Identification of Ubr1 as an amino acid sensor of steatosis in liver and muscle
Abstract Background Malnutrition is implicated in human metabolic disorders, including hepatic steatosis and myosteatosis. The corresponding nutrient signals and sensors as well as signalling pathways have not yet been well studied. This study aimed to unravel the nutrient‐sensing mechanisms in the...
| Main Authors: | , , , , , , |
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| Format: | Article |
| Language: | English |
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Wiley
2023-06-01
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| Series: | Journal of Cachexia, Sarcopenia and Muscle |
| Subjects: | |
| Online Access: | https://doi.org/10.1002/jcsm.13233 |
| _version_ | 1827267890442665984 |
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| author | Wanni Zhao Yansong Zhang Siyuan Lin Yajuan Li Alan Jian Zhu Hanping Shi Min Liu |
| author_facet | Wanni Zhao Yansong Zhang Siyuan Lin Yajuan Li Alan Jian Zhu Hanping Shi Min Liu |
| author_sort | Wanni Zhao |
| collection | DOAJ |
| description | Abstract Background Malnutrition is implicated in human metabolic disorders, including hepatic steatosis and myosteatosis. The corresponding nutrient signals and sensors as well as signalling pathways have not yet been well studied. This study aimed to unravel the nutrient‐sensing mechanisms in the pathogenesis of steatosis. Methods Plin2, a lipid droplet (LD) protein‐inhibiting lipolysis, is associated with steatosis in liver and muscle. Taking advantage of the Gal4‐UAS system, we used the Drosophila melanogaster wing imaginal disc as an in vivo model to study the regulation of Plin2 proteostasis and LD homeostasis. Drosophila Schneider 2 (S2) cells were used for western blotting, immunoprecipitation assays, amino acid‐binding assays and ubiquitination assays to further investigate the regulatory mechanisms of Plin2 in response to nutrient signals. Mouse AML12 hepatocytes, human JHH‐7 and SNU‐475 hepatoma cells were used for immunofluorescence, western blotting and immunoprecipitation to demonstrate that the mode of Plin2 regulation is evolutionarily conserved. In addition, we purified proteins from HEK293 cells and reconstituted in vitro cell‐free systems in amino acid‐binding assays, pulldown assays and ubiquitination assays to directly demonstrate the molecular mechanism by which Ubr1 senses amino acids to regulate Plin2 proteostasis. Results As a lipolysis inhibitor, Plin2 was significantly elevated in liver (P < 0.05) and muscle (P < 0.05) in patients with steatosis. Consistently, we found that the ubiquitin moiety can be conjugated to any Lys residue in Plin2, ensuring robust clearance of Plin2 by protein degradation. We further demonstrated that the E3 ubiquitin ligase Ubr1 targets Plin2 for degradation in an amino acid‐dependent manner. Ubr1 uses two canonical substrate‐binding pockets, independent of each other, to bind basic and bulky hydrophobic amino acids, respectively. Mechanistically, amino acid binding allosterically activates Ubr1 by alleviating Ubr1's auto‐inhibition. In the absence of amino acids, or when the amino acid‐binding capacity of Ubr1 is diminished, Ubr1‐mediated Plin2 degradation is inactivated, leading to steatosis. Conclusions We identified Ubr1 as an amino acid sensor regulating Plin2 proteostasis, bridging the knowledge gap between steatosis and nutrient sensing. Our work may provide new strategies for the prevention and treatment of steatosis. |
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| institution | Directory Open Access Journal |
| issn | 2190-5991 2190-6009 |
| language | English |
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| spelling | doaj.art-e0a83fc017f8484cb26b1d77a92423352024-04-27T23:07:08ZengWileyJournal of Cachexia, Sarcopenia and Muscle2190-59912190-60092023-06-011431454146710.1002/jcsm.13233Identification of Ubr1 as an amino acid sensor of steatosis in liver and muscleWanni Zhao0Yansong Zhang1Siyuan Lin2Yajuan Li3Alan Jian Zhu4Hanping Shi5Min Liu6Department of Gastrointestinal Surgery/Clinical Nutrition, Key Laboratory of Cancer FSMP for State Market Regulation, Beijing Shijitan Hospital Capital Medical University Beijing ChinaMinistry of Education Key Laboratory of Cell Proliferation and Differentiation, School of Life Sciences Peking University Beijing ChinaMinistry of Education Key Laboratory of Cell Proliferation and Differentiation, School of Life Sciences Peking University Beijing ChinaMinistry of Education Key Laboratory of Cell Proliferation and Differentiation, School of Life Sciences Peking University Beijing ChinaMinistry of Education Key Laboratory of Cell Proliferation and Differentiation, School of Life Sciences Peking University Beijing ChinaDepartment of Gastrointestinal Surgery/Clinical Nutrition, Key Laboratory of Cancer FSMP for State Market Regulation, Beijing Shijitan Hospital Capital Medical University Beijing ChinaMinistry of Education Key Laboratory of Cell Proliferation and Differentiation, School of Life Sciences Peking University Beijing ChinaAbstract Background Malnutrition is implicated in human metabolic disorders, including hepatic steatosis and myosteatosis. The corresponding nutrient signals and sensors as well as signalling pathways have not yet been well studied. This study aimed to unravel the nutrient‐sensing mechanisms in the pathogenesis of steatosis. Methods Plin2, a lipid droplet (LD) protein‐inhibiting lipolysis, is associated with steatosis in liver and muscle. Taking advantage of the Gal4‐UAS system, we used the Drosophila melanogaster wing imaginal disc as an in vivo model to study the regulation of Plin2 proteostasis and LD homeostasis. Drosophila Schneider 2 (S2) cells were used for western blotting, immunoprecipitation assays, amino acid‐binding assays and ubiquitination assays to further investigate the regulatory mechanisms of Plin2 in response to nutrient signals. Mouse AML12 hepatocytes, human JHH‐7 and SNU‐475 hepatoma cells were used for immunofluorescence, western blotting and immunoprecipitation to demonstrate that the mode of Plin2 regulation is evolutionarily conserved. In addition, we purified proteins from HEK293 cells and reconstituted in vitro cell‐free systems in amino acid‐binding assays, pulldown assays and ubiquitination assays to directly demonstrate the molecular mechanism by which Ubr1 senses amino acids to regulate Plin2 proteostasis. Results As a lipolysis inhibitor, Plin2 was significantly elevated in liver (P < 0.05) and muscle (P < 0.05) in patients with steatosis. Consistently, we found that the ubiquitin moiety can be conjugated to any Lys residue in Plin2, ensuring robust clearance of Plin2 by protein degradation. We further demonstrated that the E3 ubiquitin ligase Ubr1 targets Plin2 for degradation in an amino acid‐dependent manner. Ubr1 uses two canonical substrate‐binding pockets, independent of each other, to bind basic and bulky hydrophobic amino acids, respectively. Mechanistically, amino acid binding allosterically activates Ubr1 by alleviating Ubr1's auto‐inhibition. In the absence of amino acids, or when the amino acid‐binding capacity of Ubr1 is diminished, Ubr1‐mediated Plin2 degradation is inactivated, leading to steatosis. Conclusions We identified Ubr1 as an amino acid sensor regulating Plin2 proteostasis, bridging the knowledge gap between steatosis and nutrient sensing. Our work may provide new strategies for the prevention and treatment of steatosis.https://doi.org/10.1002/jcsm.13233Amino acidDegradationHepatic steatosisLipid dropletMyosteatosisPlin2 |
| spellingShingle | Wanni Zhao Yansong Zhang Siyuan Lin Yajuan Li Alan Jian Zhu Hanping Shi Min Liu Identification of Ubr1 as an amino acid sensor of steatosis in liver and muscle Journal of Cachexia, Sarcopenia and Muscle Amino acid Degradation Hepatic steatosis Lipid droplet Myosteatosis Plin2 |
| title | Identification of Ubr1 as an amino acid sensor of steatosis in liver and muscle |
| title_full | Identification of Ubr1 as an amino acid sensor of steatosis in liver and muscle |
| title_fullStr | Identification of Ubr1 as an amino acid sensor of steatosis in liver and muscle |
| title_full_unstemmed | Identification of Ubr1 as an amino acid sensor of steatosis in liver and muscle |
| title_short | Identification of Ubr1 as an amino acid sensor of steatosis in liver and muscle |
| title_sort | identification of ubr1 as an amino acid sensor of steatosis in liver and muscle |
| topic | Amino acid Degradation Hepatic steatosis Lipid droplet Myosteatosis Plin2 |
| url | https://doi.org/10.1002/jcsm.13233 |
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