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Avesani A, Marino V, Zanzoni S, Koch KW, Dell'Orco D. Molecular properties of human guanylate cyclase-activating protein 2 (GCAP2) and its retinal dystrophy-associated variant G157R. J Biol Chem 2021; 296:100619. [PMID: 33812995 PMCID: PMC8113879 DOI: 10.1016/j.jbc.2021.100619] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2021] [Revised: 03/25/2021] [Accepted: 03/30/2021] [Indexed: 12/31/2022] Open
Abstract
In murine and bovine photoreceptors, guanylate cyclase-activating protein 2 (GCAP2) activates retinal guanylate cyclases (GCs) at low Ca2+ levels, thus contributing to the Ca2+/cGMP negative feedback on the cyclase together with its paralog guanylate cyclase-activating protein 1, which has the same function but different Ca2+ sensitivity. In humans, a GCAP2 missense mutation (G157R) has been associated with inherited retinal degeneration (IRD) via an unknown molecular mechanism. Here, we characterized the biochemical properties of human GCAP2 and the G157R variant, focusing on its dimerization and the Ca2+/Mg2+-binding processes in the presence or absence of N-terminal myristoylation. We found that human GCAP2 and its bovine/murine orthologs significantly differ in terms of oligomeric properties, cation binding, and GC regulation. Myristoylated GCAP2 endothermically binds up to 3 Mg2+ with high affinity and forms a compact dimer that may reversibly dissociate in the presence of Ca2+. Conversely, nonmyristoylated GCAP2 does not bind Mg2+ over the physiological range and remains as a monomer in the absence of Ca2+. Both myristoylated and nonmyristoylated GCAP2 bind Ca2+ with high affinity. At odds with guanylate cyclase-activating protein 1 and independently of myristoylation, human GCAP2 does not significantly activate retinal GC1 in a Ca2+-dependent fashion. The IRD-associated G157R variant is characterized by a partly misfolded, molten globule-like conformation with reduced affinity for cations and prone to form aggregates, likely mediated by hydrophobic interactions. Our findings suggest that GCAP2 might be mostly implicated in processes other than phototransduction in human photoreceptors and suggest a possible molecular mechanism for G157R-associated IRD.
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Affiliation(s)
- Anna Avesani
- Department of Neurosciences, Biomedicine and Movement Sciences, Biological Chemistry Section, University of Verona, Verona, Italy
| | - Valerio Marino
- Department of Neurosciences, Biomedicine and Movement Sciences, Biological Chemistry Section, University of Verona, Verona, Italy
| | - Serena Zanzoni
- Centro Piattaforme Tecnologiche, University of Verona, Verona, Italy
| | - Karl-Wilhelm Koch
- Department of Neuroscience, Division of Biochemistry, University of Oldenburg, Oldenburg, Germany
| | - Daniele Dell'Orco
- Department of Neurosciences, Biomedicine and Movement Sciences, Biological Chemistry Section, University of Verona, Verona, Italy.
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2
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Plana-Bonamaisó A, López-Begines S, Fernández-Justel D, Junza A, Soler-Tapia A, Andilla J, Loza-Alvarez P, Rosa JL, Miralles E, Casals I, Yanes O, de la Villa P, Buey RM, Méndez A. Post-translational regulation of retinal IMPDH1 in vivo to adjust GTP synthesis to illumination conditions. eLife 2020; 9:56418. [PMID: 32254022 PMCID: PMC7176436 DOI: 10.7554/elife.56418] [Citation(s) in RCA: 40] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2020] [Accepted: 03/30/2020] [Indexed: 02/06/2023] Open
Abstract
We report the in vivo regulation of Inosine-5´-monophosphate dehydrogenase 1 (IMPDH1) in the retina. IMPDH1 catalyzes the rate-limiting step in the de novo synthesis of guanine nucleotides, impacting the cellular pools of GMP, GDP and GTP. Guanine nucleotide homeostasis is central to photoreceptor cells, where cGMP is the signal transducing molecule in the light response. Mutations in IMPDH1 lead to inherited blindness. We unveil a light-dependent phosphorylation of retinal IMPDH1 at Thr159/Ser160 in the Bateman domain that desensitizes the enzyme to allosteric inhibition by GDP/GTP. When exposed to bright light, living mice increase the rate of GTP and ATP synthesis in their retinas; concomitant with IMPDH1 aggregate formation at the outer segment layer. Inhibiting IMPDH activity in living mice delays rod mass recovery. We unveil a novel mechanism of regulation of IMPDH1 in vivo, important for understanding GTP homeostasis in the retina and the pathogenesis of adRP10 IMPDH1 mutations.
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Affiliation(s)
- Anna Plana-Bonamaisó
- Department of Physiological Sciences, School of Medicine, Campus Universitari de Bellvitge, University of Barcelona, Barcelona, Spain.,Institut de Neurociències, Campus Universitari de Bellvitge, University of Barcelona, Barcelona, Spain
| | - Santiago López-Begines
- Department of Physiological Sciences, School of Medicine, Campus Universitari de Bellvitge, University of Barcelona, Barcelona, Spain
| | - David Fernández-Justel
- Metabolic Engineering Group, Department of Microbiology and Genetics. University of Salamanca, Salamanca, Spain
| | - Alexandra Junza
- CIBER of Diabetes and Associated Metabolic Diseases (CIBERDEM), Madrid, Spain.,Metabolomics Platform, IISPV, Department of Electronic Engineering, Universitat Rovira i Virgili, Tarragona, Spain
| | - Ariadna Soler-Tapia
- Department of Physiological Sciences, School of Medicine, Campus Universitari de Bellvitge, University of Barcelona, Barcelona, Spain
| | - Jordi Andilla
- ICFO-Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology, Castelldefels, Spain
| | - Pablo Loza-Alvarez
- ICFO-Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology, Castelldefels, Spain
| | - Jose Luis Rosa
- Department of Physiological Sciences, School of Medicine, Campus Universitari de Bellvitge, University of Barcelona, Barcelona, Spain.,Institut d'Investigació Biomèdica de Bellvitge (IDIBELL), Campus Universitari de Bellvitge, University of Barcelona, Barcelona, Spain
| | - Esther Miralles
- Centres Cientifics i Tecnològics (CCiTUB), University of Barcelona, Parc Científic de Barcelona, Barcelona, Spain
| | - Isidre Casals
- Centres Cientifics i Tecnològics (CCiTUB), University of Barcelona, Parc Científic de Barcelona, Barcelona, Spain
| | - Oscar Yanes
- CIBER of Diabetes and Associated Metabolic Diseases (CIBERDEM), Madrid, Spain.,Metabolomics Platform, IISPV, Department of Electronic Engineering, Universitat Rovira i Virgili, Tarragona, Spain
| | - Pedro de la Villa
- Physiology Unit, Dept of Systems Biology, School of Medicine, University of Alcalá, Madrid, Spain.,Visual Neurophysiology Group-IRYCIS, Madrid, Spain
| | - Ruben M Buey
- Metabolic Engineering Group, Department of Microbiology and Genetics. University of Salamanca, Salamanca, Spain
| | - Ana Méndez
- Department of Physiological Sciences, School of Medicine, Campus Universitari de Bellvitge, University of Barcelona, Barcelona, Spain.,Institut de Neurociències, Campus Universitari de Bellvitge, University of Barcelona, Barcelona, Spain.,Institut d'Investigació Biomèdica de Bellvitge (IDIBELL), Campus Universitari de Bellvitge, University of Barcelona, Barcelona, Spain
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3
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GCAP neuronal calcium sensor proteins mediate photoreceptor cell death in the rd3 mouse model of LCA12 congenital blindness by involving endoplasmic reticulum stress. Cell Death Dis 2020; 11:62. [PMID: 31980596 PMCID: PMC6981271 DOI: 10.1038/s41419-020-2255-0] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2019] [Revised: 01/09/2020] [Accepted: 01/10/2020] [Indexed: 01/01/2023]
Abstract
Loss-of-function mutations in the retinal degeneration 3 (RD3) gene cause inherited retinopathy with impaired rod and cone function and fast retinal degeneration in patients and in the natural strain of rd3 mice. The underlying physiopathology mechanisms are not well understood. We previously proposed that guanylate cyclase-activating proteins (GCAPs) might be key Ca2+-sensors mediating the physiopathology of this disorder, based on the demonstrated toxicity of GCAP2 when blocked in its Ca2+-free form at photoreceptor inner segments. We here show that the retinal degeneration in rd3 mice is substantially delayed by GCAPs ablation. While the number of retinal photoreceptor cells is halved in 6 weeks in rd3 mice, it takes 8 months to halve in rd3/rd3 GCAPs-/- mice. Although this substantial morphological rescue does not correlate with recovery of visual function due to very diminished guanylate cyclase activity in rd3 mice, it is very informative of the mechanisms underlying photoreceptor cell death. By showing that GCAP2 is mostly in its Ca2+-free-phosphorylated state in rd3 mice, we infer that the [Ca2+]i at rod inner segments is permanently low. GCAPs are therefore retained at the inner segment in their Ca2+-free, guanylate cyclase activator state. We show that in this conformational state GCAPs induce endoplasmic reticulum (ER) stress, mitochondrial swelling, and cell death. ER stress and mitochondrial swelling are early hallmarks of rd3 retinas preceding photoreceptor cell death, that are substantially rescued by GCAPs ablation. By revealing the involvement of GCAPs-induced ER stress in the physiopathology of Leber's congenital amaurosis 12 (LCA12), this work will aid to guide novel therapies to preserve retinal integrity in LCA12 patients to expand the window for gene therapy intervention to restore vision.
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Activation of Rod Input in a Model of Retinal Degeneration Reverses Retinal Remodeling and Induces Formation of Functional Synapses and Recovery of Visual Signaling in the Adult Retina. J Neurosci 2019; 39:6798-6810. [PMID: 31285302 DOI: 10.1523/jneurosci.2902-18.2019] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2018] [Revised: 05/28/2019] [Accepted: 06/18/2019] [Indexed: 12/31/2022] Open
Abstract
A major cause of human blindness is the death of rod photoreceptors. As rods degenerate, synaptic structures between rod and rod bipolar cells disappear and the rod bipolar cells extend their dendrites and occasionally make aberrant contacts. Such changes are broadly observed in blinding disorders caused by photoreceptor cell death and are thought to occur in response to deafferentation. How the remodeled retinal circuit affects visual processing following rod rescue is not known. To address this question, we generated male and female transgenic mice wherein a disrupted cGMP-gated channel (CNG) gene can be repaired at the endogenous locus and at different stages of degeneration by tamoxifen-inducible cre-mediated recombination. In normal rods, light-induced closure of CNG channels leads to hyperpolarization of the cell, reducing neurotransmitter release at the synapse. Similarly, rods lacking CNG channels exhibit a resting membrane potential that was ~10 mV hyperpolarized compared to WT rods, indicating diminished glutamate release. Retinas from these mice undergo stereotypic retinal remodeling as a consequence of rod malfunction and degeneration. Upon tamoxifen-induced expression of CNG channels, rods recovered their structure and exhibited normal light responses. Moreover, we show that the adult mouse retina displays a surprising degree of plasticity upon activation of rod input. Wayward bipolar cell dendrites establish contact with rods to support normal synaptic transmission, which is propagated to the retinal ganglion cells. These findings demonstrate remarkable plasticity extending beyond the developmental period and support efforts to repair or replace defective rods in patients blinded by rod degeneration.SIGNIFICANCE STATEMENT Current strategies for treatment of neurodegenerative disorders are focused on the repair of the primary affected cell type. However, the defective neurons function within a complex neural circuitry, which also becomes degraded during disease. It is not known whether rescued neurons and the remodeled circuit will establish communication to regain normal function. We show that the adult mammalian neural retina exhibits a surprising degree of plasticity following rescue of rod photoreceptors. The wayward dendrites of rod bipolar cells re-establish contact with rods to support normal synaptic transmission, which is propagated to the retinal ganglion cells. These findings support efforts to repair or replace defective rods in patients blinded by rod cell loss.
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5
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Altobelli GG, Van Noorden S, Cimini V. Calcium-binding protein and some neuropeptides in the retina of Octopus vulgaris: A morpho-histochemical study. J Cell Physiol 2018; 233:6866-6876. [PMID: 29682745 DOI: 10.1002/jcp.26570] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2017] [Accepted: 02/27/2018] [Indexed: 01/08/2023]
Abstract
The existence of both calcium-binding proteins (CBPs) and neuropeptides in the retina and brain of various species of vertebrates and invertebrates is well documented. Octopus retina is particularly interesting because it represents a case of convergent evolution. The aim of this study was to characterize the distribution of two CBPs, calretinin and calbindin, in Octopus retina using morphology, in situ hybridization, immunocytochemistry and Western blot. Calretinin-like immunoreactivity was found in the photoreceptor cells, but unexpectedly also in the supporting cells. In situ hybridization and Western blot analysis confirmed these results. No immunoreactivity was found for calbindin. Two neuropeptides, Substance P and calcitonin gene-related peptide (CGRP), as well as neurofilament protein and glial fibrillary acidic protein were also localized in the Octopus retina by immunocytochemistry. Our work provides new insights about calcium-binding proteins and neuropeptide distribution in Octopus retina and suggests a functional role for calretinin, a highly conserved protein, in visual signal transduction of cephalopods.
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Affiliation(s)
- Giovanna G Altobelli
- Department of Advanced Biomedical Sciences, Federico II University of Naples, Naples, Italy
| | | | - Vincenzo Cimini
- Department of Advanced Biomedical Sciences, Federico II University of Naples, Naples, Italy
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6
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Inamdar SM, Lankford CK, Laird JG, Novbatova G, Tatro N, Whitmore SS, Scheetz TE, Baker SA. Analysis of 14-3-3 isoforms expressed in photoreceptors. Exp Eye Res 2018; 170:108-116. [PMID: 29486162 DOI: 10.1016/j.exer.2018.02.022] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2017] [Revised: 02/02/2018] [Accepted: 02/23/2018] [Indexed: 11/18/2022]
Abstract
The 14-3-3 family of proteins has undergone considerable expansion in higher eukaryotes with humans and mice expressing seven isoforms (β, ε, η, γ, θ, ζ, and σ) from seven distinct genes (YWHAB, YWAHE, YWHAH, YWHAG, YWHAQ, YWHAZ, and SFN). Growing evidence indicates that while highly conserved, these isoforms are not entirely functionally redundant as they exhibit unique tissue expression profiles, subcellular localization, and biochemical functions. A key limitation in our understanding of 14-3-3 biology lies in our limited knowledge of cell-type specific 14-3-3 expression. Here we provide a characterization of 14-3-3 expression in whole retina and isolated rod photoreceptors using reverse-transcriptase digital droplet PCR. We find that all 14-3-3 genes with the exception of SFN are expressed in mouse retina with YWHAQ and YWHAE being the most highly expressed. Rod photoreceptors are enriched in YWHAE (14-3-3 ε). Immunohistochemistry revealed that 14-3-3 ε and 14-3-3 ζ exhibit unique distributions in photoreceptors with 14-3-3 ε restricted to the inner segment and 14-3-3 ζ localized to the outer segment. Our data demonstrates that, in the retina, 14-3-3 isoforms likely serve specific functions as they exhibit unique expression levels and cell-type specificity. As such, future investigations into 14-3-3 function in rod photoreceptors should be centered on 14-3-3 ε and 14-3-3 ζ, depending on the subcellular region of question.
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Affiliation(s)
- Shivangi M Inamdar
- Department of Biochemistry, University of Iowa, Iowa City, IA 52242, USA
| | - Colten K Lankford
- Department of Biochemistry, University of Iowa, Iowa City, IA 52242, USA
| | - Joseph G Laird
- Department of Biochemistry, University of Iowa, Iowa City, IA 52242, USA
| | - Gulnara Novbatova
- Department of Biochemistry, University of Iowa, Iowa City, IA 52242, USA
| | - Nicole Tatro
- Department of Ophthalmology & Visual Sciences and Institute for Vision Research, University of Iowa, Iowa City, IA 52242, USA
| | - S Scott Whitmore
- Department of Ophthalmology & Visual Sciences and Institute for Vision Research, University of Iowa, Iowa City, IA 52242, USA
| | - Todd E Scheetz
- Department of Ophthalmology & Visual Sciences and Institute for Vision Research, University of Iowa, Iowa City, IA 52242, USA
| | - Sheila A Baker
- Department of Biochemistry, University of Iowa, Iowa City, IA 52242, USA; Department of Ophthalmology & Visual Sciences and Institute for Vision Research, University of Iowa, Iowa City, IA 52242, USA.
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7
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López-Begines S, Plana-Bonamaisó A, Méndez A. Molecular determinants of Guanylate Cyclase Activating Protein subcellular distribution in photoreceptor cells of the retina. Sci Rep 2018; 8:2903. [PMID: 29440717 PMCID: PMC5811540 DOI: 10.1038/s41598-018-20893-1] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2017] [Accepted: 01/26/2018] [Indexed: 11/10/2022] Open
Abstract
Retinal guanylate cyclase (RetGC) and guanylate cyclase activating proteins (GCAPs) play an important role during the light response in photoreceptor cells. Mutations in these proteins are linked to distinct forms of blindness. RetGC and GCAPs exert their role at the ciliary outer segment where phototransduction takes place. We investigated the mechanisms governing GCAP1 and GCAP2 distribution to rod outer segments by expressing selected GCAP1 and GCAP2 mutants as transient transgenes in the rods of GCAP1/2 double knockout mice. We show that precluding GCAP1 direct binding to RetGC (K23D/GCAP1) prevented its distribution to rod outer segments, while preventing GCAP1 activation of RetGC post-binding (W94A/GCAP1) did not. We infer that GCAP1 translocation to the outer segment strongly depends on GCAP1 binding affinity for RetGC, which points to GCAP1 requirement to bind to RetGC to be transported. We gain further insight into the distinctive regulatory steps of GCAP2 distribution, by showing that a phosphomimic at position 201 is sufficient to retain GCAP2 at proximal compartments; and that the bovine equivalent to blindness-causative mutation G157R/GCAP2 results in enhanced phosphorylation in vitro and significant retention at the inner segment in vivo, as likely contributing factors to the pathophysiology.
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Affiliation(s)
- Santiago López-Begines
- Bellvitge Biomedical Research Institute (IDIBELL), Barcelona, Spain.,Department of Physiology, University of Barcelona School of Medicine-Bellvitge Health Science Campus, Barcelona, Spain
| | - Anna Plana-Bonamaisó
- Department of Physiology, University of Barcelona School of Medicine-Bellvitge Health Science Campus, Barcelona, Spain
| | - Ana Méndez
- Bellvitge Biomedical Research Institute (IDIBELL), Barcelona, Spain. .,Department of Physiology, University of Barcelona School of Medicine-Bellvitge Health Science Campus, Barcelona, Spain.
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8
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Wang T, Tsang SH, Chen J. Two pathways of rod photoreceptor cell death induced by elevated cGMP. Hum Mol Genet 2017; 26:2299-2306. [PMID: 28379353 DOI: 10.1093/hmg/ddx121] [Citation(s) in RCA: 42] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2016] [Accepted: 03/22/2017] [Indexed: 11/14/2022] Open
Abstract
Cyclic-GMP is a second messenger in phototransduction, a G-protein signaling cascade that conveys photon absorption by rhodopsin to a change in current at the rod photoreceptor outer segment plasma membrane. Basal cGMP level is strictly controlled by the opposing actions of phosphodiesterase (PDE6) and retinal guanylyl cyclases (GCs), and mutations in genes that disrupt cGMP homeostasis leads to retinal degeneration in humans through mechanisms that are incompletely understood. The purpose of this study is to examine two distinct cellular targets of cGMP: the cGMP-gated (CNG) channels and protein kinase G (PRKG), and how each may contribute to rod cell death. Using a mouse genetic approach, we found that abolishing expression of CNG channels prolongs rod survival caused by elevated cGMP in a PDE6 mutant mouse model. This observation supports the use of channel blockers to delay rod death, which is expected to prolong useful vision through enhanced cone survival. However, the absence of CNG channel alone also caused abnormal cGMP accumulation. In a mouse model of CNG channel loss-of-function, abolishing PRKG1 expression had a long-lasting effect in promoting rod cell survival. Our data strongly implicate two distinct cGMP-mediated cell death pathways, and suggest that therapeutic designs targeting both pathways will be more effective at slowing photoreceptor cell death caused by elevated cGMP.
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Affiliation(s)
- Tian Wang
- Zilkha Neurogenetic Institute, Department of Cell & Neurobiology, Keck School of Medicine, University of Southern California, Los Angeles, CA 90089, USA
| | - Stephen H Tsang
- Jonas Children's Vision Care, and Bernard & Shirlee Brown Glaucoma Laboratory, Departments of Ophthalmology and Pathology & Cell Biology, Institute of Human Nutrition, Herbert Irving Comprehensive Cancer Center, Columbia University, NY 10032, USA.,Edward S. Harkness Eye Institute, New York-Presbyterian Hospital, NY 10032, USA
| | - Jeannie Chen
- Zilkha Neurogenetic Institute, Department of Cell & Neurobiology, Keck School of Medicine, University of Southern California, Los Angeles, CA 90089, USA
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9
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Sulmann S, Wallisch M, Scholten A, Christoffers J, Koch KW. Mapping Calcium-Sensitive Regions in the Neuronal Calcium Sensor GCAP2 by Site-Specific Fluorescence Labeling. Biochemistry 2016; 55:2567-77. [DOI: 10.1021/acs.biochem.6b00005] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Stefan Sulmann
- Biochemistry
Group, Department of Neurosciences, Carl von Ossietzky Universität Oldenburg, D-26111 Oldenburg, Germany
| | - Melanie Wallisch
- Institut
für Chemie, Carl von Ossietzky Universität Oldenburg, D-26111 Oldenburg, Germany
| | - Alexander Scholten
- Biochemistry
Group, Department of Neurosciences, Carl von Ossietzky Universität Oldenburg, D-26111 Oldenburg, Germany
| | - Jens Christoffers
- Institut
für Chemie, Carl von Ossietzky Universität Oldenburg, D-26111 Oldenburg, Germany
| | - Karl-Wilhelm Koch
- Biochemistry
Group, Department of Neurosciences, Carl von Ossietzky Universität Oldenburg, D-26111 Oldenburg, Germany
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10
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Vinberg F, Wang T, Molday RS, Chen J, Kefalov VJ. A new mouse model for stationary night blindness with mutant Slc24a1 explains the pathophysiology of the associated human disease. Hum Mol Genet 2015; 24:5915-29. [PMID: 26246500 DOI: 10.1093/hmg/ddv319] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2015] [Accepted: 07/31/2015] [Indexed: 11/12/2022] Open
Abstract
Mutations that affect calcium homeostasis (Ca(2+)) in rod photoreceptors are linked to retinal degeneration and visual disorders such as retinitis pigmentosa and congenital stationary night blindness (CSNB). It is thought that the concentration of Ca(2+) in rod outer segments is controlled by a dynamic balance between influx via cGMP-gated (CNG) channels and extrusion via Na(+)/Ca(2+), K(+) exchangers (NCKX1). The extrusion-driven lowering of rod [Ca(2+)]i following light exposure controls their light adaptation and response termination. Mutant NCKX1 has been linked to autosomal-recessive stationary night blindness. However, whether NCKX1 contributes to light adaptation has not been directly tested and the mechanisms by which human NCKX1 mutations cause night blindness are not understood. Here, we report that the deletion of NCKX1 in mice results in malformed outer segment disks, suppressed expression and function of rod CNG channels and a subsequent 100-fold reduction in rod responses, while preserving normal cone responses. The compensating loss of CNG channel function in the absence of NCKX1-mediated Ca(2+) extrusion may prevent toxic Ca(2+) buildup and provides an explanation for the stationary nature of the associated disorder in humans. Surprisingly, the lack of NCKX1 did not compromise rod background light adaptation, suggesting additional Ca(2+)-extruding mechanisms exist in these cells.
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Affiliation(s)
- Frans Vinberg
- Ophthalmology and Visual Sciences, Washington University School of Medicine, St. Louis, MO, USA
| | - Tian Wang
- Cell and Neurobiology, Zilkha Neurogenetic Institute, University of Southern California, Los Angeles, CA, USA and
| | - Robert S Molday
- Biochemistry/Molecular Biology, University of British Columbia, Vancouver, Canada
| | - Jeannie Chen
- Cell and Neurobiology, Zilkha Neurogenetic Institute, University of Southern California, Los Angeles, CA, USA and
| | - Vladimir J Kefalov
- Ophthalmology and Visual Sciences, Washington University School of Medicine, St. Louis, MO, USA,
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11
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Zernii EY, Grigoriev II, Nazipova AA, Scholten A, Kolpakova TV, Zinchenko DV, Kazakov AS, Senin II, Permyakov SE, Dell'Orco D, Philippov PP, Koch KW. Regulatory function of the C-terminal segment of guanylate cyclase-activating protein 2. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2015; 1854:1325-37. [PMID: 26001899 DOI: 10.1016/j.bbapap.2015.05.005] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/24/2015] [Revised: 04/22/2015] [Accepted: 05/13/2015] [Indexed: 12/13/2022]
Abstract
Neuronal responses to Ca2+-signals are provided by EF-hand-type neuronal Ca2+-sensor (NCS) proteins, which have similar core domains containing Ca2+-binding and target-recognizing sites. NCS proteins vary in functional specificity, probably depending on the structure and conformation of their non-conserved C-terminal segments. Here, we investigated the role of the C-terminal segment in guanylate cyclase activating protein-2, GCAP2, an NCS protein controlling the Ca2+-dependent regulation of photoreceptor guanylate cyclases. We obtained two chimeric proteins by exchanging C-terminal segments between GCAP2 and its photoreceptor homolog recoverin, a Ca2+-sensor controlling rhodopsin kinase (RK) activity. The exchange affected neither the structural integrity of GCAP2 and recoverin nor the Ca2+-sensitivity of GCAP2. Intrinsic fluorescence, circular dichroism, biochemical studies and hydrophobic dye probing revealed Ca2+-dependent conformational transition of the C-terminal segment of GCAP2 occurring in the molecular environment of both proteins. In Ca2+-GCAP2, the C-terminal segment was constrained and its replacement provided the protein with approximately two-fold inhibitory activity towards RK, suggesting that the segment contributes to specific target recognition by interfering with RK-binding. Upon Ca2+-release, it became less constrained and more available for phosphorylation by cyclic nucleotide-dependent protein kinase. The transition from the Ca2+-bound to the apo-state exposed hydrophobic sites in GCAP2, and was associated with its activating function without affecting its dimerization. The released C-terminal segment participated further in photoreceptor membrane binding making it sensitive to phosphorylation. Thus, the C-terminal segment in GCAP2 confers target selectivity, facilitates membrane binding and provides sensitivity of the membrane localization of the protein to phosphorylation by signaling kinases.
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Affiliation(s)
- Evgeni Yu Zernii
- Department of Cell Signaling, Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, 119992 Russia
| | - Ilya I Grigoriev
- Department of Cell Signaling, Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, 119992 Russia
| | - Aliya A Nazipova
- Protein Research Group, Institute for Biological Instrumentation of the Russian Academy of Sciences, Pushchino, Moscow region, 142290 Russia
| | - Alexander Scholten
- Department of Neurosciences, Biochemistry Group, University of Oldenburg, Oldenburg, 26111 Germany
| | - Tatiana V Kolpakova
- Department of Cell Signaling, Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, 119992 Russia
| | - Dmitry V Zinchenko
- Branch of Shemyakin and Ovchinnikov Institute of Bioorganic Chemistry of the Russian Academy of Sciences, Pushchino, Moscow region, 142290 Russia
| | - Alexey S Kazakov
- Protein Research Group, Institute for Biological Instrumentation of the Russian Academy of Sciences, Pushchino, Moscow region, 142290 Russia
| | - Ivan I Senin
- Department of Cell Signaling, Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, 119992 Russia
| | - Sergei E Permyakov
- Protein Research Group, Institute for Biological Instrumentation of the Russian Academy of Sciences, Pushchino, Moscow region, 142290 Russia
| | - Daniele Dell'Orco
- Department of Life Sciences and Reproduction, Section of Biological Chemistry and Center for BioMedical Computing, University of Verona, Verona, 37134 Italy
| | - Pavel P Philippov
- Department of Cell Signaling, Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, 119992 Russia
| | - Karl-W Koch
- Department of Neurosciences, Biochemistry Group, University of Oldenburg, Oldenburg, 26111 Germany.
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Wang T, Chen J. Induction of the unfolded protein response by constitutive G-protein signaling in rod photoreceptor cells. J Biol Chem 2014; 289:29310-21. [PMID: 25183010 DOI: 10.1074/jbc.m114.595207] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Phototransduction is a G-protein signal transduction cascade that converts photon absorption to a change in current at the plasma membrane. Certain genetic mutations affecting the proteins in the phototransduction cascade cause blinding disorders in humans. Some of these mutations serve as a genetic source of "equivalent light" that activates the cascade, whereas other mutations lead to amplification of the light response. How constitutive phototransduction causes photoreceptor cell death is poorly understood. We showed that persistent G-protein signaling, which occurs in rod arrestin and rhodopsin kinase knock-out mice, caused a rapid and specific induction of the PERK pathway of the unfolded protein response. These changes were not observed in the cGMP-gated channel knock-out rods, an equivalent light condition that mimics light-stimulated channel closure. Thus transducin signaling, but not channel closure, triggers rapid cell death in light damage caused by constitutive phototransduction. Additionally, we show that in the albino light damage model cell death was not associated with increase in global protein ubiquitination or unfolded protein response induction. Taken together, these observations provide novel mechanistic insights into the cell death pathway caused by constitutive phototransduction and identify the unfolded protein response as a potential target for therapeutic intervention.
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Affiliation(s)
- Tian Wang
- From the Program in Genetic, Molecular and Cellular Biology and the Zilkha Neurogenetic Institute, Department of Cell & Neurobiology, Keck School of Medicine, University of Southern California, Los Angeles, California 90089
| | - Jeannie Chen
- the Zilkha Neurogenetic Institute, Department of Cell & Neurobiology, Keck School of Medicine, University of Southern California, Los Angeles, California 90089
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