RESUMO
AIM: To construct the recombinant plasmid of pGPC3-EGFP containing human AFP(542-550) gene, EGFP gene and GPC3 gene to express fusion protein GPC3-hAFP(542-550)-EGFP and to discover its localization on cytoplasmic membrane. METHODS: GPC3 gene was obtained from total RNA of human placental tissues by RT-PCR; After the enhanced green fluorescent protein (EGFP) gene was amplified from pEGFP-N1 plasmid and the gene segment of-KOZAK-GPCN + afp(542-550)-was chemically synthesized, the recombinant plasmid pcDNA3.1(+)/GPCN+afp(542-550)-EGFP-GPCC (pGPC3-EGFP) containing three chimeric genes of strong epitope hAFP(542-550), GPI-anchored protein GPC3 and EGFP was constructed. The fusion protein (GPC3-hAFP(542-550)-EGFP) was detected on RNA and protein levels at 24 h and 48 h after pGPC3-EGFP was transfected into HepG2 (GPC3(+)AFP(+)) via lipofectamine 2000. EGFP expression was observed by fluorescent microscopy after pGPC3-EGFP was transfected into HepG2 using pEGFP-N1 plasmid transfection as a positive control. The fusion protein in both membrane proteins and soluble proteins extracted from the transfected 293 cells (GPC3(-)AFP(-)) was detected by Western blot using GPC3 monoclonal antibody as primary antibody. RESULTS: The recombinant plasmid pGPC3-EGFP was successfully constructed through restriction endonuclease digestion and sequencing; pGPC3-EGFP expression in HepG2 cells was detected not only by RT-PCR using specific primers (GPCN-F and EGFP-r) but also by Western blot using GFP polyclonal antibody and GPC3 monoclonal antibody. Green fluoresce was mainly found around pGPC3-EGFP transfected HepG2 cell periphery beside sporadic distribution in cytoplasm, but that of pEGFP-N1 transfected HepG2 cell was evenly distributed in the whole cell. Moreover, the fusion protein was not detected in soluble proteins but membrane proteins extracted from transfected 293 cells. CONCLUSION: The recombinant plasmid of pGPC3-EGFP based on protein engineering theory can express fusion protein (GPC3-hAFP(542-550)-EGFP) in eukaryotic cells. Furthermore, the fusion protein is still located on cytoplasmic membrane, which is a characteristic of GPI-anchored membrane protein, and is a new GPI-reanchored protein.
