No abstract

Abstract-The recently cloned (pro)renin receptor [(P)RR] mediates renin-stimulated cellular effects by activating mitogen-activated protein kinases and promotes nonproteolytic prorenin activation. In vivo, (P)RR is said to be blocked with a peptide consisting of 10 amino acids from the prorenin prosegment called the "handle-region" peptide (HRP). We tested whether human prorenin and renin induce extracellular signal-regulated kinase (ERK) 1/2 activation and whether the direct renin inhibitor aliskiren or the HRP inhibits the receptor. We detected the (P)RR mRNA and protein in isolated human monocytes and in U937 monocytes. In U937 cells, we found that both human renin and prorenin induced a long-lasting ERK 1/2 phosphorylation despite angiotensin II type 1 and 2 receptor blockade. In contrast to angiotensin II-ERK signaling, renin and prorenin signaling did not involve the epidermal growth factor receptor. A mitogen-activated protein kinase kinase 1/2 inhibitor inhibited both renin and prorenin-induced ERK 1/2 phosphorylation. Neither aliskiren nor HRP inhibited binding of I-prorenin to (P)RR. Aliskiren did not inhibit renin and prorenin-induced ERK 1/2 phosphorylation and kinase activity. Fluorescence-activated cell sorter analysis showed that, although fluorescein isothiocyanate-labeled HRP bound to U937 cells, HRP did not inhibit renin or prorenin-induced ERK 1/2 activation. In conclusion, prorenin and renin-induced ERK 1/2 activation are independent of angiotensin II. The signal transduction is different from that evoked by angiotensin II. Aliskiren has no (P)RR blocking effect and did not inhibit ERK 1/2 phosphorylation or kinase activity. Finally, we found no evidence that HRP affects renin or prorenin binding and signaling. Key Words: renin Ⅲ prorenin Ⅲ (pro)renin receptor Ⅲ aliskiren Ⅲ signal transduction A liskiren is a recent Food and Drug Administrationapproved, low-molecular weight, direct renin inhibitor that binds to the enzymatically active cleft of renin. Direct renin inhibition in a double-transgenic rat model of high human renin hypertension demonstrated target organ protection. 1,2 A novel (pro)renin receptor [(P)RR] has been cloned that signals when exposed to either renin or prorenin. 3 The (P)RR, correctly termed "RR/ATP6AP2," is a single transmembrane domain protein of 350 amino acids with a large unglycosylated and highly hydrophobic N-terminal domain and a short cytoplasmic tail of Ϸ20 amino acids. The (P)RR is a protein conserved among species. 4 The (P)RR enhances renin catalytic activity and allows prorenin to display catalytic activity without its proteolytic conversion to renin ("nonproteolytic activation"). Such nonproteolytic activation involves unfolding of the prosegment from the enzymatic cleft, mediated by a (P)RR-induced conformational change in the prorenin molecule. This (P)RR-induced prorenin activation could explain how prorenin exerts pathological effects in diabetic patients, where prorenin represents Յ95% of total circulating renin. Nevertheless, this hypothesis remain...

Background-In a double-transgenic human renin and human angiotensinogen rat model, we found that mineralocorticoid receptor (MR) blockade ameliorated angiotensin II (Ang II)-induced renal and cardiac damage. How Ang II and aldosterone (Ald) might interact is ill defined. Methods and Results-We investigated the effects of Ang II (10 Ϫ7 mol/L) and Ald (10 Ϫ7 mol/L) on extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK) signaling in vascular smooth muscle cells (VSMCs) with Western blotting and confocal microscopy. Ang II induced ERK 1/2 and JNK phosphorylation by 2 minutes. Ald achieved the same at 10 minutes. Ang IIϩAld had a potentiating effect by 2 minutes. Two oxygen radical scavengers and the epidermal growth factor receptor (EGFR) antagonist AG1478 reduced Ang II-, Ald-, and combination-induced ERK1/2 phosphorylation. Preincubating the cells with the MR blocker spironolactone (10 Ϫ6 mol/L) abolished Ang II-induced ROS generation, EGFR transactivation, and ERK1/2 phosphorylation. Conclusions-Ald potentiates Ang II-induced ERK-1/2 and JNK phosphorylation. Oxygen radicals, the MR, and the EGFR play a role in early signaling induced by Ang II and Ald in VSMCs. These in vitro data may help explain the effects of MR blockade on Ang II-induced end-organ damage in vivo.