1,519 research outputs found
The ubiquitin ligase Siah is a novel regulator of Zeb1 in breast cancer
No full textElucidating the mechanisms that underlie metastasis is of paramount importance to understanding tumor progression and to the development of novel therapeutics. Epithelial to Mesenchymal Transition (EMT) plays a vital role in tumor cell dissemination and is regulated by a core cassette of transcription factors. Despite recent advances, the molecular pathways that regulate the EMT program have not yet been fully delineated. We show that Siah ubiquitin ligases regulate Zeb1 protein, a key EMT transcription factor. The induction of EMT in breast cancer cells leads to the down-regulation of Siah, while the loss of Siah induces a mesenchymal phenotype, concurrent with an up-regulation of Zeb1. Overexpression of Siah in vitro mediates Zeb1 degradation, which can be blocked with a Siah peptide inhibitor. Thus, this work demonstrates that Siah is a novel regulator of EMT. This work is the first to identify a mechanism of post-translational regulation of the key Epithelial to Mesenchymal Transition transcription factor Zeb1
I Siah Substrate!
No full textProteins are targeted to the E3 RING ubiquitin ligase Siah through a PxAxVxP degron motif. In this issue of Structure, House et al. (2006) present the structural basis by which Siah recognizes its degron with high affinity and specificity
Numerical analysis of time-dependent behavior of Siah Bisheh Cavern
No full textThe understanding of time dependent effects or creep behavior is important in further development of knowledge in the field of rock mechanics. Increasing pressure on support system because of creep behavior of rock is one of the most important problems in underground structure which surrounded with weak rock mass. This paper presents a time dependent behavior analysis of Siah Bisheh pumped storage powerhouse cavern with complex geometry, available geological formations and diverse geotechnical properties of rocks, is under construction on the Chalus River at the north of Iran. Because of the fractured and jointed rock mass, the Discrete Element method Code 3DEC used to compute convergence and pressure on the support system. The power constitutive creep model which is able to model the primary and secondary creep regions of rock masses is applied. In this paper, results of the Siah Bisheh cavern as a case study de align with a comparison between long - term deformation data from in situ measurements and obtained data from an analytical solution and numerical simulations with special consideration of anisotropic effects will be presented. The differences between the obtained values might be because of discontinuous media or different inputs parameters were used for analysis
Elucidation of the Substrate Binding Site of Siah Ubiquitin Ligase
No full textSummaryThe Siah family of RING proteins function as ubiquitin ligase components, contributing to the degradation of multiple targets involved in cell growth, differentiation, angiogenesis, oncogenesis, and inflammation. Previously, a binding motif (degron) was recognized in many of the Siah degradation targets, suggesting that Siah itself may facilitate substrate recognition. We report the crystal structure of the Siah in complex with a peptide containing the degron motif. Binding is within a groove formed in part by the zinc fingers and the first two β strands of the TRAF-C domain of Siah. We show that residues in the degron, previously described to facilitate binding to Siah, interact with the protein. Mutagenesis of Siah at sites of interaction also abrogates both in vitro peptide binding and destabilization of a known Siah target
Structure-Based Design of Covalent Siah Inhibitors
No full textSummaryThe E3 ubiquitin ligase Siah regulates key cellular events that are central to cancer development and progression. A promising route to Siah inhibition is disrupting its interactions with adaptor proteins. However, typical of protein-protein interactions, traditional unbiased approaches to ligand discovery did not produce viable hits against this target, despite considerable effort and a multitude of approaches. Ultimately, a rational structure-based design strategy was successful for the identification of Siah inhibitors in which peptide binding drives specific covalent bond formation with the target. X-ray crystallography, mass spectrometry, and functional data demonstrate that these peptide mimetics are efficient covalent inhibitors of Siah and antagonize Siah-dependent regulation of Erk and Hif signaling in the cell. The proposed strategy may result useful as a general approach to the design of peptide-based inhibitors of other protein-protein interactions
The ubiquitin ligase Siah is a novel regulator of Zeb1 in breast cancer
No full textElucidating the mechanisms that underlie metastasis is of paramount importance to understanding tumor progression and to the development of novel therapeutics. Epithelial to Mesenchymal Transition (EMT) plays a vital role in tumor cell dissemination and is regulated by a core cassette of transcription factors. Despite recent advances, the molecular pathways that regulate the EMT program have not yet been fully delineated. We show that Siah ubiquitin ligases regulate Zeb1 protein, a key EMT transcription factor. The induction of EMT in breast cancer cells leads to the down-regulation of Siah, while the loss of Siah induces a mesenchymal phenotype, concurrent with an up-regulation of Zeb1. Overexpression of Siah in vitro mediates Zeb1 degradation, which can be blocked with a Siah peptide inhibitor. Thus, this work demonstrates that Siah is a novel regulator of EMT. This work is the first to identify a mechanism of post-translational regulation of the key Epithelial to Mesenchymal Transition transcription factor Zeb1
Siah-1b is a direct transcriptional target of p53: Identification of the functional p53 responsive element in the siah-1b promoter
No full textInternational audienceSiah proteins are E3 ubiquitin ligases. They are homologues of the Drosophila seven in absentia (Sina), a protein required for the R7 photoreceptor development. We have previously found that the expression of human siah-1 and its mouse homologue siah-1b are induced by p53 during apoptosis and tumor reversion. So far, no evidence that the siah-1b gene is a direct transcriptional target of p53 has been provided. In the present study we investigate this issue. Northern blot analysis with a specific probe demonstrates an increase in siah-1b transcription on activation of endogenous and inducible exogenous p53. To explore whether this effect is directly mediated by p53 we analyzed 20 kb of chromosome X DNA, containing the siah-1b locus. A p53-binding site was identified in the siah-1b promoter, located at nucleotides -2155/-2103 relative to the translational start site. This site is composed of two half-sites, conforming to the p53-binding consensus sequence but separated by a nonclassical 33-bp spacer. In luciferase assays, p53 induces a substantial increase in siah-1b promoter activity. Gel shift and DNase-I-footprinting studies, combined with mutational analysis and chromatin immunoprecipitation, indicate that p53 effectively binds the siah-1b promoter in vitro and in vivo. Thus, the siah-1b gene is a direct transcriptional target of p53
Elucidation of the substrate binding site of Siah ubiquitin ligase
No full textThe Siah family of RING proteins function as ubiquitin ligase components, contributing to the degradation of multiple targets involved in cell growth, differentiation, angiogenesis, oncogenesis, and inflammation. Previously, a binding motif (degron) was recognized in many of the Siah degradation targets, suggesting that Siah itself may facilitate substrate recognition. We report the crystal structure of the Siah in complex with a peptide containing the degron motif. Binding is within a groove formed in part by the zinc fingers and the first two ß strands of the TRAF-C domain of Siah. We show that residues in the degron, previously described to facilitate binding to Siah, interact with the protein. Mutagenesis of Siah at sites of interaction also abrogates both in vitro peptide binding and destabilization of a known Siah target
ICP0 interacts with SIAH-1 via two minimal interaction motifs.
No full text(A) Schematic representation of HSV-2 ICP0 indicating the position of the RING domain (yellow), the USP7 interaction domain (blue), the nuclear localization signal (brown) and the two SIAH interaction motifs VxP1 and VxP2 (red). The primary amino acid sequence surrounding the predicted SIAH binding motifs is depicted together with the consensus motif and the position of the inactivating NxN mutation. (B) HEK293T cells were transfected with plasmids encoding GFP-tagged ICP0 and its mutants and the cell lysates were incubated with GST or GST-SIAH-1-loaded glutathione sepharose beads. The upper SDS-PAGE gel shows a Coomassie staining of the respective input control (lysate) and the eluates from the GST or GST-SIAH-1 beads. Below, a contrast enhanced section of the gel with putative ICP0 bands indicated by asterisks. ICP0 was detected by Western blotting using an antibody against the C-terminal GFP tag. Size markers in kDa. (C) HEK293T cells were transfected with plasmids encoding GFP-tagged ICP0 and its mutants and HA-tagged SIAH-1. The ICP0-GFP proteins were immunoprecipitated from the lysates, ICP0 and SIAH-1 were detected by SDS-PAGE and Western blotting using antibodies against the GFP and HA-tags. (D) HEK293T cells were transfected with plasmids encoding the inactive mutant HA-SIAH-1C44S and GFP-ICP0ΔRING or GFP-ICP0ΔRING/NxN1/2 as indicated. Immunoprecipitation from the cell lysates was performed using control mouse IgG or anti-SIAH-1. ICP0 and SIAH-1 were detected by SDS-PAGE and Western blotting using antibodies against SIAH-1 or the GFP-tag. The lower panel shows the analysis of the RIPA buffer-insoluble pellet after cell lysis.</p
The Upper Palaeozoic Godar–E-Siah Complex of Jandaq : Evidence and significance of a North Palaeotethyan succession In Central Iran
No full textThe Upper Palaeozoic Godar-e-Siah Complex of Jandaq, Central Iran, comprises three isolated, faultbounded
outcrops exposing Palaeozoic fossiliferous carbonates, volcanics and siliciclastics, which are
markedly distinct from the surrounding sedimentary successions. The three outcrops, that emerge below
Cretaceous and younger sediments, are the Chah Rizab outcrop, the Godar-e-Siah northern outcrop, and
the Godar-e-Siah central outcrop. Their sedimentary successions strongly differ from the typical passive
margin successions of Gondwanan affinity that characterize the Yazd, Lut and Tabas blocks of Central Iran
and the Alborz in North Iran. To understand the origin of these profound differences, we first calibrated
the age of the Jandaq successions: U-Pb radiometric zircons ages, obtained from granitoid boulders in the
conglomerates at Chah Rizab and in the Godar-e-Siah northern outcrop, gave a Late Devonian to
Mississippian age. Biostratigraphic data from brachiopods and fusulinids from the Godar-e-Siah northern
and central outcrops indicate a Pennsylvanian age. The age of the successions is thus post-Visean to
Pennsylvanian. The petrographic composition of the siliciclastic deposits indicates the erosion of a magmatic
arc. To understand where the Jandaq complex could have been located at that time, we have
assessed the palaeobiogeographic affinity of the faunas. The collected brachiopods and fusulinids assemblages
are mostly similar to coeval faunas from Spain, Donbass, Urals, and Yukon Territory (Canada) and
have a North-Palaeotethyan affinity. The Godar-e-Siah Complex of Jandaq likely represents part of the
southern active margin of Eurasia (northern margin of the Palaeotethys), in contrast to the surrounding
Central and North Iran blocks, which were at that time located along the southern margin of the
Neotethys.
Our investigations confirm a complex palaeogeographic evolution for the studied outcrops, suggesting
that they represent fragments of the southern Eurasian active margin - today preserved in NE Iran - displaced
by crustal-scale wrench motions related to the opening and closure of the Sabzear Ocean and to
the Cenozoic activity of the Great Kavir-Doruneh Fault and its possible precursors
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