Optineurin Increases Cell Survival and Translocates to the Nucleus in a Rab8-dependent Manner upon an Apoptotic Stimulus
Telethon Institute of Genetics and Medicine, Via Pietro Castellino 111, 80131 Napoli, Italy. Journal of Biological Chemistry
(Impact Factor: 4.57).
07/2006; 281(23):16147-56. DOI: 10.1074/jbc.M601467200
In glaucoma the retinal ganglion cells of the retina die through the induction of apoptosis leading to excavation of the optic nerve and blindness. Mutations in the optineurin (optic neuropathy inducing) protein were found associated with an adult form of glaucoma. To date, the role of optineurin in the neurodegeneration process that occurs during glaucoma is still unknown. We now report that in response to an apoptotic stimulus, optineurin changes subcellular localization and translocates from the Golgi to the nucleus. This translocation is dependent on the GTPase activity of Rab8, an interactor of optineurin. Furthermore, we demonstrate that the overexpression of optineurin protects cells from H2O2-induced cell death and blocks cytochrome c release from the mitochondria. A mutated form of optineurin, E50K, identified in normal tension glaucoma patients loses its ability to translocate to the nucleus and when overexpressed compromises the mitochondrial membrane integrity resulting in cells that are less fit to survive under stress conditions. The correlation between optineurin function and cell survival will be key to begin to understand retinal ganglion cell biology and signaling and to design general "survival" strategies to treat a disease of such a complex etiology as glaucoma.
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- "Furthermore, the suggested distribution of the OPTN protein in cells and its effects on organelles have also been inconsistent across studies. De Marco et al. (2006) found that the localization of overexpressed OPTN was transformed from cytoplasmic to nuclear when stimulated by apoptosis, which increased the survival of NIH3T3 cells. Park et al. (2006) found that the overexpression of OPTN in retinal pigment epithelial cells and in trabecular cells could form fluorescent foci, which were suggested to induce the fragmentation of Golgi. "
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ABSTRACT: The objectives of this study were to investigate the distributions of abnormally expressed optineurin (OPTN) proteins in retinal ganglion cells (RGC5s) of transgenic rats and their effects on subcellular morphological structures. Green fluorescent protein labeled EGFP wild-type (OPTNWT), E50K mutant type (OPTNE50K), and OPTN siRNA (si-OPTN) eukaryotic expression plasmids were constructed and transfected into RGC5s. Intracellular structures were labeled with organelle specific fluorescent dyes. Construct localization and cell morphologies were visualized by confocal fluorescence microscopy. OPTNWT was observed to be distributed as fine punctate fluorescent particles in the cytoplasm around the nucleus, along with exhibiting nuclear expression. OPTNE50K exhibited similar distribution but with non-uniform fluorescence particle size. si-OPTN distribution was similar to that of EGFP: uniform across the cytoplasm and nucleus. Compared with the negative control group, OPTNWT, and OPTNE50K and to a lesser degree pEGFP-transfected cells exhibited fracture and loss of myofilament proteins and mitochondrial swelling and cytoplasmic accumulation, along with abnormal lysosomal distribution and increased volume, and Golgi fragmentation. However, si- OPTN transfected cells exhibited no significant damage. Therefore, we demonstrated that the E50K mutation disrupts the uniformity of OPTN protein distribution upon exogenous overexpression. Furthermore, these results suggested that si-OPTN transfection, and thus potentially OPTN knockdown, did not impact subcellular morphology of RGC5 cells, whereas transfection, especially when combined with wild-type or mutant OPTN expression, led to substantial abnormalities in subcellular morphological structures. These findings lay a foundation for further research into the function of the OPTN protein.
Available from: Melissa Erin Murray
- "The turnover of endogenous OPTN involves mainly the ubiquitin-proteasome system , but when up-regulated or mutant, autophagy comes in to play . Although OPTN is localized to the Golgi complex, OPTN translocates from the Golgi to the nucleus in a Rab8 dependent manner on apoptotic stimulation, resulting in increases in its own transcription and thereby preventing cell death . In "
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ABSTRACT: Optineurin (OPTN) is a multifunctional protein involved in cellular morphogenesis, vesicle trafficking, maintenance of the Golgi complex, and transcription activation through its interactions with the Rab8, myosin 6 (MYO6), huntingtin. Recently, OPTN immunoreactivity has been reported in intranuclear inclusions in patients with neuronal intranuclear inclusions disease (NIID). Other studies have shown that the RNA-binding protein, fused in sarcoma (FUS), is a component of intranuclear inclusions in NIID. We aimed to investigate the relationship between OPTN, its binding protein MYO6 and FUS in this study. In control subjects, OPTN (C-terminal) (OPTN-C) and MYO6 immunoreactivity was mainly demonstrated in the cytoplasm of neurons. In NIID patients, both neuronal intranuclear inclusions (NII) and glial intranuclear inclusions (GII) were immunopositive for MYO6 as well as OPTN-C. However, the intensity of OPTN-C immunostaining of the neuronal cytoplasm with and without NII was less than that of the control subjects. Double immunofluorescence staining for OPTN-C, ubiquitin (Ub), p62 and FUS revealed co-localization of these proteins within NII. Moreover, Ub positive inclusions were co-localized with MYO6. The percentage of co-localization of Ub with OPTN-C, FUS or MYO6 in NII was 100%, 52% and 92%, respectively. Ultrastructurally, the inclusions consisted of thin and thick filaments. Both filaments were immunopositive for Ub and OPTN-C. These findings suggest that OPTN plays a central role in the disease pathogenesis, and that OPTN may be a major component of NII.
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- "However, it is known that overexpression of OPTN in NIH3T3 cells protects cells from H2O2-induced cell death . The inhibitory effect of OPTN on TNFα-induced NF-κB activation is also well known , . "
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ABSTRACT: The optineurin gene, OPTN, is one of the causative genes of primary open-angle glaucoma. Although oligomerization of optineurin in cultured cells was previously observed by gel filtration analysis and blue native gel electrophoresis (BNE), little is known about the characteristics of optineurin oligomers. Here, we aimed to analyze the oligomeric state of optineurin and factors affecting oligomerization, such as environmental stimuli or mutations in OPTN. Using BNE or immunoprecipitation followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), we demonstrated that both endogenous and transfected optineurin exist as oligomers, rather than monomers, in NIH3T3 cells. We also applied an in situ proximity ligation assay to visualize the self-interaction of optineurin in fixed HeLaS3 cells and found that the optineurin oligomers were localized diffusely in the cytoplasm. Optineurin oligomers were usually detected as a single band of a size equal to that of the optineurin monomer upon SDS-PAGE, while an additional protein band of a larger size was observed when cells were treated with H2O2. We showed that larger protein complex is optineurin oligomers by immunoprecipitation and termed it covalent optineurin oligomers. In cells expressing OPTN bearing the most common glaucoma-associated mutation, E50K, covalent oligomers were formed even without H2O2 stimulation. Antioxidants inhibited the formation of E50K-induced covalent oligomers to various degrees. A series of truncated constructs of OPTN was used to reveal that covalent oligomers may be optineurin trimers and that the ubiquitin-binding domain is essential for formation of these trimers. Our results indicated that optineurin trimers may be the basic unit of these oligomers. The oligomeric state can be affected by many factors that induce covalent bonds, such as H2O2 or E50K, as demonstrated here; this provides novel insights into the pathogenicity of E50K. Furthermore, regulation of the oligomeric state should be studied in the future.
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