Renin/prorenin receptors

The existence of a tissue renin-angiotensin (RAS) system independent of the circulating RAS has prompted the search for cellular binding sites for angiotensinogen and for renin in order to explain their tissue uptake. Two receptors that bind with similar affinity mature renin and prorenin were identified, the mannose-6-phosphate receptor (M6P-R) and a specific receptor. The M6P-R is a clearance receptor that binds exclusively the glycosylated forms of renin and prorenin. Binding of renin and prorenin to the M6P-R is followed by internalization and degradation, and the intracellular proteolysis of prorenin in mature renin did not provoke any generation of intracellular angiotensins. In contrast to the M6P-R, (pro) renin bound to the specific receptor was not degraded. Instead, receptor-bound renin showed increased catalytic activity, and receptor-bound prorenin exhibited full catalytic activity. This 'gain of activity' was explained by a conformational change of the (pro) renin molecule upon binding. Furthermore, (pro) renin binding provoked a rapid activation of the mitogen-activated protein kinases p44/p42, indicating that the receptor has mediated specific, angiotensin II-independent effects of (pro) renin. This receptor represents an elegant concept to explain the existence of active prorenin in vivo, and it provides a pathological role for prorenin in situations with paradoxical low renin and high prorenin concentrations such as in diabetes. Experimental models of rats overexpressing the receptor either in vascular smooth muscle cells and developing high blood pressure or with ubiquitous expression associated with glomerulosclerosis and proteinuria confirm a role for the receptor in cardiovascular and renal diseases.