Expression of FSH in CHO cells. II. Stimulation of hFSH expression levels by defined medium supplements.

A Chinese Hamster Ovary (CHO-K1) derived cell line, which expresses human follicle stimulating hormone (hFSH) under the control of a beta actin promoter, was used as a model system to study heterologous glycoprotein expression. It has been shown previously that specific productivities in this cell line were three times higher in the presence of serum than in its absence. In this paper, a systematic study was made of the affects of various serum components of product levels in order to determine if the affect of serum on FSH expression could be duplicated by defined medium supplements. Culture media were supplemented with growth factors, direct activators of secondary messengers, steroids, lipids and various sugars. It was shown that the components with the most stimulatory affect of hFSH expression were sodium butyrate, mevalonate and hydrocortisone. Although butyrate has been shown to elevate transcription of some genes, it was concluded that this could not have been the only mechanism of action, since mevalonate and hydrocortisone are both implicated in the lipid pathway of protein glycosylation, but not with transcriptional activation of the beta actin promoter. Conversely, actual supply of dolichol-linked oligosaccharide for glycosylation was probably not rate limiting, since butyrate has never been reported to affect the supply of this comerabolite, but glycosylation is likely to be implicated in some way.