Enhancement of papillomavirus L1 gene expression and the immune responses of DNA vaccine and its mechanisms
Objective To explore the approaches and the possible mechanisms of the papillomavirus (PV) L1 gene expression and the immune responses of DNA vaccinations. Methods Recombinant eukaryotic expression vectors containing codon optimized BPVL1-GFP (HL1-GFP) fusion gene and wild type BPVL1-GFP (WL1-GFP) fusion gene transfected HaCAT cells alone or cotransfected with pSVyRNAser separately. The transient expressions of the fusion proteins were examined by fluorescence microscopy and Western blot method. Message RNA expression of different L1 genes was measured by semi-quantitative RT-PCR. For in vivo studies, some female BALB/c mice were immunized intramuscularly with wild-type and codon modified L1 DNA vaccine individually, meanwhile, some other female BALB/c mice were immunized with the combination of pSVtRNAser and L1 DNA vaccine. Results Fluorescence microscopy and Western blot results showed that HL1-GFP gene readily expressed in HaCAT cells, while WL1-GFP gene failed to express. Semi-quantitative RT-PCR suggested that there was no significant difference in mRNA expression levels between HL1 and WL1 genes. Cells cotransfected with pS-VtRNAser and WLl-GFP gene produced higher levels of L1 protein than those transfected with WL1 gene only. In vivo study results indicated that mice immunized with HLl DNA vaccination elicited significandy higher levels of L1-specific serum IgG than those with WLl immunization. The mice immunized with tRNAser and WL1 gene produced higher IgG antibody level than those with WLl immunization only. Conclusion Codon usage optimization can significandy enhance PV L1 protein expression in mammalian cells and the humoral immune response of DNA vaccine, and supplementation of exogenous tRNA can also promote wild-type L1 protein expression in mammalian cells and the humoral immune response.