Abstract
The inability to produce recombinant glycoproteins with authentic N-glycans is a limitation of many heterologous protein expression systems. In the baculovirus-insect cell system, this limitation has been addressed by glycoengineering insect cell lines with mammalian genes encoding protein N-glycosylation functions ("glycogenes") under the transcriptional control of constitutive promoters. However, a potential problem with this approach is that the metabolic load imposed by the expression of multiple transgenes could adversely impact the growth and/or stability of glycoengineered insect cell lines. Thus, we created a new transgenic insect cell line (SfSWT-5) with an inducibly mammalianized protein N-glycosylation pathway. Expression of all six glycogenes was induced when uninfected SfSWT-5 cells were cultured in growth medium containing doxycycline. Higher levels of expression and induction were observed when SfSWT-5 cells were cultured with doxycycline and infected with a baculovirus. Interestingly, there were no major differences in the short-term growth properties of SfSWT-5 cells cultured with or without doxycycline. Furthermore, there were no major differences in the phenotypic stability of these cells after continuous culture for over 300 passages with or without doxycycline. Baculovirus-infected Sf9 and SfSWT-5 cells produced about the same amounts of a model recombinant glycoprotein, but only the latter sialylated this product and sialylation was more pronounced when the cells were treated with doxycycline. In summary, this is the first report of a lower eukaryotic system with an inducibly mammalianized protein N-glycosylation pathway and the first to examine how the presumed metabolic load imposed by multiple transgene expression impacts insect cell growth and stability.