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Bolhuis DL, Emanuele MJ, Brown NG. Friend or foe? Reciprocal regulation between E3 ubiquitin ligases and deubiquitinases. Biochem Soc Trans 2024; 52:BST20230454. [PMID: 38414432 PMCID: PMC11349938 DOI: 10.1042/bst20230454] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2023] [Revised: 01/31/2024] [Accepted: 02/06/2024] [Indexed: 02/29/2024]
Abstract
Protein ubiquitination is a post-translational modification that entails the covalent attachment of the small protein ubiquitin (Ub), which acts as a signal to direct protein stability, localization, or interactions. The Ub code is written by a family of enzymes called E3 Ub ligases (∼600 members in humans), which can catalyze the transfer of either a single ubiquitin or the formation of a diverse array of polyubiquitin chains. This code can be edited or erased by a different set of enzymes termed deubiquitinases (DUBs; ∼100 members in humans). While enzymes from these distinct families have seemingly opposing activities, certain E3-DUB pairings can also synergize to regulate vital cellular processes like gene expression, autophagy, innate immunity, and cell proliferation. In this review, we highlight recent studies describing Ub ligase-DUB interactions and focus on their relationships.
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Affiliation(s)
- Derek L Bolhuis
- Department of Biochemistry and Biophysics, UNC Chapel Hill School of Medicine, Chapel Hill, NC, 27599
| | - Michael J Emanuele
- Department of Pharmacology and Lineberger Comprehensive Care Center, UNC Chapel Hill School of Medicine, Chapel Hill, NC, 27599
| | - Nicholas G Brown
- Department of Pharmacology and Lineberger Comprehensive Care Center, UNC Chapel Hill School of Medicine, Chapel Hill, NC, 27599
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2
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Cervia LD, Shibue T, Borah AA, Gaeta B, He L, Leung L, Li N, Moyer SM, Shim BH, Dumont N, Gonzalez A, Bick NR, Kazachkova M, Dempster JM, Krill-Burger JM, Piccioni F, Udeshi ND, Olive ME, Carr SA, Root DE, McFarland JM, Vazquez F, Hahn WC. A Ubiquitination Cascade Regulating the Integrated Stress Response and Survival in Carcinomas. Cancer Discov 2023; 13:766-795. [PMID: 36576405 PMCID: PMC9975667 DOI: 10.1158/2159-8290.cd-22-1230] [Citation(s) in RCA: 11] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2022] [Revised: 12/12/2022] [Accepted: 12/22/2022] [Indexed: 12/29/2022]
Abstract
Systematic identification of signaling pathways required for the fitness of cancer cells will facilitate the development of new cancer therapies. We used gene essentiality measurements in 1,086 cancer cell lines to identify selective coessentiality modules and found that a ubiquitin ligase complex composed of UBA6, BIRC6, KCMF1, and UBR4 is required for the survival of a subset of epithelial tumors that exhibit a high degree of aneuploidy. Suppressing BIRC6 in cell lines that are dependent on this complex led to a substantial reduction in cell fitness in vitro and potent tumor regression in vivo. Mechanistically, BIRC6 suppression resulted in selective activation of the integrated stress response (ISR) by stabilization of the heme-regulated inhibitor, a direct ubiquitination target of the UBA6/BIRC6/KCMF1/UBR4 complex. These observations uncover a novel ubiquitination cascade that regulates ISR and highlight the potential of ISR activation as a new therapeutic strategy. SIGNIFICANCE We describe the identification of a heretofore unrecognized ubiquitin ligase complex that prevents the aberrant activation of the ISR in a subset of cancer cells. This provides a novel insight on the regulation of ISR and exposes a therapeutic opportunity to selectively eliminate these cancer cells. See related commentary Leli and Koumenis, p. 535. This article is highlighted in the In This Issue feature, p. 517.
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Affiliation(s)
- Lisa D. Cervia
- Broad Institute of MIT and Harvard, Cambridge, Massachusetts
- Department of Medical Oncology, Dana-Farber Cancer Institute, Harvard Medical School, Boston, Massachusetts
| | - Tsukasa Shibue
- Broad Institute of MIT and Harvard, Cambridge, Massachusetts
| | - Ashir A. Borah
- Broad Institute of MIT and Harvard, Cambridge, Massachusetts
| | - Benjamin Gaeta
- Broad Institute of MIT and Harvard, Cambridge, Massachusetts
| | - Linh He
- Broad Institute of MIT and Harvard, Cambridge, Massachusetts
| | - Lisa Leung
- Broad Institute of MIT and Harvard, Cambridge, Massachusetts
| | - Naomi Li
- Broad Institute of MIT and Harvard, Cambridge, Massachusetts
- Department of Medical Oncology, Dana-Farber Cancer Institute, Harvard Medical School, Boston, Massachusetts
| | - Sydney M. Moyer
- Broad Institute of MIT and Harvard, Cambridge, Massachusetts
- Department of Medical Oncology, Dana-Farber Cancer Institute, Harvard Medical School, Boston, Massachusetts
| | - Brian H. Shim
- Broad Institute of MIT and Harvard, Cambridge, Massachusetts
- Department of Medical Oncology, Dana-Farber Cancer Institute, Harvard Medical School, Boston, Massachusetts
| | - Nancy Dumont
- Broad Institute of MIT and Harvard, Cambridge, Massachusetts
| | | | - Nolan R. Bick
- Broad Institute of MIT and Harvard, Cambridge, Massachusetts
| | | | | | | | | | | | - Meagan E. Olive
- Broad Institute of MIT and Harvard, Cambridge, Massachusetts
| | - Steven A. Carr
- Broad Institute of MIT and Harvard, Cambridge, Massachusetts
| | - David E. Root
- Broad Institute of MIT and Harvard, Cambridge, Massachusetts
| | | | | | - William C. Hahn
- Broad Institute of MIT and Harvard, Cambridge, Massachusetts
- Department of Medical Oncology, Dana-Farber Cancer Institute, Harvard Medical School, Boston, Massachusetts
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3
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Kolobynina KG, Rapp A, Cardoso MC. Chromatin Ubiquitination Guides DNA Double Strand Break Signaling and Repair. Front Cell Dev Biol 2022; 10:928113. [PMID: 35865631 PMCID: PMC9294282 DOI: 10.3389/fcell.2022.928113] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2022] [Accepted: 06/16/2022] [Indexed: 11/13/2022] Open
Abstract
Chromatin is the context for all DNA-based molecular processes taking place in the cell nucleus. The initial chromatin structure at the site of the DNA damage determines both, lesion generation and subsequent activation of the DNA damage response (DDR) pathway. In turn, proceeding DDR changes the chromatin at the damaged site and across large fractions of the genome. Ubiquitination, besides phosphorylation and methylation, was characterized as an important chromatin post-translational modification (PTM) occurring at the DNA damage site and persisting during the duration of the DDR. Ubiquitination appears to function as a highly versatile “signal-response” network involving several types of players performing various functions. Here we discuss how ubiquitin modifiers fine-tune the DNA damage recognition and response and how the interaction with other chromatin modifications ensures cell survival.
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Vilfranc CL, Che LX, Patra KC, Niu L, Olowokure O, Wang J, Shah SA, Du CY. BIR repeat-containing ubiquitin conjugating enzyme (BRUCE) regulation of β-catenin signaling in the progression of drug-induced hepatic fibrosis and carcinogenesis. World J Hepatol 2021; 13:343-361. [PMID: 33815677 PMCID: PMC8006081 DOI: 10.4254/wjh.v13.i3.343] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/12/2020] [Revised: 01/15/2021] [Accepted: 03/09/2021] [Indexed: 02/06/2023] Open
Abstract
BACKGROUND BIR repeat-containing ubiquitin conjugating enzyme (BRUCE) is a liver tumor suppressor, which is downregulated in a large number of patients with liver diseases. BRUCE facilitates DNA damage repair to protect the mouse liver against the hepatocarcinogen diethylnitrosamine (DEN)-dependent acute liver injury and carcinogenesis. While there exists an established pathologic connection between fibrosis and hepatocellular carcinoma (HCC), DEN exposure alone does not induce robust hepatic fibrosis. Further studies are warranted to identify new suppressive mechanisms contributing to DEN-induced fibrosis and HCC.
AIM To investigate the suppressive mechanisms of BRUCE in hepatic fibrosis and HCC development.
METHODS Male C57/BL6/J control mice [loxp/Loxp; albumin-cre (Alb-cre)-] and BRUCE Alb-Cre KO mice (loxp/Loxp; Alb-Cre+) were injected with a single dose of DEN at postnatal day 15 and sacrificed at different time points to examine liver disease progression.
RESULTS By using a liver-specific BRUCE knockout (LKO) mouse model, we found that BRUCE deficiency, in conjunction with DEN exposure, induced hepatic fibrosis in both premalignant as well as malignant stages, thus recapitulating the chronic fibrosis background often observed in HCC patients. Activated in fibrosis and HCC, β-catenin activity depends on its stabilization and subsequent translocation to the nucleus. Interestingly, we observed that livers from BRUCE KO mice demonstrated an increased nuclear accumulation and elevated activity of β-catenin in the three stages of carcinogenesis: Pre-malignancy, tumor initiation, and HCC. This suggests that BRUCE negatively regulates β-catenin activity during liver disease progression. β-catenin can be activated by phosphorylation by protein kinases, such as protein kinase A (PKA), which phosphorylates it at Ser-675 (pSer-675-β-catenin). Mechanistically, BRUCE and PKA were colocalized in the cytoplasm of hepatocytes where PKA activity is maintained at the basal level. However, in BRUCE deficient mouse livers or a human liver cancer cell line, both PKA activity and pSer-675-β-catenin levels were observed to be elevated.
CONCLUSION Our data support a “BRUCE-PKA-β-catenin” signaling axis in the mouse liver. The BRUCE interaction with PKA in hepatocytes suppresses PKA-dependent phosphorylation and activation of β-catenin. This study implicates BRUCE as a novel negative regulator of both PKA and β-catenin in chronic liver disease progression. Furthermore, BRUCE-liver specific KO mice serve as a promising model for understanding hepatic fibrosis and HCC in patients with aberrant activation of PKA and β-catenin.
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Affiliation(s)
- Chrystelle L Vilfranc
- Department of Cancer Biology, University of Cincinnati, Cincinnati, OH 45267, United States
| | - Li-Xiao Che
- Department of Cancer Biology, University of Cincinnati, Cincinnati, OH 45267, United States
| | - Krushna C Patra
- Department of Cancer Biology, University of Cincinnati, Cincinnati, OH 45267, United States
| | - Liang Niu
- Department of Environmental and Public Health Sciences, University of Cincinnati, Cincinnati, OH 45267, United States
| | - Olugbenga Olowokure
- Department of Internal Medicine, University of Cincinnati, Cincinnati, OH 45267, United States
| | - Jiang Wang
- Department of Pathology and Laboratory Medicine, University of Cincinnati, Cincinnati, OH 45267, United States
| | - Shimul A Shah
- Department of Surgery, University of Cincinnati, Cincinnati, OH 45267, United States
| | - Chun-Ying Du
- Department of Cancer Biology, University of Cincinnati, Cincinnati, OH 45267, United States
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Buljan M, Ciuffa R, van Drogen A, Vichalkovski A, Mehnert M, Rosenberger G, Lee S, Varjosalo M, Pernas LE, Spegg V, Snijder B, Aebersold R, Gstaiger M. Kinase Interaction Network Expands Functional and Disease Roles of Human Kinases. Mol Cell 2020; 79:504-520.e9. [PMID: 32707033 PMCID: PMC7427327 DOI: 10.1016/j.molcel.2020.07.001] [Citation(s) in RCA: 56] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2019] [Revised: 02/14/2020] [Accepted: 06/30/2020] [Indexed: 12/30/2022]
Abstract
Protein kinases are essential for signal transduction and control of most cellular processes, including metabolism, membrane transport, motility, and cell cycle. Despite the critical role of kinases in cells and their strong association with diseases, good coverage of their interactions is available for only a fraction of the 535 human kinases. Here, we present a comprehensive mass-spectrometry-based analysis of a human kinase interaction network covering more than 300 kinases. The interaction dataset is a high-quality resource with more than 5,000 previously unreported interactions. We extensively characterized the obtained network and were able to identify previously described, as well as predict new, kinase functional associations, including those of the less well-studied kinases PIM3 and protein O-mannose kinase (POMK). Importantly, the presented interaction map is a valuable resource for assisting biomedical studies. We uncover dozens of kinase-disease associations spanning from genetic disorders to complex diseases, including cancer.
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Affiliation(s)
- Marija Buljan
- Institute of Molecular Systems Biology, ETH Zurich, 8093 Zurich, Switzerland; Empa, Swiss Federal Laboratories for Materials Science and Technology, 9014 St. Gallen, Switzerland
| | - Rodolfo Ciuffa
- Institute of Molecular Systems Biology, ETH Zurich, 8093 Zurich, Switzerland
| | - Audrey van Drogen
- Institute of Molecular Systems Biology, ETH Zurich, 8093 Zurich, Switzerland
| | - Anton Vichalkovski
- Institute of Molecular Systems Biology, ETH Zurich, 8093 Zurich, Switzerland
| | - Martin Mehnert
- Institute of Molecular Systems Biology, ETH Zurich, 8093 Zurich, Switzerland
| | - George Rosenberger
- Institute of Molecular Systems Biology, ETH Zurich, 8093 Zurich, Switzerland; Columbia University Department of Systems Biology, New York, NY 10032, USA
| | - Sohyon Lee
- Institute of Molecular Systems Biology, ETH Zurich, 8093 Zurich, Switzerland
| | - Markku Varjosalo
- Institute of Biotechnology, University of Helsinki, Helsinki 00014, Finland
| | - Lucia Espona Pernas
- Institute of Molecular Systems Biology, ETH Zurich, 8093 Zurich, Switzerland
| | - Vincent Spegg
- Department of Molecular Mechanisms of Disease, University of Zurich, 8057 Zurich, Switzerland
| | - Berend Snijder
- Institute of Molecular Systems Biology, ETH Zurich, 8093 Zurich, Switzerland
| | - Ruedi Aebersold
- Institute of Molecular Systems Biology, ETH Zurich, 8093 Zurich, Switzerland; Faculty of Science, University of Zurich, Zurich, Switzerland.
| | - Matthias Gstaiger
- Institute of Molecular Systems Biology, ETH Zurich, 8093 Zurich, Switzerland.
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Che L, Alavattam KG, Stambrook PJ, Namekawa SH, Du C. BRUCE preserves genomic stability in the male germline of mice. Cell Death Differ 2020; 27:2402-2416. [PMID: 32139899 DOI: 10.1038/s41418-020-0513-4] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2019] [Revised: 01/30/2020] [Accepted: 01/31/2020] [Indexed: 01/01/2023] Open
Abstract
BRUCE is a DNA damage response protein that promotes the activation of ATM and ATR for homologous recombination (HR) repair in somatic cells, making BRUCE a key protector of genomic stability. Preservation of genomic stability in the germline is essential for the maintenance of species. Here, we show that BRUCE is required for the preservation of genomic stability in the male germline of mice, specifically in spermatogonia and spermatocytes. Conditional knockout of Bruce in the male germline leads to profound defects in spermatogenesis, including impaired maintenance of spermatogonia and increased chromosomal anomalies during meiosis. Bruce-deficient pachytene spermatocytes frequently displayed persistent DNA breaks. Homologous synapsis was impaired, and nonhomologous associations and rearrangements were apparent in up to 10% of Bruce-deficient spermatocytes. Genomic instability was apparent in the form of chromosomal fragmentation, translocations, and synapsed quadrivalents and hexavalents. In addition, unsynapsed regions of rearranged autosomes were devoid of ATM and ATR signaling, suggesting an impairment in the ATM- and ATR-dependent DNA damage response of meiotic HR. Taken together, our study unveils crucial functions for BRUCE in the maintenance of spermatogonia and in the regulation of meiotic HR-functions that preserve the genomic stability of the male germline.
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Affiliation(s)
- Lixiao Che
- Department of Cell and Cancer Biology, University of Cincinnati College of Medicine, Cincinnati, OH, 45267, USA
| | - Kris G Alavattam
- Division of Reproductive Sciences, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, 45229, USA
| | - Peter J Stambrook
- Department of Molecular Genetics, University of Cincinnati College of Medicine, Cincinnati, OH, 45267, USA
| | - Satoshi H Namekawa
- Division of Reproductive Sciences, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, 45229, USA
| | - Chunying Du
- Department of Cell and Cancer Biology, University of Cincinnati College of Medicine, Cincinnati, OH, 45267, USA.
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7
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Ubiquitin-specific protease 8 (USP8/UBPy): a prototypic multidomain deubiquitinating enzyme with pleiotropic functions. Biochem Soc Trans 2020; 47:1867-1879. [PMID: 31845722 PMCID: PMC6925526 DOI: 10.1042/bst20190527] [Citation(s) in RCA: 33] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2019] [Revised: 11/29/2019] [Accepted: 12/02/2019] [Indexed: 01/07/2023]
Abstract
Protein modification by ubiquitin is one of the most versatile posttranslational regulations and counteracted by almost 100 deubiquitinating enzymes (DUBs). USP8 was originally identified as a growth regulated ubiquitin-specific protease and is like many other DUBs characterized by its multidomain architecture. Besides the catalytic domain, specific protein-protein interaction modules were characterized which contribute to USP8 substrate recruitment, regulation and targeting to distinct protein complexes. Studies in mice and humans impressively showed the physiological relevance and non-redundant function of USP8 within the context of the whole organism. USP8 knockout (KO) mice exhibit early embryonic lethality while induced deletion in adult animals rapidly causes lethal liver failure. Furthermore, T-cell specific ablation disturbs T-cell development and function resulting in fatal autoimmune inflammatory bowel disease. In human patients, somatic mutations in USP8 were identified as the underlying cause of adrenocorticotropic hormone (ACTH) releasing pituitary adenomas causing Cushing's disease (CD). Here we provide an overview of the versatile molecular, cellular and pathology associated function and regulation of USP8 which appears to depend on specific protein binding partners, substrates and the cellular context.
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8
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Ge C, Vilfranc CL, Che L, Pandita RK, Hambarde S, Andreassen PR, Niu L, Olowokure O, Shah S, Waltz SE, Zou L, Wang J, Pandita TK, Du C. The BRUCE-ATR Signaling Axis Is Required for Accurate DNA Replication and Suppression of Liver Cancer Development. Hepatology 2019; 69:2608-2622. [PMID: 30693543 PMCID: PMC6541504 DOI: 10.1002/hep.30529] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/14/2018] [Accepted: 01/23/2019] [Indexed: 01/10/2023]
Abstract
Replication fork stability during DNA replication is vital for maintenance of genomic stability and suppression of cancer development in mammals. ATR (ataxia-telangiectasia mutated [ATM] and RAD3-related) is a master regulatory kinase that activates the replication stress response to overcome replication barriers. Although many downstream effectors of ATR have been established, the upstream regulators of ATR and the effect of such regulation on liver cancer remain unclear. The ubiquitin conjugase BRUCE (BIR Repeat containing Ubiquitin-Conjugating Enzyme) is a guardian of chromosome integrity and activator of ATM signaling, which promotes DNA double-strand break repair through homologous recombination. Here we demonstrate the functions for BRUCE in ATR activation in vitro and liver tumor suppression in vivo. BRUCE is recruited to induced DNA damage sites. Depletion of BRUCE inhibited multiple ATR-dependent signaling events during replication stress, including activation of ATR itself, phosphorylation of its downstream targets CHK1 and RPA, and the mono-ubiquitination of FANCD2. Consequently, BRUCE deficiency resulted in stalled DNA replication forks and increased firing of new replication origins. The in vivo impact of BRUCE loss on liver tumorigenesis was determined using the hepatocellular carcinoma model induced by genotoxin diethylnitrosamine. Liver-specific knockout of murine Bruce impaired ATR activation and exacerbated inflammation, fibrosis and hepatocellular carcinoma, which exhibited a trabecular architecture, closely resembling human hepatocellular carcinoma (HCC). In humans, the clinical relevance of BRUCE down-regulation in liver disease was found in hepatitis, cirrhosis, and HCC specimens, and deleterious somatic mutations of the Bruce gene was found in human hepatocellular carcinoma in the Cancer Genome Atlas database. Conclusion: These findings establish a BRUCE-ATR signaling axis in accurate DNA replication and suppression of liver cancer in mice and humans and provides a clinically relevant HCC mouse model.
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Affiliation(s)
- Chunmin Ge
- Department of Cancer and Cell Biology, University of Cincinnati, Cincinnati, Ohio 45267
| | | | - Lixiao Che
- Department of Cancer and Cell Biology, University of Cincinnati, Cincinnati, Ohio 45267
| | - Raj K. Pandita
- Department of Radiation Oncology, Houston Methodist Research Institute, Houston Texas 77030
| | - Shashank Hambarde
- Department of Radiation Oncology, Houston Methodist Research Institute, Houston Texas 77030
| | - Paul R. Andreassen
- Division of Experimental Hematology and Cancer Biology, Cincinnati Children Hospital Medical Center, Cincinnati, Ohio 45229
| | - Liang Niu
- Department of Environmental Health, University of Cincinnati, Cincinnati, Ohio 45267
| | - Olugbenga Olowokure
- Department of Internal Medicine, University of Cincinnati, Cincinnati, Ohio 45267
| | - Shimul Shah
- University of Cincinnati College of Medicine, University of Cincinnati, Cincinnati, Ohio 45267
| | - Susan E. Waltz
- Department of Cancer and Cell Biology, University of Cincinnati, Cincinnati, Ohio 45267
| | - Lee Zou
- Department of Pathology, Massachusetts General Hospital Cancer Center; Harvard Medical School, Charlestown, MA 02129
| | - Jiang Wang
- Department of Pathology, University of Cincinnati, Cincinnati, Ohio 45267
| | - Tej K. Pandita
- Department of Radiation Oncology, Houston Methodist Research Institute, Houston Texas 77030
| | - Chunying Du
- Department of Cancer and Cell Biology, University of Cincinnati, Cincinnati, Ohio 45267,Corresponding author: Chunying Du, Ph.D. Phone: (513) 558-4803,
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Che L, Yang X, Ge C, El-Amouri SS, Wang QE, Pan D, Herzog TJ, Du C. Loss of BRUCE reduces cellular energy level and induces autophagy by driving activation of the AMPK-ULK1 autophagic initiating axis. PLoS One 2019; 14:e0216553. [PMID: 31091257 PMCID: PMC6519829 DOI: 10.1371/journal.pone.0216553] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2018] [Accepted: 04/23/2019] [Indexed: 12/21/2022] Open
Abstract
Autophagy is an intracellular catabolic system. It delivers cellular components to lysosomes for degradation and supplies nutrients that promote cell survival under stress conditions. Although much is known regarding starvation-induced autophagy, the regulation of autophagy by cellular energy level is less clear. BRUCE is an ubiquitin conjugase and ligase with multi-functionality. It has been reported that depletion of BRUCE inhibits starvation-induced autophagy by blockage of the fusion step. Herein we report a new function for BRUCE in the dual regulation of autophagy and cellular energy. Depletion of BRUCE alone (without starvation) in human osteosarcoma U2OS cells elevated autophagic activity as indicted by the increased LC3B-II protein and its autophagic puncta as well as further increase of both by chloroquine treatment. Such elevation results from enhanced induction of autophagy since the numbers of both autophagosomes and autolysosomes were increased, and recruitment of ATG16L onto the initiating membrane structure phagophores was increased. This concept is further supported by elevated lysosomal enzyme activities. In contrast to starvation-induced autophagy, BRUCE depletion did not block fusion of autophagosomes with lysosomes as indicated by increased lysosomal cleavage of the GFP-LC3 fusion protein. Mechanistically, BRUCE depletion lowered the cellular energy level as indicated by both a higher ratio of AMP/ATP and the subsequent activation of the cellular energy sensor AMPK (pThr-172). The lower energy status co-occurred with AMPK-specific phosphorylation and activation of the autophagy initiating kinase ULK1 (pSer-555). Interestingly, the higher autophagic activity by BRUCE depletion is coupled with enhanced cisplatin resistance in human ovarian cancer PEO4 cells. Taken together, BRUCE depletion promotes induction of autophagy by lowering cellular energy and activating the AMPK-ULK1-autophagy axis, which could contribute to ovarian cancer chemo-resistance. This study establishes a BRUCE-AMPK-ULK1 axis in the regulation of energy metabolism and autophagy, as well as provides insights into cancer chemo-resistance.
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Affiliation(s)
- Lixiao Che
- Department of Cancer and Cell Biology, University of Cincinnati College of Medicine, Cincinnati, Ohio, United States of America
| | - Xingyuan Yang
- Department of Cancer and Cell Biology, University of Cincinnati College of Medicine, Cincinnati, Ohio, United States of America
| | - Chunmin Ge
- Department of Cancer and Cell Biology, University of Cincinnati College of Medicine, Cincinnati, Ohio, United States of America
| | - Salim S. El-Amouri
- Division of Experimental Hematology and Cancer Biology, Cincinnati Children’s Hospital Medical Center, Cincinnati, Ohio, United States of America
| | - Qi-En Wang
- Department of Radiology, Ohio State University, Columbus, Ohio, United States of America
| | - Dao Pan
- Division of Experimental Hematology and Cancer Biology, Cincinnati Children’s Hospital Medical Center, Cincinnati, Ohio, United States of America
- Department of Pediatrics, University of Cincinnati College of Medicine, Cincinnati, Ohio, United States of America
| | - Thomas J. Herzog
- Division of Obstetrics and Gynecology, University of Cincinnati, Cincinnati, Ohio, United States of America
- University of Cincinnati Cancer Institute, Cincinnati, Ohio, United States of America
| | - Chunying Du
- Department of Cancer and Cell Biology, University of Cincinnati College of Medicine, Cincinnati, Ohio, United States of America
- University of Cincinnati Cancer Institute, Cincinnati, Ohio, United States of America
- * E-mail:
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