Secretion of green fluorescent protein from recombinant baculovirus-infected insect cells.

Trichoplusia ni (High Five) and Spodoptera frugiperda (Sf21) cells were engineered for expression of epitope (Flag)-tagged signal peptide-green fluorescent protein (GFP) fusions to examine the suitability of GFP as a secretory marker. The recombinant baculovirus-infected cells became fluorescent, and the High Five cells but not Sf21 cells secreted GFP in the culture medium as detected by the presence in the culture supernatant of a Flag-immunoreactive 30-kDa species and the characteristic 510-nm GFP fluorescence peak. Signal peptides derived from ecdysteroid UDP-glucosyltransferase of Autographa californica nuclear polyhedrosis virus and from rat brain glutamate receptor were both able to promote secretion of GFP. GFP may thus be used as a research tool in the study of the secretory process in insect cells both in cell biology and in biotechnological applications.