SECRETION AND REGULATION OF A NEUROPEPTIDE-PROCESSING ENZYME BY ATT-20 CELLS

The mouse anterior pituitary-derived cell line AtT-20 has been widely used to study the biosynthesis and secretion of peptide hormones, such as ACTH, and peptide-processing enzymes, such as carboxypeptidase-E (CPE). Although AtT-20 cells do not express dynorphin (Dyn), previous studies using gene transfer have revealed that these cells are capable of processing pro-Dyn into peptides such as Dyn-B-13. A Dyn-converting enzyme (DCE) has been identified in AtT-20 cells; this enzyme processes Dyn-B-29 to Dyn-B-13. By several criteria, the enzyme activity secreted from AtT-20 cells is similar to the previously characterized enzyme activity in rat brain and bovine pituitary. In AtT-20 cells, the DCE activity and CPE activity are localized to a similar secretory compartment. Upon stimulation with a beta-adrenergic agonist, a phorbol ester, a calcium ionophore, or forskolin, the secretion of DCE activity was increased; this rise was parallel to the secretion of CPE activity and ACTH. These data suggest that DCE activity is in the regulated pathway of secretion. In AtT-20 cells treated with glucocorticoid for up to 7 days, cellular levels of beta-endorphin decreased to half the control levels. In contrast, the levels of DCE activity did not decline in response to this treatment, suggesting that the enzyme activity was not coregulated with the endogenous hormone. Taken together, the data presented here support a role for DCE in posttranslational processing of regulatory peptides.