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)

Growing evidence suggests that the proteasome may be dysfunctional in a number of neurodegenerative disorders, including Lewy body diseases. We have reported previously that application of pharmacological inhibitors of the proteasome to cultured cortical neurons leads to apoptotic death and formation of ubiquitinated cytoplasmic inclusions. A number of cell cycle regulatory proteins are known to be degraded by the proteasome. In light of the emerging role of aberrant cell-cycle activation in neuronal cell death, we have assessed the involvement of cell-cycle components in the effects induced by proteasomal inhibitors in cortical neurons. Death and mitochondrial dysfunction induced by lactacystin and other pharmacological inhibitors of the proteasome were prevented by flavopiridol, a specific inhibitor of cyclin-dependent kinases (Cdks). Molecular expression of the Cdk inhibitors p16 or p27, or of dominant-negative Cdk2, Cdk4, or Cdk6 was also protective against lactacystin-induced death. Flavopiridol blocked the induction of retinoblastoma protein (pRb) phosphorylation that occurred after lactacystin application, and expression of a mutant pRb that lacked phosphorylation sites was neuroprotective. These results suggest that in cortical neurons, proteasomal inhibition leads to a cell death pathway that is dependent on Cdk activation and pRb inactivation. Although cyclins D1 and E were sequestered within the ubiquitinated inclusions formed at late time points after lactacystin application, the formation of ubiquitinated inclusions was unaffected by Cdk inhibition. This suggests that there are parallel pathways regulating neuronal death and inclusion formation elicited by proteasomal inhibition in cortical neurons.
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PMID:Cyclin-dependent kinase activity is required for apoptotic death but not inclusion formation in cortical neurons after proteasomal inhibition. 1259 12

Interactions between proteasome and cyclin-dependent kinase inhibitors have been examined in human leukemia cells in relation to induction of apoptosis. Simultaneous exposure (24 h) of U937 myelomonocytic leukemia cells to 100 nM flavopiridol and 300 nM MG-132 resulted in a marked increase in mitochondrial injury (cytochrome c, Smac/DIABLO release, loss of deltaPsi(m)), caspase activation, and synergistic induction of cell death, accompanied by a marked decrease in clonogenic potential. Similar effects were observed with other proteasome inhibitors (e.g., Bortezomib (VELCADE trade mark bortezomib or injection), lactacystin, LLnL) and cyclin-dependent kinase inhibitors (e.g., roscovitine), as well as other leukemia cell types (e.g., HL-60, Jurkat, Raji). In U937 cells, synergistic interactions between MG-132 and flavopiridol were associated with multiple perturbations in expression/activation of signaling- and survival-related proteins, including downregulation of XIAP and Mcl-1, activation of JNK and p34(cdc2), and diminished expression of p21(CIP1). The lethal effects of MG-132/flavopiridol were not reduced in leukemic cells ectopically expressing Bcl-2, but were partially attenuated in cells ectopically expressing dominant-negative caspase-8 or CrmA. Flavopiridol/proteasome inhibitor-mediated lethality was also significantly diminished by agents and siRNA blocking JNK activation. Lastly, coadministration of MG-132 with flavopiridol resulted in diminished DNA binding of NF-kappaB. Notably, pharmacologic interruption of the NF-kappaB pathway (e.g., by BAY 11-7082, PDTC, or SN-50) or molecular dysregulation of NF-kappaB (i.e., in cells ectopically expressing an IkappaBalpha super-repressor) mimicked the actions of proteasome inhibitors in promoting flavopiridol-induced mitochondrial injury, JNK activation, and apoptosis. Together, these findings indicate that proteasome inhibitors strikingly lower the apoptotic threshold of leukemic cells exposed to pharmacologic CDK inhibitors, and suggest that interruption of the NF-kappaB cytoprotective pathway and JNK activation both play key roles in this phenomenon. They also raise the possibility that combining proteasome and CDK inhibitors could represent a novel antileukemic strategy.
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PMID:Proteasome inhibitors potentiate leukemic cell apoptosis induced by the cyclin-dependent kinase inhibitor flavopiridol through a SAPK/JNK- and NF-kappaB-dependent process. 1456 39

Human cytomegalovirus (HCMV) infection leads to dysregulation of multiple cell cycle-regulatory proteins. In this study, we examined the effects of inhibition of cyclin-dependent kinase (cdk) activity on viral replication. With the drug Roscovitine, a specific inhibitor of cyclin-dependent kinases 1, 2, 5, 7, and 9, we have shown that during the first 6 h of infection, cyclin-dependent kinase-dependent events occurred that included the regulated processing and accumulation of the immediate-early (IE) UL122-123 transcripts and UL36-37 transcripts. Altered processing of UL122-123 led to a loss of IE1-72 and an increase in IE2-86. The ratio of spliced to unspliced UL37 transcripts also changed. These effects did not require de novo protein synthesis or degradation of proteins by the proteasome. Addition of Roscovitine at the beginning of the infection was also associated with inhibition of expression of selected viral early gene products, viral DNA replication, and late viral gene expression. When Roscovitine was added after the first 6 h of infection, the effects on IE gene expression were no longer observed and viral replication proceeded through the late phase, but viral titers were reduced. The reduction in viral titer was observed even when Roscovitine was first added at 48 h postinfection, indicating that cyclin-dependent kinase activity is required at both IE and late times. Flavopiridol, another specific inhibitor of cyclin-dependent kinases, had similar effects on IE and early gene expression. These results underscore the importance of accurate RNA processing and reiterate the significant role of cell cycle-regulatory factors in HCMV infection.
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PMID:Cyclin-dependent kinase activity is required at early times for accurate processing and accumulation of the human cytomegalovirus UL122-123 and UL37 immediate-early transcripts and at later times for virus production. 1545 41

The cyclin-dependent kinase inhibitor flavopiridol is undergoing clinical trials as an antitumor drug. We show here that pretreatment of different human breast cancer cell lines with flavopiridol facilitates tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis. In breast tumor cells, apoptosis induction by TRAIL is blocked at the level of apical caspase-8 activation. Flavopiridol treatment enhances TRAIL-induced formation of death-inducing signaling complex and early processing of procaspase-8. Subsequently, a TRAIL-induced, mitochondria-operated pathway of apoptosis is activated in cells treated with flavopiridol. Down-regulation of cellular FLICE-inhibitory proteins (c-FLIP; c-FLIP(L) and c-FLIP(S)) is observed on flavopiridol treatment. c-FLIP loss and apoptosis sensitization by flavopiridol are both prevented in cells treated with an inhibitor of the ubiquitin-proteasome system. Furthermore, targeting c-FLIP directly with small interfering RNA oligonucleotides also sensitizes various human breast tumor cell lines to TRAIL-induced apoptosis. Our results indicate that flavopiridol sensitizes breast cancer cells to TRAIL-induced apoptosis by facilitating early events in the apoptotic pathway, and this combination treatment could be regarded as a potential therapeutic tool against breast tumors.
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PMID:Flavopiridol induces cellular FLICE-inhibitory protein degradation by the proteasome and promotes TRAIL-induced early signaling and apoptosis in breast tumor cells. 1695 Dec 3

Inhibitors of histone deacetylases (HDAC) inhibit malignant cell growth and induce apoptosis through unknown mechanisms. Here, we report that the expression status of adenomatous polyposis coli (APC) protein determines the relative sensitivity of colon cancer cells to HDAC inhibitor-induced apoptosis. HCA-7 cells (expressing wild-type beta-catenin and APC proteins) are more sensitive to apoptosis induced by HDAC inhibitors valproic acid (VPA) and suberoylanilide hydroxamic acid than SW620 or HT-29 cells (both expressing mutant APC). When wild-type APC protein was expressed using an inducible expression system, HT-29 cells became sensitive to apoptosis in response to VPA. Conversely, knocking down of endogenous APC protein by small interfering RNA (siRNA) blocked VPA-induced apoptosis in HCA-7 cells. APC mediated VPA-induced apoptosis through down-regulation of survivin. The level of survivin protein decreased in HCA-7 and HT-29/APC cells, but not in SW620 and HT-29/beta-Gal cells after VPA treatment. Whereas knocking down of survivin by siRNA sensitized SW620 cells to VPA-induced apoptosis, overexpression of survivin blocked VPA-induced apoptosis in HCA-7 cells. Down-regulation of survivin transcription occurred through changes in GSK-3beta/beta-catenin/Tcf-4 signaling molecules. VPA also induced proteasome-mediated degradation of survivin protein in HCA-7 cells. Furthermore, we have shown that APC mutation-mediated resistance to apoptosis can be overcome by cotreatment with Flavopiridol, which promotes survivin degradation. These results suggest that APC is a critical determinant of HDAC inhibitor-induced apoptosis in colon cancer cells and survivin is a potential target to enhance apoptotic response to HDAC inhibitors.
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PMID:Adenomatous polyposis coli determines sensitivity to histone deacetylase inhibitor-induced apoptosis in colon cancer cells. 1698 69