Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0038362 (stomatitis)
 8,852 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The epithelial brush border Na+/H+ exchanger isoform 3 (NHE3) is regulated by growth factors and protein kinases. When stably expressed in PS120 fibroblasts, NHE3 is stimulated by serum and fibroblast growth factor (FGF) and inhibited by phorbol esters. To examine the role of phosphorylation of NHE3 in growth factor/protein kinase regulation, NHE3 was C-terminally tagged with an 11-amino acid epitope of the vesicular stomatitis virus glycoprotein (VSVG) and stably expressed in Na+/H+ exchanger null PS120 fibroblasts (PS120/NHE3V). NHE3V was regulated by serum, FGF, and phorbol ester in a manner identical to wild type non-VSVG-tagged NHE3. Phosphorylation of NHE3V was evaluated via immunoprecipitation with anti-VSVG antibody after in vivo labeling of PS120/NHE3V cells with [32P]orthophosphate. NHE3V was phosphorylated under basal conditions. However, FGF and PMA, under conditions in which these agonists regulate NHE3V, altered neither the amount of phosphorylation of NHE3V as analyzed by one-dimensional SDS-polyacrylamide gel electrophoresis and autoradiography nor two-dimensional phosphopeptide maps of tryptic digests of NHE3V. In contrast, while changes in NHE3V phosphorylation were not observed with serum exposure by one-dimensional SDS-polyacrylamide gel electrophoresis, two-dimensional studies showed increases in two phosphopeptides. Under all these conditions, phosphoamino acid analysis showed that NHE3V was phosphorylated only on serine residues. By cell surface protein biotinylation studies under basal conditions, at least 27% of the NHE3V was expressed on the cell surface. To further analyze the phosphorylation status of the surface and intracellular forms of NHE3V under basal conditions and determine whether the amount of phosphorylation of the surface form changes upon serum, FGF, and PMA regulation, the surface form of NHE3V was separated from intracellular form by biotinylation/avidin-agarose precipitation. Under basal conditions, both intracellular and surface forms of NHE3V were phosphorylated. However, the amount of phosphorylation of the surface form of NHE3V did not change upon stimulation by serum and FGF and inhibition by PMA based on one-dimensional SDS-polyacrylamide gel electrophoresis and autoradiography. Thus, we conclude that when expressed in PS120 cells, while NHE3 is a phosphoprotein under basal conditions, its regulation by FGF and PMA is not by changes in the phosphorylation of NHE3, while regulation by serum may involve changes in its phosphorylation. Regulation of NHE3 probably involves intermediate associated regulatory proteins. The function of basal phosphorylation of NHE3 is not known.
 ...
PMID:Regulation of the epithelial brush border Na+/H+ exchanger isoform 3 stably expressed in fibroblasts by fibroblast growth factor and phorbol esters is not through changes in phosphorylation of the exchanger. 921 92

Cell biological approaches were used to examine the location and function of the brush border (BB) Na(+)/H(+) exchanger NHE3 in the opossum kidney (OK) polarized renal proximal tubule cell line. NHE3 epitope tagged with the vesicular stomatitis virus glycoprotein epitope (NHE3V) was stably expressed and called OK-E3V cells. On the basis of cell surface biotinylation studies, these cells had 10-15% of total NHE3 on the BB. Intracellular NHE3V largely colocalized with Rab11 and to a lesser extent with EEA1. The BB location of NHE3V was examined by confocal microscopy relative to the lectins wheat germ aggluttinin (WGA) and phytohemagluttin E (PHA-E), as well as the B subunit of cholera toxin (CTB). The cells were pyramidal, and NHE3 was located in microvilli in the center of the apical surface. In contrast, PHA-E, WGA, and CTB were diffusely distributed on the BB. Detergent extraction showed that total NHE3V was largely soluble in Triton X-100, whereas virtually all surface NHE3V was insoluble. Sucrose density gradient centrifugation demonstrated that total NHE3V migrated at the same size as approximately 400- and approximately 900-kDa standards, whereas surface NHE3V was enriched in the approximately 900-kDa form. Under basal conditions, NHE3 cycled between the cell surface and the recycling pathway through a phosphatidylinositol (PI) 3-kinase-dependent mechanism. Measurements of surface and intracellular pH were obtained by using FITC-WGA. Internalization of FITC-WGA occurred largely into the juxtanuclear compartment that contained Rab11 and NHE3V. pH values on the apical surface and in endosomes in the presence of the NHE3 blocker, S3226, were elevated, showing that NHE3 functioned to acidify both compartments. In conclusion, NHE3V in OK cells exists in distinct domains both in the center of the apical surface and in a juxtanuclear compartment. In the BB fraction, NHE3 is largely in the detergent-insoluble fraction in lipid rafts and/or in large heterogenous complexes ranging from approximately 400 to approximately 900 kDa.
 ...
PMID:Na(+)/H(+) exchanger 3 is in large complexes in the center of the apical surface of proximal tubule-derived OK cells. 1217 49