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 (K(d)) and maximum number of binding sites (B(max))
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 B(max). 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