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Jing S, Yi X. Exome sequencing reveals PPEF2 variant associated with high myopia. Gene 2024; 897:148091. [PMID: 38110044 DOI: 10.1016/j.gene.2023.148091] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2023] [Revised: 12/08/2023] [Accepted: 12/14/2023] [Indexed: 12/20/2023]
Abstract
High myopia (HM) is a serious blinding eye disease, and genetic factors play an important role in the development of HM. In this study, whole exome sequencing (WES) was used to identify a novel variant c.A875G of the PPEF2 for a large Uyghur family with nonsyndromic HM. The variant was verified to cosegregate with HM in the family using Sanger sequencing. Another novel variant c.1959C > G in PPEF2 was identified in one of 100 sporadic cases of HM by multiplex PCR targeted amplicon sequencing (MTA-seq). The Ppef2 was verified that mainly expressed in the retinal pigment epithelium (RPE), choroid and retina tissues. Immunofluorescence (IF) and immunohistochemistry (IHC) assays showed that the PPEF2 was strongly expressed in the inner segment layer formed by photoreceptor protrusions, as well as in the outer nuclear layer. Compared with the wild-type, the c.A875G resulted in reduced protein levels but had no effect on protein subcellular localization in cells. In addition, the c.A875G variant resulted in a decreased migratory and proliferative capacity but promoted apoptosis in cells. In summary, PPEF2 was identified as a novel HM-causing gene, and this variant in PPEF2 might cause HM by regulating the migration, proliferation and apoptosis of myopia-related cells.
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Affiliation(s)
- Sili Jing
- Shaanxi Eye Hospital, Xi'an People's Hospital (Xi'an Fourth Hospital), Affiliated People's Hospital of Northwest University, Xian, 710004, China; Ophthalmology, Xinjiang Medical University Affiliated First Hospital, Urumqi, Xinjiang, China
| | - Xianglong Yi
- Ophthalmology, Xinjiang Medical University Affiliated First Hospital, Urumqi, Xinjiang, China.
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Smylla TK, Wagner K, Huber A. The Role of Reversible Phosphorylation of Drosophila Rhodopsin. Int J Mol Sci 2022; 23:ijms232314674. [PMID: 36499010 PMCID: PMC9740569 DOI: 10.3390/ijms232314674] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2022] [Revised: 11/18/2022] [Accepted: 11/21/2022] [Indexed: 11/27/2022] Open
Abstract
Vertebrate and fly rhodopsins are prototypical GPCRs that have served for a long time as model systems for understanding GPCR signaling. Although all rhodopsins seem to become phosphorylated at their C-terminal region following activation by light, the role of this phosphorylation is not uniform. Two major functions of rhodopsin phosphorylation have been described: (1) inactivation of the activated rhodopsin either directly or by facilitating binding of arrestins in order to shut down the visual signaling cascade and thus eventually enabling a high-temporal resolution of the visual system. (2) Facilitating endocytosis of activated receptors via arrestin binding that in turn recruits clathrin to the membrane for clathrin-mediated endocytosis. In vertebrate rhodopsins the shutdown of the signaling cascade may be the main function of rhodopsin phosphorylation, as phosphorylation alone already quenches transducin activation and, in addition, strongly enhances arrestin binding. In the Drosophila visual system rhodopsin phosphorylation is not needed for receptor inactivation. Its role here may rather lie in the recruitment of arrestin 1 and subsequent endocytosis of the activated receptor. In this review, we summarize investigations of fly rhodopsin phosphorylation spanning four decades and contextualize them with regard to the most recent insights from vertebrate phosphorylation barcode theory.
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Lavoie-Ouellet C, Clark MÈ, Ruiz J, Saindon AA, Leclerc P. The protein phosphatase with EF-hand domain 1 is a calmodulin-binding protein that interacts with proteins involved in sperm capacitation, binding to the zona pellucida, and motility. Mol Reprod Dev 2021; 88:302-317. [PMID: 33783058 DOI: 10.1002/mrd.23467] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2020] [Revised: 03/08/2021] [Accepted: 03/09/2021] [Indexed: 11/12/2022]
Abstract
Spermatozoa are highly specialized cells whose fertilizing and motility functions highly depend on intracellular Ca2+ -mediated events and protein posttranslational modifications like phosphorylation. Our group previously identified PPEF1, the Ser/Thr phosphatase with EF-hand domain 1, among calmodulin-affinity pulled down sperm proteins. As the mammalian ortholog of the Drosophila phosphatase rdgC that dephosphorylates rhodopsin, PPEF1 has been studied mostly in the retina. The presence and importance of this Ca2+ /calmodulin-binding protein phosphatase has not been studied in sperm or testicular functions despite its high expression level. In this study, we show that PPEF1 is present in testicular germ cells, and in mouse, human and bull spermatozoa where it is localized predominantly in the neck and acrosome areas. Different transcript variants encoding four predicted isoforms were detected by reverse transcription polymerase chain reaction in bull testis, spermatocytes and spermatids. Phosphatase activity of immunoprecipitated sperm PPEF1 was detected using the substrate pNPP and analysis of the coimmunoprecipitated proteins reveal an enrichment in the biological processes of sperm capacitation, binding to the zona pellucida and motility. Although this is the first demonstration of the presence of PPEF1 in sperm and testicular germ cells, its involvement in sperm fertilizing ability and motility, and the mechanisms regulating its activity remain to be further investigated.
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Affiliation(s)
- Camille Lavoie-Ouellet
- Département d'Obstétrique, gynécologie et reproduction, Centre de recherche en reproduction, développement et santé intergénérationnelle, Université Laval, Axe reproduction, santé de la mère et de l'enfant, Centre de recherche du CHU de Québec-Université Laval, Quebec City, Québec, Canada
| | - Marie-Ève Clark
- Département d'Obstétrique, gynécologie et reproduction, Centre de recherche en reproduction, développement et santé intergénérationnelle, Université Laval, Axe reproduction, santé de la mère et de l'enfant, Centre de recherche du CHU de Québec-Université Laval, Quebec City, Québec, Canada
| | - Juliana Ruiz
- Département d'Obstétrique, gynécologie et reproduction, Centre de recherche en reproduction, développement et santé intergénérationnelle, Université Laval, Axe reproduction, santé de la mère et de l'enfant, Centre de recherche du CHU de Québec-Université Laval, Quebec City, Québec, Canada
| | - Andrée-Anne Saindon
- Département d'Obstétrique, gynécologie et reproduction, Centre de recherche en reproduction, développement et santé intergénérationnelle, Université Laval, Axe reproduction, santé de la mère et de l'enfant, Centre de recherche du CHU de Québec-Université Laval, Quebec City, Québec, Canada
| | - Pierre Leclerc
- Département d'Obstétrique, gynécologie et reproduction, Centre de recherche en reproduction, développement et santé intergénérationnelle, Université Laval, Axe reproduction, santé de la mère et de l'enfant, Centre de recherche du CHU de Québec-Université Laval, Quebec City, Québec, Canada
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Damulewicz M, Mazzotta GM. One Actor, Multiple Roles: The Performances of Cryptochrome in Drosophila. Front Physiol 2020; 11:99. [PMID: 32194430 PMCID: PMC7066326 DOI: 10.3389/fphys.2020.00099] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2019] [Accepted: 01/27/2020] [Indexed: 01/19/2023] Open
Abstract
Cryptochromes (CRYs) are flavoproteins that are sensitive to blue light, first identified in Arabidopsis and then in Drosophila and mice. They are evolutionarily conserved and play fundamental roles in the circadian clock of living organisms, enabling them to adapt to the daily 24-h cycles. The role of CRYs in circadian clocks differs among different species: in plants, they have a blue light-sensing activity whereas in mammals they act as light-independent transcriptional repressors within the circadian clock. These two different functions are accomplished by two principal types of CRYs, the light-sensitive plant/insect type 1 CRY and the mammalian type 2 CRY acting as a negative autoregulator in the molecular circadian clockwork. Drosophila melanogaster possesses just one CRY, belonging to type 1 CRYs. Nevertheless, this single CRY appears to have different functions, specific to different organs, tissues, and even subset of cells in which it is expressed. In this review, we will dissect the multiple roles of this single CRY in Drosophila, focusing on the regulatory mechanisms that make its pleiotropy possible.
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Affiliation(s)
- Milena Damulewicz
- Department of Cell Biology and Imaging, Jagiellonian University, Kraków, Poland
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Ca2+ Signaling in Drosophila Photoreceptor Cells. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2020; 1131:857-879. [DOI: 10.1007/978-3-030-12457-1_34] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
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Brautigan DL, Shenolikar S. Protein Serine/Threonine Phosphatases: Keys to Unlocking Regulators and Substrates. Annu Rev Biochem 2019; 87:921-964. [PMID: 29925267 DOI: 10.1146/annurev-biochem-062917-012332] [Citation(s) in RCA: 110] [Impact Index Per Article: 22.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Protein serine/threonine phosphatases (PPPs) are ancient enzymes, with distinct types conserved across eukaryotic evolution. PPPs are segregated into types primarily on the basis of the unique interactions of PPP catalytic subunits with regulatory proteins. The resulting holoenzymes dock substrates distal to the active site to enhance specificity. This review focuses on the subunit and substrate interactions for PPP that depend on short linear motifs. Insights about these motifs from structures of holoenzymes open new opportunities for computational biology approaches to elucidate PPP networks. There is an expanding knowledge base of posttranslational modifications of PPP catalytic and regulatory subunits, as well as of their substrates, including phosphorylation, acetylation, and ubiquitination. Cross talk between these posttranslational modifications creates PPP-based signaling. Knowledge of PPP complexes, signaling clusters, as well as how PPPs communicate with each other in response to cellular signals should unlock the doors to PPP networks and signaling "clouds" that orchestrate and coordinate different aspects of cell physiology.
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Affiliation(s)
- David L Brautigan
- Center for Cell Signaling and Department of Microbiology, Immunology and Cancer Biology, University of Virginia School of Medicine, Charlottesville, Virginia 22908, USA;
| | - Shirish Shenolikar
- Signature Research Programs in Cardiovascular and Metabolic Disorders and Neuroscience and Behavioral Disorders, Duke-NUS Medical School, Singapore 169857
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Bhattarai UR, Li F, Katuwal Bhattarai M, Masoudi A, Wang D. Phototransduction and circadian entrainment are the key pathways in the signaling mechanism for the baculovirus induced tree-top disease in the lepidopteran larvae. Sci Rep 2018; 8:17528. [PMID: 30510155 PMCID: PMC6277413 DOI: 10.1038/s41598-018-35885-4] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2018] [Accepted: 11/07/2018] [Indexed: 01/13/2023] Open
Abstract
The tree-top disease is an altered behavioral state, displayed by baculovirus-infected lepidopteran larvae, and characterized by climbing to an elevated position before death. The detailed molecular mechanism underlying this phenomenal behavior change has not been reported yet. Our study focused on the transcriptomic changes in the host larvae due to baculovirus infection from pre-symptomatic to tree-top disease stage. Enrichment map visualization of the gene sets grouped based on the functional annotation similarity revealed 34 enriched pathways in signaling mechanism cluster during LdMNPV induced tree-top disease in third instar Lymantria dispar asiatica larvae. Directed light bioassay demonstrated the positively phototactic larvae during tree-top disease and the gene expression analysis showed altered rhythmicity of the host’s core circadian genes (per and tim) during the course of infection emphasizing the role of Circadian entrainment and Phototransduction pathways in the process, which also showed maximum interactions (>50% shared genes with 24 and 23 pathways respectively) among other signaling pathways in the enrichment map. Our study provided valuable insights into different pathways and genes, their coordinated response and molecular regulation during baculovirus infection and also improved our understanding regarding signaling mechanisms in LdMNPV induced tree-top disease.
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Affiliation(s)
- Upendra Raj Bhattarai
- State Key Laboratory of Crop Stress Biology for Arid Areas, Northwest A&F University, Yangling, Shaanxi, 712100, P. R. China
| | - Fengjiao Li
- State Key Laboratory of Crop Stress Biology for Arid Areas, Northwest A&F University, Yangling, Shaanxi, 712100, P. R. China
| | - Mandira Katuwal Bhattarai
- State Key Laboratory of Crop Stress Biology for Arid Areas, Northwest A&F University, Yangling, Shaanxi, 712100, P. R. China
| | - Abolfazl Masoudi
- State Key Laboratory of Crop Stress Biology for Arid Areas, Northwest A&F University, Yangling, Shaanxi, 712100, P. R. China
| | - Dun Wang
- State Key Laboratory of Crop Stress Biology for Arid Areas, Northwest A&F University, Yangling, Shaanxi, 712100, P. R. China.
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Voolstra O, Strauch L, Mayer M, Huber A. Functional characterization of the three Drosophila retinal degeneration C (RDGC) protein phosphatase isoforms. PLoS One 2018; 13:e0204933. [PMID: 30265717 PMCID: PMC6161916 DOI: 10.1371/journal.pone.0204933] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2018] [Accepted: 09/17/2018] [Indexed: 11/26/2022] Open
Abstract
Drosophila retinal degeneration C (RDGC) is the founding member of the PPEF family of protein phosphatases. RDGC mediates dephosphorylation of the visual pigment rhodopsin and the TRP ion channel. From the rdgC locus, three protein isoforms, termed RDGC-S, -M, and -L, with different N-termini are generated. Due to fatty acylation, RDGC-M and -L are attached to the plasma membrane while RDGC-S is soluble. To assign physiological roles to these RDGC isoforms, we constructed flies that express various combinations of RDGC protein isoforms. Expression of the RDGC-L isoform alone did not fully prevent rhodopsin hyperphosphorylation and resulted in impaired photoreceptor physiology and in decelerated TRP dephosphorylation at Ser936. However, expression of RDGC-L alone as well as RDGC-S/M was sufficient to prevent degeneration of photoreceptor cells which is a hallmark of the rdgC null mutant. Membrane-attached RDGC-M displayed higher activity of TRP dephosphorylation than the soluble isoform RDGC-S. Taken together, in vivo activities of RDGC splice variants are controlled by their N-termini.
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Affiliation(s)
- Olaf Voolstra
- Department of Biochemistry, Institute of Physiology, University of Hohenheim, Stuttgart, Germany
- * E-mail:
| | - Lisa Strauch
- Department of Biochemistry, Institute of Physiology, University of Hohenheim, Stuttgart, Germany
| | - Matthias Mayer
- 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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Mazzotta GM, Bellanda M, Minervini G, Damulewicz M, Cusumano P, Aufiero S, Stefani M, Zambelli B, Mammi S, Costa R, Tosatto SCE. Calmodulin Enhances Cryptochrome Binding to INAD in Drosophila Photoreceptors. Front Mol Neurosci 2018; 11:280. [PMID: 30177872 PMCID: PMC6109769 DOI: 10.3389/fnmol.2018.00280] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2017] [Accepted: 07/24/2018] [Indexed: 12/13/2022] Open
Abstract
Light is the main environmental stimulus that synchronizes the endogenous timekeeping systems in most terrestrial organisms. Drosophila cryptochrome (dCRY) is a light-responsive flavoprotein that detects changes in light intensity and wavelength around dawn and dusk. We have previously shown that dCRY acts through Inactivation No Afterpotential D (INAD) in a light-dependent manner on the Signalplex, a multiprotein complex that includes visual-signaling molecules, suggesting a role for dCRY in fly vision. Here, we predict and demonstrate a novel Ca2+-dependent interaction between dCRY and calmodulin (CaM). Through yeast two hybrid, coimmunoprecipitation (Co-IP), nuclear magnetic resonance (NMR) and calorimetric analyses we were able to identify and characterize a CaM binding motif in the dCRY C-terminus. Similarly, we also detailed the CaM binding site of the scaffold protein INAD and demonstrated that CaM bridges dCRY and INAD to form a ternary complex in vivo. Our results suggest a process whereby a rapid dCRY light response stimulates an interaction with INAD, which can be further consolidated by a novel mechanism regulated by CaM.
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Affiliation(s)
| | - Massimo Bellanda
- Department of Chemical Sciences, University of Padova, Padova, Italy
| | | | - Milena Damulewicz
- Department of Cell Biology and Imaging, Institute of Zoology and Biomedical Research, Faculty of Biology and Earth Sciences, Jagiellonian University, Kraków, Poland
| | - Paola Cusumano
- Department of Biology, University of Padova, Padova, Italy
| | - Simona Aufiero
- Department of Biomedical Sciences, University of Padova, Padova, Italy
| | - Monica Stefani
- Department of Chemical Sciences, University of Padova, Padova, Italy
| | - Barbara Zambelli
- Department of Pharmacy and Biotechnology, University of Bologna, Bologna, Italy
| | - Stefano Mammi
- Department of Chemical Sciences, University of Padova, Padova, Italy
| | - Rodolfo Costa
- Department of Biology, University of Padova, Padova, Italy
| | - Silvio C E Tosatto
- Department of Biomedical Sciences, University of Padova, Padova, Italy.,CNR Institute of Neuroscience, Padova, Italy
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Moehlman AT, Casey AK, Servage K, Orth K, Krämer H. Adaptation to constant light requires Fic-mediated AMPylation of BiP to protect against reversible photoreceptor degeneration. eLife 2018; 7:e38752. [PMID: 30015618 PMCID: PMC6066327 DOI: 10.7554/elife.38752] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2018] [Accepted: 07/16/2018] [Indexed: 12/13/2022] Open
Abstract
In response to environmental, developmental, and pathological stressors, cells engage homeostatic pathways to maintain their function. Among these pathways, the Unfolded Protein Response protects cells from the accumulation of misfolded proteins in the ER. Depending on ER stress levels, the ER-resident Fic protein catalyzes AMPylation or de-AMPylation of BiP, the major ER chaperone and regulator of the Unfolded Protein Response. This work elucidates the importance of the reversible AMPylation of BiP in maintaining the Drosophila visual system in response to stress. After 72 hr of constant light, photoreceptors of fic-null and AMPylation-resistant BiPT366A mutants, but not wild-type flies, display loss of synaptic function, disintegration of rhabdomeres, and excessive activation of ER stress reporters. Strikingly, this phenotype is reversible: photoreceptors regain their structure and function within 72 hr once returned to a standard light:dark cycle. These findings show that Fic-mediated AMPylation of BiP is required for neurons to adapt to transient stress demands.
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Affiliation(s)
- Andrew T Moehlman
- Department of NeuroscienceUT Southwestern Medical CenterDallasUnited States
| | - Amanda K Casey
- Department of Molecular BiologyUT Southwestern Medical CenterDallasUnited States
| | - Kelly Servage
- Department of Molecular BiologyUT Southwestern Medical CenterDallasUnited States
- Department of BiochemistryUT Southwestern Medical CenterDallasUnited States
- Howard Hughes Medical InstituteDallasUnited States
| | - Kim Orth
- Department of Molecular BiologyUT Southwestern Medical CenterDallasUnited States
- Department of BiochemistryUT Southwestern Medical CenterDallasUnited States
- Howard Hughes Medical InstituteDallasUnited States
| | - Helmut Krämer
- Department of NeuroscienceUT Southwestern Medical CenterDallasUnited States
- Department of Cell BiologyUT Southwestern Medical CenterDallasUnited States
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Strauch L, Pfannstiel J, Huber A, Voolstra O. Solubility and subcellular localization of the three Drosophila RDGC phosphatase variants are determined by acylation. FEBS Lett 2018; 592:2403-2413. [PMID: 29920663 DOI: 10.1002/1873-3468.13163] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2018] [Revised: 06/06/2018] [Accepted: 06/11/2018] [Indexed: 01/26/2023]
Abstract
Protein phosphorylation is an abundant molecular switch that regulates a multitude of cellular processes. In contrast to other subfamilies of phosphoprotein phosphatases, the PPEF subfamily is only poorly investigated. Drosophila retinal degeneration C (RDGC) constitutes the founding member of the PPEF subfamily. RDGC dephosphorylates the visual pigment rhodopsin and the ion channel TRP.However, rdgC null mutant flies exhibit rhodopsin and TRP hyperphosphorylation, altered photoreceptor physiology, and retinal degeneration. Here, we report the identification of a third RDGC protein variant and show that the three RDGC isoforms harbor different N-termini that determine solubility and subcellular targeting due to fatty acylation. Taken together, solubility and subcellular targeting of RDGC splice variants are determined by their N-termini.
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Affiliation(s)
- Lisa Strauch
- Department of Biosensorics, Institute of Physiology, University of Hohenheim, Stuttgart, Germany
| | - Jens Pfannstiel
- Core Facility, Mass Spectrometry Unit, University of Hohenheim, Stuttgart, Germany
| | - Armin Huber
- Department of Biosensorics, Institute of Physiology, University of Hohenheim, Stuttgart, Germany
| | - Olaf Voolstra
- Department of Biosensorics, Institute of Physiology, University of Hohenheim, Stuttgart, Germany
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12
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Emerging Paradigms of G Protein-Coupled Receptor Dephosphorylation. Trends Pharmacol Sci 2017; 38:621-636. [DOI: 10.1016/j.tips.2017.04.002] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2017] [Revised: 03/31/2017] [Accepted: 04/06/2017] [Indexed: 12/21/2022]
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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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Light-Driven Processes Control Both Rhodopsin Maturation and Recycling in Mosquito Photoreceptors. J Neurosci 2016; 36:11051-11058. [PMID: 27798185 DOI: 10.1523/jneurosci.1754-16.2016] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2016] [Accepted: 09/07/2016] [Indexed: 11/21/2022] Open
Abstract
Many invertebrates carry out a daily cycle of shedding and rebuilding of the photoreceptor's photosensitive rhabdomeric membranes. The mosquito Aedes aegypti shows a robust response, losing nearly all Aaop1 rhodopsin from the rhabdomeric membranes during the shedding process at dawn. Here, we made use of Aaop1 antibodies capable of distinguishing newly synthesized, glycosylated rhodopsin from mature nonglycosylated rhodopsin to characterize the fate of Aaop1 during the shedding and rebuilding processes. The rhabdomeric rhodopsin is moved into large cytoplasmic vesicles at dawn and is subsequently degraded during the standard 12 h daytime period. The endocytosed rhodopsin is trafficked back to the photosensitive membranes if animals are shifted back to dark conditions during the morning hours. During the daytime period, small vesicles containing newly synthesized and glycosylated Aaop1 rhodopsin accumulate within the cytoplasm. At dusk, these vesicles are lost as the newly synthesized Aaop1 is converted to the nonglycosylated form and deposited in the rhabdomeres. We demonstrate that light acts though a novel signaling pathway to block rhodopsin maturation, thus inhibiting the deglycosylation and rhabdomeric targeting of newly synthesized Aaop1 rhodopsin. Therefore, light controls two cellular processes responsible for the daily renewal of rhodopsin: rhodopsin endocytosis at dawn and inhibition of rhodopsin maturation until dusk. SIGNIFICANCE STATEMENT Organisms use multiple strategies to maximize visual capabilities in different light conditions. Many invertebrates show a daily cycle of shedding the photoreceptor's rhabdomeric membranes at dawn and rebuilding these during the following night. We show here that the Aedes aegypti mosquito possesses two distinct light-driven cellular signaling processes for modulating rhodopsin content during this cycle. One of these, endocytosis of rhabdomeric rhodopsin, has been described previously. The second, a light-activated cellular pathway acting to inhibit the anterograde movement of newly synthesized rhodopsin, is revealed here for the first time. The discovery of this cellular signaling pathway controlling a G-protein-coupled receptor is of broad interest due to the prominent role of this receptor family across all areas of neuroscience.
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Jaiswal M, Haelterman NA, Sandoval H, Xiong B, Donti T, Kalsotra A, Yamamoto S, Cooper TA, Graham BH, Bellen HJ. Impaired Mitochondrial Energy Production Causes Light-Induced Photoreceptor Degeneration Independent of Oxidative Stress. PLoS Biol 2015; 13:e1002197. [PMID: 26176594 PMCID: PMC4503542 DOI: 10.1371/journal.pbio.1002197] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2015] [Accepted: 06/10/2015] [Indexed: 11/19/2022] Open
Abstract
Two insults often underlie a variety of eye diseases including glaucoma, optic atrophy, and retinal degeneration—defects in mitochondrial function and aberrant Rhodopsin trafficking. Although mitochondrial defects are often associated with oxidative stress, they have not been linked to Rhodopsin trafficking. In an unbiased forward genetic screen designed to isolate mutations that cause photoreceptor degeneration, we identified mutations in a nuclear-encoded mitochondrial gene, ppr, a homolog of human LRPPRC. We found that ppr is required for protection against light-induced degeneration. Its function is essential to maintain membrane depolarization of the photoreceptors upon repetitive light exposure, and an impaired phototransduction cascade in ppr mutants results in excessive Rhodopsin1 endocytosis. Moreover, loss of ppr results in a reduction in mitochondrial RNAs, reduced electron transport chain activity, and reduced ATP levels. Oxidative stress, however, is not induced. We propose that the reduced ATP level in ppr mutants underlies the phototransduction defect, leading to increased Rhodopsin1 endocytosis during light exposure, causing photoreceptor degeneration independent of oxidative stress. This hypothesis is bolstered by characterization of two other genes isolated in the screen, pyruvate dehydrogenase and citrate synthase. Their loss also causes a light-induced degeneration, excessive Rhodopsin1 endocytosis and reduced ATP without concurrent oxidative stress, unlike many other mutations in mitochondrial genes that are associated with elevated oxidative stress and light-independent photoreceptor demise. Some mitochondrial disorders cause blindness through increased oxidative stress. This study shows that in other such disorders, light-activated photoreceptors degenerate because the shortfall in mitochondrial energy production impairs rhodopsin trafficking and induces toxicity. Mitochondrial dysfunction is associated with a number of metabolic and neurological diseases such as Leigh syndrome and progressive blindness. Increased oxidative stress, which is often associated with mitochondrial dysfunction, is thought to be a common cause of disease progression. Here, we identified nuclear genes that encode mitochondrial proteins, whose loss causes the demise of photoreceptor neurons. Contrary to the common idea that this degeneration is triggered by elevated levels of oxidative stress, we find no change in the levels of oxidative stress. We show that activating photoreceptor neurons with light significantly increases energy production, and that this process is required to sustain their activity. Mitochondrial dysfunction impairs this capacity and leads to a premature termination of the light response. This in turn impairs the cycling of the light-sensitive receptor Rhodopsin in photoreceptors, and Rhodopsin accumulates in the cell inducing toxicity. This distinct mechanism of degeneration suggests that different mitochondrial diseases may follow different paths of disease progression and would hence respond differently to treatments.
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Affiliation(s)
- Manish Jaiswal
- Department of Molecular and Human Genetics, Baylor College of Medicine (BCM), Houston, Texas, United States of America
- Howard Hughes Medical Institute, BCM, Houston, Texas, United States of America
| | - Nele A. Haelterman
- Program in Developmental Biology, BCM, Houston, Texas, United States of America
| | - Hector Sandoval
- Department of Molecular and Human Genetics, Baylor College of Medicine (BCM), Houston, Texas, United States of America
| | - Bo Xiong
- Program in Developmental Biology, BCM, Houston, Texas, United States of America
| | - Taraka Donti
- Department of Molecular and Human Genetics, Baylor College of Medicine (BCM), Houston, Texas, United States of America
| | - Auinash Kalsotra
- Department of Pathology and Immunology, BCM, Houston, Texas, United States of America
| | - Shinya Yamamoto
- Department of Molecular and Human Genetics, Baylor College of Medicine (BCM), Houston, Texas, United States of America
- Program in Developmental Biology, BCM, Houston, Texas, United States of America
- Jan and Dan Duncan Neurological Research Institute, Texas Children’s Hospital (TCH), Houston, Texas, United States of America
| | - Thomas A. Cooper
- Program in Developmental Biology, BCM, Houston, Texas, United States of America
- Department of Pathology and Immunology, BCM, Houston, Texas, United States of America
| | - Brett H. Graham
- Department of Molecular and Human Genetics, Baylor College of Medicine (BCM), Houston, Texas, United States of America
| | - Hugo J. Bellen
- Department of Molecular and Human Genetics, Baylor College of Medicine (BCM), Houston, Texas, United States of America
- Howard Hughes Medical Institute, BCM, Houston, Texas, United States of America
- Program in Developmental Biology, BCM, Houston, Texas, United States of America
- Jan and Dan Duncan Neurological Research Institute, Texas Children’s Hospital (TCH), Houston, Texas, United States of America
- Department of Neuroscience, BCM, Houston, Texas, United States of America
- * E-mail:
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16
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Dimers of G-protein coupled receptors as versatile storage and response units. Int J Mol Sci 2014; 15:4856-77. [PMID: 24651459 PMCID: PMC3975428 DOI: 10.3390/ijms15034856] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2014] [Revised: 02/28/2014] [Accepted: 03/04/2014] [Indexed: 11/17/2022] Open
Abstract
The status and use of transmembrane, extracellular and intracellular domains in oligomerization of heptahelical G-protein coupled receptors (GPCRs) are reviewed and for transmembrane assemblies also supplemented by new experimental evidence. The transmembrane-linked GPCR oligomers typically have as the minimal unit an asymmetric ~180 kDa pentamer consisting of receptor homodimer or heterodimer and a G-protein αβγ subunit heterotrimer. With neuropeptide Y (NPY) receptors, this assembly is converted to ~90 kDa receptor monomer-Gα complex by receptor and Gα agonists, and dimers/heteropentamers are depleted by neutralization of Gαi subunits by pertussis toxin. Employing gradient centrifugation, quantification and other characterization of GPCR dimers at the level of physically isolated and identified heteropentamers is feasible with labeled agonists that do not dissociate upon solubilization. This is demonstrated with three neuropeptide Y (NPY) receptors and could apply to many receptors that use large peptidic agonists.
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17
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Abstract
The Drosophila "transient receptor potential" channel is the prototypical TRP channel, belonging to and defining the TRPC subfamily. Together with a second TRPC channel, trp-like (TRPL), TRP mediates the transducer current in the fly's photoreceptors. TRP and TRPL are also implicated in olfaction and Malpighian tubule function. In photoreceptors, TRP and TRPL are localised in the ~30,000 packed microvilli that form the photosensitive "rhabdomere"-a light-guiding rod, housing rhodopsin and the rest of the phototransduction machinery. TRP (but not TRPL) is assembled into multimolecular signalling complexes by a PDZ-domain scaffolding protein (INAD). TRPL (but not TRP) undergoes light-regulated translocation between cell body and rhabdomere. TRP and TRPL are also found in photoreceptor synapses where they may play a role in synaptic transmission. Like other TRPC channels, TRP and TRPL are activated by a G protein-coupled phospholipase C (PLCβ4) cascade. Although still debated, recent evidence indicates the channels can be activated by a combination of PIP2 depletion and protons released by the PLC reaction. PIP2 depletion may act mechanically as membrane area is reduced by cleavage of PIP2's bulky inositol headgroup. TRP, which dominates the light-sensitive current, is Ca(2+) selective (P Ca:P Cs >50:1), whilst TRPL has a modest Ca(2+) permeability (P Ca:P Cs ~5:1). Ca(2+) influx via the channels has profound positive and negative feedback roles, required for the rapid response kinetics, with Ca(2+) rapidly facilitating TRP (but not TRPL) and also inhibiting both channels. In trp mutants, stimulation by light results in rapid depletion of microvillar PIP2 due to lack of Ca(2+) influx required to inhibit PLC. This accounts for the "transient receptor potential" phenotype that gives the family its name and, over a period of days, leads to light-dependent retinal degeneration. Gain-of-function trp mutants with uncontrolled Ca(2+) influx also undergo retinal degeneration due to Ca(2+) cytotoxicity. In vertebrate retina, mice knockout studies suggest that TRPC6 and TRPC7 mediate a PLCβ4-activated transducer current in intrinsically photosensitive retinal ganglion cells, expressing melanopsin. TRPA1 has been implicated as a "photo-sensing" TRP channel in human melanocytes and light-sensitive neurons in the body wall of Drosophila.
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18
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Xiong B, Bellen HJ. Rhodopsin homeostasis and retinal degeneration: lessons from the fly. Trends Neurosci 2013; 36:652-60. [PMID: 24012059 DOI: 10.1016/j.tins.2013.08.003] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2013] [Revised: 08/02/2013] [Accepted: 08/12/2013] [Indexed: 11/16/2022]
Abstract
Rhodopsins (Rh) are G protein-coupled receptors that function as light-sensors in photoreceptors. In humans, Rh mutations cause retinitis pigmentosa (RP), a degenerative disease that ultimately results in blindness. Studies in Drosophila have provided many insights into basic Rh biology and have identified pathways that lead to retinal degeneration. It has been shown that, because Rh is very abundant in photoreceptors, its accumulation in numerous organelles induces severe stress and results in degeneration of these cells. Moreover, genetic lesions that affect proper activation of membrane-bound Rh lead to disruption in Ca(2+) homeostasis which also causes photoreceptor degeneration. We review here the molecular signals involved in Rh homeostasis and the mechanisms underlying retinal degeneration in flies, and discuss possible links to human diseases.
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Affiliation(s)
- Bo Xiong
- Program in Developmental Biology, Baylor College of Medicine, Houston, Texas 77030, USA
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19
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Raghu P, Yadav S, Mallampati NBN. Lipid signaling in Drosophila photoreceptors. Biochim Biophys Acta Mol Cell Biol Lipids 2012; 1821:1154-65. [PMID: 22487656 DOI: 10.1016/j.bbalip.2012.03.008] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2011] [Revised: 03/20/2012] [Accepted: 03/22/2012] [Indexed: 11/19/2022]
Abstract
Drosophila photoreceptors are sensory neurons whose primary function is the transduction of photons into an electrical signal for forward transmission to the brain. Photoreceptors are polarized cells whose apical domain is organized into finger like projections of plasma membrane, microvilli that contain the molecular machinery required for sensory transduction. The development of this apical domain requires intense polarized membrane transport during development and it is maintained by post developmental membrane turnover. Sensory transduction in these cells involves a high rate of G-protein coupled phosphatidylinositol 4,5 bisphosphate [PI(4,5)P(2)] hydrolysis ending with the activation of ion channels that are members of the TRP superfamily. Defects in this lipid-signaling cascade often result in retinal degeneration, which is a consequence of the loss of apical membrane homeostasis. In this review we discuss the various membrane transport challenges of photoreceptors and their regulation by ongoing lipid signaling cascades in these cells. This article is part of a Special Issue entitled Lipids and Vesicular Transport.
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Affiliation(s)
- Padinjat Raghu
- National Centre for Biological Sciences, TIFR, GKVK Campus, Bellary Road, Banglore 560065, India.
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20
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Hardie RC. Phototransduction mechanisms in Drosophila microvillar photoreceptors. ACTA ACUST UNITED AC 2011. [DOI: 10.1002/wmts.20] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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21
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Miskei M, Ádám C, Kovács L, Karányi Z, Dombrádi V. Molecular evolution of phosphoprotein phosphatases in Drosophila. PLoS One 2011; 6:e22218. [PMID: 21789237 PMCID: PMC3137614 DOI: 10.1371/journal.pone.0022218] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2011] [Accepted: 06/20/2011] [Indexed: 12/25/2022] Open
Abstract
Phosphoprotein phosphatases (PPP), these ancient and important regulatory enzymes are present in all eukaryotic organisms. Based on the genome sequences of 12 Drosophila species we traced the evolution of the PPP catalytic subunits and noted a substantial expansion of the gene family. We concluded that the 18–22 PPP genes of Drosophilidae were generated from a core set of 8 indispensable phosphatases that are present in most of the insects. Retropositons followed by tandem gene duplications extended the phosphatase repertoire, and sporadic gene losses contributed to the species specific variations in the PPP complement. During the course of these studies we identified 5, up till now uncharacterized phosphatase retrogenes: PpY+, PpD5+, PpD6+, Pp4+, and Pp6+ which are found only in some ancient Drosophila. We demonstrated that all of these new PPP genes exhibit a distinct male specific expression. In addition to the changes in gene numbers, the intron-exon structure and the chromosomal localization of several PPP genes was also altered during evolution. The G−C content of the coding regions decreased when a gene moved into the heterochromatic region of chromosome Y. Thus the PPP enzymes exemplify the various types of dynamic rearrangements that accompany the molecular evolution of a gene family in Drosophilidae.
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Affiliation(s)
- Márton Miskei
- Centre for Agricultural and Applied Economic Sciences, Institute of Horticultural Sciences, Department of Plant Biotechnology, University of Debrecen, Debrecen, Hungary
| | - Csaba Ádám
- Department of Medical Chemistry, Research Center for Molecular Medicine, Medical and Health Science Center, University of Debrecen, Debrecen, Hungary
| | - László Kovács
- Department of Medical Chemistry, Research Center for Molecular Medicine, Medical and Health Science Center, University of Debrecen, Debrecen, Hungary
| | - Zsolt Karányi
- First Department of Medicine, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
| | - Viktor Dombrádi
- Department of Medical Chemistry, Research Center for Molecular Medicine, Medical and Health Science Center, University of Debrecen, Debrecen, Hungary
- * E-mail:
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22
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Dependence on a retinophilin/myosin complex for stability of PKC and INAD and termination of phototransduction. J Neurosci 2010; 30:11337-45. [PMID: 20739554 DOI: 10.1523/jneurosci.2709-10.2010] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Normal termination of signaling is essential to reset signaling cascades, especially those such as phototransduction that are turned on and off with great rapidity. Genetic approaches in Drosophila led to the identification of several proteins required for termination, including protein kinase C (PKC), NINAC (neither inactivation nor afterpotential C) p174, which consists of fused protein kinase and myosin domains, and a PDZ (postsynaptic density-95/Discs Large/zona occludens-1) scaffold protein, INAD (inactivation no afterpotential D). Here, we describe a mutation affecting a poorly characterized but evolutionarily conserved protein, Retinophilin (Retin), which is expressed primarily in the phototransducing compartment of photoreceptor cells, the rhabdomeres. Retin and NINAC formed a complex and were mutually dependent on each other for expression. Loss of retin resulted in an age-dependent impairment in termination of phototransduction. Mutations that affect termination of the photoresponse typically lead to a reduction in levels of the major rhodopsin (Rh1) to attenuate signaling. Consistent with the slower termination in retin(1), the mutant photoreceptor cells exhibited increased endocytosis of Rh1 and a decline in Rh1 protein. The slower termination in retin(1) was a consequence of a cascade of defects, which began with the reduction in NINAC p174 levels. The diminished p174 concentration caused a decrease in INAD. Because PKC requires interaction with INAD for protein stability, this leads to reduction in PKC levels. The decline in PKC was age dependent and paralleled the onset of the termination phenotype in retin(1) mutant flies. We conclude that the slower termination of the photoresponse in retin(1) resulted from a requirement for the Retin/NINAC complex for stability of INAD and PKC.
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23
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Premkumar LS. Targeting TRPV1 as an alternative approach to narcotic analgesics to treat chronic pain conditions. AAPS J 2010; 12:361-70. [PMID: 20440589 PMCID: PMC2895451 DOI: 10.1208/s12248-010-9196-y] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2010] [Accepted: 04/19/2010] [Indexed: 12/24/2022] Open
Abstract
In spite of intense research efforts and after the dedicated Decade of Pain Control and Research, there are not many alternatives to opioid-based narcotic analgesics in the therapeutic armamentarium to treat chronic pain conditions. Chronic opioid treatment is associated with sedation, tolerance, dependence, hyperalgesia, respiratory depression, and constipation. Since the affective component is an integral part of pain perception, perhaps it is inevitable that potent analgesics possess the property of impacting pain pathways in the supraspinal structures. The question still remains to be answered is that whether a powerful analgesic can be devoid of narcotic effect and addictive potentials. Local anesthetics are powerful analgesics for acute pain by blocking voltage-gated sodium channels that are involved in generation and propagation of action potentials. Antidepressants and anticonvulsants have proven to be useful in the treatment of certain modalities of pain. In neuropathic pain conditions, the complexity arises because of the notion that neuronal circuitry is altered, as occurs in phantom pain, in that pain is perceived even in the absence of peripheral nociceptive inputs. If the locus of these changes is in the central nervous system, commonly used analgesics may not be very useful. This review focuses on the recent advances in nociceptive transmission and nociceptive transient receptor potential vanilloid 1 channel as a target for treating chronic pain conditions with its agonists/antagonists.
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Affiliation(s)
- Louis S Premkumar
- Department of Pharmacology, Southern Illinois University School of Medicine, Springfield, Illinois 62702, USA.
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24
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Kutuzov MA, Bennett N, Andreeva AV. Protein phosphatase with EF-hand domains 2 (PPEF2) is a potent negative regulator of apoptosis signal regulating kinase-1 (ASK1). Int J Biochem Cell Biol 2010; 42:1816-22. [PMID: 20674765 DOI: 10.1016/j.biocel.2010.07.014] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2010] [Revised: 07/09/2010] [Accepted: 07/21/2010] [Indexed: 11/28/2022]
Abstract
The function of protein phosphatases with EF-hand domains (PPEF) in mammals is not known. Large-scale expression profiling experiments suggest that PPEF expression may correlate with stress protective responses, cell survival, growth, proliferation, or neoplastic transformation. Apoptosis signal regulating kinase-1 (ASK1) is a MAP kinase kinase kinase implicated in cancer, cardiovascular and neurodegenerative diseases. ASK1 is activated by oxidative stress and induces pro-apoptotic or inflammatory signalling, largely via sustained activation of MAP kinases p38 and/or JNK. We identify human PPEF2 as a novel interacting partner and a negative regulator of ASK1. In COS-7 or HEK 293A cells treated with H(2)O(2), expression of PPEF2 abrogated sustained activation of p38 and one of the JNK p46 isoforms, and prevented ASK1-dependent caspase-3 cleavage and activation. PPEF2 efficiently suppressed H(2)O(2)-induced activation of ASK1. Overexpessed as well as endogenous ASK1 co-immunoprecipitated with PPEF2. PPEF2 was considerably more potent both as a suppressor of ASK1 activation and as its interacting partner as compared to protein phosphatase 5 (PP5), a well-known negative regulator of ASK1. PPEF2 was found to form complexes with endogenous Hsp70 and to a lesser extent Hsp90, which are also known interacting partners of PP5. These data identify, for the first time, a possible downstream signalling partner of a mammalian PPEF phosphatase, and suggest that, despite structural divergence, PPEF and PP5 phosphatases may share common interacting partners and functions.
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Affiliation(s)
- Mikhail A Kutuzov
- Department of Pharmacology (MC 868), University of Illinois at Chicago, Chicago, IL 60612, USA.
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25
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Andreeva AV, Kutuzov MA. PPEF/PP7 protein Ser/Thr phosphatases. Cell Mol Life Sci 2009; 66:3103-10. [PMID: 19662497 PMCID: PMC11115641 DOI: 10.1007/s00018-009-0110-7] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2009] [Accepted: 07/15/2009] [Indexed: 12/14/2022]
Abstract
PPEF/PP7 represents one of the five subfamilies of the PPP protein Ser/Thr phosphatases. Studies published in recent years point to a role of plant PP7 at a crossroad of different pathways of light and stress signalling. In animals, PPEFs are highly expressed in sensory neurons, and Drosophila PPEF phosphatase, rdgC, is essential for dephosphorylation of rhodopsin. Expression profiling suggests that mammalian PPEF may play a role in stress-protective responses, cell survival, growth, proliferation, and oncogenesis. Despite structural similarities of the catalytic domains and the fact that some of these phosphatases are involved in light perception both in animals and in plants, the plant and non-plant representatives of this group have distinct domain architecture and appear not to be orthologues.
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Affiliation(s)
- Alexandra V. Andreeva
- Department of Pharmacology (M/C 868), College of Medicine, University of Illinois, 909 S. Wolcott Ave., Chicago, IL 60612 USA
| | - Mikhail A. Kutuzov
- Department of Pharmacology (M/C 868), College of Medicine, University of Illinois, 909 S. Wolcott Ave., Chicago, IL 60612 USA
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26
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Liu CH, Satoh AK, Postma M, Huang J, Ready DF, Hardie RC. Ca2+-dependent metarhodopsin inactivation mediated by calmodulin and NINAC myosin III. Neuron 2008; 59:778-89. [PMID: 18786361 DOI: 10.1016/j.neuron.2008.07.007] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2008] [Revised: 06/03/2008] [Accepted: 07/09/2008] [Indexed: 10/21/2022]
Abstract
Phototransduction in flies is the fastest known G protein-coupled signaling cascade, but how this performance is achieved remains unclear. Here, we investigate the mechanism and role of rhodopsin inactivation. We determined the lifetime of activated rhodopsin (metarhodopsin = M( *)) in whole-cell recordings from Drosophila photoreceptors by measuring the time window within which inactivating M( *) by photoreisomerization to rhodopsin could suppress responses to prior illumination. M( *) was inactivated rapidly (tau approximately 20 ms) under control conditions, but approximately 10-fold more slowly in Ca2+-free solutions. This pronounced Ca2+ dependence of M( *) inactivation was unaffected by mutations affecting phosphorylation of rhodopsin or arrestin but was abolished in mutants of calmodulin (CaM) or the CaM-binding myosin III, NINAC. This suggests a mechanism whereby Ca2+ influx acting via CaM and NINAC accelerates the binding of arrestin to M( *). Our results indicate that this strategy promotes quantum efficiency, temporal resolution, and fidelity of visual signaling.
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Affiliation(s)
- Che-Hsiung Liu
- Department of Physiology, Development and Neuroscience, Cambridge University, Cambridge CB23DY, UK
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27
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Wang T, Montell C. Phototransduction and retinal degeneration in Drosophila. Pflugers Arch 2007; 454:821-47. [PMID: 17487503 DOI: 10.1007/s00424-007-0251-1] [Citation(s) in RCA: 215] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2007] [Accepted: 03/05/2007] [Indexed: 01/05/2023]
Abstract
Drosophila visual transduction is the fastest known G-protein-coupled signaling cascade and has therefore served as a genetically tractable animal model for characterizing rapid responses to sensory stimulation. Mutations in over 30 genes have been identified, which affect activation, adaptation, or termination of the photoresponse. Based on analyses of these genes, a model for phototransduction has emerged, which involves phosphoinoside signaling and culminates with opening of the TRP and TRPL cation channels. Many of the proteins that function in phototransduction are coupled to the PDZ containing scaffold protein INAD and form a supramolecular signaling complex, the signalplex. Arrestin, TRPL, and G alpha(q) undergo dynamic light-dependent trafficking, and these movements function in long-term adaptation. Other proteins play important roles either in the formation or maturation of rhodopsin, or in regeneration of phosphatidylinositol 4,5-bisphosphate (PIP2), which is required for the photoresponse. Mutation of nearly any gene that functions in the photoresponse results in retinal degeneration. The underlying bases of photoreceptor cell death are diverse and involve mechanisms such as excessive endocytosis of rhodopsin due to stable rhodopsin/arrestin complexes and abnormally low or high levels of Ca2+. Drosophila visual transduction appears to have particular relevance to the cascade in the intrinsically photosensitive retinal ganglion cells in mammals, as the photoresponse in these latter cells appears to operate through a remarkably similar mechanism.
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Affiliation(s)
- Tao Wang
- Department of Biological Chemistry, Center for Sensory Biology, The Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
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28
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Landry CR, Castillo-Davis CI, Ogura A, Liu JS, Hartl DL. Systems-level analysis and evolution of the phototransduction network in Drosophila. Proc Natl Acad Sci U S A 2007; 104:3283-8. [PMID: 17360639 PMCID: PMC1805570 DOI: 10.1073/pnas.0611402104] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Networks of interacting genes are responsible for generating life's complexity and for mediating how organisms respond to their environment. Thus, a basic understanding of genetic variation in gene networks in natural populations is important for elucidating how changes at the genetic level map to higher levels of biological organization. Here, using the well-characterized phototransduction network in Drosophila, we analyze variation in gene expression within and between two closely related species, Drosophila melanogaster and Drosophila simulans, under different environmental conditions. Gene expression levels in the pathway are largely conserved between these two sibling species. For most genes in the network, differences in level of gene expression between species are correlated with degree of polymorphism within species. However, one gene encoding the light-induced ion channel TRPL (transient receptor potential-like) shows an excess of expression divergence relative to polymorphism, suggesting a possible role for natural selection in shaping this expression difference between species. Finally, this difference in TRPL expression likely has significant functional consequences, because it is known that a high level of rhabdomeral TRPL leads to increased sensitivity to dim background light and an increased response to a wider range of light intensities. These results provide a preliminary quantification of variation and divergence of gene expression between species in a known gene network and provide a foundation for a system-level understanding of functional and evolutionary change.
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Affiliation(s)
| | - Cristian I. Castillo-Davis
- Statistics, Harvard University, Cambridge, MA 02138
- To whom correspondence may be addressed at the present address:
Department of Biology, University of Maryland, College Park, MD 20742. E-mail:
| | - Atsushi Ogura
- Departments of *Organismic and Evolutionary Biology and
| | - Jun S. Liu
- Statistics, Harvard University, Cambridge, MA 02138
| | - Daniel L. Hartl
- Departments of *Organismic and Evolutionary Biology and
- To whom correspondence may be addressed at:
Department of Organismic and Evolutionary Biology, Harvard University, 16 Divinity Avenue, Cambridge, MA 02138. E-mail:
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29
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Mills E, Price HP, Johner A, Emerson JE, Smith DF. Kinetoplastid PPEF phosphatases: dual acylated proteins expressed in the endomembrane system of Leishmania. Mol Biochem Parasitol 2006; 152:22-34. [PMID: 17169445 PMCID: PMC1885993 DOI: 10.1016/j.molbiopara.2006.11.008] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2006] [Revised: 11/02/2006] [Accepted: 11/14/2006] [Indexed: 12/02/2022]
Abstract
Bioinformatic analyses have been used to identify potential downstream targets of the essential enzyme N-myristoyl transferase in the TriTryp species, Leishmania major, Trypanosoma brucei and Trypanosoma cruzi. These database searches predict ∼60 putative N-myristoylated proteins with high confidence, including both previously characterised and novel molecules. One of the latter is an N-myristoylated protein phosphatase which has high sequence similarity to the Protein Phosphatase with EF-Hand (PPEF) proteins identified in sensory cells of higher eukaryotes. In L. major and T. brucei, the PPEF-like phosphatases are encoded by single-copy genes and are constitutively expressed in all parasite life cycle stages. The N-terminus of LmPPEF is a substrate for N-myristoyl transferase and is also palmitoylated in vivo. The wild type protein has been localised to the endocytic system by immunofluorescence. The catalytic and fused C-terminal domains of the kinetoplastid and other eukaryotic PPEFs share high sequence similarity, but unlike their higher eukaryotic relatives, the C-terminal parasite EF-hand domains are degenerate and do not bind calcium.
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Affiliation(s)
- Elena Mills
- Wellcome Trust Laboratories for Molecular Parasitology, Centre for Molecular Microbiology and Infection, Imperial College London, London SW7 2AZ, UK
| | - Helen P. Price
- Wellcome Trust Laboratories for Molecular Parasitology, Centre for Molecular Microbiology and Infection, Imperial College London, London SW7 2AZ, UK
- Immunology and Infection Unit, Department of Biology, University of York, Heslington, York YO10 5YW, UK
| | - Andrea Johner
- Immunology and Infection Unit, Department of Biology, University of York, Heslington, York YO10 5YW, UK
| | - Jenny E. Emerson
- Wellcome Trust Laboratories for Molecular Parasitology, Centre for Molecular Microbiology and Infection, Imperial College London, London SW7 2AZ, UK
| | - Deborah F. Smith
- Wellcome Trust Laboratories for Molecular Parasitology, Centre for Molecular Microbiology and Infection, Imperial College London, London SW7 2AZ, UK
- Immunology and Infection Unit, Department of Biology, University of York, Heslington, York YO10 5YW, UK
- Corresponding author at: Immunology and Infection Unit, Department of Biology, University of York, Heslington, York YO10 5YW, UK. Tel.: +44 1904 328843; fax: +44 1904 328844.
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30
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Kwon Y, Montell C. Dependence on the Lazaro phosphatidic acid phosphatase for the maximum light response. Curr Biol 2006; 16:723-9. [PMID: 16513351 DOI: 10.1016/j.cub.2006.02.057] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2005] [Revised: 02/16/2006] [Accepted: 02/17/2006] [Indexed: 11/27/2022]
Abstract
The Drosophila phototransduction cascade serves as a paradigm for characterizing the regulation of sensory signaling and TRP channels in vivo . Activation of these channels requires phospholipase C (PLC) and may depend on subsequent production of diacylglycerol (DAG) and downstream metabolites . DAG could potentially be produced through a second pathway involving the combined activities of a phospholipase D (PLD) and a phosphatidic acid (PA) phosphatase (PAP). However, a role for a PAP in the regulation of TRP channels has not been described. Here, we report the identification of a PAP, referred to as Lazaro (Laza). Mutations in laza caused a reduction in the light response and faster termination kinetics. Loss of laza suppressed the severity of the phenotype caused by mutation of the DAG kinase, RDGA , indicating that Laza functions in opposition to RDGA. We also showed that the retinal degeneration resulting from overexpression of the PLD was suppressed by elimination of Laza. These data demonstrate a requirement for a PLD/PAP-dependent pathway for achieving the maximal light response. The genetic interactions with both rdgA and Pld indicate that Laza functions in the convergence of both PLC- and PLD-coupled signaling in vivo.
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Affiliation(s)
- Young Kwon
- Department of Biological Chemistry, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
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31
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Wang T, Jiao Y, Montell C. Dissecting independent channel and scaffolding roles of the Drosophila transient receptor potential channel. ACTA ACUST UNITED AC 2006; 171:685-94. [PMID: 16301334 PMCID: PMC2171549 DOI: 10.1083/jcb.200508030] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Drosophila transient receptor potential (TRP) serves dual roles as a cation channel and as a molecular anchor for the PDZ protein, INAD (inactivation no afterpotential D). Null mutations in trp cause impairment of visual transduction, mislocalization of INAD, and retinal degeneration. However, the impact of specifically altering TRP channel function is not known because existing loss-of-function alleles greatly reduce protein expression. In the current study we describe the isolation of a set of new trp alleles, including trp14 with an amino acid substitution juxtaposed to the TRP domain. The trp14 flies stably express TRP and display normal molecular anchoring, but defective channel function. Elimination of the anchoring function alone in trpΔ1272, had minor effects on retinal morphology whereas disruption of channel function caused profound light-induced cell death. This retinal degeneration was greatly suppressed by elimination of the Na+/Ca2+ exchanger, CalX, indicating that the cell death was due primarily to deficient Ca2+ entry rather than disruption of the TRP-anchoring function.
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MESH Headings
- Alleles
- Amino Acid Sequence
- Animals
- Animals, Genetically Modified
- Antiporters/genetics
- Antiporters/physiology
- Arrestins/genetics
- Arrestins/physiology
- Blotting, Western
- Calcium/metabolism
- Cations
- Drosophila Proteins/chemistry
- Drosophila Proteins/genetics
- Drosophila Proteins/metabolism
- Drosophila Proteins/physiology
- Drosophila melanogaster
- Electroretinography
- Gene Expression Regulation
- Genes, Insect
- Immunoprecipitation
- Light
- Microscopy, Electron, Transmission
- Molecular Sequence Data
- Mutation
- Mutation, Missense
- Phenotype
- Photoreceptor Cells, Invertebrate/pathology
- Protein Structure, Tertiary
- Retina/pathology
- Retinal Diseases/genetics
- Sequence Homology, Amino Acid
- Signal Transduction
- Sodium-Calcium Exchanger/chemistry
- Time Factors
- Transient Receptor Potential Channels/metabolism
- Transient Receptor Potential Channels/physiology
- Vision, Ocular
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Affiliation(s)
- Tao Wang
- Department of Biological Chemistry, The Johns Hopkins University School of Medicine, Baltimore, MD 21205
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32
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Lee SJ, Montell C. Suppression of constant-light-induced blindness but not retinal degeneration by inhibition of the rhodopsin degradation pathway. Curr Biol 2005; 14:2076-85. [PMID: 15589149 DOI: 10.1016/j.cub.2004.11.054] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2004] [Revised: 10/12/2004] [Accepted: 10/12/2004] [Indexed: 12/14/2022]
Abstract
BACKGROUND Continuous exposure to light, even at relatively low intensities, leads to retinal damage and blindness in wild-type animals. However, the molecular mechanisms underlying constant-light-induced blindness are poorly understood. It has been presumed that the visual impairment resulting from long-term, continuous exposure to ambient light is a secondary consequence of the effects of light on retinal morphology, but this has not been addressed. RESULTS To characterize the mechanism underlying light-induced blindness, we applied a molecular genetic approach using the fruit fly, Drosophila melanogaster. We found that the temporal loss of the photoresponse was paralleled by a gradual decline in the concentration of rhodopsin. The decline in rhodopsin and the visual response were suppressed by a C-terminal truncation of rhodopsin, by mutations in arrestin, and by elimination of a lysosomal protein, Sunglasses. Conversely, the visual impairment was greatly enhanced by mutation of the rhodopsin phosphatase, rdgC. Surprisingly, the mutations that suppressed light-induced blindness did not reduce the severity of the retinal degeneration resulting from constant light. Moreover, mutations known to suppress retinal degeneration did not ameliorate the light-induced blindness. CONCLUSIONS These data demonstrate that the constant light-induced blindness and retinal degeneration result from defects in distinct molecular pathways. Our results support a model in which visual impairment caused by continuous illumination occurs through an arrestin-dependent pathway that promotes degradation of rhodopsin.
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Affiliation(s)
- Seung-Jae Lee
- Department of Biological Chemistry, The Johns Hopkins University School of Medicine, Baltimore, MD 21205 USA
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33
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Lee SJ, Montell C. Light-dependent translocation of visual arrestin regulated by the NINAC myosin III. Neuron 2004; 43:95-103. [PMID: 15233920 DOI: 10.1016/j.neuron.2004.06.014] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2004] [Revised: 04/03/2004] [Accepted: 06/02/2004] [Indexed: 11/16/2022]
Abstract
The rhodopsin regulatory protein, visual arrestin, undergoes light-dependent trafficking in mammalian and Drosophila photoreceptor cells, though the mechanisms underlying these movements are poorly understood. In Drosophila, the movement of the visual arrestin, Arr2, functions in long-term adaptation and is dependent on interaction with phosphoinositides (PIs). However, the basis for the requirement for PIs for light-dependent shuttling was unclear. Here, we demonstrated that the dynamic trafficking of Arr2 into the phototransducing compartment, the rhabdomere, required the eye-enriched myosin III, NINAC. We showed that defects in ninaC resulted in a long-term adaptation phenotype similar to that which occurred in arr2 mutants. The interaction between Arr2 and NINAC was PI dependent and NINAC bound directly to PIs. These data demonstrate that the light-dependent translocation of Arr2 into the rhabdomeres requires PI-mediated interactions between Arr2 and the NINAC myosin III.
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Affiliation(s)
- Seung-Jae Lee
- Department of Biological Chemistry, The Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
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34
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Lee SJ, Xu H, Montell C. Rhodopsin kinase activity modulates the amplitude of the visual response in Drosophila. Proc Natl Acad Sci U S A 2004; 101:11874-9. [PMID: 15289614 PMCID: PMC511067 DOI: 10.1073/pnas.0402205101] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
A feature shared between Drosophila rhodopsin and nearly all other G protein-coupled receptors is agonist-dependent protein phosphorylation. Despite extensive analyses of Drosophila phototransduction, the identity and function of the rhodopsin kinase (RK) have been elusive. Here, we provide evidence that G protein-coupled receptor kinase 1 (GPRK1), which is most similar to the beta-adrenergic receptor kinases, G protein-coupled receptor kinase 2 (GRK2) and GRK3, is the fly RK. We show that GPRK1 is enriched in photoreceptor cells, associates with the major Drosophila rhodopsin, Rh1, and phosphorylates the receptor. As is the case with mammalian GRK2 and GRK3, Drosophila GPRK1 includes a C-terminal pleckstrin homology domain, which binds to phosphoinositides and the Gbetagamma subunit. To address the role of GPRK1, we generated transgenic flies that expressed higher and lower levels of RK activity. Those flies with depressed levels of RK activity displayed a light response with a much larger amplitude than WT. Conversely, the amplitude of the light response was greatly suppressed in transgenic flies expressing abnormally high levels of RK activity. These data point to an evolutionarily conserved role for GPRK1 in modulating the amplitude of the visual response.
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Affiliation(s)
- Seung-Jae Lee
- Department of Biological Chemistry, The Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
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35
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Yoo JH, Cheong MS, Park CY, Moon BC, Kim MC, Kang YH, Park HC, Choi MS, Lee JH, Jung WY, Yoon HW, Chung WS, Lim CO, Lee SY, Cho MJ. Regulation of the Dual Specificity Protein Phosphatase, DsPTP1, through Interactions with Calmodulin. J Biol Chem 2004; 279:848-58. [PMID: 14570888 DOI: 10.1074/jbc.m310709200] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Reversible phosphorylation is a key mechanism for the control of intercellular events in eukaryotic cells. In animal cells, Ca2+/CaM-dependent protein phosphorylation and dephosphorylation are implicated in the regulation of a number of cellular processes. However, little is known on the functions of Ca2+/CaM-dependent protein kinases and phosphatases in Ca2+ signaling in plants. From an Arabidopsis expression library, we isolated cDNA encoding a dual specificity protein phosphatase 1, which is capable of hydrolyzing both phosphoserine/threonine and phosphotyrosine residues of the substrates. Using a gel overlay assay, we identified two Ca2+-dependent CaM binding domains (CaMBDI in the N terminus and CaMBDII in the C terminus). Specific binding of CaM to two CaMBD was confirmed by site-directed mutagenesis, a gel mobility shift assay, and a competition assay using a Ca2+/CaM-dependent enzyme. At increasing concentrations of CaM, the biochemical activity of dual specificity protein phosphatase 1 on the p-nitrophenyl phosphate (pNPP) substrate was increased, whereas activity on the phosphotyrosine of myelin basic protein (MBP) was inhibited. Our results collectively indicate that calmodulin differentially regulates the activity of protein phosphatase, dependent on the substrate. Based on these findings, we propose that the Ca2+ signaling pathway is mediated by CaM cross-talks with a protein phosphorylation signal pathway in plants via protein dephosphorylation.
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Affiliation(s)
- Jae Hyuk Yoo
- Division of Applied Life Science, Plant Molecular Biology and Biotechnology Research Center, Gyeongsang National University, Jinju 660-701, Korea
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36
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Oberwinkler J. Calcium homeostasis in fly photoreceptor cells. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2003; 514:539-83. [PMID: 12596943 DOI: 10.1007/978-1-4615-0121-3_32] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/05/2022]
Abstract
In fly photoreceptor cells, two processes dominate the Ca2+ homeostasis: light-induced Ca2+ influx through members of the TRP family of ion channels, and Ca2+ extrusion by Na+/Ca2+ exchange. Ca2+ release from intracellular stores is quantitatively insignificant. Both, the light-activated channels and the Ca2+-extruding exchangers are located in or close to the rhabdomeric microvilli, small protrusions of the plasma membrane. The microvilli also contain the molecular machinery necessary for generating quantum bumps, short electrical responses caused by the absorption of a single photon. Due to this anatomical arrangement, the light-induced Ca2+ influx results in two separate Ca2+ signals that have different functions: a global, homogeneous increase of the Ca2+ concentration in the cell body, and rapid but large amplitude Ca2+ transients in the microvilli. The global rise of the Ca2+ concentration mediates light adaptation, via regulatory actions on the phototransduction cascade, the voltage-gated K+ channels and small pigment granules controlling the light intensity. The local Ca2+ transients in the microvilli are responsible for shaping the quantum bumps into fast, all-or-nothing events. They achieve this by facilitating strongly the phototransduction cascade at early stages ofthe light response and subsequently inhibiting it. Many molecular targets of these feedback mechanisms have been identified and characterized due to the availability of numerous Drosophila mutant showing defects in the phototransduction.
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37
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Lee SJ, Xu H, Kang LW, Amzel LM, Montell C. Light adaptation through phosphoinositide-regulated translocation of Drosophila visual arrestin. Neuron 2003; 39:121-32. [PMID: 12848937 DOI: 10.1016/s0896-6273(03)00390-8] [Citation(s) in RCA: 91] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Photoreceptor cells adapt to bright or continuous light, although the molecular mechanisms underlying this phenomenon are incompletely understood. Here, we report a mechanism of light adaptation in Drosophila, which is regulated by phosphoinositides (PIs). We found that light-dependent translocation of arrestin was defective in mutants that disrupt PI metabolism or trafficking. Arrestin bound to PIP(3) in vitro, and mutation of this site delayed arrestin shuttling and resulted in defects in the termination of the light response, which is normally accelerated by prior exposure to light. Disruption of the arrestin/PI interaction also suppressed retinal degeneration caused by excessive endocytosis of rhodopsin/arrestin complexes. These findings indicate that light-dependent trafficking of arrestin is regulated by direct interaction with PIs and is required for light adaptation. Since phospholipase C activity is required for activation of Drosophila phototransduction, these data point to a dual role of PIs in phototransduction.
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Affiliation(s)
- Seung-Jae Lee
- Department of Biological Chemistry, The Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
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38
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Klee CB, Means AR. Keeping up with calcium: conference on calcium-binding proteins and calcium function in health and disease. EMBO Rep 2002; 3:823-7. [PMID: 12223462 PMCID: PMC1084235 DOI: 10.1093/embo-reports/kvf182] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Affiliation(s)
- Claude B Klee
- Laboratory of Biochemistry, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892-4255, USA
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39
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Kutuzov MA, Solov'eva OV, Andreeva AV, Bennett N. Protein Ser/Thr phosphatases PPEF interact with calmodulin. Biochem Biophys Res Commun 2002; 293:1047-52. [PMID: 12051765 DOI: 10.1016/s0006-291x(02)00338-8] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Regulation of protein dephosphorylation by cytoplasmic Ca(2+) levels and calmodulin (CaM) is well established and considered to be mediated solely by calcineurin. Yet, recent identification of protein phosphatases with EF-hand domains (PPEF/rdgC) point to the existence of another group of Ca(2+)-dependent protein phosphatases. We have recently hypothesised that PPEF/rdgC phosphatases might possess CaM-binding sites of the IQ-type in their N-terminal domains. We now employed yeast two-hybrid system and surface plasmon resonance (SPR) to test this hypothesis. We found that entire human PPEF2 interacts with CaM in the in vivo tests and that its N-terminal domain binds to CaM in a Ca(2+)-dependent manner with nanomolar affinity in vitro. The fragments corresponding to the second exons of PPEF1 and PPEF2, containing the IQ motifs, are sufficient for specific Ca(2+)-dependent interaction with CaM both in vivo and in vitro. These findings demonstrate the existence of mammalian CaM-binding protein Ser/Thr phosphatases distinct from calcineurin and suggest that the activity of PPEF phosphatases may be controlled by Ca(2+) in a dual way: via C-terminal Ca(2+)-binding domain and via interaction of the N-terminal domain with CaM.
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Affiliation(s)
- Mikhail A Kutuzov
- Laboratoire de Biophysique Moléculaire et Cellulaire URA CNRS No. 520, Département de Biologie Moléculaire et Structurale, CEA-Grenoble, 38054 Grenoble cedex 9, France.
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