Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.4.25.1 (proteasome)
28,817 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Wingless/Wnt signaling directs cell-fate choices during embryonic development. In Drosophila, Wingless signaling mediates endoderm induction and the establishment of segment polarity in the developing embryo. The fly Wingless cascade is strikingly similar to the vertebrate Wnt signaling pathway, which controls a number of key developmental decisions such as dorsal-ventral patterning in Xenopus. Factors of the TCF/LEF HMG domain family (Tcfs) have recently been established as the downstream effectors of the Wingless/Wnt signal transduction pathways. Upon Wingless/Wnt signaling, a cascade is initiated that results in the accumulation of cytoplasmic beta-catenin (or its fly homolog, Armadillo). There is also a concomitant translocation of beta-catenin/Armadillo to the nucleus, where it interacts with a specific sequence motif at the N terminus of Tcfs to generate a transcriptionally active complex. This bipartite transcription factor is targeted to the upstream regulatory regions of Tcf target genes including Siamois and Nodal related gene-3 in Xenopus, engrailed and Ultrabithorax in Drosophila via the sequence-specific HMG box, and mediates their transcriptional activation by virtue of transactivation domains contributed by beta-catenin/Armadillo. In the absence of Wingless/Wnt signals, a key negative regulator of the pathway, GSK3 beta, is activated, which mediates the downregulation of cytoplasmic beta-catenin/Armadillo via the ubiquitin-proteasome pathway. In the absence of nuclear beta-catenin, the Tcfs recruit the corepressor protein Groucho to the target gene enhancers and actively repress their transcription. An additional corepressor protein, CREB-binding protein (CBP), may also be involved in this repression of Tcf target gene activity. Several other proteins, including adenomatous polyposis coli (APC), GSK3 beta, and Axin/Conductin, are instrumental in the regulation of beta-catenin/Armadillo. In APC-deficient colon carcinoma cell lines, beta-catenin accumulates and is constitutively complexed with nuclear Tcf-4. A proportion of APC wild-type colon carcinomas and melanomas also contains constitutive nuclear Tcf-4/beta-catenin complexes as a result of dominant mutations in the N terminus of beta-catenin that render it insensitive to downregulation by APC, GSK3 beta, and Axin/Conductin. This results in the unregulated expression of Tcf-4 target genes such as c-myc. Based on the established role for Tcf-4 in maintaining intestinal stem cells it is likely that deregulation of c-myc expression as a result of constitutive Tcf-4/beta-catenin activity promotes uncontrolled intestinal cell proliferation. This would readily explain the formation of intestinal polyps during colon carcinogenesis. Similar mechanisms leading to deregulation of Tcf target gene activity are likely to be involved in melanoma and other forms of cancer.
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PMID:The Yin-Yang of TCF/beta-catenin signaling. 1054 54

The tumour suppressor gene adenomatous polyposis coli (APC) is mutated in sporadic and familial colorectal tumours. APC is involved in the proteasome-mediated degradation of beta-catenin, through its interaction with beta-catenin, GSK-3 beta and Axin. APC also interacts with the microtubule cytoskeleton and has been localized to clusters near the distal ends of microtubules at the edges of migrating epithelial cells. Moreover, in Xenopus laevis epithelial cells, APC has been shown to move along microtubules and accumulate at their growing plus ends. However, the mechanism of APC accumulation and the nature of these APC clusters remain unknown. We show here that APC interacts with the kinesin superfamily (KIF) 3A-KIF3B proteins, microtubule plus-end-directed motor proteins, through an association with the kinesin superfamily-associated protein 3 (KAP3). The interaction of APC with KAP3 was required for its accumulation in clusters, and mutant APCs derived from cancer cells were unable to accumulate efficiently in clusters. These results suggest that APC and beta-catenin are transported along microtubules by KAP3-KIF3A-KIF3B, accumulate in the tips of membrane protrusions, and may thus regulate cell migration.
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PMID:Identification of a link between the tumour suppressor APC and the kinesin superfamily. 1191 92

The Wnt signalling cascade plays an important role during embryonic patterning and cell fate determination and is highly conserved throughout evolution. Factors of the TCF/LEF HMG domain family (Tcfs) are the downstream effectors of this signal transduction pathway. Upon Wnt signalling, a cascade is initiated that results in the translocation of beta-catenin to the nucleus, where it interacts with Tcf to generate a transcriptionally active complex. This bipartite transcription factor is targeted to the upstream regulatory regions of Tcf target genes. In the absence of Wnt signals, beta-catenin is degraded in the cytoplasm via the ubiquitin-proteasome pathway. Several proteins are instrumental in achieving this tight regulation of beta-catenin levels in the cell, including adenomatous polyposis coli (APC), GSK3 beta, and Axin/Conductin. Deregulation of the Wnt signalling pathway is implicated in several forms of cancer, such as colon carcinoma and melanoma. This deregulation is achieved via mutation of APC, beta-catenin or Axin, resulting in elevated beta-catenin levels and the presence of constitutively active Tcf-beta-catenin complexes in the nucleus. The accompanying inappropriate activation of target genes is considered to be a critical, early event in this carcinogenesis. In addition to regulating beta-catenin levels, normal healthy cells have evolved a second level of regulation, by manipulating the activity of the Tcf proteins themselves. In the absence of Wnt signalling, Tcf complexes with several transcriptional repressor proteins ensuring active repression of Tcf target genes. In this review the dual role of Tcf proteins in the Wnt signalling cascade will be discussed.
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PMID:TCF: Lady Justice casting the final verdict on the outcome of Wnt signalling. 1193 63

CCAAT/enhancer-binding protein alpha (C/EBPalpha), a basic leucine zipper transcription factor, is involved in mitotic growth arrest and differentiation. Given that numerous proteins involved in cell cycle regulation are degraded via the ubiquitin-proteasome system, we examined whether the C/EBPalpha protein is degraded via a proteasomal mechanism. In cycloheximide-treated BALB/MK2 keratinocytes we found that C/EBPalpha is a short-lived protein with a half-life of approximately 1 h. Treatment with proteasome inhibitors, MG-132 or lactacystin, blocked the degradation of the C/EBPalpha protein. Higher molecular weight species of ubiquitinated C/EBPalpha were detected in BALB/MK2, and in vitro studies confirmed that C/EBPalpha is degraded by the proteasome in an ATP- and ubiquitin-dependent manner. GSK3 is a known C/EBPalpha kinase and treatment of keratinocytes with LiCl, an inhibitor of GSK3 resulted in: (i) a 5-fold increase in C/EBPalpha protein levels, (ii) increased electrophoretic mobility of C/EBPalpha, and (iii) no increase in C/EBPalpha mRNA levels suggesting that GSK3-mediated phosphorylation of C/EBPalpha may target it for proteasomal degradation. However, a mutant C/EBPalpha containing T to A mutations in the GSK3 phosphorylation sites (T222A and T226A) retained its response to LiCl, and additional pharmacological inhibitors of GSK3 did not alter C/EBPalpha levels indicating the effects of LiCl on C/EBPalpha are GSK3-independent. LiCl treatment of BALB/MK2 cells inhibited C/EBPalpha degradation and produced a 6-fold increase in the half-life of C/EBPalpha protein. In vitro studies revealed that LiCl inhibited proteasome activity and the ensuing degradation of C/EBPalpha. These results demonstrate C/EBPalpha is degraded via a ubiquitin-dependent proteasomal pathway, and LiCl stabilizes C/EBPalpha through a GSK3-independent pathway involving direct inhibition of proteasome activity.
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PMID:Lithium stabilizes the CCAAT/enhancer-binding protein alpha (C/EBPalpha) through a glycogen synthase kinase 3 (GSK3)-independent pathway involving direct inhibition of proteasomal activity. 1266 82

The oncoprotein BCL-3 is a nuclear transcription factor that activates NF-kappaB target genes through formation of heterocomplexes with p50 or p52. BCL-3 is phosphorylated in vivo, but specific BCL-3 kinases have not been identified so far. In this report, we show that BCL-3 is a substrate for the protein kinase GSK3 and that GSK3-mediated BCL-3 phosphorylation, which is inhibited by Akt activation, targets its degradation through the proteasome pathway. This phosphorylation modulates its association with HDAC1, -3, and -6 and attenuates its oncogenicity by selectively controlling the expression of a subset of newly identified target genes such as SLPI and Cxcl1. Our results therefore suggest that constitutive BCL-3 phosphorylation by GSK3 regulates BCL-3 turnover and transcriptional activity.
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PMID:GSK3-mediated BCL-3 phosphorylation modulates its degradation and its oncogenicity. 1546 20

Many studies have implicated phosphorylated tau in the Alzheimer disease process. However, the cellular fate of phosphorylated tau has only recently been described. Recent work has shown that tau phosphorylation at substrate sites for the kinases Cdk5 and GSK3-beta can trigger the binding of tau to the chaperones Hsc70 and Hsp27. The binding of phosphorylated tau to Hsc70 implied that the complex may be a substrate for the E3 ligase CHIP and this possibility was experimentally verified. The presence of this system in cells suggests that phosphorylated tau may hold toxic dangers for cell viability, and the response of the cell is to harness a variety of protective mechanisms. These include binding to chaperones, which may prevent more toxic conformations of the protein, ubiquitination which will direct the protein to the proteasome, segregation of tau aggregates from the cellular machinery, and recruitment of Hsp27 which will confer anti-apoptotic properties to the cell.
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PMID:Phosphorylated tau and the neurodegenerative foldopathies. 1561 47

Peroxisome proliferator-activated receptor gamma (PPARgamma) is a nuclear receptor regulating an array of diverse functions in a variety of cell types including regulation of genes associated with growth and differentiation. Its most notable function is to regulate development of adipose tissue, which involves coordinating expression of many hundreds of genes responsible for establishment of the mature adipocyte phenotype. Our recent studies have demonstrated a role for MEK/ERK signaling and CCAAT/enhancer binding proteins (C/EBP)beta in regulating expression of PPARgamma during adipogenesis. Furthermore, we have shown that cAMP-dependent signaling along with C/EBPbeta leads to the stimulation of PPARgamma activity by mechanisms that probably involve production of PPARgamma ligands. Additionally, we have recently demonstrated that phosphorylation of C/EBPbeta at a consensus ERK/GSK3 site is required for the PPARgamma-associated expression of adiponectin during the terminal stages of adipogenesis. GSK3beta also influences PPARgamma activity by regulating the turnover and subcellular localization of beta-catenin, a potent transcriptional activator of Wnt signaling. In fact, we have recently shown a crosstalk between PPARgamma and beta-catenin signaling. Specifically, activation of PPARgamma induces the degradation of beta-catenin during preadipocyte differentiation by mechanisms that require GSK3beta and the proteasome. In contrast, expression of a GSK3beta-phosphorylation-defective beta-catenin renders beta-catenin resistant to the degradatory action of PPARgamma. Interestingly, expression of the mutant beta-catenin blocks expression of adiponectin and C/EBPalpha in response to the activation of PPARgamma.
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PMID:Regulation of PPARgamma activity during adipogenesis. 1571 76

Alzheimer's disease is a genetically complex disorder associated with multiple genetic defects, either mutational or of susceptibility. Although potentially associated with an accelerated stochastically driven aging process, Alzheimer's disease is an independent clinical entity in which the aging process exerts a deleterious effect on brain activity in conjunction with polymodal genetic factors and other pathological conditions (i.e., age-related cerebrovascular deterioration) and environmental factors (i.e., nutrition). Alzheimer's disease genetics does not explain in full the etiopathogenesis of this disease. Therefore, it is likely that environmental factors and/or epigenetic phenomena also contribute to Alzheimer's disease pathology and phenotypic expression of dementia. The genomics of Alzheimer's disease is still in its infancy, but this field is aiding the understanding of novel aspects of this disease, including genetic epidemiology, multifactorial risk factors, pathogenic mechanisms associated with genetic networks and genetically regulated metabolic cascades. Alzheimer's disease genomics is also helping to develop new strategies in pharmacogenomic research and prevention. Functional genomics, proteomics, pharmacogenomics, high-throughput methods, combinatorial chemistry and modern bioinformatics will greatly contribute to accelerate drug development for Alzheimer's disease and other complex disorders. The multifactorial genetic dysfunction in dementia includes mutational loci (APP, PS1, PS2, TAU) and diverse susceptibility loci (APOE, alpha2M, alphaACT, LRP1, IL1 alpha, TNF, ACE, BACE, BCHE, CST3, MTHFR, GSK3 beta, NOS3 and many other genes) distributed across the human genome, probably converging in a common pathogenic mechanism that leads to premature neuronal death, in which mitochondrial DNA mutations may contribute to increased genetic variability and heterogeneity. In Alzheimer's disease, multiple pathogenic events, including genetic factors, accumulation of aberrant or misfolded proteins, protofibril formation, ubiquitin-proteasome system dysfunction, excitotoxic reactions, oxidative and nitrosative stress, mitochondrial injury, synaptic failure, altered metal homeostasis, dysfunction of axonal and dendritic transport, and chaperone misoperation may converge in pathogenic pathways leading to premature death and neurodegeneration. Some of these mechanisms are common to several neurodegenerative disorders, which differ depending upon the gene(s) affected and the involvement of specific genetic networks, together with epigenetic factors and environmental events. Many genes potentially associated with Alzheimer's disease in some studies cannot be confirmed as candidate genes in replication studies, indicating that methodological problems and genomic complexity are leading to erroneous conclusions. A different approach to Alzheimer's disease functional genomics is to integrate individual genetic information in polygenic genotypes (haplotype-like model) and to investigate genotype-phenotype correlations and genotype-related pharmacogenomic behaviors. The application of functional genomics to Alzheimer's disease can be a suitable strategy for molecular diagnosis and for understanding pathophysiological mechanisms associated with Alzheimer's disease-related neurodegeneration. Furthermore, the pharmacogenomics of Alzheimer's disease may contribute in the future to optimize drug development and therapeutics, increasing efficacy and safety, and reducing side-effects and unnecessary costs.
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PMID:Molecular genetics of Alzheimer's disease and aging. 1647 Feb 48

The Hedgehog (Hh) signaling pathway governs cell growth and patterning in animal development. Malfunction of several pathway components, including the key transcriptional effector Ci/Gli proteins, leads to a variety of human disorders including several malignancies. Ci/Gli activity is controlled by multi-layered regulatory mechanisms, the most prominent of which is the ubiquitin-mediated proteolysis. In the absence of Hh, Ci/Gli is proteolytically processed into a truncated form that functions as a transcriptional repressor of the Hh pathway. Ci processing is mediated by an SCF (Skip1/Cul1/F-box protein) ubiquitin ligase in which the F-box protein Slimb/beta-TRCP bridges Ci to the ubiquitin ligase. Recent studies in Drosophila and mammalian cultured cells have demonstrated that sequential phosphorylation of Ci/Gli by PKA, GSK3, and CKI creates multiple docking sites that can recruit SCF(Slimb/beta-TRCP), which then promotes Ci/Gli ubiquitination followed by proteasome-mediated processing. Recently, an E3 ubiquitin ligase consisting of the BTB (Broad Complex, Tramtrack, and Bric a Brac) protein HIB (Hh induced MATH and BTB protein) and Cullin 3 (Cul3) has been identified that acts in a negative feedback loop to fine-tune Hh signaling responses by degrading full length Ci. In eye imaginal discs where Hh signals coordinate cell proliferation and differentiation, HIB is highly expressed in the differentiating cells to prevent aberrant Hh signaling activity and ensure normal eye development. Tissue- and developmental stage-specific expression of HIB and its homologs in vertebrates may provide a conserved mechanism for ensuring precision in spatial and temporal control of Hh signaling.
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PMID:Regulation of Hh/Gli signaling by dual ubiquitin pathways. 1710 30

Anthrax lethal toxin (LeTx) is a virulence factor causing immune suppression and toxic shock of Bacillus anthracis infected host. It inhibits cytokine production and cell proliferation/differentiation in various immune cells. This study showed that a brief exposure of LeTx caused a continual MEK1 cleavage and prevented tumor necrosis factor-alpha (TNF) production in response to lipopolysaccharide (LPS) in non-proliferating cells such as human peripheral blood mononuclear cells or mouse primary peritoneal macrophages. In human monocytic cell lines U-937 and THP-1, LeTx induced cell cycle arrest in G0-G1 phase by rapid down-regulation of cyclin D1/D2 and checkpoint kinase 1 through MEK1 inhibition. However, THP-1 cells adaptively adjusted to LeTx and overrode cell cycle arrest by activating the phosphatidylinositol 3-kinase/Akt signaling pathway. Inhibitory Ser-9 phosphorylation of glycogen synthase kinase 3beta (GSK3beta) by Akt prevented proteasome-mediated cyclin D1 degradation and induced cell cycle progress in LeTx-intoxicated THP-1 cells. Recovery from cell cycle arrest was required before recovering from on-going MEK1 cleavage and suppression of TNF production. Furthermore, pretreatment with LeTx or the GSK3-specific inhibitor SB-216763, or transfection with dominant active mutant Akt or degradation-defected mutant cyclin D1 protected cells from LeTx-induced cell cycle arrest, on-going MEK1 cleavage and suppression of TNF production. These results indicate that modulation of phosphatidylinositol 3-kinase/Akt/GSK3beta signaling cascades can be beneficial for protecting or facilitating recovery from cellular LeTx intoxication in cells that depend on basal MEK1 activity for proliferation.
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PMID:Critical role of the phosphatidylinositol 3-kinase/Akt/glycogen synthase kinase-3 signaling pathway in recovery from anthrax lethal toxin-induced cell cycle arrest and MEK cleavage in macrophages. 1795 Dec 52


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