EGF–Induced Down–Regulation of Pax6 to Promote Corneal Epithelial Cell Proliferation

Abstract

Abstract: : Purpose: Epidermal Growth factor (EGF) plays important roles in regulating corneal epithelial proliferation/differentiation during wound healing. The purpose of the study is to investigate the requirement of suppressing corneal epithelial lineage–specific Pax 6 activity in EGF–induced proliferation. Methods:Human and rabbit corneal epithelial cells (HCE and RCE cells) were cultured in in DMEM/F12 medium contained 10% FBS in 37 °C incubator gassed with 5% CO₂.. Northern blot and Western analysis were used to determine target gene and protein expressions. Expression levels of genes were manipulated by gene transfection and siRNA techniques. Corneal epithelial cell proliferation was measured by MTT assay. Results:We found in the study EGF stimulated corneal epithelial cell growth through inhibition of Pax6 activity. 1) EGF–induced CTCF activation subsequently inhibited pax6 expression by interacting with a CTCF–specific region upstream of Pax6 P0 promoter. 2) Suppression of EGF–induced Erk activation by specific inhibitor or by the dominant expression of a silent Erk mutant effectively abolished the effects of EGF stimulation on regulations of CTCF and Pax6. 3) Down–regulation of Pax6 expression induced by EGF is required for corneal epithelial proliferation because overexpression of Pax6 in these cells attenuated EGF–induced proliferation. 4) Knockdown of Pax6 mRNA with siRNA significantly promoted EGF–induced proliferation of corneal epithelial cells. Conclusions: Our results revealed a new regulatory mechanism that involves cellular signaling events and Pax6 transcription regulation in growth factor–mediated proliferation. This suggests in corneal epithelial cells that inhibition of Pax6 expression is a prerequisite for EGF to elicit controls of cell growth and fate.

Keywords: cornea: epithelium • gene/expression • proliferation