101
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Kodadek T. No Splicing, no dicing: non-proteolytic roles of the ubiquitin-proteasome system in transcription. J Biol Chem 2009; 285:2221-6. [PMID: 19955182 DOI: 10.1074/jbc.r109.077883] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The ubiquitin-proteasome pathway (UPP) is responsible for most programmed turnover of proteins in eukaryotic cells, and this activity has been known for some time to be involved in transcriptional regulation. More recently, intersections of the UPP and transcription have been discovered that are not proteolytic in nature and appear to revolve around the chaperonin-like activities of the ATPases in the 19 S regulatory subunit of the proteasome. Moreover, monoubiquitylation, which does not signal degradation, has been found to be a key modification of many transcription factors and histones. These various non-proteolytic roles of the UPP in transcription are reviewed here, and plausible mechanistic models are discussed.
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Affiliation(s)
- Thomas Kodadek
- Department of Chemistry, The Scripps Research Institute, Scripps Florida, Jupiter, Florida 33458, USA.
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102
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Yamada T, Mehta RR, Lekmine F, Christov K, King ML, Majumdar D, Shilkaitis A, Green A, Bratescu L, Beattie CW, Das Gupta TK. A peptide fragment of azurin induces a p53-mediated cell cycle arrest in human breast cancer cells. Mol Cancer Ther 2009; 8:2947-58. [PMID: 19808975 DOI: 10.1158/1535-7163.mct-09-0444] [Citation(s) in RCA: 78] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
We report that amino acids 50 to 77 of azurin (p28) preferentially enter the human breast cancer cell lines MCF-7, ZR-75-1, and T47D through a caveolin-mediated pathway. Although p28 enters p53 wild-type MCF-7 and the isogenic p53 dominant-negative MDD2 breast cancer cell lines, p28 only induces a G(2)-M-phase cell cycle arrest and apoptosis in MCF-7 cells. p28 exerts its antiproliferative activity by reducing proteasomal degradation of p53 through formation of a p28:p53 complex within a hydrophobic DNA-binding domain (amino acids 80-276), increasing p53 levels and DNA-binding activity. Subsequent elevation of the cyclin-dependent kinase inhibitors p21 and p27 reduces cyclin-dependent kinase 2 and cyclin A levels in a time-dependent manner in MCF-7 cells but not in MDD2 cells. These results suggest that p28 and similar peptides that significantly reduce proteasomal degradation of p53 by a MDM2-independent pathway(s) may provide a unique series of cytostatic and cytotoxic (apoptotic) chemotherapeutic agents.
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Affiliation(s)
- Tohru Yamada
- Department of Surgical Oncology, University of Illinois College of Medicine, Chicago, Illinois, USA
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103
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Yang X, Li H, Zhou Z, Wang WH, Deng A, Andrisani O, Liu X. Plk1-mediated phosphorylation of Topors regulates p53 stability. J Biol Chem 2009; 284:18588-92. [PMID: 19473992 PMCID: PMC2707202 DOI: 10.1074/jbc.c109.001560] [Citation(s) in RCA: 76] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2009] [Revised: 05/20/2009] [Indexed: 11/06/2022] Open
Abstract
Polo-like kinase 1 (Plk1) overexpression is associated with tumorigenesis by an unknown mechanism. Likewise, Plk1 was suggested to act as a negative regulator of tumor suppressor p53, but the mechanism remains to be determined. Herein, we have identified topoisomerase I-binding protein (Topors), a p53-binding protein, as a Plk1 target. We show that Plk1 phosphorylates Topors on Ser(718) in vivo. Significantly, expression of a Plk1-unphosphorylatable Topors mutant (S718A) leads to a dramatic accumulation of p53 through inhibition of p53 degradation. Topors is an ubiquitin and small ubiquitin-like modifier ubiquitin-protein isopeptide ligase (SUMO E3) ligase. Plk1-mediated phosphorylation of Topors inhibits Topors-mediated sumoylation of p53, whereas p53 ubiquitination is enhanced, leading to p53 degradation. These results demonstrate that Plk1 modulates Topors activity in suppressing p53 function and identify a likely mechanism for the tumorigenic potential of Plk1.
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Affiliation(s)
- Xiaoming Yang
- From the College of Chemistry, Sichuan University, Chengdu 610064, China and
- the Departments of Biochemistry and
| | | | | | - Wen-Horng Wang
- Basic Medical Sciences, Purdue University, West Lafayette, Indiana 47907
| | - Anping Deng
- From the College of Chemistry, Sichuan University, Chengdu 610064, China and
| | - Ourania Andrisani
- Basic Medical Sciences, Purdue University, West Lafayette, Indiana 47907
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104
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Schob C, Orth U, Gal A, Kindler S, Chakarova CF, Bhattacharya SS, Rüther K. Mutations inTOPORS: A Rare Cause of Autosomal Dominant Retinitis Pigmentosa in Continental Europe? Ophthalmic Genet 2009; 30:96-8. [DOI: 10.1080/13816810802695543] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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105
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106
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Corcoran CA, Montalbano J, Sun H, He Q, Huang Y, Sheikh MS. Identification and characterization of two novel isoforms of Pirh2 ubiquitin ligase that negatively regulate p53 independent of RING finger domains. J Biol Chem 2009; 284:21955-21970. [PMID: 19483087 DOI: 10.1074/jbc.m109.024232] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Pirh2 is a newly identified E3 ubiquitin ligase known to inhibit tumor suppressor p53 function via ubiquitination and proteasomal degradation. We have identified two novel Pirh2 splice variants that encode different Pirh2 isoforms and named these Pirh2B and Pirh2C. Accordingly, the full-length protein is now classified as isoform Pirh2A. The central region of Pirh2 harbors a RING finger domain that is critical for its ubiquitin ligase function. The Pirh2B isoform lacks amino acids 171-179, whereas Pirh2C is missing C-terminal amino acids 180-261, which for each isoform results in a RING domain deletion and the abrogation of ubiquitin ligase activity. Our findings further indicate that the Pirh2B isoform but not the Pirh2C isoform is capable of binding to Pirh2A, suggesting that the C-terminal region absent in Pirh2C is critical for Pirh2-Pirh2 interactions. Similar to Pirh2A, both Pirh2B and Pirh2C interact with p53; however, interactions between p53 and Pirh2B appear stronger than those between p53 and Pirh2C. Interestingly, although both Pirh2B and Pirh2C are not able to promote in vitro p53 ubiquitination, both are capable of negatively regulating p53 protein stability and promoting the intracellular ubiquitination of p53. Furthermore, like Pirh2A, both isoforms are able to inhibit p53 transcriptional activity. We have also for the first time demonstrated that Pirh2A as well as the novel isoforms also interact directly with MDM2 within a region encompassing MDM2 acidic and zinc finger domains. It is therefore possible that Pirh2A and the novel Pirh2 isoforms identified in this study may also modulate p53 function by engaging MDM2.
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Affiliation(s)
- Chad A Corcoran
- Department of Pharmacology, State University of New York, Upstate Medical University, Syracuse, New York 13210
| | - JoAnne Montalbano
- Department of Pharmacology, State University of New York, Upstate Medical University, Syracuse, New York 13210
| | - Hong Sun
- Department of Pharmacology, State University of New York, Upstate Medical University, Syracuse, New York 13210
| | - Qin He
- Department of Pharmacology, State University of New York, Upstate Medical University, Syracuse, New York 13210
| | - Ying Huang
- Department of Pharmacology, State University of New York, Upstate Medical University, Syracuse, New York 13210
| | - M Saeed Sheikh
- Department of Pharmacology, State University of New York, Upstate Medical University, Syracuse, New York 13210
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107
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Expression of Epstein–Barr virus BZLF1 immediate-early protein induces p53 degradation independent of MDM2, leading to repression of p53-mediated transcription. Virology 2009; 388:204-11. [DOI: 10.1016/j.virol.2009.03.017] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2009] [Revised: 02/25/2009] [Accepted: 03/20/2009] [Indexed: 11/21/2022]
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108
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Zunino R, Braschi E, Xu L, McBride HM. Translocation of SenP5 from the nucleoli to the mitochondria modulates DRP1-dependent fission during mitosis. J Biol Chem 2009; 284:17783-95. [PMID: 19411255 DOI: 10.1074/jbc.m901902200] [Citation(s) in RCA: 123] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
The mechanisms that ensure an equal inheritance of cellular organelles during mitosis are an important area of study in cell biology. For the mitochondria fragment during mitosis, however, the cellular links that signal these changes are largely unknown. We recently identified a SUMO protease, SenP5, that deSUMOylates a number of mitochondrial targets, including the dynamin-related fission GTPase, DRP1. In interphase, SenP5 resides primarily within the nucleoli, in addition to a cytosolic pool. Here we report the relocalization of SenP5 from the nucleoli to the mitochondrial surface at G2/M transition prior to nuclear envelope breakdown. The recruitment of SenP5 results in a significant loss in mitochondrial SUMOylation, and a concomitant increase in the labile pool of DRP1 that drives mitochondrial fragmentation. Importantly, silencing of SenP5 leads to an arrest in the cell cycle precisely at the time when the protease is translocated to the mitochondria. These data indicate that transition of SenP5 to the mitochondria plays an important role in mitochondrial fragmentation during mitosis. The altered intracellular localization of SenP5 represents the first example of the mitochondrial recruitment of a SUMO protease and provides new insights into the mechanisms of interorganellar communication during the cell cycle.
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Affiliation(s)
- Rodolfo Zunino
- University of Ottawa Heart Institute, Ottawa, Ontario K1Y 4W7, Canada
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109
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Takeuchi T, Iwahara S, Saeki Y, Sasajima H, Yokosawa H. Link between the ubiquitin conjugation system and the ISG15 conjugation system: ISG15 conjugation to the UbcH6 ubiquitin E2 enzyme. J Biochem 2009; 138:711-9. [PMID: 16428300 DOI: 10.1093/jb/mvi172] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
ISG15 is a ubiquitin-like protein that is upregulated on treatment with interferon. ISG15 is considered to be covalently conjugated to cellular proteins through a sequential reaction similar to that of the ubiquitin conjugation system consisting of E1/E2/E3 enzymes: UBE1L and UbcH8 have been reported to function as E1 and E2 enzymes, respectively, for ISG15 conjugation. Several cellular proteins have been identified as targets for ISG15 conjugation, but the roles of ISG15 conjugation remain unclear. In this study, we found that UbcH6 and UbcH8, E2 enzymes for ubiquitin conjugation, are covalently modified by ISG15. We also found that UbcH6 is capable of forming a thioester intermediate with ISG15 through Cys131. We determined that the Lys136 residue near the catalytic site Cys131 is the ISG15 conjugation site in UbcH6. We isolated ISG15-modified and unmodified UbcH6 proteins, and analyzed their abilities to form thioester intermediates with ubiquitin. A ubiquitin thioester intermediate was detected in the case of unmodified UbcH6, but not in that of ISG15-modified UbcH6, strongly suggesting that ISG15 conjugation to UbcH6 suppresses its ubiquitin E2 enzyme activity. Thus, we provide evidence for a link between the ubiquitin conjugation system and the ISG15 conjugation system.
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Affiliation(s)
- Tomoharu Takeuchi
- Department of Biochemistry, Graduate School of Pharmaceutical Sciences, Hokkaido University, Sapporo 060-0812
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110
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Grabbe C, Dikic I. Functional Roles of Ubiquitin-Like Domain (ULD) and Ubiquitin-Binding Domain (UBD) Containing Proteins. Chem Rev 2009; 109:1481-94. [DOI: 10.1021/cr800413p] [Citation(s) in RCA: 91] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Affiliation(s)
- Caroline Grabbe
- Institute of Biochemistry II and Cluster of Excellence Macromolecular Complexes, Goethe University Frankfurt am Main, Theodor-Stern-Kai 7, D-60590 Frankfurt (Main), Germany, Mediterranean Institute for Life Sciences, 21000 Split, Croatia, and Department of Immunology, School of Medicine, University of Split, Soltanska 2, 21 000 Split, Croatia
| | - Ivan Dikic
- Institute of Biochemistry II and Cluster of Excellence Macromolecular Complexes, Goethe University Frankfurt am Main, Theodor-Stern-Kai 7, D-60590 Frankfurt (Main), Germany, Mediterranean Institute for Life Sciences, 21000 Split, Croatia, and Department of Immunology, School of Medicine, University of Split, Soltanska 2, 21 000 Split, Croatia
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111
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Abstract
Post-translational modification of the cell's proteome by ubiquitin and ubiquitin-like proteins provides dynamic functional regulation. Ubiquitin and SUMO are well-studied post-translational modifiers that typically impart distinct effects on their targets. The recent discovery that modification by SUMO can target proteins for ubiquitination and proteasomal degradation sets a new paradigm in the field, and offers insights into the roles of SUMO and ubiquitin in genome stability.
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112
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Park HJ, Zheng H, Kulkarni D, Kerrigan J, Pungaliya P, Saleem A, Rubin EH. Identification of phosphorylation sites of TOPORS and a role for serine 98 in the regulation of ubiquitin but not SUMO E3 ligase activity. Biochemistry 2009; 47:13887-96. [PMID: 19053840 DOI: 10.1021/bi801904q] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
TOPORS is the first example of a protein that possesses both ubiquitin and SUMO E3 ligase activity. The ubiquitination activity maps to a conserved RING domain in the N-terminal region of the protein, which is not required for sumoylation activity. Similar to other E3 ligases, it is likely that the ubiquitin and sumoylation activities of TOPORS are regulated by post-translational modifications. Therefore, we employed mass spectrometry to identify post-translational modifications of TOPORS. Several putative phosphorylated regions were identified in conserved regions of the protein. We investigated the role of phosphorylation of serine 98, which is adjacent to the RING domain, in both cells and in vitro. Mutation of serine 98 to aspartic acid resulted in an increase in the ubiquitin ligase activity of TOPORS both in cells and in vitro. In addition, this mutation increased the binding of TOPORS to the E2 enzyme UbcH5a both in vitro and in cells. Conversely, a phospho-deficient mutant (S98A) exhibited little change in ubiquitin ligase activity compared to wild-type TOPORS, both in cells and in vitro. Neither of the mutants affected the localization of TOPORS to punctate nuclear regions. In addition, neither mutant affected the SUMO ligase activity of TOPORS in cells or in vitro. Molecular modeling studies support a role for serine 98 in regulating TOPORS-E2 interactions. Our findings indicate that phosphorylation of serine 98 regulates the ubiquitin but not the SUMO ligase activity of TOPORS, consistent with a potential binary switch function for TOPORS in protein ubiquitination versus sumoylation.
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Affiliation(s)
- Hye-Jin Park
- Departments of Pharmacology and Medicine, The Cancer Institute of New Jersey, Robert Wood Johnson Medical School, University of Medicine and Dentistry of New Jersey, 195 Little Albany Street, New Brunswick, New Jersey 08901, USA
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113
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Kim KI, Baek SH. Small ubiquitin-like modifiers in cellular malignancy and metastasis. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2009; 273:265-311. [PMID: 19215907 DOI: 10.1016/s1937-6448(08)01807-8] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Small ubiquitin-like modifiers (SUMOs) mediate a variety of cellular functions of protein targets mainly in the nucleus but in other cellular compartments as well, and thereby participate in maintaining cellular homeostasis. SUMO system plays important roles in transcriptional regulation, DNA damage responses, maintaining genome integrity, and signaling pathways. Thus, in some cases, loss of regulated control on SUMOylation/deSUMOylation processes causes a defect in maintaining homeostasis and hence gives a cue to cancer development and progression. Furthermore, recent studies have revealed that SUMO system is involved in cancer metastasis. In this review, we will summarize the possible role of SUMO system in cancer development, progression, and metastasis and discuss future directions.
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Affiliation(s)
- Keun Il Kim
- Department of Biological Sciences, Research Center for Women's Disease, Sookmyung Women's University, Seoul, Korea
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114
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Molecular basis of Pirh2-mediated p53 ubiquitylation. Nat Struct Mol Biol 2008; 15:1334-42. [PMID: 19043414 DOI: 10.1038/nsmb.1521] [Citation(s) in RCA: 74] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2008] [Accepted: 10/30/2008] [Indexed: 11/08/2022]
Abstract
Pirh2 (p53-induced RING-H2 domain protein; also known as Rchy1) is an E3 ubiquitin ligase involved in a negative-feedback loop with p53. Using NMR spectroscopy, we show that Pirh2 is a unique cysteine-rich protein comprising three modular domains. The protein binds nine zinc ions using a variety of zinc coordination schemes, including a RING domain and a left-handed beta-spiral in which three zinc ions align three consecutive small beta-sheets in an interleaved fashion. We show that Pirh2-p53 interaction is dependent on the C-terminal zinc binding module of Pirh2, which binds to the tetramerization domain of p53. As a result, Pirh2 preferentially ubiquitylates the tetrameric form of p53 in vitro and in vivo, suggesting that Pirh2 regulates protein turnover of the transcriptionally active form of p53.
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115
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Markowski MC, Bowen C, Gelmann EP. Inflammatory cytokines induce phosphorylation and ubiquitination of prostate suppressor protein NKX3.1. Cancer Res 2008; 68:6896-901. [PMID: 18757402 DOI: 10.1158/0008-5472.can-08-0578] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Inflammation of the prostate is a risk factor for the development of prostate cancer. In the aging prostate, regions of inflammatory atrophy are foci for prostate epithelial cell transformation. Expression of the suppressor protein NKX3.1 is reduced in regions of inflammatory atrophy and in preinvasive prostate cancer. Inflammatory cytokines tumor necrosis factor (TNF)-alpha and interleukin-1beta accelerate NKX3.1 protein loss by inducing rapid ubiquitination and proteasomal degradation. The effect of TNF-alpha is mediated via the COOH-terminal domain of NKX3.1 where phosphorylation of serine 196 is critical for cytokine-induced degradation. Mutation of serine 196 to alanine abrogates phosphorylation at that site and the effect of TNF-alpha on NKX3.1 ubiquitination and protein loss. This is in contrast to control of steady-state NKX3.1 turnover, which is mediated by serine 185. Mutation of serine 185 to alanine increases NKX3.1 protein stability by inhibiting ubiquitination and doubling the protein half-life. A third COOH-terminal serine at position 195 has a modulating effect on both steady-state protein turnover and on ubiquitination induced by TNF-alpha. Thus, cellular levels of the NKX3.1 tumor suppressor are affected by inflammatory cytokines that target COOH-terminal serine residues to activate ubiquitination and protein degradation. Our data suggest that strategies to inhibit inflammation or to inhibit effector kinases may be useful approaches to prostate cancer prevention.
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Affiliation(s)
- Mark C Markowski
- Department of Medicine, Herbert Irving Comprehensive Cancer Center, Columbia University, New York, New York 10032, USA
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116
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Prives C, White E. Does control of mutant p53 by Mdm2 complicate cancer therapy? Genes Dev 2008; 22:1259-64. [PMID: 18483214 DOI: 10.1101/gad.1680508] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Missense mutant forms of p53 are expressed at high levels in some human cancers and may contribute to oncogenesis. In this issue of Genes & Development, Terzian and colleagues (pp. 1337-1344) describe a mutant p53 knock-in mouse in which normal tissues and some tumors have low levels of mutant p53 protein unless Mdm2 or p16(INK4A) are absent. Once stabilized, mutant p53 promotes metastasis. Therefore, therapies that release p53 from Mdm2 might have unwanted consequences when cells have sustained a mutation in p53.
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Affiliation(s)
- Carol Prives
- Department of Biological Sciences, Columbia University, New York, New York 10027, USA
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117
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Liu B, Shuai K. Regulation of the sumoylation system in gene expression. Curr Opin Cell Biol 2008; 20:288-93. [PMID: 18468876 DOI: 10.1016/j.ceb.2008.03.014] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2008] [Accepted: 03/20/2008] [Indexed: 11/17/2022]
Abstract
Protein sumoylation has emerged as an important regulatory mechanism for the transcriptional machinery. Sumoylation is a highly dynamic process that is regulated in response to cellular stimuli or pathogenic challenges. Altered activity of the small ubiquitin-like modifier (SUMO) conjugation system is associated with human cancers and inflammation. Thus, understanding the regulation of protein sumoylation is important for the design of SUMO-based therapeutic strategies for the treatment of human diseases. Recent studies indicate that the sumoylation system can be regulated through multiple mechanisms, including the regulation of the expression of various components of the sumoylation pathway, and the modulation of the activity of SUMO enzymes. In addition, extracellular stimuli can signal the nucleus to trigger the rapid promoter recruitment of SUMO E3 ligases, resulting in the immediate repression of transcription. Finally, the sumoylation system can also be regulated through crosstalk with other post-translational modifications, including phosphorylation, ubiquitination, and acetylation.
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Affiliation(s)
- Bin Liu
- Division of Hematology-Oncology, Department of Medicine, University of California Los Angeles, Los Angeles, CA 90095, United States
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118
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A SIM-ultaneous role for SUMO and ubiquitin. Trends Biochem Sci 2008; 33:201-8. [PMID: 18403209 DOI: 10.1016/j.tibs.2008.02.001] [Citation(s) in RCA: 179] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2007] [Revised: 02/08/2008] [Accepted: 02/12/2008] [Indexed: 11/22/2022]
Abstract
Ubiquitin and ubiquitin-like proteins (Ubls) share a beta-GRASP fold and have key roles in cellular growth and suppression of genome instability. Despite their common fold, SUMO and ubiquitin are classically portrayed as distinct, and they can have antagonistic roles. Recently, a new family of proteins, the small ubiquitin-related modifier (SUMO)-targeted ubiquitin ligases (STUbLs), which directly connect sumoylation and ubiquitylation, has been discovered. Uniquely, STUbLs use SUMO-interaction motifs (SIMs) to recognize their sumoylated targets. STUbLs are global regulators of protein sumoylation levels, and cells lacking STUbLs display genomic instability and hypersensitivity to genotoxic stress. The human STUbL, RNF4, is implicated in several diseases including cancer, highlighting the importance of characterizing the cellular functions of STUbLs.
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119
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Abstract
The small ubiquitin-like modifier proteins (Smt3 in yeast and SUMOs 1-4 in vertebrates) are members of the ubiquitin super family. Like ubiquitin, the SUMOs are protein modifiers that are covalently attached to the epsilon-amino group of lysine residues in the substrates. The application of proteomics to the SUMO field has greatly expanded both the number of known targets and the number of identified target lysines. As new refinements of proteomic techniques are developed and applied to sumoylation, an explosion of novel data is likely in the next 5 years. This ability to examine sumoylated proteins globally, rather than individually, will lead to new insights into both the functions of the individual SUMO types, and how dynamic changes in overall sumoylation occur in response to alterations in cellular environment. In addition, there is a growing appreciation for the existence of cross-talk mechanisms between the sumoylation and ubiquitinylation processes. Rather than being strictly parallel, these two systems have many points of intersection, and it is likely that the coordination of these two systems is a critical contributor to the regulation of many fundamental cellular events.
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Affiliation(s)
- Van G Wilson
- Department of Microbial & Molecular Pathogenesis, College of Medicine, Texas A&M Health Science Center, College Station, TX 77843-1114, USA.
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120
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Guan B, Pungaliya P, Li X, Uquillas C, Mutton LN, Rubin EH, Bieberich CJ. Ubiquitination by TOPORS regulates the prostate tumor suppressor NKX3.1. J Biol Chem 2007; 283:4834-40. [PMID: 18077445 DOI: 10.1074/jbc.m708630200] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The NKX3.1 gene located at 8p21.2 encodes a homeodomain-containing transcription factor that acts as a haploinsufficient tumor suppressor in prostate cancer. Diminished protein expression of NKX3.1 has been observed in prostate cancer precursors and carcinomas. TOPORS is a ubiquitously expressed E3 ubiquitin ligase that can ubiquitinate tumor suppressor p53. Here we report interaction between NKX3.1 and TOPORS. NKX3.1 can be ubiquitinated by TOPORS in vitro and in vivo, and overexpression of TOPORS leads to NKX3.1 proteasomal degradation in prostate cancer cells. Conversely, small interfering RNA-mediated knockdown of TOPORS leads to an increased steady-state level and prolonged half-life of NKX3.1. These data establish TOPORS as a negative regulator of NKX3.1 and implicate TOPORS in prostate cancer progression.
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Affiliation(s)
- Bin Guan
- Department of Biological Sciences, University of Maryland, Baltimore County, Baltimore, Maryland 21250, USA
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121
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Chakarova CF, Papaioannou MG, Khanna H, Lopez I, Waseem N, Shah A, Theis T, Friedman J, Maubaret C, Bujakowska K, Veraitch B, Abd El-Aziz MM, Prescott DQ, Parapuram SK, Bickmore WA, Munro PMG, Gal A, Hamel CP, Marigo V, Ponting CP, Wissinger B, Zrenner E, Matter K, Swaroop A, Koenekoop RK, Bhattacharya SS. Mutations in TOPORS cause autosomal dominant retinitis pigmentosa with perivascular retinal pigment epithelium atrophy. Am J Hum Genet 2007; 81:1098-103. [PMID: 17924349 DOI: 10.1086/521953] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2007] [Accepted: 07/17/2007] [Indexed: 11/03/2022] Open
Abstract
We report mutations in the gene for topoisomerase I-binding RS protein (TOPORS) in patients with autosomal dominant retinitis pigmentosa (adRP) linked to chromosome 9p21.1 (locus RP31). A positional-cloning approach, together with the use of bioinformatics, identified TOPORS (comprising three exons and encoding a protein of 1,045 aa) as the gene responsible for adRP. Mutations that include an insertion and a deletion have been identified in two adRP-affected families--one French Canadian and one German family, respectively. Interestingly, a distinct phenotype is noted at the earlier stages of the disease, with an unusual perivascular cuff of retinal pigment epithelium atrophy, which was found surrounding the superior and inferior arcades in the retina. TOPORS is a RING domain-containing E3 ubiquitin ligase and localizes in the nucleus in speckled loci that are associated with promyelocytic leukemia bodies. The ubiquitous nature of TOPORS expression and a lack of mutant protein in patients are highly suggestive of haploinsufficiency, rather than a dominant negative effect, as the molecular mechanism of the disease and make rescue of the clinical phenotype amenable to somatic gene therapy.
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122
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Hammer E, Heilbronn R, Weger S. The E3 ligase Topors induces the accumulation of polysumoylated forms of DNA topoisomerase I in vitro and in vivo. FEBS Lett 2007; 581:5418-24. [PMID: 17976381 DOI: 10.1016/j.febslet.2007.10.040] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2007] [Revised: 10/22/2007] [Accepted: 10/22/2007] [Indexed: 11/30/2022]
Abstract
Human Topors has originally been identified as binding partner of p53 and DNA topoisomerase I (TOP1). It can function as both an ubiquitin and SUMO-1 E3 ligase for p53. Here we demonstrate that Topors enhances the formation of high-molecular weight SUMO-1 conjugates of TOP1 in a reconstituted in vitro system and also in human osteosarcoma cells, similar to treatment with CPT. In contrast to the situation observed with p53, overall sumoylation levels were rather unaffected. Experiments with TOP1 point mutants strongly suggest that the high-molecular weight conjugates represent SUMO-1 chains formed on a limited number of SUMO-1 acceptor sites.
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Affiliation(s)
- Eva Hammer
- Institute of Virology, Charité Campus Benjamin Franklin, Free University of Berlin, Hindenburgdamm 27, 12203 Berlin, Germany
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123
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Abstract
While wild-type p53 is normally a rapidly degraded protein, mutant forms of p53 are stabilized and accumulate to high levels in tumor cells. In this study, we show that mutant and wild-type p53 proteins are ubiquitinated and degraded through overlapping but distinct pathways. While Mdm2 can drive the degradation of both mutant and wild-type p53, our data suggest that the ability of Mdm2 to function as a ubiquitin ligase is less important in the degradation of mutant p53, which is heavily ubiquitinated in an Mdm2-independent manner. Our initial attempts to identify ubiquitin ligases that are responsible for the ubiquitination of mutant p53 have suggested a role for the chaperone-associated ubiquitin ligase CHIP (C terminus of Hsc70-interacting protein), although other unidentified ubiquitin ligases also appear to contribute. The contribution of Mdm2 to the degradation of mutant p53 may reflect the ability of Mdm2 to deliver the ubiquitinated mutant p53 to the proteasome.
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Affiliation(s)
- Natalia Lukashchuk
- The Beatson Institute for Cancer Research, Switchback Rd., Glasgow G61 1BD, United Kingdom
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124
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Pungaliya P, Kulkarni D, Park HJ, Marshall H, Zheng H, Lackland H, Saleem A, Rubin EH. TOPORS functions as a SUMO-1 E3 ligase for chromatin-modifying proteins. J Proteome Res 2007; 6:3918-23. [PMID: 17803295 DOI: 10.1021/pr0703674] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
TOPORS is the first example of a protein with both ubiquitin and SUMO-1 E3 ligase activity and has been implicated as a tumor suppressor in several different malignancies. To gain insight into the cellular role of TOPORS, a proteomic screen was performed to identify candidate sumoylation substrates. The results indicate that many of the putative substrates are involved in chromatin modification or transcriptional regulation. Transfection studies confirmed mammalian Sin3A as a sumoylation substrate for TOPORS. These findings suggest that TOPORS may function as a tumor suppressor by regulating mSin3A and other proteins involved in chromatin modification.
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Affiliation(s)
- Pooja Pungaliya
- Department of Pharmacology, The Cancer Institute of New Jersey, Robert Wood Johnson Medical School, University of Medicine and Dentistry of New Jersey, 195 Little Albany Street, New Brunswick, New Jersey 08901, USA
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125
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Chen Z, Knutson E, Wang S, Martinez LA, Albrecht T. Stabilization of p53 in human cytomegalovirus-initiated cells is associated with sequestration of HDM2 and decreased p53 ubiquitination. J Biol Chem 2007; 282:29284-95. [PMID: 17698841 DOI: 10.1074/jbc.m705349200] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Human cytomegalovirus (HCMV) induces serum- or density-arrested human lung (LU) cells to traverse the cell cycle, providing it with a strategy to replicate in post-mitotic cells that are its cellular substrate in vivo. HCMV infection also induces high cellular levels of p53, seemingly in contradiction to the observed cell cycle progression. This study was undertaken to examine the mechanism(s) of the increased p53 abundance. HCMV infection caused a 4-fold increase in p53 that preceded a substantial increase in p53 transcripts by more than 24 h. p53 was stabilized in HCMV-infected cells (from a half-life of less than 30 min to about 8 h) and was less sensitive to proteasome-mediated degradation. Ubiquitination of p53 in mock-infected LU cells was sensitive to inhibition by trans-4-iodo, 4'-boranyl-chalcone, consistent with HDM2-catalyzing ubiquitination of p53. In HCMV-infected cells, ubiquitination of p53 was essentially undetectable. Although HDM2 had a nuclear distribution in mock-infected LU cells, in HCMV-infected cells HDM2 was translocated to the cytoplasm beginning at 12 h and demonstrated decreased cellular abundance thereafter. HDM2 was stabilized in the HCMV-infected cells by MG132, indicating a shift from p53 to HDM2 ubiquitination. p53 demonstrated a predominantly nuclear distribution in HCMV-infected cells through 48 h, resulting in p53 and HDM2 in distinct subcellular compartments. The principal mechanism responsible for increased p53 stabilization was nuclear export and degradation of HDM2. Thus, HCMV uses a shift from p53 to HDM2 ubiquitination and destabilization to obtain protracted high levels of p53, while promoting cell cycle traverse.
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Affiliation(s)
- Zhenping Chen
- Department of Microbiology and Immunology, University of Texas Medical Branch, Galveston, Texas 77555-1019, USA
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126
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Ii T, Mullen JR, Slagle CE, Brill SJ. Stimulation of in vitro sumoylation by Slx5-Slx8: evidence for a functional interaction with the SUMO pathway. DNA Repair (Amst) 2007; 6:1679-91. [PMID: 17669696 PMCID: PMC2100399 DOI: 10.1016/j.dnarep.2007.06.004] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2007] [Revised: 06/13/2007] [Accepted: 06/14/2007] [Indexed: 11/15/2022]
Abstract
The yeast genes SLX5 and SLX8 were identified based on their requirement for viability in the absence of the Sgs1 DNA helicase. Loss of these genes results in genome instability, nibbled colonies, and other phenotypes associated with defects in sumoylation. The Slx5 and Slx8 proteins form a stable complex and each subunit contains a single RING-finger domain at its C-terminus. To determine the physiological function of the Slx5-8 complex, we explored its interaction with the SUMO pathway. Curing 2micro circle from the mutants, suppressed their nibbled colony phenotype and partially improved their growth rate, but did not affect their sensitivity to hydroxyurea. The increase in sumoylation observed in slx5Delta and slx8Delta mutants was found to be dependent on the Siz1 SUMO ligase. Physical interactions between the Slx5-8 complex and both Ubc9 and Smt3 were identified and characterized. Using in vitro reactions, we show that Slx5, Slx8, or the Slx5-8 complex stimulates the formation of SUMO chains and the sumoylation of a test substrate. Interestingly, a functional RING-finger domain is not required for this stimulation in vitro. These biochemical data demonstrate for the first time that the Slx5 and Slx8 complex is capable of interacting directly with the SUMO pathway.
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Affiliation(s)
| | | | | | - Steven J. Brill
- *To whom correspondence should be addressed, Phone (732) 235-4197, Fax (732) 235-4880,
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127
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Abstract
A number of proteins are activated by stress stimuli but none so spectacularly or with the degree of complexity as the tumour suppressor p53 (human p53 gene or protein). Once stabilized, p53 is responsible for the transcriptional activation of a series of proteins involved in cell cycle control, apoptosis and senescence. This protein is present at low levels in resting cells but after exposure to DNA-damaging agents and other stress stimuli it is stabilized and activated by a series of post-translational modifications that free it from MDM2 (mouse double minute 2 but used interchangeably to denote human also), a ubiquination ligase that ubiquitinates it prior to proteasome degradation. The stability of p53 is also influenced by a series of other interacting proteins. In this review, we discuss the post-translational modifications to p53 in response to different stresses and the consequences of these changes.
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Affiliation(s)
- M F Lavin
- The Queensland Institute of Medical Research, Brisbane, Queensland, Australia.
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128
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Abstract
Over the years, p53 has been shown to sit at the centre of an increasingly complex web of incoming stress signals and outgoing effector pathways. The number and diversity of stress signals that lead to p53 activation illustrates the breadth of p53's remit - responding to a wide variety of potentially oncogenic insults to prevent tumour development. Interestingly, different stress signals can use different and independent pathways to activate p53, and there is some evidence that different stress signals can mediate different responses. How each of the responses to p53 contributes to inhibition of malignant progression is beginning to be clarified, with the hope that identification of responses that are key to tumour suppression will allow a more focused and effective search for new therapeutic targets. In this review, we will highlight some recently identified roles for p53 in tumour suppression, and discuss some of the numerous mechanisms through which p53 can be regulated and activated.
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Affiliation(s)
- H F Horn
- The Beatson Institute for Cancer Research, Garscube Estate, Switchback Road, Glasgow, UK
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129
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Chen C, Seth AK, Aplin AE. Genetic and expression aberrations of E3 ubiquitin ligases in human breast cancer. Mol Cancer Res 2007; 4:695-707. [PMID: 17050664 DOI: 10.1158/1541-7786.mcr-06-0182] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Recent studies revealed that E3 ubiquitin ligases play important roles in breast carcinogenesis. Clinical research studies have found that (epi)-genetic (deletion, amplification, mutation, and promoter methylation) and expression aberration of E3s are frequent in human breast cancer. Furthermore, many studies have suggested that many E3s are either oncogenes or tumor suppressor genes in breast cancer. In this review, we provide a comprehensive summary of E3s, which have genetic and/or expression aberration in breast cancer. Most cancer-related E3s regulate the cell cycle, p53, transcription, DNA repair, cell signaling, or apoptosis. An understanding of the oncogenic potential of the E3s may facilitate identifying and developing individual E3s as diagnosis markers and drug targets in breast cancer.
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Affiliation(s)
- Ceshi Chen
- The Center for Cell Biology and Cancer Research, Albany Medical College, 47 New Scotland Avenue, Albany, NY 12208, USA.
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130
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Russo J, Balogh GA, Heulings R, Mailo DA, Moral R, Russo PA, Sheriff F, Vanegas J, Russo IH. Molecular basis of pregnancy-induced breast cancer protection. Eur J Cancer Prev 2007; 15:306-42. [PMID: 16835503 DOI: 10.1097/00008469-200608000-00006] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
We have postulated that the lifetime protective effect of an early pregnancy against breast cancer is due to the complete differentiation of the mammary gland characterized by a specific genomic signature imprinted by the physiological process of pregnancy. In the present work, we show evidence that the breast tissue of postmenopausal parous women has had a shifting of stem cell 1 to stem cell 2 with a genomic signature different from similar structures derived from postmenopausal nulliparous women that have stem cell 1. Those genes that are significantly different are grouped in major categories on the basis of their putative functional significance. Among them are those gene transcripts related to immune surveillance, DNA repair, transcription, chromatin structure/activators/co-activators, growth factor and signal transduction pathway, transport and cell trafficking, cell proliferation, differentiation, cell adhesion, protein synthesis and cell metabolism. From these data, it was concluded that during pregnancy there are significant genomic changes that reflect profound alterations in the basic physiology of the mammary gland that explain the protective effect against carcinogenesis. The implication of this knowledge is that when the genomic signature of protection or refractoriness to carcinogenesis is acquired by the shifting of stem cell 1 to stem cell 2, the hormonal milieu induced by pregnancy or pregnancy-like conditions is no longer required. This is a novel concept that challenges the current knowledge that a chemopreventive agent needs to be given for a long period to suppress a metabolic pathway or abrogate the function of an organ.
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Affiliation(s)
- Jose Russo
- Breast Cancer Research Laboratory, Fox Chase Cancer Center, Philadelphia, Pennsylvania 19111, USA.
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131
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Konstantinopoulos PA, Papavassiliou AG. The potential of proteasome inhibition in the treatment of colon cancer. Expert Opin Investig Drugs 2007; 15:1067-75. [PMID: 16916273 DOI: 10.1517/13543784.15.9.1067] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Proteasome inhibition is an entirely novel approach to the treatment of malignant disease. By interfering with the ubiquitin-proteasome degradation system, proteasome inhibitors affect numerous cellular processes that are commonly deregulated in cancer cells including gene transcription, cell-cycle regulation, apoptosis, cell migration and DNA repair. This review outlines the physiology of the ubiquitin-proteasome pathway, discusses preclinical and clinical data regarding the activity of proteasome inhibitors against colon cancer and evaluates the rationale for the use of proteasome inhibitors as monotherapy or in combination with other anticancer therapies (i.e., chemotherapy, radiation therapy and other molecular-targeted therapies) in colon cancer.
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132
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Zhu Q, Wani G, Yao J, Patnaik S, Wang QE, El-Mahdy MA, Praetorius-Ibba M, Wani AA. The ubiquitin–proteasome system regulates p53-mediated transcription at p21waf1 promoter. Oncogene 2007; 26:4199-208. [PMID: 17224908 DOI: 10.1038/sj.onc.1210191] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
The ubiquitin (Ub)-proteasome system (UPS) promotes the proteasomal degradation of target proteins by decorating them with Ub labels. Emerging evidence indicates a role of UPS in regulating gene transcription. In this study, we provided evidence for the involvement of UPS in the transcriptional activation function of tumor suppressor p53. We showed that both ubiquitylation and proteasomal functions are required for efficient transcription mediated by p53. Disruption of transcription by actinomycin D, 5,6-dichloro-1-beta-D-ribofuranosyl-benzimadazole or alpha-amanitin leads to accumulation of cellular p53 protein. Proteasome inhibition by MG132 increases the occupancy of p53 protein at p53-responsive p21(waf1) promoter. In addition, the Sug-1 component of 19S proteasome physically interacts with p53 in vitro and in vivo. Moreover, in response to ultraviolet-induced DNA damage, both the 19S proteasomal components, Sug1 and S1, are recruited to p21(waf1) promoter region in a kinetic pattern similar to that of p53. These results suggested that UPS positively regulates p53-mediated transcription at p21(waf1) promoter.
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Affiliation(s)
- Q Zhu
- Department of Radiology, The Ohio State University, Columbus, OH 43210, USA
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133
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Yang W, Rozan LM, McDonald ER, Navaraj A, Liu JJ, Matthew EM, Wang W, Dicker DT, El-Deiry WS. CARPs are ubiquitin ligases that promote MDM2-independent p53 and phospho-p53ser20 degradation. J Biol Chem 2006; 282:3273-81. [PMID: 17121812 DOI: 10.1074/jbc.m610793200] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Caspase 8/10-associated RING proteins (CARPs) are a recently described family of protein ubiquitin ligases that interact with and negatively regulate death receptor-mediated apoptosis. Because CARPs are overexpressed in cancer and their silencing reduces cell viability and sensitizes tumor cells to chemotherapeutic agents, we investigated their relationship to p53 tumor suppressor signaling. p53 is a major determinant of chemosensitivity, and its levels are increased following DNA damage through N-terminal phosphorylation and inhibition of degradation. Although p53 is well known to be negatively regulated by several ubiquitin ligases including MDM2, none are known to target phosphorylated p53 for degradation. CARPs physically interact with and ubiquitinate p53, targeting it for degradation in the absence of MDM2. Serine 20-phosphorylated p53 is also ubiquitinated by CARPs. CARP silencing stimulates p53 expression and promotes downstream effects, including transcriptional activation and tumor suppression.
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Affiliation(s)
- Wensheng Yang
- Laboratory of Molecular Oncology and Cell Cycle Regulation, Department of Medicine, The Abramson Comprehensive Cancer Center, University of Pennsylvania School of Medicine, PA 19104, USA
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134
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Kostic M, Matt T, Martinez-Yamout MA, Dyson HJ, Wright PE. Solution Structure of the Hdm2 C2H2C4 RING, a Domain Critical for Ubiquitination of p53. J Mol Biol 2006; 363:433-50. [PMID: 16965791 DOI: 10.1016/j.jmb.2006.08.027] [Citation(s) in RCA: 104] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2006] [Revised: 08/09/2006] [Accepted: 08/10/2006] [Indexed: 11/16/2022]
Abstract
Regulation of the transcriptional response to the tumor suppressor p53 occurs at many levels, including control of its transcriptional activity, and of its stability and concentration within the cell. p53 stability is regulated by the protein Hdm2, an E3 ubiquitin ligase that binds to p53 and promotes its ubiquitination and degradation. The C-terminal domain of Hdm2, which is critical for this activity, has been classified as a RING domain on the basis of sequence homology, although it lacks the canonical set of zinc ligands (RING domains typically have C3HC4 or C4C4 zinc coordination). Here, we report the solution structure of the C2H2C4 RING domain of Hdm2(429-491), which reveals a symmetrical dimer with a unique cross-brace zinc-binding scheme. Each subunit has one Cys4 Zn site and one His2Cys2 Zn site. The global fold of each subunit is similar to those reported for other RING domains, with a compact betabetaalphabeta fold, a small hydrophobic core, and two Zn ions, which are essential for maintaining the domain structure. The dimer structure is maintained by an extensive interface that buries a large hydrophobic area on each subunit. It has been proposed that Hdm2 and its homologue HdmX form a stable heterodimer through their RING domains, resulting in a synergistic increase in observed E3 activity. To test this proposal, we prepared an HdmX RING construct and showed by NMR titration that it forms a tight 1:1 complex with the Hdm2 RING. The resonances most perturbed by heterodimer formation are located within the subunit interface of the homodimer, far removed from the surface expected to form the docking site of the E2 ubiquitin-conjugating enzyme, providing a structure-based rationale for the function of the RING domains in p53 ubiquitination.
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Affiliation(s)
- Milka Kostic
- Department of Molecular Biology and Skaggs Institute for Chemical Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA
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135
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Buchwald G, van der Stoop P, Weichenrieder O, Perrakis A, van Lohuizen M, Sixma TK. Structure and E3-ligase activity of the Ring-Ring complex of polycomb proteins Bmi1 and Ring1b. EMBO J 2006; 25:2465-74. [PMID: 16710298 PMCID: PMC1478191 DOI: 10.1038/sj.emboj.7601144] [Citation(s) in RCA: 333] [Impact Index Per Article: 18.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2005] [Accepted: 04/21/2006] [Indexed: 11/08/2022] Open
Abstract
Polycomb group proteins Ring1b and Bmi1 (B-cell-specific Moloney murine leukaemia virus integration site 1) are critical components of the chromatin modulating PRC1 complex. Histone H2A ubiquitination by the PRC1 complex strongly depends on the Ring1b protein. Here we show that the E3-ligase activity of Ring1b on histone H2A is enhanced by Bmi1 in vitro. The N-terminal Ring-domains are sufficient for this activity and Ring1a can replace Ring1b. E2 enzymes UbcH5a, b, c or UbcH6 support this activity with varying processivity and selectivity. All four E2s promote autoubiquitination of Ring1b without affecting E3-ligase activity. We solved the crystal structure of the Ring-Ring heterodimeric complex of Ring1b and Bmi1. In the structure the arrangement of the Ring-domains is similar to another H2A E3 ligase, the BRCA1/BARD1 complex, but complex formation depends on an N-terminal arm of Ring1b that embraces the Bmi1 Ring-domain. Mutation of a critical residue in the E2/E3 interface shows that catalytic activity resides in Ring1b and not in Bmi1. These data provide a foundation for understanding the critical enzymatic activity at the core of the PRC1 polycomb complex, which is implicated in stem cell maintenance and cancer.
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Affiliation(s)
- Gretel Buchwald
- Division of Molecular Carcinogenesis and Center for Biomedical Genetics, Netherlands Cancer Institute, Amsterdam, Netherlands
| | - Petra van der Stoop
- Division of Molecular Genetics and Center for Biomedical Genetics, Netherlands Cancer Institute, Amsterdam, The Netherlands
| | - Oliver Weichenrieder
- Division of Molecular Carcinogenesis and Center for Biomedical Genetics, Netherlands Cancer Institute, Amsterdam, Netherlands
| | - Anastassis Perrakis
- Division of Molecular Carcinogenesis and Center for Biomedical Genetics, Netherlands Cancer Institute, Amsterdam, Netherlands
| | - Maarten van Lohuizen
- Division of Molecular Genetics and Center for Biomedical Genetics, Netherlands Cancer Institute, Amsterdam, The Netherlands
| | - Titia K Sixma
- Division of Molecular Carcinogenesis and Center for Biomedical Genetics, Netherlands Cancer Institute, Amsterdam, Netherlands
- Division of Molecular Carcinogenesis and Center for Biomedical Genetics, Netherlands Cancer Institute, Plesmanlaan 121, 1066 CX Amsterdam, Netherlands. Tel.: +31 20 5121959; Fax: +31 20 5121954; E-mail:
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136
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Espinosa A, Zhou W, Ek M, Hedlund M, Brauner S, Popovic K, Horvath L, Wallerskog T, Oukka M, Nyberg F, Kuchroo VK, Wahren-Herlenius M. The Sjögren’s Syndrome-Associated Autoantigen Ro52 Is an E3 Ligase That Regulates Proliferation and Cell Death. THE JOURNAL OF IMMUNOLOGY 2006; 176:6277-85. [PMID: 16670339 DOI: 10.4049/jimmunol.176.10.6277] [Citation(s) in RCA: 126] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Patients affected by Sjögren's syndrome and systemic lupus erythematosus (SLE) carry autoantibodies to an intracellular protein denoted Ro52. Although the serologic presence of Ro52 autoantibodies is used clinically for diagnostic purposes, the function of the protein or why it is targeted as an autoantigen in several rheumatic conditions has not been elucidated. In this study, we show that the expression of Ro52 is significantly increased in PBMC of patients with Sjögren's syndrome and SLE, and demonstrate that Ro52 is a RING-dependent E3 ligase involved in ubiquitination. Overexpression of Ro52, but not of Ro52 lacking the RING domain, in a mouse B cell line lead to decreased growth in steady state and increased cell death after activation via the CD40 pathway. The role of Ro52 in activation-mediated cell death was further confirmed as a reduction in Ro52 expression restored cell viability. These findings suggest that the increased expression of the Ro52 autoantigen in patients may be directly involved in the reduced cellular proliferation and increased apoptotic cell death observed in Sjögren's syndrome and SLE, and may thus contribute to the autoantigenic load and induction of autoimmune B and T cell responses observed in rheumatic patients.
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Affiliation(s)
- Alexander Espinosa
- Rheumatology Unit, Department of Medicine, Karolinska Institutet at Danderyd Hospital, Karolinska Institutet, S-17176 Stockholm, Sweden
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137
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Abstract
Although early studies have suggested that the oncoprotein Mdm2 is the primary E3 ubiquitin ligase for the p53 tumor suppressor, an increasing amount of data suggests that p53 ubiquitination and degradation are more complex than once thought. The discoveries of MdmX, HAUSP, ARF, COP1, Pirh2, and ARF-BP1 continue to uncover the multiple facets of this pathway. There is no question that Mdm2 plays a pivotal role in downregulating p53 activities in numerous cellular settings. Nevertheless, growing evidence challenges the conventional view that Mdm2 is essential for p53 turnover.
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Affiliation(s)
- Christopher L. Brooks
- Institute for Cancer Genetics and Department of Pathology, College of Physicians and Surgeons, Columbia University, 1150 St. Nicholas Avenue, New York, New York 10032
| | - Wei Gu
- Institute for Cancer Genetics and Department of Pathology, College of Physicians and Surgeons, Columbia University, 1150 St. Nicholas Avenue, New York, New York 10032
- Correspondence:
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138
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Nery FC, Rui E, Kuniyoshi TM, Kobarg J. Evidence for the interaction of the regulatory protein Ki-1/57 with p53 and its interacting proteins. Biochem Biophys Res Commun 2006; 341:847-55. [PMID: 16455055 DOI: 10.1016/j.bbrc.2006.01.036] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2006] [Accepted: 01/11/2006] [Indexed: 12/15/2022]
Abstract
Ki-1/57 is a cytoplasmic and nuclear phospho-protein of 57 kDa and interacts with the adaptor protein RACK1, the transcription factor MEF2C, and the chromatin remodeling factor CHD3, suggesting that it might be involved in the regulation of transcription. Here, we describe yeast two-hybrid studies that identified a total of 11 proteins interacting with Ki-1/57, all of which interact or are functionally associated with p53 or other members of the p53 family of proteins. We further found that Ki-1/57 is able to interact with p53 itself in the yeast two-hybrid system when the interaction was tested directly. This interaction could be confirmed by pull down assays with purified proteins in vitro and by reciprocal co-immunoprecipitation assays from the human Hodgkin analogous lymphoma cell line L540. Furthermore, we found that the phosphorylation of p53 by PKC abolishes its interaction with Ki-1/57 in vitro.
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Affiliation(s)
- Flávia C Nery
- Centro de Biologia Molecular Estrutural, Laboratório Nacional de Luz Síncrotron, Rua Giuseppe Máximo Scolfaro 10.000, C.P. 6192, 13084-971 Campinas, SP, Brazil
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139
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Taylor C, Jobin C. Ubiquitin protein modification and signal transduction: implications for inflammatory bowel diseases. Inflamm Bowel Dis 2005; 11:1097-107. [PMID: 16306773 DOI: 10.1097/01.mib.0000187577.26043.e5] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
A dysregulated immune response to luminal antigen(s) is associated with the development of inflammatory bowel diseases (IBDs). A complex network of inflammatory and immune mediators released by immune and nonimmune cells participate in the physiopathology of IBD. At the molecular level, events leading to the improper use of the signaling grid are likely responsible for the dysregulated activation of various transcription factors and subsequent induction of inflammatory genes. The posttranslational modification of signaling proteins by the ubiquitin system is a critical event in activation or repression of transcription factors. Two important transcriptional pathways in which ubiquitin is central are the nuclear factor-kappaB and hypoxia inducible factor-1 (HIF-1) pathways, both of which are important components of intestinal homeostasis. In this review, we discuss the role of ubiquitin modification in relation to nuclear factor-kappaB and HIF-1 signaling and consider its impact on intestinal inflammation. A greater understanding of posttranslational ubiquitin modification may lead to the identification of new therapeutic opportunities for the treatment of IBD.
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Affiliation(s)
- Cormac Taylor
- The Conway Institute, University College Dublin, Dublin, Ireland
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140
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Capelson M, Corces VG. The ubiquitin ligase dTopors directs the nuclear organization of a chromatin insulator. Mol Cell 2005; 20:105-16. [PMID: 16209949 DOI: 10.1016/j.molcel.2005.08.031] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2005] [Revised: 08/10/2005] [Accepted: 08/29/2005] [Indexed: 10/25/2022]
Abstract
Chromatin insulators are gene regulatory elements implicated in the establishment of independent chromatin domains. The gypsy insulator of D. melanogaster confers its activity through a protein complex that consists of three known components, Su(Hw), Mod(mdg4)2.2, and CP190. We have identified a factor, Drosophila Topoisomerase I-interacting RS protein (dTopors) that interacts with the insulator protein complex and is required for gypsy insulator function. In the absence of Mod(mdg4)2.2, nuclear clustering of insulator complexes is disrupted and insulator activity is compromised. Overexpression of dTopors in the mod(mdg4)2.2 null mutant rescues insulator activity and restores the formation of nuclear insulator bodies. dTopors associates with the nuclear lamina, and mutations in lamin disrupt dTopors localization as well as nuclear organization and activity of the gypsy insulator. Thus, dTopors appears to be involved in the establishment of chromatin organization through its ability to mediate the association of insulator complexes with a fixed nuclear substrate.
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Affiliation(s)
- Maya Capelson
- Department of Biology, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218, USA
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141
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Weger S, Hammer E, Heilbronn R. Topors acts as a SUMO-1 E3 ligase for p53 in vitro and in vivo. FEBS Lett 2005; 579:5007-12. [PMID: 16122737 DOI: 10.1016/j.febslet.2005.07.088] [Citation(s) in RCA: 122] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2005] [Revised: 07/13/2005] [Accepted: 07/18/2005] [Indexed: 12/22/2022]
Abstract
Human Topors, which was originally identified as cellular binding partner of DNA topoisomerase I and of p53, has recently been shown to function as an ubiquitin E3 ligase for p53 in a manner dependent on its N'-terminally located RING finger. Here, we demonstrate that Topors also enhances the conjugation of the small ubiquitin-like modifier 1 (SUMO-1) to p53 in vivo and in a reconstituted in vitro system. The Topors SUMO-1 E3 ligase activity does not depend upon its RING finger motif. In HeLa cells, Topors induced p53 sumoylation was accompanied by an increase in endogenous p53 protein levels. Furthermore, Topors enhances the sumoylation of a variety of other, yet unidentified, cellular proteins.
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Affiliation(s)
- Stefan Weger
- Institute of Infectious Diseases, Department of Virology, Charité Campus Benjamin Franklin, Free University of Berlin, Hindenburgdamm 27, 12203 Berlin, Germany.
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142
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Kirkpatrick DS, Denison C, Gygi SP. Weighing in on ubiquitin: the expanding role of mass-spectrometry-based proteomics. Nat Cell Biol 2005; 7:750-7. [PMID: 16056266 PMCID: PMC1224607 DOI: 10.1038/ncb0805-750] [Citation(s) in RCA: 170] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Mass-spectrometry-based proteomics has become an essential tool for the qualitative and quantitative analysis of cellular systems. The biochemical complexity and functional diversity of the ubiquitin system are well suited to proteomic studies. This review summarizes advances involving the identification of ubiquitinated proteins, the elucidation of ubiquitin-modification sites and the determination of polyubiquitin chain linkages, as well as offering a perspective on the application of emerging technologies for mechanistic and functional studies of protein ubiquitination.
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Affiliation(s)
| | | | - Steven P. Gygi
- Department of Cell Biology and
- Taplin Biological Mass Spectrometry Facility, Harvard Medical School, Boston, Massachusetts 02115, USA
- Correspondence: Steven P. Gygi, Department of Cell Biology, Harvard Medical School, 240 Longwood Avenue, Boston, Massachusetts 02115, USA, 617-432-3155,
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143
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Kulikov R, Boehme KA, Blattner C. Glycogen synthase kinase 3-dependent phosphorylation of Mdm2 regulates p53 abundance. Mol Cell Biol 2005; 25:7170-80. [PMID: 16055726 PMCID: PMC1190268 DOI: 10.1128/mcb.25.16.7170-7180.2005] [Citation(s) in RCA: 103] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
The Mdm2 oncoprotein regulates abundance and activity of the p53 tumor suppressor protein. For efficient degradation of p53, Mdm2 needs to be phosphorylated at several contiguous residues within the central conserved domain. We show that glycogen synthase kinase 3 (GSK-3) phosphorylated the Mdm2 protein in vitro and in vivo in the central domain. Inhibition of GSK-3 rescued p53 from degradation in an Mdm2-dependent manner while its association with Mdm2 was not affected. Likewise, inhibition of GSK-3 did not alter localization of p53 and Mdm2 or the interaction of Mdm2 and MdmX. Ionizing radiation, which leads to p53 accumulation, directed phosphorylation of GSK-3 at serine 9, which preceded and overlapped with the increase in p53 levels. Moreover, expression of a GSK-3 mutant where serine 9 was replaced with an alanine reduced the accumulation of p53 and induction of its target p21(WAF-1). We therefore conclude that inhibition of GSK-3 contributes to hypophosphorylation of Mdm2 in response to ionizing rays, and in consequence to p53 stabilization.
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Affiliation(s)
- Roman Kulikov
- Institut für Genetik, Forschungszentrum Karlsruhe, Germany
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144
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Bredel M, Bredel C, Juric D, Harsh GR, Vogel H, Recht LD, Sikic BI. High-resolution genome-wide mapping of genetic alterations in human glial brain tumors. Cancer Res 2005; 65:4088-96. [PMID: 15899798 DOI: 10.1158/0008-5472.can-04-4229] [Citation(s) in RCA: 124] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
High-resolution genome-wide mapping of exact boundaries of chromosomal alterations should facilitate the localization and identification of genes involved in gliomagenesis and may characterize genetic subgroups of glial brain tumors. We have done such mapping using cDNA microarray-based comparative genomic hybridization technology to profile copy number alterations across 42,000 mapped human cDNA clones, in a series of 54 gliomas of varying histogenesis and tumor grade. This gene-by-gene approach permitted the precise sizing of critical amplicons and deletions and the detection of multiple new genetic aberrations. It has also revealed recurrent patterns of occurrence of distinct chromosomal aberrations as well as their interrelationships and showed that gliomas can be clustered into distinct genetic subgroups. A subset of detected alterations was shown predominantly associated with either astrocytic or oligodendrocytic tumor phenotype. Finally, five novel minimally deleted regions were identified in a subset of tumors, containing putative candidate tumor suppressor genes (TOPORS, FANCG, RAD51, TP53BP1, and BIK) that could have a role in gliomagenesis.
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Affiliation(s)
- Markus Bredel
- Division of Oncology, Center for Clinical Sciences Research, Stanford University School of Medicine, Stanford, California 94305-5151, USA.
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145
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Kohn KW, Pommier Y. Molecular interaction map of the p53 and Mdm2 logic elements, which control the Off-On switch of p53 in response to DNA damage. Biochem Biophys Res Commun 2005; 331:816-27. [PMID: 15865937 DOI: 10.1016/j.bbrc.2005.03.186] [Citation(s) in RCA: 78] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2005] [Indexed: 01/17/2023]
Abstract
The molecular network that controls responses to genotoxic stress is centered at p53 and Mdm2. Recent findings have shown this network to be more complex than previously envisioned. Using a notation specifically designed for circuit diagram-like representations of bioregulatory networks, we have prepared an updated molecular interaction map of the immediate connections of p53 and Mdm2, which are described as logic elements of the network. We use the map as the basis for a comprehensive review of current concepts of signal processing by these logic elements (an interactive version of the maps-eMIMs can be examined at ). We also used molecular interaction maps to propose a p53 Off-On switch in response to DNA damage.
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Affiliation(s)
- Kurt W Kohn
- Laboratory of Molecular Pharmacology, Center for Cancer Research, National Cancer Institute, NIH, Bethesda, MD 20892, USA.
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146
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Coutts AS, La Thangue NB. The p53 response: emerging levels of co-factor complexity. Biochem Biophys Res Commun 2005; 331:778-85. [PMID: 15865933 DOI: 10.1016/j.bbrc.2005.03.150] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2005] [Indexed: 11/26/2022]
Affiliation(s)
- Amanda S Coutts
- Division of Biochemistry and Molecular Biology, Davidson Building, University of Glasgow, Glasgow G12 8QQ, UK
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147
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Lin L, Ozaki T, Takada Y, Kageyama H, Nakamura Y, Hata A, Zhang JH, Simonds WF, Nakagawara A, Koseki H. topors, a p53 and topoisomerase I-binding RING finger protein, is a coactivator of p53 in growth suppression induced by DNA damage. Oncogene 2005; 24:3385-96. [PMID: 15735665 DOI: 10.1038/sj.onc.1208554] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The RING family zinc-finger protein topors (topoisomerase I-binding protein) binds not only topoisomerase I, but also p53 and the AAV-2 Rep78/68 proteins. topors maps to human chromosome 9p21, which contains candidate tumor suppressor genes implicated in small cell lung cancers. In this study, we isolated the murine counterpart of topors and investigated its impact on p53 function. The deduced amino-acid sequence of mouse topors exhibits extensive similarity to human topors. Overexpressed myc-tagged topors associates with and stabilizes p53, and enhances the p53-dependent transcriptional activities of p21(Waf1), MDM2 and Bax promoters and elevates endogenous p21(Waf1) mRNA levels. Overexpression of topors consequently results in the suppression of cell growth by cell cycle arrest and/or by the induction of apoptosis. Taken together, these studies identify topors as a positive regulator of p53. The expression of topors is induced by exposure to the genotoxic reagents cisplatin and camptothecin, a DNA topoisomerase I inhibitor. We therefore postulate that topors mediates p53-dependent cellular responses induced by DNA damage, suggesting its physiological role as a tumor suppressor.
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Affiliation(s)
- Ling Lin
- Department of Molecular Embryology, Graduate School of Medicine, Chiba University, 1-8-1 Inohana, Chuo-ku, Chiba 260-8670, Japan
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148
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Abstract
The p53 pathway responds to stresses that can disrupt the fidelity of DNA replication and cell division. A stress signal is transmitted to the p53 protein by post-translational modifications. This results in the activation of the p53 protein as a transcription factor that initiates a program of cell cycle arrest, cellular senescence or apoptosis. The transcriptional network of p53-responsive genes produces proteins that interact with a large number of other signal transduction pathways in the cell and a number of positive and negative autoregulatory feedback loops act upon the p53 response. There are at least seven negative and three positive feedback loops described here, and of these, six act through the MDM-2 protein to regulate p53 activity. The p53 circuit communicates with the Wnt-beta-catenin, IGF-1-AKT, Rb-E2F, p38 MAP kinase, cyclin-cdk, p14/19 ARF pathways and the cyclin G-PP2A, and p73 gene products. There are at least three different ubiquitin ligases that can regulate p53 in an autoregulatory manner: MDM-2, Cop-1 and Pirh-2. The meaning of this redundancy and the relative activity of each of these feedback loops in different cell types or stages of development remains to be elucidated. The interconnections between signal transduction pathways will play a central role in our understanding of cancer.
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Affiliation(s)
- Sandra L Harris
- The Cancer Institute of New Jersey and the Institute for Advanced Study, New Jersey, NJ, USA
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149
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Vichi A, Payne DM, Pacheco-Rodriguez G, Moss J, Vaughan M. E3 ubiquitin ligase activity of the trifunctional ARD1 (ADP-ribosylation factor domain protein 1). Proc Natl Acad Sci U S A 2005; 102:1945-50. [PMID: 15684077 PMCID: PMC548593 DOI: 10.1073/pnas.0409800102] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Protein ubiquitinylation plays a key role in many important cellular processes. Ubiquitinylation requires the E1 ubiquitin-activating enzyme, an E2 ubiquitin-conjugating enzyme, and, frequently, a substrate-specific E3 ubiquitin-protein ligase. In one class of E3 ubiquitin ligases, the catalytic domain contains a zinc-binding RING finger motif. ARD1 (ADP-ribosylation factor domain protein 1), with a RING finger domain in the N-terminal region, two predicted B-Boxes, and a coiled-coil protein interaction motif immediately preceding an ADP-ribosylation factor domain at the C terminus, belongs to the TRIM (Tripartite motif) or RBCC (RING, B-Box, coiled-coil) family. The region containing the B-Boxes and the coiled-coil motif acts as a GTPase-activating protein for the ADP-ribosylation factor domain of ARD1. We report here that full-length ARD1 or the RING finger domain (residues 1-110) produced polyubiquitinylated proteins in vitro in the presence of mammalian E1, an E2 enzyme (UbcH6 or UbcH5a, -5b, or -5c), ATP, and ubiquitin. Deletion of the RING region or point mutations within the RING sequence abolished ARD1 E3 ligase activity. All data are consistent with a potential function for ARD1 as an E3 ubiquitin ligase in cells.
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Affiliation(s)
- Alessandro Vichi
- Pulmonary-Critical Care Medicine Branch, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892-1434, USA.
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