Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UNIPROT:P43146 (tumour suppressor)
 5,935 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The BRCA1 tumour suppressor and its heterodimeric partner BARD1 constitute an E3-ubiquitin (Ub) ligase and function in DNA repair by unknown mechanisms. We show here that the Caenorhabditis elegans BRCA1/BARD1 (CeBCD) complex possesses an E3-Ub ligase responsible for ubiquitylation at DNA damage sites following ionizing radiation (IR). The DNA damage checkpoint promotes the association of the CeBCD complex with E2-Ub conjugating enzyme, Ubc5(LET-70), leading to the formation of an active E3-Ub ligase on chromatin following IR. Correspondingly, defects in Ubc5(let-70) or the DNA damage checkpoint genes atl-1 or mre-11 abolish CeBCD-dependent ubiquitylation in vivo. Extending these findings to human cells reveals a requirement for UbcH5c, the MRN complex, gamma-H2AX and a co-dependence for ATM and ATR kinases for BRCA1-dependent ubiquitylation at DNA damage sites. Furthermore, we demonstrate that the DNA damage checkpoint promotes the association between BRCA1 and UbcH5c to form an active E3-Ub ligase on chromatin after IR. These data reveal that BRCA1-dependent ubiquitylation is activated at sites of DNA repair by the checkpoint as part of a conserved DNA damage response.
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PMID:A conserved pathway to activate BRCA1-dependent ubiquitylation at DNA damage sites. 1662 14

The past two decades have seen a dramatic change in cancer treatment paradigms. Anticancer agents are no longer being developed based on empiricism and serendipity, but are now being aimed to inhibit a validated target that is relatively specific for tumours rather than normal cells. The vast majority of cancers arise from multiple genetic lesions; thus, sophisticated drug cocktails, or single drugs acting on multiple downstream targets will be needed for successful cancer therapy. Three emerging concepts that are addressing these therapeutic needs and that are key to blocking steps in tumourigenesis will be highlighted in this review: (a) attacking cancer cell immortality by targeting the telomere/telomerase complex; (b) targeting oncogene activation by inhibiting the molecular chaperone Hsp90; and (c) stabilizing tumour suppressor proteins by modulating the ubiquitin-proteasome system.
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PMID:Highlights in experimental therapeutics. 1664

The BRCA1 tumour suppressor and its heterodimeric partner BARD1 play crucial roles in coordinating cellular responses to DNA damage. Evidence also implicates these proteins in transcriptional regulation, cell cycle progression and meiotic sex chromosome inactivation, but their mode of action remains elusive. The demonstration that the BRCA1/BARD1 heterodimer constitutes an E3-ubiquitin (Ub) ligase raises the possibility that ubiquitylation of specific targets may allow BRCA1/BARD1 to impact on diverse cellular processes. It is clear that the E3-Ub ligase activity of BRCA1/BARD1 is of critical functional importance as tumour-derived BRCA1 mutations have been identified that eliminate this activity. Recent work and data presented here indicates that BRCA1/BARD1 function is largely conserved in C. elegans. Indeed, studies in C. elegans and human cells have illuminated how the E3-ubiquitin (Ub) ligase activity is regulated in response to DNA damage. However, bone fide targets for BRCA1-dependent ubiquitylation are not known and their identification remains critical to the understanding of the role of BRCA1 in tumorigenesis.
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PMID:BRCA1-mediated ubiquitylation. 1686 94

Hypoxia-inducible factor 1alpha (HIF-1alpha) degradation under normoxia is critical to modulating vascular growth. This degradation is mediated during normoxia by the von Hippel-Lindau tumour suppressor protein (VHL)-E3 ubiquitin ligase in partnership with the E2 enzyme UbcH5. In current models of the functionally similar Skp1, cullin, F-box (SCF)-E3 ligase, the E3 binds the target protein and the E2 catalyses ubiquitin transfer to lysines in an appropriately positioned domain. In the present study, we report that for efficient ubiquitination of HIF-1alpha to occur, three conserved lysines are required in both the HIF-1alpha and endothelial Per-ARNT-Sim domain protein (EPAS) sequences. The site of ubiquitin attachment via UbcH5 was mapped, and is shown to involve three HIF-1alpha lysines, K532, K538 and K547, and the same aligned lysines in EPAS. Only one of these lysines need to be intact for full ubiquitination to occur, analogous to the mechanism of Sic1 ubiquitination by the SCF/Cdc34 complex and further strengthening the functional link between the VHL and SCF-E3 ubiquitin ligases. We also report that lysines can be moved around the HIF-1alpha sequence with only minor losses in ubiquitination efficiency, thus suggesting HIF-1alpha and EPAS regulation by hypoxia depends primarily on an interaction with VHL per se, rather than the highly specific positioning of flanking lysine acceptors.
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PMID:HIF-1alpha and EPAS ubiquitination mediated by the VHL tumour suppressor involves flexibility in the ubiquitination mechanism, similar to other RING E3 ligases. 1686 77

The amount of folded functional protein in a cell is controlled by a number of factors, including the relative rates of its biosynthetic and specific degradation processes, and its intrinsic thermodynamic stability. Mutation-induced loss of stability is a common cause of disease. Many oncogenic mutants of the tumour suppressor p53, for example, reduce the intrinsic thermodynamic stability of the protein in vitro. We have analysed the level of recombinant folded human p53 core domain (p53C) and its mutants in Escherichia coli spanning a stability range of 6 kcal/mol to assess the effects of intrinsic thermodynamic stability in vivo in the absence of specific ubiquitin-mediated pathways in human cells. The levels of folded protein were measured fluorimetrically in living cells by fusing the gene of p53C upstream to that of green fluorescent protein and measuring the fluorescence relative to a control at various temperatures. At a fixed temperature, the amount of fluorescence is correlated with the thermodynamic stability of the mutant. The level of each protein varied with temperature according to a sigmoid curve that paralleled the melting in vitro, but the apparent T(m) was lower in vivo, because steady-state levels are observed rather than true thermodynamic equilibria. Our results show clearly that changes in the intrinsic thermodynamic stability of p53 reduce the level of folded and hence functional p53 substantially in E. coli, and provide insights into the correlation between protein instability and disease at the cellular level.
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PMID:Correlation of levels of folded recombinant p53 in escherichia coli with thermodynamic stability in vitro. 1763 95

The E7 protein encoded by the oncogenic human papillomavirus type 16 has been shown to bind and inactivate insulin-like growth factor-binding protein-3 (IGFBP-3), the pro-apoptotic product of a tumour suppressor gene; however, the molecular mechanism underlying E7-induced inactivation of IGFBP-3 remained uncertain. In this study, we map the IGFBP-3-binding domain for E7 to the nuclear localization signal in the conserved C-terminal domain of IGFBP-3. Moreover, we demonstrate that both proteins interact in the nucleus and that E7 induces polyubiquitination and proteasome-dependent proteolysis of nuclear IGFBP-3 in cervical cancer cells. This leads to a dramatic shortening of the half-life of nuclear IGFBP-3, whereas the stability of an E7-non-binding IGFBP-3 mutant is not affected by E7. Finally, we show that E7-mediated destruction of nuclear IGFBP-3 correlates with the inhibition of IGFBP-3-induced apoptotic cell death. These data are consistent with E7-induced ubiquitin/proteasome-dependent inactivation of nuclear IGFBP-3.
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PMID:Human papillomavirus type 16 E7 oncoprotein inhibits apoptosis mediated by nuclear insulin-like growth factor-binding protein-3 by enhancing its ubiquitin/proteasome-dependent degradation. 1782 6

The promyelocytic leukemia (PML) tumour suppressor is the organiser of PML nuclear bodies, which are domains the precise functions of which are still disputed. We show that upon several types of stress, endogenous PML proteins form nucleolar caps and eventually engulf nucleolar components. Only two specific PML splice variants (PML-I and PML-IV) are efficiently targeted to the nucleolus and the abundant PML-I isoform is required for the targeting of endogenous PML proteins to this organelle. We identified a nucleolar targeting domain within the evolutionarily conserved C-terminus of PML-I. This domain contains a predicted exonuclease III fold essential for the targeting of the PML-I C-terminus to nucleolar fibrillar centres. Furthermore, spontaneous or oncogene retrieval-induced senescence is associated with the formation of very large PML nuclear bodies that initially contain nucleolar components. Later, poly-ubiquitin conjugates are found on the outer shell or within most of these senescence-associated PML bodies. Thus, unexpectedly, the scarcely studied PML-I isoform links PML bodies, nucleolus, senescence and proteolysis.
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PMID:A nucleolar targeting signal in PML-I addresses PML to nucleolar caps in stressed or senescent cells. 1787 36

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.
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PMID:Protein tyrosine phosphatase H1 is a target of the E6 oncoprotein of high-risk genital human papillomaviruses. 1794 17

The proteasome constitutes the central proteolytic component of the highly conserved ubiquitin-proteasome system, which is required for the maintenance and regulation of basic cellular processes, including differentiation, proliferation, cell cycling, gene transcription and apoptosis. Here we show that inhibition of proteasomal proteolytic activity by the proteasome inhibitors bortezomib and lactacystin suppresses essential immune functions of human CD4(+) T cells activated by allogeneic dendritic cells (DCs). In activated CD4(+) T cells, proteasome inhibition induces apoptosis accompanied by rapid accumulation and stabilization of the tumour suppressor protein p53. Activated CD4(+) T cells surviving proteasome inhibition undergo inhibition of proliferation by induction of G(1) phase cell-cycle arrest. Induction of G(1) arrest is accompanied by the accumulation of cyclin-dependent kinase inhibitors p21(WAF1/CIP1) and p27(KIP1) and the disappearance of cyclin A, cyclin D2 and proliferating cell nuclear antigen, proteins known to regulate G(1) to S phase cell-cycle transitions. Expression of the activation-associated cell surface receptors CD25, CD28, CD120b and CD134 as well as production of interferon-gamma (IFN-gamma), tumour necrosis factor-alpha (TNF-alpha), interleukin-4 (IL-4) and IL-5 is suppressed in response to proteasome inhibition in CD4(+) T cells activated by DCs. Expression of CD25, IFN-gamma, TNF-alpha, IL-4 and IL-5 is known to be mediated by the transcriptional activity of nuclear factor of activated T cells (NFAT), and we show here that proteasome inhibition suppresses activation and nuclear translocation of NFATc2 in activated CD4(+) T cells. Thus, the proteasome is required for essential immune functions of activated CD4(+) T cells and can be defined as a molecular target for the suppression of deregulated and unwanted T-cell-mediated immune responses.
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PMID:Proteasome inhibition suppresses essential immune functions of human CD4+ T cells. 1821 57

AMPK (AMP-activated protein kinase)-related kinases regulate cell polarity as well as proliferation and are activated by the LKB1-tumour suppressor kinase. In the present study we demonstrate that the AMPK-related kinases, NUAK1 (AMPK-related kinase 5) and MARK4 (microtubule-affinity-regulating kinase 4), are polyubiquitinated in vivo and interact with the deubiquitinating enzyme USP9X (ubiquitin specific protease-9). Knockdown of USP9X increased polyubiquitination of NUAK1 and MARK4, whereas overexpression of USP9X inhibited ubiquitination. USP9X, catalysed the removal of polyubiquitin chains from wild-type NUAK1, but not from a non-USP9X-binding mutant. Topological analysis revealed that ubiquitin monomers attached to NUAK1 and MARK4 are linked by Lys(29) and/or Lys(33) rather than the more common Lys(48)/Lys(63). We find that AMPK and other AMPK-related kinases are also polyubiquitinated in cells. We identified non-USP9X-binding mutants of NUAK1 and MARK4 and find that these are hyper-ubiquitinated and not phosphorylated at their T-loop residue targeted by LKB1 when expressed in cells, suggesting that polyubiquitination may inhibit these enzymes. The results of the present study demonstrate that NUAK1 and MARK4 are substrates of USP9X and provide the first evidence that AMPK family kinases are regulated by unusual Lys(29)/Lys(33)-linked polyubiquitin chains.
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PMID:Control of AMPK-related kinases by USP9X and atypical Lys(29)/Lys(33)-linked polyubiquitin chains. 1836 52


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