The studies on the transfection of EGFP-fused porcine circovirus Type 2 genome.

This study described construction and transfection of an EGFP-fused Porcine Circovirus Type 2 (PCV2) genome and the recovery of the virus. Posttransfection, PCV2 (ORF1)-EGFP/pSK, PCV2 (ORF3)-EGFP/pSK, PCV2 (ORF4)-EGFP/pSK and PCV2(ORF5)-EGFP/pSK showed no fluorescent signals in transfected cells, while green fluorescent signals were observed in the nuclei of PK-15 cells after PCV2 (ORF2)-EGFP/pSK transfection. The presence of ORF2-EGFP fusion protein was demonstrated by dual signals of green fluorescence and anti-PCV2 antibodies conjugated with rhodamine in an immunofluorescence assay (IFA). Furthermore, the released EGFP-fused PCV2 genome was demonstrated by real-time PCR.

The nuclear localization signal sequence of porcine circovirus type 2 ORF2 enhances intracellular delivery of plasmid DNA.

The phospholipid bilayer of the cell membrane is a natural barrier that prevents large molecules from entering the cell. Cationic liposomes are commonly used for transfection of plasmid DNA but they have high cost and toxicity. Many reports have shown that cell-penetrating peptides (CPP) are able to translocate across the cell membrane efficiently. The VP22 peptide of herpes simplex virus (HSV) was synthesized as a CPP. Two fusion protein candidates, containing binding/condensing protein (VP22-TmHU) and porcine circovirus type 2 nuclear localization signal (VP22-TmHU-PCV2.NLS), were constructed and expressed in E. coli in an attempt to improve delivery of plasmid DNA (pDNA). Firstly, as shown by the electrophoretic mobility shift assay (EMSA), VP22-TmHU (VT) and VP22-TmHU-PCV2.NLS (VTN) were able to bind to pDNA (pEGFP-N1) effectively. Secondly, intracellular transport of pEGFP-N1 was observed by fluorescence microscopy and quantified by flow cytometry after transfection. VTN was successful in delivering pEGFP-N1 intracellularly but VT was not. Thirdly, two protein candidates were combined with Lipofectamine, and both VT and VTN enhanced the transfection rate to 65%, compared to 25% with Lipofectamine alone. Lastly, mice were injected intramuscularly with PBS, pcDNA3-ORF2, pcDNA3-ORF2 plus Lipofectamine, pcDNA3-ORF2 plus VT, pcDNA3-ORF2 plus VT plus Lipofectamine, pcDNA3-ORF2 plus VTN, and pcDNA3-ORF2 plus VTN plus Lipofectamine. The highest level of antibodies raised against PCV2 ORF2 Cap protein was detected with pcDNA3-ORF2 plus VTN. Contrary to the in vitro results, VTN delivered pDNA effectively in vivo without Lipofectamine. In summary, the nuclear localization signal sequence of porcine circovirus type 2 ORF2 can enhance intracellular delivery of pDNA.