Proteolytic processing of human prorenin in renal and non-renal tissues

Proteolytic processing of human prorenin in renal and non-renal tissues. Previous studies have demonstrated that the mouse proprotein convertase PC1 (mPC1) accurately cleaves human prorenin to generate active renin and that this processing event appears to require co-packaging in secretory granules. In the current study, we have tested human PC1 (hPC1; also called PC3) for its ability to activate human prorenin. Our results suggest that while hPC1 is capable of carrying out the specific cleavage of human prorenin, it does so at a reduced efficiency as compared to mPC1. This difference is due to sequences in the carboxy-terminus of PC1 as demonstrated by the activity of hybrid hPC1/mPC1 molecules. These studies demonstrate that PC1 cleavage of prorenin can occur in humans and identify a functionally important region in the hPC1 protein for this interaction. Moreover, the localization of PC1 in human tissues suggests that it may participate in the generation of active renin in the adrenal medulla and possibly in certain adrenal tumors

Evidence for intracellular generation of angiotensin II in rat juxtaglomerular cells

AbstractThe formation of the vasoactive peptide angiotensin II (AII) is dependent on the sequential action of two enzymes, renin and angiotensin converting enzyme (ACE), on the substrate angiotensinogen. Although the renin-producing cells of the kidney do not express angiotensinogen, they contain large amounts of AII in the same storage granules that contain renin. When renin expression is suppressed in these cells, AII also disappears. In the current study, we have tested whether the renin-associated disappearance of AII in renal juxtaglomerular (JG) cells is due to a renin-dependent down-regulation of granule biosynthesis and whether receptor-mediated internalization of AII could account for its concentration in these cells. Our results support a model whereby AII peptides are generated within JG cells, presumably by a mechanism which involves the action of endogenous renin on internalized, exogenous angiotensinogen

Transcriptome Analysis of Human Reninomas as an Approach to Understanding Juxtaglomerular Cell Biology

International audienceRenin, a key component in the regulation of blood pressure in mammals, is produced by the rare and highly specialized juxtaglomerular cells of the kidney. Chronic stimulation of renin release results in a recruitment of new juxtaglomerular cells by the apparent conversion of adjacent smooth muscle cells along the afferent arterioles. Because juxtaglomerular cells rapidly dedifferentiate when removed from the kidney, their developmental origin and the mechanism that explains their phenotypic plasticity remain unclear. To overcome this limitation, we have performed RNA expression analysis on 4 human renin-producing tumors. The most highly expressed genes that were common between the reninomas were subsequently used for in situ hybridization in kidneys of 5-day-old mice, adult mice, and adult mice treated with captopril. From the top 100 genes, 10 encoding for ligands were selected for further analysis. Medium of human embryonic kidney 293 cells transfected with the mouse cDNA encoding these ligands was applied to (pro)renin-synthesizing As4.1 cells. Among the ligands, only platelet-derived growth factor B reduced the medium and cellular (pro)renin levels, as well as As4.1 renin gene expression. In addition, platelet-derived growth factor B-exposed As4.1 cells displayed a more elongated and aligned shape with no alteration in viability. This was accompanied by a downregulated expression of α-smooth muscle actin and an upregulated expression of interleukin-6, suggesting a phenotypic shift from myoendocrine to inflammatory. Our results add 36 new genes to the list that characterize renin-producing cells and reveal a novel role for platelet-derived growth factor B as a regulator of renin-synthesizing cells

Angiotensin II type I receptor modulates intracellular free Mg2+ in renally derived cells via Na+-dependent Ca2+-independent mechanisms

Treatment of Madin-Darby canine kidney (MDCK) cells with the peptide hormone angiotensin II (Ang II) results in an increase in the concentrations of cytosolic free calcium ([Ca(2+)](i)) and sodium ([Na(+)](i)) with a concomitant decrease in cytosolic free Mg(2+) concentration ([Mg(2+)](i)). In the present study we demonstrate that this hormone-induced decrease in [Mg(2+)](i) is independent of [Ca(2+)](i) but dependent on extracellular Na(+). [Mg(2+)](i), [Ca(2+)](i), and [Na(+)](i) were measured in Ang II-stimulated MDCK cells by fluorescence digital imaging using the selective fluoroprobes mag-fura-2AM, fura-2AM, and sodium-binding benzofuran isophthalate (acetoxymethyl ester), respectively. Ang II decreased [Mg(2+)](i) and increased [Na(+)](i) in a dose-dependent manner. These effects were inhibited by irbesartan (selective AT(1) receptor blocker) but not by PD123319 (selective AT(2) receptor blocker). Imipramine and quinidine (putative inhibitors of the Na(+)/Mg(2+) exchanger) and removal of extracellular Na(+) abrogated Ang II-mediated [Mg(2+)](i) effects. In cells pretreated with thapsigargin (reticular Ca(2+)-ATPase inhibitor), Ang II-stimulated [Ca(2+)](i) transients were attenuated (p < 0.01), whereas agonist-induced [Mg(2+)](i) responses were unchanged. Clamping the [Ca(2+)](i) near 50 nmol/liter with 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetrakis(acetoxymethyl ester) inhibited Ang II-induced [Ca(2+)](i) increases but failed to alter Ang II-induced [Mg(2+)](i) responses. Benzamil, a selective blocker of the Na(+)/Ca(2+) exchanger, inhibited [Na(+)](i) but not [Mg(2+)](i) responses. Our data demonstrate that in MDCK cells, AT(1) receptors modulate [Mg(2+)](i) via a Na(+)-dependent Mg(2+) transporter that is not directly related to [Ca(2+)](i). These data support the notion that rapid modulation of [Mg(2+)](i) is not simply a result of Mg(2+) redistribution from intracellular buffering sites by Ca(2+) and provide evidence for the existence of a Na(+)-dependent, hormonally regulated transporter for Mg(2+) in renally derived cells