Expression of FSH in CHO cells I. Comparison of promoter types and effects of their respective inducers

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Abstract
The expression levels of recombinant human follicle stimulating hormone (r-hFSH) were studied in several CHO-K1 derived cell lines. The cell lines varied in the promoter used to control r-hFSH expression and in the subunit gene copy ratio. FSH is a heterodimeric molecule, with 2 N-glycosylation sites per peptide chain, and shares a common alpha subunit with the other gonadotropins. Serum stimulated FSH production in the beta actin promoter cell lines 2–3 times over the 7–10 ng/106 cells/h levels obtained in protein-free medium. Serum seemed to have roles other than purely at the transcriptional level judging by the increased free alpha to dimer ratio secreted from cell cultrured in serum-free medium. Zinc induced FSH expression in metallothionein cell lines, with a 3-fold induction at 50μM concentrations compared to 0μM zinc, giving specific productivities of about 7–10 ng/106 cells/h, but the induction kinetics were complicated, and suggested other roles for zinc in addition to activation of the metallothionein promoter. Evidence suggested significant post-transcriptional regulation of FSH expression.