Interferon-γ (IFN-γ) induced intercellular adhesion molecule-1 (ICAM-1) expression in human NCI-H292 epithelial cells, as shown by enzyme-linked immunosorbent assay and immunofluorescence staining. The enhanced ICAM-1 expression resulted in increased adhesion of U937 cells to NCI-H292 cells. Tyrosine kinase inhibitors (genistein or herbimycin), Src family inhibitor (PP2), or a phosphatidylinositol-phospholipase C inhibitor (U73122) attenuated the IFN-γ-induced ICAM-1 expression. Protein kinase C (PKC) inhibitors (staurosporine or Ro 31-8220) also inhibited IFN-γ-induced response. 12-O-Tetradecanoylphorbol-13-acetate (TPA), a PKC activator, stimulated ICAM-1 expression; this effect was inhibited by tyrosine kinase or Src inhibitor. ICAM-1 promoter activity was enhanced by IFN-γ and TPA in cells transfected with pIC339-Luc, containing the downstream NF-κB and γ-activated site (GAS) sites, but not in cells transfected with GAS-deletion mutant, pIC135 (ΔAP2). Electrophoretic gel mobility shift assay demonstrated that GAS-binding complexes in IFN-γ-stimulated cells contained STAT1α. The IFN-γ-induced ICAM-1 promoter activity was inhibited by tyrosine kinase inhibitors, a phosphatidylinositol-phospholipase C inhibitor, or PKC inhibitors, and the TPA-induced ICAM-1 promoter activity was also inhibited by tyrosine kinase inhibitors. Cotransfection with a PLC-γ2 mutant inhibited IFN-γ- but not TPA-induced ICAM-1 promoter activity. However, cotransfection with dominant negative mutants of PKCα or c-Src inhibited both IFN-γ- and TPA-induced ICAM-1 promoter activity. The ICAM-1 promoter activity was stimulated by cotransfection with wild type PLC-γ2, PKCα, c-Src, JAK1, or STAT1. An immunocomplex kinase assay showed that both IFN-γ and TPA activated c-Src and Lyn activities and that these effects were inhibited by staurosporine and herbimycin. Thus, in NCI-H292 epithelial cells, IFN-γ activates PLC-γ2 via an upstream tyrosine kinase to induce activation of PKC-α and c-Src or Lyn, resulting in activation of STAT1α, and GAS in the ICAM-1 promoter, followed by initiation of ICAM-1 expression and monocyte adhesion.