Retinoids enhance the number of EGF receptors in corneal endothelial cells.

Corneal endothelium appears to be an important target tissue for retinoids and epidermal growth factor (EGF). We report here that retinoic acid, or its synthetic analogue CBS-211 A (10(-8)-10(-7) M) dose-dependently enhances the mitogenic effect of EGF on cultured bovine corneal endothelial cells (BCEC). Furthermore, retinoid treatment, especially with CBS-211 A, increases the EGF-binding capacity of BCEC without any modification of EGF receptor affinity. The addition of cycloheximide (0.5 microgram ml-1) to cultures simultaneously with retinoids suppressed the retinoid effect on EGF-binding, whereas this protein synthesis inhibitor was ineffective when added 24 hr later. These results suggest that retinoids could induce the expression of EGF receptors on BCEC as an early event. This study, which demonstrates a cooperation between retinoids and EGF in corneal endothelium, could explain the beneficial effect of retinoic acid previously reported on this tissue repair in vivo. Our data could offer clues for new pharmaceutical strategies in ophthalmology therapy.