Glaucoma–Causing Myocilin Mutants Associate With the Peroxisomal Targeting Signal–1 Receptor (PTS1R)

Abstract

Abstract: : Purpose:Specific polymorphisms in the myocilin gene (GLC1A, MYOC, TIGR) have been shown to cause open angle glaucoma (OAG) with varying age–of–onset and degree of severity. The C–terminal tail of myocilin (₅₀₂SKM) encodes a putative peroxisomal targeting signal–1 receptor (PTS1R) sequence. We asked whether the C–terminal SKM motif can interact with PTS1R and be directed to the peroxisome. Methods: Interaction of the C–terminal half of myocilin with PTS1R was determined by yeast two–hybrid analysis and confirmed by mammalian two–hybrid analysis and co–immunoprecipitation. Visualization of intracellular mutant myocilin localization was done by confocal microscopy analysis. Results: We present data showing either a direct or indirect association between mutant, disease–causing myocilin and PTS1R. The interaction between myocilin and PTS1R is dependent on the specific myocilin mutation, with more severe, early onset OAG mutations having a higher degree of association. Direct association of mutant myocilin with PTS1R occurs with the early or moderate onset mutations Y437H and G364V by direct exposure of a cryptic PTS1 signal. Indirect association with PTS1R occurs with the late–onset Q368X mutation by piggyback association of mutant myocilin with wild–type myocilin and subsequent exposure of the wild–type cryptic PTS1 signal. Conclusions: Our data suggest that the gain–of–function cause of myocilin–based glaucoma may be due to altered peroxisomal function as a result of mutant myocilin interaction with PTS1R.

Keywords: proteins encoded by disease genes • pathology: human • trabecular meshwork