Background: Recent evidence suggests that angiotensin II (Ang II) induces a variety of proinflammatory mediators including chemokines. Nuclear factor-kappaB (NF-kappaB) activation plays an important role in Ang II-mediated inflammation. The present study investigated which Ang II receptor subtype is involved in NF-kappaB activation. We focused particularly on the Ang II subtype 2 (AT2) receptor because we previously observed that Ang II-induction of the chemokine RANTES in vitro and in vivo is mediated through AT2 receptors.
Methods: AT1 or AT2 receptors were selectively overexpressed in COS7 cells that normally do not express Ang II receptors. In addition, rat glomerular endothelial cells (GER) that express AT1 and AT2 receptors and PC12 cells that exclusively exhibit AT2 receptors were studied also. Ang II-receptor expression was confirmed by Western blots of membrane lysates. NF-kappaB DNA binding in vitro was detected by electrophoretic shift assays. In addition, in vivo transactivation of a reporter gene construct with kappa enhancer coupled to luciferase also was investigated. Expression of the inhibitor of kappaB alpha (IkappaB-alpha) was detected by Western blots.
Results: In AT1 or AT2 receptor transfected cells, but not untransfected COS7 cells, 10-7 mol/L Ang II induced NF-kappaB DNA binding in vitro, as detected by electrophoretic shift assays and in vivo transactivation of a reporter gene construct. The AT2 receptor antagonist PD 123319 but not losartan attenuated Ang II-mediated NF-kappaB activation in COS7 cells transfected with AT2 receptors. While Ang II also induced NF-kappaB activation in PC12 cells, this activation was blocked by PD 123319. Finally, stimulation of GERs with Ang II led to the activation of NF-kappaB through both subtypes of Ang II receptors. Nuclear extracts from COS7 cells transfected with AT2 receptors and PC12 cells with NF-kappaB DNA-binding activity consisted of p50/p65 complexes. There was no difference in subunit composition of nuclear proteins from Ang II-stimulated AT1 receptor transfected COS7 cells. An artificial peptide (p-Amino-Phe6-Ang II) with a high affinity for the AT2 receptor also activated NF-kappaB. Ang II-induced activation of NF-kappaB was associated with degradation of IkappaB-alpha in all studied cell lines.
Conclusions: Our results clearly demonstrate in various cell lines that Ang II induces NF-kappaB activation through AT2 receptors. These data may have important therapeutic consequences, because potential Ang II-mediated proinflammatory renal and cardiovascular effects may not be totally antagonized by the currently increased clinical use of AT1 receptor antagonists.