Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P51532 (transcriptional activator)
 6,546 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The transcription factor c-Fos is a short-lived cellular protein. The levels of the protein fluctuate significantly and abruptly during changing pathophysiological conditions. Thus, it is clear that degradation of the protein plays an important role in its tightly regulated activity. We examined the involvement of the ubiquitin pathway in c-Fos breakdown. Using a mutant cell line, ts20, that harbors a thermolabile ubiquitin-activating enzyme, E1, we demonstrate that impaired function of the ubiquitin system stabilizes c-Fos in vivo. In vitro, we reconstituted a cell-free system and demonstrated that the protein is multiply ubiquitinated. The adducts serve as essential intermediates for degradation by the 26S proteasome. We show that both conjugation and degradation are significantly stimulated by c-Jun, with which c-Fos forms the active heterodimeric transcriptional activator AP-1. Analysis of the enzymatic cascade involved in the conjugation process reveals that the ubiquitin-carrier protein E2-F1 and its human homolog UbcH5, which target the tumor suppressor p53 for degradation, are also involved in c-Fos recognition. The E2 enzyme acts along with a novel species of ubiquitin-protein ligase, E3. This enzyme is distinct from other known E3s, including E3 alpha/UBR1, E3 beta, and E6-AP. We have purified the novel enzyme approximately 350-fold and demonstrated that it is a homodimer with an apparent molecular mass of approximately 280 kDa. It contains a sulfhydryl group that is essential for its activity, presumably for anchoring activated ubiquitin as an intermediate thioester prior to its transfer to the substrate. Taken together, our in vivo and in vitro studies strongly suggest that c-Fos is degraded in the cell by the ubiquitin-proteasome proteolytic pathway in a process that requires a novel recognition enzyme.
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PMID:Degradation of the proto-oncogene product c-Fos by the ubiquitin proteolytic system in vivo and in vitro: identification and characterization of the conjugating enzymes. 852 78

The hypoxia-inducible factor 1 transcriptional activator complex (HIF-1) is involved in the activation of the erythropoietin and several other hypoxia-responsive genes. The HIF-1 complex is composed of two protein subunits: HIF-1beta/ARNT (aryl hydrocarbon receptor nuclear translocator), which is constitutively expressed, and HIF-1alpha, which is not present in normal cells but induced under hypoxic conditions. The HIF-1alpha subunit is continuously synthesized and degraded under normoxic conditions, while it accumulates rapidly following exposure to low oxygen tensions. The involvement of the ubiquitin-proteasome system in the proteolytic destruction of HIF-1 in normoxia was studied by the use of specific inhibitors of the proteasome system. Lactacystin and MG-132 were found to protect the degradation of the HIF-1 complex in cells transferred from hypoxia to normoxia. The same inhibitors were able to induce HIF-1 complex formation when added to normoxic cells. Final confirmation of the involvement of the ubiquitin-proteasome system in the regulated degradation of HIF-1alpha was obtained by the use of ts20TGR cells, which contain a temperature-sensitive mutant of E1, the ubiquitin-activating enzyme. Exposure of ts20 cells, under normoxic conditions, to the non-permissive temperature induced a rapid and progressive accumulation of HIF-1. The effect of proteasome inhibitors on the normoxic induction of HIF-1 binding activity was mimicked by the thiol reducing agent N-(2-mercaptopropionyl)-glycine and by the oxygen radical scavenger 2-acetamidoacrylic acid. Furthermore, N-(2-mercaptopropionyl)-glycine induced gene expression as measured by the stimulation of a HIF-1-luciferase expression vector and by the induction of erythropoietin mRNA in normoxic Hep 3B cells. These last findings strongly suggest that the hypoxia induced changes in HIF-1alpha stability and subsequent gene activation are mediated by redox-induced changes.
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PMID:Hypoxia-inducible factor 1alpha (HIF-1alpha) protein is rapidly degraded by the ubiquitin-proteasome system under normoxic conditions. Its stabilization by hypoxia depends on redox-induced changes. 927 21

Saccharomyces cerevisiae SCF(Met30) ubiquitin-protein ligase controls cell cycle function and sulfur amino acid metabolism. We report here that the SCF(Met30 )complex mediates the transcriptional repression of the MET gene network by triggering degradation of the transcriptional activator Met4p when intracellular S-adenosylmethionine (AdoMet) increases. This AdoMet-induced Met4p degradation is dependent upon the 26S proteasome function. Unlike Met4p, the other components of the specific transcriptional activation complexes that are assembled upstream of the MET genes do not appear to be regulated at the protein level. We provide evidence that the interaction between Met4p and the F-box protein Met30p occurs irrespective of the level of intracellular AdoMet, suggesting that the timing of Met4p degradation is not controlled by its interaction with the SCF(Met30) complex. We also demonstrate that Met30p is a short-lived protein, which localizes within the nucleus. Furthermore, transcription of the MET30 gene is regulated by intracellular AdoMet levels and is dependent upon the Met4p transcription activation function. Thus Met4p appears to control its own degradation by regulating the amount of assembled SCF(Met30) ubiquitin ligase.
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PMID:Feedback-regulated degradation of the transcriptional activator Met4 is triggered by the SCF(Met30 )complex. 1063 32

The Saccharomyces cerevisiae Gal4 protein is a paradigmatic transcriptional activator containing a C-terminal acidic activation domain (AD) of 34 amino acids. A mutation that results in the truncation of about two-thirds of the Gal4AD (gal4D) results in a crippled protein with only 3% the activity of the wild-type activator. We show here that although the Gal4D protein is not intrinsically deficient in DNA binding, it is nonetheless unable to stably occupy GAL promoters in vivo. This is because of the activity of the proteasomal ATPases, including Sug1/Rpt6, which bind to Gal4D via the remainder of the AD and strip it off of DNA. A mutation that suppressed the Gal4D "no growth on galactose" phenotype repressed the stripping activity of the ATPase complex but not other activities. We further demonstrate that Gal4D is hypersensitive to this stripping activity because of its failure to be monoubiquitylated efficiently in vivo and in vitro. Evidence is presented that the piece of the AD that is deleted in Gal4D protein is likely a recognition element for the E3 ubiquitin-protein ligase that modifies Gal4. These data argue that acidic ADs comprise at least two small peptide subdomains, one of which is responsible for activator monoubiquitylation and another that interacts with the proteasomal ATPases, coactivators and other transcription factors. This study validates the physiological importance of Gal4 monoubiquitylation and clarifies its major role as that of protecting the activator from being destabilized by the proteasomal ATPases.
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PMID:Activation domain-dependent monoubiquitylation of Gal4 protein is essential for promoter binding in vivo. 1832 36

Human T-cell leukemia virus type 1 (HTLV-1) encodes a protein derived from the antisense strand of the proviral genome designated HBZ (HTLV-1 basic leucine zipper factor). HBZ is the only viral gene consistently expressed in infected patients and adult T-cell leukemia/lymphoma (ATL) tumor cell lines. It functions to antagonize many activities of the Tax viral transcriptional activator, suppresses apoptosis, and supports proliferation of ATL cells. Factors that regulate the stability of HBZ are thus important to the pathophysiology of ATL development. Using affinity-tagged protein and shotgun proteomics, we identified UBR5 as a novel HBZ-binding partner. UBR5 is an E3 ubiquitin-protein ligase that functions as a key regulator of the ubiquitin proteasome system in both cancer and developmental biology. Herein, we investigated the role of UBR5 in HTLV-1-mediated T-cell transformation and leukemia/lymphoma development. The UBR5/HBZ interaction was verified in vivo using over-expression constructs, as well as endogenously in T-cells. shRNA-mediated knockdown of UBR5 enhanced HBZ steady-state levels by stabilizing the HBZ protein. Interestingly, the related HTLV-2 antisense-derived protein, APH-2, also interacted with UBR5 in vivo. However, knockdown of UBR5 did not affect APH-2 protein stability. Co-immunoprecipitation assays identified ubiquitination of HBZ and knockdown of UBR5 resulted in a decrease in HBZ ubiquitination. MS/MS analysis identified seven ubiquitinated lysines in HBZ. Interestingly, UBR5 expression was upregulated in established T lymphocytic leukemia/lymphoma cell lines and the later stage of T-cell transformation in vitro. Finally, we demonstrated loss of UBR5 decreased cellular proliferation in transformed T-cell lines. Overall, our study provides evidence for UBR5 as a host cell E3 ubiquitin-protein ligase responsible for regulating HBZ protein stability. Additionally, our data suggests UBR5 plays an important role in maintaining the proliferative phenotype of transformed T-cell lines.
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PMID:Stability of the HTLV-1 Antisense-Derived Protein, HBZ, Is Regulated by the E3 Ubiquitin-Protein Ligase, UBR5. 2944 Oct 57

The expression of ubiquitin specific peptidase 22 (USP22) is upregulated in several types of cancer, and has been implicated in tumorigenesis. Pirarubicin (THP), an anthracycline antineoplastic drug, can induce apoptosis of several types of cancer cells. However, the molecular mechanisms underlying the action of THP remain to be elucidated. In the current study, treatment with THP induced HeLa cell apoptosis and decreased USP22 expression in a dose- and time-dependent manner. THP reduced the USP22 promoter-regulated luciferase activity, regardless of the mutation of transcriptional activator MYB or E3 ubiquitin-protein ligase SP1 binding sequences; however, this effect was abrogated by the mutation of cyclic AMP-responsive element-binding protein (CREB) binding sequence in HeLa cells. Furthermore, the inhibition on the USP22 promoter activity by THP was not affected by overexpression of CREB-1 in HeLa cells. Additionally, treatment with THP significantly decreased the phosphorylation of CREB-1 at ser133 in HeLa cells. Quantitative chromatin immunoprecipitation assay revealed that THP significantly inhibited the binding of CREB-1 to the USP22 promoter in HeLa cells. The present study demonstrated that THP decreased USP22 expression and promoted HeLa cell apoptosis partially by inhibiting the phosphorylation of CREB-1. The current results may provide novel insights into the molecular mechanisms underlying the pharmacological effect of THP on cancer cell apoptosis.
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PMID:Pirarubicin reduces USP22 expression by inhibiting CREB-1 phosphorylation in HeLa cells. 3100 54