Studies on the antiviral mechanisms of protein kinase inhibitors K-252a and KT5926 against the replication of vesicular stomatitis virus

We investigated the Antiviral mechanisms of K-252a, a broad non-specific protein kinase inhibitor which was isolated from Nocardiopsis sp. and its derivative (KT5926), against vesicular stomatitis virus (VSV) replication in BHK-21 cells. Although K-252a (5 microM) and KT5926 (15 microM) similarly suppressed the viral primary and secondary transcriptions and genomic RNA synthesis in vivo, the inhibitory mechanisms did not seem to be the same; phosphorylation of the viral NS protein was suppressed by K-252a, which might account for the decreased viral RNA synthesis caused by K-252a. On the other hand, KT5926, being known to preferentially inhibit Myosin light chain kinase (MLCK), had little effect on NS protein phosphorylation. Cellular Casein Kinase II, which is believed to be involved in the phosphorylation of the N-terminal side (domain I) of NS protein, was not inhibited at all by KT5926 even at 15 microM under in vitro assay conditions, and was only weakly inhibited by K-252a at 1 to 10 microM. Neither inhibitor seemed to directly affect viral protein synthesis, but affected it indirectly as a secondary effect of reduced viral RNA synthesis. These results suggest that both the KT5926-sensitive and the KT5926-resistant but K-252a-sensitive functions are involved in the essential processes of viral RNA synthesis. The KT5926-sensitive function(s) might not be involved in the NS protein phosphorylation, but may participate in some other way in the process of virus replication. On the other hand, the KT5926-resistant, K-252a-sensitive function(s) are probably involved in NS protein phosphorylation. The possible nature of those functions is discussed.