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RA Saleem, FB Berry, MA Walter; Analysis of FOXC1 Missense Mutations Reveals Minimal Thresholds of FOXC1 Activity for Normal Development . Invest. Ophthalmol. Vis. Sci. 2002;43(13):2447.
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Purpose: FOXC1 is a member of the forkhead/winged-helix family of transcription factors. Mutations in FOXC1 cause ocular anterior segment defects and increase the risk of early onset glaucoma. The consequences of 5 missense mutations on FOXC1 function have been previously determined. Recently, five new FOXC1 missense mutations underlying AR malformations have been identified (P79L, P79T, I91S, I91T, R127H). The effects of these FOXC1 mutations on the ability of the FOXC1 protein to bind DNA and activate gene expression were investigated. Methods: Site-directed mutagenesis was used to introduce these changes to the FOXC1 cDNA. Epitope-tagged FOXC1 constructs were expressed in COS-7 cells, producing products of the correct size by Western analysis. The effect of each additional missense mutation on FOXC1-DNA interactions was tested by electrophoretic mobility shift assays (EMSAs) while the effect of each missense mutation on the transactivation ability of FOXC1 was tested using a dual luciferase reporter assay. Results: Preliminary results indicate that while all the missense mutations tested show reduced transactivation of a luciferase reporter gene in comparison to wild type FOXC1, the levels of residual activity of the mutant forms of FOXC1 vary greatly. Additionally, EMSAs have revealed that FOXC1 carrying P79L, I91S or I91T is still able to bind an in vitro derived FOXC1 binding site at near wt FOXC1 levels. Further analyses of the effects of these missense mutations on FOXC1 binding specificity and the nature of the transactivation disruption are underway. Conclusion: Combined with previous work, these experiments show that missense mutations in FOXC1 are able to disrupt the stability of FOXC1 protein, the interaction of FOXC1 with DNA, and/or the transactivation potential of FOXC1. These experiments will help provide a greater understanding how disease-causing missense mutations perturb FOXC1 function and help to define critical thresholds of FOXC1 function. The previously described S82T FOXC1 transactivates at 57% of wild type levels, indicating that FOXC1 protein levels and activity must be tightly controlled during development. This work will provide a basis for understanding the role of FOXC1 in normal development. Funded by CIHR and AHFMR support.
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