Stimulation of baculovirus transcriptome expression in mammalian cells by baculoviral transcriptional activators.

Autographa californica multiple nucleopolyhedrovirus (AcMNPV), the type species of the family Baculoviridae, is an insect-specific virus that can enter a variety of mammalian cells. The potential of this versatile virus for protein expression or gene therapy in mammalian cells has become the focus of many studies. In most mammalian cells, transduced AcMNPV genes are either not expressed or expressed at an extremely low level. Here, we studied the effects of the two major AcMNPV trans-activators, IE1 and IE2, on the activation of AcMNPV genome in Vero E6 cells. Microarray analysis showed that when IE1 was overexpressed, it significantly activated genes gp64 and pe38, and upregulated ie2, he65, pcna, orf16, orf17 and orf25. Although, there were only two genes, pe38 and orf17, that were activated by IE2, we discovered interestingly that the combination of IE1 and IE2 factors had a synergistic effect on activation of the AcMNPV genome in mammalian cells, and activated around 38 %, or 59 out of the 155 genes placed on the microarray. This is the first detailed study of baculoviral transcription regulation in mammalian cells, and it shows that the baculoviral genome can be activated in a mammalian system, and also that the two major trans-activators, IE1 and IE2, play a central role in this activation.