Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.4.21.1 (chymotrypsin)
 10,938 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A 60,000-dalton polypeptide (p60) has been identified in the feline leukemia virus (FeLV) pseudotype of Moloney sarcoma virus [MSV(FeLV)]. This polypeptide is present in the purified virus complex in concentrations greater than either the murine p30 or the feline p27. Purified p60 crossreacts immunologically with murine p30 group antiserum and contains several interspecies determinants, whereas the group specific determinant of FeLV p27 is not detected. Comparison of peptide fingerprints of p60 and murine p30 show many peptides in common. Limited digestion of p60 with either trypsin or chymotrypsin produced p30-35 and p20 peptides which retain the MuLV p30 group and interspecies antigenic activities. The p30 produced by both enzymes comigrates in polyacrylamide gels with the murine p30 of MSV(FeLV), thus suggesting that p60 may be an uncleaved precursor to p30.
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PMID:A p60 polypeptide in the feline leukemia virus pseudotype of Moloney sarcoma virus with murine leukemia virus p30 antigenic determinants. 4 60

Although the hepatitis delta virus genome contains multiple open reading frames, only one of these reading frames is known to be expressed during replication of the virus. This open reading frame encodes two distinct molecular species of hepatitis delta antigen (HDAg), p24 delta and p27 delta, depending on the location of the stop codon which terminates translation. We found antibody specific for p27 delta to be capable of precipitating p24 delta in extracts of infected liver, indicating that p27 delta and p24 delta form heterologous complexes in vivo. After cross-linking with 0.05% glutaraldehyde, specific HDAg dimers were detected in antigen prepared from both the liver and serum of an HDV-infected woodchuck carrier of woodchuck hepatitis virus. Guanidine HCl-denatured HDAg extracted from liver and dialyzed against phosphate-buffered saline sedimented in rate-zonal sucrose density gradients as 15S multimeric complexes. These 15S multimers were stable in the presence of 1.2% Nonidet P-40. After RNase digestion, the 15S complex was reduced to a 12S complex without associated RNA, while boiling for 3 min in 1% sodium dodecyl sulfate-0.5% 2-mercaptoethanol further reduced the 15S complex to 3S HDAg monomers. In the absence of glutaraldehyde cross-linking, HDAg extracted from liver migrated as monomer species in reducing and nonreducing gels, suggesting that the conserved cysteine residue present in p27 delta does not play a role in the formation of either dimers or multimers. On the other hand, an amino-terminal chymotrypsin-digested HDAg fragment, with a predicted length of 81 or less amino acids, retained the ability to form dimers, consistent with the hypothesis that a coiled-coil motif present between residues 27 and 58 may play a role in HDAg protein interactions in vivo.
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PMID:Hepatitis delta virus antigen forms dimers and multimeric complexes in vivo. 767 57

Lovastatin and simvastatin are HMG-CoA reductase inhibitors widely used as antihyperlipidemic drugs, which also display antiproliferative properties. In the present paper, we provide evidence that both lovastatin and simvastatin are modulators of the purified bovine pituitary 20 S proteasome, since they mildly stimulate the chymotrypsin-like activity and inhibit the peptidylglutamylpeptide hydrolyzing activity without interfering with the trypsin-like activity. However, those effects are only observed when the closed ring forms of the drugs are used, while the opened ring form of lovastatin acts as a mild inhibitor of the chymotrypsin like activity. The closed ring form of lovastatin is much more potent as a cytotoxic agent on the Colon-26 (C-26) colon carcinoma cell line than the opened ring form, which is only mildly cytostatic. Moreover, neither the cytotoxic effects nor the effects on 20 S proteasome activities are prevented by mevalonate, which by itself inhibits the trypsin-like activity of the proteasome. Neither the opened ring nor the closed ring form of lovastatin induces an accumulation of ubiquitin-protein conjugates, which is observed after treatment with lactacystin, a selective proteasome inhibitor. In contrast with the opened ring form of lovastatin, the closed ring form induces the disappearance of detectable p27(kip1) from C-26 cells. Altogether, our results indicate that the closed ring form of lovastatin induces cytotoxic effects independent of its HMG-CoA inhibiting activity, however, those effects are mediated by a complex modulation of proteasome activity rather than by inhibition of the 20 S proteasome.
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PMID:Lovastatin and simvastatin are modulators of the proteasome. 1108 75

Isoprenoid inhibitors are being evaluated as agents for the treatment of cancer. Their antitumor activity is attributed to inhibition of post-translational modification of Ras, which is crucial for its translocation and attachment to the plasma membrane, and ultimate involvement in signal transduction. However, whether blocking of Ras is solely responsible for the observed antitumor activity is unresolved. In this report, we propose an alternate mechanism. Using breast tumor models, we show that agents possessing a lactone moiety, including statins (such as lovastatin) and the isoprenoid inhibitors (such as FTI-277 and GGTI-298), mediate their cell cycle inhibitory activities by blocking the chymotrypsin activity of the proteasome in vitro. This results in the accumulation of cyclin-dependent kinase inhibitors p21 and p27 with subsequent G(1) arrest. Cells devoid of p21 were refractory to the growth-inhibitory activity of lovastatin, FTI-277, and GGTI-298. However, in these p21 null cells, isoprenylation of key substrates of farnesyl transferase (such as Ras) and of geranylgeranyl transferase (such as RAP-1) were inhibited by FTI-277 and GGTI-298, respectively, suggesting that although both these isoprenoid inhibitors reached and inhibited their intended targets, inhibition of the isoprenylation of Ras and RAP-1A are not sufficient to mediate G(1) arrest. We also show that the cell cycle effects can be attributed to the functional lactone moiety of the aforementioned agents. Collectively, our data suggest that FTI and GGTI and other agents containing an active lactone moiety mediate G(1) arrest via inhibition of the proteasome and up-regulation of p21, independent of the inhibition of isoprenylation of Ras or RAP-1.
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PMID:Farnesyl and geranylgeranyl transferase inhibitors induce G1 arrest by targeting the proteasome. 1642 40

Withaferin A (WA) is a steroidal lactone purified from medicinal plant "Indian Winter Cherry" that is widely researched for its variety of properties, including antitumor effects. However, the primary molecular target of WA is unknown. By chemical structure analysis, we hypothesized that Withaferin A might be a natural proteasome inhibitor. Computational modeling studies consistently predict that C1 and C24 of WA are highly susceptible toward a nucleophilic attack by the hydroxyl group of N-terminal threonine of the proteasomal chymotrypsin subunit beta5. Furthermore, WA potently inhibits the chymotrypsin-like activity of a purified rabbit 20S proteasome (IC50=4.5 microM) and 26S proteasome in human prostate cancer cultures (at 5-10 microM) and xenografts (4-8 mg/kg/day). Inhibition of prostate tumor cellular proteasome activity in cultures and in vivo by WA results in accumulation of ubiquitinated proteins and three proteasome target proteins (Bax, p27, and IkappaB-alpha) accompanied by androgen receptor protein suppression (in androgen-dependent LNCaP cells) and apoptosis induction. Treatment of WA under conditions of the aromatic ketone reduction, or reduced form of Celastrol, had significantly decreased the proteasome-inhibitory and apoptosis-inducing activities. Treatment of human prostate PC-3 xenografts with WA for 24 days resulted in 70% inhibition of tumor growth in nude mice, associated with 56% inhibition of the tumor tissue proteasomal chymotrypsinlike activity. Our results demonstrate that the tumor proteasome beta5 subunit is the primary target of WA, and inhibition of the proteasomal chymotrypsin-like activity by WA in vivo is responsible for, or contributes to, the antitumor effect of this ancient medicinal compound.
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PMID:The tumor proteasome is a primary target for the natural anticancer compound Withaferin A isolated from "Indian winter cherry". 2581 35

Pristimerin is a natural product derived from the Celastraceae and Hippocrateaceae families that were used as folk medicines for anti inflammation in ancient times. Although it has been shown that pristimerin induces apoptosis in breast cancer cells, the involved mechanism of action is unknown. The purpose of the current study is to investigate the primary target of pristimerin in human cancer cells, using prostate cancer cells as a working model. Nucleophilic susceptibility and in silico docking studies show that C6 of pristimerin is highly susceptible towards a nucleophilic attack by the hydroxyl group of N-terminal threonine of the proteasomal chymotrypsin subunit. Consistently, pristimerin potently inhibits the chymotrypsin-like activity of a purified rabbit 20S proteasome (IC50 2.2 micromol/L) and human prostate cancer 26S proteasome (IC50 3.0 micromol/L). The accumulation of ubiquitinated proteins and three proteasome target proteins, Bax, p27 and I kappa B-alpha, in androgen receptor (AR)-negative PC-3 prostate cancer cells supports the conclusion that proteasome inhibition by pristimerin is physiologically functional. This observed proteasome inhibition subsequently led to the induction of apoptotic cell death in a dose- and kinetic-dependent manner. Furthermore, in AR-positive, androgen-dependent LNCaP and AR-positive, androgen-independent C4-2B prostate cancer cells, proteasome inhibition by pristimerin results in suppression of AR protein prior to apoptosis. Our data demonstrate, for the first time, that the proteasome is a primary target of pristimerin in prostate cancer cells and inhibition of the proteasomal chymotrypsin-like activity by pristimerin is responsible for its cancer cell death-inducing property.
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PMID:Pristimerin induces apoptosis by targeting the proteasome in prostate cancer cells. 1754 80