Semaphorins are a family of glycoproteins that play an important role in repulsive axon guidance during embryogenesis. We have now investigated the effect of corneal epithelial cells oil the expression of Sema3A in corneal fibroblasts with the use of a coculture system in which the two cell types are separated by a collagen vitrigel membrane. Reverse transcription-polymerase chain reaction and immunoblot analyses revealed that the presence of immortalized corneal epithelial (HCE) cells increased the expression of Sema3A in human corneal fibroblasts at both the mRNA and protein levels. This effect of HCE cells was mimicked by recombinant human epidermal growth factor (EGF) in a concentration and time-dependent manner. An inhibitor of the tyrosine kinase activity of the EGF receptor, PD153035, blocked the EGF-induced up-regulation of both Sema3A mRNA and protein in corneal fibroblasts. Depletion of EGF in HCE cells by RNA interference largely abolished the effect of these cells on Sema3A expression in corneal fibroblasts. These findings indicate that EGF released from corneal epithelial Cells Up-regulates the expression of Sema3A in corneal fibroblasts. This effect of EGF may play all important role in maintenance of corneal structure and repair of corneal damage. (C) 2008 Elsevier Inc. All rights reserved,