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SI Tomarev, M Torrado, R Trivedi, I Karavanova; Optimedin, A New Olfactomedin-related Protein, Interacts With Myocilin . Invest. Ophthalmol. Vis. Sci. 2002;43(13):3011.
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Purpose: Available data suggest that disease-causing mutations in the MYOC gene act as gain of function and that such mutations may modify interactions of myocilin with other proteins. We investigated interactions of myocilin with optimedin, a new olfactomedin-related protein that has been previously identified by us. Methods: Expression patterns of the rat optimedin and Myoc genes were analyzed by northern and in situ hybridization. Intracellular localization of optimedin fused to different tag epitopes was investigated by confocal microscopy. Interaction of optimedin with myocilin was studied by GST pull-down, far-western, and immunoprecipitation assays. Results: In eye tissues, the rat optimedin gene is highly expressed in epithelial cells of the posterior iris and ciliary body, as well as in ganglion and amacrine cells of the retina. It is also expressed in different brain regions. The rat Myoc gene expression was very strong in the trabecular meshwork region and in the sclera. In the rat retina, Myoc expression was detected mainly in the pigmented epithelial cells. Two identified forms of optimedin are different at their N-terminuses and contain potential signal sequences. Optimedin shows preferential Golgi localization and is secreted from cultured cells. Optimedin and myocilin interact with each other in vitro as judged by GST pull-down, co-immunoprecipitation, and far-western binding assays. The olfactomedin domain is more important for interaction between optimedin and myocilin than the N-terminal part of the protein. The N-terminal domains of optimedin and myocilin are essential for homodimers formation. Co-transfection of Ile477Ser or Tyr437His myocilin mutants together with optimedin indicated that the presence of the mutated myocilin protein may interfere with the secretion of optimedin. Conclusion: We suggest that mutations in the olfactomedin domain of myocilin may modify the balance between myocilin and optimedin in the tissues of the irido-corneal angle that in turn may interfere with normal development and function of these tissues and contribute to the glaucoma progression.
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