title: Angiotensin AT4 ligands are potent, competitive inhibitors of insulin regulated aminopeptidase (IRAP).
abstract: 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-beta-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.
authors.affiliation: Baker Heart Research Institute, Melbourne Howard Florey Institute of Experimental Physiology and Medicine, University of Melbourne, Parkville, Victoria, Australia.
authors.forename: Rebecca A
authors.initials: RA
authors.lastname: Lew
authors.forename: Tomris
authors.initials: T
authors.lastname: Mustafa
authors.forename: Siying
authors.initials: S
authors.lastname: Ye
authors.forename: Sharon G
authors.initials: SG
authors.lastname: McDowall
authors.forename: Siew Yeen
authors.initials: SY
authors.lastname: Chai
authors.forename: Anthony L
authors.initials: AL
authors.lastname: Albiston
mesh_terms: D000626:Aminopeptidases / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000378:metabolism*; D000804:Angiotensin II / Q000031:analogs & derivatives* / Q000494:pharmacology*; D057911:Angiotensin Receptor Antagonists; D001667:Binding, Competitive / Q000187:drug effects; D002460:Cell Line; D010122:Cystinyl Aminopeptidase; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006454:Hemoglobins / Q000494:pharmacology; D006801:Humans; D007668:Kidney / Q000166:cytology / Q000378:metabolism; D007930:Leucine / Q000031:analogs & derivatives* / Q000378:metabolism; D008024:Ligands; D009842:Oligopeptides / Q000494:pharmacology; D010446:Peptide Fragments / Q000494:pharmacology; D010455:Peptides / Q000737:chemistry / Q000378:metabolism; D011945:Receptors, Angiotensin / Q000737:chemistry / Q000378:metabolism*; D011994:Recombinant Proteins; D013379:Substrate Specificity / Q000502:physiology
chemical_list: C090830:AT4 receptor; D057911:Angiotensin Receptor Antagonists; D004791:Enzyme Inhibitors; D006454:Hemoglobins; D008024:Ligands; C118983:Nle(1)-AngIV; D009842:Oligopeptides; D010446:Peptide Fragments; D010455:Peptides; D011945:Receptors, Angiotensin; D011994:Recombinant Proteins; C104765:divalinal-angiotensin IV; D000804:Angiotensin II; C012877:angiotensin II, des-Asp(1)-des-Arg(2)-Ile(5)-; C040135:leucine-beta-naphthylamide; C074309:LVV-hemorphin-7; D000626:Aminopeptidases; D010122:Cystinyl Aminopeptidase; C105964:leucyl-cystinyl aminopeptidase; D007930:Leucine