High level expression of tissue inhibitor of metalloproteinases in Chinese hamster ovary cells using glutamine synthetase gene amplification.

We have used a glutamine synthetase (GS) gene as an amplifiable marker in Chinese hamster ovary (CHO) cells. GS was combined with an efficient transcription unit to produce tissue inhibitor of metalloproteinases (TIMP). Initial transfectant cell-lines selected using a GS gene secreted up to 9 micrograms TIMP/10(6) cells/24h. After one round of GS gene amplification expression levels of 110 micrograms TIMP/10(6) cells/24h were achieved. These GS gene amplified CHO cells, when adapted to grow in suspension, accumulated 180mg/l in shake flask culture. This system therefore provides a rapid method of achieving high level gene expression in mammalian cells.