Activation of oxidative stress-regulated Bcl-3 suppresses CTCF in corneal epithelial cells

Epidermal growth factor (EGF)-induced corneal epithelial wound healing through nuclear factor κB subtype-regulated CCCTC binding factor (CTCF) activation

Epidermal growth factor (EGF) plays an important role in corneal epithelial migration and proliferation to improve the wound healing process. This study aimed to understand the role of NFκB in EGF-induced corneal epithelial wound healing through regulation of CTCF activity, which plays important roles in cell motility and migration to promote wound healing. The effect of NFκB p50 on corneal epithelial wound healing was investigated by comparing the eyes of wild-type and p50 knockout mice. We found that there was a significant retardation in corneal epithelial wound healing in the corneas of p50 knockout mice. Wound closure rates were measured in human corneal epithelial cells transfected with an NFκB activation-sensitive CTCF expression construct to demonstrate the effect of human CTCF expression under the control of EGF-induced NFκB activation on wound healing. EGF stimulation activated NFκB, which directly triggered the expression of the exogenous human CTCF in transfected cells and, subsequently, promoted human corneal epithelial cell motility, migration, and wound healing. Overexpression of CTCF in corneal epithelial cells and mouse corneas significantly enhanced the wound healing process. Furthermore, the effect of overexpressing NFκB p50 in corneal epithelial cells on the promotion of wound healing was abolished by knockdown of CTCF with CTCF-specific shRNA. Thus, a direct regulatory relationship between EGF-induced NFκB p50 and CTCF activation affecting corneal epithelial wound healing has been established, indicating that CTCF is, indeed, a NFκB p50-targeted and effective gene product in the core transcriptional network downstream from the growth factor-induced NFκB signaling pathway.

Ocular surface development and gene expression

The ocular surface-a continuous epithelial surface with regional specializations including the surface and glandular epithelia of the cornea, conjunctiva, and lacrimal and meibomian glands connected by the overlying tear film-plays a central role in vision. Molecular and cellular events involved in embryonic development, postnatal maturation, and maintenance of the ocular surface are precisely regulated at the level of gene expression by a well-coordinated network of transcription factors. A thorough appreciation of the biological characteristics of the ocular surface in terms of its gene expression profiles and their regulation provides us with a valuable insight into the pathophysiology of various blinding disorders that disrupt the normal development, maturation, and/or maintenance of the ocular surface. This paper summarizes the current status of our knowledge related to the ocular surface development and gene expression and the contribution of different transcription factors to this process.

Role of CTCF in EGF-induced migration of immortalized human corneal epithelial cells

PURPOSE

EGF-induced activation of the epigenetic CCCTC binding factor (CTCF) plays an important role in corneal epithelial cell proliferation by suppressing the Pax6 gene. The present study focused on further understanding the role of CTCF in mediating EGF-induced migration of immortalized human corneal epithelial cells.

METHODS

CTCF activities in human corneal epithelial cells immortalized by telomerase (HTCE cells) and SV-40 (HCE cells) transformation were suppressed and enhanced by CTCF mRNA knockdown and by overexpressing CTCF cDNA, respectively. EGF-induced cell migration was evaluated by linear scratch wound healing, a cell migration assay, and live cell motility GFP-tracking with a fluorescence microscope. Immunochemical analysis was performed for detecting focal adhesion changes in EGF-induced and CTCF activity-altered cells.

RESULTS

EGF-induced wound closure and cell migration rates of human corneal epithelial cells were significantly suppressed and enhanced by CTCF mRNA knockdown and by overexpression of CTCF, respectively. CTCF mRNA knockdown also markedly suppressed cell motility, determined by using a live-cell-tracking system in GFP-tag-expressed HTCE cells. Finally, alterations of EGF-stimulated focal adhesion were observed in CTCF knockdown HTCE cells by immunostaining of F-actin and vinculin in cytoskeleton reorganization.

CONCLUSIONS

CTCF, an epigenetic regulator and transcription factor, involves EGF-induced increases in cell motility and migration. CTCF plays an essential role in growth factor-regulated human corneal epithelial cell wound healing.