Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0038187 (starvation)
 24,951 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

GCN2 is a protein kinase in Saccharomyces cerevisiae that is required for increased expression of the transcriptional activator GCN4 in amino acid-starved cells. GCN2 stimulates GCN4 synthesis at the translational level by phosphorylating the alpha subunit of eukaryotic translation initiation factor 2 (eIF-2). We identified a truncated form of the GLC7 gene, encoding the catalytic subunit of a type 1 protein phosphatase, by its ability to restore derepression of GCN4 expression in a strain containing the partially defective gcn2-507 allele. Genetic analysis suggests that the truncated GLC7 allele has a dominant negative phenotype, reducing the level of native type 1 protein phosphatase activity in the cell. The truncated form of GLC7 does not suppress the regulatory defect associated with a gcn2 deletion or a mutation in the phosphorylation site of eIF-2 alpha (Ser-51). In addition, the presence of multiple copies of wild-type GLC7 impairs the derepression of GCN4 that occurs in response to amino acid starvation or dominant-activating mutations in GCN2. These findings suggest that the phosphatase activity of GLC7 acts in opposition to the kinase activity of GCN2 in modulating the level of eIF-2 alpha phosphorylation and the translational efficiency of GCN4 mRNA. This conclusion is supported by biochemical studies showing that the truncated GLC7 allele increases the level of eIF-2 alpha phosphorylation in the gcn2-507 mutant to a level approaching that seen in wild-type cells under starvation conditions. The truncated GLC7 allele also leads to reduced glycogen accumulation, indicating that this protein phosphatase is involved in regulating diverse metabolic pathways in yeast cells.
 ...
PMID:Truncated protein phosphatase GLC7 restores translational activation of GCN4 expression in yeast mutants defective for the eIF-2 alpha kinase GCN2. 133 44

We show that phosphorylation of the alpha subunit of eukaryotic translation initiation factor 2 (eIF-2) by the protein kinase GCN2 mediates translational control of the yeast transcriptional activator GCN4. In vitro, GCN2 specifically phosphorylates the alpha subunit of rabbit or yeast eIF-2. In vivo, phosphorylation of eIF-2 alpha increases in response to amino acid starvation, which is dependent on GCN2. Substitution of Ser-51 with alanine eliminates phosphorylation of eIF-2 alpha by GCN2 in vivo and in vitro and abolishes increased expression of GCN4 and amino acid biosynthetic genes under its control in amino acid-starved cells. The Asp-51 substitution mimics the phosphorylated state and derepresses GCN4 in the absence of GCN2. Thus, an established mechanism for regulating total protein synthesis in mammalian cells mediates gene-specific translational control in yeast.
 ...
PMID:Phosphorylation of initiation factor 2 alpha by protein kinase GCN2 mediates gene-specific translational control of GCN4 in yeast. 173 68

Phosphorylation of the alpha subunit of eukaryotic translation initiation factor 2 (eIF-2 alpha) impairs translation initiation by inhibiting the guanine nucleotide exchange factor for eIF-2, known as eIF-2B. In Saccharomyces cerevisiae, phosphorylation of eIF-2 alpha by the protein kinase GCN2 specifically stimulates translation of GCN4 mRNA in addition to reducing general protein synthesis. We isolated mutations in several unlinked genes that suppress the growth-inhibitory effect of eIF-2 alpha phosphorylation catalyzed by mutationally activated forms of GCN2. These suppressor mutations, affecting eIF-2 alpha and the essential subunits of eIF-2B encoded by GCD7 and GCD2, do not reduce the level of eIF-2 alpha phosphorylation in cells expressing the activated GCN2c kinase. Four GCD7 suppressors were shown to reduce the derepression of GCN4 translation in cells containing wild-type GCN2 under starvation conditions or in GCN2c strains. A fifth GCD7 allele, constructed in vitro by combining two of the GCD7 suppressors mutations, completely impaired the derepression of GCN4 translation, a phenotype characteristic of deletions in GCN1, GCN2, or GCN3. This double GCD7 mutation also completely suppressed the lethal effect of expressing the mammalian eIF-2 alpha kinase dsRNA-PK in yeast cells, showing that the translational machinery had been rendered completely insensitive to phosphorylated eIF-2. None of the GCD7 mutations had any detrimental effect on cell growth under nonstarvation conditions, suggesting that recycling of eIF-2 occurs efficiently in the suppressor strains. We propose that GCD7 and GCD2 play important roles in the regulatory interaction between eIF-2 and eIF-2B and that the suppressor mutations we isolated in these genes decrease the susceptibility of eIF-2B to the inhibitory effects of phosphorylated eIF-2 without impairing the essential catalytic function of eIF-2B in translation initiation.
 ...
PMID:Mutations in the GCD7 subunit of yeast guanine nucleotide exchange factor eIF-2B overcome the inhibitory effects of phosphorylated eIF-2 on translation initiation. 816 76

The transcriptional activator protein GCN4 is responsible for increased transcription of more than 30 different amino acid biosynthetic genes in response to starvation for a single amino acid. This induction depends on increased expression of GCN4 at the translational level. We show that starvation for purines also stimulates GCN4 translation by the same mechanism that operates in amino acid-starved cells, being dependent on short upstream open reading frames in the GCN4 mRNA leader, the phosphorylation site in the alpha subunit of eukaryotic translation initiation factor 2 (eIF-2 alpha), the protein kinase GCN2, and translational activators of GCN4 encoded by GCN1 and GCN3. Biochemical experiments show that eIF-2 alpha is phosphorylated in response to purine starvation and that this reaction is completely dependent on GCN2. As expected, derepression of GCN4 in purine-starved cells leads to a substantial increase in HIS4 expression, one of the targets of GCN4 transcriptional activation. gcn mutants that are defective for derepression of amino acid biosynthetic enzymes also exhibit sensitivity to inhibitors of purine biosynthesis, suggesting that derepression of GCN4 is required for maximal expression of one or more purine biosynthetic genes under conditions of purine limitation. Analysis of mRNAs produced from the ADE4, ADE5,7, ADE8, and ADE1 genes indicates that GCN4 stimulates the expression of these genes under conditions of histidine starvation, and it appeared that ADE8 mRNA was also derepressed by GCN4 in purine-starved cells. Our results indicate that the general control response is more global than was previously imagined in terms of the type of nutrient starvation that elicits derepression of GCN4 as well as the range of target genes that depend on GCN4 for transcriptional activation.
 ...
PMID:Translation of the yeast transcriptional activator GCN4 is stimulated by purine limitation: implications for activation of the protein kinase GCN2. 833 37

Phosphorylation of the alpha subunit of eukaryotic translation initiation factor 2 (eIF-2 alpha) by the protein kinase GCN2 mediates increased translation of the transcriptional activator GCN4 in amino acid-starved yeast cells. We show that this key phosphorylation event and the attendant translational induction of GCN4 are dependent on the product of a previously uncharacterized gene, GCN1. Inactivation of GCN1 did not affect the level of eIF-2 alpha phosphorylation when mammalian eIF-2 alpha kinases were expressed in yeast cells in place of GCN2, arguing against an involvement of GCN1 in dephosphorylation of eIF-2 alpha. In addition, while GCN1 is required in vivo for phosphorylation of eIF-2 alpha by GCN2, cell extracts from gcn1 delta strains contained wild-type levels of GCN2 eIF-2 alpha-kinase activity. On the basis of these results, we propose that GCN1 is not needed for GCN2 kinase activity per se but is required for in vivo activation of GCN2 in response to the starvation signal, uncharged tRNA. GCN1 encodes a protein of 297 kDa with an 88-kDa region that is highly similar in sequence to translation elongation factor 3 identified in several fungal species. This sequence similarity raises the possibility that GCN1 interacts with ribosomes or tRNA molecules and functions in conjunction with GCN2 in monitoring uncharged tRNA levels during the process of translation elongation.
 ...
PMID:GCN1, a translational activator of GCN4 in Saccharomyces cerevisiae, is required for phosphorylation of eukaryotic translation initiation factor 2 by protein kinase GCN2. 849 69

To elucidate the molecular mechanisms of cell death, we have cloned a new gene, designated death-upregulated gene (DUG), from rat insulinoma cells. DUG is constitutively expressed at very low levels in normal cells but is dramatically upregulated in apoptotic cells following serum/glucose starvation or death receptor ligation by Fas ligand. The DUG mRNA is present in two splicing forms: a long form that encodes a protein of 469 amino acids and a short form that gives rise to a polypeptide of 432 amino acids. The predicted DUG protein sequence contains two putative nuclear localization signals and multiple phosphorylation sites for protein kinases and two conserved MA3 domains. Importantly, DUG is homologous to eukaryotic translation initiation factor (eIF) 4G and binds to eIF4A presumably through MA3 domains. Upon transfection, DUG inhibits both intrinsic and extrinsic pathways of apoptosis. Thus, DUG is a novel homologue of eIF4G that regulates apoptosis.
 ...
PMID:DUG is a novel homologue of translation initiation factor 4G that binds eIF4A. 1222 May 11

Eukaryotic cells respond to starvation by decreasing the rate of general protein synthesis while inducing translation of specific mRNAs encoding transcription factors GCN4 (yeast) or ATF4 (humans). Both responses are elicited by phosphorylation of translation initiation factor 2 (eIF2) and the attendant inhibition of its nucleotide exchange factor eIF2B-decreasing the binding to 40S ribosomes of methionyl initiator tRNA in the ternary complex (TC) with eIF2 and GTP. The reduction in TC levels enables scanning ribosomes to bypass the start codons of upstream open reading frames in the GCN4 mRNA leader and initiate translation at the authentic GCN4 start codon. We exploited the fact that GCN4 translation is a sensitive reporter of defects in TC recruitment to identify the catalytic and regulatory subunits of eIF2B. More recently, we implicated the C-terminal domain of eIF1A in 40S-binding of TC in vivo. Interestingly, we found that TC resides in a multifactor complex (MFC) with eIF3, eIF1, and the GTPase-activating protein for eIF2, known as eIF5. Our biochemical and genetic analyses indicate that physical interactions between MFC components enhance TC binding to 40S subunits and are required for wild-type translational control of GCN4. MFC integrity and eIF3 function also contribute to post-assembly steps in the initiation pathway that impact GCN4 expression. Thus, apart from its critical role in the starvation response, GCN4 regulation is a valuable tool for dissecting the contributions of multiple translation factors in the eukaryotic initiation pathway.
 ...
PMID:Study of translational control of eukaryotic gene expression using yeast. 1583 98

Translational control directed by the eukaryotic translation initiation factor 2 alpha-subunit (eIF2alpha) kinase GCN2 is important for coordinating gene expression programs in response to nutritional deprivation. The GCN2 stress response, conserved from yeast to mammals, is critical for resistance to nutritional deficiencies and for the control of feeding behaviors in rodents. The mouse protein IMPACT has sequence similarities to the yeast YIH1 protein, an inhibitor of GCN2. YIH1 competes with GCN2 for binding to a positive regulator, GCN1. Here, we present evidence that IMPACT is the functional counterpart of YIH1. Overexpression of IMPACT in yeast lowered both basal and amino acid starvation-induced levels of phosphorylated eIF2alpha, as described for YIH1 (31). Overexpression of IMPACT in mouse embryonic fibroblasts inhibited phosphorylation of eIF2alpha by GCN2 under leucine starvation conditions, abolishing expression of its downstream target genes, ATF4 (CREB-2) and CHOP (GADD153). IMPACT bound to the minimal yeast GCN1 segment required for interaction with yeast GCN2 and YIH1 and to native mouse GCN1. At the protein level, IMPACT was detected mainly in the brain. IMPACT was found to be abundant in the majority of hypothalamic neurons. Scattered neurons expressing this protein at higher levels were detected in other regions such as the hippocampus and piriform cortex. The abundance of IMPACT correlated inversely with phosphorylated eIF2alpha levels in different brain areas. These results suggest that IMPACT ensures constant high levels of translation and low levels of ATF4 and CHOP in specific neuronal cells under amino acid starvation conditions.
 ...
PMID:IMPACT, a protein preferentially expressed in the mouse brain, binds GCN1 and inhibits GCN2 activation. 1593 39

The integrity of eukaryotic translation initiation factor (eIF) interactions in ribosomal pre-initiation complexes is critical for the proper regulation of GCN4 mRNA translation in response to amino acid availability. Increased phosphorylation of eIF2 under amino acid starvation conditions leads to a corresponding increase in GCN4 mRNA translation. The carboxyl-terminal domain (CTD) of eIF5 (eIF5-CTD) has been identified as a potential nucleation site for pre-initiation complex assembly. To further characterize eIF5 and delineate its role in GCN4 translational control, we isolated mutations leading to temperature sensitivity (Ts- phenotype) targeted at TIF5, the structural gene encoding eIF5 in yeast (Saccharomyces cerevisiae). Nine single point mutations were isolated, in addition to an allele in which the last 15 amino acids were deleted. The nine point mutations clustered in the eIF5-CTD, which contains two conserved aromatic/acidic boxes. Six of the point mutations derepressed GCN4 translation independent of eIF2 phosphorylation (Gcd- phenotype) at a permissive temperature, directly implicating eIF5-CTD in the eIF2/GTP/Met-tRNA(i)Met ternary complex binding process required for GCN4 translational control. In addition, stronger restriction of eIF5-CTD function at an elevated temperature led to failure to derepress GCN4 translation (Gcn- phenotype) in all of the mutants, most likely due to leaky scanning of the first upstream open reading frame of GCN4 mRNA. This latter result directly implicates eIF5-CTD in the process of accurate scanning for, or recognition of, AUG codons. Taken together, our results indicate that eIF5-CTD plays a critical role in both the assembly of the 43S complex and the post-assembly process in the 48S complex, likely during the scanning process.
 ...
PMID:Eukaryotic translation initiation factor 5 is critical for integrity of the scanning preinitiation complex and accurate control of GCN4 translation. 1596 4

Global inhibition of protein synthesis is a hallmark of many cellular stress conditions. Even though specific mRNAs defy this (e.g., yeast GCN4 and mammalian ATF4), the extent and variation of such resistance remain uncertain. In this study, we have identified yeast mRNAs that are translationally maintained following either amino acid depletion or fusel alcohol addition. Both stresses inhibit eukaryotic translation initiation factor 2B, but via different mechanisms. Using microarray analysis of polysome and monosome mRNA pools, we demonstrate that these stress conditions elicit widespread yet distinct translational reprogramming, identifying a fundamental role for translational control in the adaptation to environmental stress. These studies also highlight the complex interplay that exists between different stages in the gene expression pathway to allow specific preordained programs of proteome remodeling. For example, many ribosome biogenesis genes are coregulated at the transcriptional and translational levels following amino acid starvation. The transcriptional regulation of these genes has recently been connected to the regulation of cellular proliferation, and on the basis of our results, the translational control of these mRNAs should be factored into this equation.
 ...
PMID:Global gene expression profiling reveals widespread yet distinctive translational responses to different eukaryotic translation initiation factor 2B-targeting stress pathways. 1622 85


1 2 3 4 5 Next >>