Inhibitory effect of protein kinase C inhibitor on the replication of influenza type A virus.

The growth of influenza virus A/PR/8/34 in MDCK cells was inhibited by 1-(5-isoquinolinesulphonyl)-2-methylpiperazine dihydrochloride (H7) which is a potent inhibitor of protein kinase C, but not by an effective inhibitor of cyclic nucleotide-dependent protein kinases. Analysing the inhibitory effect of H7 during the replication cycle of influenza virus, we found that the primary transcripts were sufficiently synthesized in infected cells exposed to H7. The primary transcripts synthesized in the presence and absence of H7 were active in directing the synthesis of viral polypeptides both in a cell-free system and in the system containing H7. In the system where infected cells were exposed to H7, the viral positive-sense RNAs were also significantly amplified 6 h after infection. However, the synthesis of viral proteins other than nucleoprotein from viral primary or amplified (secondary) mRNAs was extremely restricted. The synthesis of host cellular proteins in mock-infected cells was significantly retained in the presence of H7. These results suggest that the selective inhibition of influenza virus translation following the transcription of viral mRNA was induced by H7 in infected cells.