Use of regulated secretion in protein production from animal cells: an evaluation with the AtT-20 model cell line

Regulated secretion, i.e., the ability of certain specialized animal cells to store secretory proteins intracellularly and release them upon stimulation, may be used to realize production schemes that facilitate downstream processing of protein products. Mouse AtT-20 cells expressing recombinant human insulin and human growth hormone (hGH) were found to secrete the proteins at relatively low and constant rates when exposed to media with no secretion agonists: basal rates were 1.0-1.6 microU insulin-related peptides and 0.38 ng hGH/10(5) cells-h. When induced with 8 brorno-cyclic AMP (BrcAMP), the cells secreted recombinant proteins at initial rates 3.5-9-fold higher. A cycling secretion experiment was conducted with the insulin-producing cells in which the cells were exposed alternately to complete growth medium and to secretion medium with BrcAMP. During the first three cycles, the cells secreted immunoreactive insulin at the foregoing high induced rates when they were exposed to BrcAMP. The cells then started to detach from the culture surface, leading to a reduction of BrcAMP-induced secretion. Operational modifications that may result in improved system performance are discussed.