Signaling and distribution of NPR-Bi, the human splice form of the natriuretic peptide receptor type B.
Recently, we described a splice variant of the human natriuretic peptide receptor type B (NPR-Bi) in human proximal tubule cells [immortalized human kidney epithelial cells (IHKE-1) that lacks a functional guanylate cyclase domain (Hirsch JR, Meyer M, Mägert HJ, Forssmann WG, Mollerup S, Herter P, Weber G, Cermak R, Ankorina-Stark I, Schlatter E, and Kruhøffer M. J Am Soc Nephrol 10: 472-480, 1999). Its signaling pathway does not include cGMP, cAMP, or Ca2+ but leads to inhibition of K+ channels. In patch-clamp experiments, effects of tyrosine kinase receptor blockers on C-type natriuretic peptide (CNP)-mediated depolarizations of membrane voltages (Vm) of IHKE-1 cells were tested. The epidermal growth factor (EGF) receptor blocker genistein (10 microM) abolished the effect of CNP (0.2 +/- 0.4 mV, n = 7), and comparable results were obtained with 10 microM daidzein (n = 8). Aminogenistein (10 microM, n = 5) and tyrphostin AG1295 (10 microM, n = 5) had no significant effects. EGF (1 nM) hyperpolarized cells by -5.3 +/- 0.8 mV (n = 5). This effect was completely blocked by genistein or daidzein. The Cl- channel blocker NPPB (10 microM, n = 5) inhibited the EGF-mediated hyperpolarization. mRNA expression of NPR-B and NPR-Bi shows reversed patterns along the human nephron. NPR-B is highly expressed in glomeruli and proximal tubules, whereas NPR-Bi shows strong signals in the distal nephron. Expression of NPR-Bi in the cortical collecting duct was also confirmed with immunohistochemistry. In other human tissues, NPR-Bi shows strongest expression in pancreas and lung, whereas in the heart and liver NPR-B is the dominating receptor. In conclusion, CNP inhibits an apical K+ channel in IHKE-1 cells independently of cGMP and so far this effect can only be blocked by genistein and daidzein. Tyrosine phosphorylation might be the missing link in the signaling pathway of CNP/NPR-Bi.
Hirsch
Jochen R
JR
Medizinische Klinik und Poliklinik D, Experimentelle Nephrologie, Domagkstr. 3a, D-48149 Münster, Germany.
Skutta
Nikola
N
Schlatter
Eberhard
E
D002461:Cell Line, Transformed; D006152:Cyclic GMP / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004968:Estrogens, Non-Steroidal / Q000494:pharmacology; D015870:Gene Expression; D019833:Genistein / Q000031:analogs & derivatives / Q000494:pharmacology; D006162:Guanylate Cyclase / Q000235:genetics* / Q000378:metabolism*; D006801:Humans; D007529:Isoflavones / Q000494:pharmacology; D007684:Kidney Tubules / Q000166:cytology / Q000378:metabolism*; D020098:Natriuretic Peptide, C-Type / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000378:metabolism; D012326:RNA Splicing / Q000502:physiology*; D017461:Receptors, Atrial Natriuretic Factor / Q000235:genetics* / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D020032:Tyrphostins / Q000494:pharmacology; D000099242:Atrial Natriuretic Factor Receptor B
D006152:Cyclic GMP; D004791:Enzyme Inhibitors; D004968:Estrogens, Non-Steroidal; D019833:Genistein; D006162:Guanylate Cyclase; D007529:Isoflavones; D020098:Natriuretic Peptide, C-Type; D011188:Potassium; D017461:Receptors, Atrial Natriuretic Factor; D020032:Tyrphostins; D000099242:Atrial Natriuretic Factor Receptor B; C407689:6,7-dimethoxy-2-phenylquinoxaline; C004742:daidzein