Substance P-induced cadherin expression and its signal transduction in a cloned human corneal epithelial cell line

Although the absence of Substance P (SP), a neurotransmitter in the trigeminal nerve, has been speculated as a cause for developing neurotrophic keratitis, its exact pathogenesis is still not clarified. In a previous report, we showed with electron microscopic examination that epithelial cell attachment was weakened in denervated corneas. In this study, SV40-transformed human corneal epithelial cells (HCE-Ts) were used to explore the molecular mechanisms responsible for mediating regulation of E-cadherin expression in response to Substance P receptor stimulation. Expression of the mRNAs for specific SP receptors, neurokinin (NK)-1R, NK-2R, and NK-3R, was demonstrated with RT-PCR. The cells were treated with various concentrations of SP in vitro, and the expression of an adhesion molecule E-cadherin was analyzed by immunofluorescence, immunoblotting, and enzyme-linked immunosorbent assay (ELISA) using an anti-E-cadherin antibody. E-cadherin expression was increased by SP in a dose-dependent manner both in the cytosolic fraction and in the cell membrane fraction. This increase in E-cadherin expression was completely inhibited by Calphostin C (PKC inhibitor) and KN-62 (CaMK inhibitor), but not by H-89 (PKA inhibitor), indicating that SP-induced E-cadherin expression involves the activation of protein kinase C (PKC) and calmodulin kinase (CaMK). SP did not affect cell proliferation at all. All these findings indicate that SP induced E-cadherin expression through PKC and CaMK activation and suggest that a lack of SP may account in part for the pathogenesis of neurotrophic keratitis.