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Johnson N, Vilardi F, Lang S, Leznicki P, Zimmermann R, High S. TRC40 can deliver short secretory proteins to the Sec61 translocon. J Cell Sci 2012; 125:3612-20. [PMID: 22505607 PMCID: PMC3445324 DOI: 10.1242/jcs.102608] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Whilst the co-translational translocation of nascent proteins across the mammalian endoplasmic reticulum (ER) is well defined, the capacity of this organelle for post-translational translocation is poorly delineated. Here we identify two human secretory protein precursors, apelin and statherin, as bona fide substrates for post-translational translocation across the ER membrane. Further studies, in combination with Hyalophora cecropia preprocecropin A (ppcecA), show that all three proteins bind to TRC40 and can utilise this component for their delivery to the ER membrane in a well-established in vitro system. However, ppcecA is not an obligate TRC40 substrate, and it can also be delivered to the ER by an alternative TRC40-independent pathway. Upon arrival at the ER membrane, these short secretory proteins appear to be ubiquitously transported across the ER membrane through the Sec61 translocon, apparently irrespective of their delivery route. We speculate that the post-translational translocation of secretory proteins in higher eukaryotes is more prevalent than previously acknowledged.
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Affiliation(s)
- Nicholas Johnson
- Faculty of Life Sciences, The University of Manchester, Michael Smith Building, Oxford Road, Manchester M13 9PT, UK
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52
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Nandrot EF, Silva KE, Scelfo C, Finnemann SC. Retinal pigment epithelial cells use a MerTK-dependent mechanism to limit the phagocytic particle binding activity of αvβ5 integrin. Biol Cell 2012; 104:326-41. [PMID: 22289110 DOI: 10.1111/boc.201100076] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2011] [Accepted: 01/24/2012] [Indexed: 02/06/2023]
Abstract
BACKGROUND INFORMATION αvβ5 integrin and Mer tyrosine kinase (MerTK) receptors reside at the apical surface of the retinal pigment epithelium (RPE) in the eye to promote the diurnal, synchronised phagocytosis of shed photoreceptor outer segment fragments (POS) that is critical for vision. Phagocytosis assays studying RPE cells in culture have defined roles for αvβ5 in POS surface binding and for MerTK in engulfment of bound POS. Both receptors have thus far only been studied separately. It is therefore unknown if αvβ5 integrin activity in POS binding is independent of the engulfment function of RPE cells. This study investigates how increasing αvβ5 receptor levels affect POS binding and internalisation by wild-type (wt), αvβ5- or MerTK-deficient RPE. RESULTS β5 integrin-green fluorescent protein (β5-GFP) fusion proteins formed heterodimeric receptors with endogenous αv integrin subunits at the apical surface of mouse or rat RPE cells that co-immunoprecipitated focal adhesion kinase and redistributed with bound POS such as endogenous αvβ5 receptors. In β5(-/-) RPE cells, de novo formation of αvβ5-GFP receptors restored POS binding and internalisation up to, but not, above wt POS uptake levels. In wt RPE cells, increasing levels of αvβ5 surface receptors by over-expressing β5-GFP only moderately stimulated POS binding, even if POS internalisation was inhibited pharmacologically or by lowering incubation temperatures. In contrast, the same increase in αvβ5 receptor levels dramatically enhanced POS binding of RPE cells lacking MerTK. Furthermore, decreasing MerTK expression by RNA interference increased POS binding to endogenous αvβ5 receptors of wt RPE cells. CONCLUSIONS Expressing β5-GFP is sufficient to reverse phagocytic deficiencies of RPE cells derived from β5(-/-) mice, indicating that these cells do not irreversibly lose other components of the phagocytic machinery. RPE cells expressing the engulfment receptor MerTK control POS binding by limiting activity of endogenous αvβ5 and αvβ5-GFP integrins, although they reside at the apical, phagocytic surface. In contrast, RPE cells permanently or transiently losing MerTK expression lack this regulatory mechanism and bind excess POS via surface αvβ5 receptors. Taken together, these data reveal a novel feedback mechanism that restricts binding of POS to surface αvβ5 integrin receptors in RPE cells.
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Affiliation(s)
- Emeline F Nandrot
- Department of Ophthalmology, Margaret M. Dyson Vision Research Institute, Weill Medical College of Cornell University, New York, NY 10065, USA
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53
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de la Fuente M, Noble DN, Verma S, Nieman MT. Mapping human protease-activated receptor 4 (PAR4) homodimer interface to transmembrane helix 4. J Biol Chem 2012; 287:10414-10423. [PMID: 22318735 DOI: 10.1074/jbc.m112.341438] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Thrombin activates platelets by binding and cleaving protease-activated receptors 1 and 4 (PAR1 and PAR4). Because of the importance of PAR4 activation on platelets in humans and mice and emerging roles for PAR4 in other tissues, experiments were done to characterize the interaction between PAR4 homodimers. Bimolecular fluorescence complementation and bioluminescence resonance energy transfer (BRET) were used to examine the PAR4 homodimer interface. In bimolecular fluorescence complementation experiments, PAR4 formed homodimers that were disrupted by unlabeled PAR4 in a concentration-dependent manner, but not by rhodopsin. In BRET experiments, the PAR4 homodimers showed a specific interaction as indicated by a hyperbolic BRET signal in response to increasing PAR4-GFP expression. PAR4 did not interact with rhodopsin in BRET assays. The threshold maximum BRET signal was disrupted in a concentration-dependent manner by unlabeled PAR4. In contrast, rhodopsin was unable to disrupt the BRET signal, indicating that the disruption of the PAR4 homodimer is not due to nonspecific interactions. A panel of rho-PAR4 chimeras and PAR4 point mutants has mapped the dimer interface to hydrophobic residues in transmembrane helix 4. Finally, mutations that disrupted dimer formation had reduced calcium mobilization in response to the PAR4 agonist peptide. These results link the loss of dimer formation to a loss of PAR4 signaling.
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Affiliation(s)
- María de la Fuente
- Division of Hematolgy/Oncology, Case Western Reserve University, Cleveland, Ohio 44106
| | - Daniel N Noble
- Division of Hematolgy/Oncology, Case Western Reserve University, Cleveland, Ohio 44106
| | - Sheetal Verma
- Division of Hematolgy/Oncology, Case Western Reserve University, Cleveland, Ohio 44106
| | - Marvin T Nieman
- Division of Hematolgy/Oncology, Case Western Reserve University, Cleveland, Ohio 44106; Department of Pharmacology, Case Western Reserve University, Cleveland, Ohio 44106.
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54
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Yu CC, Nandrot EF, Dun Y, Finnemann SC. Dietary antioxidants prevent age-related retinal pigment epithelium actin damage and blindness in mice lacking αvβ5 integrin. Free Radic Biol Med 2012; 52:660-670. [PMID: 22178979 PMCID: PMC3267844 DOI: 10.1016/j.freeradbiomed.2011.11.021] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/12/2011] [Revised: 11/08/2011] [Accepted: 11/14/2011] [Indexed: 10/14/2022]
Abstract
In the aging human eye, oxidative damage and accumulation of pro-oxidant lysosomal lipofuscin cause functional decline of the retinal pigment epithelium (RPE), which contributes to age-related macular degeneration. In mice with an RPE-specific phagocytosis defect due to lack of αvβ5 integrin receptors, RPE accumulation of lipofuscin suggests that the age-related blindness we previously described in this model may also result from oxidative stress. Cellular and molecular targets of oxidative stress in the eye remain poorly understood. Here we identify actin among 4-hydroxynonenal (HNE) adducts formed specifically in β5(-/-) RPE but not in neural retina with age. HNE modification directly correlated with loss of resistance of actin to detergent extraction, suggesting cytoskeletal damage in aging RPE. Dietary enrichment with natural antioxidants, grapes or marigold extract containing macular pigments lutein/zeaxanthin, was sufficient to prevent HNE-adduct formation, actin solubility, lipofuscin accumulation, and age-related cone and rod photoreceptor dysfunction in β5(-/-) mice. Acute generation of HNE adducts directly destabilized actin but not tubulin cytoskeletal elements of RPE cells. These findings identify destabilization of the actin cytoskeleton as a consequence of a physiological, sublethal oxidative burden of RPE cells in vivo that is associated with age-related blindness and that can be prevented by consuming an antioxidant-rich diet.
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Affiliation(s)
- Chia-Chia Yu
- Department of Biological Sciences, Fordham University, Bronx, NY 10458, USA
| | - Emeline F Nandrot
- Institut National de la Santé et de la Recherche Médicale, U968, Paris 75012, France; Institut de la Vision, Université Pierre et Marie Curie-Paris 06, UMR_S 968, Paris 75012, France; Centre National de la Recherche Scientifique, UMR_7210, Paris 75012, France
| | - Ying Dun
- Department of Biological Sciences, Fordham University, Bronx, NY 10458, USA
| | - Silvia C Finnemann
- Department of Biological Sciences, Fordham University, Bronx, NY 10458, USA.
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55
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Mao Y, Finnemann SC. Essential diurnal Rac1 activation during retinal phagocytosis requires αvβ5 integrin but not tyrosine kinases focal adhesion kinase or Mer tyrosine kinase. Mol Biol Cell 2012; 23:1104-14. [PMID: 22262456 PMCID: PMC3302737 DOI: 10.1091/mbc.e11-10-0840] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
Diurnal phagocytosis of shed photoreceptor outer-segment particles by retinal pigment epithelial (RPE) cells belongs to a group of conserved clearance mechanisms employing αv integrins upstream of tyrosine kinases and Rho GTPases. In this study, we tested the interdependence of the tyrosine kinases focal adhesion kinase (FAK) and Mer tyrosine kinase (MerTK) and Rho GTPases during engulfment. RPE cells activated and redistributed Rac1, but not RhoA or Cdc42, during phagocytosis. Toxin B, overexpression of dominant-negative Rac1, or decreasing Rac1 expression prevented particle engulfment. Fluorescence microscopy showed that Rac1 inhibition had no obvious effect on F-actin arrangement in resting RPE but prevented recruitment of F-actin to surface-bound phagocytic particles. Quantification of active GTP-Rac1 in wild-type and mutant RPE in culture and in vivo revealed that Rac1 activation during phagocytosis requires αvβ5 integrin and its ligand milk fat globule EGF factor-8 (MFG-E8) but not the receptor tyrosine kinase MerTK. Abolishing tyrosine kinase signaling downstream of αvβ5 toward MerTK by inhibiting FAK specifically or tyrosine kinases generally neither prevented Rac1 activation nor F-actin recruitment during phagocytosis. Likewise, inhibiting Rac1 had no effect on FAK or MerTK activation. We conclude that MerTK activation via FAK and F-actin recruitment via Rac1 both require MFG-E8-ligated αvβ5 integrin. Both pathways are independently activated and required for clearance phagocytosis.
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Affiliation(s)
- Yingyu Mao
- Department of Biological Sciences, Fordham University, Bronx, NY 10458, USA
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56
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Abstract
Counting rhodopsin-positive phagosomes residing in the retinal pigment epithelium (RPE) in the eye at different times of day allows a quantitative assessment of engulfment and digestion phases of diurnal RPE phagocytosis, which efficiently clears shed photoreceptor outer segment fragments (POS) from the neural retina. Comparing such activities among age- and background-matched experimental wild-type and mutant mice or rats serves to identify roles for specific proteins in the phagocytic process. Here, we describe experimental procedures for mouse eye harvest, embedding, sectioning, immunofluorescence labeling of rod POS phagosomes in RPE cells in sagittal eye sections, imaging of POS phagosomes in the RPE by laser scanning confocal microscopy, and POS quantification.
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57
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Salom D, Cao P, Sun W, Kramp K, Jastrzebska B, Jin H, Feng Z, Palczewski K. Heterologous expression of functional G-protein-coupled receptors in Caenorhabditis elegans. FASEB J 2011; 26:492-502. [PMID: 22090314 DOI: 10.1096/fj.11-197780] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
New strategies for expression, purification, functional characterization, and structural determination of membrane-spanning G-protein-coupled receptors (GPCRs) are constantly being developed because of their importance to human health. Here, we report a Caenorhabditis elegans heterologous expression system able to produce milligram amounts of functional native and engineered GPCRs. Both bovine opsin [(b)opsin] and human adenosine A(2A) subtype receptor [(h)A(2A)R] expressed in neurons or muscles of C. elegans were localized to cell membranes. Worms expressing these GPCRs manifested changes in motor behavior in response to light and ligands, respectively. With a newly devised protocol, 0.6-1 mg of purified homogenous 9-cis-retinal-bound bovine isorhodopsin [(b)isoRho] and ligand-bound (h)A(2A)R were obtained from C. elegans from one 10-L fermentation at low cost. Purified recombinant (b)isoRho exhibited its signature absorbance spectrum and activated its cognate G-protein transducin in vitro at a rate similar to native rhodopsin (Rho) obtained from bovine retina. Generally high expression levels of 11 native and mutant GPCRs demonstrated the potential of this C. elegans system to produce milligram quantities of high-quality GPCRs and possibly other membrane proteins suitable for detailed characterization.
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58
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Sakami S, Maeda T, Bereta G, Okano K, Golczak M, Sumaroka A, Roman AJ, Cideciyan AV, Jacobson SG, Palczewski K. Probing mechanisms of photoreceptor degeneration in a new mouse model of the common form of autosomal dominant retinitis pigmentosa due to P23H opsin mutations. J Biol Chem 2011; 286:10551-67. [PMID: 21224384 DOI: 10.1074/jbc.m110.209759] [Citation(s) in RCA: 209] [Impact Index Per Article: 16.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Rhodopsin, the visual pigment mediating vision under dim light, is composed of the apoprotein opsin and the chromophore ligand 11-cis-retinal. A P23H mutation in the opsin gene is one of the most prevalent causes of the human blinding disease, autosomal dominant retinitis pigmentosa. Although P23H cultured cell and transgenic animal models have been developed, there remains controversy over whether they fully mimic the human phenotype; and the exact mechanism by which this mutation leads to photoreceptor cell degeneration remains unknown. By generating P23H opsin knock-in mice, we found that the P23H protein was inadequately glycosylated with levels 1-10% that of wild type opsin. Moreover, the P23H protein failed to accumulate in rod photoreceptor cell endoplasmic reticulum but instead disrupted rod photoreceptor disks. Genetically engineered P23H mice lacking the chromophore showed accelerated photoreceptor cell degeneration. These results indicate that most synthesized P23H protein is degraded, and its retinal cytotoxicity is enhanced by lack of the 11-cis-retinal chromophore during rod outer segment development.
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Affiliation(s)
- Sanae Sakami
- Department of Pharmacology, Case Western Reserve University, Cleveland, Ohio 44106, USA
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59
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Zhuang X, Adipietro KA, Datta S, Northup JK, Ray K. Rab1 small GTP-binding protein regulates cell surface trafficking of the human calcium-sensing receptor. Endocrinology 2010; 151:5114-23. [PMID: 20861236 PMCID: PMC2954715 DOI: 10.1210/en.2010-0422] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
The human calcium-sensing receptor (hCaR) is a family-3/C G-protein-coupled receptor that regulates Ca(2+) homeostasis by controlling parathyroid hormone secretion. Here we investigated the role of Rab1, a small GTP-binding protein that specifically regulates protein transport from the endoplasmic reticulum to the Golgi, in cell surface transport of the hCaR. Cell surface expression of hCaR transiently expressed in human embryonic kidney 293 cells was strongly augmented by coexpression of Rab1 and attenuated by disruption of endogenous Rab1 function by expression of the dominant-negative Rab1N124I mutant or depletion of Rab1 with small interfering RNA. Rab1N124I expression also partially attenuated cell surface expression and signaling response to gain-of-function mutants of hCaR with truncated carboxyl-terminal sequences at positions 895 and 903. These carboxyl-tail truncations are similar to a deletion between residues S895 and V1075 found in a patient family causing autosomal dominant hypocalcemia. In addition, coexpression with wild-type Rab1 increased cell surface expression of the loss-of-function missense mutation R185Q, located on the hCaR amino-terminal extracellular ligand-binding domain (ECD), which causes familial hypocalciuric hypercalcemia. Truncated hCaR variants containing either the ECD with the first transmembrane helix or only the ECD also display Rab1-dependent cell surface expression or secretion into the culture medium, respectively. These data reveal a role for Rab1 in hCaR trafficking from the endoplasmic reticulum to the Golgi that regulates receptor cell surface expression and thereby cell signaling responsiveness to extracellular calcium.
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Affiliation(s)
- Xiaolei Zhuang
- Laboratory of Cellular Biology, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, Maryland 20892, USA
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60
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Katti C, Kempler K, Porter ML, Legg A, Gonzalez R, Garcia-Rivera E, Dugger D, Battelle BA. Opsin co-expression in Limulus photoreceptors: differential regulation by light and a circadian clock. ACTA ACUST UNITED AC 2010; 213:2589-601. [PMID: 20639420 DOI: 10.1242/jeb.043869] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
A long-standing concept in vision science has held that a single photoreceptor expresses a single type of opsin, the protein component of visual pigment. However, the number of examples in the literature of photoreceptors from vertebrates and invertebrates that break this rule is increasing. Here, we describe a newly discovered Limulus opsin, Limulus opsin5, which is significantly different from previously characterized Limulus opsins, opsins1 and 2. We show that opsin5 is co-expressed with opsins1 and 2 in Limulus lateral and ventral eye photoreceptors and provide the first evidence that the expression of co-expressed opsins can be differentially regulated. We show that the relative levels of opsin5 and opsin1 and 2 in the rhabdom change with a diurnal rhythm and that their relative levels are also influenced by the animal's central circadian clock. An analysis of the sequence of opsin5 suggests it is sensitive to visible light (400-700 nm) but that its spectral properties may be different from that of opsins1 and 2. Changes in the relative levels of these opsins may underlie some of the dramatic day-night changes in Limulus photoreceptor function and may produce a diurnal change in their spectral sensitivity.
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Affiliation(s)
- C Katti
- Whitney Laboratory for Marine Bioscience, University of Florida, 9505 Ocean Shore Boulevard, St Augustine, FL 32080, USA
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61
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Concepcion F, Chen J. Q344ter mutation causes mislocalization of rhodopsin molecules that are catalytically active: a mouse model of Q344ter-induced retinal degeneration. PLoS One 2010; 5:e10904. [PMID: 20532191 PMCID: PMC2880002 DOI: 10.1371/journal.pone.0010904] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2010] [Accepted: 04/22/2010] [Indexed: 11/29/2022] Open
Abstract
Q344ter is a naturally occurring rhodopsin mutation in humans that causes autosomal dominant retinal degeneration through mechanisms that are not fully understood, but are thought to involve an early termination that removed the trafficking signal, QVAPA, leading to its mislocalization in the rod photoreceptor cell. To better understand the disease mechanism(s), transgenic mice that express Q344ter were generated and crossed with rhodopsin knockout mice. Dark-reared Q344ter(rho+/-) mice exhibited retinal degeneration, demonstrating that rhodopsin mislocalization caused photoreceptor cell death. This degeneration is exacerbated by light-exposure and is correlated with the activation of transducin as well as other G-protein signaling pathways. We observed numerous sub-micrometer sized vesicles in the inter-photoreceptor space of Q344ter(rho+/-) and Q344ter(rho-/-) retinas, similar to that seen in another rhodopsin mutant, P347S. Whereas light microscopy failed to reveal outer segment structures in Q344ter(rho-/-) rods, shortened and disorganized rod outer segment structures were visible using electron microscopy. Thus, some Q344ter molecules trafficked to the outer segment and formed disc structures, albeit inefficiently, in the absence of full length wildtype rhodopsin. These findings helped to establish the in vivo role of the QVAPA domain as well as the pathways leading to Q344ter-induced retinal degeneration.
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Affiliation(s)
- Francis Concepcion
- Department of Cell and Neurobiology and Department of Ophthalmology, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, California, United States of America
| | - Jeannie Chen
- Department of Cell and Neurobiology and Department of Ophthalmology, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, California, United States of America
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Leznicki P, Clancy A, Schwappach B, High S. Bat3 promotes the membrane integration of tail-anchored proteins. J Cell Sci 2010; 123:2170-8. [PMID: 20516149 DOI: 10.1242/jcs.066738] [Citation(s) in RCA: 107] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The membrane integration of tail-anchored proteins at the endoplasmic reticulum (ER) is post-translational, with different tail-anchored proteins exploiting distinct cytosolic factors. For example, mammalian TRC40 has a well-defined role during delivery of tail-anchored proteins to the ER. Although its Saccharomyces cerevisiae equivalent, Get3, is known to function in concert with at least four other components, Get1, Get2, Get4 and Get5 (Mdy2), the role of additional mammalian proteins during tail-anchored protein biogenesis is unclear. To this end, we analysed the cytosolic binding partners of Sec61beta, a well-defined substrate of TRC40, and identified Bat3 as a previously unknown interacting partner. Depletion of Bat3 inhibits the membrane integration of Sec61beta, but not of a second, TRC40-independent, tail-anchored protein, cytochrome b5. Thus, Bat3 influences the in vitro membrane integration of tail-anchored proteins using the TRC40 pathway. When expressed in Saccharomyces cerevisiae lacking a functional GET pathway for tail-anchored protein biogenesis, Bat3 associates with the resulting cytosolic pool of non-targeted chains and diverts it to the nucleus. This Bat3-mediated mislocalisation is not dependent upon Sgt2, a recently identified component of the yeast GET pathway, and we propose that Bat3 either modulates the TRC40 pathway in higher eukaryotes or provides an alternative fate for newly synthesised tail-anchored proteins.
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Affiliation(s)
- Pawel Leznicki
- Faculty of Life Sciences, University of Manchester, Oxford Road, Manchester, M13 9PT, UK
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63
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Golczak M, Kiser PD, Lodowski DT, Maeda A, Palczewski K. Importance of membrane structural integrity for RPE65 retinoid isomerization activity. J Biol Chem 2010; 285:9667-9682. [PMID: 20100834 PMCID: PMC2843217 DOI: 10.1074/jbc.m109.063941] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2009] [Revised: 12/21/2009] [Indexed: 01/17/2023] Open
Abstract
Regeneration of visual chromophore in the vertebrate visual cycle involves the retinal pigment epithelium-specific protein RPE65, the key enzyme catalyzing the cleavage and isomerization of all-trans-retinyl fatty acid esters to 11-cis-retinol. Although RPE65 has no predicted membrane spanning domains, this protein predominantly associates with microsomal fractions isolated from bovine retinal pigment epithelium (RPE). We have re-examined the nature of RPE65 interactions with native microsomal membranes by using extraction and phase separation experiments. We observe that hydrophobic interactions are the dominant forces that promote RPE65 association with these membranes. These results are consistent with the crystallographic model of RPE65, which features a large lipophilic surface that surrounds the entrance to the catalytic site of this enzyme and likely interacts with the hydrophobic core of the endoplasmic reticulum membrane. Moreover, we report a critical role for phospholipid membranes in preserving the retinoid isomerization activity and physical properties of RPE65. Isomerase activity measured in bovine RPE was highly sensitive to phospholipase A(2) treatment, but the observed decline in 11-cis-retinol production did not directly reflect inhibition by products of lipid hydrolysis. Instead, a direct correlation between the kinetics of phospholipid hydrolysis and retinoid isomerization suggests that the lipid membrane structure is critical for RPE65 enzymatic activity. We also provide evidence that RPE65 operates in a multiprotein complex with retinol dehydrogenase 5 and retinal G protein-coupled receptor in RPE microsomes. Modifications in the phospholipid environment affecting interactions with these protein components may be responsible for the alterations in retinoid metabolism observed in phospholipid-depleted RPE microsomes. Thus, our results indicate that the enzymatic activity of native RPE65 strongly depends on its membrane binding and phospholipid environment.
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Affiliation(s)
| | | | | | - Akiko Maeda
- Ophthalmology and Visual Sciences, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106
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64
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Is the lifetime of light-stimulated cGMP phosphodiesterase regulated by recoverin through its regulation of rhodopsin phosphorylation? Behav Brain Sci 2010. [DOI: 10.1017/s0140525x00039522] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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65
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66
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67
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68
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69
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The role of rhodopsin glycosylation in protein folding, trafficking, and light-sensitive retinal degeneration. J Neurosci 2009; 29:15145-54. [PMID: 19955366 DOI: 10.1523/jneurosci.4259-09.2009] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Several mutations in the N terminus of the G-protein-coupled receptor rhodopsin disrupt NXS/T consensus sequences for N-linked glycosylation (located at N2 and N15) and cause sector retinitis pigmentosa in which the inferior retina preferentially degenerates. Here we examined the role of rhodopsin glycosylation in biosynthesis, trafficking, and retinal degeneration (RD) using transgenic Xenopus laevis expressing glycosylation-defective human rhodopsin mutants. Although mutations T4K and T4N caused RD, N2S and T4V did not, demonstrating that glycosylation at N2 was not required for photoreceptor viability. In contrast, similar mutations eliminating glycosylation at N15 (N15S and T17M) caused rod death. Expression of T17M was more toxic than T4K to transgenic photoreceptors, further suggesting that glycosylation at N15 plays a more important physiological role than glycosylation at N2. Together, these results indicate that the structure of the rhodopsin N terminus must be maintained by an appropriate amino acid sequence surrounding N2 and may require a carbohydrate moiety at N15. The mutant rhodopsins were rendered less toxic in their dark inactive states, because RD was abolished or significantly reduced when transgenic tadpoles expressing T4K, T17M, and N2S/N15S were protected from light exposure. Regardless of their effect on rod viability, all of the mutants primarily localized to the outer segment and Golgi and showed little or no endoplasmic reticulum accumulation. Thus, glycosylation was not crucial for rhodopsin biosynthesis or trafficking. Interestingly, expression of similar bovine rhodopsin mutants did not cause rod cell death, possibly attributable to greater stability of bovine rhodopsin.
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72
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Ray-Sinha A, Cross BC, Mironov A, Wiertz E, High S. Endoplasmic reticulum-associated degradation of a degron-containing polytopic membrane protein. Mol Membr Biol 2009; 26:448-64. [PMID: 19878048 PMCID: PMC3428838 DOI: 10.3109/09687680903333839] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
The presence of two basic amino acids strategically located within a single spanning transmembrane region has previously been shown to act as a signal for the endoplasmic reticulum associated degradation (ERAD) of several polypeptides. In contrast, the functionality of this degron motif within the context of a polytopic membrane protein has not been established. Using opsin as a model system, we have investigated the consequences of inserting the degron motif in the first of its seven transmembrane (TM) spans. Whilst these basic residue reduce the binding of the targeting factor, signal recognition particle, to the first TM span, this has no effect on membrane integration in vitro or in vivo. This most likely reflects the presence of multiple TM spans that can act as targeting signals within in the nascent opsin chain. We find that the degron motif leads to the efficient retention of mutant opsin chains at the endoplasmic reticulum. The mutant opsin polypeptides are degraded via a proteasomal pathway that involves the actions of the E3 ubiquitin ligase HRD1. In contrast, wild-type opsin remains stable for a prolonged period even when artificially accumulated at the endoplasmic reticulum. We conclude that a single dibasic degron motif is sufficient to initiate both the ER retention and subsequent degradation of ospin via an ERAD pathway.
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Affiliation(s)
| | - Benedict C.S. Cross
- Faculty of Life Sciences, University of Manchester, Michael Smith Building, Oxford Road, Manchester M13 9PT, UK
| | - Aleksandr Mironov
- Faculty of Life Sciences, University of Manchester, Michael Smith Building, Oxford Road, Manchester M13 9PT, UK
| | | | - Stephen High
- Faculty of Life Sciences, University of Manchester, Michael Smith Building, Oxford Road, Manchester M13 9PT, UK
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73
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Katti C, Dalal JS, Dosé AC, Burnside B, Battelle BA. Cloning and distribution of myosin 3B in the mouse retina: differential distribution in cone outer segments. Exp Eye Res 2009; 89:224-37. [PMID: 19332056 DOI: 10.1016/j.exer.2009.03.011] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2009] [Revised: 03/17/2009] [Accepted: 03/18/2009] [Indexed: 11/30/2022]
Abstract
Class III myosins are important for the function and survival of photoreceptors and ciliary hair cells. Although vertebrates possess two class III myosin genes, myo3A and myo3B, recent studies have focused on Myo3A because mutations in the human gene are implicated in progressive hearing loss. Myo3B may compensate for defects in Myo3A, yet little is known about its distribution and function. This study focuses on Myo3B expression in the mouse retina. We cloned two variants of myo3B from mouse retina and determined that they are expressed early in retinal development. In this study we show for the first time in a mammal that both Myo3B and Myo3A proteins are present in inner segments of all photoreceptors. Myo3B is also present in outer segments of S opsin-immunoreactive cones but not M opsin dominant cones. Myo3B is also detected in rare cells of the inner nuclear layer and some ganglion cells. Myo3B may have diverse roles in retinal neurons. In photoreceptor inner segments Myo3B is positioned appropriately to prevent photoreceptor loss of function caused by Myo3A defects.
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Affiliation(s)
- Christiana Katti
- Department of Neuroscience and Whitney Laboratory for Marine Bioscience, University of Florida, St Augustine, FL 32080, USA
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74
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Salom D, Wu N, Sun W, Dong Z, Palczewski K, Jordan S, Salon JA. Heterologous expression and purification of the serotonin type 4 receptor from transgenic mouse retina. Biochemistry 2009; 47:13296-307. [PMID: 19053287 DOI: 10.1021/bi8018527] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Recent breakthroughs in the solution of X-ray structures for G protein-coupled receptors (GPCRs) with diffusible ligands have employed extensively mutated or recombined receptor fusion proteins heterologously expressed in conventional in vitro cell-based systems. While these advances now show that crystallization of non-rhodopsin members of this superfamily can be accomplished, the use of radically modified proteins may limit the relevance of the derived structures for precision-guided drug design. To better enable the study of native GPCR structures, we report here efforts to engineer an in vivo expression system that harnesses the photoreceptor system of the retina to express heterologous GPCRs with native human sequences in a biochemically homogeneous and pharmacologically functional conformation. As an example, we show that the human 5HT4 receptor, when placed under the influence of the mouse opsin promoter and an opsin rod outer segment (ROS) targeting sequence, localized to ROS of transgenic mouse retina. The resulting receptor protein was uniformly glycosylated and pharmacologically intact as demonstrated by immunoblotting and radioligand binding assays. Upon solubilization, the retinal 5HT4 receptor retained the binding properties of its initial state in retinal membranes. With the engineered T7 monoclonal epitope sequence, the solubilized receptor was easily purified by one-step immunoaffinity chromatography and the purified receptor in detergent solution preserved its ligand binding properties. This expression method may prove generally useful for generating functional, high-quality GPCR protein.
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Affiliation(s)
- David Salom
- Polgenix Inc., 11000 Cedar Avenue, Suite 260, Cleveland, Ohio 44106, USA
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75
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Wang Q, Zhang X, Zhang L, He F, Zhang G, Jamrich M, Wensel TG. Activation-dependent hindrance of photoreceptor G protein diffusion by lipid microdomains. J Biol Chem 2008; 283:30015-24. [PMID: 18713731 DOI: 10.1074/jbc.m803953200] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
The dynamics of G protein-mediated signal transduction depend on the two-dimensional diffusion of membrane-bound G proteins and receptors, which has been suggested to be rate-limiting for vertebrate phototransduction, a highly amplified G protein-coupled signaling pathway. Using fluorescence recovery after photobleaching (FRAP), we measured the diffusion of the G protein transducin alpha-subunit (Galpha(t)) and the G protein-coupled receptor rhodopsin on disk membranes of living rod photoreceptors from transgenic Xenopus laevis. Treatment with either methyl-beta-cyclodextrin or filipin III to disrupt cholesterol-containing lipid microdomains dramatically accelerated diffusion of Galpha(t) in its GTP-bound state and of the rhodopsin-Galphabetagamma(t) complex but not of rhodopsin or inactive GDP-bound Galphabetagamma. These results imply an activity-dependent sequestration of G proteins into cholesterol-dependent lipid microdomains, which limits diffusion and exclude the majority of free rhodopsin and the free G protein heterotrimer. Our data offer a novel demonstration of lipid microdomains in the internal membranes of living sensory neurons.
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Affiliation(s)
- Qiong Wang
- Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, Texas 77030, USA
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76
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Favaloro V, Spasic M, Schwappach B, Dobberstein B. Distinct targeting pathways for the membrane insertion of tail-anchored (TA) proteins. J Cell Sci 2008; 121:1832-40. [PMID: 18477612 PMCID: PMC2727622 DOI: 10.1242/jcs.020321] [Citation(s) in RCA: 112] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
Tail-anchored (TA) proteins are characterised by a C-terminal transmembrane region that mediates post-translational insertion into the membrane of the endoplasmic reticulum (ER). We have investigated the requirements for membrane insertion of three TA proteins, RAMP4, Sec61beta and cytocrome b5. We show here that newly synthesised RAMP4 and Sec61beta can accumulate in a cytosolic, soluble complex with the ATPase Asna1 before insertion into ER-derived membranes. Membrane insertion of these TA proteins is stimulated by ATP, sensitive to redox conditions and blocked by alkylation of SH groups by N-ethylmaleimide (NEM). By contrast, membrane insertion of cytochrome b5 is not found to be mediated by Asna1, not stimulated by ATP and not affected by NEM or an oxidative environment. The Asna1-mediated pathway of membrane insertion of RAMP4 and Sec61beta may relate to functions of these proteins in the ER stress response.
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Affiliation(s)
- Vincenzo Favaloro
- Zentrum für Molekulare Biologie der Universität Heidelberg (ZMBH), DKFZ-ZMBH Allianz, Heidelberg, Germany
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77
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Specific transmembrane segments are selectively delayed at the ER translocon during opsin biogenesis. Biochem J 2008; 411:495-506. [PMID: 18248332 DOI: 10.1042/bj20071597] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
A site-specific cross-linking approach was used to study the integration of TM (transmembrane) segments 4-7 of the polytopic membrane protein, opsin, at the ER (endoplasmic reticulum). We found that although TM4 exits the ER translocon rapidly, TM segments 5, 6 and 7 are all retained at the translocon until opsin biosynthesis is terminated. Furthermore, although artificial extension of the nascent chain is not sufficient to release the C-terminal region of opsin from the translocon, substitution of the native TM segment 7 with a more hydrophobic TM segment results in its rapid lateral exit into the lipid bilayer. We conclude that the intrinsic properties of a TM segment determine the timing of its membrane integration rather than its relative location within the polypeptide chain. A pronounced and prolonged association of opsin TM5 with the translocon-associated component PAT-10 was also observed, suggesting that PAT-10 may facilitate the assembly of distinct opsin subdomains during membrane integration. The results of the present study strongly support a model in which the ER translocon co-ordinates the integration of selected TM segments in response to the specific requirements of the precursor being synthesized.
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78
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Snelson CD, Santhakumar K, Halpern ME, Gamse JT. Tbx2b is required for the development of the parapineal organ. Development 2008; 135:1693-702. [PMID: 18385257 DOI: 10.1242/dev.016576] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Structural differences between the left and right sides of the brain exist throughout the vertebrate lineage. By studying the zebrafish pineal complex, which exhibits notable asymmetries, both the genes and the cell movements that result in left-right differences can be characterized. The pineal complex consists of the midline pineal organ and the left-sided parapineal organ. The parapineal is responsible for instructing the asymmetric architecture of the bilateral habenulae, the brain nuclei that flank the pineal complex. Using in vivo time-lapse confocal microscopy, we find that the cells that form the parapineal organ migrate as a cluster of cells from the pineal complex anlage to the left side of the brain. In a screen for mutations that disrupted brain laterality, we identified a nonsense mutation in the T-box2b (tbx2b) gene, which encodes a transcription factor expressed in the pineal complex anlage. The tbx2b mutant makes fewer parapineal cells, and they remain as individuals near the midline rather than migrating leftward as a group. The reduced number and incorrect placement of parapineal cells result in symmetric development of the adjacent habenular nuclei. We conclude that tbx2b functions to specify the correct number of parapineal cells and to regulate their asymmetric migration.
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Affiliation(s)
- Corey D Snelson
- Department of Biological Sciences, Vanderbilt University, VU Station B, Box 35-1634, Nashville, TN 37235, USA
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79
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Redundant and unique roles of retinol dehydrogenases in the mouse retina. Proc Natl Acad Sci U S A 2007; 104:19565-70. [PMID: 18048336 DOI: 10.1073/pnas.0707477104] [Citation(s) in RCA: 87] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Highly abundant short-chain alcohol dehydrogenases (RDHs) in the retina were assumed to be involved in the recycling of 11-cis-retinal chromophore in the visual cycle. Mutations in human RDH genes are associated with Fundus albipunctatus, a mild form of night blindness (RDH5) and an autosomal recessive, childhood-onset severe retinal dystrophy (RDH12). Rdh12 knockout mice were found to be susceptible to light-induced photoreceptor apoptosis, whereas Rdh5 and Rdh8 knockout mice displayed only delayed dark adaptation. However, each knockout mouse eventually regenerated normal levels of visual pigments, suggesting that RDHs compensate for each other in the visual cycle. Here, we established RDH double knockout (Rdh8(-/-)Rdh12(-/-)) and triple knockout (Rdh5(-/-)Rdh8(-/-)Rdh12(-/-)) mice generated on various genetic backgrounds including a rod alpha-transducin knockout to test cone function. RDH activity was severely reduced in Rdh8(-/-)Rdh12(-/-) retina extracts, whereas Rdh8(-/-) RDH activity was intermediate and Rdh12(-/-) RDH activity was reduced only slightly. Surprisingly, all multiple knockout mice produced sufficient amounts of the chromophore to regenerate rhodopsin and cone pigments in vivo. Three-month-old Rdh8(-/-)Rdh12(-/-) mice characteristically displayed a slowly progressing rod-cone dystrophy accompanied by accumulation of N-retinylidene-N-retinylethanolamine (A2E), a toxic substance known to contribute to retinal degeneration. A2E accumulation and retinal degeneration were prevented by application of retinylamine, a potent retinoid cycle inhibitor. The results suggest that RDH8 and RDH12 are dispensable in support of the visual cycle but appear to be key components in clearance of free all-trans-retinal, thereby preventing A2E accumulation and photoreceptor cell death.
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80
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Overlack N, Maerker T, Latz M, Nagel-Wolfrum K, Wolfrum U. SANS (USH1G) expression in developing and mature mammalian retina. Vision Res 2007; 48:400-12. [PMID: 17923142 DOI: 10.1016/j.visres.2007.08.021] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2007] [Revised: 08/16/2007] [Accepted: 08/20/2007] [Indexed: 11/30/2022]
Abstract
The human Usher syndrome (USH) is the most common form of combined deaf-blindness. Usher type I (USH1), the most severe form, is characterized by profound congenital deafness, constant vestibular dysfunction and prepubertal-onset of retinitis pigmentosa. Five corresponding genes of the six USH1 genes have been cloned so far. The USH1G gene encodes the SANS (scaffold protein containing ankyrin repeats and SAM domain) protein which consists of protein motifs known to mediate protein-protein interactions. Recent studies indicated SANS function as a scaffold protein in the protein interactome related to USH. Here, we generated specific antibodies for SANS protein expression analyses. Our study revealed SANS protein expression in NIH3T3 fibroblasts, murine tissues containing ciliated cells and in mature and developing mammalian retinas. In mature retinas, SANS was localized in inner and outer plexiform retinal layers, and in the photoreceptor cell layer. Subcellular fractionations, tangential cryosections and immunocytochemistry revealed SANS in synaptic terminals, cell-cell adhesions of the outer limiting membrane and ciliary apparati of photoreceptor cells. Analyses of postnatal developmental stages of murine retinas demonstrated SANS localization in differentiating ciliary apparati and in fully developed cilia, synapses, and cell-cell adhesions of photoreceptor cells. Present data provide evidence that SANS functions as a scaffold protein in USH protein networks during ciliogenesis, at the mature ciliary apparatus, the ribbon synapse and the cell-cell adhesion of mammalian photoreceptor cells. Defects of SANS may cause dysfunction of the entire network leading to retinal degeneration, the ocular symptom characteristic for USH patients.
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Affiliation(s)
- Nora Overlack
- Department of Cell and Matrix Biology, Institute of Zoology, Johannes Gutenberg-University of Mainz, Germany
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81
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Tam BM, Moritz OL. Dark rearing rescues P23H rhodopsin-induced retinal degeneration in a transgenic Xenopus laevis model of retinitis pigmentosa: a chromophore-dependent mechanism characterized by production of N-terminally truncated mutant rhodopsin. J Neurosci 2007; 27:9043-53. [PMID: 17715341 PMCID: PMC6672211 DOI: 10.1523/jneurosci.2245-07.2007] [Citation(s) in RCA: 71] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
To elucidate the molecular mechanisms underlying the light-sensitive retinal degeneration caused by the rhodopsin mutation P23H, which causes retinitis pigmentosa (RP) in humans, we expressed Xenopus laevis, bovine, human, and murine forms of P23H rhodopsin in transgenic X. laevis rod photoreceptors. All P23H rhodopsins caused aggressive retinal degeneration associated with low expression levels and retention of P23H rhodopsin in the endoplasmic reticulum (ER), suggesting involvement of protein misfolding and ER stress. However, light sensitivity varied dramatically between these RP models, with complete or partial rescue by dark rearing in the case of bovine and human P23H rhodopsin, and no rescue for X. laevis P23H rhodopsin. Rescue by dark rearing required an intact 11-cis-retinal chromophore binding site within the mutant protein and was associated with truncation of the P23H rhodopsin N terminus. This yielded an abundant nontoxic approximately 27 kDa form that escaped the ER and was transported to the rod outer segment. The truncated protein was produced in the greatest quantities in dark-reared retinas expressing bovine P23H rhodopsin and was not observed with X. laevis P23H rhodopsin. These results are consistent with a mechanism involving enhanced protein folding in the presence of 11-cis-retinal chromophore, with ER exit assisted by proteolytic truncation of the N terminus. This study provides a molecular mechanism for light sensitivity observed in other transgenic models of RP and for phenotypic variation among RP patients.
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Affiliation(s)
- Beatrice M. Tam
- Department of Ophthalmology and Visual Sciences, Centre for Macular Research, University of British Columbia, Vancouver, British Columbia, Canada V5Z 3N9
| | - Orson L. Moritz
- Department of Ophthalmology and Visual Sciences, Centre for Macular Research, University of British Columbia, Vancouver, British Columbia, Canada V5Z 3N9
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82
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Li N, Salom D, Zhang L, Harris T, Ballesteros JA, Golczak M, Jastrzebska B, Palczewski K, Kurahara C, Juan T, Jordan S, Salon JA. Heterologous expression of the adenosine A1 receptor in transgenic mouse retina. Biochemistry 2007; 46:8350-9. [PMID: 17580959 DOI: 10.1021/bi700154h] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Traditional cell-based systems used to express integral membrane receptors have yet to produce protein samples of sufficient quality for structural study. Herein we report an in vivo method that harnesses the photoreceptor system of the retina to heterologously express G protein-coupled receptors in a biochemically homogeneous and pharmacologically functional conformation. As an example we show that the adenosine A1 receptor, when placed under the influence of the mouse opsin promoter and rhodopsin rod outer segment targeting sequence, localized to the photoreceptor cells of transgenic retina. The resulting receptor protein was uniformly glycosylated and pharmacologically well behaved. By comparison, we demonstrated in a control experiment that opsin, when expressed in the liver, had a complex pattern of glycosylation. Upon solubilization, the retinal adenosine A1 receptor retained binding characteristics similar to its starting material. This expression method may prove generally useful for generating high-quality G protein-coupled receptors for structural studies.
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Affiliation(s)
- Ning Li
- Novasite Pharmaceuticals Inc., San Diego, California 92121, USA
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83
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Niebauer RT, White JF, Fei Z, Grisshammer R. Characterization of monoclonal antibodies directed against the rat neurotensin receptor NTS1. J Recept Signal Transduct Res 2007; 26:395-415. [PMID: 17118789 DOI: 10.1080/10799890600928228] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
G protein-coupled receptors (GPCRs) are integral membrane proteins that mediate cellular responses to a variety of ligands and represent major drug targets. Despite their medical importance, detailed structural information is limited because only one GPCR has been crystallized and its structure determined. To develop tools to aid in the formation of well-ordered crystals, we generated monoclonal antibodies with high affinity to the rat neurotensin receptor. All antibodies bound to the C-terminus of the receptor, which may reflect the selection strategy used to identify high-affinity binders. Further characterization revealed that some antibodies bound to the receptor in a sodium chloride sensitive manner, but others did not. Epitope mapping revealed distinct antigenic regions within the receptor C-terminus. Tight binding of Fab fragments to the receptor was verified by size exclusion chromatography.
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Affiliation(s)
- Ronald T Niebauer
- Department of Health and Human Services, Laboratory of Molecular Biology of the National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland, USA
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84
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Mancia F, Brenner-Morton S, Siegel R, Assur Z, Sun Y, Schieren I, Mendelsohn M, Axel R, Hendrickson WA. Production and characterization of monoclonal antibodies sensitive to conformation in the 5HT2c serotonin receptor. Proc Natl Acad Sci U S A 2007; 104:4303-8. [PMID: 17360519 PMCID: PMC1838597 DOI: 10.1073/pnas.0700301104] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
mAbs that are sensitive to protein conformation can be helpful in studies of protein structure and function; in particular, mAb fragments are useful reagents in membrane protein crystallization. We immunized mice with the rat 5HT2c serotonin receptor and derived clonal hybridoma cells, which we tested for specific antigen reactivity by using the complementarity of purified protein from bacteria and receptor-embedded mammalian cell membranes. Nine mAbs met our criteria for specificity, affinity, and sensitivity to conformational features. Epitopes were mapped in various additional tests. Five of the nine mAbs have cytoplasmic epitopes, and two of these are sensitive to the ligand state of the receptor. These properties should be useful both for structural analysis and in probes of function.
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Affiliation(s)
- Filippo Mancia
- *Department of Biochemistry and Molecular Biophysics and
| | | | - Risa Siegel
- *Department of Biochemistry and Molecular Biophysics and
| | - Zahra Assur
- *Department of Biochemistry and Molecular Biophysics and
| | - Yonghua Sun
- the Howard Hughes Medical Institute, Columbia University, New York, NY 10032
| | - Ira Schieren
- the Howard Hughes Medical Institute, Columbia University, New York, NY 10032
| | | | - Richard Axel
- *Department of Biochemistry and Molecular Biophysics and
- the Howard Hughes Medical Institute, Columbia University, New York, NY 10032
| | - Wayne A. Hendrickson
- *Department of Biochemistry and Molecular Biophysics and
- the Howard Hughes Medical Institute, Columbia University, New York, NY 10032
- To whom correspondence should be addressed. E-mail:
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85
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Chen J, Shi G, Concepcion FA, Xie G, Oprian D, Chen J. Stable rhodopsin/arrestin complex leads to retinal degeneration in a transgenic mouse model of autosomal dominant retinitis pigmentosa. J Neurosci 2006; 26:11929-37. [PMID: 17108167 PMCID: PMC6674877 DOI: 10.1523/jneurosci.3212-06.2006] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Over 100 rhodopsin mutation alleles have been associated with autosomal dominant retinitis pigmentosa (ADRP). These mutations appear to cause photoreceptor cell death through diverse molecular mechanisms. We show that K296E, a rhodopsin mutation associated with ADRP, forms a stable complex with arrestin that is toxic to mouse rod photoreceptors. This cell death pathway appears to be conserved from flies to mammals. A genetics approach to eliminate arrestin unmasked the constitutive activity of K296E and caused photoreceptor cell death through a transducin-dependent mechanism that is similar to light damage. Expressing K296E in the arrestin/transducin double knock-out background prevented transducin signaling and led to substantially improved retinal morphology but did not fully prevent cell death caused by K296E. The adverse effect of K296E in the arrestin/transducin knock-out background can be mimicked by constant exposure to low light. Furthermore, we found that arrestin binding causes K296E to mislocalize to the wrong cellular compartment. Accumulation of stable rhodopsin/arrestin complex in the inner segment may be an important mechanism for triggering the cell death pathway in the mammalian photoreceptor cell.
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Affiliation(s)
- Jiayan Chen
- Zilkha Neurogenetic Institute
- Neuroscience Graduate Program, and
| | | | - Francis A. Concepcion
- Zilkha Neurogenetic Institute
- Department of Cell and Neurobiology and Department of Ophthalmology, Keck School of Medicine, University of Southern California, Los Angeles, California 90033, and
| | - Guifu Xie
- Department of Biochemistry and Volen Center for Complex Systems, Brandeis University, Waltham, Massachusetts 02545
| | - Daniel Oprian
- Department of Biochemistry and Volen Center for Complex Systems, Brandeis University, Waltham, Massachusetts 02545
| | - Jeannie Chen
- Zilkha Neurogenetic Institute
- Neuroscience Graduate Program, and
- Department of Cell and Neurobiology and Department of Ophthalmology, Keck School of Medicine, University of Southern California, Los Angeles, California 90033, and
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86
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Stie J, Jesaitis AJ. Reorganization of the human neutrophil plasma membrane is associated with functional priming: implications for neutrophil preparations. J Leukoc Biol 2006; 81:672-85. [PMID: 17170075 DOI: 10.1189/jlb.0806513] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Changes in the functional and plasma membrane organizational states of human neutrophils were examined using two isolation procedures, which may simulate altered physiological states in vivo. A gelatin-based method of blood-neutrophil isolation was used to model in vivo priming, and neutrophils isolated by this method were compared with control populations prepared by a pyrogen-free, dextran-based method. Gelatin-prepared neutrophils were functionally primed for adherence and agonist-stimulated superoxide generation relative to unprimed, control neutrophils. The organizational state of the membrane cortex was examined by mapping the subcellular distribution of select cortical and transmembrane proteins by several methods, including subcellular fractionation, indirect immunofluorescence, and compositional analysis of Triton X-100-insoluble membrane skeleton preparations. Filamentous actin, fodrin, and the fodrin anchor, CD45, were largely cytoplasmic in unprimed neutrophils but translocated to plasma membranes upon priming, whereas CD43 and ezrin were exclusively surface-associated in both populations. Isopycnic sucrose density gradient analysis of N(2)-cavitated neutrophils revealed a major shift in the distribution of surface-associated transmembrane and membrane cortical components relative to the plasma membrane marker alkaline phosphatase in primed but not unprimed neutrophils. Similar results were obtained after neutrophil stimulation with known priming agents, LPS, TNF-alpha, or GM-CSF. Together, these results may suggest that priming of suspended, circulating neutrophils is associated with a large-scale reorganization of the plasma membrane and associated membrane cortex in a process that is independent of cellular adhesion and gross morphologic polarization.
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Affiliation(s)
- Jamal Stie
- Montana State University, Department of Microbiology, 109 Lewis Hall, Bozeman, MT 59717, USA
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87
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Ismail N, Crawshaw SG, High S. Active and passive displacement of transmembrane domains both occur during opsin biogenesis at the Sec61 translocon. J Cell Sci 2006; 119:2826-36. [PMID: 16787949 DOI: 10.1242/jcs.03018] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
We used a site-specific crosslinking approach to study the membrane integration of the polytopic protein opsin at the endoplasmic reticulum. We show that transmembrane domain 1 occupies two distinct Sec61-based environments during its integration. However, transmembrane domains 2 and 3 exit the Sec61 translocon more rapidly in a process that suggests a displacement model for their integration where the biosynthesis of one transmembrane domain would facilitate the exit of another. In order to investigate this hypothesis further, we studied the integration of the first and third transmembrane domains of opsin in the absence of any additional C-terminal transmembrane domains. In the case of transmembrane domain 1, we found that its lateral exit from the translocon is clearly dependent upon the synthesis of subsequent transmembrane domains. By contrast, the lateral exit of the third transmembrane domain occurred independently of any such requirement. Thus, even within a single polypeptide chain, distinct transmembrane domains display different requirements for their integration through the endoplasmic reticulum translocon, and the displacement of one transmembrane domain by another is not a global requirement for membrane integration.
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Affiliation(s)
- Nurzian Ismail
- Faculty of Life Sciences, University of Manchester, The Michael Smith Building, Oxford Road, Manchester, M13 9PT, UK
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88
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Allison WT, Hallows TE, Johnson T, Hawryshyn CW, Allen DM. Photic history modifies susceptibility to retinal damage in albino trout. Vis Neurosci 2006; 23:25-34. [PMID: 16597348 DOI: 10.1017/s0952523806231031] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2004] [Accepted: 09/29/2005] [Indexed: 11/07/2022]
Abstract
Albino vertebrates exposed to intense light typically lose photoreceptors via apoptosis, and thus serve as useful models of retinal degeneration. In contrast, albino rainbow trout exposed to intense light maintain populations of rod and cone nuclei despite substantial damage to rod outer segments (ROS). The aim of this study was to differentiate between two hypotheses that could account for this divergent result: (1) trout rod nuclei remain intact during light damage, or (2) rod nuclei die but are replaced by cell proliferation. A further aim was to examine whether photic history modulates retinal damage, as in rodents. Albino and normally pigmented trout were moved from defined photic regimes into full daylight, while some were not moved to serve as protected controls. ROS were always maintained in pigmented fish and in albinos protected from full daylight. In albinos exposed to full daylight, ROS were removed over most of the central retina, whereas rod nuclei were maintained in the outer nuclear layer over 10 days. Pyknotic and TUNEL-labeled rod nuclei were abundant in affected albinos at all time-points tested. Rod death occurred without a decrease in the number of rod nuclei, confirming that proliferation must be replacing cells. Indeed a transient increase in proliferation was observed in retinal progenitors of albinos receiving 5 days of damaging light. This proliferative response was decreased with further damage. Cones remained intact even in areas where rod nuclei had degenerated. Pretreatment with light of moderate versus low intensity light affected the cell death and proliferative responses, and the ectopic localization of rod opsin. We conclude that apoptotic demise of rods, but not cones, occurred during light damage in retinas of albino trout and proliferative responses have a limited a capacity to replace lost rods.
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Affiliation(s)
- W Ted Allison
- The University of Michigan, Department of Molecular, Cellular, and Developmental Biology, Ann Arbor, Michigan, USA
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89
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Tam BM, Xie G, Oprian DD, Moritz OL. Mislocalized rhodopsin does not require activation to cause retinal degeneration and neurite outgrowth in Xenopus laevis. J Neurosci 2006; 26:203-9. [PMID: 16399688 PMCID: PMC6674333 DOI: 10.1523/jneurosci.3849-05.2006] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Mutations in the C terminus of rhodopsin disrupt a rod outer segment localization signal, causing rhodopsin mislocalization and aggressive forms of retinitis pigmentosa (RP). Studies of cultured photoreceptors suggest that activated mislocalized rhodopsin can cause cell death via inappropriate G-protein-coupled signaling. To determine whether this pathway occurs in vivo, we developed a transgenic Xenopus laevis model of RP based on the class I rhodopsin mutation Q344Ter (Q350Ter in X. laevis). We used a second mutation, K296R, to block the ability of rhodopsin to bind chromophore and activate transducin. We compared the effects of expression of both mutants on X. laevis retinas alone and in combination. K296R did not significantly alter the cellular distribution of rhodopsin and did not induce retinal degeneration. Q350Ter caused rhodopsin mislocalization and induced an RP-like degeneration, including loss of rods and development of sprouts or neurites in some remaining rods, but did not affect the distribution of endogenous rhodopsin. The double mutant K296R/Q350Ter caused a similar degeneration and neurite outgrowth. In addition, we found no protective effects of dark rearing in these animals. Our results demonstrate that the degenerative effects of mislocalized rhodopsin are not mediated by the activated form of rhodopsin and therefore do not proceed via conventional G-protein-coupled signaling.
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Affiliation(s)
- Beatrice M Tam
- Department of Ophthalmology and Visual Sciences, Centre for Macular Research, University of British Columbia, Vancouver, British Columbia, V5Z 3N9, Canada
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90
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Piscitelli CL, Angel TE, Bailey BW, Hargrave P, Dratz EA, Lawrence CM. Equilibrium between Metarhodopsin-I and Metarhodopsin-II Is Dependent on the Conformation of the Third Cytoplasmic Loop. J Biol Chem 2006; 281:6813-25. [PMID: 16407202 DOI: 10.1074/jbc.m510175200] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Rhodopsin is a G-protein-coupled receptor (GPCR) that is the light detector in the rod cells of the eye. Rhodopsin is the best understood member of the large GPCR superfamily and is the only GPCR for which atomic resolution structures have been determined. However, these structures are for the inactive, dark-adapted form. Characterization of the conformational changes in rhodopsin caused by light-induced activation is of wide importance, because the metarhodopsin-II photoproduct is analogous to the agonist-occupied conformation of other GPCRs, and metarhodopsin-I may be similar to antagonist-occupied GPCR conformations. In this work we characterize the interaction of antibody K42-41L with the metarhodopsin photoproducts. K42-41L is shown to inhibit formation of metarhodopsin-II while it stabilizes the metarhodopsin-I state. Thus, K42-41L recognizes an epitope accessible in dark-adapted rhodopsin and metarhodopsin-I that is lost upon formation of metarhodopsin-II. Previous work has shown that the peptide TGALQERSK is able to mimic the K42-41L epitope, and we have now determined the structure of the K42-41L-peptide complex. The structure demonstrates a central role for elements of the rhodopsin C3 loop, particularly Gln238 and Glu239, in the interaction with K42-41L. Geometric constraints taken from the antibody-bound peptide were used to model the epitope on the rhodopsin surface. The resulting model suggests that K42-41L locks the C3 loop into an extended conformation that is intermediate between two compact conformations seen in crystal structures of dark-adapted rhodopsin. Together, the structural and functional data strongly suggest that the equilibrium between metarhodopsin-I and metarhodopsin-II is dependent upon the conformation of the C3 loop. The biological implications of this model and its possible relations to dimeric and multimeric complexes of rhodopsin are discussed.
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Affiliation(s)
- Chayne L Piscitelli
- Department of Chemistry, Montana State University, Bozeman, Montana 59717, USA
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91
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Zhang L, Salom D, He J, Okun A, Ballesteros J, Palczewski K, Li N. Expression of functional G protein-coupled receptors in photoreceptors of transgenic Xenopus laevis. Biochemistry 2006; 44:14509-18. [PMID: 16262251 DOI: 10.1021/bi051386z] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
G protein-coupled receptors (GPCRs) constitute the largest superfamily of transmembrane signaling proteins; however, the only known GPCR crystal structure is that of rhodopsin. This disparity reflects the difficulty in generating purified GPCR samples of sufficient quantity and quality. Rhodopsin, the light receptor of retinal rod neurons, is produced in large amounts of homogeneous quality in the vertebrate retina. We used transgenic Xenopus laevis to convert these retina rod cells into bioreactors to successfully produce 20 model GPCRs. The receptors accumulated in rod outer segments and were homogeneously glycosylated. Ligand and [(35)S]GTPgammaS binding assays of the 5HT(1A) and EDG(1) GPCRs confirmed that they were properly folded and functional. 5HT(1A)R was highly purified by taking advantage of the rhodopsin C-terminal immunoaffinity tag common to all GPCR constructs. We have also developed an automated system that can generate hundreds of transgenic tadpoles per day. This expression approach could be extended to other animal model systems and become a general method for the production of large numbers of GPCRs and other membrane proteins for pharmacological and structural studies.
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Affiliation(s)
- Li Zhang
- Novasite Pharmaceuticals, Inc., San Diego, California 92121, USA
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92
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Matsumoto SC, Labovsky V, Roncoroni M, Guida MC, Giménez L, Mitelman J, Gori H, Jurgelevicius R, Grillo A, Manfredi P, Levin MJ, Paveto C. Retinal dysfunction in patients with chronic Chagas' disease is associated to anti‐Trypanosoma cruziantibodies that cross‐react with rhodopsin. FASEB J 2006; 20:550-2. [PMID: 16423878 DOI: 10.1096/fj.05-4654fje] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
To investigate retinal involvement in chronic Chagas' disease, we performed electroretinography and retinal fluorescein angiography studies in chagasic patients. Our results demonstrated a dissociated electrophysiological response characterized by both an abnormal reduction of the electroretinographic b-wave amplitude and a delayed latency, under the dark-adaptated condition. These alterations are compatible with a selective dysfunction of the rods. Antibodies raised against Trypanosoma cruzi that also interact with beta1-adrenergic receptor blocked light stimulation of cGMP-phosphodiesterase in bovine rod membranes. The specificity from the antibody-rhodopsin interaction was confirmed by Western blot analysis and antigenic competition experiments. Our results suggest an immunomediated rhodopsin blockade. T. cruzi infection probably induces an autoimmune response against rhodopsin in the chronic phase of Chagas' disease through a molecular mimicry mechanism similar to that described previously on cardiac human beta1-adrenergic and M2-cholinergic receptors, all related to the same subfamily of G-protein-coupled receptors.
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Affiliation(s)
- Silvia C Matsumoto
- Department of Neurology, Hospital Dr. Teodoro Alvarez, Buenos Aires, Argentina
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93
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Ridge KD, Abdulaev NG, Zhang C, Ngo T, Brabazon DM, Marino JP. Conformational changes associated with receptor-stimulated guanine nucleotide exchange in a heterotrimeric G-protein alpha-subunit: NMR analysis of GTPgammaS-bound states. J Biol Chem 2006; 281:7635-48. [PMID: 16407225 DOI: 10.1074/jbc.m509851200] [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] [Indexed: 11/06/2022] Open
Abstract
Solution NMR studies of a (15)N-labeled G-protein alpha-subunit (G(alpha)) chimera ((15)N-ChiT)-reconstituted heterotrimer have shown previously that G-protein betagamma-subunit (G(betagamma)) association induces a "pre-activated" conformation that likely facilitates interaction with the agonist-activated form of a G-protein-coupled receptor (R*) and guanine nucleotide exchange (Abdulaev, N. G., Ngo, T., Zhang, C., Dinh, A., Brabazon, D. M., Ridge, K. D., and Marino, J. P. (2005) J. Biol. Chem. 280, 38071-38080). Here we demonstrated that the (15)N-ChiT-reconstituted heterotrimer can form functional complexes under NMR experimental conditions with light-activated, detergent-solubilized rhodopsin (R*), as well as a soluble mimic of R*. NMR methods were used to track R*-triggered guanine nucleotide exchange and release of guanosine 5'-O-3-thiotriphosphate (GTPgammaS)/Mg(2+)-bound ChiT. A heteronuclear single quantum correlation (HSQC) spectrum of R*-generated GTPgammaS/Mg(2+)-bound ChiT revealed (1)HN, (15)N chemical shift changes relative to GDP/Mg(2+)-bound ChiT that were similar, but not identical, to those observed for the GDP.AlF(4)(-)/Mg(2+)-bound state. Line widths observed for R*-generated GTPgammaS/Mg(2+)-bound (15)N-ChiT, however, indicated that it is more conformationally dynamic relative to the GDP/Mg(2+)- and GDP.AlF(4)(-)/Mg(2+)-bound states. The increased dynamics appeared to be correlated with G(betagamma) and R* interactions because they are not observed for GTPgammaS/Mg(2+)-bound ChiT generated independently of R*. In contrast to R*, a soluble mimic that does not catalytically interact with G-protein (Abdulaev, N. G., Ngo, T., Chen, R., Lu, Z., and Ridge, K. D. (2000) J. Biol. Chem. 275, 39354-39363) is found to form a stable complex with the GTPgammaS/Mg(2+)-exchanged heterotrimer. The HSQC spectrum of (15)N-ChiT in this complex displays a unique chemical shift pattern that nonetheless shares similarities with the heterotrimer and GTPgammaS/Mg(2+)-bound ChiT. Overall, these results demonstrated that R*-induced changes in G(alpha) can be followed by NMR and that guanine nucleotide exchange can be uncoupled from heterotrimer dissociation.
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Affiliation(s)
- Kevin D Ridge
- Center for Membrane Biology, Department of Biochemistry and Molecular Biology, University of Texas Health Science Center, Houston, TX 77030, USA.
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94
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Ochrietor JD, Clamp MF, Moroz TP, Grubb JH, Shah GN, Waheed A, Sly WS, Linser PJ. Carbonic anhydrase XIV identified as the membrane CA in mouse retina: strong expression in Müller cells and the RPE. Exp Eye Res 2005; 81:492-500. [PMID: 16126196 DOI: 10.1016/j.exer.2005.03.010] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2005] [Revised: 03/11/2005] [Accepted: 03/21/2005] [Indexed: 11/24/2022]
Abstract
The presence of carbonic anhydrase (CA) activity in the neural retina has been known for several decades. CA-II, a soluble cytoplasmic isoform expressed by Müller cells and a subset of amacrine cells, was thought to be the sole source of CA activity in the neural retina. However, CA-II deficient mice retain CA activity in the neural retina, which implies that another isoform must be present in that tissue. Recently CA-XIV, an integral membrane protein, was cloned and characterized. We, therefore, sought to determine whether CA-XIV is expressed in the neural retina, and hence is responsible for the CA activity observed in CA-II null animals. Immunohistochemical analyses of histological sections from CA-II null, CA-XIV null, and control mice were performed to localize the CA-XIV isoform, as well as other known retinal markers. Immunoblotting and real-time RT-PCR analyses were also performed to test for CA-XIV expression in retina and other mouse tissues. We determined herein that CA-XIV, a approximately 45kDa membrane protein, is expressed in retina, as it is in kidney. In the retina, CA-XIV is expressed on the plasma membrane of Müller cells. CA-XIV is also found on both the apical and basal membranes of the retinal pigmented epithelium. The data presented here indicate that like CA-II, CA-XIV is highly expressed in the neural retina and, like CA-II, more specifically by the Müller cells. The cellular compartmentalization of the two isoforms in the Müller cell-one cytoplasmic and the other on the plasma membrane-suggest that the two enzymes have specific and unique functions. Future studies will be necessary to assign functions to CA-II and CA-XIV in the mouse neural retina.
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Affiliation(s)
- Judith D Ochrietor
- Whitney Laboratory for Marine Bioscience, The University of Florida, 9505 Ocean Shore Blvd, St Augustine, FL 32080, USA
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95
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Acland GM, Aguirre GD, Bennett J, Aleman TS, Cideciyan AV, Bennicelli J, Dejneka NS, Pearce-Kelling SE, Maguire AM, Palczewski K, Hauswirth WW, Jacobson SG. Long-term restoration of rod and cone vision by single dose rAAV-mediated gene transfer to the retina in a canine model of childhood blindness. Mol Ther 2005; 12:1072-82. [PMID: 16226919 PMCID: PMC3647373 DOI: 10.1016/j.ymthe.2005.08.008] [Citation(s) in RCA: 328] [Impact Index Per Article: 17.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2005] [Revised: 08/01/2005] [Accepted: 08/19/2005] [Indexed: 10/25/2022] Open
Abstract
The short- and long-term effects of gene therapy using AAV-mediated RPE65 transfer to canine retinal pigment epithelium were investigated in dogs affected with disease caused by RPE65 deficiency. Results with AAV 2/2, 2/1, and 2/5 vector pseudotypes, human or canine RPE65 cDNA, and constitutive or tissue-specific promoters were similar. Subretinally administered vectors restored retinal function in 23 of 26 eyes, but intravitreal injections consistently did not. Photoreceptoral and postreceptoral function in both rod and cone systems improved with therapy. In dogs followed electroretinographically for 3 years, responses remained stable. Biochemical analysis of retinal retinoids indicates that mutant dogs have no detectable 11-cis-retinal, but markedly elevated retinyl esters. Subretinal AAV-RPE65 treatment resulted in detectable 11-cis-retinal expression, limited to treated areas. RPE65 protein expression was limited to retinal pigment epithelium of treated areas. Subretinal AAV-RPE65 vector is well tolerated and does not elicit high antibody levels to the vector or the protein in ocular fluids or serum. In long-term studies, wild-type cDNA is expressed only in target cells. Successful, stable restoration of rod and cone photoreceptor function in these dogs has important implications for treatment of human patients affected with Leber congenital amaurosis caused by RPE65 mutations.
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Affiliation(s)
- Gregory M Acland
- Baker Institute, Cornell University, Hungerford Hill Road, Ithaca, NY 14853, USA.
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96
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Abstract
The deactivation of visual pigments involved in phototransduction is critical for recovering sensitivity after exposure to light in rods and cones of the vertebrate retina. In rods, phosphorylation of rhodopsin by rhodopsin kinase (GRK1) and the subsequent binding of visual arrestin completely terminates phototransduction. Although signal termination in cones is predicted to occur via a similar mechanism as in rods, there may be differences due to the expression of related but distinct gene products. While rods only express GRK1, cones in some species express only GRK1 or GRK7 and others express both GRKs. In the mouse, cone opsin is phosphorylated by GRK1, but this has not been demonstrated in mammals that express GRK7 in cones. We compared cone opsin phosphorylation in intact retinas from the 13-lined ground squirrel (GS) and pig, cone- and rod-dominant mammals, respectively, which both express GRK7. M opsin phosphorylation increased during continuous exposure to light, then declined between 3 and 6 min. In contrast, rhodopsin phosphorylation continued to increase during this time period. In GS retina homogenates, anti-GS GRK7 antibody blocked M opsin phosphorylation by 73%. In pig retina homogenates, only 20% inhibition was observed, possibly due to phosphorylation by GRK1 released from rods during homogenization. Our results suggest that GRK7 phosphorylates M opsin in both of these mammals. Using an in vitro GTPgammaS binding assay, we also found that the ability of recombinant M opsin to activate G(t) was greatly reduced by phosphorylation. Therefore, phosphorylation may participate directly in the termination of phototransduction in cones by decreasing the activity of M opsin.
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Affiliation(s)
- Peng Liu
- Department of Cell and Developmental Biology, The University of North Carolina at Chapel Hill, North Carolina 27599-7090, USA
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97
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Crawshaw S, Martoglio B, Meacock S, High S. A misassembled transmembrane domain of a polytopic protein associates with signal peptide peptidase. Biochem J 2005; 384:9-17. [PMID: 15373738 PMCID: PMC1134083 DOI: 10.1042/bj20041216] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The endoplasmic reticulum (ER) exerts a quality control over newly synthesized proteins and a variety of components have been implicated in the specific recognition of aberrant or misfolded polypeptides. We have exploited a site-specific cross-linking approach to search for novel ER components that may specifically recognize the misassembled transmembrane domains present in truncated polytopic proteins. We find that a single probe located in the transmembrane domain of a truncated opsin fragment is cross-linked to several ER proteins. These components are distinct from subunits of the Sec61 complex and represent a 'post-translocon' environment. In this study, we identify one of these post-translocon cross-linking partners as the signal peptide peptidase (SPP). We find that the interaction of truncated opsin chains with SPP is mediated by its second transmembrane domain, and propose that this interaction may contribute to the recognition of misassembled transmembrane domains during membrane protein quality control at the ER.
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Affiliation(s)
- Samuel G. Crawshaw
- *Faculty of Life Sciences, University of Manchester, Michael Smith Building, Oxford Road, Manchester M13 9PT, U.K
| | - Bruno Martoglio
- †Institute of Biochemistry, Swiss Federal Institute of Technology (ETH), ETH-Hoenggerberg, 8093 Zürich, Switzerland
| | - Suzanna L. Meacock
- *Faculty of Life Sciences, University of Manchester, Michael Smith Building, Oxford Road, Manchester M13 9PT, U.K
| | - Stephen High
- *Faculty of Life Sciences, University of Manchester, Michael Smith Building, Oxford Road, Manchester M13 9PT, U.K
- To whom correspondence should be addressed (email )
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98
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Cideciyan AV, Jacobson SG, Aleman TS, Gu D, Pearce-Kelling SE, Sumaroka A, Acland GM, Aguirre GD. In vivo dynamics of retinal injury and repair in the rhodopsin mutant dog model of human retinitis pigmentosa. Proc Natl Acad Sci U S A 2005; 102:5233-8. [PMID: 15784735 PMCID: PMC555975 DOI: 10.1073/pnas.0408892102] [Citation(s) in RCA: 140] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Genetic and environmental factors modify the severity of human neurodegenerations. Retinal degenerations caused by rhodopsin gene mutations show severity differences within and between families and even within regions of the same eye. Environmental light is thought to contribute to this variation. In the naturally occurring dog model of the human disorder, we found that modest light levels, as used in routine clinical practice, dramatically accelerated the neurodegeneration. Dynamics of acute retinal injury (consisting of abnormal intraretinal light scattering) were visualized in vivo in real time with high-resolution optical imaging. Long term consequences included fast or slow retinal degeneration or repair of injury depending on the dose of light exposure. These experiments provide a platform to study mechanisms of neuronal injury, repair, compensation, and degeneration. The data also argue for a gene-specific clinical trial of light reduction in human rhodopsin disease.
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Affiliation(s)
- Artur V Cideciyan
- Department of Ophthalmology, University of Pennsylvania, Philadelphia, PA 19104, USA.
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99
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Maeda A, Maeda T, Imanishi Y, Kuksa V, Alekseev A, Bronson JD, Zhang H, Zhu L, Sun W, Saperstein DA, Rieke F, Baehr W, Palczewski K. Role of photoreceptor-specific retinol dehydrogenase in the retinoid cycle in vivo. J Biol Chem 2005; 280:18822-32. [PMID: 15755727 PMCID: PMC1283069 DOI: 10.1074/jbc.m501757200] [Citation(s) in RCA: 127] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The retinoid cycle is a recycling system that replenishes the 11-cis-retinal chromophore of rhodopsin and cone pigments. Photoreceptor-specific retinol dehydrogenase (prRDH) catalyzes reduction of all-trans-retinal to all-trans-retinol and is thought to be a key enzyme in the retinoid cycle. We disrupted mouse prRDH (human gene symbol RDH8) gene expression by targeted recombination and generated a homozygous prRDH knock-out (prRDH-/-) mouse. Histological analysis and electron microscopy of retinas from 6- to 8-week-old prRDH-/- mice revealed no structural differences of the photoreceptors or inner retina. For brief light exposure, absence of prRDH did not affect the rate of 11-cis-retinal regeneration or the decay of Meta II, the activated form of rhodopsin. Absence of prRDH, however, caused significant accumulation of all-trans-retinal following exposure to bright lights and delayed recovery of rod function as measured by electroretinograms and single cell recordings. Retention of all-trans-retinal resulted in slight overproduction of A2E, a condensation product of all-trans-retinal and phosphatidylethanolamine. We conclude that prRDH is an enzyme that catalyzes reduction of all-trans-retinal in the rod outer segment, most noticeably at higher light intensities and prolonged illumination, but is not an essential enzyme of the retinoid cycle.
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MESH Headings
- Alcohol Oxidoreductases/metabolism
- Alcohol Oxidoreductases/physiology
- Animals
- Blotting, Southern
- Catalysis
- Cell Line
- Cell Line, Tumor
- Chromatography, High Pressure Liquid
- DNA, Complementary/metabolism
- Electrophoresis, Polyacrylamide Gel
- Electroretinography
- Eye/metabolism
- Genetic Vectors
- Genotype
- Humans
- Immunoblotting
- Immunohistochemistry
- Insecta
- Kinetics
- Light
- Mice
- Mice, Inbred C57BL
- Mice, Knockout
- Mice, Transgenic
- Microscopy, Electron, Transmission
- Models, Chemical
- Models, Genetic
- Mutation
- Phosphatidylethanolamines/metabolism
- Photoreceptor Cells, Vertebrate/metabolism
- Polymerase Chain Reaction
- RNA, Messenger/metabolism
- Recombination, Genetic
- Retina/metabolism
- Retinaldehyde/chemistry
- Retinoids/chemistry
- Retinoids/metabolism
- Rhodopsin/chemistry
- Rhodopsin/metabolism
- Time Factors
- Transgenes
- Vitamin A/metabolism
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Affiliation(s)
| | | | | | | | | | | | - Houbin Zhang
- Departments of Ophthalmology and Visual Sciences
- Neurobiology and Anatomy, University of Utah, Salt Lake City, Utah 84112
| | - Li Zhu
- From the Departments of Ophthalmology
| | - Wenyu Sun
- From the Departments of Ophthalmology
| | | | | | - Wolfgang Baehr
- Departments of Ophthalmology and Visual Sciences
- Biology, and
- Neurobiology and Anatomy, University of Utah, Salt Lake City, Utah 84112
| | - Krzysztof Palczewski
- From the Departments of Ophthalmology
- Pharmacology, and
- Chemistry, University of Washington, Seattle, Washington 98195 and the
- To whom correspondence should be addressed: Dept. of Ophthalmology, University of Washington, Box 356485, Seattle, WA 98195-6485. Tel.: 206-543-9074; Fax: 206-221-6784; E-mail:
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100
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Maeda A, Crabb JW, Palczewski K. Microsomal glutathione S-transferase 1 in the retinal pigment epithelium: protection against oxidative stress and a potential role in aging. Biochemistry 2005; 44:480-9. [PMID: 15641772 PMCID: PMC1351247 DOI: 10.1021/bi048016f] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
High oxygen tension, exposure to light, and the biochemical events of vision generate significant oxidative stress in the retina and the retinal pigment epithelium (RPE). Understanding the mechanisms and basis of susceptibility to progressive retinal diseases involving oxidative damage such as age-related macular degeneration (AMD) remains a major challenge. Here microsomal glutathione S-transferase (MGST1) is shown to be a dominant, highly expressed enzyme in bovine and mouse RPE microsomes that displays significant reduction activity toward synthetic peroxides, oxidized RPE lipids, and oxidized retinoids. This enzymatic reduction activity (GPx) can be partially neutralized with a monoclonal anti-MGST1 antibody developed in this study. MGST1-transfected HEK293 cells exhibited greater viability (70 +/- 4% survival) compared with untransfected control cells (46 +/- 4% survival) when challenged with 20 microM H(2)O(2), and greater viability of MGST1-transfected cells following challenge with oxidized docosahexaenoic acid was also observed. Cultured ARPE19 cells transfected with silencing MGST1 siRNAs exhibited lower expression of MGST1 (12% and 26% of the controls) and significantly lower GPx activity (44 +/- 13%) and, thus, were more susceptible to oxidative damage. Immunoblotting revealed that the in vivo expression of MGST1 in mouse RPE decreases 3-4-fold with age, to trace levels in 18-month-old mice. GPx activity in the RPE was also found to be reduced in 12-month-old mice to approximately 67%. These results support an important protective function for MGST1 against oxidative insult in the RPE that decreases with age and suggest that this enzyme may play a role in the development of age-related diseases such as AMD.
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Affiliation(s)
| | | | - Krzysztof Palczewski
- * Address correspondence to this author at the Department of Ophthalmology, University of Washington, Box 356485, Seattle, WA 98195-6485. Phone: 206-543-9074. Fax: 206-221-6784. E-mail:
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