Three-dimensional structure of guanylyl cyclase activating protein-2, a calcium-sensitive modulator of photoreceptor guanylyl cyclases.
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Guanylyl cyclase activating protein-2 (GCAP-2) is a Ca2+-sensitive regulator of phototransduction in retinal photoreceptor cells. GCAP-2 activates retinal guanylyl cyclases at low Ca2+ concentration (<100 nM) and inhibits them at high Ca2+ (>500 nM). The light-induced lowering of the Ca2+ level from approximately 500 nM in the dark to approximately 50 nM following illumination is known to play a key role in visual recovery and adaptation. We report here the three-dimensional structure of unmyristoylated GCAP-2 with three bound Ca2+ ions as determined by nuclear magnetic resonance spectroscopy of recombinant, isotopically labeled protein. GCAP-2 contains four EF-hand motifs arranged in a compact tandem array like that seen previously in recoverin. The root mean square deviation of the main chain atoms in the EF-hand regions is 2.2 A in comparing the Ca2+-bound structures of GCAP-2 and recoverin. EF-1, as in recoverin, does not bind calcium because it contains a disabling Cys-Pro sequence. GCAP-2 differs from recoverin in that the calcium ion binds to EF-4 in addition to EF-2 and EF-3. A prominent exposed patch of hydrophobic residues formed by EF-1 and EF-2 (Leu24, Trp27, Phe31, Phe45, Phe48, Phe49, Tyr81, Val82, Leu85, and Leu89) may serve as a target-binding site for the transmission of calcium signals to guanylyl cyclase. (+info)
Cancer-associated retinopathy during treatment for small-cell lung carcinoma.
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A 70-year-old woman with small-cell lung carcinoma (c-T4N2M0) was treated by six courses of combination chemotherapy (carboplatin and etoposide). After two weeks, she complained of a sense of darkness and night blindness. A Western blot analysis showed that the patient's serum bound with the recombinant 23-kDa retinal cancer-associated retinopathy (CAR) antigen at 1:1,000 dilution. Her visual acuity became so poor that she could only recognise a hand motion at 50 cm despite treatment with corticosteroids and combination chemotherapy. The patient was diagnosed as having a rare type of CAR because CAR is usually found before the diagnosis of primary cancer. (+info)
Low expression of alphaA-crystallins and rhodopsin kinase of photoreceptors in retinal dystrophy rat.
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PURPOSE: The Royal College of Surgeons (RCS) rat has been extensively characterized as a model for inherited retinal dystrophy such as retinitis pigmentosa. In the present study, compositions of retinal proteins were compared between RCS (rdy-/-) and control (rdy+/+) rats during progression of the disease to understand the molecular pathologic course of the retinal degeneration. METHODS: Protein mapping was performed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) or two-dimensional (2D)-PAGE using whole retinas or rod outer segments (ROS) obtained by a sucrose-density gradient centrifugation method from RCS or control rats at the age of 3 to 8 weeks. RESULTS: 2D-PAGE showed that retinal proteins of RCS rats were generally less abundant than those of the control animals and that the difference became more evident with aging. However, no significant difference was observed in the protein-mapping patterns in 2D-PAGE between RCS and control rats in any ages tested. Analysis by SDS-PAGE of ROS proteins and by western blot using antibodies against opsin, rhodopsin kinase (RK), recoverin, or arrestin demonstrated that a 20-kDa protein and RK were selectively less abundant in RCS than in control rats. Edman sequence analysis of the proteolytic peptides obtained by in-gel digestion of the corresponding protein band using endoproteinase Lys C identified the 20-kDa protein as alphaA-crystallin. Reverse transcription-polymerase chain reaction confirmed selective low levels of mRNA expressions of alphaA-crystallins and RK in RCS rats. CONCLUSIONS: This study demonstrates that decreased expression of alphaA-crystallins and RK in RCS rats, may have significant roles in the development of retinal dystrophy. (+info)
Cancer-associated retinopathy induced by both anti-recoverin and anti-hsc70 antibodies in vivo.
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PURPOSE: In a previous study, both recoverin and heat shock cognate protein 70 (hsc 70) were found as autoantigens recognized by sera from four patients with cancer-associated retinopathy (CAR). This observation suggested that autoimmune reactions against recoverin and hsc 70 might be involved together in the pathogenesis of CAR. The purpose of the present study is to investigate the effects of these autoantibodies on retinas in vivo. METHODS: Functional and morphologic properties of the retinas were evaluated after anti-recoverin and/or anti-hsc 70 antibodies were intravitreously injected into Lewis rats' eyes. RESULTS: Responses in electroretinogram (ERG) of eyes penetrated with anti-hsc 70 antibody were comparable with the control, but those with anti-recoverin antibody were remarkably reduced during the 3-week period after the injection. Such anti-recoverin antibody-induced reduction was significantly enhanced by copenetration with anti-hsc 70 antibody. Immunofluorescence microscopy demonstrated that after intravitreal injection, anti-recoverin antibody penetrated toward the outer nuclear layer (ONL) and outer segments within 12 to 24 hours, and the presence of the antibody in the retina diminished during the next few days. Histopathology revealed significant thinning of the ONL and inner nuclear layer (INL) in the affected retina in comparison with the control. Throughout the ONL and INL, apoptotic cells were recognized by TdT-dUTP terminal nick-end labeling. The antibody-induced retinal dysfunction was effectively treated by administrations of either corticosteroid or cyclosporin A. CONCLUSIONS: These observations suggest that anti-recoverin- and anti-hsc 70 antibody-induced retinal dysfunction in Lewis rat is a good model to study the pathophysiology of CAR. (+info)
Segregation of on and off bipolar cell axonal arbors in the absence of retinal ganglion cells.
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Retinal cells that respond selectively to light onset or offset are segregated into On and Off pathways. Here, we describe the development of cone bipolar cells whose axonal arbors at maturity synapse onto ganglion cell dendrites confined to On and Off strata of the inner plexiform layer (IPL). In particular, we sought to determine whether the formation of this segregated pattern is dependent on the presence of ganglion cells. Developing bipolar cells were visualized using an antibody against recoverin, the calcium binding protein that labels On and Off cone bipolar cells in the adult rat retina. Recoverin-positive cells were apparent in the ventricular zone on the day of birth [postnatal day 0 (P0)], before bipolar cells begin to migrate to the inner nuclear layer. Two distinct strata were first apparent in the IPL at P8, with the Off pathway maturing earlier than the On pathway. There was no indication of exuberant bipolar cell projections. Throughout development, there were also a small number of recoverin-positive cells of unknown origin in the ganglion cell layer. To assess whether the formation of On and Off cone bipolar cell projections is dependent on the presence of ganglion cells, these target neurons were eliminated by unilateral section of the optic nerve. This was done on the day of birth, resulting in a total loss of ganglion cells 5-6 d before bipolar cell axons innervate the IPL. In retinas with optic nerve sections, On and Off cone bipolar cells were present, albeit at a lower than normal density, and the axonal arbors of these interneurons were organized into two distinct strata. This indicates that ganglion cells are not essential for the formation of segregated On and Off bipolar cell inputs. These results lend support to the hypothesis that specific ingrowth patterns of bipolar cell terminal arbors could regulate the formation of stratified retinal ganglion cell dendrites. (+info)
Human melanoma-associated retinopathy (MAR) antibodies alter the retinal ON-response of the monkey ERG in vivo.
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PURPOSE: Melanoma-associated retinopathy (MAR) is a paraneoplastic condition that causes visual symptoms of night-blindness and photopsias. The electroretinogram (ERG) of MAR patients is characteristically abnormal in a way that implicates retinal depolarizing bipolar cell (DBC) dysfunction. Whether an injection of IgG from MAR patients into the vitreous of monkeys would alter the ERG acutely as a demonstration of a functional basis for patients' visual symptoms was explored. METHODS: MAR IgG was isolated from three visually symptomatic melanoma patients. Control IgG was from melanoma patients with no vision problems. The ERG was monitored after intravitreal injections into monkey eyes. One eye was injected with 2-amino-4-phosphonobutyric acid (APB), which is known to block DBC ON-pathway responses. Retinal immunocytochemistry was performed using fluorescein isothiocyanate-labeled goat anti-human IgG. RESULTS: Within 1 to 3 hours after MAR IgG injection, the ERG photopic b-wave was diminished, with far less effect on the a- and d-waves. These changes are characteristic of DBC dysfunction and were similar to the effects of APB. The scotopic ERG b-wave, which reflects activity of rod-driven DBCs, showed a loss of amplitude and threshold sensitivity after MAR IgG. Retinal immunocytochemistry with anti-IgG antibody showed IgG penetration throughout the retinal layers, but staining was not specific for a single type of retinal neuron. CONCLUSIONS: Intravitreal injection of human MAR IgG altered the monkey ERG acutely in ways that implicate functional disruption of retinal DBC signaling. These results support the hypothesis that MAR IgG circulating antibodies are responsible for the reported visual symptoms. Bipolar cells in the ON-pathway appear to be affected more than OFF-pathway bipolar cells of the cone pathway in this acute preparation. (+info)
Amino acid residues of S-modulin responsible for interaction with rhodopsin kinase.
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S-modulin in frog or its bovine homologue, recoverin, is a 23-kDa EF-hand Ca(2+)-binding protein found in rod photoreceptors. The Ca(2+)-bound form of S-modulin binds to rhodopsin kinase (Rk) and inhibits its activity. Through this regulation, S-modulin is thought to modulate the light sensitivity of a rod. In the present study, we tried to identify the interaction site of the Ca(2+)-bound form of S-modulin to Rk. First, we mapped roughly the interaction regions by using partial peptides of S-modulin. The result suggested that a specific region near the amino terminus is the interaction site of S-modulin. We then identified the essential amino acid residues in this region by using S-modulin mutant proteins: four amino acid residues (Phe(22), Glu(26), Phe(55), and Thr(92)) were suggested to interact with Rk. These residues are located in a small closed pocket in the Ca(2+)-free, inactive form of S-modulin, but exposed to the surface of the molecule in the Ca(2+)-bound, active form of S-modulin. Two additional amino acid residues (Tyr(108) and Arg(150)) were found to be crucial for the Ca(2+)-dependent conformational changes of S-modulin. (+info)
Aberrant expression of photoreceptor-specific calcium-binding protein (recoverin) in cancer cell lines.
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Cancer-associated retinopathy (CAR) is an ocular manifestation of a paraneoplastic syndrome whereby immunological reactions to retinal antigens aberrantly expressed in tumor cells lead to the degeneration of retinal photoreceptor cells. In our previous study (H. Ohguro et al., Invest. Ophthalmol. Vis. Sci., 40: 82-89, 1999), recoverin, a retina-specific calcium-binding protein, and heat shock cognate protein 70 (hsc 70) were identified as autoantigens recognized by sera from patients with CAR. Therefore, we suggested that autoimmune reactions against both recoverin and hsc 70 might be involved in the pathogenesis of CAR. To elucidate the initial step of the molecular pathology of CAR, we examined the expression of recoverin and hsc 70 by reverse transcription-PCR and Western blot using cell lines of several kinds of cancers, including lung small cell carcinoma, lung adenocarcinoma, gastric cancer, pancreatic cancer, breast cancer, uterine cervical cancer, endometrial cancer, and leukemia. Recoverin was expressed in 21 of the 31 cancer cell lines. The expression levels of hsc 70 were significantly higher in cancer cell lines than in noncancerous cell lines. However, no difference in the expression levels of hsc 70 was observed between recoverin-positive and -negative cell lines. Immunofluorescence labeling by the affinity-purified recoverin antibody revealed the immunoreactivity to recoverin as a granular pattern within the cancer cells. Lung adenocarcinoma A549 cells, which did not express recoverin, exhibited a significant reduction in cell proliferation upon transfection with human recoverin cDNA. Taken together, our present data suggest that the retina-specific calcium-binding protein recoverin is expressed in more than 50% of a variety of cancer cells and may play a significant role in the cell proliferation of these tumor cells. (+info)