Replacement of the transmembrane anchor in angiotensin I-converting enzyme(ACE) with a glycosylphosphatidylinositol tail affects activation of the B-2 bradykinin receptor by ACE inhibitors

To investigate further the relationship of angiotensin I-converting enzyme (ACE) inhibitors to activation of the B-2 bradykinin (BK) receptor, we tran sfected Chinese hamster ovary cells to stably express the human receptor an d either wild-type ACE (WT-ACE), an ACE construct with most of the cytosoli c portion deleted (Cytdel-ACE), or ACE with a glycosylphosphatidylinositol (GPI) anchor replacing the transmembrane and cytosolic domains (GPI-ACE). B K or its ACE-resistant analogue were the agonists, All activities (arachido nic acid release and calcium mobilization) were blocked by the B-2, antagon ist HOE 140. B-2, was desensitized by repeated administration of BK but res ensitized to agonist by ACE inhibitors in the cells expressing both B-2 and either WT-ACE or Cyt-del-ACE. In GPI-ACE expressing cells, the B-2 recepto r was still activated by the agonists, but ACE inhibitors did not resensiti ze. Pretreatment with filipin returned the sensitivity to inhibitors. In im munocytochemistry, GPI-ACE showed patchy, uneven distribution on the plasma membrane that was restored by filipin, Thus, ACE inhibitors were inactive as long as GPI-ACE was sequestered in cholesterol-rich membrane domains. WT -ACE and B-2 receptor in Chinese hamster ovary cells co-immunoprecipitated with antibody to receptor, suggesting an interaction on the cell membrane. ACE inhibitors augment BK effects on receptors indirectly only when enzyme and receptor molecules are sterically close, possibly forming a heterodimer .