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Zeger M, Stanisławczyk LS, Bulić M, Binder AM, Huber A. tsCRISPR based identification of Rab proteins required for the recycling of Drosophila TRPL ion channel. Front Cell Dev Biol 2024; 12:1444953. [PMID: 39372952 PMCID: PMC11450138 DOI: 10.3389/fcell.2024.1444953] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2024] [Accepted: 09/05/2024] [Indexed: 10/08/2024] Open
Abstract
In polarized cells, the precise regulation of protein transport to and from the plasma membrane is crucial to maintain cellular function. Dysregulation of intracellular protein transport in neurons can lead to neurodegenerative diseases such as Retinitis Pigmentosa, Alzheimer's and Parkinson's disease. Here we used the light-dependent transport of the TRPL (transient receptor potential-like) ion channel in Drosophila photoreceptor cells to study the role of Rab proteins in TRPL recycling. TRPL is located in the rhabdomeric membrane of dark-adapted flies, but it is transported out of the rhabdomere upon light exposure and localizes at the Endoplasmatic Reticulum within 12 h. Upon subsequent dark adaptation, TRPL is recycled back to the rhabdomeric membrane within 90 min. To screen for Rab proteins involved in TRPL recycling, we established a tissue specific (ts) CRISPR/Cas9-mediated knock-out of individual Rab genes in Drosophila photoreceptors and assessed TRPL localization using an eGFP tagged TRPL protein in the intact eyes of these mutants. We observed severe TRPL recycling defects in the knockouts of Rab3, Rab4, Rab7, Rab32, and RabX2. Using immunohistochemistry, we further showed that Rab3 and RabX2 each play a significant role in TRPL recycling and also influence TRPL transport. We localized Rab3 to the late endosome in Drosophila photoreceptors and observed disruption of TRPL transport to the ER in Rab3 knock-out mutants. TRPL transport from the ER to the rhabdomere ensues from the trans-Golgi where RabX2 is located. We observed accumulated TRPL at the trans-Golgi in RabX2 knock-out mutants. In summary, our study reveals the requirement of specific Rab proteins for different steps of TRPL transport in photoreceptor cells and provides evidence for a unique retrograde recycling pathway of TRPL from the ER via the trans-Golgi.
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Affiliation(s)
| | | | | | | | - Armin Huber
- Department of Biochemistry, Institute of Biology, University of Hohenheim, Stuttgart, Germany
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Feizy N, Leuchtenberg SF, Steiner C, Würtz B, Fliegner L, Huber A. In vivo identification of Drosophila rhodopsin interaction partners by biotin proximity labeling. Sci Rep 2024; 14:1986. [PMID: 38263196 PMCID: PMC10805788 DOI: 10.1038/s41598-024-52041-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2023] [Accepted: 01/12/2024] [Indexed: 01/25/2024] Open
Abstract
Proteins exert their function through protein-protein interactions. In Drosophila, G protein-coupled receptors like rhodopsin (Rh1) interact with a G protein to activate visual signal transduction and with arrestins to terminate activation. Also, membrane proteins like Rh1 engage in protein-protein interactions during folding within the endoplasmic reticulum, during their vesicular transport and upon removal from the cell surface and degradation. Here, we expressed a Rh1-TurboID fusion protein (Rh1::TbID) in Drosophila photoreceptors to identify in vivo Rh1 interaction partners by biotin proximity labeling. We show that Rh1::TbID forms a functional rhodopsin that mediates biotinylation of arrestin 2 in conditions where arrestin 2 interacts with rhodopsin. We also observed biotinylation of Rh1::TbID and native Rh1 as well as of most visual signal transduction proteins. These findings indicate that the signaling components in the rhabdomere approach rhodopsin closely, within a range of ca. 10 nm. Furthermore, we have detected proteins engaged in the maturation of rhodopsin and elements responsible for the trafficking of membrane proteins, resembling potential interaction partners of Rh1. Among these are chaperons of the endoplasmic reticulum, proteins involved in Clathrin-mediated endocytosis as well as previously unnoticed contributors to rhodopsin transportation, such as Rab32, Vap33, or PIP82.
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Affiliation(s)
- Nilofar Feizy
- Department of Biochemistry, Institute of Biology, University of Hohenheim, Stuttgart, Germany
| | | | - Christine Steiner
- Department of Biochemistry, Institute of Biology, University of Hohenheim, Stuttgart, Germany
| | - Berit Würtz
- Mass Spectrometry Unit, Core Facility Hohenheim, University of Hohenheim, Stuttgart, Germany
| | - Leo Fliegner
- Department of Biochemistry, Institute of Biology, University of Hohenheim, Stuttgart, Germany
| | - Armin Huber
- Department of Biochemistry, Institute of Biology, University of Hohenheim, Stuttgart, Germany.
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Križaj D, Cordeiro S, Strauß O. Retinal TRP channels: Cell-type-specific regulators of retinal homeostasis and multimodal integration. Prog Retin Eye Res 2023; 92:101114. [PMID: 36163161 PMCID: PMC9897210 DOI: 10.1016/j.preteyeres.2022.101114] [Citation(s) in RCA: 17] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2022] [Revised: 08/03/2022] [Accepted: 08/08/2022] [Indexed: 02/05/2023]
Abstract
Transient receptor potential (TRP) channels are a widely expressed family of 28 evolutionarily conserved cationic ion channels that operate as primary detectors of chemical and physical stimuli and secondary effectors of metabotropic and ionotropic receptors. In vertebrates, the channels are grouped into six related families: TRPC, TRPV, TRPM, TRPA, TRPML, and TRPP. As sensory transducers, TRP channels are ubiquitously expressed across the body and the CNS, mediating critical functions in mechanosensation, nociception, chemosensing, thermosensing, and phototransduction. This article surveys current knowledge about the expression and function of the TRP family in vertebrate retinas, which, while dedicated to transduction and transmission of visual information, are highly susceptible to non-visual stimuli. Every retinal cell expresses multiple TRP subunits, with recent evidence establishing their critical roles in paradigmatic aspects of vertebrate vision that include TRPM1-dependent transduction of ON bipolar signaling, TRPC6/7-mediated ganglion cell phototransduction, TRP/TRPL phototransduction in Drosophila and TRPV4-dependent osmoregulation, mechanotransduction, and regulation of inner and outer blood-retina barriers. TRP channels tune light-dependent and independent functions of retinal circuits by modulating the intracellular concentration of the 2nd messenger calcium, with emerging evidence implicating specific subunits in the pathogenesis of debilitating diseases such as glaucoma, ocular trauma, diabetic retinopathy, and ischemia. Elucidation of TRP channel involvement in retinal biology will yield rewards in terms of fundamental understanding of vertebrate vision and therapeutic targeting to treat diseases caused by channel dysfunction or over-activation.
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Affiliation(s)
- David Križaj
- Departments of Ophthalmology, Neurobiology, and Bioengineering, University of Utah, Salt Lake City, USA
| | - Soenke Cordeiro
- Institute of Physiology, Faculty of Medicine, Christian-Albrechts-University Kiel, Germany
| | - Olaf Strauß
- Experimental Ophthalmology, Department of Ophthalmology, Charité - Universitätsmedizin Berlin, a Corporate Member of Freie Universität, Humboldt-University, The Berlin Institute of Health, Berlin, Germany.
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Heckman CA, Ademuyiwa OM, Cayer ML. How filopodia respond to calcium in the absence of a calcium-binding structural protein: non-channel functions of TRP. Cell Commun Signal 2022; 20:130. [PMID: 36028898 PMCID: PMC9414478 DOI: 10.1186/s12964-022-00927-y] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/25/2021] [Accepted: 06/21/2022] [Indexed: 11/18/2022] Open
Abstract
Background For many cell types, directional locomotion depends on their maintaining filopodia at the leading edge. Filopodia lack any Ca2+-binding structural protein but respond to store-operated Ca2+ entry (SOCE). Methods SOCE was induced by first replacing the medium with Ca2+-free salt solution with cyclopiazonic acid (CPA). This lowers Ca2+ in the ER and causes stromal interacting molecule (STIM) to be translocated to the cell surface. After this priming step, CPA was washed out, and Ca2+ influx restored by addition of extracellular Ca2+. Intracellular Ca2+ levels were measured by calcium orange fluorescence. Regulatory mechanisms were identified by pharmacological treatments. Proteins mediating SOCE were localized by immunofluorescence and analyzed after image processing. Results Depletion of the ER Ca2+ increased filopodia prevalence briefly, followed by a spontaneous decline that was blocked by inhibitors of endocytosis. Intracellular Ca2+ increased continuously for ~ 50 min. STIM and a transient receptor potential canonical (TRPC) protein were found in separate compartments, but an aquaporin unrelated to SOCE was present in both. STIM1- and TRPC1-bearing vesicles were trafficked on microtubules. During depletion, STIM1 migrated to the surface where it coincided with Orai in punctae, as expected. TRPC1 was partially colocalized with Vamp2, a rapidly releasable pool marker, and with phospholipases (PLCs). TRPC1 retreated to internal compartments during ER depletion. Replenishment of extracellular Ca2+ altered the STIM1 distribution, which came to resemble that of untreated cells. Vamp2 and TRPC1 underwent exocytosis and became homogeneously distributed on the cell surface. This was accompanied by an increased prevalence of filopodia, which was blocked by inhibitors of TRPC1/4/5 and endocytosis. Conclusions Because the media were devoid of ligands that activate receptors during depletion and Ca2+ replenishment, we could attribute filopodia extension to SOCE. We propose that the Orai current stimulates exocytosis of TRPC-bearing vesicles, and that Ca2+ influx through TRPC inhibits PLC activity. This allows regeneration of the substrate, phosphatidylinositol 4,5 bisphosphate (PIP2), a platform for assembling proteins, e. g. Enabled and IRSp53. TRPC contact with PLC is required but is broken by TRPC dissemination. This explains how STIM1 regulates the cell’s ability to orient itself in response to attractive or repulsive cues. Video Abstract
Supplementary Information The online version contains supplementary material available at 10.1186/s12964-022-00927-y.
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Affiliation(s)
- C A Heckman
- Department of Biological Sciences, 217 Life Science Building, Bowling Green State University, Bowling Green, OH, 43403-0001, USA.
| | - O M Ademuyiwa
- Department of Biological Sciences, 217 Life Science Building, Bowling Green State University, Bowling Green, OH, 43403-0001, USA
| | - M L Cayer
- Center for Microscopy and Microanalysis, Bowling Green State University, Bowling Green, OH, 43403, USA
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Wagner K, Smylla TK, Lampe M, Krieg J, Huber A. Phospholipase D and retromer promote recycling of TRPL ion channel via the endoplasmic reticulum. Traffic 2021; 23:42-62. [PMID: 34719094 DOI: 10.1111/tra.12824] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2021] [Revised: 10/20/2021] [Accepted: 10/26/2021] [Indexed: 12/27/2022]
Abstract
Plasma membrane protein trafficking is of fundamental importance for cell function and cell integrity of neurons and includes regulated protein recycling. In this work, we report a novel role of the endoplasmic reticulum (ER) for protein recycling as discovered in trafficking studies of the ion channel TRPL in photoreceptor cells of Drosophila. TRPL is located within the rhabdomeric membrane from where it is endocytosed upon light stimulation and stored in the cell body. Conventional immunohistochemistry as well as stimulated emission depletion super-resolution microscopy revealed TRPL storage at the ER after illumination, suggesting an unusual recycling route of TRPL. Our results also imply that both phospholipase D (PLD) and retromer complex are required for correct recycling of TRPL to the rhabdomeric membrane. Loss of PLD activity in PLD3.1 mutants results in enhanced degradation of TRPL. In the retromer mutant vps35MH20 , TRPL is trapped in a Rab5-positive compartment. Evidenced by epistatic analysis in the double mutant PLD3.1 vps35MH20 , PLD activity precedes retromer function. We propose a model in which PLD and retromer function play key roles in the transport of TRPL to an ER enriched compartment.
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Affiliation(s)
- Krystina Wagner
- Department of Biochemistry, University of Hohenheim, Institute of Biology, Stuttgart, Germany
| | - Thomas K Smylla
- Department of Biochemistry, University of Hohenheim, Institute of Biology, Stuttgart, Germany
| | - Marko Lampe
- European Molecular Biology Laboratory, Advanced Light Microscopy Core Facility, Heidelberg, Germany
| | - Jana Krieg
- Department of Biochemistry, University of Hohenheim, Institute of Biology, Stuttgart, Germany
| | - Armin Huber
- Department of Biochemistry, University of Hohenheim, Institute of Biology, Stuttgart, Germany
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6
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Smylla TK, Wagner K, Huber A. Application of Fluorescent Proteins for Functional Dissection of the Drosophila Visual System. Int J Mol Sci 2021; 22:8930. [PMID: 34445636 PMCID: PMC8396179 DOI: 10.3390/ijms22168930] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2021] [Revised: 08/13/2021] [Accepted: 08/14/2021] [Indexed: 11/22/2022] Open
Abstract
The Drosophila eye has been used extensively to study numerous aspects of biological systems, for example, spatio-temporal regulation of differentiation, visual signal transduction, protein trafficking and neurodegeneration. Right from the advent of fluorescent proteins (FPs) near the end of the millennium, heterologously expressed fusion proteins comprising FPs have been applied in Drosophila vision research not only for subcellular localization of proteins but also for genetic screens and analysis of photoreceptor function. Here, we summarize applications for FPs used in the Drosophila eye as part of genetic screens, to study rhodopsin expression patterns, subcellular protein localization, membrane protein transport or as genetically encoded biosensors for Ca2+ and phospholipids in vivo. We also discuss recently developed FPs that are suitable for super-resolution or correlative light and electron microscopy (CLEM) approaches. Illustrating the possibilities provided by using FPs in Drosophila photoreceptors may aid research in other sensory or neuronal systems that have not yet been studied as well as the Drosophila eye.
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Affiliation(s)
- Thomas K. Smylla
- Department of Biochemistry, Institute of Biology, University of Hohenheim, 70599 Stuttgart, Germany; (K.W.); (A.H.)
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Schopf K, Smylla TK, Huber A. Immunocytochemical Labeling of Rhabdomeric Proteins in Drosophila Photoreceptor Cells Is Compromised by a Light-dependent Technical Artifact. J Histochem Cytochem 2019; 67:745-757. [PMID: 31246149 PMCID: PMC6764007 DOI: 10.1369/0022155419859870] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
Drosophila photoreceptor cells are employed as a model system
for studying membrane protein transport. Phototransduction proteins like
rhodopsin and the light-activated TRPL ion channel are transported within the
photoreceptor cell, and they change their subcellular distribution in a
light-dependent way. Investigating the transport mechanisms for rhodopsin and
ion channels requires accurate histochemical methods for protein localization.
By using immunocytochemistry the light-triggered translocation of TRPL has been
described as a two-stage process. In stage 1, TRPL accumulates at the rhabdomere
base and the adjacent stalk membrane a few minutes after onset of illumination
and is internalized in stage 2 by endocytosis after prolonged light exposure.
Here, we show that a commonly observed crescent shaped antibody labeling pattern
suggesting a fast translocation of rhodopsin, TRP, and TRPL to the rhabdomere
base is a light-dependent antibody staining artifact. This artifact is most
probably caused by the profound structural changes in the microvillar membranes
of rhabdomeres that result from activation of the signaling cascade. By using
alternative labeling methods, either eGFP-tags or the self-labeling SNAP-tag, we
show that light activation of TRPL transport indeed results in fast changes of
the TRPL distribution in the rhabdomere but not in the way described
previously.
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Affiliation(s)
- Krystina Schopf
- Department of Biochemistry, Institute of Physiology, University of Hohenheim, Stuttgart, Germany
| | - Thomas K Smylla
- Department of Biochemistry, Institute of Physiology, University of Hohenheim, Stuttgart, Germany
| | - Armin Huber
- Department of Biochemistry, Institute of Physiology, University of Hohenheim, Stuttgart, Germany
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Katz B, Minke B. The Drosophila light-activated TRP and TRPL channels - Targets of the phosphoinositide signaling cascade. Prog Retin Eye Res 2018; 66:200-219. [DOI: 10.1016/j.preteyeres.2018.05.001] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2018] [Revised: 04/29/2018] [Accepted: 05/02/2018] [Indexed: 01/28/2023]
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Oberacker T, Bajorat J, Ziola S, Schroeder A, Röth D, Kastl L, Edgar BA, Wagner W, Gülow K, Krammer PH. Enhanced expression of thioredoxin-interacting-protein regulates oxidative DNA damage and aging. FEBS Lett 2018; 592:2297-2307. [PMID: 29897613 PMCID: PMC6099297 DOI: 10.1002/1873-3468.13156] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2018] [Revised: 05/18/2018] [Accepted: 05/30/2018] [Indexed: 12/23/2022]
Abstract
The "free radical theory of aging" suggests that reactive oxygen species (ROS) are responsible for age-related loss of cellular functions and, therefore, represent the main cause of aging. Redox regulation by thioredoxin-1 (TRX) plays a crucial role in responses to oxidative stress. We show that thioredoxin-interacting protein (TXNIP), a negative regulator of TRX, plays a major role in maintaining the redox status and, thereby, influences aging processes. This role of TXNIP is conserved from flies to humans. Age-dependent upregulation of TXNIP results in decreased stress resistance to oxidative challenge in primary human cells and in Drosophila. Experimental overexpression of TXNIP in flies shortens lifespan due to elevated oxidative DNA damage, whereas downregulation of TXNIP enhances oxidative stress resistance and extends lifespan.
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Affiliation(s)
- Tina Oberacker
- Tumor Immunology Program (D030)German Cancer Research Center (DKFZ)HeidelbergGermany
| | - Jörg Bajorat
- Tumor Immunology Program (D030)German Cancer Research Center (DKFZ)HeidelbergGermany
| | - Sabine Ziola
- Tumor Immunology Program (D030)German Cancer Research Center (DKFZ)HeidelbergGermany
| | - Anne Schroeder
- Tumor Immunology Program (D030)German Cancer Research Center (DKFZ)HeidelbergGermany
| | - Daniel Röth
- Tumor Immunology Program (D030)German Cancer Research Center (DKFZ)HeidelbergGermany
| | - Lena Kastl
- Tumor Immunology Program (D030)German Cancer Research Center (DKFZ)HeidelbergGermany
| | - Bruce A. Edgar
- German Cancer Research Center (DKFZ)Center for Molecular BiologyUniversity of Heidelberg AllianceGermany
- Huntsman Cancer InstituteUniversity of UtahSalt Lake CityUTUSA
| | - Wolfgang Wagner
- Department for Stem Cell Biology and Cellular EngineeringHelmholtz‐Institute for Biomedical EngineeringRWTH Aachen University Medical SchoolGermany
| | - Karsten Gülow
- Tumor Immunology Program (D030)German Cancer Research Center (DKFZ)HeidelbergGermany
- Internal Medicine IUniversity Hospital RegensburgGermany
| | - Peter H. Krammer
- Tumor Immunology Program (D030)German Cancer Research Center (DKFZ)HeidelbergGermany
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The Phosphorylation State of the Drosophila TRP Channel Modulates the Frequency Response to Oscillating Light In Vivo. J Neurosci 2017; 37:4213-4224. [PMID: 28314815 DOI: 10.1523/jneurosci.3670-16.2017] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2016] [Revised: 02/13/2017] [Accepted: 02/28/2017] [Indexed: 11/21/2022] Open
Abstract
Drosophila photoreceptors respond to oscillating light of high frequency (∼100 Hz), while the detected maximal frequency is modulated by the light rearing conditions, thus enabling high sensitivity to light and high temporal resolution. However, the molecular basis for this adaptive process is unclear. Here, we report that dephosphorylation of the light-activated transient receptor potential (TRP) ion channel at S936 is a fast, graded, light-dependent, and Ca2+-dependent process that is partially modulated by the rhodopsin phosphatase retinal degeneration C (RDGC). Electroretinogram measurements of the frequency response to oscillating lights in vivo revealed that dark-reared flies expressing wild-type TRP exhibited a detection limit of oscillating light at relatively low frequencies, which was shifted to higher frequencies upon light adaptation. Strikingly, preventing phosphorylation of the S936-TRP site by alanine substitution in transgenic Drosophila (trpS936A ) abolished the difference in frequency response between dark-adapted and light-adapted flies, resulting in high-frequency response also in dark-adapted flies. In contrast, inserting a phosphomimetic mutation by substituting the S936-TRP site to aspartic acid (trpS936D ) set the frequency response of light-adapted flies to low frequencies typical of dark-adapted flies. Light-adapted rdgC mutant flies showed relatively high S936-TRP phosphorylation levels and light-dark phosphorylation dynamics. These findings suggest that RDGC is one but not the only phosphatase involved in pS936-TRP dephosphorylation. Together, this study indicates that TRP channel dephosphorylation is a regulatory process that affects the detection limit of oscillating light according to the light rearing condition, thus adjusting dynamic processing of visual information under varying light conditions.SIGNIFICANCE STATEMENTDrosophila photoreceptors exhibit high temporal resolution as manifested in frequency response to oscillating light of high frequency (≤∼100 Hz). Light rearing conditions modulate the maximal frequency detected by photoreceptors, thus enabling them to maintain high sensitivity to light and high temporal resolution. However, the precise mechanisms for this process are not fully understood. Here, we show by combination of biochemistry and in vivo electrophysiology that transient receptor potential (TRP) channel dephosphorylation at a specific site is a fast, light-activated and Ca2+-dependent regulatory process. TRP dephosphorylation affects the detection limit of oscillating light according to the adaptation state of the photoreceptor cells by shifting the detection limit to higher frequencies upon light adaptation. This novel mechanism thus adjusts dynamic processing of visual information under varying light conditions.
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Schopf K, Huber A. Membrane protein trafficking in Drosophila photoreceptor cells. Eur J Cell Biol 2016; 96:391-401. [PMID: 27964885 DOI: 10.1016/j.ejcb.2016.11.002] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2016] [Revised: 11/21/2016] [Accepted: 11/28/2016] [Indexed: 10/20/2022] Open
Abstract
Membrane protein trafficking occurs throughout the lifetime of neurons and includes the initial protein synthesis and anterograde transport to the plasma membrane as well as internalization, degradation, and recycling of plasma membrane proteins. Defects in protein trafficking can result in neuronal degeneration and underlie blinding diseases such as retinitis pigmentosa as well as other neuronal disorders. Drosophila photoreceptor cells have emerged as a model system for identifying the components and mechanisms involved in membrane protein trafficking in neurons. Here we summarize the current knowledge about trafficking of three Drosophila phototransduction proteins, the visual pigment rhodopsin and the two light-activated ion channels TRP (transient receptor potential) and TRPL (TRP-like). Despite some common requirements shared by rhodopsin and TRP, details in the trafficking of these proteins differ considerably, suggesting the existence of several trafficking pathways for these photoreceptor proteins.
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Affiliation(s)
- Krystina Schopf
- University of Hohenheim, Institute of Physiology, Department of Biosensorics, Stuttgart, Germany
| | - Armin Huber
- University of Hohenheim, Institute of Physiology, Department of Biosensorics, Stuttgart, Germany.
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12
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The GTP- and Phospholipid-Binding Protein TTD14 Regulates Trafficking of the TRPL Ion Channel in Drosophila Photoreceptor Cells. PLoS Genet 2015; 11:e1005578. [PMID: 26509977 PMCID: PMC4624897 DOI: 10.1371/journal.pgen.1005578] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2015] [Accepted: 09/15/2015] [Indexed: 01/04/2023] Open
Abstract
Recycling of signaling proteins is a common phenomenon in diverse signaling pathways. In photoreceptors of Drosophila, light absorption by rhodopsin triggers a phospholipase Cβ-mediated opening of the ion channels transient receptor potential (TRP) and TRP-like (TRPL) and generates the visual response. The signaling proteins are located in a plasma membrane compartment called rhabdomere. The major rhodopsin (Rh1) and TRP are predominantly localized in the rhabdomere in light and darkness. In contrast, TRPL translocates between the rhabdomeral plasma membrane in the dark and a storage compartment in the cell body in the light, from where it can be recycled to the plasma membrane upon subsequent dark adaptation. Here, we identified the gene mutated in trpl translocation defective 14 (ttd14), which is required for both TRPL internalization from the rhabdomere in the light and recycling of TRPL back to the rhabdomere in the dark. TTD14 is highly conserved in invertebrates and binds GTP in vitro. The ttd14 mutation alters a conserved proline residue (P75L) in the GTP-binding domain and abolishes binding to GTP. This indicates that GTP binding is essential for TTD14 function. TTD14 is a cytosolic protein and binds to PtdIns(3)P, a lipid enriched in early endosome membranes, and to phosphatidic acid. In contrast to TRPL, rhabdomeral localization of the membrane proteins Rh1 and TRP is not affected in the ttd14P75L mutant. The ttd14P75L mutation results in Rh1-independent photoreceptor degeneration and larval lethality suggesting that other processes are also affected by the ttd14P75L mutation. In conclusion, TTD14 is a novel regulator of TRPL trafficking, involved in internalization and subsequent sorting of TRPL into the recycling pathway that enables this ion channel to return to the plasma membrane. Protein trafficking in neurons occurs throughout the lifetime of a cell and includes the internalization and redistribution of plasma membrane proteins. Regulated protein trafficking controls the equipment of the plasma membrane with receptors and ion channels and thereby attenuates or enhances neuronal function. Defects in recycling of plasma membrane proteins can cause detrimental neurodegenerative diseases such as Alzheimer’s disease, Parkinson’s disease and Down´s syndrome. In Drosophila photoreceptors, the TRPL ion channel, together with the TRP channel, mediates vision and light-dependently shuttles between an endomembrane storage compartment and the apical plasma membrane. Here, we report the identification of a mutation in the ttd14 gene that inhibits TRPL-trafficking in both directions and also results in photoreceptor degeneration. The TTD14 protein contains a region with weak homology to a PX-domain, which is also found in proteins that sort cargo in the endosome and enable protein recycling. We characterize TTD14 as a new regulator of photoreceptor maintenance and ion channel trafficking that binds to GTP and PtdIns(3)P, a phospholipid enriched in early endosomes.
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13
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Pertusa M, González A, Hardy P, Madrid R, Viana F. Bidirectional modulation of thermal and chemical sensitivity of TRPM8 channels by the initial region of the N-terminal domain. J Biol Chem 2014; 289:21828-43. [PMID: 24917670 DOI: 10.1074/jbc.m114.565994] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
TRPM8, a nonselective cation channel activated by cold, voltage, and cooling compounds such as menthol, is the principal molecular detector of cold temperatures in primary sensory neurons of the somatosensory system. The N-terminal domain of TRPM8 consists of 693 amino acids, but little is known about its contribution to channel function. Here, we identified two distinct regions within the initial N terminus of TRPM8 that contribute differentially to channel activity and proper folding and assembly. Deletion or substitution of the first 40 residues yielded channels with augmented responses to cold and menthol. The thermal threshold of activation of these mutants was shifted 2 °C to higher temperatures, and the menthol dose-response curve was displaced to lower concentrations. Site-directed mutagenesis screening revealed that single point mutations at positions Ser-26 or Ser-27 by proline caused a comparable increase in the responses to cold and menthol. Electrophysiological analysis of the S27P mutant revealed that the enhanced sensitivity to agonists is related to a leftward shift in the voltage dependence of activation, increasing the probability of channel openings at physiological membrane potentials. In addition, we found that the region encompassing positions 40-60 is a key element in the proper folding and assembly of TRPM8. Different deletions and mutations within this region rendered channels with an impaired function that are retained within the endoplasmic reticulum. Our results suggest a critical contribution of the initial region of the N-terminal domain of TRPM8 to thermal and chemical sensitivity and the proper biogenesis of this polymodal ion channel.
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Affiliation(s)
- María Pertusa
- From the Departamento de Biología, Facultad de Química y Biología, Universidad de Santiago de Chile, 9160000 Santiago, Chile and the Instituto de Neurociencias de Alicante, Universidad Miguel Hernández-Consejo Superior de Investigaciones Científicas, 03550 Alicante, Spain
| | - Alejandro González
- From the Departamento de Biología, Facultad de Química y Biología, Universidad de Santiago de Chile, 9160000 Santiago, Chile and
| | - Paulina Hardy
- From the Departamento de Biología, Facultad de Química y Biología, Universidad de Santiago de Chile, 9160000 Santiago, Chile and
| | - Rodolfo Madrid
- From the Departamento de Biología, Facultad de Química y Biología, Universidad de Santiago de Chile, 9160000 Santiago, Chile and
| | - Félix Viana
- the Instituto de Neurociencias de Alicante, Universidad Miguel Hernández-Consejo Superior de Investigaciones Científicas, 03550 Alicante, Spain
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Katz B, Oberacker T, Richter D, Tzadok H, Peters M, Minke B, Huber A. Drosophila TRP and TRPL are assembled as homomultimeric channels in vivo. J Cell Sci 2013; 126:3121-33. [PMID: 23687378 DOI: 10.1242/jcs.123505] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Family members of the cationic transient receptor potential (TRP) channels serve as sensors and transducers of environmental stimuli. The ability of different TRP channel isoforms of specific subfamilies to form heteromultimers and the structural requirements for channel assembly are still unresolved. Although heteromultimerization of different mammalian TRP channels within single subfamilies has been described, even within a subfamily (such as TRPC) not all members co-assemble with each other. In Drosophila photoreceptors two TRPC channels, TRP and TRP-like protein (TRPL) are expressed together in photoreceptors where they generate the light-induced current. The formation of functional TRP-TRPL heteromultimers in cell culture and in vitro has been reported. However, functional in vivo assays have shown that each channel functions independently of the other. Therefore, the issue of whether TRP and TRPL form heteromultimers in vivo is still unclear. In the present study we investigated the ability of TRP and TRPL to form heteromultimers, and the structural requirements for channel assembly, by studying assembly of GFP-tagged TRP and TRPL channels and chimeric TRP and TRPL channels, in vivo. Interaction studies of tagged and native channels as well as native and chimeric TRP-TRPL channels using co-immunoprecipitation, immunocytochemistry and electrophysiology, critically tested the ability of TRP and TRPL to interact. We found that TRP and TRPL assemble exclusively as homomultimeric channels in their native environment. The above analyses revealed that the transmembrane regions of TRP and TRPL do not determine assemble specificity of these channels. However, the C-terminal regions of both TRP and TRPL predominantly specify the assembly of homomeric TRP and TRPL channels.
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Affiliation(s)
- Ben Katz
- Department of Medical Neurobiology, Faculty of Medicine and the Edmond and Lily Safra Center for Brain Sciences, Hebrew University, Jerusalem 91120, Israel
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15
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Cerny AC, Oberacker T, Pfannstiel J, Weigold S, Will C, Huber A. Mutation of light-dependent phosphorylation sites of the Drosophila transient receptor potential-like (TRPL) ion channel affects its subcellular localization and stability. J Biol Chem 2013; 288:15600-13. [PMID: 23592784 DOI: 10.1074/jbc.m112.426981] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The Drosophila phototransduction cascade terminates in the opening of the ion channel transient receptor potential (TRP) and TRP-like (TRPL). Contrary to TRP, TRPL undergoes light-dependent subcellular trafficking between rhabdomeric photoreceptor membranes and an intracellular storage compartment, resulting in long term light adaptation. Here, we identified in vivo phosphorylation sites of TRPL that affect TRPL stability and localization. Quantitative mass spectrometry revealed a light-dependent change in the TRPL phosphorylation pattern. Mutation of eight C-terminal phosphorylation sites neither affected multimerization of the channels nor the electrophysiological response of flies expressing the mutated channels. However, these mutations resulted in mislocalization and enhanced degradation of TRPL after prolonged dark-adaptation. Mutation of subsets of the eight C-terminal phosphorylation sites also led to a reduction of TRPL content and partial mislocalization in the dark. This suggests that a light-dependent switch in the phosphorylation pattern of the TRPL channel mediates stable expression of TRPL in the rhabdomeres upon prolonged dark-adaptation.
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Affiliation(s)
- Alexander C Cerny
- Department of Biosensorics, Institute of Physiology, University of Hohenheim, 70599 Stuttgart, Germany
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16
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Montell C. Drosophila visual transduction. Trends Neurosci 2012; 35:356-63. [PMID: 22498302 DOI: 10.1016/j.tins.2012.03.004] [Citation(s) in RCA: 152] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2011] [Revised: 03/06/2012] [Accepted: 03/11/2012] [Indexed: 11/26/2022]
Abstract
Visual transduction in the Drosophila compound eye functions through a pathway that couples rhodopsin to phospholipase C (PLC) and the opening of transient receptor potential (TRP) channels. This cascade differs from phototransduction in mammalian rods and cones, but is remarkably similar to signaling in mammalian intrinsically photosensitive retinal ganglion cells (ipRGCs). In this review, I focus on recent advances in the fly visual system, including the discovery of a visual cycle and insights into the machinery and mechanisms involved in generating a light response in photoreceptor cells.
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Affiliation(s)
- Craig Montell
- Departments of Biological Chemistry and Neuroscience, Center for Sensory Biology, The Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
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17
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Lieu MH, Vallejos MJ, Michael E, Tsunoda S. Mechanisms underlying stage-1 TRPL channel translocation in Drosophila photoreceptors. PLoS One 2012; 7:e31622. [PMID: 22363689 PMCID: PMC3282777 DOI: 10.1371/journal.pone.0031622] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2010] [Accepted: 01/16/2012] [Indexed: 11/22/2022] Open
Abstract
BACKGROUND TRP channels function as key mediators of sensory transduction and other cellular signaling pathways. In Drosophila, TRP and TRPL are the light-activated channels in photoreceptors. While TRP is statically localized in the signaling compartment of the cell (the rhabdomere), TRPL localization is regulated by light. TRPL channels translocate out of the rhabdomere in two distinct stages, returning to the rhabdomere with dark-incubation. Translocation of TRPL channels regulates their availability, and thereby the gain of the signal. Little, however, is known about the mechanisms underlying this trafficking of TRPL channels. METHODOLOGY/PRINCIPAL FINDINGS We first examine the involvement of de novo protein synthesis in TRPL translocation. We feed flies cycloheximide, verify inhibition of protein synthesis, and test for TRPL translocation in photoreceptors. We find that protein synthesis is not involved in either stage of TRPL translocation out of the rhabdomere, but that re-localization to the rhabdomere from stage-1, but not stage-2, depends on protein synthesis. We also characterize an ex vivo eye preparation that is amenable to biochemical and genetic manipulation. We use this preparation to examine mechanisms of stage-1 TRPL translocation. We find that stage-1 translocation is: induced with ATP depletion, unaltered with perturbation of the actin cytoskeleton or inhibition of endocytosis, and slowed with increased membrane sterol content. CONCLUSIONS/SIGNIFICANCE Our results indicate that translocation of TRPL out of the rhabdomere is likely due to protein transport, and not degradation/re-synthesis. Re-localization from each stage to the rhabdomere likely involves different strategies. Since TRPL channels can translocate to stage-1 in the absence of ATP, with no major requirement of the cytoskeleton, we suggest that stage-1 translocation involves simple diffusion through the apical membrane, which may be regulated by release of a light-dependent anchor in the rhabdomere.
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Affiliation(s)
- Minh-Ha Lieu
- Department of Biology, Boston University, Boston, Massachusetts, United States of America
| | - Maximiliano J. Vallejos
- Department of Biomedical Sciences, Colorado State University, Fort Collins, Colorado, United States of America
| | - Emily Michael
- Department of Biology, Boston University, Boston, Massachusetts, United States of America
| | - Susan Tsunoda
- Department of Biomedical Sciences, Colorado State University, Fort Collins, Colorado, United States of America
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