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

---

Query: EC:3.4.25.1 (proteasome)
28,817 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The bovine papillomavirus E2 proteins regulate viral transcription, replication, and episomal genome maintenance. We have previously mapped the major phosphorylation sites of the E2 proteins to serine residues 298 and 301 and shown that mutation of serine residue 301 to alanine leads to a dramatic (10- to 20-fold) increase in viral DNA copy number. In this study we analyzed how phosphorylation regulates E2 protein function. S301 is located in a PEST sequence; these sequences are often found in proteins with a short half-life and can be regulated by phosphorylation. We show here that the E2 protein is ubiquitinated and degraded by the proteasome. Mutation of serine 301 to alanine increases the half-life of E2 from approximately 50 min to 160 min. Furthermore, the A301 E2 protein shows greatly reduced ubiquitination and degradation by the proteasome. These results suggest that the E2 protein level is regulated by phosphorylation, which in turn determines viral episomal copy number.
...
PMID:Proteasome-mediated degradation of the papillomavirus E2-TA protein is regulated by phosphorylation and can modulate viral genome copy number. 1084 85

The targeting of proteolytic substrates is accomplished by a family of ubiquitin-conjugating (E2) enzymes and a diverse set of substrate recognition (E3) factors. The ligation of a multiubiquitin chain to a substrate can promote its degradation by the proteasome. However, the mechanism that facilitates the translocation of a substrate to the proteasome in vivo is poorly understood. We have discovered that E2 proteins, including Ubc1, Ubc2, Ubc4, and Ubc5, can interact with the 26S proteasome. Significantly, the interaction between Ubc4 and the proteasome is strongly induced by heat stress, consistent with the requirement for this E2 for efficient stress tolerance. A catalytically inactive derivative of Ubc4 (Ubc4(C86A)), which causes toxicity in yeast cells, can also bind the proteasome. Purified proteasomes can ligate ubiquitin to a test substrate without the addition of exogenous E2 protein, suggesting that the ubiquitylation of some proteolytic substrates might be directly coupled to degradation by the proteasome.
...
PMID:Evidence for an interaction between ubiquitin-conjugating enzymes and the 26S proteasome. 1084 95

The E2 proteins of papillomaviruses regulate both viral transcription and DNA replication. The human papillomavirus type 18 (HPV18) E2 protein has been shown to repress transcription of the oncogenic E6 and E7 genes, inducing growth arrest in HeLa cells. Using HPV18 E2 fused to the green fluorescent protein (GFP), we showed that this protein was short-lived in transfected HeLa cells. Real-time microscopy experiments indicated that the E2-dependent signal increased for roughly 24 h after transfection and then rapidly disappeared, indicating that E2 was unstable in HeLa cells and could confer instability to GFP. Similar studies done with a protein lacking the transactivation domain indicated that this truncation strongly stabilizes the E2 protein. In vitro, full-length E2 or the transactivation domain alone was efficiently ubiquitinated, whereas deletion of the transactivation domain strongly decreased the ubiquitination of the E2 protein. Proteasome inhibition in cells expressing E2 increased its half-life about sevenfold, which was comparable to the half-life of the amino-terminally truncated protein. These characteristics of E2 instability were independent of the E2-mediated G(1) growth arrest in HeLa cells, as they were reproduced in MCF7 cells, where E2 does not affect the cell cycle. Altogether, these experiments showed that the HPV18 E2 protein was degraded by the ubiquitin-proteasome pathway through its amino-terminal transactivation domain. Tight regulation of the stability of the HPV 18 E2 protein may be essential to avoid accumulation of a potent transcriptional repressor and antiproliferative agent during the viral vegetative cycle.
...
PMID:Stability of the human papillomavirus type 18 E2 protein is regulated by a proteasome degradation pathway through its amino-terminal transactivation domain. 1146 97

The major phosphorylation sites of the bovine papillomavirus E2 transactivator protein are two serine residues, 298 and 301, that are located in a flexible hinge region between the DNA binding and transactivation domains. Phosphorylation of serine residue 301 promotes ubiquitination and rapid degradation of the E2 protein by the proteasome pathway. To understand the mechanism through which phosphorylation regulates the intracellular levels of this unique papillomavirus regulatory protein, we have carried out an extensive mutational analysis of the region surrounding the phosphorylation sites of the E2 protein. Our results indicate that casein kinase II phosphorylates serine 301. However, phosphorylation of serine 301 is not a sufficient recognition motif for proteasomal degradation; other residues that directly surround the phosphorylation sites are crucial for E2 degradation. The phenotypes of E2 proteins mutated in this region indicate that phosphorylation of serine 301 induces a conformational change that leads to degradation of the E2 protein. In support of this model, circular dichroism studies of the conformational tendencies of peptides from this region indicate that phosphorylation at position 301 decreases the local thermodynamic stability of this region. Thus, this region appears to have evolved to display a marginal local thermodynamic stability that can be regulated by phosphorylation, leading to targeted degradation of the E2 protein.
...
PMID:Casein Kinase II phosphorylation-induced conformational switch triggers degradation of the papillomavirus E2 protein. 1501 86

Proteasomal-mediated rapid turnover of proteins is often modulated by phosphorylation of PEST sequences. The E2 protein from papillomavirus participates in gene transcription, DNA replication, and episomal genome maintenance. Phosphorylation of a PEST sequence located in a flexible region accelerates its degradation. NMR analysis of a 29 amino acid peptide fragment derived from this region shows pH-dependent polyproline II and alpha helix structures, connected by a turn. Phosphorylation, in particular that at serine 301, disrupts the overall structure, and point mutations have either stabilizing or destabilizing effects. There is an excellent correlation between the thermodynamic stability of different peptides and the half-life of E2 proteins containing the same mutations in vivo. The structure around the PEST region appears to have evolved a marginal stability that is finely tunable by phosphorylation. Thus, conformational stability, rather than recognition of a phosphate modification, modulates the degradation of this PEST sequence by the proteasome machinery.
...
PMID:Molecular basis for phosphorylation-dependent, PEST-mediated protein turnover. 1647 50

The E6 proteins of high-risk genital human papillomaviruses (HPV), such as HPV types 16 and 18, possess a conserved C-terminal PDZ-binding motif, which mediates interaction with some cellular PDZ domain proteins. The binding of E6 usually results in their ubiquitin-mediated degradation. The ability of E6 to bind to PDZ domain proteins correlates with the oncogenic potential. Using a yeast two-hybrid system, GST pull-down experiments and coimmunoprecipitations, we identified the protein tyrosine phosphatase H1 (PTPH1/PTPN3) as a novel target of the PDZ-binding motif of E6 of HPV16 and 18. PTPH1 has been suggested to function as tumour suppressor protein, since mutational analysis revealed somatic mutations in PTPH1 in a minor fraction of various human tumours. We show here that HPV16 E6 accelerated the proteasome-mediated degradation of PTPH1, which required the binding of E6 to the cellular ubiquitin ligase E6-AP and to PTPH1. The endogenous levels of PTPH1 were particularly low in HPV-positive cervical carcinoma cell lines. The reintroduction of the E2 protein into the HPV16-positive cervical carcinoma cell line SiHa, known to lead to a sharp repression of E6 expression and to induce growth suppression, resulted in an increase of the amount of PTPH1. Our data suggest that reducing the level of PTPH1 may contribute to the oncogenic activity of high-risk genital E6 proteins.
...
PMID:Protein tyrosine phosphatase H1 is a target of the E6 oncoprotein of high-risk genital human papillomaviruses. 1794 17

Glial cell missing homolog 1 (GCM1) is an important transcription factor regulating placental cell fusion. Recently, we have demonstrated that GCM1 is a labile protein and that the F-box protein FBXW2 (F-box and WD repeat domain containing 2) mediates GCM1 ubiquitination for proteasomal degradation. Multiple factors are involved in the ubiquitin-proteasome degradation system. Therefore, in order to better understand the mechanism regulating GCM1 stability, we further isolated and characterized the E2 ubiquitin-conjugating enzyme responsible for FBXW2-mediated ubiquitination of GCM1 in this study. We prepared and screened a variety of E2 proteins in an in vitro ubiquitination assay system for GCM1 and found that UBE2D2 is required for the SCF(FBXW2) E3 ligase in regulation of GCM1 ubiquitination. We also demonstrated that the enzyme activity of UBE2D2 is required for GCMa ubiquitination and for association with the SCF(FBXW2) complex. Moreover, knocking down UBE2D2 expression by RNA interference not only suppressed FBXW2-mediated GCM1 ubiquitination, but also prolonged the half-life of GCM1 in vivo. Our results suggest that UBE2D2 is a functional E2 protein which, together with FBXW2, regulates GCM1 stability in the placenta.
...
PMID:Ubiquitin-conjugating enzyme UBE2D2 is responsible for FBXW2 (F-box and WD repeat domain containing 2)-mediated human GCM1 (glial cell missing homolog 1) ubiquitination and degradation. 1870 17

The regulation of human papillomavirus (HPV) gene expression by the E2 protein is a critical feature of the viral life cycle. Previous studies have shown an important role in transcription for the ubiquitin-proteasome pathway, but its role in HPV gene expression has not been addressed. We now show that HPV E2 requires an active proteasome for its optimal transcriptional activator function. This involves an interaction with the Mdm2 ubiquitin ligase, which together with E2 acts synergistically to activate the HPV type 16 promoter. We also show that HPV E2 recruits Mdm2 onto HPV promoter sequences, providing an explanation for this cooperative activity.
...
PMID:The Mdm2 ubiquitin ligase enhances transcriptional activity of human papillomavirus E2. 1900 34

Brd4 is a chromatin adaptor containing tandem bromodomains binding to acetylated histone H3 and H4. Although Brd4 has been implicated in the transcriptional control of papillomavirus-encoded E2 protein, it is unclear how Brd4 regulates E2 function and whether the involvement of Brd4 in transactivation and transrepression is common to different types of E2 proteins. Using DNase I footprinting performed with in vitro reconstituted human papillomavirus (HPV) chromatin and nucleosome-free DNA templates, we found that Brd4 facilitates E2 binding to its cognate sequences in chromatin depending on bromodomains and the E2-interacting region of Brd4. Moreover, the coactivator and corepressor function of Brd4 requires at least one intact bromodomain and is mediated by its direct association with E2 proteins encoded by cancer-inducing high risk HPV-16 and HPV-18, wart-causing low risk HPV-11, and bovine papillomavirus type 1, in part through enhancing the protein stability of E2 that is normally degraded via the ubiquitin-dependent proteasome pathway. Our findings indicate that a chromatin adaptor can bridge and enhance the binding of a sequence-specific transcription factor to chromatin and further promote the stability of a labile transcription factor via direct protein-protein interaction.
...
PMID:Chromatin adaptor Brd4 modulates E2 transcription activity and protein stability. 1903 68

The E2 protein of human papillomavirus (HPV) binds to specific sites in the viral genome to regulate its transcription, replication, and maintenance in infected cells. Like most regulatory proteins, E2 is rapidly turned over. A high-throughput assay was developed to quantify the expression and stability of E2 in vivo, based on its fusion to Renilla luciferase (RLuc). The steady-state levels of Rluc-E2 were quantified by measuring the amounts of associated luciferase activity, and its degradation was measured by monitoring the decrease in enzymatic activity occurring after a block of translation with cycloheximide. Using this assay, the E2 proteins from a low-risk (HPV11) and a high-risk (HPV31) human papillomavirus (HPV) type were found to have short half-lives of 60 min in C33A cervical carcinoma cells and to be ubiquitinated and degraded by the proteasome. Analysis of mutant proteins showed that the instability of E2 is independent of its DNA-binding and transcriptional activities but is encoded within its transactivation domain, the region that binds to the cellular chromatin factor bromodomain-containing protein 4 (Brd4) to regulate viral gene transcription. Overexpression of Brd4, or of its C-terminal E2-interaction domain, was found to increase the steady-state levels and stability of wild-type E2 but not of E2 mutants defective for binding Brd4. These results indicate that the stability of E2 is increased upon complex formation with Brd4 and highlight the value of the luciferase assay for the study of E2 degradation.
...
PMID:Proteasomal degradation of the papillomavirus E2 protein is inhibited by overexpression of bromodomain-containing protein 4. 1921 38


1 2 Next >>

---