The acidic activation domains of the baculovirus transactivators IE1 and IE0 are functional for transcriptional activation in both insect and mammalian cells

The acidic activation domains (AADs) of the baculovirus transactivators IE1 and IE0 are essential for transcriptional transactivation. To compare the relative transcriptional activation potentials of IE1 and IE0 AADs of Autographa californica multiple nucleopolyhedrovirus (AcMNPV) and Orgyia pseudotsugata MNPV (OpMNPV), we constructed two ecdysone receptor (EcR)-based inducible expression systems to analyse six baculovirus AADs in two insect cell lines (Ld652Y and Sf9) and two mammalian cell lines (NIH-3T3 and CHO). For insect cell expression, the AADs were fused to the C, D, E and F domains of the spruce budworm Choristoneura fumiferana EcR. For mammalian cell expression the AADs were fused to the E and F domains of mammalian Mus musculus retinoid X receptor. In Ld652Y and Sf9 cells, chimeric proteins containing the AcMNPV AADs activated gene expression to higher levels than those containing the OpMNPV AADs. In NIH-3T3 cells, chimeras containing AcMNPV IE1 and IE0 AADs consistently activated gene expression to higher levels than the archetypal mammalian herpesvirus VP16 AAD. In contrast, OpMNPV AADs only activated expression by 5-15% relative to the VP16 AAD. In CHO cells, both AcMNPV and OpMNPV AADs exhibited intermediate transactivation levels relative to VP16 AAD. These results show that the baculovirus AADs are functional for transcriptional activation in mammalian cells and that AcMNPV AADs generally appear to be more potent than OpMNPV AADs in both insect and mammalian cells.