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Y. Ito, F. Berry, T. Footz, A. O. Khan, M. Walter; Molecular Characterization of a Novel FOXC1 Mutation Found in a Patient With Aniridia. Invest. Ophthalmol. Vis. Sci. 2008;49(13):1653.
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FOXC1 mutations cause human Axenfeld-Rieger Syndrome (ARS), which is characterized by malformations to the anterior segment of the eye and an elevated risk to develop glaucoma. For the first time, we report a novel FOXC1 W152G missense mutation in a newborn male with aniridia. Molecular analysis was carried out to determine the functional consequences of the FOXC1 W152G mutation.
After screening for FOXC1 mutations, the W152G mutation was identified in a patient with aniridia. The W152G mutation was introduced into the FOXC1 cDNA by site-directed mutagenesis. The levels of W152G protein expression and the mutant protein’s ability to localize to the nucleus, transactivate a reporter gene, and bind to DNA were determined.
A novel mutation in FOXC1 was identified in a patient with aniridia. Immunoblotting indicated that the W152G mutant FOXC1 protein was stably expressed at levels similar to the wild type protein. Altered migration of FOXC1 W152G immunoreactive bands as compared to the wild type FOXC1 revealed that the W152G protein is differently phosphorylated than the wild type protein. A partial digest with trypsin suggested that the W152G mutation results in misfolding of the FOXC1 protein. A majority of the W152G protein was unable to localize completely to the nucleus and interestingly, a fraction of the mutant proteins showed perinuclear localization to aggresomes. Further analyses revealed that the W152G FOXC1 mutant protein was unable to transactivate a luciferase reporter gene.
A mutation of FOXC1 can, in rare circumstances, cause aniridia as well as ARS. Many of the effects of the W152G missense mutation are similar to a previously studied FOXC1 L130F missense mutation, identified in two related individuals with ARS, including the altered migration pattern of the immunoreactive bands, and disruptions to the protein’s ability to localize to the nucleus and transactivate a reporter gene. Since the W152 and L130 residues interact at the same hydrophobic pocket, our results suggest that this region may be particularly important for the normal folding and functioning of the FOXC1 protein. Furthermore, an additional mutation of a residue within this hydrophobic pocket, I87M, resulted in no detectable levels of protein. Thus, alterations to this hydrophobic pocket in FOXC1 have severe effects upon the normal functioning of the FOXC1 protein.
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