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

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

Fat-soluble ligands, including sex steroid hormones and environmental toxins, activate ligand-dependent DNA-sequence-specific transcriptional factors that transduce signals through target-gene-selective transcriptional regulation. However, the mechanisms of cellular perception of fat-soluble ligand signals through other target-selective systems remain unclear. The ubiquitin-proteasome system regulates selective protein degradation, in which the E3 ubiquitin ligases determine target specificity. Here we characterize a fat-soluble ligand-dependent ubiquitin ligase complex in human cell lines, in which dioxin receptor (AhR) is integrated as a component of a novel cullin 4B ubiquitin ligase complex, CUL4B(AhR). Complex assembly and ubiquitin ligase activity of CUL4B(AhR) in vitro and in vivo are dependent on the AhR ligand. In the CUL4B(AhR) complex, ligand-activated AhR acts as a substrate-specific adaptor component that targets sex steroid receptors for degradation. Thus, our findings uncover a function for AhR as an atypical component of the ubiquitin ligase complex and demonstrate a non-genomic signalling pathway in which fat-soluble ligands regulate target-protein-selective degradation through a ubiquitin ligase complex.
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PMID:Dioxin receptor is a ligand-dependent E3 ubiquitin ligase. 1739 71

The mammalian target-of-rapamycin (mTOR) signaling pathway serves as a major regulator of cell growth, cell size and metabolism. In vivo, mTOR exists in two complexes, both of which contain the catalytic subunit mTOR, the invariable subunit mLST8, and a complex specific subunit Raptor or Rictor, forming either the rapamycin-sensitive mTORC1 or rapamycin-insensitive mTORC2, respectively. The exact functions of Raptor or Rictor in these complexes are still unclear. Here we demonstrate that mTORC1-mediated signaling events require the function of the 26S proteasome. Inhibition of the 26S proteasome by MG132 leads to the rapid inhibition of phosphorylation of the mTORC1 substrates S6 kinase and 4E-BP1. We have further discovered that the WD40 repeat proteins Raptor and mLST8 bind the CUL4-DDB1 ubiquitin E3 ligase. Loss of CUL4B or DDB1 specifically blocks the phosphorylation of S6 kinase at threonine 389 and 4E-BP1 at serine 65 and threonines 37 and 46, while loss of CUL4B enhances the phosphorylation of AKT at serine 473. These phosphorylation effects are identical to those resulting from the inactivation of Raptor. Our data suggest that the CUL4-DDB1 ubiquitin ligase interacts with Raptor and regulates the mTORC1- mediated signaling pathway through ubiquitin-dependent proteolysis.
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PMID:mTORC1 signaling requires proteasomal function and the involvement of CUL4-DDB1 ubiquitin E3 ligase. 1823 24

Loss of the CDK inhibitor p27(KIP1) is widely linked with poor prognosis in human cancer. In Wnt10b-expressing mammary tumors, levels of p27(KIP1) were extremely low; conversely, Wnt10b-null mammary cells expressed high levels of this protein, suggesting Wnt-dependent regulation of p27(KIP1). Interestingly we found that Wnt-induced turnover of p27(KIP1) was independent from classical SCF(SKP2)-mediated degradation in both mouse and human cells. Instead, turnover required Cullin 4A and Cullin 4B, components of an alternative E3 ubiquitin ligase induced in response to active Wnt signaling. We found that CUL4A was a novel Wnt target gene in both mouse and human cells and that CUL4A physically interacted with p27(KIP1) in Wnt-responding cells. We further demonstrated that both Cul4A and Cul4B were required for Wnt-induced p27(KIP1) degradation and S-phase progression. CUL4A and CUL4B are therefore components of a conserved Wnt-induced proteasome targeting (WIPT) complex that regulates p27(KIP1) levels and cell cycle progression in mammalian cells.
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PMID:A functional link between Wnt signaling and SKP2-independent p27 turnover in mammary tumors. 1905 88

Intra-uterine growth restriction (IUGR) is defined by a restriction of fetal growth during gestation. It is a prevalent significant public health problem that jeopardizes neonatal health but also that can have deleterious consequences later in adult life. Cullins constitute a family of seven proteins involved in cell scaffold and in selective proteolysis via the ubiquitin-proteasome system. Most Cullins are critical for early embryonic development and mutations in some Cullin genes have been identified in human syndromes including growth retardation. Our work hypothesis is that Cullins, particularly CUL4B and CUL7, are involved in placental diseases and especially in IUGR. Thus, expression of Cullins and their cofactors was analyzed in normal and pathological placentas. We show that they present a constant significant over-expression in IUGR placentas, whose extent is dependent on the position of the interrogated fragment along the cDNAs, suggesting the existence of different isoforms of the genes. Particularly, the CUL7 gene is up-regulated up to 10 times in IUGR and 15 times in preeclampsia associated with IUGR. The expression of cofactors of Cullins participating to functional complexes has also been evaluated and showed a similar significant increase in IUGR. Promoters of Cullin genes appeared to be under the control of the SP1 transcription factor. Finally, methylation levels of the CUL7 promoter in placental tissues are modulated according to the pathological conditions, with a significant hypomethylation in IUGR. These results concur to pinpoint the Cullin family as a new set of markers of IUGR.
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PMID:Cullins in human intra-uterine growth restriction: expressional and epigenetic alterations. 2223 87

The NEDD8-Cullin E3 ligase pathway plays an important role in protein homeostasis, in particular the degradation of cell cycle regulators and transcriptional control networks. To characterize NEDD8-cullin target proteins, we performed a quantitative proteomic analysis of cells treated with MLN4924, a small molecule inhibitor of the NEDD8 conjugation pathway. MRFAP1 and its interaction partner, MORF4L1, were among the most up-regulated proteins after NEDD8 inhibition in multiple human cell lines. We show that MRFAP1 has a fast turnover rate in the absence of MLN4924 and is degraded via the ubiquitin-proteasome system. The increased abundance of MRFAP1 after MLN4924 treatment results from a decreased rate of degradation. Characterization of the binding partners of both MRFAP1 and MORF4L1 revealed a complex protein-protein interaction network. MRFAP1 bound to a number of E3 ubiquitin ligases, including CUL4B, but not to components of the NuA4 complex, including MRGBP, which bound to MORF4L1. These data indicate that MRFAP1 may regulate the ability of MORF4L1 to interact with chromatin-modifying enzymes by binding to MORF4L1 in a mutually exclusive manner with MRGBP. Analysis of MRFAP1 expression in human tissues by immunostaining with a MRFAP1-specific antibody revealed that it was detectable in only a small number of tissues, in particular testis and brain. Strikingly, analysis of the seminiferous tubules of the testis showed the highest nuclear staining in the spermatogonia and much weaker staining in the spermatocytes and spermatids. MRGBP was inversely correlated with MRFAP1 expression in these cell types, consistent with an exchange of MORF4L1 interaction partners as cells progress through meiosis in the testis. These data highlight an important new arm of the NEDD8-cullin pathway.
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PMID:Characterization of MRFAP1 turnover and interactions downstream of the NEDD8 pathway. 2203 70

The Cullin-RING finger ligases (CRLs) are involved in the ubiquitin-mediated degradation of cell cycle regulators and play an important role in gametogenesis. Cullin 4 (CUL4) is a conserved core component of a new class of ubiquitin E3 ligase, and participates in the proteolysis of several regulatory proteins through the ubiquitin-proteasome pathway. The mammals encode two paralogs of CUL4, CUL4A and CUL4B, and the two Cul4 genes are functionally redundant. However, Drosophila or other metazoans only contain one Cul4 gene. Here we cloned the Cul4 gene and confirmed that there is only one protein of CUL4 in Eriocheir sinensis, a full length Cul4 comprised of 2777 nucleotides, an open-reading frame of 2373bp encoding 790 amino acid residues. The expression level of Cul4 mRNAs, as demonstrated by quantitative real-time PCR, varied significantly during testis development, with the greatest transcript levels found at an early stage. Localization analysis using antibodies against CUL4A/4B in the reproductive system showed that EsCUL4 mainly distribute in spermatogonia and primary spermatocytes, and gradually reduced during the development and maturation of sperm. The results indicated that a single CUL4 protein may play a role in spermatogenesis in E. sinensis.
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PMID:Involvement of the single Cul4 gene of Chinese mitten crab Eriocheir sinensis in spermatogenesis. 2433 19

Long noncoding RNAs (lncRNAs) play multiple key regulatory roles in various cellular pathways. However, their functions in HIV-1 latent infection remain largely unknown. Here we show that a lncRNA named NRON, which is highly expressed in resting CD4(+) T lymphocytes, could be involved in HIV-1 latency by specifically inducing Tat protein degradation. Our results suggest that NRON lncRNA potently suppresses the viral transcription by decreasing the cellular abundance of viral transactivator protein Tat. NRON directly links Tat to the ubiquitin/proteasome components including CUL4B and PSMD11, thus facilitating Tat degradation. Depletion of NRON, especially in combination with a histone deacetylase (HDAC) inhibitor, significantly reactivates the viral production from the HIV-1-latently infected primary CD4(+) T lymphocytes. Our data indicate that lncRNAs play a role in HIV-1 latency and their manipulation could be a novel approach for developing latency-reversing agents.
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PMID:Long noncoding RNA NRON contributes to HIV-1 latency by specifically inducing tat protein degradation. 2729 71

The amyloid precursor protein (APP), whose mutations cause Alzheimer disease, plays an important in vivo role and facilitates transmitter release. Because the APP cytosolic region (ACR) is essential for these functions, we have characterized its brain interactome. We found that the ACR interacts with proteins that regulate the ubiquitin-proteasome system, predominantly with the E3 ubiquitin-protein ligases Stub1, which binds the NH2 terminus of the ACR, and CRL4(CRBN), which is formed by Cul4a/b, Ddb1, and Crbn, and interacts with the COOH terminus of the ACR via Crbn. APP shares essential functions with APP-like protein-2 (APLP2) but not APP-like protein-1 (APLP1). Noteworthy, APLP2, but not APLP1, interacts with Stub1 and CRL4(CRBN), pointing to a functional pathway shared only by APP and APLP2. In vitro ubiquitination/ubiquitome analysis indicates that these E3 ligases are enzymatically active and ubiquitinate the ACR residues Lys(649/650/651/676/688) Deletion of Crbn reduces ubiquitination of Lys(676) suggesting that Lys(676) is physiologically ubiquitinated by CRL4(CRBN) The ACR facilitated in vitro ubiquitination of presynaptic proteins that regulate exocytosis, suggesting a mechanism by which APP tunes transmitter release. Other dementia-related proteins, namely Tau and apoE, interact with and are ubiquitinated via the ACR in vitro This, and the evidence that CRBN and CUL4B are linked to intellectual disability, prompts us to hypothesize a pathogenic mechanism, in which APP acts as a modulator of E3 ubiquitin-protein ligase(s), shared by distinct neuronal disorders. The well described accumulation of ubiquitinated protein inclusions in neurodegenerative diseases and the link between the ubiquitin-proteasome system and neurodegeneration make this concept plausible.
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PMID:Amyloid Precursor Protein (APP) May Act as a Substrate and a Recognition Unit for CRL4CRBN and Stub1 E3 Ligases Facilitating Ubiquitination of Proteins Involved in Presynaptic Functions and Neurodegeneration. 2732 2

The E3 ubiquitin ligase HUWE1/Mule/ARF-BP1 plays an important role in diverse biological processes including DNA damage repair and apoptosis. Our previous study has shown that in response to DNA damage HUWE1 was downregulated in CUL4B-mediated ubiquitination and subsequent proteasomal degradation, and CUL4B-mediated regulation of HUWE1 was important for cell survival upon DNA damage. CUL4B is a core component of the CUL4B Ring ligase complexes containing ROC1, DDB1 and a DDB1-Cullin Associated Factors (DCAFs), the latter of which are DDB1-binding WD40 adaptors critical for substrate recognition and recruitment. However, the identity of DCAF in CRL4B that mediates degradation of HUWE1 remains elusive. Here we report that RBBP7 is the DCAF in the CRL4B complex bridging the DDB1-CUL4B-ROC1 to HUWE1. Loading of HUWE1 to the E3 ubiquitin ligase complex resulted in its polyubiquitination, and consequently its proteasome mediated degradation. Overexpression of RBBP7 promoted HUWE1 protein degradation, while depletion of RBBP7 stabilized HUWE1, and hence accelerated the degradation of MCL-1 and BRCA1, two substrates of HUWE1 that are critical in apoptosis and DNA damage repair. Taken together, these data reveal CRL4B^RBBP7 is the E3 ligase responsible for the proteasomal degradation of HUWE1, and further provide a potential strategy for cancer therapy by targeting HUWE1 and the CUL4B E3 ligase complex.
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PMID:CRL4B^RBBP7 targets HUWE1 for ubiquitination and proteasomal degradation. 2973 75

Objective: The E3 ligase, CRL4, plays diverse roles in different cellular processes, such as DNA damage, transcriptional regulation, cell cycle progression, and cell apoptosis. Our previous study showed that CUL4A and CUL4B had a strong association with tobacco smoking risk in lung squamous cell carcinoma (SCC) and small cell lung carcinoma (SCLC). This study aimed to define the potential mechanism underlying the roles of CUL4A and CUL4B in the development of SCC and SCLC. Methods: We determined the role of CUL4A and CUL4B in the cell cycle and apoptosis of SCC and SCLC, and identified the key apoptosis-related gene involved in the oncogenic activity of CUL4B by Western blot, immunohistochemical staining, flow cytometry, and enzyme inhibition experiments. Results: We found that depletion of CUL4A and CUL4B reduced the proliferation of SCC and SCLC cells. CUL4A^knockdown but not CUL4B^knockdown arrested cells in G1 phase while upregulating P21 and CUL4B^knockdown promoted cell apoptosis through upregulation of FOXO3A. Accordingly, CUL4B decreased FOXO3A expression by activating the ERK signaling pathway and mediating FOXO3A degradation via the ubiquitin-proteasome pathway. Conclusions: These results identified the function of E3 ligase CRL4 in regulating SCC and SCLC cell proliferation, which provides a potential strategy for cancer therapy by targeting FOXO3A and the E3 ligase, CRL4.
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PMID:CUL4 E3 ligase regulates the proliferation and apoptosis of lung squamous cell carcinoma and small cell lung carcinoma. 3258 74


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