14-3-3sigma controls corneal epithelial cell proliferation and differentiation through the Notch signaling pathway.

14-3-3sigma (also called stratifin) is specifically expressed in the stratified squamous epithelium and its function was recently shown to be linked to epidermal stratification and differentiation in the skin. In this study, we investigated its role in corneal epithelium cell proliferation and differentiation. We showed that the 14-3-3sigma mutation in repeated epilation (Er) mutant mice results in a dominant negative truncated protein. Primary corneal epithelial cells expressing the dominant negative protein failed to undergo high calcium-induced cell cycle arrest and differentiation. We further demonstrated that blocking endogenous 14-3-3sigma activity in corneal epithelial cells by overexpressing dominative negative 14-3-3sigma led to reduced Notch activity and Notch1/2 transcription. Significantly, expression of the active Notch intracellular domain overcame the block in epithelial cell differentiation in 14-3-3sigma mutant-expressing corneal epithelial cells. We conclude that 14-3-3sigma is critical for regulating corneal epithelial proliferation and differentiation by regulating Notch signaling activity.