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Angiotensin II is an important effector molecule controlling blood pressure and volume in the cardiovascular system. Its importance is manifested by the efficacy of angiotensin-converting enzyme inhibitors in the treatment of hypertension and congestive heart failure. Angiotensin II interacts with two pharmacologically distinct subtypes of cell-surface receptors, AT1 and AT2. AT1 receptors seem to mediate the major cardiovascular effects of angiotensin II. Here we report the isolation by expression cloning of a complementary DNA encoding a unique protein with the pharmacological specificity of a vascular AT1 receptor. Hydropathic modelling of the deduced protein suggests that it shares the seven-transmembrane-region motif with the G protein-coupled receptor superfamily. Knowledge of the AT1 receptor primary sequence should now permit structural analysis, definition of the angiotensin II receptor gene family and delineation of the contribution of AT receptors to the genetic component of hypertension.

The peptide angiotensin II is the effector molecule of the reninangiotensin system. All the haemodynamic effects of angiotensin II, including vasoconstriction and adrenal aldosterone release, are mediated through a single class of cell-surface receptors known as AT1 (refs 1, 2). These receptors contain the structural features of the G-protein-coupled receptor superfamily. We show here that angiotensin II induces the rapid phosphorylation of tyrosine in the intracellular kinases Jak2 and Tyk2 in rat aortic smooth-muscle cells and that this phosphorylation is associated with increased activity of Jak2. The Jak family substrates STAT1 and STAT2 (for signal transducers and activators of transcription) are rapidly tyrosine-phosphorylated in response to angiotensin II. We also find that Jak2 co-precipitates with the AT1 receptor, indicating that G-protein-coupled receptors may be able to signal through the intracellular phosphorylation pathways used by cytokine receptors.

ACE-related carboxypeptidase (ACE2) may counterbalance the angiotensin (ANG) II-promoting effects of ACE in tissues where both enzymes are found. Alterations in renal ACE and ACE2 expression have been described in experimental models of diabetes, but ACE2 activity was not assessed in previous studies. We developed a microplatebased fluorometric method for the concurrent determination of ACE and ACE2 activity in tissue samples. Enzymatic activity (relative fluorescence unit [RFU] ⅐ g protein ؊1 ⅐ h ؊1 ) was examined in ACE and ACE2 knockout mice and in two rodent models of diabetes, the db/db and streptozotocin ( and r ‫؍‬ ؊0.522, respectively). We conclude that in renal cortex from diabetic mice, ACE2 expression is increased at the posttranscriptional level. The availability of an assay for concurrent measurement of ACE and ACE2 activity should be helpful in the evaluation of kidney-specific alterations in the balance of these two carboxypeptidases, which are involved in the control of local ANG II formation and degradation. Diabetes 55

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