Angiotensin-Converting Enzyme (ACE) Dimerization Is the Initial Step in the ACE Inhibitor-Induced ACE Signaling Cascade in Endothelial Cells

The binding of angiotensin-converting enzyme (ACE) inhibitors to ACE initiates a signaling cascade that involves the phosphorylation of the enzyme on Ser1270 as well as activation of the c-Jun NH2-terminal kinase (JNK) and leads to alterations in gene expression. To clarify how ACE inhibitors activate this pathway, we determined their effect on the ability of the enzyme to dimerize and the role of ACE dimerization in the initiation of the ACE signaling cascade. In endothelial cells, ACE was detected as a monomer as well as a dimer in native gel electrophoresis and dimerization/oligomerization was confirmed using the split-ubiquitin assay in yeast. ACE inhibitors elicited a rapid, concentration-dependent increase in the dimer/monomer ratio that correlated with that of the ACE inhibitorinduced phosphorylation of ACE. Cell treatment with galactose and glucose to prevent the putative lectin-mediated self-association of ACE or with specific antibodies shielding the N terminus of ACE failed to affect either the basal or the ACE inhibitor-induced dimerization of the enzyme. In ACE-expressing Chinese hamster ovary cells, ACE inhibitors elicited ACE dimerization and phosphorylation as well as the activation of JNK with similar kinetics to those observed in endothelial cells. However, these effects were prevented by the mutation of the essential Zn2+-complexing histidines in the C-terminal active site of the enzyme. Mutation of the N-terminal active site of ACE was without effect. Together, our data suggest that ACE inhibitors can initiate the ACE signaling pathway by inducing ACE dimerization, most probably via the C-terminal active site of the enzyme.