Multiple kinase events, involving both tyrosine (tyr) kinase and serine/threonine (ser/thr) kinase activity, are required for IFN-γ-induced class II MHC mRNA and protein expression in primary rat astrocytes. In this study, we examined the necessity of ser/thr and tyr kinase activity for IFN- γ-induced stimulation of class II MHC gene expression in the human astroglioma cell lines CRT and CH235, as well as the involvement of these kinases in IFN-γ-induced expression of the class II transactivator (CIITA), a protein critical for IFN-γ-induced transcription of class II MHC genes. We show that general ser/thr kinase inhibitors, inhibitors of the ser/thr kinase mitogen-activated protein kinase (MAPK), and tyr kinase inhibitors reduce IFN-γ-induced class II MHC mRNA and protein expression in a dose-dependent manner. As well, these inhibitors abrogate IFN-γ-induced CIITA mRNA expression in the astroglioma cell lines. We have further demonstrated that cells constitutively expressing the CIITA protein (2fTGH.CIITA) show no decrease in CIITA or class II MHC mRNA expression in the presence of ser/thr and tyr kinase inhibitors. Collectively, these data indicate that ser/thr kinase activity, possibly MAPK, and tyr kinase activity are required for IFN- γ-induced expression of CIITA mRNA, and the subsequent expression of class II MHC genes.