Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P41181 (collecting duct)
 5,183 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Carbonic anhydrase (CA) IV facilitates HCO(3) reabsorption in the renal proximal tubule by catalyzing the reversible hydration of CO(2). CAIV is tethered to cell membranes via a glycosylphosphatidylinositol (GPI) lipid anchor. As there is basolateral as well as apical CAIV staining in proximal tubule, the molecular identity of basolateral CAIV was examined. Biotinylation of confluent monolayers of rat inner medullary collecting duct cells stably transfected with rabbit CAIV showed apical and basolateral CAIV, and in the cell transfectants expressing high levels of CAIV, a transmembrane form was targeted to the basolateral membrane. Basolateral expression of CAIV ( approximately 46 kDa) was confirmed in normal kidney tissue by Western blotting of vesicle fractions enriched for basolateral membranes by Percoll density fractionation. We examined the mode of membrane linkage of basolaterally expressed CAIV in the kidney cortex. CAIV detected in basolateral or apical membrane vesicles exhibited similar molecular size by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis following deglycosylation, and was equally sensitive to phosphatidylinositol-specific phospholipase C digestion, indicating that CAIV is expressed on the basolateral membrane as a GPI-anchored protein. Half of the hydratase activity of basolateral vesicles was resistant to SDS denaturation, compatible with being CAIV. Thus, GPI-anchored CAIV resides in the basolateral membrane of proximal tubule epithelia where it may facilitate HCO(3) reabsorption via association with kNBC1.
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PMID:Basolateral carbonic anhydrase IV in the proximal tubule is a glycosylphosphatidylinositol-anchored protein. 1722 67

Several pathophysiological conditions, including nephrotic syndrome, are characterized by increased renal activity of the epithelial Na(+) channel (ENaC). We recently identified plasmin in nephrotic urine as a stimulator of ENaC activity and undertook this study to investigate the mechanism by which plasmin stimulates ENaC activity. Cy3-labeled plasmin was found to bind to the surface of the mouse cortical collecting duct cell line, M-1. Binding depended on a glycosylphosphatidylinositol (GPI)-anchored protein. Biotin-label transfer showed that plasmin interacted with the GPI-anchored protein prostasin on M-1 cells and that plasmin cleaved prostasin. Prostasin activates ENaC by cleavage of the gamma-subunit, which releases an inhibitory peptide from the extracellular domain. Removal of GPI-anchored proteins from the M-1 cells with phosphatidylinositol-specific phospholipase C (PI-PLC) inhibited plasmin-stimulated ENaC current in monolayers of M-1 cells at low plasmin concentration (1-4 microg/ml). At a high plasmin concentration of 30 microg/ml, there was no difference between cell layers treated with or without PI-PLC. Knockdown of prostasin attenuated binding of plasmin to M1 cells and blocked plasmin-stimulated ENaC current in single M-1 cells, as measured by whole-cell patch clamp. In M-1 cells expressing heterologous FLAG-tagged prostasin, gammaENaC and prostasin were colocalized. A monoclonal antibody directed against the inhibitory peptide of gammaENaC produced specific immunofluorescence labeling of M-1 cells. Pretreatment with plasmin abolished labeling of M-1 cells in a prostasin-dependent way. We conclude that, at low concentrations, plasmin interacts with GPI-anchored prostasin, which leads to cleavage of the gamma-subunit and activation of ENaC, while at higher concentrations, plasmin directly activates ENaC.
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PMID:Prostasin-dependent activation of epithelial Na+ channels by low plasmin concentrations. 1979 56