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

Mannose-6-phosphate (man-6-P)/insulin-like growth factor-II (man-6-P/IgF-II ) receptors are involved in the activation of recombinant human prorenin by cardiomyocytes. To investigate the kinetics of this process, the nature of activation, the existence of other prorenin receptors, and binding of nati ve prorenin, neonatal rat cardiomyocytes were incubated with recombinant, r enal, or amniotic fluid prorenin with or without man-6-P. Intact and activa ted prorenin were measured in cell lysates with prosegment- and renin-speci fic antibodies, respectively. The dissociation constant (K-d) and maximum n umber of binding sites (B-max) for prorenin binding to man-6-P/IGF-II recep tors were 0.6 +/- 0.1 nM and 3,840 +/- 510 receptors/myocyte, respectively. The capacity for prorenin internalization was greater than 10 times B-max. Levels of internalized intact prorenin decreased rapidly (half-life = 5 +/ - 3 min) indicating proteolytic prosegment removal. Prorenin subdivision in to man-6-P-free and man-6P-containing fractions revealed that only the latt er was bound. Cells also bound and activated renal but not amniotic fluid p rorenin. We concluded that cardiomyocytes display high-affinity binding of renal but not extrarenal prorenin exclusively via man-6-P/IGF-II receptors. Binding precedes internalization and proteolytic activation to renin there by supporting the concept of cardiac angiotensin formation by renal proreni n.