Early events play a decisive role in virus multiplication. We have shown previously that activation of MAPK/ERK1/2 (
mitogen-activated protein kinase/
extracellular-signal-regulated kinase 1/2) and
protein kinase A are pivotal for vaccinia virus (VV) multiplication [de Magalhães, Andrade, Silva, Sousa, Ropert, Ferreira, Kroon, Gazzinelli and Bonjardim (2001) J. Biol. Chem. 276, 38353-38360]. In the present study, we show that VV
infection provoked a sustained activation of both ERK1/2 and RSK2 (
ribosomal S6 kinase 2). Our results also provide evidence that this pattern of
kinase activation depends on virus multiplication and ongoing
protein synthesis and is maintained independently of virus DNA synthesis. It is noteworthy that the VGF (VV
growth factor), although involved, is not essential for prolonged ERK1/2 activation. Furthermore, our findings suggest that the VV-stimulated ERK1/2 activation also seems to require actin dynamics, microtubule polymerization and
tyrosine kinase phosphorylation. The VV-stimulated pathway
MEK/ERK1/2/RSK2 (where
MEK stands for
MAPK/ERK kinase) leads to phosphorylation of the ternary complex factor Elk-1 and expression of the early growth response (egr-1) gene, which kinetically paralleled the
kinase activation. The recruitment of this pathway is biologically relevant, since its disruption caused a profound effect on viral
thymidine kinase gene expression,
viral DNA replication and VV multiplication. This pattern of sustained
kinase activation after VV
infection is unique. In addition, by connecting upstream signals generated at the cytoskeleton and by
tyrosine kinase, the
MEK/ERK1/2/RSK2 cascade seems to play a decisive role not only at early stages of the
infection, i.e. post-penetration, but is also crucial to define the fate of virus progeny.