Biopharmaceuticals, including therapeutic antibodies, are rapidly
growing products in the pharmaceutical market. Mammalian cells, such as
Chinese hamster ovary (CHO) cells, are widely used as production hosts
because recombinant antibodies require complex three-dimensional
structures modified with sugar chains. Recombinant protein production
using mammalian cells is generally performed in conjunction with cell
growth. In this study, we developed a technology that controls cell
growth and recombinant protein production to induce recombinant protein
production with arbitrary timing. Expression of green fluorescent
protein (GFP) gene and a single-chain antibody fused with the Fc-region
of the human IgG1 (scFv-Fc) gene can be induced and mediated by the
estrogen receptor-based artificial transcription factor Gal4-ERT2-VP16
and corresponding inducer drugs. We generated CHO cells using an
artificial gene expression system. The addition of various
concentrations of inducer drugs to the culture medium allowed control of
proliferation and transgene expression of the engineered CHO cells. Use
of 4-hydroxytamoxifen, an antagonist of estrogen, as an inducing agent
yielded high gene expression at a concentration more than 10-fold lower
than that of β-estradiol. When scFv-Fc was continuously produced under
inducing conditions, stable production was possible for more than 2
weeks while maintaining high specific productivity (57 pg
cell-1 day-1). This artificial gene
expression control system that utilizes the estrogen response of
estrogen receptors can be an effective method for inducible production
of biopharmaceuticals.