Specific prorenin/renin binding (ProBP) Identification and characterization of a novel membrane site

Abstract

Renin can be detected in cardiovascular and other tissues but it disappears after bilateral nephrectomy indicating that tissues can take up or bind renal renin from the circulation. If renin uptake is the result of specific binding, plasma prorenin may be a natural antagonist of tissue directed renin-angiotensin systems. To investigate if specific prorenin/renin uptake occurs in rat tissues, binding studies were performed, with rat microsomal membrane preparations using recombinant rat prorenin metabolically labeled with 35S-methionine as a probe. A high affinity binding site for both renin and prorenin was identified. Affinities for prorenin and renin were approximately 200 and 900 pmol/L, respectively. Binding was reversible, saturable, and pH and temperature dependent. The relative binding capacities of membranes from various rat tissues were as follows (fmol/mg): renal cortex (55), liver (54), testis (63), lung (31), brain (18), renal medulla (15), adrenal (17), aorta (7), heart (4), and skeletal muscle (1). Bound prorenin was displaced by rat and human renin or prorenin but not by the prosequence of rat prorenin, angiotensin I or II, rat or human angiotensinogen, the renin inhibitor SQ30697, atrial natriuretic factor, amylase, insulin, bovine serum albumin, hemoglobin, heparin, lysozyme, ovalbumin, cytochrome C, pepsin, pepsinogen, ribonuclease A, mannose-6-phosphate, alpha-methyl mannoside, gonadotropin releasing hormone, or an antibody to hog renin binding protein. these results demonstrate specific binding of prorenin to a site in rat tissues, herein named ProBP, that also binds renin. It is possible that differences in prorenin/renin binding capacity determine the activity of tissue-directed renin-angiotensin systems and that prorenin is a natural antagonist. Alternatively, a prorenin/renin receptor may have been identified that may function by transducing an intracellular signal.

High-affinity prorenin binding to cardiac man-6-P/IGF-II receptors precedes proteolytic activation to renin

“…IGF-II receptors and/or give rise to the appearance of alternative (pro)renin receptors or uptake mechanisms (4,8,46,48,53).…”

“…At present it is unlikely that the man-6-P/IGF-II receptor is the only renin-and prorenin-binding receptor, because excess man-6-P did not block prorenin binding to microsomal membrane fractions prepared from various rat tissues (53). In addition, it is not known whether intracellular prorenin activation occurs proteolytically or nonproteolytically.…”

“…Therefore, the heart must sequester renin from the circulation to synthesize ANG II locally. Renin may diffuse into the interstitial space (18,28) or bind to renin receptors and/or renin-binding proteins (8,46,53). Because renin in blood is predominantly present in the form of its inactive precursor prorenin (11), it is also conceivable that the heart sequesters prorenin instead of renin.…”

Effects of Human Prorenin in Rats Transgenic for Human Angiotensinogen

“…After an initial 30-minute period of baseline perfusion, perfusate for measurement of peptides was collected after 3,6,9,12,15,20,25,30,35,40, and 45 minutes. All perfusate samples were collected over a period of 9 seconds in the presence of a cocktail containing 26 mmol/L phenanthroline (Sigma Chemie), 125 mmol/L EDTA (Sigma Chemie), and a human specific renin inhibitor (remikiren, Hoffmann-La Roche) (10 Ϫ5 mol/L) to prevent any Ang formation outside the hindlimb.…”

“…5,6 Several reninbinding proteins have been described; nevertheless, the mechanism of renin uptake is still unclear. 7-10 Sealey et al 9 described a prorenin/renin-binding receptor. By competing for binding to this receptor or to other receptors, prorenin may be a natural antagonist of tissue-directed RAS.…”