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)

It has been shown that ultraviolet (UV) radiation induces the ubiquitination of the large subunit of RNA polymerase II (RNAP II-LS) as well as its proteasomal degradation. Studies in mammalian cells have indicated that highly phosphorylated forms of RNAP II-LS are preferentially ubiquitinated, but studies in Saccharomyces cerevisiae have provided evidence that unphosphorylated RNAP II-LS is an equally suitable substrate. In the present study, an antibody (ARNA-3) that recognizes all forms of RNAP II-LS, regardless of the phosphorylation status of its C-terminal domain (CTD), was utilized to evaluate the degradation of total cellular RNAP II-LS in human fibroblasts under basal conditions or after UV-C (10J/m(2)) irradiation. It was found that UV radiation rapidly shifted the phosphorylation profile of RNAP II-LS from a mixture of dephosphorylated and phosphorylated forms to entirely more phosphorylated forms. This shift in phosphorylation status was not blocked by pharmacologic inhibition of either the ERK or p38 pathways, both of which have been implicated in the cellular UV response. In addition to shifting the phosphorylation profile, UV radiation led to net degradation of total RNAP II-LS. UV-induced degradation of RNAP II-LS was also greatly reduced in the presence of the transcriptional and CTD kinase inhibitor DRB. Using a panel of protease inhibitors, it was shown that the bulk of UV-induced degradation is proteasome-dependent. However, the UV-induced loss of hypophosphorylated RNAP II-LS was proteasome-independent. Lastly, UV radiation induced a similar shift to all hyperphosphorylated RNAP II-LS in Cockayne syndrome (CS) cells of complementation groups A or B (CSA or CSB) when compared to appropriate controls. The UV-induced degradation rates of RNAP II-LS were not significantly altered when comparing CSA or CSB to repair competent control cells. The implications for the cellular UV response are discussed.
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PMID:Ultraviolet radiation alters the phosphorylation of RNA polymerase II large subunit and accelerates its proteasome-dependent degradation. 1151 29

Mutations in the CSA or CSB complementation genes cause the Cockayne syndrome, a severe genetic disorder that results in patients' death in early adulthood. CSA and CSB act in a transcription-coupled repair (TCR) pathway, but their functional relationship is not understood. We have previously shown that CSA is a subunit of an E3 ubiquitin ligase complex. Here we demonstrate that CSB is a substrate of this ligase: Following UV irradiation, CSB is degraded at a late stage of the repair process in a proteasome- and CSA-dependent manner. Moreover, we demonstrate the importance of CSB degradation for post-TCR recovery of transcription and for the Cockayne syndrome. Our results unravel for the first time the functional relationship between CSA and CSB.
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PMID:CSA-dependent degradation of CSB by the ubiquitin-proteasome pathway establishes a link between complementation factors of the Cockayne syndrome. 1675 Nov 80

Expansions of CAG repeat tracts in the germ line underlie several neurological diseases. In human patients and mouse models, CAG repeat tracts display an ongoing instability in neurons, which may exacerbate disease symptoms. It is unclear how repeats are destabilized in nondividing cells, but it cannot involve DNA replication. We showed previously that transcription through CAG repeats induces their instability (Y. Lin, V. Dion, and J. H. Wilson, Nat. Struct. Mol. Biol. 13:179-180). Here, we present a genetic analysis of the link between transcription-induced repeat instability and nucleotide excision repair (NER) in human cells. We show that short interfering RNA-mediated knockdown of CSB, a component specifically required for transcription-coupled NER (TC-NER), and knockdowns of ERCC1 and XPG, which incise DNA adjacent to damage, stabilize CAG repeat tracts. These results suggest that TC-NER is involved in the pathway for transcription-induced CAG repeat instability. In contrast, knockdowns of OGG1 and APEX1, key components involved in base excision repair, did not affect repeat instability. In addition, repeats are stabilized by knockdown of transcription factor IIS, consistent with a requirement for RNA polymerase II (RNAPII) to backtrack from a transcription block. Repeats also are stabilized by knockdown of either BRCA1 or BARD1, which together function as an E3 ligase that can ubiquitinate arrested RNAPII. Treatment with the proteasome inhibitor MG132, which stabilizes repeats, confirms proteasome involvement. We integrate these observations into a tentative pathway for transcription-induced CAG repeat instability that can account for the contractions observed here and potentially for the contractions and expansions seen with human diseases.
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PMID:Transcription-induced CAG repeat contraction in human cells is mediated in part by transcription-coupled nucleotide excision repair. 1759 97

Cockayne syndrome (CS) is caused by mutations in CSA and CSB. The CSA and CSB proteins have been linked to both promoting transcription-coupled repair and restoring transcription following DNA damage. We show that UV stress arrests transcription of approximately 70% of genes in CSA- or CSB-deficient cells due to the constitutive presence of ATF3 at CRE/ATF sites. We found that CSB, CSA/DDB1/CUL4A, and MDM2 were essential for ATF3 ubiquitination and degradation by the proteasome. ATF3 removal was concomitant with the recruitment of RNA polymerase II and the restart of transcription. Preventing ATF3 ubiquitination by mutating target lysines prevented recovery of transcription and increased cell death following UV treatment. Our data suggest that the coordinate action of CSA and CSB, as part of the ubiquitin/proteasome machinery, regulates the recruitment timing of DNA-binding factors and provide explanations about the mechanism of transcription arrest following genotoxic stress.
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PMID:Cockayne's Syndrome A and B Proteins Regulate Transcription Arrest after Genotoxic Stress by Promoting ATF3 Degradation. 2922 35

Cytokinesis is monitored by a molecular machinery that promotes the degradation of the intercellular bridge, a transient protein structure connecting the two daughter cells. Here, we found that CSA and CSB, primarily defined as DNA repair factors, are located at the midbody, a transient structure in the middle of the intercellular bridge, where they recruit CUL4 and MDM2 ubiquitin ligases and the proteasome. As a part of this molecular machinery, CSA and CSB contribute to the ubiquitination and the degradation of proteins such as PRC1, the Protein Regulator of Cytokinesis, to ensure the correct separation of the two daughter cells. Defects in CSA or CSB result in perturbation of the abscission leading to the formation of long intercellular bridges and multinucleated cells, which might explain part of the Cockayne syndrome phenotypes. Our results enlighten the role played by CSA and CSB as part of a ubiquitin/proteasome degradation process involved in transcription, DNA repair, and cell division.
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PMID:The Cockayne syndrome group A and B proteins are part of a ubiquitin-proteasome degradation complex regulating cell division. 3319 95