[Intein-mediated F309SfVIII ligation with enhanced secretion of its heavy chain.]

Coagulation factor VIII (fVIII) is a secretion protein and plays a crucial role in the coagulation cascade. Hemophilia A resulted from deficiency of fVIII is the most common X-linked recessive bleeding disorder. Gene therapy is recognized as an attractive strategy for the eventual cure of this disease. However, the gene therapy is hampered by the big size of fVIII gene when using the most promising gene vectors, adeno-associated virus (AAV) vectors. In this study we explored the intein-mediated protein trans-splicing to deliver a Phe(309)-->Ser mutant full-length fVIII (F309SfVIII) gene by using a dual-vector system. An intein is a protein sequence embedded within a precursor protein and can excise itself through protein splicing. The F309SfVIII is proven to be beneficial to its secretion. The F309SfVIII gene was broken into heavy and light chains before Ser(1239) in B domain and fused with the coding sequences of Ssp DnaB intein respectively to construct a pair of plasmid vectors by inserting them into the pcDNA3.1 vectors. Forty-eight hours after co- or separate transfection of 293 cells, the co-transfected cell lysate showed an obvious ligated F309SfVIII protein band by Western blot with a polyclonal antibody against fVIII. The amounts of secreted F309SfVIII protein in culture supernatants and their bioactivities were (71+/-9) ng/mL and (0.38+/-0.09) IU/mL determined by ELISA and Coatest assay respectively. The supernatant from combined cells with separate transfections also displayed lower levels of F309SfVIII antigen and fVIII activity [(25+/-6) ng/mL and (0.12+/-0.05) IU/mL], indicating the F309SfVIII could be formed by splicing both before and after secretion. The content of F309SfVIII heavy chain protein from co-transfected cell supernatant was higher than that of intein-fused heavy chain transfection alone [(135+/-10) ng/mL vs (37+/-7) ng/mL, P<0.01)]. These data demonstrated that intein could be used as a technical strategy in a dual-vector system delivering F309SfVIII gene with improved secretion of fVIII providing an alternative approach to circumvent the packaging limitation of AAV for F309SfVIII gene transfer, which encourages our continuing study in hemophilia A gene therapy in vivo.