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

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Abstract
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 native prorenin, neonatal rat cardiomyocytes were incubated with recombinant, renal, or amniotic fluid prorenin with or without man-6-P. Intact and activated prorenin were measured in cell lysates with prosegment- and renin-specific antibodies, respectively. The dissociation constant (Kd) and maximum number of binding sites (Bmax) for prorenin binding to man-6-P/IGF-II receptors were 0.6 ± 0.1 nM and 3,840 ± 510 receptors/myocyte, respectively. The capacity for prorenin internalization was greater than 10 times Bmax. Levels of internalized intact prorenin decreased rapidly (half-life = 5 ± 3 min) indicating proteolytic prosegment removal. Prorenin subdivision into man-6-P-free and man-6-P-containing fractions revealed that only the latter was bound. Cells also bound and activated renal but not amniotic fluid prorenin. 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 thereby supporting the concept of cardiac angiotensin formation by renal prorenin.