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)

Hs1VU in E. coli is a new type of ATP-dependent protease composed of two heat shock proteins, the HslU ATPase and the HslV peptidase related to certain beta-type subunits of the 20S proteasome. Here we show that the ATP-dependent hydrolysis of N-carbobenzoxy-Gly-Gly-Leu-7-amido-4-methylcoumarin by the HslVU protease can be markedly stimulated by poly-L-lysine, that is known to activate the casein-degrading activity of the 20S proteasome. However, poly-L-lysine showed little or no effect on the peptidase activity of HslV itself. Instead, it stimulated the hydrolysis of ATP by HslU several-fold. Histone that could stimulate the ATPase activity of HslU also increased the rate of the ATP-dependent peptide hydrolysis by HslV, although to a much lesser extent than by poly-L-lysine. Thus, the poly-L-lysine-mediated increase in the ATPase activity of HslU appears to be responsible for the dramatic activation of the ATP-dependent peptide hydrolysis by HslV. These results suggest that, in the reconstituted HslVU complex, the peptide hydrolysis by HslV occurs in a tightly coupled process with the cleavage of ATP by HslU.
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PMID:Poly-L-lysine activates both peptide and ATP hydrolysis by the ATP-dependent HslVU protease in Escherichia coli. 895 32

The 20S proteasome is localized in the cytosol and nuclei of mammalian cells. Previous work has shown that the cytosolic 20S proteasome is largely responsible for the selective recognition and degradation of oxidatively damaged cytosolic proteins. Since nuclear proteins are also susceptible to oxidative damage (e.g., from metabolic free radical production, ionizing radiation, xenobiotics, chemotherapy) we investigated the degradation of oxidatively damaged histones, in the presence and in the absence of DNA, by the 20S proteasome. We find that both soluble histones and DNA-bound histones are susceptible to selective proteolytic degradation by the 20S proteasome following mild oxidative damage. In contrast, more severe oxidative damage actually decreases the proteolytic susceptibility of histones. Soluble H1 showed the highest basal and maximal absolute proteolytic rates. Histone fraction H4 exhibited the greatest relative increase in proteolytic susceptibility following oxidation, almost 14-fold, and this occurred at a peroxide exposure of 5 mM. At the other end of the spectrum, histone H2A exhibited a maximal proteolytic response to H2O2 of only 6-fold, and this required an H2O2 exposure of 15 mM. An oxidation of reconstituted linear DNA plasmid-histone complex makes up to 95% of the histones bound to DNA susceptible to degradation, whereas undamaged protein-DNA complexes are not substrates for the proteasome. Severe oxidation by high concentrations of H2O2 appears to decreases the proteolytic susceptibility of histones due to the formation of cross-linked histone-DNA aggregates which appear to inhibit the proteasome. We conclude that the degradation of nuclear proteins is highly selective and requires prior damage of the substrate protein, such as that caused by oxidation.
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PMID:Influence of DNA binding on the degradation of oxidized histones by the 20S proteasome. 998 29

We have examined the activity of cyclin-dependent kinase 3 (cdk3) during G1-phase of the cell cycle in Chinese Hamster Ovary (CHO) fibroblasts. Histone H1 kinase activity associated with anti-cdk3 immunoprecipitates peaked during a brief window of time, 2-3 h prior to the restriction point. In vitro cdk3 activity was sensitive to roscovitine, a drug previously shown to inhibit cdks 1, 2, and 5, but not cdk4 or 6. Early G1-phase activation of cdk3 was downregulated by treatment of cells with MG132, an inhibitor of the proteasome, and by the protein synthesis inhibitor cycloheximide. These results provide evidence for a pre-restriction point cdk3 activity that requires both the synthesis of a regulatory subunit and degradation of an inhibitor.
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PMID:Evidence for a pre-restriction point Cdk3 activity. 1196 94

Histone deacetylases (HDACs) are thought to function as critical mediators of transcriptional repression. However, the physiological targets and posttranslational modifications of the class II HDACs are largely unknown. Here we show that the C terminus of HDAC 6 is both necessary and sufficient for specific association with polyubiquitin. This region contains a putative zinc finger but lacks significant similarity to other known ubiquitin binding domains. Thus, we have designated this region as a PAZ domain, for Polyubiquitin Associated Zinc finger. Although the PAZ domain possesses homology with the zinc finger of deubiquitinating enzymes, it is dispensable for the deubiquitinating activity we find associated with HDAC6 following immunopurification. We also show that both HDAC 5 and HDAC 6 are ubiquitinated in vitro and in vivo. However, both of these proteins are stable in vivo and do not appear to be targeted for rapid degradation by the proteasome. Thus, HDAC6 is linked to the ubiquitin system via ubiquitin conjugation, polyubiquitin binding, and copurification with deubiquitinating enzymes.
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PMID:Histone deacetylase 6 binds polyubiquitin through its zinc finger (PAZ domain) and copurifies with deubiquitinating enzymes. 1235 39

Several reports have described an activity that modifies nitrotyrosine-containing proteins and their immunoreactivity to nitrotyrosine Abs. Without knowing the product of the reaction, this new activity has been called a "denitrase." In those studies, some nonspecific proteins, which have multiple tyrosine residues, e.g., albumin, were used as a substrate. Therefore, the studies were based on an unknown mechanism of reaction and potentially a high background. To solve these problems, one of the most important things is to find a more suitable substrate for assay of the enzyme. We developed an assay strategy for determining the substrate for denitrase combining 2D-gel electrophoresis and an on-blot enzyme assay. The resulting substrate from RAW 264.7 cells was Histone H1.2, an isoform protein of linker histone. Histone H1.2 has only one tyrosine residue in the entire molecule, which ensures the exact position of the substrate to be involved. It has been reported that Histones are the most prominent nitrated proteins in cancer tissues. It was also demonstrated that tyrosine nitration of Histone H1 occurs in vivo. These findings lead us to the idea that Histone H1.2 might be an intrinsic substrate for denitrase. We nitrated recombinant and purified Histone H1.2 chemically and subjected it to an on-blot enzyme assay to characterize the activity. Denitrase activity behaved as an enzymatic activity because the reaction was time dependent and was destroyed by heat or trypsin treatment. The activity was shown to be specific for Histone H1.2, to differ from proteasome activity, and to require no additional cofactors.
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PMID:Histone H1.2 is a substrate for denitrase, an activity that reduces nitrotyrosine immunoreactivity in proteins. 1271 31

Histone-modifying enzymes play essential roles in physiological and aberrant gene regulation. Since histone deacetylases (HDACs) are promising targets of cancer therapy, it is important to understand the mechanisms of HDAC regulation. Selective modulators of HDAC isoenzymes could serve as efficient and well-tolerated drugs. We show that HDAC2 undergoes basal turnover by the ubiquitin-proteasome pathway. Valproic acid (VPA), in addition to selectively inhibiting the catalytic activity of class I HDACs, induces proteasomal degradation of HDAC2, in contrast to other inhibitors such as trichostatin A (TSA). Basal and VPA-induced HDAC2 turnover critically depend on the E2 ubiquitin conjugase Ubc8 and the E3 ubiquitin ligase RLIM. Ubc8 gene expression is induced by both VPA and TSA, whereas only TSA simultaneously reduces RLIM protein levels and therefore fails to induce HDAC2 degradation. Thus, poly-ubiquitination and proteasomal degradation provide an isoenzyme-selective mechanism for downregulation of HDAC2.
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PMID:The histone deacetylase inhibitor valproic acid selectively induces proteasomal degradation of HDAC2. 1284 3

Histone deacetylases (HDACs) affect cell growth at the transcriptional level by regulating the acetylation status of nucleosomal histones. HDAC inhibition induces differentiation and/or apoptosis in transformed cells. We recently showed that HDAC inhibitors, such as suberoylanilide hydroxamic acid (SAHA), potently induce apoptosis of human multiple myeloma (MM) cells. In this study, we focused on MM as a model to study the transcriptional profile of HDAC inhibitor treatment on tumor cells and to address their pathophysiological implications with confirmatory mechanistic and functional assays. We found that MM cells are irreversibly committed to cell death within few hours of incubation with SAHA. The hallmark molecular profile of MM cells before their commitment to SAHA-induced cell death is a constellation of antiproliferative and/or proapoptotic molecular events, including down-regulation of transcripts for members of the insulin-like growth factor (IGF)/IGF-1 receptor (IGF-1R) and IL-6 receptor (IL-6R) signaling cascades, antiapoptotic molecules (e.g., caspase inhibitors), oncogenic kinases, DNA synthesis/repair enzymes, and transcription factors (e.g., XBP-1, E2F-1) implicated in MM pathophysiology. Importantly, SAHA treatment suppresses the activity of the proteasome and expression of its subunits, and enhances MM cell sensitivity to proteasome inhibition by bortezomib (PS-341). SAHA also enhances the anti-MM activity of other proapoptotic agents, including dexamethasone, cytotoxic chemotherapy, and thalidomide analogs. These findings highlight the pleiotropic antitumor effects of HDAC inhibition, and provide the framework for future clinical applications of SAHA to improve patient outcome in MM.
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PMID:Transcriptional signature of histone deacetylase inhibition in multiple myeloma: biological and clinical implications. 1469 87

Histone acetyltransferases (HATs), and p300/CBP in particular, have been implicated in cancer cell growth and survival, and as such, HATs represent novel, therapeutically relevant molecular targets for drug development. In this study, we demonstrate that the small molecule natural product curcumin, whose medicinal properties have long been recognized in India and Southeast Asia, is a selective HAT inhibitor. Furthermore the data indicate that alpha, beta unsaturated carbonyl groups in the curcumin side chain function as Michael reaction sites and that the Michael reaction acceptor functionality of curcumin is required for its HAT-inhibitory activity. In cells, curcumin promoted proteasome-dependent degradation of p300 and the closely related CBP protein without affecting the HATs PCAF or GCN5. In addition to inducing p300 degradation curcumin inhibited the acetyltransferase activity of purified p300 as assessed using either histone H3 or p53 as substrate. Radiolabeled curcumin formed a covalent association with p300, and tetrahydrocurcumin displayed no p300 inhibitory activity, consistent with a Michael reaction-dependent mechanism. Finally, curcumin was able to effectively block histone hyperacetylation in both PC3-M prostate cancer cells and peripheral blood lymphocytes induced by the histone deacetylase inhibitor MS-275. These data thus identify the medicinal natural product curcumin as a novel lead compound for development of possibly therapeutic, p300/CBP-specific HAT inhibitors.
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PMID:Curcumin is an inhibitor of p300 histone acetylatransferase. 1678 65

Histone deacetylases (HDAC) play a critical role in chromatin modification and gene expression. Recent evidence indicates that HDACs can also regulate functions of nonhistone proteins by catalyzing the removal of acetylated lysine residues. Here, we show that the HDAC inhibitor LBH589 down-regulates DNA methyltransferase 1 (DNMT1) protein expression in the nucleus of human breast cancer cells. Cotreatment with the proteasomal inhibitor MG-132 abolishes the ability of LBH589 to reduce DNMT1, suggesting that the proteasomal pathway mediates DNMT1 degradation on HDAC inhibition. Deletion of the NH(2)-terminal 120 amino acids of DNMT1 diminishes LBH589-induced ubiquitination, indicating that this domain is essential for its proteasomal degradation. DNMT1 recruits the molecular chaperone heat shock protein 90 (Hsp90) to form a chaperone complex. Treatment with LBH589 induces hyperacetylation of Hsp90, thereby inhibiting the association of DNMT1 with Hsp90 and promoting ubiquitination of DNMT1. In addition, inactivation of HDAC1 activity by small interfering RNA and MS-275 is associated with Hsp90 acetylation in conjunction with reduction of DNMT1 protein expression. We conclude that the stability of DNMT1 is maintained in part through its association with Hsp90. Disruption of Hsp90 function by HDAC inhibition is a unique mechanism that mediates the ubiquitin-proteasome pathway for DNMT1 degradation. Our studies suggest a new role for HDAC1 and identify a novel mechanism of action for the HDAC inhibitors as down-regulators of DNMT1.
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PMID:Inhibition of histone deacetylases promotes ubiquitin-dependent proteasomal degradation of DNA methyltransferase 1 in human breast cancer cells. 1850 31

Histone deacetylases (HDAC) modify the architecture of chromatin, leading to decreased gene expression, an effect that is reversed by HDAC inhibition. The balance between deacetylation and acetylation is central to many biological events including the regulation of cell proliferation and cancer but also the differentiation of immune T cells. The effects of HDAC inhibition on the interaction between antitumor effector T cells and tumor cells are not known. Here, we studied presentation of a universal self-tumor antigen, telomerase reverse transcriptase, in human tumor cells during HDAC inhibition. We found that HDAC inhibition with trichostatin A was associated with a decreased presentation and diminished killing of tumor cells by CTLs. Using gene array analysis, we found that HDAC inhibition resulted in a decrease of genes coding for proteasome catalytic proteins and for tapasin, an endoplasmic reticulum resident protein involved in the MHC class I pathway of endogenous antigen presentation. Our findings indicate that epigenetic changes in tumor cells decrease self-tumor antigen presentation and contribute to reduced recognition and killing of tumor cells by cytotoxic T lymphocytes. This mechanism could contribute to tumor escape from immune surveillance.
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PMID:Presentation of telomerase reverse transcriptase, a self-tumor antigen, is down-regulated by histone deacetylase inhibition. 1882 67


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