Differential Effects of Protein Tyrosine Kinase Inhibitors on Interferon- γ-Induction of Major Histocompatibility Complex Class II and Intercellular Adhesion Molecule-1 Expression in Human Corneal Epithelial Cells

Abstract

Purpose: Interferon (IFN)-γ induces major histocompatibility complex (MHC) class II and intercellular adhesion molecule-1 (ICAM-1) expression on human corneal epithelial (HCE) cells. So far, it has not been clarified whether both inductions by IFN-γ use the same signal transduction pathway. Therefore, in the present study, we tried to determine the significance of the protein tyrosine kinase (PTK)-dependent signaling pathway in the induction of both MHC class II and ICAM-1 expression by IFN-γ in cultured HCE cells. Methods: Cultured HCE cells were treated with human recombinant IFN-γ. The induction of protein tyrosine phosphorylation of proteins including PTKs, janus kinase (JAK)1, and JAK2, was examined by Western blotting and immunoprecipitation. The effects of treatment of HCE cells with specific PTK inhibitors on IFN-γ-induction of MHC class II and ICAM-1 expression were examined by flow cytometry. Results: IFN 1 (Interferon) induced tyrosine phosphorylation of multiple substrates, particularly that of 75,000; 90,000; 130,000; and 160,000 molecular weight proteins including JAK1 and JAK2 in cultured HCE cells. The PTK inhibitors, herbimycin A and genistein, inhibited tyrosine phosphorylation of those proteins. Also, these PTK inhibitors prevented IFN-γ-induction of MHC class II synthesis and surface expression. However, neither herbimycin A nor genistein had any effect on IFN-γ-induction of ICAM-1 expression. Conclusions: Tyrosine phosphorylation of proteins including JAK1 and JAK2 is essential for IFN-γ-induction of MHC class II expression, but not critical for that of ICAM-1 expression in cultured HCE cells. In addition, it is suggested that the IFN-γ-induction of MHC class II requires PTK activities not only in the primary JAK-signal transducers and activators of transcription (STAT) pathway but also in the subsequent pathway mediated by IFN-γ-induced intermediate proteins.