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Bootman MD, Chehab T, Bultynck G, Parys JB, Rietdorf K. The regulation of autophagy by calcium signals: Do we have a consensus? Cell Calcium 2017; 70:32-46. [PMID: 28847414 DOI: 10.1016/j.ceca.2017.08.005] [Citation(s) in RCA: 172] [Impact Index Per Article: 24.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2017] [Revised: 08/14/2017] [Accepted: 08/14/2017] [Indexed: 12/12/2022]
Abstract
Macroautophagy (hereafter called 'autophagy') is a cellular process for degrading and recycling cellular constituents, and for maintenance of cell function. Autophagy initiates via vesicular engulfment of cellular materials and culminates in their degradation via lysosomal hydrolases, with the whole process often being termed 'autophagic flux'. Autophagy is a multi-step pathway requiring the interplay of numerous scaffolding and signalling molecules. In particular, orthologs of the family of ∼30 autophagy-regulating (Atg) proteins that were first characterised in yeast play essential roles in the initiation and processing of autophagic vesicles in mammalian cells. The serine/threonine kinase mTOR (mechanistic target of rapamycin) is a master regulator of the canonical autophagic response of cells to nutrient starvation. In addition, AMP-activated protein kinase (AMPK), which is a key sensor of cellular energy status, can trigger autophagy by inhibiting mTOR, or by phosphorylating other downstream targets. Calcium (Ca2+) has been implicated in autophagic signalling pathways encompassing both mTOR and AMPK, as well as in autophagy seemingly not involving these kinases. Numerous studies have shown that cytosolic Ca2+ signals can trigger autophagy. Moreover, introduction of an exogenous chelator to prevent cytosolic Ca2+ signals inhibits autophagy in response to many different stimuli, with suggestions that buffering Ca2+ affects not only the triggering of autophagy, but also proximal and distal steps during autophagic flux. Observations such as these indicate that Ca2+ plays an essential role as a pro-autophagic signal. However, cellular Ca2+ signals can exert anti-autophagic actions too. For example, Ca2+ channel blockers induce autophagy due to the loss of autophagy-suppressing Ca2+ signals. In addition, the sequestration of Ca2+ by mitochondria during physiological signalling appears necessary to maintain cellular bio-energetics, thereby suppressing AMPK-dependent autophagy. This article attempts to provide an integrated overview of the evidence for the proposed roles of various Ca2+ signals, Ca2+ channels and Ca2+ sources in controlling autophagic flux.
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Affiliation(s)
- Martin D Bootman
- School of Life, Health and Chemical Sciences, The Open University, MK7 6AA, UK.
| | - Tala Chehab
- School of Life, Health and Chemical Sciences, The Open University, MK7 6AA, UK
| | - Geert Bultynck
- KU Leuven, Laboratory of Molecular and Cellular Signaling, Department of Cellular and Molecular Medicine and Leuven Kanker Instituut (LKI), B-3000 Leuven, Belgium
| | - Jan B Parys
- KU Leuven, Laboratory of Molecular and Cellular Signaling, Department of Cellular and Molecular Medicine and Leuven Kanker Instituut (LKI), B-3000 Leuven, Belgium
| | - Katja Rietdorf
- School of Life, Health and Chemical Sciences, The Open University, MK7 6AA, UK
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Kintzer AF, Stroud RM. On the structure and mechanism of two-pore channels. FEBS J 2017; 285:233-243. [PMID: 28656706 DOI: 10.1111/febs.14154] [Citation(s) in RCA: 30] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2017] [Revised: 05/24/2017] [Accepted: 06/23/2017] [Indexed: 12/22/2022]
Abstract
In eukaryotes, two-pore channels (TPC1-3) comprise a family of ion channels that regulate the conductance of Na+ and Ca2+ ions across cellular membranes. TPC1-3 form endolysosomal channels, but TPC3 can also function in the plasma membrane. TPC1/3 are voltage-gated channels, but TPC2 opens in response to binding endolysosome-specific lipid phosphatidylinositol-3,5-diphosphate (PI(3,5)P2 ). Filoviruses, such as Ebola, exploit TPC-mediated ion release as a means of escape from the endolysosome during infection. Antagonists that block TPC1/2 channel conductance abrogate filoviral infections. TPC1/2 form complexes with the mechanistic target of rapamycin complex 1 (mTORC1) at the endolysosomal surface that couple cellular metabolic state and cytosolic nutrient concentrations to the control of membrane potential and pH. We determined the X-ray structure of TPC1 from Arabidopsis thaliana (AtTPC1) to 2.87Å resolution-one of the two first reports of a TPC channel structure. Here, we summarize these findings and the implications that the structure may have for understanding endolysosomal control mechanisms and their role in human health.
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Affiliation(s)
- Alexander F Kintzer
- Department of Biochemistry and Biophysics, University of California, San Francisco, CA, USA
| | - Robert M Stroud
- Department of Biochemistry and Biophysics, University of California, San Francisco, CA, USA
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53
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Methods for monitoring Ca 2+ and ion channels in the lysosome. Cell Calcium 2017; 64:20-28. [DOI: 10.1016/j.ceca.2016.12.001] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2016] [Revised: 12/07/2016] [Accepted: 12/07/2016] [Indexed: 12/22/2022]
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Cao Q, Yang Y, Zhong XZ, Dong XP. The lysosomal Ca 2+ release channel TRPML1 regulates lysosome size by activating calmodulin. J Biol Chem 2017; 292:8424-8435. [PMID: 28360104 DOI: 10.1074/jbc.m116.772160] [Citation(s) in RCA: 66] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2016] [Revised: 03/29/2017] [Indexed: 01/01/2023] Open
Abstract
Intracellular lysosomal membrane trafficking, including fusion and fission, is crucial for cellular homeostasis and normal cell function. Both fusion and fission of lysosomal membrane are accompanied by lysosomal Ca2+ release. We recently have demonstrated that the lysosomal Ca2+ release channel P2X4 regulates lysosome fusion through a calmodulin (CaM)-dependent mechanism. However, the molecular mechanism underlying lysosome fission remains uncertain. In this study, we report that enlarged lysosomes/vacuoles induced by either vacuolin-1 or P2X4 activation are suppressed by up-regulating the lysosomal Ca2+ release channel transient receptor potential mucolipin 1 (TRPML1) but not the lysosomal Na+ release channel two-pore channel 2 (TPC2). Activation of TRPML1 facilitated the recovery of enlarged lysosomes/vacuoles. Moreover, the effects of TRPML1 on lysosome/vacuole size regulation were eliminated by Ca2+ chelation, suggesting a requirement for TRPML1-mediated Ca2+ release. We further demonstrate that the prototypical Ca2+ sensor CaM is required for the regulation of lysosome/vacuole size by TRPML1, suggesting that TRPML1 may promote lysosome fission by activating CaM. Given that lysosome fission is implicated in both lysosome biogenesis and reformation, our findings suggest that TRPML1 may function as a key lysosomal Ca2+ channel controlling both lysosome biogenesis and reformation.
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Affiliation(s)
- Qi Cao
- Department of Physiology and Biophysics, Dalhousie University, Halifax, Nova Scotia B3H 4R2, Canada
| | - Yiming Yang
- Department of Physiology and Biophysics, Dalhousie University, Halifax, Nova Scotia B3H 4R2, Canada
| | - Xi Zoë Zhong
- Department of Physiology and Biophysics, Dalhousie University, Halifax, Nova Scotia B3H 4R2, Canada
| | - Xian-Ping Dong
- Department of Physiology and Biophysics, Dalhousie University, Halifax, Nova Scotia B3H 4R2, Canada.
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Mitochondrial Dysfunction and Neurodegeneration in Lysosomal Storage Disorders. Trends Mol Med 2017; 23:116-134. [DOI: 10.1016/j.molmed.2016.12.003] [Citation(s) in RCA: 83] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2016] [Revised: 12/12/2016] [Accepted: 12/13/2016] [Indexed: 12/22/2022]
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56
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Sbano L, Bonora M, Marchi S, Baldassari F, Medina DL, Ballabio A, Giorgi C, Pinton P. TFEB-mediated increase in peripheral lysosomes regulates store-operated calcium entry. Sci Rep 2017; 7:40797. [PMID: 28084445 PMCID: PMC5233950 DOI: 10.1038/srep40797] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2016] [Accepted: 12/09/2016] [Indexed: 01/04/2023] Open
Abstract
Lysosomes are membrane-bound organelles mainly involved in catabolic processes. In addition, lysosomes can expel their contents outside of the cell via lysosomal exocytosis. Some of the key steps involved in these important cellular processes, such as vesicular fusion and trafficking, require calcium (Ca2+) signaling. Recent data show that lysosomal functions are transcriptionally regulated by transcription factor EB (TFEB) through the induction of genes involved in lysosomal biogenesis and exocytosis. Given these observations, we investigated the roles of TFEB and lysosomes in intracellular Ca2+ homeostasis. We studied the effect of transient modulation of TFEB expression in HeLa cells by measuring the cytosolic Ca2+ response after capacitative Ca2+ entry activation and Ca2+ dynamics in the endoplasmic reticulum (ER) and directly in lysosomes. Our observations show that transient TFEB overexpression significantly reduces cytosolic Ca2+ levels under a capacitative influx model and ER re-uptake of calcium, increasing the lysosomal Ca2+ buffering capacity. Moreover, lysosomal destruction or damage abolishes these TFEB-dependent effects in both the cytosol and ER. These results suggest a possible Ca2+ buffering role for lysosomes and shed new light on lysosomal functions during intracellular Ca2+ homeostasis.
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Affiliation(s)
- Luigi Sbano
- Dept. of Morphology, Surgery and Experimental Medicine, Section of Pathology, Oncology and Experimental Biology, Laboratory for Technologies of Advanced Therapies (LTTA), University of Ferrara, Ferrara, 44121, Italy
| | - Massimo Bonora
- Dept. of Morphology, Surgery and Experimental Medicine, Section of Pathology, Oncology and Experimental Biology, Laboratory for Technologies of Advanced Therapies (LTTA), University of Ferrara, Ferrara, 44121, Italy
| | - Saverio Marchi
- Dept. of Morphology, Surgery and Experimental Medicine, Section of Pathology, Oncology and Experimental Biology, Laboratory for Technologies of Advanced Therapies (LTTA), University of Ferrara, Ferrara, 44121, Italy
| | - Federica Baldassari
- Dept. of Morphology, Surgery and Experimental Medicine, Section of Pathology, Oncology and Experimental Biology, Laboratory for Technologies of Advanced Therapies (LTTA), University of Ferrara, Ferrara, 44121, Italy
| | - Diego L Medina
- Telethon Institute of Genetics and Medicine (TIGEM), 80078 Pozzuoli, Naples, Italy
| | - Andrea Ballabio
- Telethon Institute of Genetics and Medicine (TIGEM), 80078 Pozzuoli, Naples, Italy.,Dept. of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas 77030, USA.,Jan and Dan Duncan Neurological Research Institute, Texas Children's Hospital, Houston, Texas 77030, USA.,Medical Genetics, Dept. of Translational Medicine, Federico II University, 80131 Naples, Italy
| | - Carlotta Giorgi
- Dept. of Morphology, Surgery and Experimental Medicine, Section of Pathology, Oncology and Experimental Biology, Laboratory for Technologies of Advanced Therapies (LTTA), University of Ferrara, Ferrara, 44121, Italy
| | - Paolo Pinton
- Dept. of Morphology, Surgery and Experimental Medicine, Section of Pathology, Oncology and Experimental Biology, Laboratory for Technologies of Advanced Therapies (LTTA), University of Ferrara, Ferrara, 44121, Italy
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Abstract
Lysosomes are key acidic Ca2+ stores. The principle Ca2+-permeable channels of the lysosome are TRP mucolipins (TRPMLs) and NAADP-regulated two-pore channels (TPCs). Recent studies, reviewed in this collection, have linked numerous neurodegenerative diseases to both gain and loss of function of TRPMLs/TPCs, as well as to defects in acidic Ca2+ store content. These diseases span rare lysosomal storage disorders such as Mucolipidosis Type IV and Niemann-Pick disease, type C, through to more common ones such as Alzheimer and Parkinson disease. Cellular phenotypes, underpinned by endo-lysosomal trafficking defects, are reversed by chemical or molecular targeting of TRPMLs and TPCs. Lysosomal Ca2+ channels therefore emerge as potential druggable targets in combatting neurodegeneration.
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Affiliation(s)
- Sandip Patel
- Department of Cell and Developmental Biology, University College London, Gower Street, London WC1E 6BT
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Abstract
Lysosomes have emerged in the last decade as an immensely important intracellular site of Ca2+ storage and signalling. More recently there has been an increase in the number of new ion channels found to be functional on lysosomes and the potential roles that these signalling pathways might play in fundamental cellular processes are being uncovered. Defects in lysosomal function have been shown to result in changes in lysosomal Ca2+ homeostasis and ultimately can result in cell death. Several neurodegenerative diseases, from rare lysosomal storage diseases through to more common diseases of ageing, have recently been identified as having alterations in lysosomal Ca2+ homeostasis that may play an important role in neuronal excitotoxicity and ultimately cell death. This review will critically summarise these recent findings.
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Affiliation(s)
- Emyr Lloyd-Evans
- School of Biosciences, Sir Martin Evans Building, Cardiff University, Museum Avenue, Cardiff, CF10 3AX
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Abstract
The neurodegenerative movement disorder Parkinson disease (PD) is prevalent in the aged population. However, the underlying mechanisms that trigger disease are unclear. Increasing work implicates both impaired Ca2+ signalling and lysosomal dysfunction in neuronal demise. Here I aim to connect these distinct processes by exploring the evidence that lysosomal Ca2+ signalling is disrupted in PD. In particular, I highlight defects in lysosomal Ca2+ content and signalling through NAADP-regulated two-pore channels in patient fibroblasts harbouring mutations in the PD-linked genes, GBA1 and LRRK2. As an emerging contributor to PD pathogenesis, the lysosomal Ca2+ signalling apparatus could represent a novel therapeutic target.
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Affiliation(s)
- Bethan S Kilpatrick
- Department of Cell and Developmental Biology, University College London, London, WC1E 6BT, UK
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Feng X, Yang J. Lysosomal Calcium in Neurodegeneration. MESSENGER (LOS ANGELES, CALIF. : PRINT) 2016; 5:56-66. [PMID: 29082116 PMCID: PMC5659362 DOI: 10.1166/msr.2016.1055] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Lysosomes are the central organelles responsible for macromolecule recycling in the cell. Lysosomal dysfunction is the primary cause of lysosomal storage diseases (LSDs), and contributes significantly to the pathogenesis of common neurodegenerative diseases. The lysosomes are also intracellular stores for calcium ions, one of the most common second messenger in the cell. Lysosomal Ca2+ is required for diverse cellular processes including signal transduction, vesicular trafficking, autophagy, nutrient sensing, exocytosis, and membrane repair. In this review, we first summarize some recent progresses in the studies of lysosome Ca2+ regulation, with a focus on the newly discovered lysosomal Ca2+ channels and the mechanisms of lysosomal Ca2+ store refilling. We then discuss how defects in lysosomal Ca2+ release and store maintenance cause lysosomal dysfunction and neurodegeneration.
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Affiliation(s)
- Xinghua Feng
- Collaborative Innovation Center of Yangtze River Delta Region Green Pharmaceuticals, College of Pharmaceutical Sciences, Zhejiang University of Technology, Hangzhou 310014, China
| | - Junsheng Yang
- Collaborative Innovation Center of Yangtze River Delta Region Green Pharmaceuticals, College of Pharmaceutical Sciences, Zhejiang University of Technology, Hangzhou 310014, China
- The Department of Molecular, Cellular, and Developmental Biology, University of Michigan, 3089 Natural Science Building (Kraus), 830 North University, Ann Arbor, MI 48109, USA
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