The histone deacetylase inhibitor sodium butyrate inhibits baculovirus-mediated transgene expression in Sf9 cells

Recent studies have indicated that histone deacetylase inhibitors (HDACis) could enhance and prolong expression of exogenous genes delivered by various viral vehicles in mammalian cells, including baculovirus vectors. In this study, the effects of HDACis on expression of a baculovirus-mediated eGFP reporter gene under control of baculovirus late promoter p10 in Sf9 cells were evaluated. It was found that sodium butyrate (NaBu) decreased the expression level of the target gene driven by p10 promoter by four to fivefold. Moreover, addition of NaBu increased DNaseI-sensitivity of transgene p10 promoter region and did not influence viral DNA replication. FACS assay has shown that both NaBu and fluorodeoxyuridine (FdUrd) blocked Sf9 cells at G1 phase and inhibited the target gene expression. Another HDACi, trichostatin, had little effects on both cell cycle and Ac-p10-eGFP expression, strongly suggesting that cell cycle arrest accounts for the mechanisms by which NaBu inhibits Ac-p10-eGFP expression. The inhibiting effects of NaBu on baculovirus transgene expression in Sf9 cells are promoter specific since the enhancement of NaBu on transgene expression in insect and mammalian cells are mediated by baculovirus harboring a murine cytomegalovirus (mCMV) immediate early promoter. This study was aimed at improving the productivity of the recombinant proteins and providing a better understanding of the epigenetic regulation of baculovirus gene expression.