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)

Increasingly, published evidence links glutamate with the pathogenesis of Alzheimer's disease. We investigated the molecular mechanism underlying glutamate-induced neurotoxicity in hippocampus, which is primarily linked to cognitive dysfunction in Alzheimer's disease. Acute exposure of rat hippocampal slices to glutamate significantly induced cell death, as determined by media lactate dehydrogenase levels and PI staining. Moreover, this was accompanied by Ca2+ influx and calpain-1 activation, as confirmed by the proteolytic pattern of spectrin. Notably, glutamate-induced calpain-1 activation decreased the level of beta-catenin, and this process appeared to be independent of glycogen synthase kinase 3beta (GSK-3beta), since glutamate also led to loss of GSK-3beta. Calpeptin, a calpain inhibitor, attenuated the glutamate-mediated degradations of spectrin, synaptophysin, and beta-catenin except GSK-3beta and modestly increased cell survival. In contrast, the NMDA receptor antagonist 2-amino-5-phosphonopentanoic acid (APV) effectively reduced all glutamate-evoked responses, i.e., the breakdowns of spectrin, synaptophysin, beta-catenin and GSK-3beta, and cell death. Pharmacological studies and in vitro calpain-1 proteolysis confirmed that in the glutamate-treated hippocampus, calpain-1-mediated decrease of beta-catenin could occur independently of GSK-3beta and of proteasome, and that GSK-3beta degradation is independent of calpain-1. These findings together provide the first direct evidence that glutamate promotes the down-regulations of beta-catenin and GSK-3beta, which potently contribute to neurotoxicity in hippocampus during excitotoxic cell death, and a molecular basis for the protection afforded by calpeptin and APV from the neurotoxic effect of glutamate.
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PMID:Concomitant degradation of beta-catenin and GSK-3 beta potently contributes to glutamate-induced neurotoxicity in rat hippocampal slice cultures. 1844 33

Succinyl-Leu-Leu-Val-Tyr-7-amino-4-methylcoumarin (SLLVY-AMC) is a fluorogenic substrate used to measure calpain activity and the "chymotrypsin-like" activity of the 20s proteasome. The goal of this study was to determine the relative role of calpains and the proteasome on SLLVY-AMC cleavage in attached and suspended renal epithelial cells (NRK-52E). The proteasome inhibitor epoxomicin did not inhibit purified calpain 1 or calpain 10 cleavage of SLLVY-AMC. Epoxomicin inhibited 11% of total SLLVY-AMC cleavage in attached cells and increasing concentrations of the calpain inhibitor calpeptin were additive. In contrast, cell suspensions had a 3.5-fold higher rate of SLLVY-AMC cleavage, epoxomicin inhibited cleavage 65% and calpeptin inhibited cleavage an additional 26%. Calpeptin alone also inhibited proteasomal activity. In conclusion, (1) SLLVY-AMC is cleaved in cells by calpain and the proteasome, (2) proteasome activity can be measured with epoxomicin, and (3) calpeptin can inhibit proteasome activity in some cases; thus limiting the use of SLLVY-AMC and calpeptin.
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PMID:Limitations of SLLVY-AMC in calpain and proteasome measurements. 1845 61

Calpain, calcium-dependent cysteine protease, is reported here to impose the crucial influence on oridonin-induced L929 cell apoptosis and autophagy. We found that inhibition of calpain increased oridonin-induced Bax activation, cytochrome c release and PARP cleavage, indicating that calpain plays an anti-apoptotic role in oridonin-induced L929 cell apoptosis. To explore this potential anti-apoptotic mechanism, we inhibited calpain and proteasome activity in oridonin-induced L929 cell apoptosis, and discovered that the inducible IkappaBalpha proteolysis was partially blocked by the inhibition of either calpain or proteasome, but completely blocked by the inhibition of both. It demonstrated that calpain and proteasome were two distinct pathways participating in IkappaBalpha degradation. To further study the role of calpain in oridonin-induced L929 cell autophagy, we discovered that calpain inhibitor decreased oridonin-induced autophagy, as well as Beclin 1 activation and the conversion from LC3-I to LC3-II. Moreover, Inhibition of autophagy by 3-MA increased oridonin-induced apoptosis. In conclusion, besides suppressing apoptosis, calpain promotes autophagy in oridonin-induced L929 cell death, and inhibition of autophagy might contribute to up-regulation of apoptosis.
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PMID:Apoptosis-suppressing and autophagy-promoting effects of calpain on oridonin-induced L929 cell death. 1846 6

The c-Myc transcription factor is commonly dysregulated in cancer. c-Myc also sensitizes cells to apoptosis induced by a variety of toxic events. c-Myc turnover is rapid and mediated by the proteasome and intracellular calpains. Therefore, c-Myc accumulation could contribute to cell death associated with protease inhibitors. We investigated the response of c-Myc-positive and c-Myc-negative rat fibroblast cells to proteasome and calpain inhibitors. Apoptosis induced by the proteasome inhibitor, epoxomycin, was c-Myc-independent, whereas apoptosis induced by the calpain inhibitor, PD150606, or by knockdown of calpain small subunit 1 (CPNS1) was strongly dependent on c-Myc. HL60 cells knocked down for c-Myc expression exhibited reduced calpain activity and decreased sensitivity to PD150606 but not epoxomycin. Calpain inhibitor- or CPNS1 knockdown-induced apoptosis in c-Myc-positive fibroblasts was associated with cell detachment and could be prevented by plating cells on fibronectin, suggesting an anoikis phenomenon. c-Myc stimulated calpain activity by suppressing calpastatin expression, the endogenous calpain inhibitor. Knockdown of calpastatin in c-Myc-negative cells led to a restoration of calpain activity, enhanced cell growth, cell cycle redistribution, anchorage independence, and tumorigenicity in immunodeficient mice. Taken together, these results indicate that c-Myc regulates calpain activity through calpastatin; apoptosis induced by calpain inhibition is dependent on c-Myc, and calpastatin knockdown promotes transformation in c-Myc-negative cells.
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PMID:Regulation of calpain activity by c-Myc through calpastatin and promotion of transformation in c-Myc-negative cells by calpastatin suppression. 1854 39

Pyrrolizidine alkaloids (PAs) are natural hepatotoxins with worldwide distribution in more than 6000 high plants including medicinal herbs or teas. The aim of this study is to investigate the signal pathway involved in PAs-induced hepatotoxicity. Our results showed that clivorine, isolated from Ligularia hodgsonii Hook, decreased cell viability and induced apoptosis in L-02 cells and mouse hepatocytes. Western-blot results showed that clivorine induced caspase-3/-9 activation, mitochondrial release of cytochrome c and decreased anti-apoptotic Bcl-xL in a time (8-48 h)- and concentration (1-100 microM)-dependent manner. Furthermore, inhibitors of pan-caspase, caspase-3 and caspase-9 significantly inhibited clivorine-induced apoptosis and rescued clivorine-decreased cell viability. Polyubiquitination of Bcl-xL was detected after incubation with 100 microM clivorine for 40 h in the presence of proteasome specific inhibitor MG132, indicating possible degradation of Bcl-xL protein. Furthermore, pretreatment with MG132 or calpain inhibitor I for 2 h significantly enhanced clivorine-decreased Bcl-xL level and cell viability. All the other tested PAs such as senecionine, isoline and monocrotaline decreased mouse hepatocytes viability in a concentration-dependent manner. Clivorine (10 microM) induced caspase-3 activation and decreased Bcl-xL was also confirmed in mouse hepatocytes. Meanwhile, another PA senecionine isolated from Senecio vulgaris L also induced apoptosis, caspase-3 activation and decreased Bcl-xL in mouse hepatocytes. In conclusion, our results suggest that PAs may share the same hepatotoxic signal pathway, which involves degradation of Bcl-xL protein and thus leading to the activation of mitochondrial-mediated apoptotic pathway.
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PMID:Involvement of Bcl-xL degradation and mitochondrial-mediated apoptotic pathway in pyrrolizidine alkaloids-induced apoptosis in hepatocytes. 1858 92

Peroxisome proliferator activator receptor gamma coactivator 1alpha (PGC-1alpha) is a transcriptional coactivator known to mediate mitochondrial biogenesis. Whereas PGC-1alpha transcription is regulated by a variety of signaling cascades, the mechanisms of PGC-1alpha degradation have received less investigation. Thus, we investigated the mechanisms responsible for PGC-1alpha degradation in renal proximal tubular cells (RPTC). Amino acid sequence analysis of the PGC-1alpha protein revealed three PEST sequence-rich regions, predictive of proteolysis by calpains and/or the proteasome. Under basal conditions, treatment with the protein synthesis inhibitor cycloheximide resulted in rapid degradation of PGC-1alpha (t(1/2)=38 min), which was blocked by the proteasome inhibitor epoxomicin, but not the calpain inhibitor calpeptin. Oxidant exposure resulted in the degradation of both endogenous and adenovirally over-expressed PGC-1alpha, which was inhibited by calpeptin but not epoxomicin. Thapsigargin-induced release of ER Ca(2+) also stimulated calpain-dependent, epoxomicin-independent degradation of PGC-1alpha. Finally, Ca(2+) addition to lysates of RPTC over-expressing PGC-1alpha resulted in calpeptin-sensitive, epoxomicin-insensitive degradation of PGC-1alpha. In summary, we suggest two distinct mechanisms regulate PGC-1alpha: basal PGC-1alpha turnover by proteasome degradation and oxidant- and Ca(2+)-mediated PGC-1alpha degradation through calpain.
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PMID:Oxidants and Ca+2 induce PGC-1alpha degradation through calpain. 1871 43

Dystrophin deficiency is the underlying molecular cause of progressive muscle weakness observed in Duchenne muscular dystrophy (DMD). Loss of functional dystrophin leads to elevated levels of intracellular Ca(2+), a key step in the cellular pathology of DMD. The cysteine protease calpain is activated in dystrophin-deficient muscle, and its inhibition is regarded as a potential therapeutic approach. In addition, previous work has shown that the ubiquitin-proteasome system also contributes to muscle protein breakdown in dystrophic muscle and, therefore, also qualifies as a potential target for therapeutic intervention in DMD. The relative contribution of calpain- and proteasome-mediated proteolysis induced by increased Ca(2+) levels was characterized in cultured muscle cells and revealed initial Ca(2+) influx-dependent calpain activity and subsequent Ca(2+)-independent activity of the ubiquitin-proteasome system. We then set out to optimize novel small-molecule inhibitors that inhibit both calpain as well as the 20S proteasome in a cellular system with impaired Ca(2+) homeostasis. On administration of such inhibitors to mdx mice, quantitative histological parameters improved significantly, in particular with compounds strongly inhibiting the 20S proteasome. To investigate the role of calpain inhibition without interfering with the ubiquitin-proteasome system, we crossed mdx mice with transgenic mice, overexpressing the endogenous calpain inhibitor calpastatin. Although our data show that proteolysis by calpain is strongly inhibited in the transgenic mdx mouse, this calpain inhibition did not ameliorate muscle histology. Our results indicate that inhibition of the proteasome rather than calpain is required for histological improvement of dystrophin-deficient muscle. In conclusion, we have identified novel proteasome inhibitors that qualify as potential candidates for pharmacological intervention in muscular dystrophy.
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PMID:Effect of calpain and proteasome inhibition on Ca2+-dependent proteolysis and muscle histopathology in the mdx mouse. 1872 18

Podoplanin/PA2.26 antigen is a small transmembrane mucin expressed in different types of cancer where it is associated with increased cell migration, invasiveness and metastasis. Little is known about the mechanisms that control podoplanin expression. Here, we show that podoplanin synthesis can be controlled at different levels. We analyzed podoplanin expression in a wide panel of tumour cell lines. The podoplanin gene (PDPN) is transcribed in cells derived from sarcomas, embryonal carcinomas, squamous cell carcinomas and endometrial tumours, while cell lines derived from colon, pancreatic, ovarian and ductal breast carcinomas do not express PDPN transcripts. PDPN is expressed as two mRNAs of approximately 2.7 and approximately 0.9 kb, both of which contain the coding sequence and arise by alternative polyadenylation. Strikingly, in most of the cell lines where PDPN transcripts were found, no podoplanin or only very low levels of the protein could be detected in Western blot. Treatment of several of these cell lines with the calpain inhibitor calpeptin resulted in podoplanin accumulation, whereas lactacystin, a specific inhibitor of the proteasome, had no effect. In vitro experiments showed that podoplanin is a substrate of calpain-1. These results indicate that at least in some tumour cells absence or reduced podoplanin protein levels are due to post-translational calpain-mediated proteolysis. We also report in this article the identification of a novel podoplanin isoform that originates by alternative splicing and differs from the standard form in lacking two cytoplasmic residues (YS). YS dipeptide is highly conserved across species, suggesting that it might be functionally relevant.
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PMID:Regulation of podoplanin/PA2.26 antigen expression in tumour cells. Involvement of calpain-mediated proteolysis. 1914 81

The detection of cell cycle proteins in Alzheimer's disease (AD) brains may represent an early event leading to neurodegeneration. To identify cell cycle modifiers with anti-Abeta properties, we assessed the effect of Differentiation-Inducing Factor-1 (DIF-1), a unique, small-molecule from Dictyostelium discoideum, on the proteolysis of the amyloid beta-protein precursor (APP) in a variety of different cell types. We show that DIF-1 slows cell cycle progression through G0/G1 that correlates with a reduction in cyclin D1 protein levels. Western blot analysis of DIF-treated cells and conditioned medium revealed decreases in the levels of secreted APP, mature APP, and C-terminal fragments. Assessment of conditioned media by sandwich ELISA showed reduced levels of Abeta40 and Abeta42, also demonstrating that treatment with DIF-1 effectively decreases the ratio of Abeta42 to Abeta40. In addition, DIF-1 significantly diminished APP phosphorylation at residue T668. Interestingly, site-directed mutagenesis of APP residue Thr668 to alanine or glutamic acid abolished the effect of DIF-1 on APP proteolysis and restored secreted levels of Abeta. Finally, DIF-1 prevented the accumulation of APP C-terminal fragments induced by the proteasome inhibitor lactacystin, and calpain inhibitor N-acetyl-leucyl-leucyl-norleucinal (ALLN). Our findings suggest that DIF-1 affects G0/G1-associated amyloidogenic processing of APP by a gamma-secretase-, proteasome- and calpain-insensitive pathway, and that this effect requires the presence of residue Thr668.
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PMID:Reduced amyloidogenic processing of the amyloid beta-protein precursor by the small-molecule Differentiation Inducing Factor-1. 1915 86

By using mini-units of tissue and protease inhibitors in short term incubation (0-180 min), we studied the role of proteolysis for ongoing DNA replication in the developing rat cerebral cortex. The protease inhibitors TLCK, TPCK, PMSF, MG-132 and PSI markedly inhibited DNA synthesis. The inhibitory effects were concentration-dependent and of early onset (within 60 min). The most selective proteasome inhibitors lactacystin and clasto-lactacystin-beta-lactone as well as the calpain inhibitor I and II had no or minimal effects on DNA synthesis. Only high concentrations of calpain inhibitor I (>or= 250 microM) and calpain inhibitor II (>or= 500 microM) gave a DNA synthesis inhibition. These results suggest that (1) ongoing DNA replication is regulated by proteolysis and (2) the proteolytic pathways involved are neither the proteasome nor the calpains.
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PMID:Ongoing DNA synthesis in the rat cerebral cortex is regulated by a proteolytic pathway independent of the proteasome and calpains. 1928 91


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