Effect of IgG Fc-fusion and KDEL-ER retention signal on prostate-specific antigen expression in plant and its immune in mice

Prostate-specific antigen (PSA) is a protein highly expressed in cancer cells of the prostate gland. In this study, the PSA recombinant protein was fused to the human immunoglobulin G crystallizable fragment (Fc) with the endoplasmic reticulum (ER) Lys-Asp-Glu-Leu (KDEL) retention signal tag for the plant expression system. Agrobacterium -mediated plant transformation was applied to generate transgenic tobacco plants expressing PSA tagged to KDEL (PSAK), PSA-Fc, and PSA-Fc fused to KDEL (PSA-FcK). Western blot analysis showed that the PSA-FcK protein was the most highly expressed among the three different proteins in the transgenic plant leaf. The PSAK, PSA-Fc, and PSA- FcK proteins were successfully purified from plant leaves. Reduced and non-reduced sodium dodecyl sulfate–polyacrylamide gel electrophoresis revealed that the PSA proteins fused to Fc and FcK were dimerized, whereas the PSA itself was not dimerized. N -glycan analysis demonstrated that the N -glycan profile of the PSA-Fc was mainly the structure with α (1,3)-fucose (Fuc) or β (1,2)-xylose (Xyl) glycan residues, whereas the PSA-Fc tagged with the KDEL ER retention signal had mainly an oligomannose-type structure. ELISA and SPR showed that PSA-FcK had a higher binding activity to Fc gamma receptor I than PSA-Fc and human Fc. In addition, PSA-FcK induced anti-PSA, and thus has the potential to be utilized as a prostate cancer vaccine.