ACTH-DEPENDENT PROTEOLYTIC ACTIVITY OF A NOVEL PHOSPHOPROTEIN (P43) INTERMEDIARY IN THE ACTIVATION OF PHOSPHOLIPASE A(2) AND STEROIDOGENESIS

Arachidonic acid (AA) and the lipooxygenase products have been shown t o play an obligatory role in the mechanism of action of LH and ACTH, a t a point after cAMP-dependent phosphorylation. We have demonstrated t he presence of a phosphoprotein (p43) that responds to cAMP signals to induce steroid synthesis in adrenocortical tissue, an effect that is blocked by phospholipase A2 inhibitors. In this report we demonstrate that p43 exhibits autoproteolytic activity that is regulated by ACTH. Protein purified from ACTH-treated animals exhibited degradation in so me of the isoforms resolved on two dimensional gel electrophoresis. Pr oteinase inhibitors (PMSF and 1,10 phenantroline) inhibited steroid sy nthesis induced by ACTH and 8-Br-cAMP in intact cells. Addition of exo genous AA reverted in part that inhibition. Here we present evidence f or a hormone-regulated proteolytic activity of p43 and for the inhibit ion of steroidogenesis by proteinase inhibitors acting prior to the re lease of arachidonic acid.