Regulation of Carboxypeptidase E by Membrane Depolarization in PC12 Pheochromocytoma Cells: Comparison with mRNAs Encoding Other Peptide‐ and Catecholamine‐Biosynthetic Enzymes

Abstract: PC12 cells, a rat pheochromocytoma cell line, have been found to express carboxypeptidase E (CPE) enzymatic activity and CPE, furin, and peptidylglycine α‐amidating monooxygenase (PAM) mRNAs. PC12 cells secrete CPE activity in response to depolarization induced by 50 mM KCl. Short‐term (1‐ to 3‐h) treatments of PC12 cells with KCl stimulates the secretion of CPE but does not appear to stimulate the synthesis of new CPE protein, based on the measurement of CPE activity and incorporation of [³⁵S]‐Met into CPE. Also, CPE mRNA is not altered by 2‐h treatments with KCl. In contrast, prolonged treatment (24–48 h) of PC12 cells with 50 mM KCl continues to stimulate the secretion of CPE activity, without altering the cellular level of CPE. Levels of CPE mRNA are significantly elevated after long‐term treatment of the cells with KCl, with increases of 35% after 5 h and 55–75% after 24 to 72 h of treatment. The level of PAM mRNA is also elevated approximately 70% after 24 h of stimulation with KCl. In contrast, the mRNA levels of furin and dopamine β‐hydroxylase (DBH) do not change on treatment of PC12 cells with KCl. These findings indicate that long‐term depolarization, which leads to a prolonged stimulation of PC12 cells to secrete CPE, also stimulates the synthesis of CPE and PAM but not furin of DBH.