Cetyltriethylammonium bromide stimulating transcription of Bombyx mori nucleopolyhedrovirus gp64 gene promoter mediated by viral factors

Gene transduction in mammalian cells using Bombyx mori nucleopolyhedrovirus assisted by glycoprotein 64 of Autographa californica multiple nucleopolyhedrovirus

Autographa californica multiple nucleopolyhedrovirus (AcMNPV), an alphabaculovirus, has been widely utilized for protein expression in not only insect cells but also mammalian cells. AcMNPV is closely related to Bombyx mori nucleopolyhedrovirus (BmNPV), and nucleotide sequences of AcMNPV genes have high similarity with those of BmNPV. However, the transduction of BmNPV into mammalian cells has not been reported. In this study, we constructed a recombinant BmNPV (BmNPVΔbgp/AcGP64/EGFP) whose surface 64 kDa glycoprotein (BmGP64) was substituted with that from AcMNPV (AcGP64). BmNPVΔbgp/AcGP64/EGFP also carried an EGFP gene under the control of the CMV promoter. BmNPVΔbgp/AcGP64/EGFP successfully transduced HEK293T cells. In comparison, a control construct (BmNPVΔbgp/BmGP64/EGFP) which possessed BmGP64 instead of AcGP64 did not express EGFP in HEK293T cells. The transduction efficiency of BmNPVΔbgp/AcGP64/EGFP was lower than that of an AcMNPV based-BacMam GFP transduction control. This result indicates that AcGP64 facilitates BmNPV transduction into HEK293T cells. BmNPV can be prepared easily on a large scale because BmNPV can infect silkworm larvae without any special equipment, even though specific diet is needed for silkworm rearing. BmNPV gene transduction into mammalian cells can potentially be applied easily for gene delivery into mammalian cells.

A constitutive super-enhancer: homologous region 3 of Bombyx mori nucleopolyhedrovirus

Transient expression assays were carried out to assess the transcriptional enhancement from the immediate-early gene (ie-1) promoters by cis-linked Bombyx mori nucleopolyhedrovirus (BmNPV) homologous region-3 (hr3). The ie-1 promoters were derived from Autographa californica multinucleocapsid nucleopolyhedrovirus (AcMNPV) and BmNPV. Hr3 was placed downstream of the luciferase (luc) gene, the resulting plasmids were used to transfect the Spodoptera frugiperda (Sf-21), Bombyx mori (Bm-5, Bm-N) cell lines and 5th instar silkworm larvae mediated by lipofectin. The results revealed that hr3 could stimulate the transcription of homologous BmNPV ie-1 promoter 1970, 2421, 683, and 1059 folds, and the heterologous AcMNPV ie-1 promoter 6462, 4046, 6980, and 605 folds, respectively. These results implied that hr3 was a super enhancer which could function both in vitro and in vivo. The 30-bp imperfect palindrome in hr3 was proved to be the essential structure for enhancing function of hr3. The utilizing of this promoter-enhancer combination in the baculovirus expression vector system (BEVS) was also carried out to further confirm the function of hr3 enhancer.