The renin-angiotensin system (RAS) is one of the most important systems in physiology and in pathology. The (pro)renin receptor [(P)RR] is a new component of the system that has attracted much attention, being potentially a new therapeutic target, because the binding of renin and of prorenin triggers the activation of the mitogen-activated protein kinase p42/p44 followed by up-regulation of the expression of profibrotic genes. and because prorenin bound to (P)RR becomes catalytically active. The introduction of a renin inhibitor in the treatment of hypertension and of organ damages, together with the discovery of (P)RR, has revived the interest for the RAS and for potential new RAS blockers, in order to optimize RAS blockade in tissues.

The discovery of a (pro)renin receptor ((P)RR) and the introduction of renin inhibitors in the clinic has brought prorenin, the inactive proenzyme form of renin, back into the spotlight. The (P)RR binds both renin and its inactive precursor prorenin, and their binding triggers intracellular signaling that up-regulates the expression of profibrotic genes. Furthermore, binding of prorenin unmasks its active site and endows prorenin with angiotensin I-generating activity. Many studies have attempted to establish a link between (P)RR and hypertension, (P)RR and tissue fibrosis associated with hypertension and with diabetic nephropathy. Models of transgenic rats overexpressing (P)RR develop high blood pressure and have glomerulosclerosis, suggesting a link between increased (P)RR and these pathologies, but no definite proof of any role of (P)RR in other models of cardiovascular or renal diseases could be established because of the absence of any specific (P)RR antagonist and of tissue-specific (P)RR null mice. Nevertheless, a study in a large cohort of Japanese men has shown a correlation between a polymorphism in the (P)RR gene and increased ambulatory blood pressure. Finally, a mutation in the (P)RR gene is responsible for mental retardation and epilepsy, indicating that (P)RR is essential during brain development.

The (pro)renin receptor [(P)RR] is a 35-kDa transmembrane protein that plays a pivotal role in angiotensin tissue generation and in nonproteolytic prorenin activation. We detected a soluble form of (P)RR [s(P)RR; 28 kDa] in the conditioned medium of cultured cells. The aims of our study were to identify the protease responsible for the generation of s(P)RR, the site of shedding, and to establish the existence of circulating s(P)RR in plasma. We identified furin as the protease responsible for the shedding of endogenous (P)RR based on the following: LoVo colon carcinoma cells devoid of active furin synthesize full-length (P)RR but do not secrete s(P)RR; transfection of Chinese hamster ovary cells with a plasmid coding for alpha1-antitrypsin Portland variant, an inhibitor of furin, completely inhibited the generation of s(P)RR, whereas addition of GM6001, an inhibitor of metalloproteases or of tumor necrosis factor-alpha protease inhibitor-1, an inhibitor of ADAM17, in the culture medium has no effect; when the cDNA coding for (P)RR was translated in vitro and incubated with recombinant furin or ADAM17, only furin was able to generate the 28 kDa-s(P)RR, and mutagenesis in the potential furin cleavage R275A/KT/R278A site abolished s(P)RR generation. Immunofluorescence study in glomerular epithelial cells showed that (P)RR was cleaved in the trans-Golgi, and coprecipitation experiments with renin showed that s(P)RR was present in plasma. In conclusion, our results show that s(P)RR is generated intracellularly by furin cleavage, and that s(P)RR detected in plasma is able to bind renin.

The (pro)renin receptor [(P)RR] is a single transmembrane protein that bind renin and prorenin and their binding trigger ERK1/2 phosphorylation. But (P)RR is also cleaved intracellularly to generate a soluble receptor [s(P)RR] which is constitutively secreted by cultured cells. Pull-down experiments indicated that s(P)RR was able to bind to and to coprecipitate with renin. Furthermore, preincubation of renin with s(P)RR inhibited ERK1/2 activation induced by renin suggesting that s(P)RR acted as a trap for renin.