Prorenin and Renin-Induced Extracellular Signal-Regulated Kinase 1/2 Activation in Monocytes Is Not Blocked by Aliskiren or the Handle-Region Peptide

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...

New insights into the renoprotective actions of the renin inhibitor aliskiren in experimental renal disease

“…Aliskiren does not inhibit binding of (pro)renin to the (P)RR, 87,118 nor does it prevent (pro)renin-induced cell signaling. 87,118,120 However, in STZ-diabetic mRen-2 rats treated with aliskiren for 10 weeks, in situ hybridization on renal sections revealed a clear reduction in gene expression of the (P)RR in the glomeruli and tubular cells compared with vehicle-control diabetic mRen-2 rats. 87 Interestingly, in vitro studies showed that aliskiren did not affect gene expression of (P)RR in mesangial cells.…”

“…However, attempts by other investigators to reproduce the cellular effects of the blocker, and its in vivo benefits (although in nondiabetic models of renal damage), have largely been unsuccessful. 115,118,131,132 Replication by others of the experimental designs used by Ichihara and coworkers may clarify some of the questions on the function of the (P)RR in DN and in tissue damage in general.…”

“…109 Furthermore, on binding to the (P)RR, prorenin, which is normally inactive, becomes catalytically active (it can cleave Aogen to form Ang I), possibly because of a conformational change induced by the binding. 109,[114][115][116] The Ang IIindependent effects of (P)RR stimulation include activation of extracellular signal-regulated kinase1/2, 109,117,118 and heat shock protein 27 119 and phosphatidylinositol-3 kinase p85a 120 pathways. The production of TGF-b and plasminogen-activator-1 is also increased, as are gene expression and production of collagen I and fibronectin, respectively.…”

Potential cross-talk between (pro)renin receptors and Wnt/frizzled receptors in cardiovascular and renal disorders

“…The handle region peptide (HRP), a putative blocker of the (P)RR, could efficiently block glomerulosclerosis, 86,88,95,96 while RAS inhibitors were unable to prevent end-stage organ damage associated with diabetes. 97,98 However, not all investigators were able to reproduce the inhibitory effects of HRP either in vivo or in vitro. 97,99 In diabetic subjects, prorenin to active renin ratio is very high.…”

“…97,98 However, not all investigators were able to reproduce the inhibitory effects of HRP either in vivo or in vitro. 97,99 In diabetic subjects, prorenin to active renin ratio is very high. This is supported from studies where the excessive non-proteolytic activation of (P)RR-bound prorenin has a major role in diabetic nephropathy and retinopathy, and cardiac fibrosis.…”