Vaccinia virus infection induces a stress response that leads to association of Hsp70 with viral proteins.

We studied the impact of vaccinia virus infection on stress protein gene expression in human cells and investigated the possibility that eukaryotic heat shock proteins interact with viral components during assembly. Infection of human monocyte-macrophages by vaccinia virus caused a dramatic decrease in levels of cellular mRNAs such as those encoding actin and tubulin. In contrast, infection did not cause a significant reduction in the levels of Hsp90 and Hsp60 mRNAs and led to substantially increased levels of Hsp70 mRNAs. The accumulation of these stress protein mRNAs was due both to increases in their transcription rate and to their stability relative to other cellular mRNAs. The relative levels of the heat shock proteins and the other cellular proteins reflected the relative levels of their mRNAs. These results indicate that stress protein gene expression is relatively refractory to the generally deleterious effects of vaccinia virus infection on host cell gene expression. The continued expression of some of these stress proteins may be beneficial to the virus; the observations that the levels of Hsp70 are greatest at the peak of viral gene expression and that a large fraction of cellular Hsp70 is associated with vaccinia virus proteins suggest that Hsp70 is involved in vaccinia virus assembly.