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Kumari Alka, Joseph R Casey; A Personalized Medicine Approach to Corneal Dystrophy: Assessment of All Reported Missense SLC4A11 Mutants as Candidates for Folding Correction. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):4660.
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© ARVO (1962-2015); The Authors (2016-present)
Mutations of SLC4A11 cause genetic endothelial corneal dystrophies: Fuchs endothelial corneal dystrophy, congenital hereditary endothelial corneal dystrophy type 2 (CHED2) and Harboyan syndrome. Misfolding of SLC4A11 protein, leading to retention in the endoplasmic reticulum (ER), is the predominant molecular defect of SLC4A11 point mutants. Current treatments for these diseases, including corneal transplant, are inadequate. Our aim is to identify ER-retained missense mutants that can be trafficked to the cell surface. This will establish the SLC4A11 genotypes of individuals who might benefit from Folding Correction Therapy, setting the stage for personalized medicine.
SLC4A11 proteins were transiently expressed in HEK293 cells at 37 °C or 30 °C. Cell lysates were analyzed on immunoblots. Abundance of cell surface protein was quantified by densitometry of mature glycosylated (upper band) and immature ER-retained protein (lower band). To determine whether any point mutations affected basolateral targeting, SLC4A11 mutants were also expressed in polarized MDCK cells and their localization was assessed by confocal immunofluorescence. The ability of SLC4A11 mutants in detergent lysates to bind to immobilized inhibitor resin (SITS-Affigel) was measured.
This study measured cell surface localization and epithelial targeting of 57 SLC4A11 missense mutants. Most SLC4A11 missense mutants were ER-retained when expressed in HEK293 cells. Interestingly, G709E, G583D, R282P, W240S, R209W, A269V, T271M, T379P, L843P and S213P SLC4A11 mutants exhibited increased processing to the plasma membrane when grown at 30 °C. Immunolocalization with e-cadherin in MDCK cells established basolateral location of SLC4A11 in polarized epithelia. Mis-trafficking of mutant SLC4A11 to the apical membrane was investigated as a possible cause of the disease for some of the mutants.
SLC4A11 mutants were categorized as 1. Candidates for folding correction therapy on the basis of their rescue to the cell surface when cultured at 30 °C and 2. Grossly-misfolded and unlikely to be able to fold under any conditions, on the basis of inability to bind inhibitor resin.
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