EXPRESSION OF FSH IN CHO CELLS .2. STIMULATION OF HFSH EXPRESSION LEVELS BY DEFINED MEDIUM SUPPLEMENTS

A Chinese Hamster Ovary (CHO-K1) derived cell line, which expresses hu man follicle stimulating hormone (hFSH) under the control of a beta ac tin promoter, was used as a model system to study heterologous glycopr otein expression. It had been shown previously that specific productiv ities in this cell line were three times higher in the presence of ser um than in its absence. In this paper, a systematic study was made of the affects of various serum components on 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 g rowth factors, direct activators of secondary messengers, steroids, li pids and various sugars. It was shown that the components with the mos t stimulatory affect of hFSH expression were sodium butyrate, mevalona te and hydrocortisone. Although butyrate has been shown to elevate tra nscription of some genes, it was concluded that this could not have be en the only mechanism of action, since mevalonate and hydrocortisone a re both implicated in the lipid pathway of protein glycosylation, but not with transcriptional activation of the beta actin promoter. Conver sely, actual supply of dolichol-linked oligosaccharide for glycosylati on was probably not rate limiting, since butyrate has never been repor ted to affect the supply of this comerabolite, but glycosylation is li kely to be implicated in some way.