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X. Shu, B. Tulloch, F. Slingsby, A.F. Wright; Effects of a Ser163Arg C1QTNF5 Mutation on Cell Adhesion . Invest. Ophthalmol. Vis. Sci. 2006;47(13):4147.
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© ARVO (1962-2015); The Authors (2016-present)
A Ser163Arg mutation in the short–chain collagen C1QTNF5 gene results in late–onset retinal and macular degeneration (L–ORMD), which resembles age–related macular degeneration. The aim was to elucidate the function of C1QTNF5 and to examine the effect of the mutation on cell function and specifically on cell adhesion.
ARPE–19 and HEK 293–EBNA cells stably expressing wildtype and mutant C1QTNF5 were examined for C1QTNF5 secretion, by immunoblotting and cell adhesion assays and immunocytochemically for evidence of cytotoxicity.
Wildtype C1QTNF5 was secreted while the mutant protein formed high molecular weight aggregates and was not secreted. The mutant protein was able to multimerise with wildtype protein. Cell adhesion assays showed reduced cell adhesion to laminin–coated plates in mutant–expressing cells, compared with wildtype and control cells. Evidence of cytotoxicity was also found in mutant–expressing cells, which showed aggregates co–localising with endoplasmic reticulum (ER) stress proteins.
Native C1QTNF5 protein is multimeric, so that heteromultimer formation may result in haploinsufficiency due to lack of secreted C1QTNF5 in L–ORMD heterozygotes. This is associated with changes in adhesion to laminin–coated plates, suggesting a role in cell adhesion. Cytotoxicity may also be present, as a result of protein aggregation and endoplasmic reticulum stress, in transient expression assays, but a true gain–of–function remains to be demonstrated in cells expressing normal levels of mutant C1QTNF5.
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