Expression of human plasminogen in Drosophila Schneider S2 cells

The cDNA that encodes full-length human plasminogen (Glu1-hPg) has been expressed in Drosophila Schneider S2 cells under the influence of the Drosophila BiP protein signal sequence, which allowed the protein to be secreted into the medium. A procedure was devised for clonal selection of high-expressing cells, which were then used for large-scale expression of 10-15 mg/liter of the protein in the culture medium. The protein produced using this system was extensively characterized and contained full-length recombinant (r) Glu1-hPg plasminogen. As with human plasma Glu1-hPg, the S2-expressed protein underwent the Cl--induced transition to the tight conformation, which resulted in a weakly activatable zymogen. The addition of the ligand, epsilon-amino caproic acid, induced the relaxed conformation of r-Glu1-hPg, which was highly activatable, again in agreement with similar data for human plasma Glu1-hPg. The thermal stability of the S2-expressed r-Glu1-hPg also correlated well with that of human plasma hPg. These studies show that intact r-Glu1-hPg can be produced in high yield in Drosophila Schneider S2 cells, which possesses similar properties to its human plasma counterpart.