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Liu Y, Li Y, Tan Q, Lv Y, Tang Y, Yang Y, Yao X, Yang F. Long-Term Exposure to Microcystin-LR Induces Gastric Toxicity by Activating the Mitogen-Activated Protein Kinase Signaling Pathway. Toxins (Basel) 2023; 15:574. [PMID: 37756000 PMCID: PMC10535883 DOI: 10.3390/toxins15090574] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2023] [Revised: 08/30/2023] [Accepted: 09/05/2023] [Indexed: 09/28/2023] Open
Abstract
Previous studies have primarily concentrated on the hepatotoxicity of MC-LR, whereas its gastric toxicity effects and mechanisms of long-term exposure under low dosage remain unknown. Herein, the gastric tissue from C57BL/6 mice fed with drinking water contaminated by low-dose MC-LR (including 1, 60, and 120 μg/L) was investigated. The results obtained showed that exposure to different concentrations of MC-LR resulted in significant shedding and necrosis of gastric epithelial cells in mice, and a down-regulation of tight junction markers, including ZO-1, Claudin1, and Occludin in the stomach, which might lead to increased permeability of the gastric mucosa. Moreover, the protein expression levels of p-RAF/RAF, p-ERK1/2/ERK1/2, Pink1, Parkin, and LC3-II/LC-3-I were increased in the gastric tissue of mice exposed to 120 μg/L of MC-LR, while the protein expression level of P62 was significantly decreased. Furthermore, we found that pro-inflammatory factors, including IL-6 and TNF-ɑ, were dramatically increased, while the anti-inflammatory factor IL-10 was significantly decreased in the gastric tissue of MC-LR-exposed mice. The activation of the MAPK signaling pathway and mitophagy might contribute to the development of gastric damage by promoting inflammation. We first reported that long-term exposure to MC-LR induced gastric toxicity by activating the MAPK signaling pathway, providing a new insight into the gastric toxic mechanisms caused by MC-LR.
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Affiliation(s)
- Ying Liu
- Hunan Province Key Laboratory of Typical Environmental Pollution and Health Hazards, School of Public Health, Hengyang Medical School, University of South China, Hengyang 421009, China
| | - Yafang Li
- Hunan Province Key Laboratory of Typical Environmental Pollution and Health Hazards, School of Public Health, Hengyang Medical School, University of South China, Hengyang 421009, China
| | - Qinmei Tan
- Hunan Province Key Laboratory of Typical Environmental Pollution and Health Hazards, School of Public Health, Hengyang Medical School, University of South China, Hengyang 421009, China
| | - Yilin Lv
- Hunan Province Key Laboratory of Typical Environmental Pollution and Health Hazards, School of Public Health, Hengyang Medical School, University of South China, Hengyang 421009, China
| | - Yan Tang
- Hunan Province Key Laboratory of Typical Environmental Pollution and Health Hazards, School of Public Health, Hengyang Medical School, University of South China, Hengyang 421009, China
| | - Yue Yang
- The First Affiliated Hospital, Hengyang Medical School, University of South China, Hengyang 421009, China
| | - Xueqiong Yao
- Hunan Province Key Laboratory of Typical Environmental Pollution and Health Hazards, School of Public Health, Hengyang Medical School, University of South China, Hengyang 421009, China
| | - Fei Yang
- Hunan Province Key Laboratory of Typical Environmental Pollution and Health Hazards, School of Public Health, Hengyang Medical School, University of South China, Hengyang 421009, China
- The First Affiliated Hospital, Hengyang Medical School, University of South China, Hengyang 421009, China
- Laboratory of Ecological Environment and Critical Human Diseases Prevention of Hunan Province, School of Basic Medical Sciences, Hengyang Medical School, University of South China, Hengyang 421009, China
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Zhang Q, Chen Y, Wang M, Zhang J, Chen Q, Liu D. Molecular responses to inorganic and organic phosphorus sources in the growth and toxin formation of Microcystis aeruginosa. WATER RESEARCH 2021; 196:117048. [PMID: 33773451 DOI: 10.1016/j.watres.2021.117048] [Citation(s) in RCA: 26] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/29/2021] [Revised: 03/04/2021] [Accepted: 03/12/2021] [Indexed: 06/12/2023]
Abstract
Toxic cyanobacteria bloom is a ubiquitous phenomenon worldwide in eutrophic lakes or reservoirs. Microcystis, is a cosmopolitan genus in cyanobacteria and exists in many different forms. Microcystis aeruginosa (M. aeruginosa) can produce microcystins (MCs) with strong liver toxicity during its growth and decomposition. Phosphorus (P) is a typical growth limiting factor of M. aeruginosa. Though different forms and concentrations of P are common in natural water, the molecular responses in the growth and MCs formation of M. aeruginosa remain unclear. In this study, laboratory experiments were conducted to determine the uptake of P, cell activity, MCs release, and related gene expression under different concentrations of dissolved inorganic phosphorus (DIP) and dissolved organic phosphorus (DOP). We found that the growth of M. aeruginosa was promoted by increasing DIP concentration but coerced under high concentration (0.6 and 1.0 mg P/L) of DOP after P starvation. The growth stress was not related to the alkaline phosphatase activity (APA). Although alkaline phosphatase (AP) could convert DOP into algae absorbable DIP, the growth status of M. aeruginosa mainly depended on the response mechanism of phosphate transporter expression to the extracellular P concentration. High-concentration DIP promoted MCs production in M. aeruginosa, while high-concentration DOP triggered the release of intracellular MCs rather than affecting MCs production. Our study revealed the molecular responses of algal growth and toxin formation under different P sources, and provided a theoretical basis and novel idea for risk management of eutrophic lakes and reservoirs.
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Affiliation(s)
- Qi Zhang
- State Key Laboratory of Hydrology-Water Resources & Hydraulic Engineering, Nanjing Hydraulic Research Institute, Nanjing 210029, China; Center for Eco-Environment Research, Nanjing Hydraulic Research Institute, Nanjing 210029, China
| | - Yuchen Chen
- Center for Eco-Environment Research, Nanjing Hydraulic Research Institute, Nanjing 210029, China
| | - Min Wang
- Center for Eco-Environment Research, Nanjing Hydraulic Research Institute, Nanjing 210029, China
| | - Jianyun Zhang
- State Key Laboratory of Hydrology-Water Resources & Hydraulic Engineering, Nanjing Hydraulic Research Institute, Nanjing 210029, China; Yangtze Institute for Conservation and Green Development, Nanjing 210098, China
| | - Qiuwen Chen
- State Key Laboratory of Hydrology-Water Resources & Hydraulic Engineering, Nanjing Hydraulic Research Institute, Nanjing 210029, China; Yangtze Institute for Conservation and Green Development, Nanjing 210098, China.
| | - Dongsheng Liu
- Center for Eco-Environment Research, Nanjing Hydraulic Research Institute, Nanjing 210029, China
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3
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Lloyd-Evans E, Waller-Evans H. Lysosomal Ca 2+ Homeostasis and Signaling in Health and Disease. Cold Spring Harb Perspect Biol 2020; 12:cshperspect.a035311. [PMID: 31653642 DOI: 10.1101/cshperspect.a035311] [Citation(s) in RCA: 38] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Calcium (Ca2+) signaling is an essential process in all cells that is maintained by a plethora of channels, pumps, transporters, receptors, and intracellular Ca2+ sequestering stores. Changes in cytosolic Ca2+ concentration govern processes as far reaching as fertilization, cell growth, and motility through to cell death. In recent years, lysosomes have emerged as a major intracellular Ca2+ storage organelle with an increasing involvement in triggering or regulating cellular functions such as endocytosis, autophagy, and Ca2+ release from the endoplasmic reticulum. This review will summarize recent work in the area of lysosomal Ca2+ signaling and homeostasis, including newly identified functions, and the involvement of lysosome-derived Ca2+ signals in human disease. In addition, we explore recent controversies in the techniques used for measurement of lysosomal Ca2+ content.
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Affiliation(s)
- Emyr Lloyd-Evans
- School of Biosciences, Cardiff University, Cardiff CF10 3AX, United Kingdom
| | - Helen Waller-Evans
- Medicines Discovery Institute, Cardiff University, Cardiff CF10 3AT, United Kingdom
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4
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Adnan M, Islam W, Noman A, Hussain A, Anwar M, Khan MU, Akram W, Ashraf MF, Raza MF. Q-SNARE protein FgSyn8 plays important role in growth, DON production and pathogenicity of Fusarium graminearum. Microb Pathog 2019; 140:103948. [PMID: 31874229 DOI: 10.1016/j.micpath.2019.103948] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2019] [Revised: 12/15/2019] [Accepted: 12/20/2019] [Indexed: 10/25/2022]
Abstract
SNAREs (Soluble N-ethylmaleimide-sensitive factor attachment protein receptors) help intracellular vesicle trafficking and membrane fusion among eukaryotes. They are vital for growth and development of phyto-pathogenic fungi such as Fusarium graminearum which causes Fusarium Head Blight (FHB) of wheat and barley. The SNARE protein Syn8 and its homologues play many roles among different organisms. Here, we have characterized FgSyn8 in F. graminearum as a homologue of Syn8. We have integrated biochemical, microbiological and molecular genetic approaches to investigate the roles of this protein. Our results reveal that FgSyn8 is indispensable for normal vegetative growth, conidiation, conidial morphology and pathogenicity of F. graminearum. Deoxynivalenol (DON) biochemical assay reveals active participation of this protein in DON production of F. graminearum. This has further been confirmed by the production of bulbous structures among the intercalary hyphae. FgSyn8 mutant strain produced defects in perithecia formation which portrays its role in sexual reproduction. In summary, our results support that the SNARE protein FgSyn8 is required for vegetative growth, sexual reproduction, DON production and pathogenicity of F. graminearum.
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Affiliation(s)
- Muhammad Adnan
- State Key Laboratory of Ecological Pest Control for Fujian and Taiwan Crops, Key Laboratory of Biopesticides and Chemical Biology of Education Ministry, Fujian Agriculture and Forestry University, Fuzhou, 350002, China.
| | - Waqar Islam
- Key Laboratory for Humid Subtropical Eco-Geographical Processes of the Ministry of Education, Institute of Geography, Fujian Normal University, Fuzhou, China
| | - Ali Noman
- Department of Botany, Government College University, Faisalabad, Pakistan
| | - Ansar Hussain
- Department of Plant Breeding and Genetics, Faculty of Agricultural Sciences, Ghazi University, Dera Ghazi Khan, Pakistan
| | - Muhammad Anwar
- Guangdong Technology Research Centre for Marine Algal Bioengineering, Guangdong Key Laboratory of Plant Epigenetics, College of Life Sciences and Oceanography, Shenzhen University, Shenzhen, 518060, China
| | - Muhammad Umar Khan
- Fujian Provincial Key Laboratory of Agro-Ecology Processing and Safety Monitoring, College of Life Science, Fujian Agriculture and Forestry University, Fuzhou, 350002, China
| | - Waheed Akram
- Guangdong Agriculture Institute, Guangzhou, China
| | | | - Muhammad Fahad Raza
- College of Life Sciences, Fujian Agriculture and Forestry University, Fuzhou, China
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5
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Luo C, Wu M, Su X, Yu F, Brautigan DL, Chen J, Zhou J. Protein phosphatase 1α interacts with a novel ciliary targeting sequence of polycystin-1 and regulates polycystin-1 trafficking. FASEB J 2019; 33:9945-9958. [PMID: 31157564 DOI: 10.1096/fj.201900338r] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Autosomal dominant polycystic kidney disease (ADPKD) is the most common genetic disorder causing renal failure. Mutations of polycystic kidney disease 1 (PKD1) account for most ADPKD cases. Defective ciliary localization of polycystin-1 (PC1), a large integral membrane protein encoded by PKD1, underlies the pathogenesis of a subgroup of patients with ADPKD. However, the mechanisms by which PC1 and other ciliary proteins traffic to the primary cilium remain poorly understood. A ciliary targeting sequence (CTS) that resides in ciliary receptors is considered to function in the process. It has been reported that the VxP motif in the intracellular C-terminal tail of PC1 functions as a CTS in an ADP ribosylation factor 4 (Arf4)/ArfGAP with SH3 domain, ankyrin repeat and PH domain 1 (ASAP1)-dependent manner. However, other recent studies have revealed that this motif is dispensable for PC1 trafficking to cilia. In this study, we identified a novel CTS consisting of 8 residues (RHKVRFEG) in the PC1 C tail. We found that this motif is sufficient to bind protein phosphatase 1 (PP1)α, a ubiquitously expressed phosphatase in the phosphoprotein phosphatase (PPP) family. Mutations in this CTS motif disrupt binding with PP1α and impair ciliary localization of PC1. Additionally, short hairpin RNA-mediated knockdown of PP1α results in reduced ciliary localization of PC1 and elongated cilia, suggesting a role for PP1α in the regulation of ciliary structure and function.-Luo, C., Wu, M., Su, X., Yu, F., Brautigan, D. L., Chen, J., Zhou, J. Protein phosphatase 1α interacts with a novel ciliary targeting sequence of polycystin-1 and regulates polycystin-1 trafficking.
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Affiliation(s)
- Chong Luo
- Kidney Disease Center, The First Affiliated Hospital-College of Medicine-National Key Clinical Department of Kidney Diseases, Institute of Nephrology, Zhejiang University, Hangzhou, China.,Harvard Center for Polycystic Kidney Disease Research-Renal Division, Department of Medicine, Brigham and Women's Hospital-Harvard Medical School, Boston, Massachusetts, USA
| | - Maoqing Wu
- Harvard Center for Polycystic Kidney Disease Research-Renal Division, Department of Medicine, Brigham and Women's Hospital-Harvard Medical School, Boston, Massachusetts, USA
| | - Xuefeng Su
- Harvard Center for Polycystic Kidney Disease Research-Renal Division, Department of Medicine, Brigham and Women's Hospital-Harvard Medical School, Boston, Massachusetts, USA
| | - Fangyan Yu
- Harvard Center for Polycystic Kidney Disease Research-Renal Division, Department of Medicine, Brigham and Women's Hospital-Harvard Medical School, Boston, Massachusetts, USA
| | - David L Brautigan
- Center for Cell Signaling, Department of Microbiology, Immunology and Cancer Biology, University of Virginia School of Medicine, Charlottesville, Virginia, USA
| | - Jianghua Chen
- Kidney Disease Center, The First Affiliated Hospital-College of Medicine-National Key Clinical Department of Kidney Diseases, Institute of Nephrology, Zhejiang University, Hangzhou, China
| | - Jing Zhou
- Harvard Center for Polycystic Kidney Disease Research-Renal Division, Department of Medicine, Brigham and Women's Hospital-Harvard Medical School, Boston, Massachusetts, USA
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6
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Chen J, Bian R, Li J, Qiu L, Lu B, Ouyang X. Chronic exposure to microcystin-LR reduces thyroid hormone levels by activating p38/MAPK and MEK/ERK signal pathway. ECOTOXICOLOGY AND ENVIRONMENTAL SAFETY 2019; 173:142-148. [PMID: 30771657 DOI: 10.1016/j.ecoenv.2019.02.024] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/27/2018] [Revised: 01/29/2019] [Accepted: 02/01/2019] [Indexed: 06/09/2023]
Abstract
Microcystin-LR (MC-LR) is the most toxic and abundant microcystin that produced by cyanobacteria. Previous studies have shown MC-LR had acute toxic to thyroid, however, the mechanism is still unclear, and the effect of long-term, low-dose MC-LR on thyroid remains uncertain. In this study, we investigated the chronic, low-dose effect of MC-LR on mouse thyroid tissues and thyroid hormone metabolism. MC-LR was orally administered to mice at 0, 1, 10, 20 and 40 μg/L for 6 consecutive months for histopathological and immunoblot analysis. Nthy-ori 3-1 cells were cultured in various concentrations of MC-LR (0, 0.5, 5, 50, 500 nmol/L) for indicated time, meanwhile the cell viability and proteins change were tested. From our study, the chronic, low-dose MC-LR exposure can disturb thyroid hormone synthesis and metabolism through activating the p38/MAPK and MEK/ERK signaling pathways, then up-regulating the expression of type 3 deiodinase. These data support the potential toxic effects of MC-LR on thyroid tissue and thyroid hormone metabolism.
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Affiliation(s)
- Jihai Chen
- Department of Geriatric Endocrinology, Geriatric Hospital of Nanjing Medical University, Luojia Road 30, Nanjing 210024, China
| | - Rongwen Bian
- Center for Chronic Diseases and Health Management, Geriatric Hospital of Nanjing Medical University, Luojia Road 30, Nanjing 210024, China
| | - Jiang Li
- Department of Pathology, Geriatric Hospital of Nanjing Medical University, Luojia Road 30, Nanjing 210024, China
| | - Liang Qiu
- Department of Laboratory, Geriatric Hospital of Nanjing Medical University, Luojia Road 30, Nanjing 210024, China
| | - Bing Lu
- Department of Geriatric Endocrinology, Geriatric Hospital of Nanjing Medical University, Luojia Road 30, Nanjing 210024, China
| | - Xiaojun Ouyang
- Department of Geriatric Endocrinology, Geriatric Hospital of Nanjing Medical University, Luojia Road 30, Nanjing 210024, China.
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7
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Lu A, Wawro P, Morgens DW, Portela F, Bassik MC, Pfeffer SR. Genome-wide interrogation of extracellular vesicle biology using barcoded miRNAs. eLife 2018; 7:41460. [PMID: 30556811 PMCID: PMC6312402 DOI: 10.7554/elife.41460] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2018] [Accepted: 12/17/2018] [Indexed: 01/05/2023] Open
Abstract
Extracellular vesicles mediate transfer of biologically active molecules between neighboring or distant cells, and these vesicles may play important roles in normal physiology and the pathogenesis of multiple disease states including cancer. However, the underlying molecular mechanisms of their biogenesis and release remain unknown. We designed artificially barcoded, exosomal microRNAs (bEXOmiRs) to monitor extracellular vesicle release quantitatively using deep sequencing. We then expressed distinct pairs of CRISPR guide RNAs and bEXOmiRs, enabling identification of genes influencing bEXOmiR secretion from Cas9-edited cells. This approach uncovered genes with unrecognized roles in multivesicular endosome exocytosis, including critical roles for Wnt signaling in extracellular vesicle release regulation. Coupling bEXOmiR reporter analysis with CRISPR-Cas9 screening provides a powerful and unbiased means to study extracellular vesicle biology and for the first time, to associate a nucleic acid tag with individual membrane vesicles.
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Affiliation(s)
- Albert Lu
- Department of Biochemistry, Stanford University School of Medicine, Stanford, United States
| | - Paulina Wawro
- Department of Biochemistry, Stanford University School of Medicine, Stanford, United States
| | - David W Morgens
- Department of Genetics, Stanford University School of Medicine, Stanford, United States
| | - Fernando Portela
- Department of Biochemistry, Stanford University School of Medicine, Stanford, United States
| | - Michael C Bassik
- Department of Genetics, Stanford University School of Medicine, Stanford, United States
| | - Suzanne R Pfeffer
- Department of Biochemistry, Stanford University School of Medicine, Stanford, United States
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8
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Karim MA, McNally EK, Samyn DR, Mattie S, Brett CL. Rab-Effector-Kinase Interplay Modulates Intralumenal Fragment Formation during Vacuole Fusion. Dev Cell 2018; 47:80-97.e6. [PMID: 30269949 DOI: 10.1016/j.devcel.2018.09.002] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2016] [Revised: 07/01/2018] [Accepted: 09/01/2018] [Indexed: 01/17/2023]
Abstract
Upon vacuolar lysosome (or vacuole) fusion in S. cerevisiae, a portion of membrane is internalized and catabolized. Formation of this intralumenal fragment (ILF) is important for organelle protein and lipid homeostasis and remodeling. But how ILF formation is optimized for membrane turnover is not understood. Here, we show that fewer ILFs form when the interaction between the Rab-GTPase Ypt7 and its effector Vps41 (a subunit of the tethering complex HOPS) is interrupted by a point mutation (Ypt7-D44N). Subsequent phosphorylation of Vps41 by the casein kinase Yck3 prevents stabilization of trans-SNARE complexes needed for lipid bilayer pore formation. Impairing ILF formation prevents clearance of misfolded proteins from vacuole membranes and promotes organelle permeability and cell death. We propose that HOPS coordinates Rab, kinase, and SNARE cycles to modulate ILF size during vacuole fusion, regulating lipid and protein turnover important for quality control and membrane integrity.
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Affiliation(s)
- Mahmoud Abdul Karim
- Department of Biology, Concordia University, 7141 Sherbrooke St. W., SP, 501.15, Montréal, QC H4R 1R6, Canada
| | - Erin Kate McNally
- Department of Biology, Concordia University, 7141 Sherbrooke St. W., SP, 501.15, Montréal, QC H4R 1R6, Canada
| | - Dieter Ronny Samyn
- Department of Biology, Concordia University, 7141 Sherbrooke St. W., SP, 501.15, Montréal, QC H4R 1R6, Canada
| | - Sevan Mattie
- Department of Biology, Concordia University, 7141 Sherbrooke St. W., SP, 501.15, Montréal, QC H4R 1R6, Canada
| | - Christopher Leonard Brett
- Department of Biology, Concordia University, 7141 Sherbrooke St. W., SP, 501.15, Montréal, QC H4R 1R6, Canada.
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Nakamura TS, Numajiri Y, Okumura Y, Hidaka J, Tanaka T, Inoue I, Suda Y, Takahashi T, Nakanishi H, Gao XD, Neiman AM, Tachikawa H. Dynamic localization of a yeast development-specific PP1 complex during prospore membrane formation is dependent on multiple localization signals and complex formation. Mol Biol Cell 2017; 28:3881-3895. [PMID: 29046399 PMCID: PMC5739302 DOI: 10.1091/mbc.e17-08-0521] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2017] [Revised: 10/06/2017] [Accepted: 10/10/2017] [Indexed: 12/27/2022] Open
Abstract
Prospore membrane formation of Saccharomyces cerevisiae provides a powerful model for understanding the mechanisms of de novo membrane formation. Protein phosphatase type1, Glc7, and a sporulation-specific targeting subunit, Gip1, show dynamic localization using multiple localization signals and regulate membrane growth during sporulation. During the developmental process of sporulation in Saccharomyces cerevisiae, membrane structures called prospore membranes are formed de novo, expand, extend, acquire a round shape, and finally become plasma membranes of the spores. GIP1 encodes a regulatory/targeting subunit of protein phosphatase type 1 that is required for sporulation. Gip1 recruits the catalytic subunit Glc7 to septin structures that form along the prospore membrane; however, the molecular basis of its localization and function is not fully understood. Here we show that Gip1 changes its localization dynamically and is required for prospore membrane extension. Gip1 first associates with the spindle pole body as the prospore membrane forms, moves onto the prospore membrane and then to the septins as the membrane extends, distributes around the prospore membrane after closure, and finally translocates into the nucleus in the maturing spore. Deletion and mutation analyses reveal distinct sequences in Gip1 that are required for different localizations and for association with Glc7. Binding to Glc7 is also required for proper localization. Strikingly, localization to the prospore membrane, but not association with septins, is important for Gip1 function. Further, our genetic analysis suggests that a Gip1–Glc7 phosphatase complex regulates prospore membrane extension in parallel to the previously reported Vps13, Spo71, Spo73 pathway.
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Affiliation(s)
- Tsuyoshi S Nakamura
- Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo 113-8657, Japan
| | - Yumi Numajiri
- Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo 113-8657, Japan
| | - Yuuya Okumura
- Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo 113-8657, Japan
| | - Junji Hidaka
- Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo 113-8657, Japan
| | - Takayuki Tanaka
- Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo 113-8657, Japan
| | - Ichiro Inoue
- Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo 113-8657, Japan
| | - Yasuyuki Suda
- Department of Molecular Cell Biology, Graduate School of Comprehensive Human Sciences and Institute of Basic Medical Sciences, University of Tsukuba, Ibaraki 305-8575, Japan
| | - Tetsuo Takahashi
- Laboratory of Glycobiology and Glycotechnology, Department of Applied Biochemistry, School of Engineering, Tokai University, Kanagawa 259-1292, Japan
| | - Hideki Nakanishi
- Key Laboratory of Carbohydrate Chemistry and Biotechnology, Ministry of Education, School of Biotechnology, Jiangnan University, Wuxi 214122, China
| | - Xiao-Dong Gao
- Key Laboratory of Carbohydrate Chemistry and Biotechnology, Ministry of Education, School of Biotechnology, Jiangnan University, Wuxi 214122, China
| | - Aaron M Neiman
- Department of Biochemistry and Cell Biology, Stony Brook University, Stony Brook, NY 11794-5215
| | - Hiroyuki Tachikawa
- Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo 113-8657, Japan
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10
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Enrich C, Rentero C, Grewal T. Annexin A6 in the liver: From the endocytic compartment to cellular physiology. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2016; 1864:933-946. [PMID: 27984093 DOI: 10.1016/j.bbamcr.2016.10.017] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/21/2016] [Revised: 10/25/2016] [Accepted: 10/26/2016] [Indexed: 12/15/2022]
Abstract
Annexin A6 (AnxA6) belongs to the conserved annexin family - a group of Ca2+-dependent membrane binding proteins. AnxA6 is the largest of all annexins and highly expressed in smooth muscle, hepatocytes, endothelial cells and cardiomyocytes. Upon activation, AnxA6 binds to negatively charged phospholipids in a wide range of intracellular localizations, in particular the plasma membrane, late endosomes/pre-lysosomes, but also synaptic vesicles and sarcolemma. In these cellular sites, AnxA6 is believed to contribute to the organization of membrane microdomains, such as cholesterol-rich lipid rafts and confer multiple regulatory functions, ranging from vesicle fusion, endocytosis and exocytosis to programmed cell death and muscle contraction. Growing evidence supports that Ca2+ and Ca2+-binding proteins control endocytosis and autophagy. Their regulatory role seems to operate at the level of the signalling pathways that initiate autophagy or at later stages, when autophagosomes fuse with endolysosomal compartments. The convergence of the autophagic and endocytic vesicles to lysosomes shares several features that depend on Ca2+ originating from lysosomes/late endosomes and seems to depend on proteins that are subsequently activated by this cation. However, the involvement of Ca2+ and its effector proteins in these autophagic and endocytic stages still remains poorly understood. Although AnxA6 makes up almost 0.25% of total protein in the liver, little is known about its function in hepatocytes. Within the endocytic route, we identified AnxA6 in endosomes and autophagosomes of hepatocytes. Hence, AnxA6 and possibly other annexins might represent new Ca2+ effectors that regulate converging steps of autophagy and endocytic trafficking in hepatocytes. This article is part of a Special Issue entitled: ECS Meeting edited by Claus Heizmann, Joachim Krebs and Jacques Haiech.
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Affiliation(s)
- Carlos Enrich
- Departament de Biomedicina, Unitat de Biologia Cellular, Centre de Recerca Biomèdica CELLEX, Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), Facultat de Medicina, Universitat de Barcelona, 08036 Barcelona, Spain.
| | - Carles Rentero
- Departament de Biomedicina, Unitat de Biologia Cellular, Centre de Recerca Biomèdica CELLEX, Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), Facultat de Medicina, Universitat de Barcelona, 08036 Barcelona, Spain
| | - Thomas Grewal
- Faculty of Pharmacy A15, University of Sydney, Sydney, NSW 2006, Australia
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11
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Martins E, Figueras A, Novoa B, Santos RS, Moreira R, Bettencourt R. Comparative study of immune responses in the deep-sea hydrothermal vent mussel Bathymodiolus azoricus and the shallow-water mussel Mytilus galloprovincialis challenged with Vibrio bacteria. FISH & SHELLFISH IMMUNOLOGY 2014; 40:485-499. [PMID: 25089010 DOI: 10.1016/j.fsi.2014.07.018] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/23/2014] [Revised: 07/08/2014] [Accepted: 07/09/2014] [Indexed: 06/03/2023]
Abstract
The deep-sea hydrothermal vent mussel Bathymodiolus azoricus and the continental European coast Mytilus galloprovincialis are two bivalves species living in highly distinct marine habitats. Mussels are filter-feeding animals that may accumulate rapidly bacteria from the environment. Contact with microorganism is thus inevitable during feeding processes where gill tissues assume a strategic importance at the interface between the external milieu and the internal body cavities promoting interactions with potential pathogens during normal filtration and a constant challenge to their immune system. In the present study B. azoricus and M. galloprovincialis were exposed to Vibrio alginolyticus, Vibrio anguillarum and Vibrio splendidus suspensions and to a mixture of these Vibrio suspensions, in order to ascertain the expression level of immune genes in gill samples, from both mussel species. The immune gene expressions were analyzed by means of quantitative-Polymerase Chain Reaction (qPCR). The gene expression results revealed that these bivalve species exhibit significant expression differences between 12 h and 24 h post-challenge times, and between the Vibrio strains used. V. splendidus induced the strongest gene expression level in the two bivalve species whereas the NF-κB and Aggrecan were the most significantly differentially expressed between the two mussel species. When comparing exposure times, both B. azoricus and M. galloprovincialis showed similar percentage of up-regulated genes at 12 h while a marked increased of gene expression was observed at 24 h for the majority of the immune genes in M. galloprovincialis. This contrasts with B. azoricus where the majority of the immune genes were down-regulated at 24 h. The 24 h post-challenge gene expression results clearly bring new evidence supporting time-dependent transcriptional activities resembling acute phase-like responses and different immune responses build-up in these two mussel species when challenged with Vibrio bacteria. High Pressure Liquid Chromatography (HPLC)-Electrospray ionization mass spectrometry (ESI-MS/MS) analyses resulted in different peptide sequences from B. azoricus and M. galloprovincialis gill tissues suggesting that naïve animals present differences, at the protein synthesis level, in their natural environment. B. azoricus proteins sequences, mostly of endosymbiont origin, were related to metabolic, energy production, protein synthesis processes and nutritional demands whereas in M. galloprovincialis putative protein functions were assumed to be related to structural and cellular integrity and signaling functions.
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Affiliation(s)
- Eva Martins
- Department of Oceanography and Fisheries, University of the Azores (DOP/UAç), Rua Prof. Doutor Frederico Machado, 9901-862 Horta, Portugal; IMAR Institute of Marine Research and LARSyS Laboratory of Robotics and Systems in Engineering and Science, 9901-862 Horta, Azores, Portugal
| | - António Figueras
- Instituto de Investigaciones Marinas, IIM - CSIC. Eduardo Cabello, 6, 36208 Vigo, Spain
| | - Beatriz Novoa
- Instituto de Investigaciones Marinas, IIM - CSIC. Eduardo Cabello, 6, 36208 Vigo, Spain
| | - Ricardo Serrão Santos
- Department of Oceanography and Fisheries, University of the Azores (DOP/UAç), Rua Prof. Doutor Frederico Machado, 9901-862 Horta, Portugal; IMAR Institute of Marine Research and LARSyS Laboratory of Robotics and Systems in Engineering and Science, 9901-862 Horta, Azores, Portugal
| | - Rebeca Moreira
- Instituto de Investigaciones Marinas, IIM - CSIC. Eduardo Cabello, 6, 36208 Vigo, Spain
| | - Raul Bettencourt
- IMAR Institute of Marine Research and LARSyS Laboratory of Robotics and Systems in Engineering and Science, 9901-862 Horta, Azores, Portugal; MARE-Marine and Environmental Science Center, University of the Azores, 9901-862 Horta, Azores, Portugal.
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12
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Ghislat G, Knecht E. Ca²⁺-sensor proteins in the autophagic and endocytic traffic. Curr Protein Pept Sci 2014; 14:97-110. [PMID: 23305313 PMCID: PMC3664516 DOI: 10.2174/13892037112139990033] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2012] [Revised: 09/19/2012] [Accepted: 11/28/2012] [Indexed: 12/21/2022]
Abstract
Autophagy and endocytosis are two evolutionarily conserved catabolic processes that comprise vesicle trafficking events for the clearance of the sequestered intracellular and extracellular cargo. Both start differently but end in the same compartment, the lysosome. Mounting evidences from the last years have established the involvement of proteins sensitive to intracellular Ca2+ in the control of the early autophagic steps and in the traffic of autophagic, endocytic and lysosomal vesicles. However, this knowledge is based on dispersed outcomes that do not set up a consensus model of the Ca2+-dependent control of autophagy and endocytosis. Here, we will provide a critical synopsis of insights from the last decade on the involvement of Ca2+-sensor proteins in the activation of autophagy and in fusion events of endocytic vesicles, autophagosomes and lysosomes.
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Affiliation(s)
- Ghita Ghislat
- Laboratorio de Biología Celular, Centro de Investigación Príncipe Felipe, C/ Eduardo Primo Yúfera 3, Valencia 46012, Spain and CIBERER, Valencia, Spain
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13
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Böhm S, Buchberger A. The budding yeast Cdc48(Shp1) complex promotes cell cycle progression by positive regulation of protein phosphatase 1 (Glc7). PLoS One 2013; 8:e56486. [PMID: 23418575 PMCID: PMC3572051 DOI: 10.1371/journal.pone.0056486] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2012] [Accepted: 01/10/2013] [Indexed: 12/11/2022] Open
Abstract
The conserved, ubiquitin-selective AAA ATPase Cdc48 regulates numerous cellular processes including protein quality control, DNA repair and the cell cycle. Cdc48 function is tightly controlled by a multitude of cofactors mediating substrate specificity and processing. The UBX domain protein Shp1 is a bona fide substrate-recruiting cofactor of Cdc48 in the budding yeast S. cerevisiae. Even though Shp1 has been proposed to be a positive regulator of Glc7, the catalytic subunit of protein phosphatase 1 in S. cerevisiae, its cellular functions in complex with Cdc48 remain largely unknown. Here we show that deletion of the SHP1 gene results in severe growth defects and a cell cycle delay at the metaphase to anaphase transition caused by reduced Glc7 activity. Using an engineered Cdc48 binding-deficient variant of Shp1, we establish the Cdc48Shp1 complex as a critical regulator of mitotic Glc7 activity. We demonstrate that shp1 mutants possess a perturbed balance of Glc7 phosphatase and Ipl1 (Aurora B) kinase activities and show that hyper-phosphorylation of the kinetochore protein Dam1, a key mitotic substrate of Glc7 and Ipl1, is a critical defect in shp1. We also show for the first time a physical interaction between Glc7 and Shp1 in vivo. Whereas loss of Shp1 does not significantly affect Glc7 protein levels or localization, it causes reduced binding of the activator protein Glc8 to Glc7. Our data suggest that the Cdc48Shp1 complex controls Glc7 activity by regulating its interaction with Glc8 and possibly further regulatory subunits.
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Affiliation(s)
- Stefanie Böhm
- Department of Biochemistry, Biocenter, University of Würzburg, Würzburg, Germany
| | - Alexander Buchberger
- Department of Biochemistry, Biocenter, University of Würzburg, Würzburg, Germany
- * E-mail:
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14
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Gómez CP, Tiemi Shio M, Duplay P, Olivier M, Descoteaux A. The protein tyrosine phosphatase SHP-1 regulates phagolysosome biogenesis. THE JOURNAL OF IMMUNOLOGY 2012; 189:2203-10. [PMID: 22826316 DOI: 10.4049/jimmunol.1103021] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The process of phagocytosis and phagosome maturation involves the recruitment of effector proteins that participate in phagosome formation and in the acidification and/or fusion with various endocytic vesicles. In the current study, we investigated the role of the Src homology region 2 domain-containing phosphatase 1 (SHP-1) in phagolysosome biogenesis. To this end, we used immortalized bone marrow macrophages derived from SHP-1-deficient motheaten mice and their wild-type littermates. We found that SHP-1 is recruited early and remains present on phagosomes for up to 4 h postphagocytosis. Using confocal immunofluorescence microscopy and Western blot analyses on purified phagosome extracts, we observed an impaired recruitment of lysosomal-associated membrane protein 1 in SHP-1-deficient macrophages. Moreover, Western blot analyses revealed that whereas the 51-kDa procathepsin D is recruited to phagosomes, it is not processed into the 46-kDa cathepsin D in the absence of SHP-1, suggesting a defect in acidification. Using the lysosomotropic agent LysoTracker as an indicator of phagosomal pH, we obtained evidence that in the absence of SHP-1, phagosome acidification was impaired. Taken together, these results are consistent with a role for SHP-1 in the regulation of signaling or membrane fusion events involved in phagolysosome biogenesis.
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Affiliation(s)
- Carolina P Gómez
- Institut National de la Recherche Scientifique-Institut Armand-Frappier, Laval, Quebec H7V 1B7, Canada
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15
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From networks of protein interactions to networks of functional dependencies. BMC SYSTEMS BIOLOGY 2012; 6:44. [PMID: 22607727 PMCID: PMC3434018 DOI: 10.1186/1752-0509-6-44] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/20/2011] [Accepted: 05/20/2012] [Indexed: 11/23/2022]
Abstract
Background As protein-protein interactions connect proteins that participate in either the same or different functions, networks of interacting and functionally annotated proteins can be converted into process graphs of inter-dependent function nodes (each node corresponding to interacting proteins with the same functional annotation). However, as proteins have multiple annotations, the process graph is non-redundant, if only proteins participating directly in a given function are included in the related function node. Results Reasoning that topological features (e.g., clusters of highly inter-connected proteins) might help approaching structured and non-redundant understanding of molecular function, an algorithm was developed that prioritizes inclusion of proteins into the function nodes that best overlap protein clusters. Specifically, the algorithm identifies function nodes (and their mutual relations), based on the topological analysis of a protein interaction network, which can be related to various biological domains, such as cellular components (e.g., peroxisome and cellular bud) or biological processes (e.g., cell budding) of the model organism S. cerevisiae. Conclusions The method we have described allows converting a protein interaction network into a non-redundant process graph of inter-dependent function nodes. The examples we have described show that the resulting graph allows researchers to formulate testable hypotheses about dependencies among functions and the underlying mechanisms.
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Alpadi K, Kulkarni A, Comte V, Reinhardt M, Schmidt A, Namjoshi S, Mayer A, Peters C. Sequential analysis of trans-SNARE formation in intracellular membrane fusion. PLoS Biol 2012; 10:e1001243. [PMID: 22272185 PMCID: PMC3260307 DOI: 10.1371/journal.pbio.1001243] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2011] [Accepted: 12/01/2011] [Indexed: 11/19/2022] Open
Abstract
SNARE complexes are required for membrane fusion in the endomembrane system. They contain coiled-coil bundles of four helices, three (Q(a), Q(b), and Q(c)) from target (t)-SNAREs and one (R) from the vesicular (v)-SNARE. NSF/Sec18 disrupts these cis-SNARE complexes, allowing reassembly of their subunits into trans-SNARE complexes and subsequent fusion. Studying these reactions in native yeast vacuoles, we found that NSF/Sec18 activates the vacuolar cis-SNARE complex by selectively displacing the vacuolar Q(a) SNARE, leaving behind a Q(bc)R subcomplex. This subcomplex serves as an acceptor for a Q(a) SNARE from the opposite membrane, leading to Q(a)-Q(bc)R trans-complexes. Activity tests of vacuoles with diagnostic distributions of inactivating mutations over the two fusion partners confirm that this distribution accounts for a major share of the fusion activity. The persistence of the Q(bc)R cis-complex and the formation of the Q(a)-Q(bc)R trans-complex are both sensitive to the Rab-GTPase inhibitor, GDI, and to mutations in the vacuolar tether complex, HOPS (HOmotypic fusion and vacuolar Protein Sorting complex). This suggests that the vacuolar Rab-GTPase, Ypt7, and HOPS restrict cis-SNARE disassembly and thereby bias trans-SNARE assembly into a preferred topology.
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Affiliation(s)
- Kannan Alpadi
- Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, Texas, United States of America
| | - Aditya Kulkarni
- Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, Texas, United States of America
| | - Veronique Comte
- Département de Biochimie, Université de Lausanne, Epalinges, Switzerland
| | - Monique Reinhardt
- Département de Biochimie, Université de Lausanne, Epalinges, Switzerland
| | - Andrea Schmidt
- Département de Biochimie, Université de Lausanne, Epalinges, Switzerland
| | - Sarita Namjoshi
- Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, Texas, United States of America
| | - Andreas Mayer
- Département de Biochimie, Université de Lausanne, Epalinges, Switzerland
| | - Christopher Peters
- Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, Texas, United States of America
- * E-mail:
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17
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Montori-Grau M, Guitart M, García-Martínez C, Orozco A, Gómez-Foix AM. Differential pattern of glycogen accumulation after protein phosphatase 1 glycogen-targeting subunit PPP1R6 overexpression, compared to PPP1R3C and PPP1R3A, in skeletal muscle cells. BMC BIOCHEMISTRY 2011; 12:57. [PMID: 22054094 PMCID: PMC3240831 DOI: 10.1186/1471-2091-12-57] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/25/2011] [Accepted: 11/04/2011] [Indexed: 01/17/2023]
Abstract
BACKGROUND PPP1R6 is a protein phosphatase 1 glycogen-targeting subunit (PP1-GTS) abundant in skeletal muscle with an undefined metabolic control role. Here PPP1R6 effects on myotube glycogen metabolism, particle size and subcellular distribution are examined and compared with PPP1R3C/PTG and PPP1R3A/G(M). RESULTS PPP1R6 overexpression activates glycogen synthase (GS), reduces its phosphorylation at Ser-641/0 and increases the extracted and cytochemically-stained glycogen content, less than PTG but more than G(M). PPP1R6 does not change glycogen phosphorylase activity. All tested PP1-GTS-cells have more glycogen particles than controls as found by electron microscopy of myotube sections. Glycogen particle size is distributed for all cell-types in a continuous range, but PPP1R6 forms smaller particles (mean diameter 14.4 nm) than PTG (36.9 nm) and G(M) (28.3 nm) or those in control cells (29.2 nm). Both PPP1R6- and G(M)-derived glycogen particles are in cytosol associated with cellular structures; PTG-derived glycogen is found in membrane- and organelle-devoid cytosolic glycogen-rich areas; and glycogen particles are dispersed in the cytosol in control cells. A tagged PPP1R6 protein at the C-terminus with EGFP shows a diffuse cytosol pattern in glucose-replete and -depleted cells and a punctuate pattern surrounding the nucleus in glucose-depleted cells, which colocates with RFP tagged with the Golgi targeting domain of β-1,4-galactosyltransferase, according to a computational prediction for PPP1R6 Golgi location. CONCLUSIONS PPP1R6 exerts a powerful glycogenic effect in cultured muscle cells, more than G(M) and less than PTG. PPP1R6 protein translocates from a Golgi to cytosolic location in response to glucose. The molecular size and subcellular location of myotube glycogen particles is determined by the PPP1R6, PTG and G(M) scaffolding.
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Affiliation(s)
- Marta Montori-Grau
- CIBER de Diabetes y Enfermedades Metabólicas Asociadas, Barcelona, Spain.
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18
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Kuehnen P, Laubner K, Raile K, Schöfl C, Jakob F, Pilz I, Päth G, Seufert J. Protein phosphatase 1 (PP-1)-dependent inhibition of insulin secretion by leptin in INS-1 pancreatic β-cells and human pancreatic islets. Endocrinology 2011; 152:1800-8. [PMID: 21427225 DOI: 10.1210/en.2010-1094] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Leptin inhibits insulin secretion from pancreatic β-cells, and in turn, insulin stimulates leptin biosynthesis and secretion from adipose tissue. Dysfunction of this adipoinsular feedback loop has been proposed to be involved in the development of hyperinsulinemia and type 2 diabetes mellitus. At the molecular level, leptin acts through various pathways, which in combination confer inhibitory effects on insulin biosynthesis and secretion. The aim of this study was to identify molecular mechanisms of leptin action on insulin secretion in pancreatic β-cells. To identify novel leptin-regulated genes, we performed subtraction PCR in INS-1 β-cells. Regulated expression of identified genes was confirmed by RT-PCR and Northern and Western blotting. Furthermore, functional impact on β-cell function was characterized by insulin-secretion assays, intracellular Ca²(+) concentration measurements, and enzyme activity assays. PP-1α, the catalytic subunit of protein phosphatase 1 (PP-1), was identified as a novel gene down-regulated by leptin in INS-1 pancreatic β-cells. Expression of PP-1α was verified in human pancreatic sections. PP-1α mRNA and protein expression is down-regulated by leptin, which culminates in reduction of PP-1 enzyme activity in β-cells. In addition, glucose-induced insulin secretion was inhibited by nuclear inhibitor of PP-1 and calyculin A, which was in part mediated by a reduction of PP-1-dependent calcium influx into INS-1 β-cells. These results identify a novel molecular pathway by which leptin confers inhibitory action on insulin secretion, and impaired PP-1 inhibition by leptin may be involved in dysfunction of the adipoinsular axis during the development of hyperinsulinemia and type 2 diabetes mellitus.
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Affiliation(s)
- Peter Kuehnen
- Institute of Experimental Pediatric Endocrinology, Charité Children's Hospital, Universitätsmedizin Berlin, Berlin, Germany.
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Wickner W. Membrane fusion: five lipids, four SNAREs, three chaperones, two nucleotides, and a Rab, all dancing in a ring on yeast vacuoles. Annu Rev Cell Dev Biol 2010; 26:115-36. [PMID: 20521906 DOI: 10.1146/annurev-cellbio-100109-104131] [Citation(s) in RCA: 217] [Impact Index Per Article: 15.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Although fusion mechanisms are highly conserved in evolution and among organelles of the exocytic and endocytic pathways, yeast vacuole homotypic fusion offers unique technical advantages: excellent genetics, clear organelle cytology, in vitro colorimetric fusion assays, and reconstitution of fusion from all-pure components, including a Rab GTPase, HOPS (homotypic fusion and vacuole protein sorting complex), four SNAREs [soluble N-ethylmaleimide-sensitive factor (NSF) attachment receptors] that snare (bind) each other, SNARE-complex disassembly chaperones, and vacuolar lipids. Vacuole fusion studies offer paradigms of the interdependence of lipids and fusion proteins to assemble a fusion microdomain, distinct lipid functions, SNARE complex proofreading through the synergy between HOPS and the SNARE disassembly chaperones, and the role of each fusion protein in promoting radical bilayer restructuring for fusion without lysis.
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Affiliation(s)
- William Wickner
- Department of Biochemistry, Dartmouth Medical School, Hanover, New Hampshire 03755-3844, USA.
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20
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Cannon JF. Function of protein phosphatase-1, Glc7, in Saccharomyces cerevisiae. ADVANCES IN APPLIED MICROBIOLOGY 2010; 73:27-59. [PMID: 20800758 DOI: 10.1016/s0065-2164(10)73002-1] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Budding yeast, Saccharomyces cerevisiae, and its close relatives are unique among eukaryotes in having a single gene, GLC7, encoding protein phosphatase-1 (PP1). This enzyme with a highly conserved amino acid sequence controls many processes in all eukaryotic cells. Therefore, the study of Glc7 function offers a unique opportunity to gain a comprehensive understanding of this critical regulatory enzyme. This review summarizes our current knowledge of how Glc7 function modulates processes in the cytoplasm and nucleus. Additionally, global Glc7 regulation is described.
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Affiliation(s)
- John F Cannon
- Department of Molecular Microbiology and Immunology, University of Missouri, Columbia, Missouri, USA.
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21
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Pryor PR, Luzio JP. Delivery of endocytosed membrane proteins to the lysosome. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2009; 1793:615-24. [DOI: 10.1016/j.bbamcr.2008.12.022] [Citation(s) in RCA: 100] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/22/2008] [Revised: 12/01/2008] [Accepted: 12/12/2008] [Indexed: 01/21/2023]
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22
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Jia Y, Pérez JC. Recombinant expression and affinity purification of snake venom gland parvalbumin in Escherichia coli. Comp Biochem Physiol A Mol Integr Physiol 2009; 153:303-8. [PMID: 19275943 DOI: 10.1016/j.cbpa.2009.03.003] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2009] [Revised: 02/25/2009] [Accepted: 03/03/2009] [Indexed: 10/21/2022]
Abstract
Parvalbumins (PV) are small, acidic, water soluble and calcium-binding proteins generally present in muscular and nervous tissues. In the present study, we identified and characterized a cDNA clone encoding PV, named AplPV, from a snake (Agkistrodon piscivorus leucostoma) venom gland cDNA library. AplPV belongs to EF-hand proteins with six alpha-helices constituting three EF-hand domains. The deduced amino acid sequence of AplPV is 91% and 68% identical to the previously characterized PVs of Boa constrictor and Cyprinus carpio, respectively. The full-length cDNA was subcloned into the expression vector pGEX and transformed into Escherichia coli (E.coli) to produce recombinant protein. The bacterially expressed GST-AplPV fusion protein was highly expressed, and effectively purified by Glutathione-Sepharose affinity chromatography. A high concentration of thrombin protease specifically cleaved and removed the GST tag from fusion protein, and further purified by Benzamidine column for removal of thrombin protease. As a result, the 12 kDa AplPV recombinant protein alone was purified. To investigate the tissue-specific biological occurrence of AplPV, a polyclonal antibody (anti-AplPV-antibody) was raised against GST-AplPV fusion protein in rabbit. Western blot analysis revealed that immunoreactive bands were exhibited in both recombinant protein and samples of venom glands, but not in any crude venom. This specific occurrence indicates a specialized function of AplPV in snake venom glands.
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Affiliation(s)
- Ying Jia
- Natural Toxins Research Center, College of Arts and Sciences, Texas A&M University-Kingsville, Kingsville, Texas 78363, USA
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23
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Caron D, Winstall É, Inaguma Y, Michaud S, Lettre F, Bourassa S, Kelly I, Poirier GG, Faure RL, Tanguay RM. Proteomic Characterization of Mouse Cytosolic and Membrane Prostate Fractions: High Levels of Free SUMO Peptides Are Androgen-Regulated. J Proteome Res 2008; 7:4492-9. [DOI: 10.1021/pr8002497] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Danielle Caron
- Department of Pediatrics, Proteomic platform, CHUL Research Center, Québec G1V 4G2, Canada, Institute for Developmental Research, Aichi Human Service Center, Kasugai, Aichi 480-0392, Japan, and Laboratory of Cellular and Developmental Genetics, Department of Medicine and CREFSIP, Université Laval, Québec G1K 7P4, Canada
| | - Éric Winstall
- Department of Pediatrics, Proteomic platform, CHUL Research Center, Québec G1V 4G2, Canada, Institute for Developmental Research, Aichi Human Service Center, Kasugai, Aichi 480-0392, Japan, and Laboratory of Cellular and Developmental Genetics, Department of Medicine and CREFSIP, Université Laval, Québec G1K 7P4, Canada
| | - Yutaka Inaguma
- Department of Pediatrics, Proteomic platform, CHUL Research Center, Québec G1V 4G2, Canada, Institute for Developmental Research, Aichi Human Service Center, Kasugai, Aichi 480-0392, Japan, and Laboratory of Cellular and Developmental Genetics, Department of Medicine and CREFSIP, Université Laval, Québec G1K 7P4, Canada
| | - Sébastien Michaud
- Department of Pediatrics, Proteomic platform, CHUL Research Center, Québec G1V 4G2, Canada, Institute for Developmental Research, Aichi Human Service Center, Kasugai, Aichi 480-0392, Japan, and Laboratory of Cellular and Developmental Genetics, Department of Medicine and CREFSIP, Université Laval, Québec G1K 7P4, Canada
| | - Francine Lettre
- Department of Pediatrics, Proteomic platform, CHUL Research Center, Québec G1V 4G2, Canada, Institute for Developmental Research, Aichi Human Service Center, Kasugai, Aichi 480-0392, Japan, and Laboratory of Cellular and Developmental Genetics, Department of Medicine and CREFSIP, Université Laval, Québec G1K 7P4, Canada
| | - Sylvie Bourassa
- Department of Pediatrics, Proteomic platform, CHUL Research Center, Québec G1V 4G2, Canada, Institute for Developmental Research, Aichi Human Service Center, Kasugai, Aichi 480-0392, Japan, and Laboratory of Cellular and Developmental Genetics, Department of Medicine and CREFSIP, Université Laval, Québec G1K 7P4, Canada
| | - Isabelle Kelly
- Department of Pediatrics, Proteomic platform, CHUL Research Center, Québec G1V 4G2, Canada, Institute for Developmental Research, Aichi Human Service Center, Kasugai, Aichi 480-0392, Japan, and Laboratory of Cellular and Developmental Genetics, Department of Medicine and CREFSIP, Université Laval, Québec G1K 7P4, Canada
| | - Guy G. Poirier
- Department of Pediatrics, Proteomic platform, CHUL Research Center, Québec G1V 4G2, Canada, Institute for Developmental Research, Aichi Human Service Center, Kasugai, Aichi 480-0392, Japan, and Laboratory of Cellular and Developmental Genetics, Department of Medicine and CREFSIP, Université Laval, Québec G1K 7P4, Canada
| | - Robert L. Faure
- Department of Pediatrics, Proteomic platform, CHUL Research Center, Québec G1V 4G2, Canada, Institute for Developmental Research, Aichi Human Service Center, Kasugai, Aichi 480-0392, Japan, and Laboratory of Cellular and Developmental Genetics, Department of Medicine and CREFSIP, Université Laval, Québec G1K 7P4, Canada
| | - Robert M. Tanguay
- Department of Pediatrics, Proteomic platform, CHUL Research Center, Québec G1V 4G2, Canada, Institute for Developmental Research, Aichi Human Service Center, Kasugai, Aichi 480-0392, Japan, and Laboratory of Cellular and Developmental Genetics, Department of Medicine and CREFSIP, Université Laval, Québec G1K 7P4, Canada
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Inoue T, Kon T, Ohkura R, Yamakawa H, Ohara O, Yokota J, Sutoh K. BREK/LMTK2 is a myosin VI-binding protein involved in endosomal membrane trafficking. Genes Cells 2008; 13:483-95. [PMID: 18429820 DOI: 10.1111/j.1365-2443.2008.01184.x] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Myosin VI is involved in a wide range of endocytic and exocytic membrane trafficking pathways; clathrin-mediated endocytosis, intracellular transport of clathrin-coated and -uncoated vesicles, AP-1B-dependent basolateral sorting in polarized epithelial cells and secretion from the Golgi complex to the cell surface. In this study, using a yeast two-hybrid screen, we identified brain-enriched kinase/lemur tyrosine kinase 2 (BREK/LMTK2), a transmembrane serine/threonine kinase with previously unknown cellular functions, as a myosin VI-interacting protein. Several binding experiments confirmed the interaction of myosin VI with BREK in vivo and in vitro. Immunocytochemical analyses revealed that BREK localizes to cytoplasmic membrane vesicles and to perinuclear recycling endosomes. Notably, cells in which BREK was depleted by siRNA were still able to internalize transferrin molecules and to transport them to early endosomes, but were unable to transport them to perinuclear recycling endosomes. Our results show that BREK is critical for the transition of endocytosed membrane vesicles from early endosomes to recycling endosomes and also suggest an involvement of myosin VI in this pathway.
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Affiliation(s)
- Takeshi Inoue
- Department of Life Sciences, Graduate School of Arts and Sciences, University of Tokyo, Komaba 3-8-1, Meguro-ku, Tokyo 153-8902, Japan
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25
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Larson JR, Bharucha JP, Ceaser S, Salamon J, Richardson CJ, Rivera SM, Tatchell K. Protein phosphatase type 1 directs chitin synthesis at the bud neck in Saccharomyces cerevisiae. Mol Biol Cell 2008; 19:3040-51. [PMID: 18480405 DOI: 10.1091/mbc.e08-02-0130] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Yeast chitin synthase III (CSIII) is targeted to the bud neck, where it is thought to be tethered by the septin-associated protein Bni4. Bni4 also associates with the yeast protein phosphatase (PP1) catalytic subunit, Glc7. To identify regions of Bni4 necessary for its targeting functions, we created a collection of 23 deletion mutants throughout the length of Bni4. Among the deletion variants that retain the ability to associate with the bud neck, only those deficient in Glc7 binding fail to target CSIII to the neck. A chimeric protein composed of the septin Cdc10 and the C-terminal Glc7-binding domain of Bni4 complements the defects of a bni4Delta mutant, indicating that the C-terminus of Bni4 is necessary and sufficient to target Glc7 and CSIII to the bud neck. A Cdc10-Glc7 chimera fails to target CSIII to the bud neck but is functional in the presence of the C-terminal Glc7-binding domain of Bni4. The conserved C-terminal PP1-binding domain of mammalian Phactr-1 can functionally substitute for the C-terminus of Bni4. These results suggest that the essential role of Bni4 is to target Glc7 to the neck and activate it toward substrates necessary for CSIII recruitment and synthesis of chitin at the bud neck.
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Affiliation(s)
- Jennifer R Larson
- Department of Biochemistry and Molecular Biology, Louisiana State University Health Sciences Center, Shreveport, LA 71130, USA
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26
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The role of calcium and other ions in sorting and delivery in the late endocytic pathway. Biochem Soc Trans 2008; 35:1088-91. [PMID: 17956286 DOI: 10.1042/bst0351088] [Citation(s) in RCA: 111] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
The passage of endocytosed receptor-bound ligands and membrane proteins through the endocytic pathway of mammalian cells to lysosomes occurs via early and late endosomes. The latter contain many luminal vesicles and are often referred to as MVBs (multivesicular bodies). The overall morphology of endosomal compartments is, in major part, a consequence of the many fusion events occurring in the endocytic pathway. Kissing events and direct fusion between late endosomes and lysosomes provide a means of delivery to lysosomes. The luminal ionic composition of organelles in the endocytic pathway is of considerable importance both in the trafficking of endocytosed ligands and in the membrane fusion events. In particular, H(+) ions play a role in sorting processes and providing an appropriate environment for the action of lysosomal acid hydrolases. Na(+)/H(+) exchangers in the endosomal membrane have been implicated in the formation of MVBs and sorting into luminal vesicles. Ca(2+) ions are required for fusion events and luminal content condensation in the lysosome. Consistent with an important role for luminal Ca(2+) in traffic through the late endocytic pathway, mutations in the gene encoding mucolipin-1, a lysosomal non-specific cation channel, result in abnormalities in lipid traffic and are associated with the autosomal recessive lysosomal storage disease MLIV (mucolipidosis type IV).
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27
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De Filippi L, Fournier M, Cameroni E, Linder P, De Virgilio C, Foti M, Deloche O. Membrane stress is coupled to a rapid translational control of gene expression in chlorpromazine-treated cells. Curr Genet 2007; 52:171-85. [PMID: 17710403 DOI: 10.1007/s00294-007-0151-0] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2007] [Revised: 07/30/2007] [Accepted: 07/31/2007] [Indexed: 11/25/2022]
Abstract
Chlorpromazine (CPZ) is a small permeable cationic amphiphilic molecule that inserts into membrane bilayers and binds to anionic lipids such as poly-phosphoinositides (PIs). Since PIs play important roles in many cellular processes, including signaling and membrane trafficking pathways, it has been proposed that CPZ affects cellular growth functions by preventing the recruitment of proteins with specific PI-binding domains. In this study, we have investigated the biological effects of CPZ in the yeast Saccharomyces cerevisiae. We screened a collection of approximately 4,800 gene knockout mutants, and found that mutants defective in membrane trafficking between the late-Golgi and endosomal compartments are highly sensitive to CPZ. Microscopy and transport analyses revealed that CPZ affects membrane structure of organelles, blocks membrane transport and activates the unfolded protein response (UPR). In addition, CPZ-treatment induces phosphorylation of the translation initiation factor (eIF2alpha), which reduces the general rate of protein synthesis and stimulates the production of Gcn4p, a major transcription factor that is activated in response to environmental stresses. Altogether, our results reveal that membrane stress within the cells rapidly activates an important gene expression program, which is followed by a general inhibition of protein synthesis. Remarkably, the increase of phosphorylated eIF2alpha and protein synthesis inhibition were also detected in CPZ-treated NIH-3T3 fibroblasts, suggesting the existence of a conserved mechanism of translational regulation that operates during a membrane stress.
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Affiliation(s)
- Loic De Filippi
- Département de Microbiologie et Médecine Moléculaire, Centre Médical Universitaire, Université de Genève, 1 rue Michel-Servet, 1211 Geneva 4, Switzerland
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28
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Meiringer CTA, Ungermann C. Probing protein palmitoylation at the yeast vacuole. Methods 2006; 40:171-6. [PMID: 17012029 DOI: 10.1016/j.ymeth.2006.06.020] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/01/2006] [Accepted: 06/23/2006] [Indexed: 11/15/2022] Open
Abstract
A protein's function depends on its localization to the right cellular compartment. A number of proteins require lipidation to associate with membranes. Protein palmitoylation is a reversible lipid modification and has been shown to mediate both membrane localization and control protein function. At the yeast vacuole, several palmitoylated proteins have been identified that are required for vacuole biogenesis, including the fusion factor Vac8, the SNARE Ykt6 and the casein kinase Yck3. Moreover, both the DHHC-CRD acyltransferase Pfa3 and Ykt6 are involved in palmitoylation at the vacuole Here, we present and discuss methods to probe for protein palmitoylation at vacuoles.
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29
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Cameroni E, De Virgilio C, Deloche O. Phosphatidylinositol 4-Phosphate Is Required for Translation Initiation in Saccharomyces cerevisiae. J Biol Chem 2006; 281:38139-49. [PMID: 17005563 DOI: 10.1074/jbc.m601060200] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The small natural product wortmannin inhibits protein synthesis by modulating several phosphatidylinositol (PI) metabolic pathways. A primary target of wortmannin in yeast is the plasma membrane-associated PI 4-kinase (PI4K) Stt4p, which is required for actin cytoskeleton organization. Here we show that wortmannin treatment or inactivation of Stt4p, but not disorganization of the actin cytoskeleton per se, leads to a rapid attenuation of translation initiation. Interestingly, inactivation of Pik1p, a wortmannin-insensitive, functionally distinct PI4K, implicated in the regulation of Golgi functions and secretion, also results in severe translation initiation defects with a marked increase of the phosphorylation of the translation initiation factor eIF2alpha. Because wortmannin largely phenocopies the effects of rapamycin (e.g. it triggers nuclear accumulation of Gln3p), it likely also inhibits the PI kinase-related, target of rapamycin (TOR) kinases. Importantly, however, neither inactivation of Stt4p nor Pik1p significantly affects TOR-controlled readouts other than translation initiation, indicating that these PI4Ks do not simply function upstream of TOR. Together, our results reveal the existence of a novel translation initiation control mechanism in yeast that is tightly coupled to the synthesis of distinct PI4P pools.
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Affiliation(s)
- Elisabetta Cameroni
- Department of Microbiology and Molecular Medicine, Centre Médical Universitaire, University of Geneva, 1 rue Michel-Servet, 1211 Geneva, Switzerland
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30
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Abstract
Cyclin-dependent kinase 5 (Cdk5) is recognized as an essential molecule in the brain, where it regulates several neuronal activities, including cytoskeletal remodeling and synaptic transmission. While activity of Cdk5 has primarily been associated with neurons, there are now substantial data indicating that the kinase's activity and function are more general. An increasing body of evidence has established Cdk5 kinase activity, the presence of the Cdk5 activators, p35 and p39, and Cdk5 functions in non-neuronal cells, including myocytes, pancreatic beta-cells, monocytic and neutrophilic leucocytes, glial cells and germ cells. In this review, we present the diverse roles of Cdk5 in several extraneuronal paradigms. The unique properties of each of the different cell types appear to involve distinct means of Cdk5 regulation and function. The potential mechanisms through which Cdk5 regulates extraneuronal cell activities such as exocytosis, gene transcription, wound healing and senescence are discussed.
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Affiliation(s)
- Jesusa L Rosales
- Department of Cell Biology and Anatomy, The Southern Alberta Cancer Research and Hotchkiss Brain Institutes, The University of Calgary, Calgary, Alberta, Canada.
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31
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Haluska CK, Riske KA, Marchi-Artzner V, Lehn JM, Lipowsky R, Dimova R. Time scales of membrane fusion revealed by direct imaging of vesicle fusion with high temporal resolution. Proc Natl Acad Sci U S A 2006; 103:15841-6. [PMID: 17043227 PMCID: PMC1613233 DOI: 10.1073/pnas.0602766103] [Citation(s) in RCA: 198] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Membrane fusion is a vital process of life involved, for example, in cellular secretion via exocytosis, signaling between nerve cells, and virus infection. In both the life sciences and bioengineering, controlled membrane fusion has many possible applications, such as drug delivery, gene transfer, chemical microreactors, or synthesis of nanomaterials. Until now, the fusion dynamics has been elusive because direct observations have been limited to time scales that exceed several milliseconds. Here, the fusion of giant lipid vesicles is induced in a controlled manner and monitored with a temporal resolution of 50 micros. Two different fusion protocols are used that are based on synthetic fusogenic molecules and electroporation. For both protocols, the opening of the fusion necks is very fast, with an average expansion velocity of centimeters per second. This velocity indicates that the initial formation of a single fusion neck can be completed in a few hundred nanoseconds.
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Affiliation(s)
- Christopher K. Haluska
- *Max Planck Institute of Colloids and Interfaces, Science Park Golm, 14424 Potsdam, Germany; and
| | - Karin A. Riske
- *Max Planck Institute of Colloids and Interfaces, Science Park Golm, 14424 Potsdam, Germany; and
| | - Valérie Marchi-Artzner
- Laboratoire de Chimie des Interactions Moléculaires, Collège de France, 75005 Paris, France
| | - Jean-Marie Lehn
- Laboratoire de Chimie des Interactions Moléculaires, Collège de France, 75005 Paris, France
| | - Reinhard Lipowsky
- *Max Planck Institute of Colloids and Interfaces, Science Park Golm, 14424 Potsdam, Germany; and
| | - Rumiana Dimova
- *Max Planck Institute of Colloids and Interfaces, Science Park Golm, 14424 Potsdam, Germany; and
- To whom correspondence should be addressed. E-mail:
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32
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Xu H, Wickner W. Bem1p Is a Positive Regulator of the Homotypic Fusion of Yeast Vacuoles. J Biol Chem 2006; 281:27158-66. [PMID: 16854988 DOI: 10.1074/jbc.m605592200] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Docked vacuoles are believed to undergo rapid lipid mixing during hemifusion and then a slow, rate-limiting completion of fusion and mixing of lumenal contents. Previous genomic analysis has suggested that Bem1p, a scaffold protein critical for cell polarity, may support vacuole fusion. We now report that bem1Delta strains have fragmented vacuoles (vps class B and C). During in vitro fusion reactions, vacuoles from bem1Delta strains showed a strong reduction in the rate of lipid mixing when compared with vacuoles from the BEM1 parent. The reduction in the overall rate of fusion with bem1Delta vacuoles was modest, consistent with lipid mixing as a non-rate-limiting step in the pathway. Although the fusion of either BEM1 (wild-type) or bem1Delta vacuoles is stimulated by recombinant Bem1p, the lipid mixing of docked bem1Delta vacuoles is highly dependent on rBem1p under certain reaction conditions. Bem1p-stimulated lipid mixing is blocked by well characterized fusion inhibitors including lipid ligands and antibodies to Ypt7p, Vps33p, and Vam3p. Although full-length Bem1p is required for maximal stimulation, a truncation mutant comprising the SH3 domains and the Phox homology (PX) domain retains modest stimulatory activity. In contrast to an earlier report (Han, B. K., Bogomolnaya, L. M., Totten, J. M., Blank, H. M., Dangott, L. J., and Polymenis, M. (2005) Genes Dev. 19, 2606-2618), we did not find phosphorylation of Bem1p at Ser-72 to be required for Bem1p-stimulated fusion. Taken together, Bem1p is a positive regulator of lipid mixing during vacuole hemifusion and fusion.
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Affiliation(s)
- Hao Xu
- Department of Biochemistry, Dartmouth Medical School, Hanover, New Hampshire 03755-3844, USA
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33
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Huang FD, Woodruff E, Mohrmann R, Broadie K. Rolling blackout is required for synaptic vesicle exocytosis. J Neurosci 2006; 26:2369-79. [PMID: 16510714 PMCID: PMC6793665 DOI: 10.1523/jneurosci.3770-05.2006] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Rolling blackout (RBO) is a putative transmembrane lipase required for phospholipase C-dependent phosphatidylinositol 4,5-bisphosphate-diacylglycerol signaling in Drosophila neurons. Conditional temperature-sensitive (TS) rbo mutants display complete, reversible paralysis within minutes, demonstrating that RBO is acutely required for movement. RBO protein is localized predominantly in presynaptic boutons at neuromuscular junction (NMJ) synapses and throughout central synaptic neuropil, and rbo TS mutants display a complete, reversible block of both central and peripheral synaptic transmission within minutes. This phenotype appears limited to adults, because larval NMJs do not manifest the acute blockade. Electron microscopy of adult rbo TS mutant boutons reveals an increase in total synaptic vesicle (SV) content, with a concomitant shrinkage of presynaptic bouton size and an accumulation of docked SVs at presynaptic active zones within minutes. Genetic tests reveal a synergistic interaction between rbo and syntaxin1A TS mutants, suggesting that RBO is required in the mechanism of N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE)-mediated SV exocytosis, or in a parallel pathway necessary for SV fusion. The rbo TS mutation does not detectably alter SNARE complex assembly, suggesting a downstream requirement in SV fusion. We conclude that RBO plays an essential role in neurotransmitter release, downstream of SV docking, likely mediating SV fusion.
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Affiliation(s)
- Fu-De Huang
- Department of Biological Sciences, Kennedy Center for Research on Human Development, Brain Institute, Vanderbilt University, Nashville, Tennessee 37235-1634, USA
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34
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Reese C, Mayer A. Transition from hemifusion to pore opening is rate limiting for vacuole membrane fusion. ACTA ACUST UNITED AC 2006; 171:981-90. [PMID: 16365164 PMCID: PMC2171322 DOI: 10.1083/jcb.200510018] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Fusion pore opening and expansion are considered the most energy-demanding steps in viral fusion. Whether this also applies to soluble N-ethyl-maleimide sensitive fusion protein attachment protein receptor (SNARE)- and Rab-dependent fusion events has been unknown. We have addressed the problem by characterizing the effects of lysophosphatidylcholine (LPC) and other late-stage inhibitors on lipid mixing and pore opening during vacuole fusion. LPC inhibits fusion by inducing positive curvature in the bilayer and changing its biophysical properties. The LPC block reversibly prevented formation of the hemifusion intermediate that allows lipid, but not content, mixing. Transition from hemifusion to pore opening was sensitive to guanosine-5'-(gamma-thio)triphosphate. It required the vacuolar adenosine triphosphatase V0 sector and coincided with its transformation. Pore opening was rate limiting for the reaction. As with viral fusion, opening the fusion pore may be the most energy-demanding step for intracellular, SNARE-dependent fusion reactions, suggesting that fundamental aspects of lipid mixing and pore opening are related for both systems.
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Affiliation(s)
- Christoph Reese
- Département de Biochimie, Université de Lausanne, 1066 Epalinges, Switzerland
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35
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Wu X, Jiang YW. Genetic/genomic evidence for a key role of polarized endocytosis in filamentous differentiation of S. cerevisiae. Yeast 2005; 22:1143-53. [PMID: 16240455 DOI: 10.1002/yea.1305] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
Unicellular S. cerevisiae cells switch from the yeast form to pseudohyphal or filamentous form in response to environmental cues. We report that wild-type BY diploids (in which yeast ORFs have been systematically deleted) undergo normal HU-induced filamentous growth and discernable nitrogen starvation-induced filamentous growth, despite their perceived filamentation-deficient S288C genetic background. This finding allowed us to perform a genome-wide survey for non-essential genes that are required for filamentous growth with the homozygous deletion strains. We report that genes involved in endocytosis are required for both HU-induced and nitrogen starvation-induced filamentous growth. Surprisingly, no known genes involved in exocytosis are required. Despite the fact that polarized growth involves transport of vesicles to the site of growth, we failed to obtain genetic/genomic evidence that exocytosis plays an essential role in filamentous growth. A possible key role of polarized endocytosis (from the growth tip) is consistent with the proposed biological function of filamentous growth as a foraging behaviour. In addition, BUD8 that encodes the distal landmark in yeast-form bipolar budding is required for nitrogen starvation-induced but not HU-induced filamentous growth. Moreover, BUD5, SPA2, PEA2 and BUD6 that regulate bipolar bud site selection do not regulate the unipolar distal budding pattern in HU-induced filamentous growth.
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Affiliation(s)
- Xiaofeng Wu
- Department of Medical Biochemistry and Genetics, Texas A&M University System, Health Science Center, 428 Reynolds Medical Building, College Station, TX 77843-1114, USA
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36
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Churchward MA, Rogasevskaia T, Höfgen J, Bau J, Coorssen JR. Cholesterol facilitates the native mechanism of Ca2+-triggered membrane fusion. J Cell Sci 2005; 118:4833-48. [PMID: 16219690 DOI: 10.1242/jcs.02601] [Citation(s) in RCA: 143] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
The process of regulated exocytosis is defined by the Ca2+-triggered fusion of two apposed membranes, enabling the release of vesicular contents. This fusion step involves a number of energetically complex steps and requires both protein and lipid membrane components. The role of cholesterol has been investigated using isolated release-ready native cortical secretory vesicles to analyze the Ca2+-triggered fusion step of exocytosis. Cholesterol is a major component of vesicle membranes and we show here that selective removal from membranes, selective sequestering within membranes, or enzymatic modification causes a significant inhibition of the extent, Ca2+ sensitivity and kinetics of fusion. Depending upon the amount incorporated, addition of exogenous cholesterol to cholesterol-depleted membranes consistently recovers the extent, but not the Ca2+ sensitivity or kinetics of fusion. Membrane components of comparable negative curvature selectively recover the ability to fuse, but are unable to recover the kinetics and Ca2+ sensitivity of vesicle fusion. This indicates at least two specific positive roles for cholesterol in the process of membrane fusion: as a local membrane organizer contributing to the efficiency of fusion, and, by virtue of its intrinsic negative curvature, as a specific molecule working in concert with protein factors to facilitate the minimal molecular machinery for fast Ca2+-triggered fusion.
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Affiliation(s)
- Matthew A Churchward
- Department of Physiology and Biophysics, Hotchkiss Brain Institute, University of Calgary, Health Sciences Centre, Faculty of Medicine, Calgary, Alberta, T2N 4N1, Canada
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37
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Sambade M, Alba M, Smardon AM, West RW, Kane PM. A genomic screen for yeast vacuolar membrane ATPase mutants. Genetics 2005; 170:1539-51. [PMID: 15937126 PMCID: PMC1365767 DOI: 10.1534/genetics.105.042812] [Citation(s) in RCA: 81] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
V-ATPases acidify multiple organelles, and yeast mutants lacking V-ATPase activity exhibit a distinctive set of growth defects. To better understand the requirements for organelle acidification and the basis of these growth phenotypes, approximately 4700 yeast deletion mutants were screened for growth defects at pH 7.5 in 60 mm CaCl(2). In addition to 13 of 16 mutants lacking known V-ATPase subunits or assembly factors, 50 additional mutants were identified. Sixteen of these also grew poorly in nonfermentable carbon sources, like the known V-ATPase mutants, and were analyzed further. The cwh36Delta mutant exhibited the strongest phenotype; this mutation proved to disrupt a previously uncharacterized V-ATPase subunit. A small subset of the mutations implicated in vacuolar protein sorting, vps34Delta, vps15Delta, vps45Delta, and vps16Delta, caused both Vma- growth phenotypes and lower V-ATPase activity in isolated vacuoles, as did the shp1Delta mutation, implicated in both protein sorting and regulation of the Glc7p protein phosphatase. These proteins may regulate V-ATPase targeting and/or activity. Eight mutants showed a Vma- growth phenotype but no apparent defect in vacuolar acidification. Like V-ATPase-deficient mutants, most of these mutants rely on calcineurin for growth, particularly at high pH. A requirement for constitutive calcineurin activation may be the predominant physiological basis of the Vma- growth phenotype.
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Affiliation(s)
- Maria Sambade
- Department of Biochemistry and Molecular Biology, SUNY Upstate Medical University, Syracuse, New York 13210, USA
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38
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Reese C, Heise F, Mayer A. Trans-SNARE pairing can precede a hemifusion intermediate in intracellular membrane fusion. Nature 2005; 436:410-4. [PMID: 15924133 DOI: 10.1038/nature03722] [Citation(s) in RCA: 106] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2005] [Accepted: 05/09/2005] [Indexed: 11/09/2022]
Abstract
The question concerning whether all membranes fuse according to the same mechanism has yet to be answered satisfactorily. During fusion of model membranes or viruses, membranes dock, the outer membrane leaflets mix (termed hemifusion), and finally the fusion pore opens and the contents mix. Viral fusion proteins consist of a membrane-disturbing 'fusion peptide' and a helical bundle that pin the membranes together. Although SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) complexes form helical bundles with similar topology, it is unknown whether SNARE-dependent fusion events on intracellular membranes proceed through a hemifusion state. Here we identify the first hemifusion state for SNARE-dependent fusion of native membranes, and place it into a sequence of molecular events: formation of helical bundles by SNAREs precedes hemifusion; further progression to pore opening requires additional peptides. Thus, SNARE-dependent fusion may proceed along the same pathway as viral fusion: both use a docking mechanism via helical bundles and additional peptides to destabilize the membrane and efficiently induce lipid mixing. Our results suggest that a common lipidic intermediate may underlie all fusion reactions of lipid bilayers.
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Affiliation(s)
- Christoph Reese
- Département de Biochimie, Université de Lausanne, Chemin des Boveresses 155, CH-1066 Epalinges, Switzerland
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39
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Lilja L, Meister B, Berggren PO, Bark C. DARPP-32 and inhibitor-1 are expressed in pancreatic β-cells. Biochem Biophys Res Commun 2005; 329:673-7. [PMID: 15737638 DOI: 10.1016/j.bbrc.2005.02.017] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2004] [Indexed: 11/20/2022]
Abstract
Insulin secretion from pancreatic beta-cells has to be tightly regulated to ensure accurate glucose homeostasis. The capacity of beta-cells to respond to extracellular stimulation is determined by several signaling pathways. One important feature of these pathways is phosphorylation and subsequent dephosphorylation of a wide range of cellular substrates. Protein phosphatase 1 (PP1) is a major eukaryotic serine/threonine protein phosphatase that controls a multitude of physiological processes. We have investigated the expression and cellular distribution of two endogenous inhibitors of PP1 activity in beta-cells. RT-PCR, Western blotting, and immunohistochemistry showed that DARPP-32 and inhibitor-1 are present in insulin-secreting endocrine beta-cells. Subcellular fractionation of mouse islets revealed that both PP1 inhibitors predominantly localized to cytosol-enriched fractions. Inhibitor-1 was also present in fractions containing plasma membrane-associated proteins. These data indicate a potential role for DARPP-32 and inhibitor-1 in the regulation of PP1 activity in pancreatic beta-cell stimulus-secretion coupling.
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Affiliation(s)
- Lena Lilja
- The Rolf Luft Center for Diabetes Research, Department of Molecular Medicine, Karolinska Institutet, Karolinska University Hospital, SE-171 76 Stockholm, Sweden
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40
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Abstract
Transport from late endosomes to lysosomes results in the formation of an endosome-lysosome hybrid organelle from which late endosomes and lysosomes must be re-formed. Recent studies indicate that the transient receptor potential (TRP)-related channel mucolipin-1 (the loss of which causes mucolipidosis type IV) and its Caenorhabditis elegans orthologue CUP-5 might control the process of lysosome re-formation by regulating calcium flux.
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Affiliation(s)
- Robert C Piper
- Department of Physiology, University of Iowa, Iowa City, IA 52242, USA.
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41
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Dietrich LEP, LaGrassa TJ, Rohde J, Cristodero M, Meiringer CTA, Ungermann C. ATP-independent control of Vac8 palmitoylation by a SNARE subcomplex on yeast vacuoles. J Biol Chem 2005; 280:15348-55. [PMID: 15701652 DOI: 10.1074/jbc.m410582200] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Yeast vacuole fusion requires palmitoylated Vac8. We previously showed that Vac8 acylation occurs early in the fusion reaction, is blocked by antibodies against Sec18 (yeast N-ethylmaleimide-sensitive fusion protein (NSF)), and is mediated by the R-SNARE Ykt6. Here we analyzed the regulation of this reaction on purified vacuoles. We show that Vac8 acylation is restricted to a narrow time window, is independent of ATP hydrolysis by Sec18, and is stimulated by the ion chelator EDTA. Analysis of vacuole protein complexes indicated that Ykt6 is part of a complex distinct from the second R-SNARE, Nyv1. We speculate that during vacuole fusion, Nyv1 is the classical R-SNARE, whereas the Ykt6-containing complex has a novel function in Vac8 palmitoylation.
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Affiliation(s)
- Lars E P Dietrich
- Biochemie-Zentrum der Universität Heidelberg, Im Neuenheimer Feld 328, 69120 Heidelberg, Germany
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42
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Fratti RA, Jun Y, Merz AJ, Margolis N, Wickner W. Interdependent assembly of specific regulatory lipids and membrane fusion proteins into the vertex ring domain of docked vacuoles. ACTA ACUST UNITED AC 2005; 167:1087-98. [PMID: 15611334 PMCID: PMC2172599 DOI: 10.1083/jcb.200409068] [Citation(s) in RCA: 180] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
Membrane microdomains are assembled by lipid partitioning (e.g., rafts) or by protein–protein interactions (e.g., coated vesicles). During docking, yeast vacuoles assemble “vertex” ring-shaped microdomains around the periphery of their apposed membranes. Vertices are selectively enriched in the Rab GTPase Ypt7p, the homotypic fusion and vacuole protein sorting complex (HOPS)–VpsC Rab effector complex, SNAREs, and actin. Membrane fusion initiates at vertex microdomains. We now find that the “regulatory lipids” ergosterol, diacylglycerol and 3- and 4-phosphoinositides accumulate at vertices in a mutually interdependent manner. Regulatory lipids are also required for the vertex enrichment of SNAREs, Ypt7p, and HOPS. Conversely, SNAREs and actin regulate phosphatidylinositol 3-phosphate vertex enrichment. Though the PX domain of the SNARE Vam7p has direct affinity for only 3-phosphoinositides, all the regulatory lipids which are needed for vertex assembly affect Vam7p association with vacuoles. Thus, the assembly of the vacuole vertex ring microdomain arises from interdependent lipid and protein partitioning and binding rather than either lipid partitioning or protein interactions alone.
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Affiliation(s)
- Rutilio A Fratti
- Department of Biochemistry, Dartmouth Medical School, Hanover, NH 03755, USA
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43
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Elbert M, Rossi G, Brennwald P. The yeast par-1 homologs kin1 and kin2 show genetic and physical interactions with components of the exocytic machinery. Mol Biol Cell 2005; 16:532-49. [PMID: 15563607 PMCID: PMC545889 DOI: 10.1091/mbc.e04-07-0549] [Citation(s) in RCA: 77] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2004] [Revised: 10/28/2004] [Accepted: 11/11/2004] [Indexed: 11/11/2022] Open
Abstract
Kin1 and Kin2 are Saccharomyces cerevisiae counterparts of Par-1, the Caenorhabditis elegans kinase essential for the establishment of polarity in the one cell embryo. Here, we present evidence for a novel link between Kin1, Kin2, and the secretory machinery of the budding yeast. We isolated KIN1 and KIN2 as suppressors of a mutant form of Rho3, a Rho-GTPase acting in polarized trafficking. Genetic analysis suggests that KIN1 and KIN2 act downstream of the Rab-GTPase Sec4, its exchange factor Sec2, and several components of the vesicle tethering complex, the Exocyst. We show that Kin1 and Kin2 physically interact with the t-SNARE Sec9 and the Lgl homologue Sro7, proteins acting at the final stage of exocytosis. Structural analysis of Kin2 reveals that its catalytic activity is essential for its function in the secretory pathway and implicates the conserved 42-amino acid tail at the carboxy terminal of the kinase in autoinhibition. Finally, we find that Kin1 and Kin2 induce phosphorylation of t-SNARE Sec9 in vivo and stimulate its release from the plasma membrane. In summary, we report the finding that yeast Par-1 counterparts are associated with and regulate the function of the exocytic apparatus via phosphorylation of Sec9.
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Affiliation(s)
- Maya Elbert
- Department of Cell and Developmental Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
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Wilson GM, Fielding AB, Simon GC, Yu X, Andrews PD, Hames RS, Frey AM, Peden AA, Gould GW, Prekeris R. The FIP3-Rab11 protein complex regulates recycling endosome targeting to the cleavage furrow during late cytokinesis. Mol Biol Cell 2004; 16:849-60. [PMID: 15601896 PMCID: PMC545916 DOI: 10.1091/mbc.e04-10-0927] [Citation(s) in RCA: 249] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
An integral part of cell division is the separation of daughter cells via cytokinesis. There is now good evidence that the completion of cytokinesis requires coordinated membrane trafficking to deliver new membrane to the tip of the furrow and to complete the abscission. Here we have examined membrane traffic in cytokinesis and describe several novel observations. First, we show that Rab11- and FIP3-containing recycling endosomes accumulate near the cleavage furrow and are required for successful completion of cytokinesis. Second, we demonstrate that the Rab11-FIP3 protein complex is intimately involved in the delivery of endosomes to the cleavage furrow. Significantly, although FIP3 recruitment to endosomes is Rab11 dependent, we find that the targeting of FIP3 to the midbody is independent of Rab11. Third, we show that the Rab11-FIP3 complex is required for a late stage of cytokinesis, possibly abscission. Finally, we demonstrate that localization of FIP3 is subject to substantial spatial and temporal regulation. These data provide the first detailed analysis of recycling endosomes in cell division and provide a new model for membrane traffic to the furrow. We propose that the dynamic Rab11-FIP3 interaction controls the delivery, targeting, and fusion of recycling endosomes with furrow during late cytokinesis and abscission.
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Affiliation(s)
- Gayle M Wilson
- Department of Cellular and Developmental Biology, School of Medicine, University of Colorado Health Sciences Center, Denver, CO 80262, USA
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Peters C, Baars TL, Bühler S, Mayer A. Mutual Control of Membrane Fission and Fusion Proteins. Cell 2004; 119:667-78. [PMID: 15550248 DOI: 10.1016/j.cell.2004.11.023] [Citation(s) in RCA: 117] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2004] [Revised: 09/27/2004] [Accepted: 10/20/2004] [Indexed: 11/24/2022]
Abstract
Membrane fusion and fission are antagonistic reactions controlled by different proteins. Dynamins promote membrane fission by GTP-driven changes of conformation and polymerization state, while SNAREs fuse membranes by forming complexes between t- and v-SNAREs from apposed vesicles. Here, we describe a role of the dynamin-like GTPase Vps1p in fusion of yeast vacuoles. Vps1p forms polymers that couple several t-SNAREs together. At the onset of fusion, the SNARE-activating ATPase Sec18p/NSF and the t-SNARE depolymerize Vps1p and release it from the membrane. This activity is independent of the SNARE coactivator Sec17p/alpha-SNAP and of the v-SNARE. Vps1p release liberates the t-SNAREs for initiating fusion and at the same time disrupts fission activity. We propose that reciprocal control between fusion and fission components exists, which may prevent futile cycles of fission and fusion.
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Affiliation(s)
- Christopher Peters
- Département de Biochimie, Université de Lausanne, Chemin des Boveresses 155, 1066 Epalinges, Switzerland.
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46
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Peng R, Gallwitz D. Multiple SNARE interactions of an SM protein: Sed5p/Sly1p binding is dispensable for transport. EMBO J 2004; 23:3939-49. [PMID: 15372079 PMCID: PMC524344 DOI: 10.1038/sj.emboj.7600410] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2004] [Accepted: 08/19/2004] [Indexed: 11/09/2022] Open
Abstract
Sec1/Munc18 (SM) proteins are central to intracellular transport and neurotransmitter release but their exact role is still elusive. Several SM proteins, like the neuronal N-Sec1 and the yeast Sly1 protein, bind their cognate t-SNAREs with high affinity. This has been thought to be critical for their function. Here, we show that various mutant forms of Sly1p and the Golgi-localized syntaxin Sed5p, which abolish their high-affinity interaction, are fully functional in vivo, indicating that the tight interaction of the two molecules per se is not relevant for proper function. Mutant Sly1p unable to bind Sed5p is excluded from core SNARE complexes, also demonstrating that Sly1p function is not directly coupled to assembled SNARE complexes thought to execute membrane fusion. We also find that wild-type Sly1p and mutant Sly1p unable to bind Sed5p directly interact with selected ER-to-Golgi and intra-Golgi nonsyntaxin SNAREs. The newly identified, direct interactions of the SM protein with nonsytaxin SNAREs might provide a molecular mechanism by which SNAREs can be activated to engage in pairing and assemble into fusogenic SNARE complexes.
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Affiliation(s)
- Renwang Peng
- Department of Molecular Genetics, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Dieter Gallwitz
- Department of Molecular Genetics, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
- Abt. Molekulare Genetik, MPI für Biophysikalische Chemie, Am Fassberg 11, 37017 Göttingen, Germany. Tel.: +49 551 201 1496; Fax: +49 551 201 1718; E-mail:
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Affiliation(s)
- Ulrich Blank
- INSERM E 0225, Bichat Medical School, 16 rue Henri Huchard, BP 416, 75870 Cedex 18, France
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Merz AJ, Wickner WT. Resolution of organelle docking and fusion kinetics in a cell-free assay. Proc Natl Acad Sci U S A 2004; 101:11548-53. [PMID: 15286284 PMCID: PMC511018 DOI: 10.1073/pnas.0404583101] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
In vitro assays of compartment mixing have been key tools in the biochemical dissection of organelle docking and fusion. Many such assays measure compartment mixing through the enzymatic modification of reporter proteins. Homotypic fusion of yeast vacuoles is measured with a coupled assay of proteolytic maturation of pro-alkaline phosphatase (pro-ALP). A kinetic lag is observed between the end of docking, marked by the acquisition of resistance to anti-SNARE reagents, and ALP maturation. We therefore asked whether the time taken for pro-ALP maturation adds a kinetic lag to the measured fusion signal. Prb1p promotes ALP maturation; overproduction of Prb1p accelerates ALP activation in detergent lysates but does not alter the measured kinetics of docking or fusion. Thus, the lag between docking and ALP activation reflects a lag between docking and fusion. Many vacuoles in the population undergo multiple rounds of fusion; methods are presented for distinguishing the first round of fusion from ongoing rounds of fusion. A simple kinetic model distinguishes between two rates, the rate of fusion and the rate at which fusion competence is lost, and allows estimation of the number of rounds of fusion completed.
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Affiliation(s)
- Alexey J Merz
- Department of Biochemistry, Dartmouth Medical School, Hanover, NH 03755, USA.
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49
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Thorngren N, Collins KM, Fratti RA, Wickner W, Merz AJ. A soluble SNARE drives rapid docking, bypassing ATP and Sec17/18p for vacuole fusion. EMBO J 2004; 23:2765-76. [PMID: 15241469 PMCID: PMC514947 DOI: 10.1038/sj.emboj.7600286] [Citation(s) in RCA: 86] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2004] [Accepted: 06/02/2004] [Indexed: 11/09/2022] Open
Abstract
Membrane fusion requires priming, the disassembly of cis-SNARE complexes by the ATP-driven chaperones Sec18/17p. Yeast vacuole priming releases Vam7p, a soluble SNARE. Vam7p reassociation during docking allows trans-SNARE pairing and fusion. We now report that recombinant Vam7p (rVam7p) enters into complex with other SNAREs in vitro and bypasses the need for Sec17p, Sec18p, and ATP. Thus, the sole essential function of vacuole priming in vitro is the release of Vam7p from cis-SNARE complexes. In 'bypass fusion', without ATP but with added rVam7p, there are sufficient unpaired vacuolar SNAREs Vam3p, Vti1p, and Nyv1p to interact with Vam7p and support fusion. However, active SNARE proteins are not sufficient for bypass fusion. rVam7p does not bypass requirements for Rho GTPases,Vps33p, Vps39p, Vps41p, calmodulin, specific lipids, or Vph1p, a subunit of the V-ATPase. With excess rVam7p, reduced levels of PI(3)P or functional Ypt7p suffice for bypass fusion. High concentrations of rVam7p allow the R-SNARE Ykt6p to substitute for Nyv1p for fusion; this functional redundancy among vacuole SNAREs may explain why nyv1delta strains lack the vacuole fragmentation seen with mutants in other fusion catalysts.
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Affiliation(s)
- Naomi Thorngren
- Department of Biochemistry, Dartmouth Medical School, Hanover, NH, USA
| | - Kevin M Collins
- Department of Biochemistry, Dartmouth Medical School, Hanover, NH, USA
| | - Rutilio A Fratti
- Department of Biochemistry, Dartmouth Medical School, Hanover, NH, USA
| | - William Wickner
- Department of Biochemistry, Dartmouth Medical School, Hanover, NH, USA
- Department of Biochemistry, 7200 Vail Building, Room 425 Remsen, Dartmouth Medical School, Hanover, NH 03755-3844, USA. Tel.: +1 603 650 1701; Fax: +1 603 650 1353; E-mail: ; Lab website: http://www.dartmouth.edu/~wickner
| | - Alexey J Merz
- Department of Biochemistry, Dartmouth Medical School, Hanover, NH, USA
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50
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Abstract
Exocytosis is a ubiquitous process occurring in every eukaryotic cell including processes as diverse as membrane expansion during growth and the highly regulated release of neurotransmitter from neurons. Work during the past decade has established that exocytotic membrane fusion is mediated by members of conserved protein families including Rab proteins and SNAREs. SNAREs are probably catalyzing membrane fusion, and major progress has been made in unraveling their molecular mechanism. In contrast, less is known about regulatory mechanisms. Here, a brief overview is given about the current state of knowledge, focusing on SNAREs involved in neuronal exocytosis.
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Affiliation(s)
- Reinhard Jahn
- Department of Neurobiology, Max-Planck-Institute for Biophysical Chemistry, Göttingen, Germany.
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