REGULATED SECRETION OF PROLACTIN BY THE MOUSE INSULINOMA CELL-LINE BETA-TC-3

Our aim is to use cultured cells capable of regulated protein secretio n for the production of recombinant proteins that require particular t ypes of post-translational modifications, Here we have generated a sta ble transfected beta TC-3 cell line, beta TC-IPR9, that secretes high levels of recombinant prolactin. Transfected cells synthesize both the 27 kDa glycosylated and a 23 kDa nonglycosylated prolactin; the 23 kD a nonglycosylated species was secreted preferentially when cells were placed in secretion medium containing isobutylmethylxanthine (IBMX) an d high concentrations of glucose, K+, and Ca2+, When the cells were cu ltured in medium containing low concentrations of glucose, K+, and Ca2 +, most of the prolactin and insulin were not secreted; much of the pr olactin was proteolytically converted to a 16 kDa form. Within the fir st 30 minutes after transferring the cells to medium containing secret agogues there was a 20-fold increase in the rate of secretion of prola ctin; all of the 16 kDa species was secreted, The recombinant cells co uld be cycled several times between medium in which prolactin was bios ynthesized and medium in which it was secreted, Preferential secretion of proteolytically processed prolactin in a medium without contaminat ing proteins offers an example of the advantage of this technology for production of other recombinant proteins.