Tyrosine kinase activation by Newcastle disease virus is required for TNF-alpha gene induction in astrocytes.

Astrocytes, when appropriately stimulated, produce a variety of cytokines including TNF-alpha. Production of TNF-alpha by astrocytes stimulated with Newcastle disease virus (NDV) is achieved by transcriptional activation and mRNA stabilization. A PKC-dependent pathway is responsible for a 10-fold increase in TNF-alpha mRNA stability by reducing poly(A) tail removal. The present study examined signal pathways induced by NDV in primary rat astrocytes that are responsible for TNF-alpha gene transcription as well as the possible source of kinase activity required for mRNA stabilization. Transcription of TNF-alpha gene in astrocytes stimulated by NDV or LPS and IFN-gamma was inhibited completely by the tyrosine kinase inhibitor herbimycin, and partially by a PKC inhibitor H7, as determined by nuclear run-on assay. HA-1004, a cyclic nucleotide-dependent kinase inhibitor, showed no effect. These results indicated that tyrosine kinase signaling pathways seemed to precede the activation of PKC in induction of TNF-alpha gene. Increase in tyrosine kinase activity in NDV-infected astrocytes was demonstrated by a two- to threefold increase in tyrosine phosphorylation of Pl-PLC gamma 1. Because astrocytes contain minimal Pl-PLC beta, and NDV-induced TNF-alpha mRNA was affected by pertussis toxin only modestly, Pl-PLC gamma 1 is likely the enzyme responsible for DAG generation and the PKC-dependent mRNA stabilization in response to NDV.