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Muli CS, Tarasov SG, Walters KJ. High-throughput assay exploiting disorder-to-order conformational switches: application to the proteasomal Rpn10:E6AP complex. Chem Sci 2024; 15:4041-4053. [PMID: 38487241 PMCID: PMC10935766 DOI: 10.1039/d3sc06370d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2023] [Accepted: 02/05/2024] [Indexed: 03/17/2024] Open
Abstract
Conformational switching is pervasively driven by protein interactions, particularly for intrinsically disordered binding partners. We developed a dually orthogonal fluorescence-based assay to monitor such events, exploiting environmentally sensitive fluorophores. This assay is applied to E3 ligase E6AP, as its AZUL domain induces a disorder-to-order switch in an intrinsically disordered region of the proteasome, the so-named Rpn10 AZUL-binding domain (RAZUL). By testing various fluorophores, we developed an assay appropriate for high-throughput screening of Rpn10:E6AP-disrupting ligands. We found distinct positions in RAZUL for fluorophore labeling with either acrylodan or Atto610, which had disparate spectral responses to E6AP binding. E6AP caused a hypsochromic shift with increased fluorescence of acrylodan-RAZUL while decreasing fluorescence intensity of Atto610-RAZUL. Combining RAZUL labeled with either acrylodan or Atto610 into a common sample achieved robust and orthogonal measurement of the E6AP-induced conformational switch. This approach is generally applicable to disorder-to-order (or vice versa) transitions mediated by molecular interactions.
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Affiliation(s)
- Christine S Muli
- Protein Processing Section, Center for Structural Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health Frederick MD 21702 USA
| | - Sergey G Tarasov
- Biophysics Resource, Center for Structural Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health Frederick MD 21702 USA
| | - Kylie J Walters
- Protein Processing Section, Center for Structural Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health Frederick MD 21702 USA
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2
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Hao X, Sun J, Zhong L, Baudry M, Bi X. UBE3A deficiency-induced autophagy is associated with activation of AMPK-ULK1 and p53 pathways. Exp Neurol 2023; 363:114358. [PMID: 36849003 PMCID: PMC10073344 DOI: 10.1016/j.expneurol.2023.114358] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2022] [Revised: 02/03/2023] [Accepted: 02/22/2023] [Indexed: 02/27/2023]
Abstract
Angelman Syndrome (AS) is a neurodevelopmental disorder caused by deficiency of the maternally expressed UBE3A gene. The UBE3A proteins functions both as an E3 ligase in the ubiquitin-proteasome system (UPS), and as a transcriptional co-activator for steroid hormone receptors. Here we investigated the effects of UBE3A deficiency on autophagy in the cerebellum of AS mice and in COS1 cells. Numbers and size of LC3- and LAMP2-immunopositive puncta were increased in cerebellar Purkinje cells of AS mice, as compared to wildtype mice. Western blot analysis showed an increase in the conversion of LC3I to LC3II in AS mice, as expected from increased autophagy. Levels of active AMPK and of one of its substrates, ULK1, a factor involved in autophagy initiation, were also increased. Colocalization of LC3 with LAMP2 was increased and p62 levels were decreased, indicating an increase in autophagy flux. UBE3A deficiency was also associated with reduced levels of phosphorylated p53 in the cytosol and increased levels in nuclei, which favors autophagy induction. UBE3A siRNA knockdown in COS-1 cells resulted in increased size and intensity of LC3-immunopositive puncta and increased the LC3 II/I ratio, as compared to control siRNA-treated cells, confirming the results found in the cerebellum of AS mice. These results indicate that UBE3A deficiency enhances autophagic activity through activation of the AMPK-ULK1 pathway and alterations in p53.
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Affiliation(s)
- Xiaoning Hao
- College of Osteopathic Medicine of the Pacific, Western University of Health Sciences, Pomona, CA 91766, USA
| | - Jiandong Sun
- College of Osteopathic Medicine of the Pacific, Western University of Health Sciences, Pomona, CA 91766, USA
| | - Li Zhong
- College of Osteopathic Medicine of the Pacific, Western University of Health Sciences, Pomona, CA 91766, USA
| | - Michel Baudry
- College of Dental Medicine, Western University of Health Sciences, Pomona, CA 91766, USA
| | - Xiaoning Bi
- College of Osteopathic Medicine of the Pacific, Western University of Health Sciences, Pomona, CA 91766, USA.
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3
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Miller J, Dakic A, Spurgeon M, Saenz F, Kallakury B, Zhao B, Zhang J, Zhu J, Ma Q, Xu Y, Lambert P, Schlegel R, Riegel AT, Liu X. AIB1 is a novel target of the high-risk HPV E6 protein and a biomarker of cervical cancer progression. J Med Virol 2022; 94:3962-3977. [PMID: 35437795 PMCID: PMC9199254 DOI: 10.1002/jmv.27795] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2022] [Revised: 04/13/2022] [Accepted: 04/17/2022] [Indexed: 11/10/2022]
Abstract
The high-risk human papillomaviruses (HPV-16, -18) are critical etiologic agents in human malignancy, most importantly in cervical cancer. These oncogenic viruses encode the E6 and E7 proteins that are uniformly retained and expressed in cervical cancers and required for maintenance of the tumorigenic phenotype. The E6 and E7 proteins were first identified as targeting the p53 and pRB tumor suppressor pathways, respectively, in host cells, thereby leading to disruption of cell cycle controls. In addition to p53 degradation, a number of other functions and critical targets for E6 have been described, including telomerase, Myc, PDZ-containing proteins, Akt, Wnt, mTORC1, as well as others. In this study, we identified Amplified in Breast Cancer 1 (AIB1) as a new E6 target. We first found that E6 and hTERT altered similar profiling of gene expression in human foreskin keratinocytes (HFK), independent of telomerase activity. Importantly, AIB1 was a common transcriptional target of both E6 and hTERT. We then verified that high-risk E6 but not low-risk E6 expression led to increases in AIB1 transcript levels by real-time RT-PCR, suggesting that AIB1 upregulation may play an important role in cancer development. Western blots demonstrated that AIB1 expression increased in HPV-16 E6 and E7 expressing (E6E7) immortalized foreskin and cervical keratinocytes, and in three of four common cervical cancer cell lines as well. Then, we evaluated the expression of AIB1 in human cervical lesions and invasive carcinoma using immunohistochemical staining. Strikingly, AIB1 showed positivity in the nucleus of cells in the immediate suprabasal epithelium, while nuclei of the basal epithelium were negative, as evident in the Cervical Intraepithelial Neoplasia 1 (CIN1) samples. As the pathological grading of cervical lesions increased from CIN1, CIN2, CIN3 carcinoma in situ and invasive carcinoma, AIB1 staining increased progressively, suggesting that AIB1 may serve as a novel histological biomarker for cervical cancer development. For cases of invasive cervical carcinoma, AIB1 staining was specific to cancerous lesions. Increased expression of AIB1 was also observed in transgenic mouse cervical neoplasia and cancer models induced by E6E7 and estrogen. Knockdown of AIB1 expression in E6E7 immortalized human cervical cells significantly abolished cell proliferation. Taken together, these data support AIB1 as a novel target of HPV E6 and a biomarker of cervical cancer progression.
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Affiliation(s)
- Jonathan Miller
- Department of Pathology, Center for Cell ReprogrammingGeorgetown University Medical SchoolWashingtonDistrict of ColumbiaUSA
| | - Aleksandra Dakic
- Department of Pathology, Center for Cell ReprogrammingGeorgetown University Medical SchoolWashingtonDistrict of ColumbiaUSA
| | - Megan Spurgeon
- McArdle Laboratory for Cancer Research, Department of OncologyUniversity of Wisconsin‐Madison School of Medicine and Public HealthMadisonWisconsinUSA
| | - Francisco Saenz
- Department of Oncology, Lombardi Comprehensive Cancer CenterGeorgetown University Medical SchoolWashingtonDistrict of ColumbiaUSA
| | - Bhaskar Kallakury
- Department of Pathology, Center for Cell ReprogrammingGeorgetown University Medical SchoolWashingtonDistrict of ColumbiaUSA
| | - Bo Zhao
- Department of Medicine, Brigham and Women's HospitalHarvard Medical SchoolBostonMassachusettsUSA
| | - Junran Zhang
- Department of Radiation Oncology, Wexner Medical CenterThe Ohio State UniversityColumbusOhioUSA
- The James Comprehensive Cancer CenterThe Ohio State UniversityColumbusOhioUSA
| | - Jian Zhu
- Department of Pathology, Wexner Medical CenterThe Ohio State UniversityColumbusOhioUSA
| | - Qin Ma
- The James Comprehensive Cancer CenterThe Ohio State UniversityColumbusOhioUSA
- Department of Biomedical Informatics, College of MedicineThe Ohio State UniversityColumbusOhioUSA
| | - Ying Xu
- Computational Systems Biology Lab, Department of Biochemistry and Molecular Biology and Institute of BioinformaticsThe University of GeorgiaAthensGeorgiaUSA
| | - Paul Lambert
- McArdle Laboratory for Cancer Research, Department of OncologyUniversity of Wisconsin‐Madison School of Medicine and Public HealthMadisonWisconsinUSA
| | - Richard Schlegel
- Department of Pathology, Center for Cell ReprogrammingGeorgetown University Medical SchoolWashingtonDistrict of ColumbiaUSA
| | - Anna T. Riegel
- Department of Oncology, Lombardi Comprehensive Cancer CenterGeorgetown University Medical SchoolWashingtonDistrict of ColumbiaUSA
| | - Xuefeng Liu
- Department of Pathology, Center for Cell ReprogrammingGeorgetown University Medical SchoolWashingtonDistrict of ColumbiaUSA
- The James Comprehensive Cancer CenterThe Ohio State UniversityColumbusOhioUSA
- Department of Pathology, Wexner Medical CenterThe Ohio State UniversityColumbusOhioUSA
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4
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Zheng Z, Zhang B, Yu H, Li S, Song N, Jin X, Li J. UBE3A activates the NOTCH pathway and promotes esophageal cancer progression by degradation of ZNF185. Int J Biol Sci 2021; 17:3024-3035. [PMID: 34421347 PMCID: PMC8375240 DOI: 10.7150/ijbs.61117] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2021] [Accepted: 06/21/2021] [Indexed: 12/19/2022] Open
Abstract
Background: Esophageal cancer is the sixth-most common fatal malignant tumor worldwide. Little is known regarding the genetic drivers that influence targeted therapy outcomes in patients with esophageal cancer. Exploring the pathogenesis of this lethal tumor could provide clues for developing appropriate therapeutic drugs. Ubiquitin-protein ligase E3A (UBE3A) reportedly promotes or suppresses various types of malignant tumors. However, the cancer-related role of UBE3A in esophageal cancer remains unclear. Methods: The relationship of UBE3A with the clinicopathological features of pancreatic tumors was bioinformatically investigated in the TCGA dataset. The protein levels of UBE3A and ZNF185 were assessed by Western blot and immunohistochemistry. The role of UBE3A and ZNF185 in esophageal cancer growth was assessed by MTS assays, colony formation assays, and experiments in mouse xenograft models. The interaction between UBE3A and ZNF185 was investigated by co-immunoprecipitation. The relationship between UBE3A, ZNF185, and NOTCH signaling pathway was explored by Western blot and quantitative real-time PCR. Results: We found that UBE3A was upregulated in patients with esophageal cancer and enhanced the cellular progression of esophageal cancer. Moreover, we found that UBE3A degraded ZNF185 in esophageal cancer. Additionally, ZNF185 suppressed the progression of esophageal cancer by inactivating the NOTCH pathway. Conclusions: These data demonstrated that aberrant expression of UBE3A led to enhanced progression of esophageal cancer through the ZNF185/NOTCH signaling axis. Therefore, UBE3A might be an ideal therapeutic candidate for esophageal cancer.
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Affiliation(s)
- Zhikun Zheng
- Department of Thoracic Surgery, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology
| | - Bin Zhang
- Cancer center, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, 430022, China
| | - Haixin Yu
- Cancer center, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, 430022, China
| | - Shoukang Li
- Department of Thoracic Surgery, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology
| | - Naicheng Song
- Department of Thoracic Surgery, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology
| | - Xin Jin
- Department of Urology, The Second Xiangya Hospital, Central South University, Changsha, Hunan, 410011, China
| | - Jinsong Li
- Department of Thoracic Surgery, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology
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5
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SRC-3, a Steroid Receptor Coactivator: Implication in Cancer. Int J Mol Sci 2021; 22:ijms22094760. [PMID: 33946224 PMCID: PMC8124743 DOI: 10.3390/ijms22094760] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2021] [Revised: 04/23/2021] [Accepted: 04/27/2021] [Indexed: 02/07/2023] Open
Abstract
Steroid receptor coactivator-3 (SRC-3), also known as amplified in breast cancer 1 (AIB1), is a member of the SRC family. SRC-3 regulates not only the transcriptional activity of nuclear receptors but also many other transcription factors. Besides the essential role of SRC-3 in physiological functions, it also acts as an oncogene to promote multiple aspects of cancer. This review updates the important progress of SRC-3 in carcinogenesis and summarizes its mode of action, which provides clues for cancer therapy.
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6
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Mathieu NA, Levin RH, Spratt DE. Exploring the Roles of HERC2 and the NEDD4L HECT E3 Ubiquitin Ligase Subfamily in p53 Signaling and the DNA Damage Response. Front Oncol 2021; 11:659049. [PMID: 33869064 PMCID: PMC8044464 DOI: 10.3389/fonc.2021.659049] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2021] [Accepted: 03/16/2021] [Indexed: 12/27/2022] Open
Abstract
Cellular homeostasis is governed by the precise expression of genes that control the translation, localization, and termination of proteins. Oftentimes, environmental and biological factors can introduce mutations into the genetic framework of cells during their growth and division, and these genetic abnormalities can result in malignant transformations caused by protein malfunction. For example, p53 is a prominent tumor suppressor protein that is capable of undergoing more than 300 posttranslational modifications (PTMs) and is involved with controlling apoptotic signaling, transcription, and the DNA damage response (DDR). In this review, we focus on the molecular mechanisms and interactions that occur between p53, the HECT E3 ubiquitin ligases WWP1, SMURF1, HECW1 and HERC2, and other oncogenic proteins in the cell to explore how irregular HECT-p53 interactions can induce tumorigenesis.
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Affiliation(s)
- Nicholas A Mathieu
- Gustaf H. Carlson School of Chemistry and Biochemistry, Clark University, Worcester, MA, United States
| | - Rafael H Levin
- Gustaf H. Carlson School of Chemistry and Biochemistry, Clark University, Worcester, MA, United States
| | - Donald E Spratt
- Gustaf H. Carlson School of Chemistry and Biochemistry, Clark University, Worcester, MA, United States
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7
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The HECT E3 Ligase E6AP/UBE3A as a Therapeutic Target in Cancer and Neurological Disorders. Cancers (Basel) 2020; 12:cancers12082108. [PMID: 32751183 PMCID: PMC7464832 DOI: 10.3390/cancers12082108] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2020] [Revised: 07/24/2020] [Accepted: 07/27/2020] [Indexed: 11/23/2022] Open
Abstract
The HECT (Homologous to the E6-AP Carboxyl Terminus)-family protein E6AP (E6-associated protein), encoded by the UBE3A gene, is a multifaceted ubiquitin ligase that controls diverse signaling pathways involved in cancer and neurological disorders. The oncogenic role of E6AP in papillomavirus-induced cancers is well known, with its action to trigger p53 degradation in complex with the E6 viral oncoprotein. However, the roles of E6AP in non-viral cancers remain poorly defined. It is well established that loss-of-function alterations of the UBE3A gene cause Angelman syndrome, a severe neurodevelopmental disorder with autosomal dominant inheritance modified by genomic imprinting on chromosome 15q. Moreover, excess dosage of the UBE3A gene markedly increases the penetrance of autism spectrum disorders, suggesting that the expression level of UBE3A must be regulated tightly within a physiologically tolerated range during brain development. In this review, current the knowledge about the substrates of E6AP-mediated ubiquitination and their functions in cancer and neurological disorders is discussed, alongside with the ongoing efforts to pharmacologically modulate this ubiquitin ligase as a promising therapeutic target.
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8
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Panov J, Simchi L, Feuermann Y, Kaphzan H. Bioinformatics Analyses of the Transcriptome Reveal Ube3a-Dependent Effects on Mitochondrial-Related Pathways. Int J Mol Sci 2020; 21:ijms21114156. [PMID: 32532103 PMCID: PMC7312912 DOI: 10.3390/ijms21114156] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2020] [Revised: 06/07/2020] [Accepted: 06/08/2020] [Indexed: 12/14/2022] Open
Abstract
The UBE3A gene encodes the ubiquitin E3-ligase protein, UBE3A, which is implicated in severe neurodevelopmental disorders. Lack of UBE3A expression results in Angelman syndrome, while UBE3A overexpression, due to genomic 15q duplication, results in autism. The cellular roles of UBE3A are not fully understood, yet a growing body of evidence indicates that these disorders involve mitochondrial dysfunction and increased oxidative stress. We utilized bioinformatics approaches to delineate the effects of murine Ube3a deletion on the expression of mitochondrial-related genes and pathways. For this, we generated an mRNA sequencing dataset from mouse embryonic fibroblasts (MEFs) in which both alleles of Ube3a gene were deleted and their wild-type controls. Since oxidative stress and mitochondrial dysregulation might not be exhibited in the resting baseline state, we also activated mitochondrial functioning in the cells of these two genotypes using TNFα application. Transcriptomes of the four groups of MEFs, Ube3a+/+ and Ube3a-/-, with or without the application of TNFα, were analyzed using various bioinformatics tools and machine learning approaches. Our results indicate that Ube3a deletion affects the gene expression profiles of mitochondrial-associated pathways. We further confirmed these results by analyzing other publicly available human transcriptome datasets of Angelman syndrome and 15q duplication syndrome.
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9
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Simchi L, Panov J, Morsy O, Feuermann Y, Kaphzan H. Novel Insights into the Role of UBE3A in Regulating Apoptosis and Proliferation. J Clin Med 2020; 9:jcm9051573. [PMID: 32455880 PMCID: PMC7290732 DOI: 10.3390/jcm9051573] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2020] [Revised: 05/05/2020] [Accepted: 05/17/2020] [Indexed: 12/13/2022] Open
Abstract
The UBE3A gene codes for a protein with two known functions, a ubiquitin E3-ligase which catalyzes ubiquitin binding to substrate proteins and a steroid hormone receptor coactivator. UBE3A is most famous for its critical role in neuronal functioning. Lack of UBE3A protein expression leads to Angelman syndrome (AS), while its overexpression is associated with autism. In spite of extensive research, our understanding of UBE3A roles is still limited. We investigated the cellular and molecular effects of Ube3a deletion in mouse embryonic fibroblasts (MEFs) and Angelman syndrome (AS) mouse model hippocampi. Cell cultures of MEFs exhibited enhanced proliferation together with reduced apoptosis when Ube3a was deleted. These findings were supported by transcriptome and proteome analyses. Furthermore, transcriptome analyses revealed alterations in mitochondria-related genes. Moreover, an analysis of adult AS model mice hippocampi also found alterations in the expression of apoptosis- and proliferation-associated genes. Our findings emphasize the role UBE3A plays in regulating proliferation and apoptosis and sheds light into the possible effects UBE3A has on mitochondrial involvement in governing this balance.
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10
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Ramirez J, Lectez B, Osinalde N, Sivá M, Elu N, Aloria K, Procházková M, Perez C, Martínez-Hernández J, Barrio R, Šašková KG, Arizmendi JM, Mayor U. Quantitative proteomics reveals neuronal ubiquitination of Rngo/Ddi1 and several proteasomal subunits by Ube3a, accounting for the complexity of Angelman syndrome. Hum Mol Genet 2019; 27:1955-1971. [PMID: 29788202 DOI: 10.1093/hmg/ddy103] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2018] [Accepted: 03/19/2018] [Indexed: 01/01/2023] Open
Abstract
Angelman syndrome is a complex neurodevelopmental disorder caused by the lack of function in the brain of a single gene, UBE3A. The E3 ligase coded by this gene is known to build K48-linked ubiquitin chains, a modification historically considered to target substrates for degradation by the proteasome. However, a change in protein abundance is not proof that a candidate UBE3A substrate is indeed ubiquitinated by UBE3A. We have here used an unbiased ubiquitin proteomics approach, the bioUb strategy, to identify 79 proteins that appear more ubiquitinated in the Drosophila photoreceptor cells when Ube3a is over-expressed. We found a significantly high number of those proteins to be proteasomal subunits or proteasome-interacting proteins, suggesting a wide proteasomal perturbation in the brain of Angelman patients. We focused on validating the ubiquitination by Ube3a of Rngo, a proteasomal component conserved from yeast (Ddi1) to humans (DDI1 and DDI2), but yet scarcely characterized. Ube3a-mediated Rngo ubiquitination in fly neurons was confirmed by immunoblotting. Using human neuroblastoma SH-SY5Y cells in culture, we also observed that human DDI1 is ubiquitinated by UBE3A, without being targeted for degradation. The novel observation that DDI1 is expressed in the developing mice brain, with a significant peak at E16.5, strongly suggests that DDI1 has biological functions not yet described that could be of relevance for Angelman syndrome clinical research.
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Affiliation(s)
- Juanma Ramirez
- Department of Biochemistry and Molecular Biology, Faculty of Science and Technology, University of the Basque Country (UPV/EHU), 48940 Leioa, Spain
| | - Benoit Lectez
- Department of Biochemistry and Molecular Biology, Faculty of Science and Technology, University of the Basque Country (UPV/EHU), 48940 Leioa, Spain
| | - Nerea Osinalde
- Department of Biochemistry and Molecular Biology, Faculty of Pharmacy (UPV/EHU), 01006 Vitoria-Gasteiz, Spain
| | - Monika Sivá
- Department of Genetics and Microbiology, Charles University, 12843 Prague, Czech Republic.,Institute of Organic Chemistry and Biochemistry of the Czech Academy of Sciences, 16610 Prague, Czech Republic.,First Faculty of Medicine, Charles University, 12108 Prague, Czech Republic
| | - Nagore Elu
- Department of Biochemistry and Molecular Biology, Faculty of Science and Technology, University of the Basque Country (UPV/EHU), 48940 Leioa, Spain
| | - Kerman Aloria
- Proteomics Core Facility-SGIKER, University of the Basque Country (UPV/EHU), 48940 Leioa, Spain
| | - Michaela Procházková
- Czech Centre for Phenogenomics and Laboratory of Transgenic Models of Diseases, Division BIOCEV, Institute of Molecular Genetics of the Czech Academy of Sciences, Vestec, Czech Republic
| | - Coralia Perez
- Functional Genomics Unit, CIC bioGUNE, 48160 Derio, Spain
| | - Jose Martínez-Hernández
- Department of Biochemistry and Molecular Biology, Faculty of Science and Technology, University of the Basque Country (UPV/EHU), 48940 Leioa, Spain.,Ikerbasque, Basque Foundation for Science, 48013 Bilbao, Spain
| | - Rosa Barrio
- Functional Genomics Unit, CIC bioGUNE, 48160 Derio, Spain
| | - Klára Grantz Šašková
- Department of Genetics and Microbiology, Charles University, 12843 Prague, Czech Republic.,Institute of Organic Chemistry and Biochemistry of the Czech Academy of Sciences, 16610 Prague, Czech Republic
| | - Jesus M Arizmendi
- Department of Biochemistry and Molecular Biology, Faculty of Science and Technology, University of the Basque Country (UPV/EHU), 48940 Leioa, Spain
| | - Ugo Mayor
- Department of Biochemistry and Molecular Biology, Faculty of Science and Technology, University of the Basque Country (UPV/EHU), 48940 Leioa, Spain.,Ikerbasque, Basque Foundation for Science, 48013 Bilbao, Spain
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11
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Structural dynamics of the E6AP/UBE3A-E6-p53 enzyme-substrate complex. Nat Commun 2018; 9:4441. [PMID: 30361475 PMCID: PMC6202321 DOI: 10.1038/s41467-018-06953-0] [Citation(s) in RCA: 50] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2018] [Accepted: 09/05/2018] [Indexed: 12/21/2022] Open
Abstract
Deregulation of the ubiquitin ligase E6AP is causally linked to the development of human disease, including cervical cancer. In complex with the E6 oncoprotein of human papillomaviruses, E6AP targets the tumor suppressor p53 for degradation, thereby contributing to carcinogenesis. Moreover, E6 acts as a potent activator of E6AP by a yet unknown mechanism. However, structural information explaining how the E6AP-E6-p53 enzyme-substrate complex is assembled, and how E6 stimulates E6AP, is largely missing. Here, we develop and apply different crosslinking mass spectrometry-based approaches to study the E6AP-E6-p53 interplay. We show that binding of E6 induces conformational rearrangements in E6AP, thereby positioning E6 and p53 in the immediate vicinity of the catalytic center of E6AP. Our data provide structural and functional insights into the dynamics of the full-length E6AP-E6-p53 enzyme-substrate complex, demonstrating how E6 can stimulate the ubiquitin ligase activity of E6AP while facilitating ubiquitin transfer from E6AP onto p53.
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12
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Lan W, Li M, Zhao K, Liu J, Wu FX, Pan Y, Wang J. LDAP: a web server for lncRNA-disease association prediction. Bioinformatics 2018; 33:458-460. [PMID: 28172495 DOI: 10.1093/bioinformatics/btw639] [Citation(s) in RCA: 87] [Impact Index Per Article: 14.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2016] [Revised: 09/21/2016] [Accepted: 10/03/2016] [Indexed: 11/12/2022] Open
Abstract
Motivation Increasing evidences have demonstrated that long noncoding RNAs (lncRNAs) play important roles in many human diseases. Therefore, predicting novel lncRNA-disease associations would contribute to dissect the complex mechanisms of disease pathogenesis. Some computational methods have been developed to infer lncRNA-disease associations. However, most of these methods infer lncRNA-disease associations only based on single data resource. Results In this paper, we propose a new computational method to predict lncRNA-disease associations by integrating multiple biological data resources. Then, we implement this method as a web server for lncRNA-disease association prediction (LDAP). The input of the LDAP server is the lncRNA sequence. The LDAP predicts potential lncRNA-disease associations by using a bagging SVM classifier based on lncRNA similarity and disease similarity. Availability and Implementation The web server is available at http://bioinformatics.csu.edu.cn/ldap Contact jxwang@mail.csu.edu.cn. Supplimentary Information Supplementary data are available at Bioinformatics online.
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Affiliation(s)
- Wei Lan
- School of Information Science and Engineering, Central South University, Changsha, China
| | - Min Li
- School of Information Science and Engineering, Central South University, Changsha, China
| | - Kaijie Zhao
- School of Information Science and Engineering, Central South University, Changsha, China
| | - Jin Liu
- School of Information Science and Engineering, Central South University, Changsha, China
| | - Fang-Xiang Wu
- Division of Biomedical Engineering, University of Saskatchewan, Saskatoon, Canada
| | - Yi Pan
- Department of Computer Science, Georgia State University, Atlanta, GA, USA
| | - Jianxin Wang
- School of Information Science and Engineering, Central South University, Changsha, China
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13
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Gulati T, Huang C, Caramia F, Raghu D, Paul PJ, Goode RJA, Keam SP, Williams SG, Haupt S, Kleifeld O, Schittenhelm RB, Gamell C, Haupt Y. Proteotranscriptomic Measurements of E6-Associated Protein (E6AP) Targets in DU145 Prostate Cancer Cells. Mol Cell Proteomics 2018; 17:1170-1183. [PMID: 29463595 DOI: 10.1074/mcp.ra117.000504] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2017] [Revised: 02/18/2018] [Indexed: 11/06/2022] Open
Abstract
Prostate cancer is a common cause of cancer-related death in men. E6AP (E6-Associated Protein), an E3 ubiquitin ligase and a transcription cofactor, is elevated in a subset of prostate cancer patients. Genetic manipulations of E6AP in prostate cancer cells expose a role of E6AP in promoting growth and survival of prostate cancer cells in vitro and in vivo However, the effect of E6AP on prostate cancer cells is broad and it cannot be explained fully by previously identified tumor suppressor targets of E6AP, promyelocytic leukemia protein and p27. To explore additional players that are regulated downstream of E6AP, we combined a transcriptomic and proteomic approach. We identified and quantified 16,130 transcripts and 7,209 proteins in castration resistant prostate cancer cell line, DU145. A total of 2,763 transcripts and 308 proteins were significantly altered on knockdown of E6AP. Pathway analyses supported the known phenotypic effects of E6AP knockdown in prostate cancer cells and in parallel exposed novel potential links of E6AP with cancer metabolism, DNA damage repair and immune response. Changes in expression of the top candidates were confirmed using real-time polymerase chain reaction. Of these, clusterin, a stress-induced chaperone protein, commonly deregulated in prostate cancer, was pursued further. Knockdown of E6AP resulted in increased clusterin transcript and protein levels in vitro and in vivo Concomitant knockdown of E6AP and clusterin supported the contribution of clusterin to the phenotype induced by E6AP. Overall, results from this study provide insight into the potential biological pathways controlled by E6AP in prostate cancer cells and identifies clusterin as a novel target of E6AP.
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Affiliation(s)
- Twishi Gulati
- From the ‡The Sir Peter MacCallum Department of Oncology, The University of Melbourne, Victoria, Australia.,§Tumor Suppression Laboratory, Peter MacCallum Cancer Centre, Melbourne, Victoria, Australia
| | - Cheng Huang
- ¶Monash Biomedical Proteomics Facility, Biomedicine Discovery Institute and Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria, Australia
| | - Franco Caramia
- §Tumor Suppression Laboratory, Peter MacCallum Cancer Centre, Melbourne, Victoria, Australia
| | - Dinesh Raghu
- From the ‡The Sir Peter MacCallum Department of Oncology, The University of Melbourne, Victoria, Australia.,§Tumor Suppression Laboratory, Peter MacCallum Cancer Centre, Melbourne, Victoria, Australia
| | - Piotr J Paul
- From the ‡The Sir Peter MacCallum Department of Oncology, The University of Melbourne, Victoria, Australia.,§Tumor Suppression Laboratory, Peter MacCallum Cancer Centre, Melbourne, Victoria, Australia
| | - Robert J A Goode
- ¶Monash Biomedical Proteomics Facility, Biomedicine Discovery Institute and Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria, Australia
| | - Simon P Keam
- §Tumor Suppression Laboratory, Peter MacCallum Cancer Centre, Melbourne, Victoria, Australia
| | - Scott G Williams
- ‖Division of Radiation Oncology and Cancer Imaging, Peter MacCallum Cancer Centre, Melbourne, Victoria, Australia
| | - Sue Haupt
- From the ‡The Sir Peter MacCallum Department of Oncology, The University of Melbourne, Victoria, Australia.,§Tumor Suppression Laboratory, Peter MacCallum Cancer Centre, Melbourne, Victoria, Australia
| | - Oded Kleifeld
- **Department of Biology, Technion-Israel Institute of Technology, Haifa, Israel
| | - Ralf B Schittenhelm
- ¶Monash Biomedical Proteomics Facility, Biomedicine Discovery Institute and Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria, Australia
| | - Cristina Gamell
- From the ‡The Sir Peter MacCallum Department of Oncology, The University of Melbourne, Victoria, Australia.,§Tumor Suppression Laboratory, Peter MacCallum Cancer Centre, Melbourne, Victoria, Australia
| | - Ygal Haupt
- From the ‡The Sir Peter MacCallum Department of Oncology, The University of Melbourne, Victoria, Australia; .,§Tumor Suppression Laboratory, Peter MacCallum Cancer Centre, Melbourne, Victoria, Australia.,‡‡Division of Radiation Oncology and Cancer Imaging, Peter MacCallum Cancer Centre, Melbourne, Victoria, Australia.,§§Department of Biochemistry and Molecular Biology, Monash University, Melbourne, Victoria, Australia.,¶¶Department of Pathology, The University of Melbourne, Melbourne, Victoria, Australia
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Relation among Aromatase P450 and Tumoral Growth in Human Prolactinomas. Int J Mol Sci 2017; 18:ijms18112299. [PMID: 29104246 PMCID: PMC5713269 DOI: 10.3390/ijms18112299] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2017] [Revised: 10/25/2017] [Accepted: 10/27/2017] [Indexed: 02/01/2023] Open
Abstract
The pituitary gland is part of hypothalamic-pituitary–gonadal axis, which controls development, reproduction, and aging in humans and animals. In addition, the pituitary gland is regulated mainly by hormones and neurotransmitters released from the hypothalamus and by systemic hormones secreted by target glands. Aromatase P450, the enzyme responsible for the catabolization of aromatizable androgens to estrogens, is expressed in different parts of body, including the pituitary gland. Moreover, aromatase P450 is involved in sexual dimorphism where alteration in the level of aromatase can initiate a number of diseases in both genders. On the other hand, the direct actions of estrogens, mainly estradiol, are well known for stimulating prolactin release. Numerous studies have shown that changes in the levels of estrogens, among other factors, have been implicated in the genesis and development of prolactinoma. The pituitary gland can produce estradiol locally in several types of endocrine cells, and it is possible that aromatase could be responsible for the maintenance of the population of lactotroph cells and the modulation of the action of central or peripheral regulators. Aromatase overexpression due to inappropriate gene regulation has clinical effects such as the pathogenesis of prolactinomas. The present study reports on the synthesis of pituitary aromatase, its regulation by gonadal steroids, and the physiological roles of aromatase on pituitary endocrine cells. The involvement of aromatase in the pathogenesis of pituitary tumors, mainly prolactinomas, through the auto-paracrine production of estradiol is reviewed.
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15
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Monogenic mouse models of autism spectrum disorders: Common mechanisms and missing links. Neuroscience 2015; 321:3-23. [PMID: 26733386 DOI: 10.1016/j.neuroscience.2015.12.040] [Citation(s) in RCA: 53] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2015] [Revised: 11/30/2015] [Accepted: 12/22/2015] [Indexed: 01/16/2023]
Abstract
Autism spectrum disorders (ASDs) present unique challenges in the fields of genetics and neurobiology because of the clinical and molecular heterogeneity underlying these disorders. Genetic mutations found in ASD patients provide opportunities to dissect the molecular and circuit mechanisms underlying autistic behaviors using animal models. Ongoing studies of genetically modified models have offered critical insight into possible common mechanisms arising from different mutations, but links between molecular abnormalities and behavioral phenotypes remain elusive. The challenges encountered in modeling autism in mice demand a new analytic paradigm that integrates behavioral assessment with circuit-level analysis in genetically modified models with strong construct validity.
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Upadhyay A, Amanullah A, Chhangani D, Mishra R, Mishra A. Selective multifaceted E3 ubiquitin ligases barricade extreme defense: Potential therapeutic targets for neurodegeneration and ageing. Ageing Res Rev 2015; 24:138-59. [PMID: 26247845 DOI: 10.1016/j.arr.2015.07.009] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2015] [Revised: 06/24/2015] [Accepted: 07/30/2015] [Indexed: 12/24/2022]
Abstract
Efficient and regular performance of Ubiquitin Proteasome System and Autophagy continuously eliminate deleterious accumulation of nonnative protiens. In cellular quality control system, E3 ubiquitin ligases are significant employees for defense mechanism against abnormal toxic proteins. Few findings indicate that lack of functions of E3 ubiquitin ligases can be a causative factor of neurodevelopmental disorders, neurodegeneration, cancer and ageing. However, the detailed molecular pathomechanism implying E3 ubiquitin ligases in cellular functions in multifactorial disease conditions are not well understood. This article systematically represents the unique characteristics, molecular nature, and recent developments in the knowledge of neurobiological functions of few crucial E3 ubiquitin ligases. Here, we review recent literature on the roles of E6-AP, HRD1 and ITCH E3 ubiquitin ligases in the neuro-pathobiological mechanisms, with precise focus on the processes of neurodegeneration, and thereby propose new lines of potential targets for therapeutic interventions.
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Szwarc MM, Lydon JP, O'Malley BW. Steroid receptor coactivators as therapeutic targets in the female reproductive system. J Steroid Biochem Mol Biol 2015; 154:32-8. [PMID: 26151740 PMCID: PMC5201167 DOI: 10.1016/j.jsbmb.2015.06.010] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/02/2015] [Revised: 06/15/2015] [Accepted: 06/16/2015] [Indexed: 11/25/2022]
Abstract
The steroid receptor coactivators (SRCs/p160/NCOA) are a family of three transcriptional coregulators initially discovered to transactivate the transcriptional potency of steroid hormone receptors. Even though SRCs were also found to modulate the activity of multiple other transcription factors, their function is still strongly associated with regulation of steroid hormone action and many studies have found that they are critical for the regulation of reproductive biology. In the case of the female reproductive tract, SRCs have been found to play crucial roles in its physiology, ranging from ovulation, implantation, to parturition. Not surprisingly, SRCs' action has been linked to numerous abnormalities and debilitating disorders of female reproductive tissues, including infertility, cancer, and endometriosis. Many of these pathologies are still in critical need of therapeutic intervention and "proof-of-principle" studies have found that SRCs are excellent targets in pathological states. Therefore, small molecule modulators of SRCs' activity could be applied in the future in the treatment of many diseases of the female reproductive system.
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Affiliation(s)
- Maria M Szwarc
- Department of Molecular and Cellular Biology, Baylor College of Medicine, One Baylor Plaza, Houston, TX, USA
| | - John P Lydon
- Department of Molecular and Cellular Biology, Baylor College of Medicine, One Baylor Plaza, Houston, TX, USA
| | - Bert W O'Malley
- Department of Molecular and Cellular Biology, Baylor College of Medicine, One Baylor Plaza, Houston, TX, USA.
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18
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Szwarc MM, Lydon JP, O'Malley BW. Reprint of "Steroid receptor coactivators as therapeutic targets in the female reproductive system". J Steroid Biochem Mol Biol 2015; 153:144-50. [PMID: 26291832 DOI: 10.1016/j.jsbmb.2015.08.012] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/02/2015] [Revised: 06/15/2015] [Accepted: 06/16/2015] [Indexed: 11/22/2022]
Abstract
The steroid receptor coactivators (SRCs/p160/NCOA) are a family of three transcriptional coregulators initially discovered to transactivate the transcriptional potency of steroid hormone receptors. Even though SRCs were also found to modulate the activity of multiple other transcription factors, their function is still strongly associated with regulation of steroid hormone action and many studies have found that they are critical for the regulation of reproductive biology. In the case of the female reproductive tract, SRCs have been found to play crucial roles in its physiology, ranging from ovulation, implantation, to parturition. Not surprisingly, SRCs' action has been linked to numerous abnormalities and debilitating disorders of female reproductive tissues, including infertility, cancer, and endometriosis. Many of these pathologies are still in critical need of therapeutic intervention and "proof-of-principle" studies have found that SRCs are excellent targets in pathological states. Therefore, small molecule modulators of SRCs' activity could be applied in the future in the treatment of many diseases of the female reproductive system.
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Affiliation(s)
- Maria M Szwarc
- Department of Molecular and Cellular Biology, Baylor College of Medicine, One Baylor Plaza, Houston, TX, USA
| | - John P Lydon
- Department of Molecular and Cellular Biology, Baylor College of Medicine, One Baylor Plaza, Houston, TX, USA
| | - Bert W O'Malley
- Department of Molecular and Cellular Biology, Baylor College of Medicine, One Baylor Plaza, Houston, TX, USA.
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Angelman syndrome-associated ubiquitin ligase UBE3A/E6AP mutants interfere with the proteolytic activity of the proteasome. Cell Death Dis 2015; 6:e1625. [PMID: 25633294 PMCID: PMC4669770 DOI: 10.1038/cddis.2014.572] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2014] [Revised: 11/25/2014] [Accepted: 11/26/2014] [Indexed: 11/08/2022]
Abstract
Angelman syndrome, a severe neurodevelopmental disease, occurs primarily due to genetic defects, which cause lack of expression or mutations in the wild-type E6AP/UBE3A protein. A proportion of the Angelman syndrome patients bear UBE3A point mutations, which do not interfere with the expression of the full-length protein, however, these individuals still develop physiological conditions of the disease. Interestingly, most of these mutations are catalytically defective, thereby indicating the importance of UBE3A enzymatic activity role in the Angelman syndrome pathology. In this study, we show that Angelman syndrome-associated mutants interact strongly with the proteasome via the S5a proteasomal subunit, resulting in an overall inhibitory effect on the proteolytic activity of the proteasome. Our results suggest that mutated catalytically inactive forms of UBE3A may cause defects in overall proteasome function, which could have an important role in the Angelman syndrome pathology.
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20
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Zhou W, Slingerland JM. Links between oestrogen receptor activation and proteolysis: relevance to hormone-regulated cancer therapy. Nat Rev Cancer 2014; 14:26-38. [PMID: 24505618 DOI: 10.1038/nrc3622] [Citation(s) in RCA: 112] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Oestrogen receptor-α (ERα) is a master transcription factor that regulates cell proliferation and homeostasis in many tissues. Despite beneficial ERα functions, sustained oestrogenic exposure increases the risk and/or the progression of various cancers, including those of the breast, endometrium and ovary. Oestrogen–ERα interaction can trigger post-translational ERα modifications through crosstalk with signalling pathways to promote transcriptional activation and ubiquitin-mediated ERα proteolysis, with co-activators that have dual roles as ubiquitin ligases. These processes are reviewed herein. The elucidation of mechanisms whereby oestrogen drives both ERα transactivation and receptor proteolysis might have important therapeutic implications not only for breast cancer but also potentially for other hormone-regulated cancers.
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21
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E6AP in the brain: one protein, dual function, multiple diseases. Mol Neurobiol 2013; 49:827-39. [PMID: 24091829 DOI: 10.1007/s12035-013-8563-y] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2013] [Accepted: 09/22/2013] [Indexed: 02/06/2023]
Abstract
E6-Associated Protein (E6AP), the founding member of the HECT (Homologus to E6AP C terminus) family of ubiquitin ligases, has been gaining increased attention from the scientific community. In addition to its ubiquitin ligase function, our laboratory has also identified steroid hormone receptor transcriptional coactivation as yet another essential function of this protein. Furthermore, it has been established that E6AP has a role in numerous diseases including cancers and neurological syndromes. In this review, we delineate genetic and biochemical knowledge of E6AP and we focus on its role in the pathobiology of neuro-developmental and neuro-aging diseases; bringing to light important gaps of knowledge related to the involvement of its well-studied ligase function versus the much less studied nuclear receptor transcriptional coactivation function in the pathogenesis of these diseases. Tackling these gaps of knowledge could reveal novel possible neuro-pathobiological mechanisms and present crucial information for the design of effective treatment modalities for devastating CNS diseases.
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22
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Role of the ubiquitin ligase E6AP/UBE3A in controlling levels of the synaptic protein Arc. Proc Natl Acad Sci U S A 2013; 110:8888-93. [PMID: 23671107 DOI: 10.1073/pnas.1302792110] [Citation(s) in RCA: 98] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Inactivation of the ubiquitin ligase E6 associated protein (E6AP) encoded by the UBE3A gene has been associated with development of the Angelman syndrome. Recently, it was reported that in mice, loss of E6AP expression results in increased levels of the synaptic protein Arc and a concomitant impaired synaptic function, providing an explanation for some phenotypic features of Angelman syndrome patients. Accordingly, E6AP has been shown to negatively regulate activity-regulated cytoskeleton-associated protein (Arc) and it has been suggested that E6AP targets Arc for ubiquitination and degradation. In our study, we provide evidence that Arc is not a direct substrate for E6AP and binds only weakly to E6AP, if at all. Furthermore, we show that down-regulation of E6AP expression stimulates estradiol-induced transcription of the Arc gene. Thus, we propose that Arc protein levels are controlled by E6AP at the transcriptional rather than at the posttranslational level.
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23
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Li JV, Chien CD, Garee JP, Xu J, Wellstein A, Riegel AT. Transcriptional repression of AIB1 by FoxG1 leads to apoptosis in breast cancer cells. Mol Endocrinol 2013; 27:1113-27. [PMID: 23660594 DOI: 10.1210/me.2012-1353] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
The oncogene nuclear receptor coactivator amplified in breast cancer 1 (AIB1) is a transcriptional coactivator that is overexpressed in various types of human cancers. However, the molecular mechanisms controlling AIB1 expression in the majority of cancers remain unclear. In this study, we identified a novel interacting protein of AIB1, forkhead-box protein G1 (FoxG1), which is an evolutionarily conserved forkhead-box transcriptional corepressor. We show that FoxG1 expression is low in breast cancer cell lines and that low levels of FoxG1 are correlated with a worse prognosis in breast cancer. We also demonstrate that transient overexpression of FoxG1 can suppress endogenous levels of AIB1 mRNA and protein in MCF-7 breast cancer cells. Exogenously expressed FoxG1 in MCF-7 cells also leads to apoptosis that can be rescued in part by AIB1 overexpression. Using chromatin immunoprecipitation, we determined that FoxG1 is recruited to a region of the AIB1 gene promoter previously characterized to be responsible for AIB1-induced, positive autoregulation of transcription through the recruitment of an activating, multiprotein complex, involving AIB1, E2F transcription factor 1, and specificity protein 1. Increased FoxG1 expression significantly reduces the recruitment of AIB1, E2F transcription factor 1 and E1A-binding protein p300 to this region of the endogenous AIB1 gene promoter. Our data imply that FoxG1 can function as a pro-apoptotic factor in part through suppression of AIB1 coactivator transcription complex formation, thereby reducing the expression of the AIB1 oncogene.
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Affiliation(s)
- Jordan V Li
- Department of Pharmacology, Lombardi Cancer Center, Georgetown University, Research Building E307, 3970 Reservoir Road Northwest, Washington, DC 20007-2197, USA
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E6AP, an E3 ubiquitin ligase negatively regulates granulopoiesis by targeting transcription factor C/EBPα for ubiquitin-mediated proteasome degradation. Cell Death Dis 2013; 4:e590. [PMID: 23598402 PMCID: PMC3641343 DOI: 10.1038/cddis.2013.120] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
CCAAT/enhancer-binding protein alpha (C/EBPα) is an important transcription factor involved in granulocytic differentiation. Here, for the first time we demonstrate that E6-associated protein (E6AP), an E3 ubiquitin ligase targets C/EBPα for ubiquitin-mediated proteasome degradation and thereby negatively modulates its functions. Wild-type E6AP promotes ubiquitin dependent proteasome degradation of C/EBPα, while catalytically inactive E6-associated protein having cysteine replaced with alanine at amino-acid position 843 (E6AP-C843A) rather stabilizes it. Further, these two proteins physically associate both in non-myeloid (overexpressed human embryonic kidney epithelium) and myeloid cells. We show that E6AP-mediated degradation of C/EBPα protein expression curtails its transactivation potential on its target genes. Noticeably, E6AP degrades both wild-type 42 kDa CCAAT-enhancer-binding protein alpha (p42C/EBPα) and mutant isoform 30 kDa CCAAT-enhancer-binding protein alpha (p30C/EBPα), this may explain perturbed p42C/EBPα/p30C/EBPα ratio often observed in acute myeloid leukemia (AML). We show that overexpression of catalytically inactive E6AP-C843A in C/EBPα inducible K562- p42C/EBPα-estrogen receptor (ER) cells inhibits β-estradiol (E2)-induced C/EBPα degradation leading to enhanced granulocytic differentiation. This enhanced granulocytic differentiation upon E2-induced activation of C/EBPα in C/EBPα stably transfected cells (β-estradiol inducible K562 cells stably expressing p42C/EBPα-ER (K562-C/EBPα-p42-ER)) was further substantiated by siE6AP-mediated knockdown of E6AP in both K562-C/EBPα-p42-ER and 32dcl3 (32D clone 3, a cell line widely used model for in vitro study of hematopoietic cell proliferation, differentiation, and apoptosis) cells. Taken together, our data suggest that E6AP targeted C/EBPα protein degradation may provide a possible explanation for both loss of expression and/or functional inactivation of C/EBPα often experienced in myeloid leukemia.
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Scheffner M, Kumar S. Mammalian HECT ubiquitin-protein ligases: biological and pathophysiological aspects. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2013; 1843:61-74. [PMID: 23545411 DOI: 10.1016/j.bbamcr.2013.03.024] [Citation(s) in RCA: 217] [Impact Index Per Article: 19.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/07/2012] [Revised: 02/18/2013] [Accepted: 03/22/2013] [Indexed: 10/27/2022]
Abstract
Members of the HECT family of E3 ubiquitin-protein ligases are characterized by a C-terminal HECT domain that catalyzes the covalent attachment of ubiquitin to substrate proteins and by N-terminal extensions of variable length and domain architecture that determine the substrate spectrum of a respective HECT E3. Since their discovery in 1995, it has become clear that deregulation of distinct HECT E3s plays an eminent role in human disease or disease-related processes including cancer, cardiovascular and neurological disorders, viral infections, and immune response. Thus, a detailed understanding of the structure-function aspects of HECT E3s as well as the identification and characterization of the substrates and regulators of HECT E3s is critical in developing new approaches in the treatment of respective diseases. In this review, we summarize what is currently known about mammalian HECT E3s, with a focus on their biological functions and roles in pathophysiology.This article is part of a Special Issue entitled: Ubiquitin-Proteasome System. Guest Editors: Thomas Sommer and Dieter H. Wolf.
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Affiliation(s)
- Martin Scheffner
- Department of Biology, Konstanz Research School Chemical Biology, University of Konstanz, Konstanz, Germany.
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PTEN suppresses the oncogenic function of AIB1 through decreasing its protein stability via mechanism involving Fbw7 alpha. Mol Cancer 2013; 12:21. [PMID: 23514585 PMCID: PMC3610140 DOI: 10.1186/1476-4598-12-21] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2012] [Accepted: 03/17/2013] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Phosphatase and tensin homologue deleted on chromosome 10 (PTEN) is a phosphatase having both protein and lipid phosphatase activities, and is known to antagonize the phosphoinositide 3-kinase/AKT (PI3K/AKT) signaling pathway, resulting in tumor suppression. PTEN is also known to play a role in the regulation of numerous transcription factors. Amplified in breast cancer 1 (AIB1) is a transcriptional coactivator that mediates the transcriptional activities of nuclear receptors and other transcription factors. The present study investigated how PTEN may regulate AIB1, which is amplified and/or overexpressed in many human carcinomas, including breast cancers. RESULTS PTEN interacted with AIB1 via its phophatase domain and regulated the transcriptional activity of AIB1 by enhancing the ubiquitin-mediated degradation of AIB1. This process did not appear to require the phosphatase activity of PTEN, but instead, involved the interaction between PTEN and F-box and WD repeat domain-containing 7 alpha (Fbw7α), the E3 ubiquitin ligase involved in the ubiquitination of AIB1. PTEN interacted with Fbw7α via its C2 domain, thereby acting as a bridge between AIB1 and Fbw7α, and this led to enhanced degradation of AIB1, which eventually accounted for its decreased transcriptional activity. At the cell level, knockdown of PTEN in MCF-7 cells promoted cell proliferation. However when AIB1 was also knocked down, knockdown of PTEN had no effect on cell proliferation. CONCLUSIONS PTEN might act as a negative regulator of AIB1 whereby the association of PTEN with both AIB1 and Fbw7α could lead to the downregulation of AIB1 transcriptional activity, with the consequence of regulating the oncogenic function of AIB1.
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Lochab S, Pal P, Kanaujiya JK, Tripathi SB, Kapoor I, Bhatt MLB, Sanyal S, Behre G, Trivedi AK. Proteomic identification of E6AP as a molecular target of tamoxifen in MCF7 cells. Proteomics 2012; 12:1363-77. [PMID: 22589186 DOI: 10.1002/pmic.201100572] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Tamoxifen (Tam) is most widely used selective estrogen receptor modulator (SERM) for treatment of hormone-responsive breast cancer. Despite being regularly used in clinical therapy for breast cancer since 1971, the mechanism of Tam action remains largely unclear. In order to gain insights into Tam-mediated antibreast cancer actions, we applied 2DE and MS based proteomics approach to identify target proteins of Tam. We identified E6-associated protein, i.e. E6AP (UBE3A) among others to be regulated by Tam that otherwise is upregulated in breast tumors. We confirmed our 2DE finding by immunoblotting and further show that Tam leads to inhibition of E6AP expression presumably by promoting its autoubiquitination, which is coupled with nuclear export and subsequent proteasome-mediated degradation. Furthermore, we show that Tam- and siE6AP-mediated inhibition of E6AP leads to enhanced G0-G1 growth arrest and apoptosis, which is also evident from significant upregulation of cytochrome-c, Bax, p21, and PARP cleavage. Taken together, our data suggest that, Tam-targeted E6AP inhibition is in fact required for Tam-mediated antibreast cancer actions. Thus, E6AP may be a therapeutic target in breast cancer.
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Affiliation(s)
- Savita Lochab
- DTDD Division, CSIR-Central Drug Research Institute, Lucknow, Uttar Pradesh, India
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Tien JCY, Xu J. Steroid receptor coactivator-3 as a potential molecular target for cancer therapy. Expert Opin Ther Targets 2012; 16:1085-96. [PMID: 22924430 DOI: 10.1517/14728222.2012.718330] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
INTRODUCTION Steroid receptor coactivator-3 (SRC-3), also called amplified-in-breast cancer-1 (AIB1), is an oncogenic coactivator in endocrine and non-endocrine cancers. Functional studies demonstrate SRC-3 promotes numerous aspects of cancer, through its capacity as a coactivator for nuclear hormone receptors and other transcription factors, and via its ability to control multiple growth pathways simultaneously. Targeting SRC-3 with specific inhibitors therefore holds future promise for clinical cancer therapy. AREAS COVERED We discuss critical advances in understanding SRC-3 as a cancer mediator and prospective drug target. We review SRC-3 structure and function and its role in distinct aspects of cancer. In addition, we discuss SRC-3 regulation and degradation. Finally, we comment on a recently discovered SRC-3 small molecular inhibitor. EXPERT OPINION Most targeted chemotherapeutic drugs block only a single cellular pathway. In response, cancers frequently acquire resistance by upregulating alternative pathways. SRC-3 coordinates multiple signaling networks, suggesting SRC-3 inhibition offers a promising therapeutic strategy. Development of an effective SRC-3 inhibitor faces critical challenges. Better understanding of SRC-3 function and interacting partners, in both the nucleus and cytosol, is required for optimized inhibitor development. Ultimately, blockade of SRC-3 oncogenic function may inhibit multiple cancer-related signaling pathways.
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Affiliation(s)
- Jean Ching-Yi Tien
- Baylor College of Medicine, Department of Molecular and Cellular Biology, One Baylor Plaza, Houston, TX 77030, USA
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Ferrero M, Ferragud J, Orlando L, Valero L, Sánchez del Pino M, Farràs R, Font de Mora J. Phosphorylation of AIB1 at mitosis is regulated by CDK1/CYCLIN B. PLoS One 2011; 6:e28602. [PMID: 22163316 PMCID: PMC3233587 DOI: 10.1371/journal.pone.0028602] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2011] [Accepted: 11/11/2011] [Indexed: 11/25/2022] Open
Abstract
Background Although the AIB1 oncogene has an important role during the early phase of the cell cycle as a coactivator of E2F1, little is known about its function during mitosis. Methodology/Principal Findings Mitotic cells isolated by nocodazole treatment as well as by shake-off revealed a post-translational modification occurring in AIB1 specifically during mitosis. This modification was sensitive to the treatment with phosphatase, suggesting its modification by phosphorylation. Using specific inhibitors and in vitro kinase assays we demonstrate that AIB1 is phosphorylated on Ser728 and Ser867 by Cdk1/cyclin B at the onset of mitosis and remains phosphorylated until exit from M phase. Differences in the sensitivity to phosphatase inhibitors suggest that PP1 mediates dephosphorylation of AIB1 at the end of mitosis. The phosphorylation of AIB1 during mitosis was not associated with ubiquitylation or degradation, as confirmed by western blotting and flow cytometry analysis. In addition, luciferase reporter assays showed that this phosphorylation did not alter the transcriptional properties of AIB1. Importantly, fluorescence microscopy and sub-cellular fractionation showed that AIB1 phosphorylation correlated with the exclusion from the condensed chromatin, thus preventing access to the promoters of AIB1-dependent genes. Phospho-specific antibodies developed against Ser728 further demonstrated the presence of phosphorylated AIB1 only in mitotic cells where it was localized preferentially in the periphery of the cell. Conclusions Collectively, our results describe a new mechanism for the regulation of AIB1 during mitosis, whereby phosphorylation of AIB1 by Cdk1 correlates with the subcellular redistribution of AIB1 from a chromatin-associated state in interphase to a more peripheral localization during mitosis. At the exit of mitosis, AIB1 is dephosphorylated, presumably by PP1. This exclusion from chromatin during mitosis may represent a mechanism for governing the transcriptional activity of AIB1.
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Affiliation(s)
- Macarena Ferrero
- Laboratory of Cellular and Molecular Biology, Centro de Investigación Príncipe Felipe (CIPF), Valencia, Spain
| | - Juan Ferragud
- Laboratory of Cellular and Molecular Biology, Centro de Investigación Príncipe Felipe (CIPF), Valencia, Spain
| | - Leonardo Orlando
- Laboratory of Cellular and Molecular Biology, Centro de Investigación Príncipe Felipe (CIPF), Valencia, Spain
| | - Luz Valero
- Laboratory of Proteomics, CIPF, Valencia, Spain
| | | | - Rosa Farràs
- Laboratory of Cytomics, CIPF, Valencia, Spain
| | - Jaime Font de Mora
- Laboratory of Cellular and Molecular Biology, Centro de Investigación Príncipe Felipe (CIPF), Valencia, Spain
- * E-mail:
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Cullin 3 mediates SRC-3 ubiquitination and degradation to control the retinoic acid response. Proc Natl Acad Sci U S A 2011; 108:20603-8. [PMID: 22147914 DOI: 10.1073/pnas.1102572108] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
SRC-3 is an important coactivator of nuclear receptors including the retinoic acid (RA) receptor α. Most of SRC-3 functions are facilitated by changes in the posttranslational code of the protein that involves mainly phosphorylation and ubiquitination. We recently reported that SRC-3 is degraded by the proteasome in response to RA. Here, by using an RNAi E3-ubiquitin ligase entry screen, we identified CUL-3 and RBX1 as components of the E3 ubiquitin ligase involved in the RA-induced ubiquitination and subsequent degradation of SRC-3. We also show that the RA-induced ubiquitination of SRC-3 depends on its prior phosphorylation at serine 860 that promotes binding of the CUL-3-based E3 ligase in the nucleus. Finally, phosphorylation, ubiquitination, and degradation of SRC-3 cooperate to control the dynamics of transcription. In all, this process participates to the antiproliferative effect of RA.
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31
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Kühnle S, Kogel U, Glockzin S, Marquardt A, Ciechanover A, Matentzoglu K, Scheffner M. Physical and functional interaction of the HECT ubiquitin-protein ligases E6AP and HERC2. J Biol Chem 2011; 286:19410-6. [PMID: 21493713 PMCID: PMC3103319 DOI: 10.1074/jbc.m110.205211] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2010] [Revised: 04/04/2011] [Indexed: 11/06/2022] Open
Abstract
Deregulation of the ubiquitin-protein ligase E6AP contributes to the development of the Angelman syndrome and to cervical carcinogenesis suggesting that the activity of E6AP needs to be under tight control. However, how E6AP activity is regulated at the post-translational level under non-pathologic conditions is poorly understood. In this study, we report that the giant protein HERC2, which is like E6AP a member of the HECT family of ubiquitin-protein ligases, binds to E6AP. The interaction is mediated by the RCC1-like domain 2 of HERC2 and a region spanning amino acid residues 150-200 of E6AP. Furthermore, we provide evidence that HERC2 stimulates the ubiquitin-protein ligase activity of E6AP in vitro and within cells and that this stimulatory effect does not depend on the ubiquitin-protein ligase activity of HERC2. Thus, the data obtained indicate that HERC2 acts as a regulator of E6AP.
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Affiliation(s)
- Simone Kühnle
- From the Department of Biology and Konstanz Research School Chemical Biology, and
| | - Ulrike Kogel
- From the Department of Biology and Konstanz Research School Chemical Biology, and
| | - Sandra Glockzin
- From the Department of Biology and Konstanz Research School Chemical Biology, and
| | - Andreas Marquardt
- Proteomics Facility, University of Konstanz, 78457 Konstanz, Germany and
| | - Aaron Ciechanover
- the Cancer and Vascular Biology Research Center, The Rappaport Faculty of Medicine and Research Institute, Technion-Israel Institute of Technology, Haifa 31096, Israel
| | | | - Martin Scheffner
- From the Department of Biology and Konstanz Research School Chemical Biology, and
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32
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Chien CD, Kirilyuk A, Li JV, Zhang W, Lahusen T, Schmidt MO, Oh AS, Wellstein A, Riegel AT. Role of the nuclear receptor coactivator AIB1-Delta4 splice variant in the control of gene transcription. J Biol Chem 2011; 286:26813-27. [PMID: 21636853 DOI: 10.1074/jbc.m110.216200] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The oncogene amplified in breast cancer 1 (AIB1) is a nuclear receptor coactivator that plays a major role in the progression of various cancers. We previously identified a splice variant of AIB1 called AIB1-Δ4 that is overexpressed in breast cancer. Using mass spectrometry, we define the translation initiation of AIB1-Δ4 at Met(224) of the full-length AIB1 sequence and have raised an antibody to a peptide representing the acetylated N terminus. We show that AIB1-Δ4 is predominantly localized in the cytoplasm, although leptomycin B nuclear export inhibition demonstrates that AIB1-Δ4 can enter and traffic through the nucleus. Our data indicate an import mechanism enhanced by other coactivators such as p300/CBP. We report that the endogenously and exogenously expressed AIB1-Δ4 is recruited as efficiently as full-length AIB1 to estrogen-response elements of genes, and it enhances estrogen-dependent transcription more effectively than AIB1. Expression of an N-terminal AIB1 protein fragment, which is lost in the AIB1-Δ4 isoform, potentiates AIB1 as a coactivator. This suggests a model whereby the transcriptional activity of AIB1 is squelched by a repressive mechanism utilizing the N-terminal domain and that the increased coactivator function of AIB1-Δ4 is due to the loss of this inhibitory domain. Finally, we show, using Scorpion primer technology, that AIB1-Δ4 expression is correlated with metastatic capability of human cancer cell lines.
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Affiliation(s)
- Christopher D Chien
- Department of Oncology, Georgetown University Medical Center, Washington, DC 20007, USA
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33
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Sun Y, Perera J, Rubin BP, Huang J. SYT-SSX1 (synovial sarcoma translocated) regulates PIASy ligase activity to cause overexpression of NCOA3 protein. J Biol Chem 2011; 286:18623-32. [PMID: 21454665 DOI: 10.1074/jbc.m110.176693] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Chromosomal translocations are a major source of genetic abnormalities causally linked to certain malignancies. Synovial sarcoma is an aggressive soft tissue tumor characterized by a chromosomal translocation between chromosome 18 and X, generating oncoproteins such as SYT-SSX1 and SYT-SSX2. The molecular mechanism underlying the oncogenic potential of SYT-SSX1/2 is not clear. Here we show that SYT-SSX1 leads to up-regulation of NCOA3, a protein critical for the formation of various cancers. The increase of NCOA3 is essential for SYT-SSX1-mediated synovial sarcoma formation. SYT-SSX1 does so by increasing the sumoylation of NCOA3 through interaction with a SUMO E3 ligase, PIASy, as well as the sumoylation of NEMO. NEMO has also been shown to physically interact with NCOA3. Increased sumoylation of NCOA3 leads to its increased steady state level and nuclear localization. Our findings represent the first example that an oncoprotein directly regulates substrate modification by a SUMO E3 ligase, and leads to overexpression of a protein essential for tumor formation. Such a mechanistic finding provides an opportunity to design specific therapeutic interventions to treat synovial sarcoma.
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Affiliation(s)
- Yin Sun
- Department of Pathology and Laboratory Medicine, David Geffen School of Medicine, University of California at Los Angeles, California 90095, USA.
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34
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Amazit L, Roseau A, Khan JA, Chauchereau A, Tyagi RK, Loosfelt H, Leclerc P, Lombès M, Guiochon-Mantel A. Ligand-dependent degradation of SRC-1 is pivotal for progesterone receptor transcriptional activity. Mol Endocrinol 2011; 25:394-408. [PMID: 21273440 PMCID: PMC3320859 DOI: 10.1210/me.2010-0458] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2010] [Accepted: 12/13/2010] [Indexed: 02/08/2023] Open
Abstract
The progesterone receptor (PR), a ligand-activated transcription factor, recruits the primary coactivator steroid receptor coactivator-1 (SRC-1) gene promoters. It is known that PR transcriptional activity is paradoxically coupled to its ligand-dependent down-regulation. However, despite its importance in PR function, the regulation of SRC-1 expression level during hormonal exposure is poorly understood. Here we report that SRC-1 expression level (but not other p160 family members) is down-regulated by the agonist ligand R5020 in a PR-dependent manner. In contrast, the antagonist RU486 fails to induce down-regulation of the coactivator and impairs PR agonist-dependent degradation of SRC-1. We show that SRC-1 proteolysis is a proteasome- and ubiquitin-mediated process that, predominantly but not exclusively, occurs in the cytoplasmic compartment in which SRC-1 colocalizes with proteasome antigens as demonstrated by confocal imaging. Moreover, SRC-1 was stabilized in the presence of leptomycin B or several proteasomal inhibitors. Two degradation motifs, amino-acids 2-16 corresponding to a PEST motif and amino acids 41-136 located in the basic helix loop helix domain of the coactivator, were identified and shown to control the stability as well as the hormone-dependent down-regulation of the coactivator. SRC-1 degradation is of physiological importance because the two nondegradable mutants that still interacted with PR as demonstrated by coimmunoprecipitation failed to stimulate transcription of exogenous and endogenous target genes, suggesting that concomitant PR/SRC-1 ligand-dependent degradation is a necessary step for PR transactivation activity. Collectively our findings are consistent with the emerging role of proteasome-mediated proteolysis in the gene-regulating process and indicate that the ligand-dependent down-regulation of SRC-1 is critical for PR transcriptional activity.
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Affiliation(s)
- Larbi Amazit
- Institut National de la Santé et de la Recherche Médicale Unité 693, 63 Rue Gabriel Péri, Le Kremlin-Bicêtre F-94276, France
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35
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Nasu J, Murakami K, Miyagawa S, Yamashita R, Ichimura T, Wakita T, Hotta H, Miyamura T, Suzuki T, Satoh T, Shoji I. E6AP ubiquitin ligase mediates ubiquitin-dependent degradation of peroxiredoxin 1. J Cell Biochem 2011; 111:676-85. [PMID: 20589759 DOI: 10.1002/jcb.22752] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
E6-associated protein (E6AP) is a cellular ubiquitin protein ligase that mediates ubiquitylation and degradation of tumor suppressor p53 in conjunction with the high-risk human papillomavirus E6 protein. We previously reported that E6AP targets annexin A1 protein for ubiquitin-dependent proteasomal degradation. To gain a better understanding of the physiological function of E6AP, we have been seeking to identify novel substrates of E6AP. Here, we identified peroxiredoxin 1 (Prx1) as a novel E6AP-binding protein using a tandem affinity purification procedure coupled with mass spectrometry. Prx1 is a 25-kDa member of the Prx family, a ubiquitous family of antioxidant peroxidases that regulate many cellular processes through intracellular oxidative signal transduction pathways. Immunoprecipitation analysis showed that E6AP binds Prx1 in vivo. Pull-down experiments showed that E6AP binds Prx1 in vitro. Ectopic expression of E6AP enhanced the degradation of Prx1 in vivo. In vivo and in vitro ubiquitylation assays revealed that E6AP promoted polyubiquitylation of Prx1. RNAi-mediated downregulation of endogenous E6AP increased the level of endogenous Prx1 protein. Taken together, our data suggest that E6AP mediates the ubiquitin-dependent proteasomal degradation of Prx1. Our findings raise a possibility that E6AP may play a role in regulating Prx1-dependent intracellular oxidative signal transduction pathways.
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Affiliation(s)
- Junichi Nasu
- Department of Virology II, National Institute of Infectious Diseases, Shinjuku-ku, Tokyo, Japan
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36
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Tsai YC, Weissman AM. The Unfolded Protein Response, Degradation from Endoplasmic Reticulum and Cancer. Genes Cancer 2010; 1:764-778. [PMID: 21331300 DOI: 10.1177/1947601910383011] [Citation(s) in RCA: 201] [Impact Index Per Article: 14.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
The endoplasmic reticulum (ER) is an essential organelle involved in many cellular functions including protein folding and secretion, lipid biosynthesis and calcium homeostasis. Proteins destined for the cell surface or for secretion are made in the ER, where they are folded and assembled into multi-subunit complexes. The ER plays a vital role in cellular protein quality control by extracting and degrading proteins that are not correctly folded or assembled into native complexes. This process, known as ER-associated degradation (ERAD), ensures that only properly folded and assembled proteins are transported to their final destinations. Besides its role in protein folding and transport in the secretory pathway, the ER regulates the biosynthesis of cholesterol and other membrane lipids. ERAD is an important means to ensure that levels of the responsible enzymes are appropriately maintained. The ER is also a major organelle for oxygen and nutrient sensing as cells adapt to their microenvironment. Stresses that disrupt ER function leads to accumulation of unfolded proteins in the ER, a condition known as ER stress. Cells adapt to ER stress by activating an integrated signal transduction pathway called the unfolded protein response (UPR) (1). The UPR represents a survival response by the cells to restore ER homeostasis. If ER stress persists, cells activate mechanisms that result in cell death. Chronic ER stress is increasingly being recognized as a factor in many human diseases such as diabetes, neurodegenerative disorders and cancer. In this review we discuss the roles of the UPR and ERAD in cancer and suggest directions for future research.
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Affiliation(s)
- Yien Che Tsai
- Laboratory of Protein Dynamics and Signaling Center for Cancer Research National Cancer Institute - Frederick Frederick, Maryland
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37
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Srinivasan S, Nawaz Z. E3 ubiquitin protein ligase, E6-associated protein (E6-AP) regulates PI3K-Akt signaling and prostate cell growth. BIOCHIMICA ET BIOPHYSICA ACTA-GENE REGULATORY MECHANISMS 2010; 1809:119-27. [PMID: 20826237 DOI: 10.1016/j.bbagrm.2010.08.011] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/18/2010] [Revised: 08/20/2010] [Accepted: 08/27/2010] [Indexed: 10/19/2022]
Abstract
This study elucidates the role of E6-associated protein, E6-AP (a dual function steroid hormone receptor coactivator and ubiquitin-protein ligase) in the regulation of PI3K-Akt signaling pathway, prostate gland growth and proliferation. Here, we report the generation of transgenic mice and prostate cancer cell line, LNCaP cells that overexpress E6-AP protein. Using these models we show that the levels of total Akt and phosphorylated Akt (active Akt) are increased in E6-AP overexpressing prostate gland and LNCaP cells suggesting that E6-AP regulates the PI3K-Akt signaling pathway. The prostate glands in our transgenic mice are ~20% larger and produce preneoplastic lesions at the age of 18 months. Our data also suggest that E6-AP modulates PI3K-Akt signaling pathway by both androgen-independent and -dependent mechanisms. In the androgen-independent mechanism, E6-AP modulates PI3K-Akt signaling by regulating the protein levels of RhoA, a small GTPase, which is a negative regulator of the Akt signaling pathway. Further, we show that E6-AP, a known coactivator of AR, amplifies the androgen-dependent activation of PI3K-Akt signaling pathway. In addition, we show that stable overexpression of E6-AP in prostate cancer cells results in increased cell size and proliferation. Overall our data suggests that E6-AP regulates both the positive and negative modulators of the PI3K-Akt pathway in prostate cells which results in increased prostate cell growth, proliferation and decreased apoptosis.This article is part of a Special Issue entitled The 26S Proteasome: When degradation is just not enough!
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Affiliation(s)
- Sathish Srinivasan
- Department of Biochemistry & Molecular Biology, Universityof Miami Miller School of Medicine, Miami, FL 33136, USA
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38
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Dirac AMG, Bernards R. The deubiquitinating enzyme USP26 is a regulator of androgen receptor signaling. Mol Cancer Res 2010; 8:844-54. [PMID: 20501646 DOI: 10.1158/1541-7786.mcr-09-0424] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The androgen receptor (AR) is a member of the nuclear receptor superfamily and is essential for male sexual development and maturation, as well as prostate cancer development. Regulation of AR signaling activity depends on several posttranslational modifications, one of these being ubiquitination. We screened a short hairpin library targeting members of the deubiquitination enzyme family and identified the X-linked deubiquitination enzyme USP26 as a novel regulator of AR signaling. USP26 is a nuclear protein that binds to AR via three important nuclear receptor interaction motifs, and modulates AR ubiquitination, consequently influencing AR activity and stability. Our data suggest that USP26 assembles with AR and other cofactors in subnuclear foci, and serves to counteract hormone-induced AR ubiquitination, thereby contributing to the regulation of AR transcriptional activity.
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Affiliation(s)
- Annette M G Dirac
- The Netherlands Cancer Institute, Plesmanlaan 121, Amsterdam, 1066 CX Netherlands.
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39
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Hsia EYC, Kalashnikova EV, Revenko AS, Zou JX, Borowsky AD, Chen HW. Deregulated E2F and the AAA+ coregulator ANCCA drive proto-oncogene ACTR/AIB1 overexpression in breast cancer. Mol Cancer Res 2010; 8:183-93. [PMID: 20124470 DOI: 10.1158/1541-7786.mcr-09-0095] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The proto-oncogene ACTR/AIB1, a coactivator for transcription factors such as the nuclear receptors and E2Fs, is frequently overexpressed in various cancers including breast cancers. However, the underlying mechanism is poorly understood. Here, we identified several functional, noncanonical E2F binding sites in the ACTR first exon and intron that are critical for ACTR gene activation. We also found that the newly identified AAA+ coregulator AAA+ nuclear coregulator cancer associated (ANCCA) is recruited to the ACTR promoter and directly controls ACTR expression in breast cancer cells. Importantly, immunohistochemistry analysis indicated that ACTR overexpression is highly correlated with the expression of E2F1 and ANCCA in a cohort of human primary and lymph node-metastasized breast cancer specimens. Along with previous findings from us and others that ACTR is involved in its own gene regulation, these results suggest that one major mechanism of ACTR overexpression in cancer is the concerted, aberrant function of the nuclear coregulators such as ANCCA and ACTR, and they point to therapeutic strategies that target the Rb-E2F axis and/or the coregulator ANCCA for ACTR-overexpressing cancers.
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Affiliation(s)
- Elaine Y C Hsia
- Department of Biochemistry and Molecular Medicine, University of California at Davis, Sacramento, CA 95817, USA
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40
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Scarpin KM, Graham JD, Mote PA, Clarke CL. Progesterone action in human tissues: regulation by progesterone receptor (PR) isoform expression, nuclear positioning and coregulator expression. NUCLEAR RECEPTOR SIGNALING 2009; 7:e009. [PMID: 20087430 PMCID: PMC2807635 DOI: 10.1621/nrs.07009] [Citation(s) in RCA: 120] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/06/2009] [Accepted: 11/11/2009] [Indexed: 12/22/2022]
Abstract
Progesterone is a critical regulator of normal female reproductive function, with diverse tissue-specific effects in the human. The effects of progesterone are mediated by its nuclear receptor (PR) that is expressed as two isoforms, PRA and PRB, which are virtually identical except that PRA lacks 164 amino acids that are present at the N-terminus of PRB. Considerable in vitro evidence suggests that the two PRs are functionally distinct and in animals, tissue-specific distribution patterns of PRA and PRB may account for some of the diversity of progesterone effects. In the human, PRA and PRB are equivalently expressed in most target cells, suggesting that alternative mechanisms control the diversity of progesterone actions. PR mediates the effects of progesterone by association with a range of coregulatory proteins and binding to specific target sequences in progesterone-regulated gene promoters. Ligand activation of PR results in redistribution into discrete subnuclear foci that are detectable by immunofluorescence, probably representing aggregates of multiple transcriptionally active PR-coregulator complexes. PR foci are aberrant in cancers, suggesting that the coregulator composition and number of complexes is altered. A large family of coregulators is now described and the range of proteins known to bind PR exceeds the complement required for transcriptional activation, suggesting that in the human, tissue-specific coregulator expression may modulate progesterone response. In this review, we examine the role of nuclear localization of PR, coregulator association and tissue-specific expression in modulating progesterone action in the human.
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Affiliation(s)
- Katherine M Scarpin
- Westmead Institute for Cancer Research, Westmead Millennium Institute, University of Sydney Western Clinical School, Westmead, NSW, Australia
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41
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Emerging roles of the ubiquitin proteasome system in nuclear hormone receptor signaling. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2009; 87:117-35. [PMID: 20374703 DOI: 10.1016/s1877-1173(09)87004-x] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Nuclear receptor (NR)-mediated transcription is intimately tied to the ubiquitin proteasome system (UPS). The UPS targets numerous NR and coregulator proteins, regulating their stability and altering their transcriptional activities through the posttranslational placement of ubiquitin marks on them. Differences in the manner in which ubiquitin is attached to target proteins or itself have distinct regulatory consequences. Protein monoubiquitination, polyubiquitination, the site of ubiquitin attachment to a target protein, and the type of polyubiquitin chain linkage all lead to different biological outcomes and have an important regulatory function in NR-mediated transcription. Consistent with its role in protein degradation, the UPS is able to limit the biological actions of both NRs and coregulators by reducing their protein concentrations in the cell. However, in spite of its destructive capabilities, the UPS can play a positive role in facilitating NR-mediated transcription as well. In addition, ubiquitin-like modifications such as SUMOylation also modify and regulate NRs and coregulators. The UPS forms a key biological system that underlies a sophisticated postranslational regulatory scheme from which complex and dynamic regulation of NR-mediated transcription can occur.
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42
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Xu J, Wu RC, O’Malley BW. Normal and cancer-related functions of the p160 steroid receptor co-activator (SRC) family. Nat Rev Cancer 2009; 9:615-30. [PMID: 19701241 PMCID: PMC2908510 DOI: 10.1038/nrc2695] [Citation(s) in RCA: 381] [Impact Index Per Article: 25.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The three homologous members of the p160 SRC family (SRC1, SRC2 and SRC3) mediate the transcriptional functions of nuclear receptors and other transcription factors, and are the most studied of all the transcriptional co-activators. Recent work has indicated that the SRCgenes are subject to amplification and overexpression in various human cancers. Some of the molecular mechanisms responsible for SRC overexpression, along with the mechanisms by which SRCs promote breast and prostate cancer cell proliferation and survival, have been identified, as have the specific contributions of individual SRC family members to spontaneous breast and prostate carcinogenesis in genetically manipulated mouse models. These studies have identified new challenges for cancer research and therapy.
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Affiliation(s)
- Jianming Xu
- Department of Molecular and Cellular Biology, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030 USA
- Luzhou Medical College, Luzhou, Sichuan 646000, China
| | - Ray-Chang Wu
- Department of Molecular and Cellular Biology, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030 USA
| | - Bert W. O’Malley
- Department of Molecular and Cellular Biology, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030 USA
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43
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Who's in charge? Nuclear receptor coactivator and corepressor function in brain and behavior. Front Neuroendocrinol 2009; 30:328-42. [PMID: 19401208 PMCID: PMC2720417 DOI: 10.1016/j.yfrne.2009.04.008] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/30/2009] [Revised: 04/15/2009] [Accepted: 04/17/2009] [Indexed: 11/20/2022]
Abstract
Steroid hormones act in brain and throughout the body to regulate a variety of functions, including development, reproduction, stress and behavior. Many of these effects of steroid hormones are mediated by their respective receptors, which are members of the steroid/nuclear receptor superfamily of transcriptional activators. A variety of studies in cell lines reveal that nuclear receptor coregulators are critical in modulating steroid receptor-dependent transcription. Thus, in addition to the availability of the hormone and the expression of its receptor, nuclear receptor coregulators are essential for efficient steroid-dependent transactivation of genes. This review will highlight the importance of nuclear receptor coregulators in modulating steroid-dependent gene expression in brain and the regulation of behavior.
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Lahusen T, Henke RT, Kagan BL, Wellstein A, Riegel AT. The role and regulation of the nuclear receptor co-activator AIB1 in breast cancer. Breast Cancer Res Treat 2009; 116:225-37. [PMID: 19418218 DOI: 10.1007/s10549-009-0405-2] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2009] [Accepted: 04/11/2009] [Indexed: 01/08/2023]
Abstract
AIB1 (amplified in breast cancer 1), also called SRC-3 and NCoA-3, is a member of the p160 nuclear receptor co-activator family and is considered an important oncogene in breast cancer. Increased AIB1 levels in human breast cancer have been correlated with poor clinical prognosis. Overexpression of AIB1 in conjunction with members of the epidermal growth factor receptor (EGF/HER) tyrosine kinase family, such as HER2, is associated with resistance to tamoxifen therapy and decreased disease-free survival. A number of functional studies in cell culture and in rodents indicate that AIB1 has a pleiotropic role in breast cancer. Initially AIB1 was shown to have a role in the estrogen-dependent proliferation of breast epithelial cells. However, AIB1 also affects the growth of hormone-independent breast cancer and AIB1 levels are limiting for IGF-1-, EGF- and heregulin-stimulated biological responses in breast cancer cells and consequently the PI3 K/Akt/mTOR and other EGFR/HER2 signaling pathways are controlled by changes in AIB1 protein levels. The cellular levels and activity of AIB1 are in turn regulated at the levels of transcription, mRNA stability, post-translational modification, and by a complex control of protein half life. In particular, AIB1 activity as well as its half-life is modulated through a number of post-translational modifications including serine, threonine and tyrosine phosphorylation via kinases that are components of multiple signal transduction pathways. This review summarizes the possible mechanisms of how dysregulation of AIB1 at multiple levels can lead to the initiation and progression of breast cancer as well as its role as a predictor of response to breast cancer therapy, and as a possible therapeutic target.
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Affiliation(s)
- Tyler Lahusen
- Department of Oncology, Lombardi Cancer Center, Georgetown University, Washington, DC, USA
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Shimoji T, Murakami K, Sugiyama Y, Matsuda M, Inubushi S, Nasu J, Shirakura M, Suzuki T, Wakita T, Kishino T, Hotta H, Miyamura T, Shoji I. Identification of annexin A1 as a novel substrate for E6AP-mediated ubiquitylation. J Cell Biochem 2009; 106:1123-35. [DOI: 10.1002/jcb.22096] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Regulation of peroxisome proliferator-activated receptors by e6-associated protein. PPAR Res 2008; 2008:746935. [PMID: 19107217 PMCID: PMC2605849 DOI: 10.1155/2008/746935] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2008] [Revised: 09/25/2008] [Accepted: 11/05/2008] [Indexed: 02/01/2023] Open
Abstract
Peroxisome proliferator-activated receptors (PPARs) are nuclear receptors (NRs) that regulate genes involved in lipid and glucose metabolism. PPAR activity is regulated by interactions with cofactors and of interest are cofactors with ubiquitin ligase activity. The E6-associated protein (E6-AP) is an E3 ubiquitin ligase that affects the activity of other NRs, although its effects on PPARs have not been examined. E6-AP inhibited the ligand-independent transcriptional activity of PPARα and PPARβ, with marginal effects on PPARγ, and decreased basal mRNA levels of PPARα target genes. Inhibition of PPARα activity required the ubiquitin ligase function of E6-AP, but occurred in a proteasome-independent manner. PPARα interacted with E6-AP, and in mice treated with PPARα agonist clofibrate, mRNA and protein levels of E6-AP were increased in wildtype, but not in PPARα null mice, indicating a PPARα-dependent regulation. These studies suggest coordinate regulation of E6-AP and PPARα, and contribute to our understanding of the role of PPARs in cellular metabolism.
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Abstract
The ubiquitin ligase E6-AP (E6-associated protein) represents a prime example for the notion that deregulated modification of proteins with ubiquitin contributes to the development of human disease: loss of E6-AP function by mutation is responsible for the development of AS (Angelman syndrome), a neurological disorder, and unscheduled activation of E6-AP by complex formation with the E6 oncoprotein of HPVs (human papillomaviruses) contributes to cervical carcinogenesis. However, while there is a considerable amount of data concerning the oncogenic properties of the E6–E6-AP complex, only little is known about the function(s) of E6-AP in neurons. This is mainly due to the fact that although some E6-AP substrates have been identified, it is at present unclear whether deregulated modification/degradation of these proteins is involved in the pathogenesis of AS. Similarly, the cellular pathways involving E6-AP remain enigmatic. To obtain insights into the physiological functions of E6-AP, we are currently employing several strategies, including quantitative affinity proteomics and RNA interference approaches. The results obtained will eventually allow the introduction of E6-AP into functional protein networks and so reveal potential targets for molecular approaches in the treatment of E6-AP-associated diseases.
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Tyrosine phosphorylation of the nuclear receptor coactivator AIB1/SRC-3 is enhanced by Abl kinase and is required for its activity in cancer cells. Mol Cell Biol 2008; 28:6580-93. [PMID: 18765637 DOI: 10.1128/mcb.00118-08] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Overexpression and activation of the steroid receptor coactivator amplified in breast cancer 1 (AIB1)/steroid receptor coactivator-3 (SRC-3) have been shown to have a critical role in oncogenesis and are required for both steroid and growth factor signaling in epithelial tumors. Here, we report a new mechanism for activation of SRC coactivators. We demonstrate regulated tyrosine phosphorylation of AIB1/SRC-3 at a C-terminal tyrosine residue (Y1357) that is phosphorylated after insulin-like growth factor 1, epidermal growth factor, or estrogen treatment of breast cancer cells. Phosphorylated Y1357 is increased in HER2/neu (v-erb-b2 erythroblastic leukemia viral oncogene homolog 2) mammary tumor epithelia and is required to modulate AIB1/SRC-3 coactivation of estrogen receptor alpha (ERalpha), progesterone receptor B, NF-kappaB, and AP-1-dependent promoters. c-Abl (v-Abl Abelson murine leukemia viral oncogene homolog 1) tyrosine kinase directly phosphorylates AIB1/SRC-3 at Y1357 and modulates the association of AIB1 with c-Abl, ERalpha, the transcriptional cofactor p300, and the methyltransferase coactivator-associated arginine methyltransferase 1, CARM1. AIB1/SRC-3-dependent transcription and phenotypic changes, such as cell growth and focus formation, can be reversed by an Abl kinase inhibitor, imatinib. Thus, the phosphorylation state of Y1357 can function as a molecular on/off switch and facilitates the cross talk between hormone, growth factor, and intracellular kinase signaling pathways in cancer.
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Ferrero M, Avivar A, García-Macías MC, Font de Mora J. Phosphoinositide 3-kinase/AKT signaling can promote AIB1 stability independently of GSK3 phosphorylation. Cancer Res 2008; 68:5450-9. [PMID: 18593948 DOI: 10.1158/0008-5472.can-07-6433] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The transcriptional coactivator AIB1 is an oncogene overexpressed in different types of tumors, including breast cancer. Although the subcellular compartimentalization of AIB1 seems to be intimately linked to abnormal proliferation, the molecular mechanisms that regulate its subcellular distribution are not well defined. Here, we report that the nuclear accumulation and half-life of AIB1 vary between cancer cell lines. Using these differences as an experimental model, our results reveal that alterations to the Akt signaling pathway and nuclear export determine the stability of AIB1 and nuclear content of this coactivator. Moreover, our results show that AIB1 is degraded in the nucleus by the proteasome in an ubiquitin-dependent manner. However, this process does not require phosphorylation by GSK3, thereby revealing an alternative mechanism for regulating the turnover of AIB1. We define a new region at the carboxy terminus of AIB1 that is required for proteasome-dependent transcriptional activation and is preceded by a PEST domain that is required for adequate protein turnover. Based on differences in Akt signaling and the subcellular distribution of AIB1 between different cell lines, our results suggest that dysregulation of nuclear shuttling and proteasomal degradation may modulate the oncogenic potential of AIB1.
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Affiliation(s)
- Macarena Ferrero
- Laboratory of Cellular and Molecular Biology, Centro de Investigación Príncipe Felipe, Valencia, Spain
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Atypical protein kinase C regulates dual pathways for degradation of the oncogenic coactivator SRC-3/AIB1. Mol Cell 2008; 29:465-76. [PMID: 18313384 DOI: 10.1016/j.molcel.2007.12.030] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2007] [Revised: 10/16/2007] [Accepted: 12/15/2007] [Indexed: 11/23/2022]
Abstract
SRC-3/AIB1 is a steroid receptor coactivator with potent growth-promoting activity, and its overexpression is sufficient to induce tumorigenesis. Previous studies indicate that the cellular level of SRC-3 is tightly regulated by both ubiquitin-dependent and ubiquitin-independent proteasomal degradation pathways. Atypical protein kinase C (aPKC) is frequently overexpressed in cancers. In the present study, we show that aPKC phosphorylates and specifically stabilizes SRC-3 in a selective ER-dependent manner. We further demonstrate that an acidic residue-rich region in SRC-3 is an important determinant for aPKC-mediated phosphorylation and stabilization. The mechanism of the aPKC-mediated stabilization appears due to a decreased interaction between SRC-3 and the C8 subunit of the 20S core proteasome, thus preventing SRC-3 degradation. Our results demonstrate a potent signaling mechanism for regulating SRC-3 levels in cells by coordinate enzymatic inhibition of both ubiquitin-dependent and ubiquitin-independent proteolytic pathways.
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