated through a mitogen-activated protein kinase signaling pathway that activates components of the protein translation machinery and stimulates glycogen synthase activity. Mice lacking FGF15 (the mouse FGF19 ortholog) fail to properly regulate blood glucose and fail to maintain normal postprandial amounts of liver glycogen. FGF19 treatment restored the loss of glycogen in diabetic animals lacking insulin. Thus, FGF19 activates a physiologically important, insulin-independent endocrine pathway that regulates hepatic protein and glycogen metabolism.Item The Roles of Codon Usage in Translation and Transcription(2020-05-01T05:00:00.000Z) Zhao, Fangzhou; Tu, Benjamin; Thomas, Philip J.; Zhang, Xuewu; Liu, YiCodon usage biases are found in all eukaryotic and prokaryotic genomes that can regulate gene expression. Although codon usage has been previously shown to regulate translation elongation speed in fungal systems, its effect in animal systems is not clear. In our first study, using a Drosophila cell-free translation system to directly compare the velocity of translation elongation, we demonstrated that optimal codons speed up translation elongation while non-optimal codons slow it down. In addition, codon usage regulates ribosome movement and stalling on mRNA during translation. Finally, we showed that codon usage affects protein structure and function both in vitro and in Drosophila cells, potentially by regulating co-translational protein folding process. This study indicates that the effects of codon usage on translation elongation speed is a conserved mechanism from fungi to animals and there is a codon usage "code" fine tuning translation elongation speed to achieve optimal co-translational folding. In addition to the role of codon usage in translation, it has also been shown to play a role in regulating gene transcription of reporter genes and there is a global correlation between codon usage and mRNA levels. To further characterize the role of codon usage in gene transcription, we performed nuclear RNA-seq in Neurospora and found that there is a genome-wide strong correlation between gene codon usage bias and nuclear RNA levels, suggesting that codon usage has a global role in impacting transcription in a translation-independent manner. To uncover the underlying mechanism, we performed a genetic screening by performing RNA-seq in over 250 Neurospora single gene knockout strains and identified 18 mutants with significantly reduced correlation between codon usage and mRNA levels. In addition, the deletion of these 18 genes resulted in mRNA level changes in a codon usage-dependent manner. Interestingly, most of these identified genes, such as set-2, are predicted to play a role in regulating transcription or chromatin structures. Together, these results further established the role of synonymous codon sequences in regulating gene transcription and identified potential factors contributing to gene transcription level in a codon dependent manner.Item The Roles of Codon Usage in Translational and Transcriptional Regulation on Gene Expression(2020-11-12) Yang, Qian; Tu, Benjamin; Liu, Yi; Cobb, Melanie H.; Thomas, Philip J.; Buszczak, MichaelCodon usage bias refers to the universal feature of genome that synonymous codons are used at different frequency. Codon usage plays critical roles in determining gene expression levels through impacting multiple fundamental cellular processes. Although the correlation between codon usage and gene expression level has long been observed, the underlying mechanisms are still largely unclear. In the first part, I demonstrate the mechanism of codon usage determining translation efficiency. The slow decoding rate of nonoptimal codon causes ribosome stalling on mRNA, which leads to premature termination of translation and reduced protein production. This process is conserved from Neurospora to Drosophila. In addition, I demonstrate that the premature termination of translation is mediated by the canonical release factor eRF1, which recognizes ribosomes stalled at nonoptimal codons. Together, I propose a model that explains the impact of codon usage on translation efficiency. In the second part, I investigate the role of promoter in codon- dependent gene expression at transcription level. I show that codon usage and sequence downstream of core promoter act in concert to determine the transcription level. Moreover, I identify the regulatory element in Hsp70 promoter that upregulates the transcription of genes containing nonoptimal codons. The differential transcriptional level is achieved through epigenetic regulations affecting nucleosome density and H3K27ac level and premature termination pathway mediated by Ars2, NEXT complex and nuclear exosome. Collectively, these results show that codon usage and promoter impact transcription through multilayer regulatory mechanisms.