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D. Balasubramanian, A. Nagabhushana, M. Chalasani, N. Jain, V. Radha, N. Rangaraj, G. Swarup; A Glaucoma-Associated Mutant of Optineurin Causes Defective Vesicular Trafficking at the Recycling Endosomes by Ubiquitin Binding. Invest. Ophthalmol. Vis. Sci. 2009;50(13):3627.
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Mutations in optineurin are associated with certain glaucomas, a group of eye diseases characterized by progressive loss of vision due to degeneration of optic nerve. The E50K is a dominant mutation associated with a severe phenotype, which selectively induces death of retinal ganglion cells. Optineurin is involved in vesicular trafficking between Golgi and plasma membrane, and in NF-ΚB regulation. However defects caused by mutations in optineurin leading to cell death and glaucoma are not known. We explore this aspect here.
Transfection of the wild type and mutant optineurin cDNA was done in retinal ganglion cells. Visualization was done using antibody and GFP tags. Confocal microscopy and live cell imaging was done, as also yeast-two-hybrid assay in order to detect interacting proteins.
Here we show that endogenous optineurin is present in recycling endosomes and is required for trafficking of transferrin receptor to perinuclear region. The E50K mutant optineurin forms larger vesicles (recycling endosomes), which show slower dynamics compared to wild-type optineurin. The E50K mutant causes reduced uptake of transferrin. Through its ubiquitin binding domain optineurin is recruited to recycling endosomes by forming a complex with ubiquitinated transferrin receptor. E50K mutant shows enhanced interaction with transferrin receptor. The formation of large vesicles by E50K, slower dynamics and its ability to induce cell death in retinal ganglion cells are mediated by ubiquitin binding.
These results suggest that optineurin regulates vesicular trafficking at recycling endosomes by ubiquitin binding and E50K mutant causes slower trafficking at the recycling endosomes, which might be responsible for the death of retinal ganglion cells leading to glaucoma.
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