A Novel Human Congenital Cataract Mutation in EPHA2 Kinase Domain (p.G668D) Alters Receptor Stability and Function

To identify the genetic defect in a four-generation Chinese family that causes autosomal dominant congenital posterior subcapsular cataracts, and to understand how this EPHA2 kinase domain mutation affects EPHA2 activity. Variants in 54 cataract-associated genes were screened by targeted next generation sequencing (NGS) and then validated by Sanger sequencing. EPHA2 wild-type cDNA was synthesized in vitro, and EPHA2 p.G668D mutant was constructed by PCR site-directed mutagenesis. Western blotting and fluorescence microscopy were used to analyze the expression level of protein and its subcellular localization, respectively. A wound-healing assay was performed to analyze changes to cell migration. A novel heterozygous missense mutation was identified in the kinase domain of the EPHA2 gene (c.2003G>A, p.G668D). This is the third congenital cataract mutation being reported in this domain. Functional study revealed that the kinase domain mutation (p.G668D) decreased EphA2 protein level (P = 0.036) via a proteasome-dependent pathway, altered its subcellular localization of the EphA2 from cell-cell contacts to a diffuse perimembranous distribution, and changed the distribution of β-catenin as well. The expression of mutant EphA2 significantly promoted the migration of human lens epithelial cells (P = 0.002). Our study presented the evidence for a novel EPHA2 kinase domain mutation that causes congenital posterior subcapsular cataracts. The first functional study on an EPHA2 kinase domain mutation that causes a congenital cataract revealed that the G668D mutation destabilized the receptor, changed its subcellular localization, and altered the activation of EphA2 with its ligand ephrin. The mutant EphA2 resulted in a reduced inhibition of cell migration. As a consequence, the c.G668D mutation promoted cell migration and caused the formation of cataracts.