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Yue Xiong - One of the best experts on this subject based on the ideXlab platform.
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SIRT7 deacetylates DDB1 and suppresses the activity of the CRL4 E3 ligase complexes
The FEBS journal, 2017Co-Authors: Ran Lin, Yue Xiong, Peng Liu, Minjia Tan, Kun-liang Guan, Hai-xin YuanAbstract:Cullin 4 (CUL4) and small ring finger protein ROC1 assemble to form E3 ubiquitin ligase (CRL4) complexes. CUL4 interacts with WD-40 proteins through the adaptor protein DNA damage-binding protein 1 (DDB1) to target substrates for ubiquitylation. Very little is known on how the CUL4 and DDB1 interaction is regulated. Here, we show that DDB1 is acetylated and acetylation promotes DDB1 binding to CUL4. We also identify nucleolar sirtuin 7 (SIRT7) as a major deacetylase that negatively regulates DDB1-CUL4 interaction. Following inhibition of nucleolar function by actinomycin D or 5-fluorouracil treatment or knocking down the gene for the RNA polymerase I component UBF, SIRT7 is mobilized from the nucleolus to the nucleoplasm and promotes DDB1 deacetylation, leading to decreased DDB1-CUL4 association and CRL4 activity. This results in the accumulation or activation of CRL4 substrates including LATS1 and p73, which contribute to cell apoptosis induced by actinomycin D and 5-fluorouracil. Our study uncovers a novel regulation of CRL4 E3 ligase complexes.
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Arabidopsis DDB1-CUL4 ASSOCIATED FACTOR1 Forms a Nuclear E3 Ubiquitin Ligase with DDB1 and CUL4 That Is Involved in Multiple Plant Developmental Processes
The Plant cell, 2008Co-Authors: Yu Zhang, Haodong Chen, Yue Xiong, Suhua Feng, Fangfang Chen, Jia Wang, Chad M. Mccall, Xing Wang DengAbstract:The human DDB1-CUL4 ASSOCIATED FACTOR (DCAF) proteins have been reported to interact directly with UV-DAMAGED DNA BINDING PROTEIN1 (DDB1) through the WDxR motif in their WD40 domain and function as substrate-recognition receptors for CULLIN4-based E3 ubiquitin ligases. Here, we identified and characterized a homolog of human DCAF1/VprBP in Arabidopsis thaliana. Yeast two-hybrid analysis demonstrated the physical interaction between DCAF1 and DDB1 from Arabidopsis, which is likely mediated via the WD40 domain of DCAF1 that contains two WDxR motifs. Moreover, coimmunoprecipitation assays showed that DCAF1 associates with DDB1, RELATED TO UBIQUITIN–modified CUL4, and the COP9 signalosome in vivo but not with CULLIN-ASSOCIATED and NEDDYLATION-DISSOCIATED1, CONSTITUTIVE PHOTOMORPHOGENIC1 (COP1), or the COP10-DET1-DDB1 complex, supporting the existence of a distinct Arabidopsis CUL4 E3 ubiquitin ligase, the CUL4-DDB1-DCAF1 complex. Transient expression of fluorescently tagged DCAF1, DDB1, and CUL4 in onion epidermal cells showed their colocalization in the nucleus, consistent with the notion that the CUL4-DDB1-DCAF1 complex functions as a nuclear E3 ubiquitin ligase. Genetic and phenotypic analysis of two T-DNA insertion mutants of DCAF1 showed that embryonic development of the dcaf1 homozygote is arrested at the globular stage, indicating that DCAF1 is essential for plant embryogenesis. Reducing the levels of DCAF1 leads to diverse developmental defects, implying that DCAF1 might be involved in multiple developmental pathways.
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wd40 protein fbw5 promotes ubiquitination of tumor suppressor tsc2 by DDB1 cul4 roc1 ligase
Genes & Development, 2008Co-Authors: Jian Hu, Sima Zacharek, Yizhou Joseph He, Robert J Duronio, Stuart D Shumway, Yue XiongAbstract:Tuberous sclerosis (TSC) is an autosomal dominant disease characterized by hamartoma formation in various organs and is caused by mutations targeting either the TSC1 or TSC2 genes. TSC1 and TSC2 proteins form a functionally interdependent dimeric complex. Phosphorylation of either TSC subunit by different kinases regulates the function of TSC and represents a major mechanism to integrate various signals into a centralized cell growth pathway. The majority of disease-associated mutations targeting either TSC1 or TSC2 results in a substantial decrease in protein level, suggesting that protein turnover also plays a critical role in TSC regulation. Here we report that TSC2 protein binds to FBW5, a DDB1-binding WD40 (DWD) protein, and is recruited by FBW5 to the DDB1–CUL4–ROC1 E3 ubiquitin ligase. Overexpression of FBW5 or CUL4A promotes TSC2 protein degradation, and this is abrogated by the coexpression of TSC1. Conversely, depletion of FBW5, DDB1, or CUL4A/B stabilizes TSC2. DDB1 or Cul4 mutations in Drosophila result in Gigas/TSC2 protein accumulation and cause growth defects that can be partially rescued by Gigas/Tsc2 reduction. These results indicate that FBW5–DDB1–CUL4–ROC1 is an E3 ubiquitin ligase regulating TSC2 protein stability and TSC complex turnover.
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WD40 protein FBW5 promotes ubiquitination of tumor suppressor TSC2 by DDB1–CUL4–ROC1 ligase
Genes & development, 2008Co-Authors: Sima Zacharek, Robert J Duronio, Stuart D Shumway, Hyun O. Lee, Yue XiongAbstract:Tuberous sclerosis (TSC) is an autosomal dominant disease characterized by hamartoma formation in various organs and is caused by mutations targeting either the TSC1 or TSC2 genes. TSC1 and TSC2 proteins form a functionally interdependent dimeric complex. Phosphorylation of either TSC subunit by different kinases regulates the function of TSC and represents a major mechanism to integrate various signals into a centralized cell growth pathway. The majority of disease-associated mutations targeting either TSC1 or TSC2 results in a substantial decrease in protein level, suggesting that protein turnover also plays a critical role in TSC regulation. Here we report that TSC2 protein binds to FBW5, a DDB1-binding WD40 (DWD) protein, and is recruited by FBW5 to the DDB1-CUL4-ROC1 E3 ubiquitin ligase. Overexpression of FBW5 or CUL4A promotes TSC2 protein degradation, and this is abrogated by the coexpression of TSC1. Conversely, depletion of FBW5, DDB1, or CUL4A/B stabilizes TSC2. DDB1 or Cul4 mutations in Drosophila result in Gigas/TSC2 protein accumulation and cause growth defects that can be partially rescued by Gigas/Tsc2 reduction. These results indicate that FBW5-DDB1-CUL4-ROC1 is an E3 ubiquitin ligase regulating TSC2 protein stability and TSC complex turnover.
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DDB1 functions as a linker to recruit receptor WD40 proteins to CUL4–ROC1 ubiquitin ligases
Genes & development, 2006Co-Authors: Chad M. Mccall, Yaxue Zeng, Yue XiongAbstract:Cullins assemble the largest family of ubiquitin ligases by binding with ROC1 and various substrate receptors. CUL4 function is linked with many cellular processes, but its substrate-recruiting mechanism remains elusive. We identified a protein motif, the DWD box (DDB1-binding WD40 protein), and demonstrated the binding of 15 DWD proteins with DDB1-CUL4A. We provide evidence supporting the critical function of the DWD box and DDB1's role as the linker mediating DWD protein association with CUL4A. A database search predicts that about one-third of WD40 proteins, 90 in humans, contain the DWD box, suggesting a potentially large number of DWD-DDB1-CUL4-ROC1 E3 ligases.
Ning Zheng - One of the best experts on this subject based on the ideXlab platform.
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A promiscuous alpha-helical motif anchors viral hijackers and substrate receptors to the CUL4-DDB1 ubiquitin ligase machinery.
Nature structural & molecular biology, 2009Co-Authors: Eva Isabelle Robert, Michel Strubin, Pieter C Van Breugel, Ning ZhengAbstract:The cullin 4-DNA-damage-binding protein 1 (CUL4-DDB1) ubiquitin ligase machinery regulates diverse cellular functions and can be subverted by pathogenic viruses. Here we report the crystal structure of DDB1 in complex with a central fragment of hepatitis B virus X protein (HBx), whose DDB1-binding activity is important for viral infection. The structure reveals that HBx binds DDB1 through an alpha-helical motif, which is also found in the unrelated paramyxovirus SV5-V protein despite their sequence divergence. Our structure-based functional analysis suggests that, like SV5-V, HBx captures DDB1 to redirect the ubiquitin ligase activity of the CUL4-DDB1 E3 ligase. We also identify the alpha-helical motif shared by these viral proteins in the cellular substrate-recruiting subunits of the E3 complex, the DDB1-CUL4-associated factors (DCAFs) that are functionally mimicked by the viral hijackers. Together, our studies reveal a common yet promiscuous structural element that is important for the assembly of cellular and virally hijacked CUL4-DDB1 E3 complexes.
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Molecular architecture and assembly of the DDB1-CUL4A ubiquitin ligase machinery.
Nature, 2006Co-Authors: Stephane Angers, Michael J. Maccoss, Randall T. Moon, Ning ZhengAbstract:Protein ubiquitination is a common form of post-translational modification that regulates a broad spectrum of protein substrates in diverse cellular pathways1. Through a three-enzyme (E1–E2–E3) cascade, the attachment of ubiquitin to proteins is catalysed by the E3 ubiquitin ligase, which is best represented by the superfamily of the cullin-RING complexes2,3. Conserved from yeast to human, the DDB1–CUL4–ROC1 complex is a recently identified cullin-RING ubiquitin ligase, which regulates DNA repair4,5,6,7,8,9,10, DNA replication11,12,13,14 and transcription15, and can also be subverted by pathogenic viruses to benefit viral infection16. Lacking a canonical SKP1-like cullin adaptor and a defined substrate recruitment module, how the DDB1–CUL4–ROC1 E3 apparatus is assembled for ubiquitinating various substrates remains unclear. Here we present crystallographic analyses of the virally hijacked form of the human DDB1–CUL4A–ROC1 machinery, which show that DDB1 uses one β-propeller domain for cullin scaffold binding and a variably attached separate double-β-propeller fold for substrate presentation. Through tandem-affinity purification of human DDB1 and CUL4A complexes followed by mass spectrometry analysis, we then identify a novel family of WD40-repeat proteins, which directly bind to the double-propeller fold of DDB1 and serve as the substrate-recruiting module of the E3. Together, our structural and proteomic results reveal the structural mechanisms and molecular logic underlying the assembly and versatility of a new family of cullin-RING E3 complexes.
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structure of DDB1 in complex with a paramyxovirus v protein viral hijack of a propeller cluster in ubiquitin ligase
Cell, 2006Co-Authors: Xiujuan Chen, Kenneth C Garbutt, Pengbo Zhou, Ning ZhengAbstract:The DDB1-Cul4A ubiquitin ligase complex promotes protein ubiquitination in diverse cellular functions and is reprogrammed by the V proteins of paramyxoviruses to degrade STATs and block interferon signaling. Here we report the crystal structures of DDB1 alone and in complex with the simian virus 5 V protein. The DDB1 structure reveals an intertwined three-propeller cluster, which contains two tightly coupled beta propellers with a large pocket in between and a third beta propeller flexibly attached on the side. The rigid double-propeller fold of DDB1 is targeted by the viral V protein, which inserts an entire helix into the double-propeller pocket, whereas the third propeller domain docks DDB1 to the N terminus of the Cul4A scaffold. Together, these results not only provide structural insights into how the virus hijacks the DDB1-Cul4A ubiquitin ligase but also establish a structural framework for understanding the multiple functions of DDB1 in the uniquely assembled cullin-RING E3 machinery.
Yongsheng Liu - One of the best experts on this subject based on the ideXlab platform.
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Role of UV-damaged DNA-binding protein-1 (DDB1) in early response to Pseudomonas syringae pv. tomato DC3000 infection in tomato
Canadian Journal of Plant Pathology, 2018Co-Authors: Danfeng Zhang, Junyang Yue, Chenyan Hua, Danyang Chen, Yi Han, Yongsheng LiuAbstract:AbstractDiseases caused by pathogens are one of the most important stress factors that affect crop yield and quality and plants have evolved a complex network of responses to infection. Tomato UV-damaged DNA-binding protein-1 (DDB1) has been implicated in playing a role in resistance against Agrobacterium infection. However, the effect of DDB1 protein on plant disease resistance is still largely unknown. Pseudomonas syringae pv. tomato DC3000 (Pst DC3000) is an important pathogen of tomato and has been used as a model for testing disease susceptibility. In this work, we compared the sensitivity to Pst DC3000 among wild-type seedlings AC+, DDB1-deficient mutants (hp1) and DDB1 over-expression (DDB1-OE) seedlings. Results showed that the hp1 mutant is more susceptible to Pst DC3000, whereas the resistance was increased in the DDB1-OE seedlings. Hydrogen peroxide, the key component of the plant defence response and the corresponding cell death phenotype were compromised in the hp1 mutant and enhanced in the ...
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the tomato dwd motif containing protein ddi1 interacts with the cul4 DDB1 based ubiquitin ligase and plays a pivotal role in abiotic stress responses
Biochemical and Biophysical Research Communications, 2014Co-Authors: Min Miao, Yunye Zhu, Maiju Qiao, Xiaofeng Tang, Wei Zhao, Fangming Xiao, Yongsheng LiuAbstract:CULLIN4(CUL4)–DAMAGED DNA BINDING PROTEIN1 (DDB1)-based ubiquitin ligase plays significant roles in multiple physiological processes via ubiquitination-mediated degradation of relevant target proteins. The DDB1–CUL4-associated factor (DCAF) acts as substrate receptor in the CUL4–DDB1 ubiquitin ligase complex and determines substrate specificity. In this study, we identified a tomato (Solanum lycopersicum) DDB1-interacting (DDI1) protein as a DCAF protein involved in response to abiotic stresses, including UV radiation, high salinity and osmotic stress. Co-immunoprecipitation and bimolecular fluorescence complementation assay indicated that DDI1 associates with CUL4–DDB1 in the nucleus. Quantitative RT-PCR analysis indicated the DDI1 gene is induced by salt, mannitol and UV-C treatment. Moreover, transgenic tomato plants with overexpression or knockdown of the DDI1 gene exhibited enhanced or attenuated tolerance to salt/mannitol/UV-C, respectively. Thus, our data suggest that DDI1 functions as a substrate receptor of the CUL4–DDB1 ubiquitin ligase, positively regulating abiotic stress response in tomato.
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The tomato DWD motif-containing protein DDI1 interacts with the CUL4–DDB1-based ubiquitin ligase and plays a pivotal role in abiotic stress responses
Biochemical and biophysical research communications, 2014Co-Authors: Min Miao, Yunye Zhu, Maiju Qiao, Xiaofeng Tang, Wei Zhao, Fangming Xiao, Yongsheng LiuAbstract:CULLIN4(CUL4)–DAMAGED DNA BINDING PROTEIN1 (DDB1)-based ubiquitin ligase plays significant roles in multiple physiological processes via ubiquitination-mediated degradation of relevant target proteins. The DDB1–CUL4-associated factor (DCAF) acts as substrate receptor in the CUL4–DDB1 ubiquitin ligase complex and determines substrate specificity. In this study, we identified a tomato (Solanum lycopersicum) DDB1-interacting (DDI1) protein as a DCAF protein involved in response to abiotic stresses, including UV radiation, high salinity and osmotic stress. Co-immunoprecipitation and bimolecular fluorescence complementation assay indicated that DDI1 associates with CUL4–DDB1 in the nucleus. Quantitative RT-PCR analysis indicated the DDI1 gene is induced by salt, mannitol and UV-C treatment. Moreover, transgenic tomato plants with overexpression or knockdown of the DDI1 gene exhibited enhanced or attenuated tolerance to salt/mannitol/UV-C, respectively. Thus, our data suggest that DDI1 functions as a substrate receptor of the CUL4–DDB1 ubiquitin ligase, positively regulating abiotic stress response in tomato.
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Roles of UV-damaged DNA binding protein 1 (DDB1) in epigenetically modifying multiple traits of agronomic importance in tomato
Plant signaling & behavior, 2012Co-Authors: Xiaofeng Tang, Min Miao, Fangming Xiao, Jikai Liu, Shengxiong Huang, Wei Shi, Dan Feng Tang, Xiangli Niu, Yongsheng LiuAbstract:Epigenetic regulation participates broadly in many fundamentally cellular and physiological processes. In this study, we found that DDB1, a protein originally identified as a factor involved in DNA repairing, plays important roles in regulating organ size, growth habit and photosynthesis in tomato via an epigenetic manner. We generated transgenic tomato plants overexpressing an alternatively spliced DDB1 transcript (DDB1F, prevalently present in tomato tissues) and found the primary transformants displayed small-fruited “cherry tomato” in companion with strikingly enhanced shoot branching and biomass, dark-green leaves with elevated chlorophyll accumulation, and increased soluble solids in fruits. Significantly, these phenotypic alterations did not segregate with the DDB1F transgene in subsequent generations, suggesting that the effect of DDB1F on multiple agronomic traits is implemented via an epigenetic manner and is inheritable over generations. We speculate that DDB1, as a core subunit in the recently identified CUL4-based E3 ligase complex, mediates the 26S proteasome-dependent degradation of a large number of proteins, some of which might be required for perpetuating epigenetic marks on chromatins.
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altered plastid levels and potential for improved fruit nutrient content by downregulation of the tomato DDB1 interacting protein cul4
Plant Journal, 2008Co-Authors: Songhu Wang, Yongsheng Liu, Jikai Liu, Xiangli Niu, Yuanyuan Feng, James J. GiovannoniAbstract:Fruits are a major source of nutrition in human diets, providing carbohydrates, fiber, vitamins and phytonutrients. Carotenoids are a principal class of compounds found in many fruits, providing nutritional benefits both as precursors to essential vitamins and as antioxidants. Molecular characterization revealed that the tomato high pigment mutant genes (hp1 and hp2) encode UV-DAMAGED DNA BINDING PROTEIN-1 (DDB1) and DE-ETIOLATED-1 (DET1) homologs, respectively, and both are essential components of the recently identified CUL4-based E3 ligase complex. Here we have isolated a tomato CUL4 homolog and performed yeast two-hybrid assays to suggest possible association of tomato DDB1 with CUL4 and DET1. Real-time RT-PCR analysis indicated that both HP1 and CUL4 are expressed constitutively. Abscisic acid is implicated in plastid division control and its application substantially enhances HP1/DDB1 mRNA accumulation. Transformation of constructs expressing CUL4-YFP and DDB1-YFP fusion proteins driven by the CaMV 35S promoter reveals that both CUL4 and DDB1 are targeted to tomato plastids and nuclei simultaneously. Using fruit-specific promoters combined with RNAi technology, we show that downregulated DDB1 expression in transgenic fruits results in a significant increase in the number of plastids and corresponding enhanced pigment accumulation. CUL4-RNAi repression lines provide insight regarding CUL4 function during tomato development, and reveal that this tomato cullin is important in the regulation of plastid number and pigmentation, which in turn have a direct impact on fruit nutrient quality.
Min Miao - One of the best experts on this subject based on the ideXlab platform.
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the tomato dwd motif containing protein ddi1 interacts with the cul4 DDB1 based ubiquitin ligase and plays a pivotal role in abiotic stress responses
Biochemical and Biophysical Research Communications, 2014Co-Authors: Min Miao, Yunye Zhu, Maiju Qiao, Xiaofeng Tang, Wei Zhao, Fangming Xiao, Yongsheng LiuAbstract:CULLIN4(CUL4)–DAMAGED DNA BINDING PROTEIN1 (DDB1)-based ubiquitin ligase plays significant roles in multiple physiological processes via ubiquitination-mediated degradation of relevant target proteins. The DDB1–CUL4-associated factor (DCAF) acts as substrate receptor in the CUL4–DDB1 ubiquitin ligase complex and determines substrate specificity. In this study, we identified a tomato (Solanum lycopersicum) DDB1-interacting (DDI1) protein as a DCAF protein involved in response to abiotic stresses, including UV radiation, high salinity and osmotic stress. Co-immunoprecipitation and bimolecular fluorescence complementation assay indicated that DDI1 associates with CUL4–DDB1 in the nucleus. Quantitative RT-PCR analysis indicated the DDI1 gene is induced by salt, mannitol and UV-C treatment. Moreover, transgenic tomato plants with overexpression or knockdown of the DDI1 gene exhibited enhanced or attenuated tolerance to salt/mannitol/UV-C, respectively. Thus, our data suggest that DDI1 functions as a substrate receptor of the CUL4–DDB1 ubiquitin ligase, positively regulating abiotic stress response in tomato.
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The tomato DWD motif-containing protein DDI1 interacts with the CUL4–DDB1-based ubiquitin ligase and plays a pivotal role in abiotic stress responses
Biochemical and biophysical research communications, 2014Co-Authors: Min Miao, Yunye Zhu, Maiju Qiao, Xiaofeng Tang, Wei Zhao, Fangming Xiao, Yongsheng LiuAbstract:CULLIN4(CUL4)–DAMAGED DNA BINDING PROTEIN1 (DDB1)-based ubiquitin ligase plays significant roles in multiple physiological processes via ubiquitination-mediated degradation of relevant target proteins. The DDB1–CUL4-associated factor (DCAF) acts as substrate receptor in the CUL4–DDB1 ubiquitin ligase complex and determines substrate specificity. In this study, we identified a tomato (Solanum lycopersicum) DDB1-interacting (DDI1) protein as a DCAF protein involved in response to abiotic stresses, including UV radiation, high salinity and osmotic stress. Co-immunoprecipitation and bimolecular fluorescence complementation assay indicated that DDI1 associates with CUL4–DDB1 in the nucleus. Quantitative RT-PCR analysis indicated the DDI1 gene is induced by salt, mannitol and UV-C treatment. Moreover, transgenic tomato plants with overexpression or knockdown of the DDI1 gene exhibited enhanced or attenuated tolerance to salt/mannitol/UV-C, respectively. Thus, our data suggest that DDI1 functions as a substrate receptor of the CUL4–DDB1 ubiquitin ligase, positively regulating abiotic stress response in tomato.
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Roles of UV-damaged DNA binding protein 1 (DDB1) in epigenetically modifying multiple traits of agronomic importance in tomato
Plant signaling & behavior, 2012Co-Authors: Xiaofeng Tang, Min Miao, Fangming Xiao, Jikai Liu, Shengxiong Huang, Wei Shi, Dan Feng Tang, Xiangli Niu, Yongsheng LiuAbstract:Epigenetic regulation participates broadly in many fundamentally cellular and physiological processes. In this study, we found that DDB1, a protein originally identified as a factor involved in DNA repairing, plays important roles in regulating organ size, growth habit and photosynthesis in tomato via an epigenetic manner. We generated transgenic tomato plants overexpressing an alternatively spliced DDB1 transcript (DDB1F, prevalently present in tomato tissues) and found the primary transformants displayed small-fruited “cherry tomato” in companion with strikingly enhanced shoot branching and biomass, dark-green leaves with elevated chlorophyll accumulation, and increased soluble solids in fruits. Significantly, these phenotypic alterations did not segregate with the DDB1F transgene in subsequent generations, suggesting that the effect of DDB1F on multiple agronomic traits is implemented via an epigenetic manner and is inheritable over generations. We speculate that DDB1, as a core subunit in the recently identified CUL4-based E3 ligase complex, mediates the 26S proteasome-dependent degradation of a large number of proteins, some of which might be required for perpetuating epigenetic marks on chromatins.
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a role of tomato uv damaged dna binding protein 1 DDB1 in organ size control via an epigenetic manner
PLOS ONE, 2012Co-Authors: Min Miao, Xiaofeng Tang, Jikai Liu, Shengxiong Huang, Lanyang Gao, Yongfeng Gao, Xiaochun SunAbstract:Epigenetic modification generally refers to phenotypic changes by a mechanism other than changes in DNA sequence and plays a significant role in developmental processes. In this study, we found that overexpression of one alternatively spliced tomato DDB1 transcript, DDB1F that is prevalently present in all tested tissues, resulted in reduction of organ size. Transgenic plants constitutively expressing the DDB1F from a strong cauliflower mosaic virus (CaMV) 35S promoter displayed moderately reduced size in vegetative organs (leaves and stems) and radically decreased size in reproductive organs (flowers, seeds and fruits), in which several genes encoding negative regulators for cell division were upregulated. Significantly, reduction of organ size conferred by overexpression of DDB1F transgene appears not to segregate in the subsequent generations, suggesting the phenotypic alternations are manipulated in an epigenetic manner and can be transmitted over generations. This notion was further substantiated by analysis of DNA methylation level at the SlWEE1 gene (encoding a negative regulator of cell division), revealing a correlation between less methylation in the promoter region and elevated expression level of this gene. Thus, our results suggest DDB1 plays an important role in regulation of the epigenetic state of genes involved in organogenesis, despite the underlying mechanism remains to be elucidated.
Michel Strubin - One of the best experts on this subject based on the ideXlab platform.
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A promiscuous alpha-helical motif anchors viral hijackers and substrate receptors to the CUL4-DDB1 ubiquitin ligase machinery.
Nature structural & molecular biology, 2009Co-Authors: Eva Isabelle Robert, Michel Strubin, Pieter C Van Breugel, Ning ZhengAbstract:The cullin 4-DNA-damage-binding protein 1 (CUL4-DDB1) ubiquitin ligase machinery regulates diverse cellular functions and can be subverted by pathogenic viruses. Here we report the crystal structure of DDB1 in complex with a central fragment of hepatitis B virus X protein (HBx), whose DDB1-binding activity is important for viral infection. The structure reveals that HBx binds DDB1 through an alpha-helical motif, which is also found in the unrelated paramyxovirus SV5-V protein despite their sequence divergence. Our structure-based functional analysis suggests that, like SV5-V, HBx captures DDB1 to redirect the ubiquitin ligase activity of the CUL4-DDB1 E3 ligase. We also identify the alpha-helical motif shared by these viral proteins in the cellular substrate-recruiting subunits of the E3 complex, the DDB1-CUL4-associated factors (DCAFs) that are functionally mimicked by the viral hijackers. Together, our studies reveal a common yet promiscuous structural element that is important for the assembly of cellular and virally hijacked CUL4-DDB1 E3 complexes.
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Hepatitis B virus X protein stimulates viral genome replication via a DDB1-dependent pathway distinct from that leading to cell death.
Journal of virology, 2005Co-Authors: Olivier Leupin, Séverine Bontron, Céline Schaeffer, Michel StrubinAbstract:The hepatitis B virus (HBV) X protein (HBx) is essential for virus infection and has been implicated in the development of liver cancer associated with chronic infection. HBx can interact with a number of cellular proteins, and in cell culture, it exhibits pleiotropic activities, among which is its ability to interfere with cell viability and stimulate HBV replication. Previous work has demonstrated that HBx affects cell viability by a mechanism that requires its binding to DDB1, a highly conserved protein implicated in DNA repair and cell cycle regulation. We now show that an interaction with DDB1 is also needed for HBx to stimulate HBV genome replication. Thus, HBx point mutants defective for DDB1 binding fail to complement the low level of replication of an HBx-deficient HBV genome when provided in trans, and one such mutant regains activity when directly fused to DDB1. Furthermore, DDB1 depletion by RNA interference specifically compromises replication of wild-type HBV, indicating that HBx produced from the viral genome also functions in a DDB1-dependent fashion. We also show that HBx in association with DDB1 acts in the nucleus and stimulates HBV replication mainly by enhancing viral mRNA levels, regardless of whether the protein is expressed from the HBV genome itself or supplied in trans. Interestingly, whereas HBx induces cell death in both HepG2 and Huh-7 hepatoma cell lines, it enhances HBV replication only in HepG2 cells, suggesting that the two activities involve distinct DDB1-dependent pathways.
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Hepatitis B virus X protein and simian virus 5 V protein exhibit similar UV-DDB1 binding properties to mediate distinct activities.
Journal of virology, 2003Co-Authors: Olivier Leupin, Séverine Bontron, Michel StrubinAbstract:The UV-damaged DNA-binding activity protein (UV-DDB) consists of two subunits, DDB1 and DDB2, and functions in DNA repair and cell cycle regulation. The DDB1 subunit is a target for the hepatitis B virus X protein (HBx). Binding of HBx to DDB1 interferes with cell growth and viability in culture and has been implicated in the establishment of viral infection. DDB1 also interacts with the V proteins encoded by several paramyxoviruses including simian virus 5 (SV5), which prevent interferon signaling by targeting either STAT1 or STAT2 proteins for proteolysis. The role of V binding to DDB1, however, remains unclear. Here we show that the V protein of SV5 (SV5-V) and HBx exhibit strikingly similar DDB1 binding properties. Thus, SV5-V and HBx bind to DDB1 in a mutually exclusive manner, and SV5-V shares with HBx the ability to enhance the steady-state levels of DDB1 and to inhibit its association with DDB2. Yet only HBx induces cell death, and SV5-V can prevent HBx from doing so by blocking its interaction with DDB1. Binding of SV5-V to DDB1 may serve another function, since SV5-V shows a decreased ability to induce STAT1 degradation in cells expressing reduced amounts of DDB1. These findings demonstrate that HBx performs a unique function through its association with DDB1 for which SV5-V cannot substitute and suggest that SV5-V and HBx have evolved to bind DDB1 to achieve distinct functions, both by a mechanism that does not involve DDB2.
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Hepatitis B Virus X Protein Associated with UV-DDB1 Induces Cell Death in the Nucleus and Is Functionally Antagonized by UV-DDB2
The Journal of biological chemistry, 2002Co-Authors: Séverine Bontron, Nathalie Lin-marq, Michel StrubinAbstract:The hepatitis B virus X protein (HBx) is essential for viral infection and strongly interferes with cell growth and viability in culture. These activities involve interaction of HBx with the DDB1 subunit of UV-damaged DNA-binding factor UV-DDB. UV-DDB consists of DDB1 and a DDB2 subunit that mediates nuclear import and has recognized functions in DNA repair and E2F1-mediated transcription. Here we show that HBx retains DDB1-binding-dependent cytotoxic activities when engineered to accumulate in the nucleus but not when excluded from the nucleus. Nuclear localization of HBx does not require binding to DDB1 and remains unaffected by ectopically expressed UV-DDB subunits, indicating that HBx reaches the nuclear compartment independently of UV-DDB. Unexpectedly, HBx appears to largely exist in association with DDB1 and is in direct competition with DDB2 for binding to DDB1. Hence, HBx-mediated cell death can be relieved by increased levels of DDB2, an effect that is not observed with a naturally occurring mutant of DDB2 that lacks DDB1-binding activity. These findings indicate that HBx acts through a pathway that involves a DDB2-independent nuclear function of DDB1 and that this activity will depend on the relative concentration of DDB1 and DDB2 in cells.