Involucrin expression in the corneal epithelium: an essential role for Sp1 transcription factors.
OBJECTIVE
Identifying the mechanism(s) that regulate gene expression during the transition of the limbal stem cell to a differentiated superficial cell is an important area of interest in the corneal epithelium.


METHODS
However, the factors that regulate gene expression during this process are not well understood. In the present study, the human involucrin (hINV) gene was used as a model to study gene expression in the corneal epithelium. Expression was studied in normal human corneal epithelial cell cultures and hINV promoter transgenic mice.


RESULTS
Studies in cultured cells revealed that an Sp transcription factor-binding site, located in the upstream regulatory region of the hINV promoter, is essential for optimal hINV gene expression. Mutation of this site reduces promoter activity. Expression of Sp1 results in an Sp1-dependent increase in activity, whereas expression of dominant-negative Sp1 inhibits promoter activity. Gel mobility shift analysis showed the interaction of Sp1 and Sp3 with the Sp DNA element. Treatment of the corneal epithelial cells with 12-O-tetradecanoylphorbol-13-acetate increased hINV gene expression and this response is associated with increased nuclear factor binding of Sp1 and Sp3 to the Sp DNA response element. Promoter mutagenesis studies in transgenic mice confirmed the importance of the Sp site, as removal of this site by promoter truncation or point mutation resulted in a complete loss of in vivo corneal epithelial cell gene expression.


CONCLUSIONS
These studies provide in vivo evidence that Sp transcription factor input is absolutely necessary for activation of involucrin gene expression in the differentiating corneal epithelium.
Adhikary
Gautam
G
Departments of Physiology and Biophysics, Case School of Medicine, 2109 Adelbert Road, Cleveland, OH 44106-4970, USA.
Crish
James F
JF
Gopalakrishnan
Ramamurthy
R
Bone
Frederic
F
Eckert
Richard L
RL
D000328:Adult; D000368:Aged; D000818:Animals; D002478:Cells, Cultured; D004247:DNA / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism; D024202:Electrophoretic Mobility Shift Assay; D019573:Epithelium, Corneal / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000502:physiology*; D006801:Humans; D051379:Mice; D008822:Mice, Transgenic; D008875:Middle Aged; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D011401:Promoter Regions, Genetic; D011498:Protein Precursors / Q000235:genetics*; D016329:Sp1 Transcription Factor / Q000502:physiology*; D051705:Sp3 Transcription Factor; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014157:Transcription Factors / Q000378:metabolism
D004268:DNA-Binding Proteins; D011498:Protein Precursors; C497121:SP3 protein, human; D016329:Sp1 Transcription Factor; C497122:Sp3 protein, mouse; D014157:Transcription Factors; D051705:Sp3 Transcription Factor; C032253:involucrin; D004247:DNA; D013755:Tetradecanoylphorbol Acetate