1
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Han SI, Nakakuki M, Nakagawa Y, Wang Y, Araki M, Yamamoto Y, Tokiwa H, Takeda H, Mizunoe Y, Motomura K, Ohno H, Kainoh K, Murayama Y, Aita Y, Takeuchi Y, Osaki Y, Miyamoto T, Sekiya M, Matsuzaka T, Yahagi N, Sone H, Daitoku H, Sato R, Kawano H, Shimano H. Rhomboid protease RHBDL4/RHBDD1 cleaves SREBP-1c at endoplasmic reticulum monitoring and regulating fatty acids. PNAS NEXUS 2023; 2:pgad351. [PMID: 37954160 PMCID: PMC10637267 DOI: 10.1093/pnasnexus/pgad351] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/27/2023] [Accepted: 10/02/2023] [Indexed: 11/14/2023]
Abstract
The endoplasmic reticulum (ER)-embedded transcription factors, sterol regulatory element-binding proteins (SREBPs), master regulators of lipid biosynthesis, are transported to the Golgi for proteolytic activation to tune cellular cholesterol levels and regulate lipogenesis. However, mechanisms by which the cell responds to the levels of saturated or unsaturated fatty acids remain underexplored. Here, we show that RHBDL4/RHBDD1, a rhomboid family protease, directly cleaves SREBP-1c at the ER. The p97/VCP, AAA-ATPase complex then acts as an auxiliary segregase to extract the remaining ER-embedded fragment of SREBP-1c. Importantly, the enzymatic activity of RHBDL4 is enhanced by saturated fatty acids (SFAs) but inhibited by polyunsaturated fatty acids (PUFAs). Genetic deletion of RHBDL4 in mice fed on a Western diet enriched in SFAs and cholesterol prevented SREBP-1c from inducing genes for lipogenesis, particularly for synthesis and incorporation of PUFAs, and secretion of lipoproteins. The RHBDL4-SREBP-1c pathway reveals a regulatory system for monitoring fatty acid composition and maintaining cellular lipid homeostasis.
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Affiliation(s)
- Song-Iee Han
- Department of Endocrinology and Metabolism, Institute of Medicine, University of Tsukuba, Tsukuba, Ibaraki 305-8575, Japan
- International Institute for Integrative Sleep Medicine (WPI-IIIS), University of Tsukuba, Tsukuba, Ibaraki 305-8575, Japan
| | - Masanori Nakakuki
- Pharmaceutical Research Center, Mochida Pharmaceutical Co., Ltd., Gotemba, Shizuoka 412-8524, Japan
| | - Yoshimi Nakagawa
- Department of Endocrinology and Metabolism, Institute of Medicine, University of Tsukuba, Tsukuba, Ibaraki 305-8575, Japan
- Division of Complex Biosystem Research, Department of Research and Development, Institute of Natural Medicine, University of Toyama, Toyama, Toyama 930-0194, Japan
| | - Yunong Wang
- Department of Endocrinology and Metabolism, Institute of Medicine, University of Tsukuba, Tsukuba, Ibaraki 305-8575, Japan
| | - Masaya Araki
- Department of Endocrinology and Metabolism, Institute of Medicine, University of Tsukuba, Tsukuba, Ibaraki 305-8575, Japan
| | - Yuta Yamamoto
- Department of Chemistry, Rikkyo University, Toshima-ku, Tokyo 171-8501, Japan
| | - Hiroaki Tokiwa
- Laboratory of Organic Chemistry, Gifu Pharmaceutical University, Daigaku-Nishi, Gifu 501-1196, Japan
| | - Hiroyuki Takeda
- Division of Proteo Drug Discovery Sciences, Proteo-Science Center, Ehime University, Matsuyama, Ehime 790-8577, Japan
| | - Yuhei Mizunoe
- Department of Endocrinology and Metabolism, Institute of Medicine, University of Tsukuba, Tsukuba, Ibaraki 305-8575, Japan
| | - Kaori Motomura
- Department of Endocrinology and Metabolism, Institute of Medicine, University of Tsukuba, Tsukuba, Ibaraki 305-8575, Japan
| | - Hiroshi Ohno
- Department of Endocrinology and Metabolism, Institute of Medicine, University of Tsukuba, Tsukuba, Ibaraki 305-8575, Japan
| | - Kenta Kainoh
- Department of Endocrinology and Metabolism, Institute of Medicine, University of Tsukuba, Tsukuba, Ibaraki 305-8575, Japan
| | - Yuki Murayama
- Department of Endocrinology and Metabolism, Institute of Medicine, University of Tsukuba, Tsukuba, Ibaraki 305-8575, Japan
| | - Yuichi Aita
- Department of Endocrinology and Metabolism, Institute of Medicine, University of Tsukuba, Tsukuba, Ibaraki 305-8575, Japan
| | - Yoshinori Takeuchi
- Department of Endocrinology and Metabolism, Institute of Medicine, University of Tsukuba, Tsukuba, Ibaraki 305-8575, Japan
| | - Yoshinori Osaki
- Department of Endocrinology and Metabolism, Institute of Medicine, University of Tsukuba, Tsukuba, Ibaraki 305-8575, Japan
| | - Takafumi Miyamoto
- Department of Endocrinology and Metabolism, Institute of Medicine, University of Tsukuba, Tsukuba, Ibaraki 305-8575, Japan
- Transborder Medical Research Center, University of Tsukuba, Tsukuba, Ibaraki 305-8577, Japan
| | - Motohiro Sekiya
- Department of Endocrinology and Metabolism, Institute of Medicine, University of Tsukuba, Tsukuba, Ibaraki 305-8575, Japan
| | - Takashi Matsuzaka
- Department of Endocrinology and Metabolism, Institute of Medicine, University of Tsukuba, Tsukuba, Ibaraki 305-8575, Japan
- Transborder Medical Research Center, University of Tsukuba, Tsukuba, Ibaraki 305-8577, Japan
| | - Naoya Yahagi
- Department of Endocrinology and Metabolism, Institute of Medicine, University of Tsukuba, Tsukuba, Ibaraki 305-8575, Japan
| | - Hirohito Sone
- Department of Internal Medicine, Faculty of Medicine, Niigata University, Niigata, Niigata 951-8510, Japan
| | - Hiroaki Daitoku
- Life Science Center for Survival Dynamics, Tsukuba Advanced Research Alliance (TARA), University of Tsukuba, Tsukuba, Ibaraki 305-8577, Japan
| | - Ryuichiro Sato
- Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, Nutri-Life Science Laboratory, The University of Tokyo, Tokyo 113-8657, Japan
| | - Hiroyuki Kawano
- Pharmaceutical Research Center, Mochida Pharmaceutical Co., Ltd., Gotemba, Shizuoka 412-8524, Japan
| | - Hitoshi Shimano
- Department of Endocrinology and Metabolism, Institute of Medicine, University of Tsukuba, Tsukuba, Ibaraki 305-8575, Japan
- International Institute for Integrative Sleep Medicine (WPI-IIIS), University of Tsukuba, Tsukuba, Ibaraki 305-8575, Japan
- Life Science Center for Survival Dynamics, Tsukuba Advanced Research Alliance (TARA), University of Tsukuba, Tsukuba, Ibaraki 305-8577, Japan
- Japan Agency for Medical Research and Development, Core Research for Evolutional Science and Technology (AMED-CREST), Chiyoda-ku, Tokyo 100-0004, Japan
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2
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Bhaduri S, Scott NA, Neal SE. The Role of the Rhomboid Superfamily in ER Protein Quality Control: From Mechanisms and Functions to Diseases. Cold Spring Harb Perspect Biol 2023; 15:a041248. [PMID: 35940905 PMCID: PMC9899648 DOI: 10.1101/cshperspect.a041248] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
The endoplasmic reticulum (ER) is an essential organelle in eukaryotic cells and is a major site for protein folding, modification, and lipid synthesis. Perturbations within the ER, such as protein misfolding and high demand for protein folding, lead to dysregulation of the ER protein quality control network and ER stress. Recently, the rhomboid superfamily has emerged as a critical player in ER protein quality control because it has diverse cellular functions, including ER-associated degradation (ERAD), endosome Golgi-associated degradation (EGAD), and ER preemptive quality control (ERpQC). This breadth of function both illustrates the importance of the rhomboid superfamily in health and diseases and emphasizes the necessity of understanding their mechanisms of action. Because dysregulation of rhomboid proteins has been implicated in various diseases, such as neurological disorders and cancers, they represent promising potential therapeutic drug targets. This review provides a comprehensive account of the various roles of rhomboid proteins in the context of ER protein quality control and discusses their significance in health and disease.
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Affiliation(s)
- Satarupa Bhaduri
- School of Biological Sciences, the Section of Cell and Developmental Biology, University of California San Diego, La Jolla, California 92093, USA
| | - Nicola A Scott
- School of Biological Sciences, the Section of Cell and Developmental Biology, University of California San Diego, La Jolla, California 92093, USA
| | - Sonya E Neal
- School of Biological Sciences, the Section of Cell and Developmental Biology, University of California San Diego, La Jolla, California 92093, USA
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3
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Shibuya K, Ebihara K, Ebihara C, Sawayama N, Isoda M, Yamamuro D, Takahashi M, Nagashima S, Ishibashi S. AAA-ATPase valosin-containing protein (VCP) binds the transcription factor SREBP1 and promotes its proteolytic activation by rhomboid protease RHBDL4. J Biol Chem 2022; 298:101936. [PMID: 35430252 PMCID: PMC9127370 DOI: 10.1016/j.jbc.2022.101936] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2022] [Revised: 03/29/2022] [Accepted: 04/01/2022] [Indexed: 11/24/2022] Open
Abstract
Valosin-containing protein (VCP) is a member of AAA-ATPase superfamily involved in various cellular functions. To investigate the pathophysiological role of VCP in metabolic disorders, we generated knock-in mice bearing an A232E mutation in VCP, a known human VCP pathogenic variant. When heterozygous mutant mice (A232E/+) were fed a high-fat diet, we observed that fatty liver was ameliorated and the proteolytic processing of the transcription factor sterol regulatory element-binding protein 1 (SREBP1) was impaired. Further co-immunoprecipitation analysis in wildtype mice revealed interactions of VCP with SREBP1 and a rhomboid protease, RHBDL4, in the liver, and these interactions were attenuated in A232E/+ mice. Consistent with these results, we show that knockdown or chemical inhibition of VCP or RHBDL4 in human hepatocytes impaired the proteolytic processing of SREBP1. Finally, we found that knockdown of E3 ligases such as glycoprotein 78 and HMG-CoA reductase degradation protein 1 disrupted the interaction of VCP with SREBP1 and impaired the proteolytic processing of SREBP1. These results suggest that VCP recognizes ubiquitinylated SREBP1 and recruits it to RHBDL4 to promote its proteolytic processing. The present study reveals a novel proteolytic processing pathway of SREBP1 and may lead to development of new therapeutic strategies to treat fatty liver diseases.
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Affiliation(s)
- Koji Shibuya
- Division of Endocrinology and Metabolism, Department of Internal Medicine, Jichi Medical University School of Medicine, Yakushiji 3311-1, Shimotsuke, Tochigi 329-0498, Japan
| | - Ken Ebihara
- Division of Endocrinology and Metabolism, Department of Internal Medicine, Jichi Medical University School of Medicine, Yakushiji 3311-1, Shimotsuke, Tochigi 329-0498, Japan.
| | - Chihiro Ebihara
- Division of Endocrinology and Metabolism, Department of Internal Medicine, Jichi Medical University School of Medicine, Yakushiji 3311-1, Shimotsuke, Tochigi 329-0498, Japan
| | - Nagisa Sawayama
- Division of Endocrinology and Metabolism, Department of Internal Medicine, Jichi Medical University School of Medicine, Yakushiji 3311-1, Shimotsuke, Tochigi 329-0498, Japan
| | - Masayo Isoda
- Division of Endocrinology and Metabolism, Department of Internal Medicine, Jichi Medical University School of Medicine, Yakushiji 3311-1, Shimotsuke, Tochigi 329-0498, Japan
| | - Daisuke Yamamuro
- Division of Endocrinology and Metabolism, Department of Internal Medicine, Jichi Medical University School of Medicine, Yakushiji 3311-1, Shimotsuke, Tochigi 329-0498, Japan
| | - Manabu Takahashi
- Division of Endocrinology and Metabolism, Department of Internal Medicine, Jichi Medical University School of Medicine, Yakushiji 3311-1, Shimotsuke, Tochigi 329-0498, Japan
| | - Shuichi Nagashima
- Division of Endocrinology and Metabolism, Department of Internal Medicine, Jichi Medical University School of Medicine, Yakushiji 3311-1, Shimotsuke, Tochigi 329-0498, Japan
| | - Shun Ishibashi
- Division of Endocrinology and Metabolism, Department of Internal Medicine, Jichi Medical University School of Medicine, Yakushiji 3311-1, Shimotsuke, Tochigi 329-0498, Japan
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4
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Gómez M, Baeza M, Cifuentes V, Alcaíno J. The SREBP (Sterol Regulatory Element-Binding Protein) pathway: a regulatory bridge between carotenogenesis and sterol biosynthesis in the carotenogenic yeast Xanthophyllomyces dendrorhous. Biol Res 2021; 54:34. [PMID: 34702374 PMCID: PMC8549280 DOI: 10.1186/s40659-021-00359-x] [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: 08/06/2021] [Accepted: 10/16/2021] [Indexed: 11/22/2022] Open
Abstract
Xanthophyllomyces dendrorhous is a basidiomycete yeast that naturally produces the red–orange carotenoid astaxanthin, which has remarkable antioxidant properties. The biosynthesis of carotenoids and sterols share some common elements that have been studied in X. dendrorhous. For example, their synthesis requires metabolites derived from the mevalonate pathway and in both specific pathways, cytochrome P450 enzymes are involved that share a single cytochrome P450 reductase, CrtR, which is essential for astaxanthin biosynthesis, but is replaceable for ergosterol biosynthesis. Research on the regulation of carotenoid biosynthesis is still limited in X. dendrorhous; however, it is known that the Sterol Regulatory Element-Binding Protein (SREBP) pathway, which is a conserved regulatory pathway involved in the control of lipid metabolism, also regulates carotenoid production in X. dendrorhous. This review addresses the similarities and differences that have been observed between mammal and fungal SREBP pathways and what it is known about this pathway regarding the regulation of the production of carotenoids and sterols in X. dendrorhous.
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Affiliation(s)
- Melissa Gómez
- Departamento de Ciencias Ecológicas, Facultad de Ciencias, Universidad de Chile, Las Palmeras 3425, Santiago, Chile
| | - Marcelo Baeza
- Departamento de Ciencias Ecológicas, Facultad de Ciencias, Universidad de Chile, Las Palmeras 3425, Santiago, Chile.,Centro de Biotecnología, Facultad de Ciencias, Universidad de Chile, Las Palmeras 3425, Santiago, Chile
| | - Víctor Cifuentes
- Departamento de Ciencias Ecológicas, Facultad de Ciencias, Universidad de Chile, Las Palmeras 3425, Santiago, Chile.,Centro de Biotecnología, Facultad de Ciencias, Universidad de Chile, Las Palmeras 3425, Santiago, Chile
| | - Jennifer Alcaíno
- Departamento de Ciencias Ecológicas, Facultad de Ciencias, Universidad de Chile, Las Palmeras 3425, Santiago, Chile. .,Centro de Biotecnología, Facultad de Ciencias, Universidad de Chile, Las Palmeras 3425, Santiago, Chile.
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5
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High-Throughput Identification of Nuclear Envelope Protein Interactions in Schizosaccharomyces pombe Using an Arrayed Membrane Yeast-Two Hybrid Library. G3-GENES GENOMES GENETICS 2020; 10:4649-4663. [PMID: 33109728 PMCID: PMC7718735 DOI: 10.1534/g3.120.401880] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The nuclear envelope (NE) contains a specialized set of integral membrane proteins that maintain nuclear shape and integrity and influence chromatin organization and gene expression. Advances in proteomics techniques and studies in model organisms have identified hundreds of proteins that localize to the NE. However, the function of many of these proteins at the NE remains unclear, in part due to a lack of understanding of the interactions that these proteins participate in at the NE membrane. To assist in the characterization of NE transmembrane protein interactions we developed an arrayed library of integral and peripheral membrane proteins from the fission yeast Schizosaccharomyces pombe for high-throughput screening using the split-ubiquitin based membrane yeast two -hybrid system. We used this approach to characterize protein interactions for three conserved proteins that localize to the inner nuclear membrane: Cut11/Ndc1, Lem2 and Ima1/Samp1/Net5. Additionally, we determined how the interaction network for Cut11 is altered in canonical temperature-sensitive cut11-ts mutants. This library and screening approach is readily applicable to characterizing the interactomes of integral membrane proteins localizing to various subcellular compartments.
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6
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Abstract
Synthesis and regulation of lipid levels and identities is critical for a wide variety of cellular functions, including structural and morphological properties of organelles, energy storage, signaling, and stability and function of membrane proteins. Proteolytic cleavage events regulate and/or influence some of these lipid metabolic processes and as a result help modulate their pleiotropic cellular functions. Proteins involved in lipid regulation are proteolytically cleaved for the purpose of their relocalization, processing, turnover, and quality control, among others. The scope of this review includes proteolytic events governing cellular lipid dynamics. After an initial discussion of the classic example of sterol regulatory element-binding proteins, our focus will shift to the mitochondrion, where a range of proteolytic events are critical for normal mitochondrial phospholipid metabolism and enforcing quality control therein. Recently, mitochondrial phospholipid metabolic pathways have been implicated as important for the proliferative capacity of cancers. Thus, the assorted proteases that regulate, monitor, or influence the activity of proteins that are important for phospholipid metabolism represent attractive targets to be manipulated for research purposes and clinical applications.
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Affiliation(s)
- Pingdewinde N. Sam
- Department of Physiology, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, United States
| | - Erica Avery
- Department of Physiology, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, United States
| | - Steven M. Claypool
- Department of Physiology, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, United States
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7
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Paschkowsky S, Recinto SJ, Young JC, Bondar AN, Munter LM. Membrane cholesterol as regulator of human rhomboid protease RHBDL4. J Biol Chem 2018; 293:15556-15568. [PMID: 30143535 DOI: 10.1074/jbc.ra118.002640] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2018] [Revised: 08/18/2018] [Indexed: 12/28/2022] Open
Abstract
In the last decade, intramembrane proteases have gained increasing attention because of their many links to various diseases. Nevertheless, our understanding as to how they function or how they are regulated is still limited, especially when it comes to human homologues. In this regard, here we sought to unravel mechanisms of regulation of the protease rhomboid-like protein-4 (RHBDL4), one of five active human serine intramembrane proteases. In view of our recent finding that human RHBDL4 efficiently cleaves the amyloid precursor protein (APP), a key protein in the pathology of Alzheimer's disease, we used established reagents to modulate the cellular cholesterol content and analyzed the effects of this modulation on RHBDL4-mediated processing of endogenous APP. We discovered that lowering membrane cholesterol levels increased the levels of RHBDL4-specific endogenous APP fragments, whereas high cholesterol levels had the opposite effect. Direct binding of cholesterol to APP did not mediate these modulating effects of cholesterol. Instead, using homology modeling, we identified two potential cholesterol-binding motifs in the transmembrane helices 3 and 6 of RHBDL4. Substitution of the essential tyrosine residues of the potential cholesterol-binding motifs to alanine increased the levels of endogenous APP C-terminal fragments, reflecting enhanced RHBDL4 activity. In summary, we provide evidence that the activity of RHBDL4 is regulated by cholesterol likely through a direct binding of cholesterol to the enzyme.
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Affiliation(s)
- Sandra Paschkowsky
- From the Department of Pharmacology and Therapeutics and Cell Information Systems Group and
| | | | - Jason C Young
- Department of Biochemistry and Groupe de Recherche Axé sur la Structure des Protéines, McGill University, Montreal, Quebec H3G 0B1, Canada and
| | - Ana-Nicoleta Bondar
- the Department of Physics, Theoretical Molecular Biophysics, Freie Universität Berlin, Arnimallee 14, Berlin 14195, Germany
| | - Lisa Marie Munter
- From the Department of Pharmacology and Therapeutics and Cell Information Systems Group and
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8
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Knockout of the SREBP system increases production of the polyketide FR901512 in filamentous fungal sp. No. 14919 and lovastatin in Aspergillus terreus ATCC20542. Appl Microbiol Biotechnol 2017; 102:1393-1405. [DOI: 10.1007/s00253-017-8685-7] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2017] [Revised: 11/27/2017] [Accepted: 11/29/2017] [Indexed: 12/19/2022]
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9
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Embedded in the Membrane: How Lipids Confer Activity and Specificity to Intramembrane Proteases. J Membr Biol 2017; 251:369-378. [PMID: 29260282 DOI: 10.1007/s00232-017-0008-5] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2017] [Accepted: 12/12/2017] [Indexed: 10/18/2022]
Abstract
Proteases, sharp yet unforgivable tools of every cell, require tight regulation to ensure specific non-aberrant cleavages. The relatively recent discovered class of intramembrane proteases has gained increasing interest due to their involvement in important signaling pathways linking them to diseases including Alzheimer's disease and cancer. Despite tremendous efforts, their regulatory mechanisms have only started to unravel. There is evidence that the membrane composition itself can regulate intramembrane protease activity and specificity. In this review, we highlight the work on γ-secretase and rhomboid proteases and summarize several studies as to how different lipids impact on enzymatic activity.
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10
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Abstract
Cellular lipid metabolism and homeostasis are controlled by sterol regulatory-element binding proteins (SREBPs). In addition to performing canonical functions in the transcriptional regulation of genes involved in the biosynthesis and uptake of lipids, genome-wide system analyses have revealed that these versatile transcription factors act as important nodes of convergence and divergence within biological signalling networks. Thus, they are involved in myriad physiological and pathophysiological processes, highlighting the importance of lipid metabolism in biology. Changes in cell metabolism and growth are reciprocally linked through SREBPs. Anabolic and growth signalling pathways branch off and connect to multiple steps of SREBP activation and form complex regulatory networks. In addition, SREBPs are implicated in numerous pathogenic processes such as endoplasmic reticulum stress, inflammation, autophagy and apoptosis, and in this way, they contribute to obesity, dyslipidaemia, diabetes mellitus, nonalcoholic fatty liver disease, nonalcoholic steatohepatitis, chronic kidney disease, neurodegenerative diseases and cancers. This Review aims to provide a comprehensive understanding of the role of SREBPs in physiology and pathophysiology at the cell, organ and organism levels.
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Affiliation(s)
- Hitoshi Shimano
- Department of Internal Medicine (Endocrinology and Metabolism), Faculty of Medicine, University of Tsukuba, Tsukuba, Ibaraki 305-8575, Japan
- International Institute for Integrative Sleep Medicine (WPI-IIIS), University of Tsukuba, Tsukuba, Ibaraki 305-8575, Japan
- Life Science Center, Tsukuba Advanced Research Alliance (TARA), University of Tsukuba, Tsukuba 305-8577, Japan
- AMED-CREST, Japan Agency for Medical Research and Development, Chiyoda-ku, Tokyo 100-0004, Japan
| | - Ryuichiro Sato
- AMED-CREST, Japan Agency for Medical Research and Development, Chiyoda-ku, Tokyo 100-0004, Japan
- Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Bunkyo, Tokyo 113-8657, Japan
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11
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Deciphering the Regulatory Network between the SREBP Pathway and Protein Secretion in Neurospora crassa. mBio 2017; 8:mBio.00233-17. [PMID: 28420736 PMCID: PMC5395666 DOI: 10.1128/mbio.00233-17] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Sterol regulatory element binding proteins (SREBPs) are conserved from yeast to mammalian cells and function in the regulation of sterol homeostasis. In fungi, the SREBP pathway has been implicated in the adaptation to hypoxia and in virulence. In Neurospora crassa and Trichoderma reesei, the SREBP pathway also negatively regulates protein secretion under lignocellulolytic conditions. Here we utilized global transcriptional profiling combined with genetic and physiological analyses to address the regulatory link between the SREBP pathway and protein secretion in N. crassa. Our results demonstrated that the function of the SREBP pathway in ergosterol biosynthesis and adaptation to hypoxia was conserved in N. crassa. Under lignocellulolytic conditions, the SREBP pathway was highly activated, resulting in the reduced expression of lytic polysaccharide monooxygenases, which require molecular oxygen for catalytic activity. Additionally, activation of the SREBP pathway under lignocellulolytic conditions repressed a set of genes predicted to be involved in the endoplasmic reticulum stress response. Here we show that the inability of a hac-1 mutant, which bears a deletion of the major regulator of the unfolded protein response (UPR), to efficiently produce cellulases and utilize cellulose was suppressed by mutations in the SREBP pathway. The analyses presented here demonstrated new SREBP pathway functions, including linkages to the UPR, and provide new clues for genetic engineering of filamentous fungi to improve their production of extracellular proteins. The role of SREBP transcription factors in the regulation of sterol biosynthesis is conserved from humans to yeast. In filamentous fungi, this pathway regulates the secretion of lignocellulolytic enzymes during plant biomass deconstruction. Here we show that the SREBP pathway in Neurospora crassa regulates the production of specific cellulases, lytic polysaccharide monooxygenases that utilize molecular oxygen. Via global transcriptional profile and genetic analyses, a relationship between the SREBP pathway and the unfolded protein response (UPR) pathway was revealed, suggesting a regulatory interplay of these two pathways in the trafficking of plant biomass-degrading enzymes. These findings have implications for our understanding of the cross talk of the SREBP and UPR pathways in other organisms and will guide the rational engineering of fungal strains to improve cellulolytic enzyme production.
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12
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Burr R, Stewart EV, Espenshade PJ. Coordinate Regulation of Yeast Sterol Regulatory Element-binding Protein (SREBP) and Mga2 Transcription Factors. J Biol Chem 2017; 292:5311-5324. [PMID: 28202541 DOI: 10.1074/jbc.m117.778209] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2017] [Indexed: 11/06/2022] Open
Abstract
The Mga2 and Sre1 transcription factors regulate oxygen-responsive lipid homeostasis in the fission yeast Schizosaccharomyces pombe in a manner analogous to the mammalian sterol regulatory element-binding protein (SREBP)-1 and SREBP-2 transcription factors. Mga2 and SREBP-1 regulate triacylglycerol and glycerophospholipid synthesis, whereas Sre1 and SREBP-2 regulate sterol synthesis. In mammals, a shared activation mechanism allows for coordinate regulation of SREBP-1 and SREBP-2. In contrast, distinct pathways activate fission yeast Mga2 and Sre1. Therefore, it is unclear whether and how these two related pathways are coordinated to maintain lipid balance in fission yeast. Previously, we showed that Sre1 cleavage is defective in the absence of mga2 Here, we report that this defect is due to deficient unsaturated fatty acid synthesis, resulting in aberrant membrane transport. This defect is recapitulated by treatment with the fatty acid synthase inhibitor cerulenin and is rescued by addition of exogenous unsaturated fatty acids. Furthermore, sterol synthesis inhibition blocks Mga2 pathway activation. Together, these data demonstrate that Sre1 and Mga2 are each regulated by the lipid product of the other transcription factor pathway, providing a source of coordination for these two branches of lipid synthesis.
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Affiliation(s)
- Risa Burr
- From the Department of Cell Biology, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
| | - Emerson V Stewart
- From the Department of Cell Biology, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
| | - Peter J Espenshade
- From the Department of Cell Biology, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
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13
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Dhingra S, Cramer RA. Regulation of Sterol Biosynthesis in the Human Fungal Pathogen Aspergillus fumigatus: Opportunities for Therapeutic Development. Front Microbiol 2017; 8:92. [PMID: 28203225 PMCID: PMC5285346 DOI: 10.3389/fmicb.2017.00092] [Citation(s) in RCA: 53] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2016] [Accepted: 01/13/2017] [Indexed: 12/29/2022] Open
Abstract
Sterols are a major component of eukaryotic cell membranes. For human fungal infections caused by the filamentous fungus Aspergillus fumigatus, antifungal drugs that target sterol biosynthesis and/or function remain the standard of care. Yet, an understanding of A. fumigatus sterol biosynthesis regulatory mechanisms remains an under developed therapeutic target. The critical role of sterol biosynthesis regulation and its interactions with clinically relevant azole drugs is highlighted by the basic helix loop helix (bHLH) class of transcription factors known as Sterol Regulatory Element Binding Proteins (SREBPs). SREBPs regulate transcription of key ergosterol biosynthesis genes in fungi including A. fumigatus. In addition, other emerging regulatory pathways and target genes involved in sterol biosynthesis and drug interactions provide additional opportunities including the unfolded protein response, iron responsive transcriptional networks, and chaperone proteins such as Hsp90. Thus, targeting molecular pathways critical for sterol biosynthesis regulation presents an opportunity to improve therapeutic options for the collection of diseases termed aspergillosis. This mini-review summarizes our current understanding of sterol biosynthesis regulation with a focus on mechanisms of transcriptional regulation by the SREBP family of transcription factors.
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Affiliation(s)
- Sourabh Dhingra
- Department of Microbiology and Immunology, Geisel School of Medicine at Dartmouth, Hanover NH, USA
| | - Robert A Cramer
- Department of Microbiology and Immunology, Geisel School of Medicine at Dartmouth, Hanover NH, USA
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Complex structure of the fission yeast SREBP-SCAP binding domains reveals an oligomeric organization. Cell Res 2016; 26:1197-1211. [PMID: 27811944 PMCID: PMC5099872 DOI: 10.1038/cr.2016.123] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2016] [Revised: 08/05/2016] [Accepted: 08/26/2016] [Indexed: 12/22/2022] Open
Abstract
Sterol regulatory element-binding protein (SREBP) transcription factors are master regulators of cellular lipid homeostasis in mammals and oxygen-responsive regulators of hypoxic adaptation in fungi. SREBP C-terminus binds to the WD40 domain of SREBP cleavage-activating protein (SCAP), which confers sterol regulation by controlling the ER-to-Golgi transport of the SREBP-SCAP complex and access to the activating proteases in the Golgi. Here, we biochemically and structurally show that the carboxyl terminal domains (CTD) of Sre1 and Scp1, the fission yeast SREBP and SCAP, form a functional 4:4 oligomer and Sre1-CTD forms a dimer of dimers. The crystal structure of Sre1-CTD at 3.5 Å and cryo-EM structure of the complex at 5.4 Å together with in vitro biochemical evidence elucidate three distinct regions in Sre1-CTD required for Scp1 binding, Sre1-CTD dimerization and tetrameric formation. Finally, these structurally identified domains are validated in a cellular context, demonstrating that the proper 4:4 oligomeric complex formation is required for Sre1 activation.
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15
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Urban S. A guide to the rhomboid protein superfamily in development and disease. Semin Cell Dev Biol 2016; 60:1-4. [PMID: 27751777 DOI: 10.1016/j.semcdb.2016.10.002] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2016] [Accepted: 10/13/2016] [Indexed: 11/28/2022]
Abstract
Rhomboid proteins are considered to be the most widespread membrane proteins across all forms of life. This superfamily comprises both active intramembrane serine proteases that catalyze the release of factors from the membrane, and a eukaryotic subset of non-catalytic members in which rhomboid architecture supports deviating functions. Although rhomboid was discovered in genetic studies of insect development, rhomboid research has broadened dramatically over the past 15 years; rhomboid enzymes are now the best biophysically understood of all intramembrane proteases, and are considered promising therapeutic targets for diseases ranging from parasitic infections to Parkinsonian neurodegeneration. Perhaps the most rapid progress has come with the catalytically inert rhomboid proteins, some of which regulate protein trafficking and/or function, and their prominence is underscored by clinical mutations. Such a diverse collection of advances mark an excellent point to review the state of this vibrant area of research, not because central questions have been answered, but instead because a firm grip in key areas has been established, and the field is now poised for breakthroughs.
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Affiliation(s)
- Siniša Urban
- Department of Molecular Biology & Genetics, Johns Hopkins University School of Medicine, Room 507 PCTB, 725 North Wolfe Street, Baltimore, MD, 21205, USA.
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16
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Hwang J, Ribbens D, Raychaudhuri S, Cairns L, Gu H, Frost A, Urban S, Espenshade PJ. A Golgi rhomboid protease Rbd2 recruits Cdc48 to cleave yeast SREBP. EMBO J 2016; 35:2332-2349. [PMID: 27655872 DOI: 10.15252/embj.201693923] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2016] [Accepted: 09/06/2016] [Indexed: 12/26/2022] Open
Abstract
Hypoxic growth of fungi requires sterol regulatory element-binding protein (SREBP) transcription factors, and human opportunistic fungal pathogens require SREBP activation for virulence. Proteolytic release of fission yeast SREBPs from the membrane in response to low oxygen requires the Golgi membrane-anchored Dsc E3 ligase complex. Using genetic interaction arrays, we identified Rbd2 as a rhomboid family protease required for SREBP proteolytic processing. Rbd2 is an active, Golgi-localized protease that cleaves the transmembrane segment of the TatA rhomboid model substrate. Epistasis analysis revealed that the Dsc E3 ligase acts on SREBP prior to cleavage by Rbd2. Using APEX2 proximity biotinylation, we demonstrated that Rbd2 binds the AAA-ATPase Cdc48 through a C-terminal SHP box. Interestingly, SREBP cleavage required Rbd2 binding of Cdc48, consistent with Cdc48 acting to recruit ubiquitinylated substrates. In support of this claim, overexpressing a Cdc48-binding mutant of Rbd2 bypassed the Cdc48 requirement for SREBP cleavage, demonstrating that Cdc48 likely plays a role in SREBP recognition. In the absence of functional Rbd2, SREBP precursor is degraded by the proteasome, indicating that Rbd2 activity controls the balance between SREBP activation and degradation.
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Affiliation(s)
- Jiwon Hwang
- Department of Cell Biology, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Diedre Ribbens
- Department of Cell Biology, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Sumana Raychaudhuri
- Department of Cell Biology, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Leah Cairns
- Howard Hughes Medical Institute, Department of Molecular Biology & Genetics, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - He Gu
- Department of Cell Biology, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Adam Frost
- Department of Biochemistry and Biophysics, University of California, San Francisco, CA, USA
| | - Siniša Urban
- Howard Hughes Medical Institute, Department of Molecular Biology & Genetics, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Peter J Espenshade
- Department of Cell Biology, Johns Hopkins University School of Medicine, Baltimore, MD, USA
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Dogga SK, Soldati-Favre D. Biology of rhomboid proteases in infectious diseases. Semin Cell Dev Biol 2016; 60:38-45. [PMID: 27567708 DOI: 10.1016/j.semcdb.2016.08.020] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2016] [Revised: 08/04/2016] [Accepted: 08/23/2016] [Indexed: 12/26/2022]
Abstract
Rhomboids are a well-conserved class of intramembrane serine proteases found in all kingdoms of life, sharing a conserved core structure of at least six transmembrane (TM) domains that contain the catalytic serine-histidine dyad. The rhomboid proteases, which cleave membrane embedded substrates within their TM domains, are emerging as an important group of enzymes controlling a myriad of biological processes. These enzymes are found in a wide variety of pathogens manifesting important roles in their pathological processes. Accordingly, they have received considerable attention as potential targets for pharmacological intervention over the past few years. This review provides a general update on rhomboid proteases and their roles in pathogenesis of human infectious agents.
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Affiliation(s)
- Sunil Kumar Dogga
- Department of Microbiology and Molecular Medicine, University of Geneva, CMU, 1 Rue Michel-Servet, CH-1211 Geneva 4, Switzerland.
| | - Dominique Soldati-Favre
- Department of Microbiology and Molecular Medicine, University of Geneva, CMU, 1 Rue Michel-Servet, CH-1211 Geneva 4, Switzerland
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18
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Substrates and physiological functions of secretase rhomboid proteases. Semin Cell Dev Biol 2016; 60:10-18. [PMID: 27497690 DOI: 10.1016/j.semcdb.2016.07.033] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2016] [Revised: 07/26/2016] [Accepted: 07/31/2016] [Indexed: 02/01/2023]
Abstract
Rhomboids are conserved intramembrane serine proteases with widespread functions. They were the earliest discovered members of the wider rhomboid-like superfamily of proteases and pseudoproteases. The secretase class of rhomboid proteases, distributed through the secretory pathway, are the most numerous in eukaryotes, but our knowledge of them is limited. Here we aim to summarise all that has been published on secretase rhomboids in a concise encyclopaedia of the enzymes, their substrates, and their biological roles. We also discuss emerging themes of how these important enzymes are regulated.
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Identification and Characterization of a Novel Aspergillus fumigatus Rhomboid Family Putative Protease, RbdA, Involved in Hypoxia Sensing and Virulence. Infect Immun 2016; 84:1866-1878. [PMID: 27068092 DOI: 10.1128/iai.00011-16] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2016] [Accepted: 04/04/2016] [Indexed: 12/22/2022] Open
Abstract
Aspergillus fumigatus is the most common pathogenic mold infecting humans and a significant cause of morbidity and mortality in immunocompromised patients. In invasive pulmonary aspergillosis, A. fumigatus spores are inhaled into the lungs, undergoing germination and invasive hyphal growth. The fungus occludes and disrupts the blood vessels, leading to hypoxia and eventual tissue necrosis. The ability of this mold to adapt to hypoxia is regulated in part by the sterol regulatory element binding protein (SREBP) SrbA and the DscA to DscD Golgi E3 ligase complex critical for SREBP activation by proteolytic cleavage. Loss of the genes encoding these proteins results in avirulence. To identify novel regulators of hypoxia sensing, we screened the Neurospora crassa gene deletion library under hypoxia and identified a novel rhomboid family protease essential for hypoxic growth. Deletion of the A. fumigatus rhomboid homolog rbdA resulted in an inability to grow under hypoxia, hypersensitivity to CoCl2, nikkomycin Z, fluconazole, and ferrozine, abnormal swollen tip morphology, and transcriptional dysregulation-accurately phenocopying deletion of srbA. In vivo, rbdA deletion resulted in increased sensitivity to phagocytic killing, a reduced inflammatory Th1 and Th17 response, and strongly attenuated virulence. Phenotypic rescue of the ΔrbdA mutant was achieved by expression and nuclear localization of the N terminus of SrbA, including its HLH domain, further indicating that RbdA and SrbA act in the same signaling pathway. In summary, we have identified RbdA, a novel putative rhomboid family protease in A. fumigatus that mediates hypoxia adaptation and fungal virulence and that is likely linked to SrbA cleavage and activation.
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Burr R, Stewart EV, Shao W, Zhao S, Hannibal-Bach HK, Ejsing CS, Espenshade PJ. Mga2 Transcription Factor Regulates an Oxygen-responsive Lipid Homeostasis Pathway in Fission Yeast. J Biol Chem 2016; 291:12171-83. [PMID: 27053105 DOI: 10.1074/jbc.m116.723650] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2016] [Indexed: 12/20/2022] Open
Abstract
Eukaryotic lipid synthesis is oxygen-dependent with cholesterol synthesis requiring 11 oxygen molecules and fatty acid desaturation requiring 1 oxygen molecule per double bond. Accordingly, organisms evaluate oxygen availability to control lipid homeostasis. The sterol regulatory element-binding protein (SREBP) transcription factors regulate lipid homeostasis. In mammals, SREBP-2 controls cholesterol biosynthesis, whereas SREBP-1 controls triacylglycerol and glycerophospholipid biosynthesis. In the fission yeast Schizosaccharomyces pombe, the SREBP-2 homolog Sre1 regulates sterol homeostasis in response to changing sterol and oxygen levels. However, notably missing is an SREBP-1 analog that regulates triacylglycerol and glycerophospholipid homeostasis in response to low oxygen. Consistent with this, studies have shown that the Sre1 transcription factor regulates only a fraction of all genes up-regulated under low oxygen. To identify new regulators of low oxygen adaptation, we screened the S. pombe nonessential haploid deletion collection and identified 27 gene deletions sensitive to both low oxygen and cobalt chloride, a hypoxia mimetic. One of these genes, mga2, is a putative transcriptional activator. In the absence of mga2, fission yeast exhibited growth defects under both normoxia and low oxygen conditions. Mga2 transcriptional targets were enriched for lipid metabolism genes, and mga2Δ cells showed disrupted triacylglycerol and glycerophospholipid homeostasis, most notably with an increase in fatty acid saturation. Indeed, addition of exogenous oleic acid to mga2Δ cells rescued the observed growth defects. Together, these results establish Mga2 as a transcriptional regulator of triacylglycerol and glycerophospholipid homeostasis in S. pombe, analogous to mammalian SREBP-1.
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Affiliation(s)
- Risa Burr
- From the Department of Cell Biology, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205 and
| | - Emerson V Stewart
- From the Department of Cell Biology, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205 and
| | - Wei Shao
- From the Department of Cell Biology, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205 and
| | - Shan Zhao
- From the Department of Cell Biology, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205 and
| | - Hans Kristian Hannibal-Bach
- the Department of Biochemistry and Molecular Biology, VILLUM Center for Bioanalytical Sciences, University of Southern Denmark, 5230 Odense, Denmark
| | - Christer S Ejsing
- the Department of Biochemistry and Molecular Biology, VILLUM Center for Bioanalytical Sciences, University of Southern Denmark, 5230 Odense, Denmark
| | - Peter J Espenshade
- From the Department of Cell Biology, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205 and
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21
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RbdB, a Rhomboid Protease Critical for SREBP Activation and Virulence in Aspergillus fumigatus. mSphere 2016; 1:mSphere00035-16. [PMID: 27303716 PMCID: PMC4863583 DOI: 10.1128/msphere.00035-16] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2016] [Accepted: 02/17/2016] [Indexed: 11/25/2022] Open
Abstract
Aspergillus fumigatus causes life-threatening infections, and treatment options remain limited. Thus, there is an urgent need to find new therapeutic targets to treat this deadly disease. Previously, we have shown that SREBP transcription factors and their regulatory components are critical for the pathobiology of A. fumigatus. Here we identify a role for RbdB, a rhomboid protease, as an essential component of SREBP activity. Our results indicate that mutants lacking rbdB have growth defects under hypoxic conditions, are hypersusceptible to voriconazole, lack extracellular siderophore production, and fail to cause disease in a murine model of invasive pulmonary aspergillosis. This study increases our understanding of the molecular mechanisms involved in SREBP activation in pathogenic fungi and provides a novel therapeutic target for future development. SREBP transcription factors play a critical role in fungal virulence; however, the mechanisms of sterol regulatory element binding protein (SREBP) activation in pathogenic fungi remains ill-defined. Screening of the Neurospora crassa whole-genome deletion collection for genes involved in hypoxia responses identified a gene for an uncharacterized rhomboid protease homolog, rbdB, required for growth under hypoxic conditions. Loss of rbdB in Aspergillus fumigatus also inhibited growth under hypoxic conditions. In addition, the A. fumigatus ΔrbdB strain also displayed phenotypes consistent with defective SREBP activity, including increased azole drug susceptibility, reduced siderophore production, and full loss of virulence. Expression of the basic helix-loop-helix (bHLH) DNA binding domain of the SREBP SrbA in ΔrbdB restored all of the phenotypes linking RdbB activity with SrbA function. Furthermore, the N-terminal domain of SrbA containing the bHLH DNA binding region was absent from ΔrbdB under inducing conditions, suggesting that RbdB regulates the protein levels of this important transcription factor. As SrbA controls clinically relevant aspects of fungal pathobiology in A. fumigatus, understanding the mechanisms of SrbA activation provides opportunities to target this pathway for therapeutic development. IMPORTANCEAspergillus fumigatus causes life-threatening infections, and treatment options remain limited. Thus, there is an urgent need to find new therapeutic targets to treat this deadly disease. Previously, we have shown that SREBP transcription factors and their regulatory components are critical for the pathobiology of A. fumigatus. Here we identify a role for RbdB, a rhomboid protease, as an essential component of SREBP activity. Our results indicate that mutants lacking rbdB have growth defects under hypoxic conditions, are hypersusceptible to voriconazole, lack extracellular siderophore production, and fail to cause disease in a murine model of invasive pulmonary aspergillosis. This study increases our understanding of the molecular mechanisms involved in SREBP activation in pathogenic fungi and provides a novel therapeutic target for future development.
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Bat-Ochir C, Kwak JY, Koh SK, Jeon MH, Chung D, Lee YW, Chae SK. The signal peptide peptidase SppA is involved in sterol regulatory element-binding protein cleavage and hypoxia adaptation in Aspergillus nidulans. Mol Microbiol 2016; 100:635-55. [PMID: 26822492 DOI: 10.1111/mmi.13341] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 01/26/2016] [Indexed: 12/22/2022]
Abstract
Using forward genetics, we revealed that the signal peptide peptidase (SPP) SppA, an aspartyl protease involved in regulated intramembrane proteolysis (RIP), is essential for hypoxia adaptation in Aspergillus nidulans, as well as hypoxia-sensitive mutant alleles of a sterol regulatory element-binding protein (SREBP) srbA and the Dsc ubiquitin E3 ligase complex dscA-E. Both null and dead activity [D337A] mutants of sppA failed to grow in hypoxia, and the growth defect of ΔsppA was complemented by nuclear SrbA-N381 expression. Additionally, SppA interacted with SrbA in the endoplasmic reticulum, where SppA localized in normoxia and hypoxia. Expression of the truncated SrbA-N414 covering the SrbA sequence prior to the second transmembrane region rescued the growth of ΔdscA but not of ΔsppA in hypoxia. Unlike ΔdscA and ΔdscA;ΔsppA double mutants, in which SrbA cleavage was blocked, the molecular weight of cleaved SrbA increased in ΔsppA compared to the control strain in immunoblot analyses. Overall, our data demonstrate the sequential cleavage of SrbA by Dsc-linked proteolysis followed by SppA, proposing a new model of RIP for SREBP cleavage in fungal hypoxia adaptation. Furthermore, the function of SppA in hypoxia adaptation was consistent in Aspergillus fumigatus, suggesting the potential roles of SppA in fungal pathogenesis.
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Affiliation(s)
- Chinbayar Bat-Ochir
- Department of Biochemistry and Center for Fungal Pathogenesis, Pai Chai University, Daejeon, 34015, Republic of Korea
| | - Jun-Yong Kwak
- Department of Biochemistry and Center for Fungal Pathogenesis, Pai Chai University, Daejeon, 34015, Republic of Korea
| | - Sun-Ki Koh
- Department of Biochemistry and Center for Fungal Pathogenesis, Pai Chai University, Daejeon, 34015, Republic of Korea
| | - Mee-Hyang Jeon
- Department of Biochemistry and Center for Fungal Pathogenesis, Pai Chai University, Daejeon, 34015, Republic of Korea
| | - Dawoon Chung
- Department of Biochemistry and Center for Fungal Pathogenesis, Pai Chai University, Daejeon, 34015, Republic of Korea
| | - Yin-Won Lee
- Department of Agricultural Biotechnology and Center for Fungal Pathogenesis, Seoul National University, Seoul, 08826, Republic of Korea
| | - Suhn-Kee Chae
- Department of Biochemistry and Center for Fungal Pathogenesis, Pai Chai University, Daejeon, 34015, Republic of Korea
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