Regulation of Involucrin Expression in Normal Human Corneal Epithelial Cells: A Role for Activator Protein One

PURPOSE: Understanding the mechanisms that regulate gene expression in the human cornea is an important goal. In the present study, the involucrin gene was used as a model to study this regulation. Human involucrin (hINV) is a structural protein that is selectively expressed in surface epithelia, including corneal epithelial cells. METHODS: Regulation of involucrin gene expression was monitored in cultures of normal human primary corneal epithelial cells. RESULTS: The studies revealed that an activator protein (AP)-1 DNA-binding site is essential for appropriate basal and stimulus-dependent hINV promoter activity. Mutation of this site, AP1-1, results in a loss of hINV promoter activity. A gel mobility supershift analysis revealed interaction of the AP1 factors, Fra-1, Fra-2, and JunB, with this element. Inhibition of AP1 function with a dominant-negative form of AP1 also inhibited expression. Treatment with 12-O-tetradecanoylphorbol-13-acetate (TPA), a protein kinase C activator, increased hINV gene expression, a response that correlates with increased nuclear AP1 factor level and binding to the hINV gene AP1-1 response element. Expression of the endogenous hINV gene is also increased by TPA treatment. CONCLUSIONS: These findings point to an important role for AP1 transcription factors in the regulation of human corneal epithelial cell involucrin gene expression.