Angiotensin AT4 ligands are potent, competitive inhibitors of insulin regulated aminopeptidase (IRAP)

• Published in: Journal of neurochemistry Vol. 86; no. 2; pp. 344 - 350
• Main Authors: Lew, Rebecca A., Mustafa, Tomris, Ye, Siying, McDowall, Sharon G., Chai, Siew Yeen, Albiston, Anthony L.
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Science Ltd 01-07-2003; Blackwell
• Subjects: Aminopeptidases - antagonists & inhibitors; Aminopeptidases - chemistry; Aminopeptidases - metabolism; Ang IV; Angiotensin II - analogs & derivatives; Angiotensin II - pharmacology; Angiotensin Receptor Antagonists; AT4 receptor; Binding, Competitive - drug effects; Biological and medical sciences; Cell Line; Cell receptors; Cell structures and functions; Cystinyl Aminopeptidase; Enzyme Activation - drug effects; Enzyme Inhibitors - pharmacology; enzyme kinetics; Fundamental and applied biological sciences. Psychology; Hemoglobins - pharmacology; hemorphin; Humans; Kidney - cytology; Kidney - metabolism; Leucine - analogs & derivatives; Leucine - metabolism; Ligands; Miscellaneous; Molecular and cellular biology; Oligopeptides - pharmacology; Peptide Fragments - pharmacology; Peptides - chemistry; Peptides - metabolism; Receptors, Angiotensin - chemistry; Receptors, Angiotensin - metabolism; Recombinant Proteins; Substrate Specificity - physiology; Ligand binding; Enzyme; Aminopeptidases; Binding site; Angiotensin receptor; Angiotensin IV; Gene expression; enzyme kinetics; Peptidases; Renin angiotensin system; Cell line; Proteolysis; AT4 receptor; Angiotensin; Hydrolases; AT4 angiotensin receptor; Kinetics; Ang IV; hemorphin
• ISSN: 0022-3042; 1471-4159
• DOI: 10.1046/j.1471-4159.2003.01852.x

Angiotensin IV (Ang IV) exerts profound effects on memory and learning, a phenomenon ascribed to its binding to a specific AT4 receptor. However the AT4 receptor has recently been identified as the insulin‐regulated aminopeptidase (IRAP). In this study, we demonstrate that AT4 receptor ligands, including Ang IV, Nle1‐Ang IV, divalinal‐Ang IV, and the structurally unrelated LVV‐hemorphin‐7, are all potent inhibitors of IRAP catalytic activity, as assessed by cleavage of leu‐β‐naphthylamide by recombinant human IRAP. Both Ang IV and divalinal–Ang IV display competitive kinetics, indicating that AT4 ligands mediate their effects by binding to the catalytic site of IRAP. The AT4 ligands also displaced [125I]‐Nle1‐Ang IV or [125I]‐divalinal1‐Ang IV from IRAP‐HEK293T membranes with high affinity, which was up to 200‐fold greater than in the catalytic assay; this difference was not consistent among the peptides, and could not be ascribed to ligand degradation. Although some AT4 ligands were subject to minor cleavage by HEK293T membranes, none were substrates for IRAP. Of a range of peptides tested, only vasopressin, oxytocin, and met‐enkephalin were rapidly cleaved by IRAP. We propose that the physiological effects of AT4 ligands result, in part, from inhibition of IRAP cleavage of neuropeptides involved in memory processing.