Abstract
Baculovirus expression system (BEVS) is one of the successful eukaryotic expression system and used widely in basic virological researches, exogenous protein productions for medical usages and structure studies, gene therapy and development of biological insecticides. In this study, we developed recombinant baculovirus as a drug screening platform by the screening rational: if the compound(s) is/are HDACis then it(they) will enhance the baculovirus-mediated gene expression in mammalian cells and also stabilize the hyperacetylation state of histone. Through this drug screeing platform, we screened 699 candidates. Comparing to the control group, there are 45 drugs whose green fluorescence intensities are three times and 14 candidates whose green fluorescence intensities are fourth times. Three candidates, I-E6 (Malotilate, MT), III-H8 (Vorinostat, SAHA) and V-G1 (Sodium salicylate), can increase the level of acetyl histone H4 in U2OS cells. SAHA and Sodium salicylate have been reported as HDACis; however, no references indicated that MT is a HDACi. On the other hand, we found that topoisomerase inhibitors: Teniposide (VM-26), Etoposide (VP-16) can significantly increase the baculovirus-mediated green fluorescent protein expression by inducing intracellular DNA damage response (DDR). Combining MT and VM-26 with the tumor suppressor protein, p53 successfully killed osteosarcoma cells (U2OS), a similar effect combining NaBt with p53. Using RNA interference (RNAi) to analyze standard HDACs (HDAC1-11) and identifing HDAC4 as the critical factor for baculovirus transduction. These findings suggest recombinant baculovirus has a new application to be a screening platform for HDACis. In addition to stabilizing intracellular histone acetylation state, DDR can also increase the efficiency of exogenous gene exprssion in baculovirus- transduced U2OS cells. HDACs involved in the inhibition of baculovirus-mediated gene expression and HDAC4 is the more critical factor.