Production of bioactive gastrin from the non‐endocrine cell lines CHO and COS‐7

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Abstract
We made a mutated progastrin cDNA construct that contains a cleavage site (‐Arg−4‐Arg−3‐Lys−2 ‐Arg−1) specific for the Kex2‐like endoprotease furin, located ahead of the bioactive gastrin. For expressing the mutated progastrin cDNA, we used two non‐endocrine cell lines, CHO and COS‐7. CHO cells exhibit amidating enzyme activity and levels of amidation enzyme mRNA as high as those in the pituitary‐derived endocrine cell line GH3, whereas COS‐7 cells have far less amidating activity and lower amounts of mRNA. Mutant progastrin‐expressing CHO cells produced mostly amidated gastrin. Gel filtration showed the size of this gastrin corresponded to that of the synthetic human gastrin‐17. In contrast, COS‐7 cells produced glycine‐extended gastrin and only a small amount of amidated gastrin. The difference in the amount of amidated gastrin products produced by the two non‐endocrine cell lines is due to differing amounts of the amidation enzyme contained in each cell line.