Differential Role of Janus Family Kinases (Jaks) in Interferon-Gamma- Induced Lung Epithelial Icam-1 Expression: Involving Protein Interactions between Jaks, Phospholipase C Gamma,C-Src, and Stat1

The signaling pathway for IFN-gamma-mediated induction of ICAM-1 expression was further studied in human NCI-H292 epithelial cells. The Tyr 701 phosphorylation of signal transducer and activator of transcription 1 (STAT1) induced by interferon-gamma (IFN-gamma) and 12-O- tetradecanoylphorbol 13-acetate (TPA) was inhibited by the protein kinase C (PKC) inhibitor staurosporine, the tyrosine kinase inhibitor herbimycin, or the Src kinase inhibitor PP 2. An association between c-Src and STAT1 was increased by IFN-gamma and TPA, indicating the direct phosphorylation of STAT1 by PKC-dependent c-Src activation. Tyrosine phosphorylation of Janus kinases (JAK) 1/2 was induced by IFN-gamma but not by TPA. In addition, ICAM-1 promoter activity induced by IFN-gamma, but not that induced by TPA, was inhibited by the dominant-negative JAK1 and JAK2 mutants . IFN-gamma induced tyrosine phosphorylation of phospholipase C ( PLC)-gamma was inhibited by AG 490 ( a JAK inhibitor), and the association between JAK1/2 and PLC- gamma was increased after IFN-gamma treatment, indicating the activation of PLC-gamma via JAK1/2 phosphorylation. ICAM -1 promoter activities induced by the overexpression of wild -type JAK1- and PLC-gamma2 were blocked by the PLCgamma2 mutant or the dominant-negative PKCalpha (Lys-->Arg), c-Src( Lys-->Met), or STAT1 (Y701M) mutants, but not by dominant- negative STAT3 (DN) mutants. These results confirmed that IFN-gamma activated PLC-gamma via JAK1/2 phosphorylation to induce PKC, c- Src, STAT1 activation, and ICAM-1 expression. The association between JAK1 /2 and STAT1 was increased by IFN-gamma but not by TPA. It was inhibited by AG 490 but not by U73122, indicating the possible involvement of the JAK1/ 2-STAT1 pathway. All the results show that IFN-gamma induces ICAM-1 expression by two different pathways in NCI-H 292 epithelial cells. One is the JAK1/2-dependent PLC-gamma pathway inducing the activations of PKCalpha, c-Src, and STAT1, and the other is the direct activation of STAT 1 by JAK1/2