TYROSINE KINASE ACTIVATION BY NEWCASTLE-DISEASE VIRUS IS REQUIRED FORTNF-ALPHA GENE INDUCTION IN ASTROCYTES

Astrocytes, when appropriately stimulated, produce a variety of cytoki nes including TNF-alpha. Production of TNF-alpha by astrocytes stimula ted with Newcastle disease virus (NDV) is achieved by transcriptional activation and mRNA stabilization. A PKC-dependent pathway is responsi ble for a 10-fold increase in TNF-alpha mRNA stability by reducing pol y(A) tai I removal. The present study examined signal pathways induced by NDV in primary rat astrocytes that are responsible for TNF-alpha g ene transcription as well as the possible source of kinase activity re quired for mRNA stabilization. Transcription of TNF-alpha gene in astr ocytes stimulated by NDV or LPS and IFN-gamma was inhibited completely by the tyrosine kinase inhibitor herbimycin, and partially by a PKC i nhibitor 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 t he activation of PKC in induction of TNF-alpha gene. Increase in tyros ine kinase activity in NDV-infected astrocytes was demonstrated by a t wo- to threefold increase in tyrosine phosphorylation of PI-PLC gamma 1. Because astrocytes contain minimal PI-PLC beta, and NDV-induced TNF -alpha mRNA was affected by pertussis toxin only modestly, PI-PLC gamm a 1 is likely the enzyme responsible for DAG generation and the PKC-de pendent mRNA stabilization in response to NDV.