Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.4.25.1 (proteasome)
 28,817 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Mammalian polyamine synthesis is regulated by a unique feedback mechanism. When cellular polyamine levels increase, antizyme, an ornithine decarboxylase (ODC) inhibitory protein, is induced by polyamine-dependent translational frameshifting. Antizyme not only inhibits ODC, a key enzyme in polyamine synthesis, it also targets the enzyme degradation by the 26S proteasome. Furthermore, it suppresses cellular uptake of polyamines. Previously, we isolated two zebrafish antizymes with different expressions and activities. This suggested that a common feedback mechanism of polyamine metabolism might operate in mammals and zebrafish (Danio rerio). In the present study, cDNAs of zebrafish ODC and antizyme inhibitor, another regulatory protein that inhibits antizyme action, were cloned. The presence of ODC and antizyme inhibitor mRNAs was confirmed by Northern blotting in embryos and adult fish, as well as in a zebrafish-derived cell line (BRF41). The activity of the ODC cDNA expression product was inhibited by short and long zebrafish antizymes, and recombinant zebrafish antizyme inhibitor reversed this inhibition. In the BRF41 cells, the ODC half-life was considerably longer than that of mammalian ODC but shorter than that of Schizosaccharomyces pombe. Spermidine elicited a rapid decay of ODC activity and ODC protein in a protein synthesis-dependent manner.
 ...
PMID:Regulation of ornithine decarboxylase by antizymes and antizyme inhibitor in zebrafish (Danio rerio). 1239 84

Interestingly, there is a major difference in turnover rate between ornithine decarboxylases (ODCs) from various trypanosomatids. ODCs from Trypanosoma brucei and Leishmania donovani are both stable proteins, whereas ODC from Crithidia fasciculata is a metabolically unstable protein in the parasite. C. fasciculata ODC is also rapidly degraded in mammalian systems, whereas the closely related L. donovani ODC is not. The degradation of C. fasciculata ODC in the mammalian systems is shown to be dependent on a functional 26 S proteasome. However, in contrast to the degradation of mammalian ODC, the degradation of C. fasciculata ODC does not involve antizyme. Instead, it appears the degradation of C. fasciculata ODC may be associated with poly-ubiquitination of the enzyme.
 ...
PMID:Turnover of trypanosomal ornithine decarboxylases. 1265 49

Ornithine decarboxylase (ODC) is the first enzyme in polyamine biosynthesis in numerous living organisms, from bacteria to mammalian cells. Its control is under negative feedback regulation by the end products of the pathway. In dimorphic fungi, ODC activity and therefore polyamine concentrations are related to the morphogenetic process. From the fission yeast Schizosaccharomyces pombe to human, polyamines induce antizyme synthesis which in turn inactivates ODC. This is hydrolyzed by the 26S proteasome without ubiquitination. The regulatory mechanism of antizyme on polyamines is conserved, although to date no antizyme homology has been identified in some fungal species. The components that are responsible for regulating polyamine levels in cells and the current knowledge of ODC regulation in dimorphic fungi are presented in this review. ODC degradation is of particular interest because inhibitors of this pathway may lead to the discovery of novel antifungal drugs.
 ...
PMID:[Mechanisms of degradation of the fungal ornithine decarboxylase]. 1282 73

Antizyme-1 (AZ1) is a protein that negatively regulates polyamine synthesis by inhibiting the key synthetic enzyme ornithine decarboxylase and targeting it for degradation by the 26 S proteasome. Recent work shows that antizyme protein translocates to the nucleus during mouse development (Gritli-Linde, A., Nilssom, J., Bohlooly, Y. M., Heby, O., and Linde, A. (2001) Dev. Dyn. 220, 259-275). However, the significance and mechanism of this phenomenon remain unclear. In this study, we expressed AZ1 fused with enhanced green fluorescent protein (EGFP) to study its localization in a living cell. We found that EGFP-AZ1 was predominantly localized in the cytoplasm and that treatment with leptomycin B, a specific inhibitor of chromosomal region maintenance 1 (CRM1) induced nuclear accumulation of EGFP-AZ1 in Chinese hamster ovary and NIH3T3 cells. Two independent nuclear export signal (NES) sequences, each containing essential hydrophobic residues, were identified in the 50 N-terminal amino acid residues and in the central part of AZ1. The activity of the second NES was inhibited by an N-terminal adjacent region and was only revealed in N-terminal truncated constructs. Both NESs were active when fused to an artificial nuclear protein SV40-NLS-EGFP-EGFP. The ability of AZ1 to shuttle between the nucleus and the cytoplasm suggests that it has a novel function in the nucleus.
 ...
PMID:Identification of nuclear export signals in antizyme-1. 1294 43

Overproduction of the ornithine decarboxylase (ODC) regulatory protein ODC-antizyme has been shown to correlate with cell growth inhibition in a variety of different cell types. Although the exact mechanism of this growth inhibition is not known, it has been attributed to the effect of antizyme on polyamine metabolism. Antizyme binds directly to ODC, targeting ODC for ubiquitin-independent degradation by the 26 S proteasome. We now show that antizyme induction also leads to degradation of the cell cycle regulatory protein cyclin D1. We demonstrate that antizyme is capable of specific, noncovalent association with cyclin D1 and that this interaction accelerates cyclin D1 degradation in vitro in the presence of only antizyme, cyclin D1, purified 26 S proteasomes, and ATP. In vivo, antizyme up-regulation induced either by the polyamine spermine or by antizyme overexpression causes reduction of intracellular cyclin D1 levels. The antizyme-mediated pathway for cyclin D1 degradation is independent of the previously characterized phosphorylation- and ubiquitination-dependent pathway, because antizyme up-regulation induces the degradation of a cyclin D1 mutant (T286A) that abrogates its ubiquitination. We propose that antizyme-mediated degradation of cyclin D1 by the proteasome may provide an explanation for the repression of cell growth following antizyme up-regulation.
 ...
PMID:Antizyme targets cyclin D1 for degradation. A novel mechanism for cell growth repression. 1527 17

ODC (ornithine decarboxylase) is the rate-limiting enzyme in polyamine biosynthesis. Polyamines are essential for cellular growth and differentiation but enhanced ODC activity is associated with cell transformation. Post-translationally, ODC is negatively regulated through members of the antizyme family. Antizymes inhibit ODC activity, promote ODC degradation through the 26 S proteasome and regulate polyamine transport. Besides the ubiquitously expressed antizymes 1 and 2, there is the tissue-specific antizyme 3 and an yet uncharacterized antizyme 4. Antizyme 1 has been shown to be negatively regulated through the AZI (antizyme inhibitor) that binds antizyme 1 with higher affinity compared with ODC. In the present study, we show by yeast two- and three-hybrid protein-protein interaction studies that AZI interacts with all members of the antizyme family and is capable of disrupting the interaction between each antizyme and ODC. In a yeast-based ODC complementation assay, we show that human ODC is able to complement fully the function of the yeast homologue of ODC. Co-expression of antizymes resulted in ODC inhibition and cessation of yeast growth. The antizyme-induced growth inhibition could be reversed by addition of putrescine or by the co-expression of AZI. The protein interactions could be confirmed by immunoprecipitation of the human ODC-antizyme 2-AZI complexes. In summary, we conclude that human AZI is capable of acting as a general inhibitor for all members of the antizyme family and that the previously not yet characterized antizyme 4 is capable of binding ODC and inhibiting its enzymic activity similar to the other members of the antizyme family.
 ...
PMID:Regulation of all members of the antizyme family by antizyme inhibitor. 1535 8

Ornithine decarboxylase (ODC) is the most notable example of a protein degraded by the 26 S proteasome without ubiquitination. Instead, ODC is targeted to degradation by direct binding to a polyamine-induced protein termed antizyme (Az). Antizyme inhibitor (AzI) is an ODC-related protein that does not retain enzymatic activity yet binds Az with higher affinity than ODC. We show here that like ODC, AzI is also a short-lived protein that undergoes proteasomal degradation. However, in contrast to ODC degradation, the degradation of AzI is ubiquitin-dependent and does not require interaction with Az. Moreover, Az binding actually stabilizes AzI by inhibiting its ubiquitination. Substituting the C terminus of AzI with that of ODC, which together with Az constitutes the complete degradation signal of ODC, does not subvert AzI degradation from the ubiquitin-dependent mode to the Az-dependent mode, suggesting dominance of the ubiquitination signal. Our results suggest opposing roles of Az in regulating the degradation of AzI and ODC.
 ...
PMID:Degradation of antizyme inhibitor, an ornithine decarboxylase homologous protein, is ubiquitin-dependent and is inhibited by antizyme. 1549 92

Polyamines are essential organic cations with multiple cellular functions. Their synthesis is controlled by a feedback regulation whose main target is ornithine decarboxylase (ODC), the rate-limiting enzyme in polyamine biosynthesis. In mammals, ODC has been shown to be inhibited and targeted for ubiquitin-independent degradation by ODC antizyme (AZ). The synthesis of mammalian AZ was reported to involve a polyamine-induced ribosomal frameshifting mechanism. High levels of polyamine therefore inhibit new synthesis of polyamines by inducing ODC degradation. We identified a previously unrecognized sequence in the genome of Saccharomyces cerevisiae encoding an orthologue of mammalian AZ. We show that synthesis of yeast AZ (Oaz1) involves polyamine-regulated frameshifting as well. Degradation of yeast ODC by the proteasome depends on Oaz1. Using this novel model system for polyamine regulation, we discovered another level of its control. Oaz1 itself is subject to ubiquitin-mediated proteolysis by the proteasome. Degradation of Oaz1, however, is inhibited by polyamines. We propose a model, in which polyamines inhibit their ODC-mediated biosynthesis by two mechanisms, the control of Oaz1 synthesis and inhibition of its degradation.
 ...
PMID:Polyamines regulate their synthesis by inducing expression and blocking degradation of ODC antizyme. 1553 83

Ornithine decarboxylase (ODC) is the rate-limiting enzyme involved in the biosynthesis of polyamines essential for cell growth and differentiation. Aberrant upregulation of ODC, however, is widely believed to be a contributing factor in tumorigenesis. Antizyme is a major regulator of ODC, inhibiting ODC activity through the formation of complexes and facilitating degradation of ODC by the 26S proteasome. Moreover, the antizyme inhibitor (AZI) serves as another factor in regulating ODC, by binding to antizyme and releasing ODC from ODC-antizyme complexes. In our previous report, we observed elevated AZI expression in tumor specimens. Therefore, to evaluate the role of AZI in regulating ODC activity in tumors, we successfully down-regulated AZI expression using RNA interference technology in A549 lung cancer cells expressing high levels of AZI. Two AZI siRNAs, which were capable to generate a hairpin dsRNA loop targeting AZI, could successively decrease the expression of AZI. Using biological assays, antizyme activity increased in AZI-siRNA-transfected cells, and ODC levels and activity were reduced as well. Moreover, silencing AZI expression decreased intracellular polyamine levels, reduced cell proliferation, and prolonged population doubling time. Our results directly demonstrate that downregulation of AZI regulates ODC activity, intracellular polyamine levels, and cell growth through regulating antizyme activity. This study also suggests that highly expressed AZI may be partly responsible for increased ODC activity and cellular transformation.
 ...
PMID:Stable siRNA-mediated silencing of antizyme inhibitor: regulation of ornithine decarboxylase activity. 1567 Jul 71

The ATP-dependent degradation of ornithine decarboxylase is an exceptional case whereby a protein is targeted to the 26S proteasome independently of ubiquitin conjugation. Rather, prior association with the polyamine-induced regulatory protein, antizyme, confers susceptibility of ornithine decarboxylase to proteasomal degradation. In this chapter we describe ornithine decarboxylase/antizyme-based in vivo and in vitro systems for the measurement of ATP-dependent, ubiquitin-independent proteasomal degradation, as well as the application of ornithine decarboxylase as a reporter for the targeting of proteins to the 26S proteasome.
 ...
PMID:Cell-free assay for ubiquitin-independent proteasomal protein degradation. 1591 28


<< Previous 1 2 3 4 5 6 7 Next >>