Active (9.6 S) and Inactive (21 S) Oligomers of NHE3 in Microdomains of the Renal Brush Border*

  title={Active (9.6 S) and Inactive (21 S) Oligomers of NHE3 in Microdomains of the Renal Brush Border*},
  author={Daniel Biemesderfer and Brenda Degray and Peter S. Aronson},
  journal={The Journal of Biological Chemistry},
  pages={10161 - 10167}
We have previously shown that Na+-H+ exchanger isoform NHE3 exists as both 9.6 and 21 S (megalin-associated) oligomers in the renal brush border (1). To characterize the oligomeric forms of the renal brush border Na+-H+ exchanger in more detail, we performed membrane fractionation studies. We found that similar amounts of NHE3 were present in microvilli and a nonmicrovillar membrane domain of high density (dense vesicles). Horseradish peroxidase-labeled endosomes were not prevalent in the dense… 

Na(+)/H(+) exchanger 3 is in large complexes in the center of the apical surface of proximal tubule-derived OK cells.

NHE3V in OK cells exists in distinct domains both in the center of the apical surface and in a juxtanuclear compartment, showing that NHE3 functioned to acidify both compartments.

Association of Na+-H+ Exchanger Isoform NHE3 and Dipeptidyl Peptidase IV in the Renal Proximal Tubule*

An unexpected association of the brush border Na+-H+ exchanger NHE3 with dipeptidyl peptidase IV in the proximal tubule is revealed, raising the possibility that association with DPPIV may affect N HE3 surface expression and/or activity.

Localization and interaction of NHERF isoforms in the renal proximal tubule of the mouse.

The present studies suggest that the organized subcellular distribution of the NHERF isoforms may play a role in the specific interactions mediating physiological control of transporter function.

Na+-H+ Exchanger Regulatory Factor 1 (NHERF1) PDZ Scaffold Binds an Internal Binding Site in the Scavenger Receptor Megalin

A novel protein interaction in proximal tubule cells is identified and specifically a new internal PDZ binding motif in the C-terminus of megalin is identified.

Regulation of Albumin Endocytosis by PSD95/Dlg/ZO-1 (PDZ) Scaffolds

NHERF1 and NHERF2 differentially regulate albumin uptake by mechanisms that ultimately alter the cell-surface levels of ClC-5.

Rho GTPases dictate the mobility of the Na/H exchanger NHE3 in epithelia: role in apical retention and targeting.

Observations suggest that modulation of the mobile fraction of NHE3 on the apical membrane can alter the number of functional exchangers on the cell surface and, consequently, the rate of transepithelial ion transport.

Dipeptidyl peptidase IV inhibition downregulates Na+ - H+ exchanger NHE3 in rat renal proximal tubule.

Findings indicate that inhibition of DPPIV catalytic activity is associated with inhibition of NHE3-mediated NaHCO3 reabsorption in rat renal proximal tubule, and inhibition of apical Na(+) - H(+) exchange is due to reduced abundance of N HE3 protein in the microvillar microdomain of the kidney brush border.

Immunolocalization of NHE8 in rat kidney.

It is concluded that NHE8 is expressed on the apical brush-border membrane of proximal tubule cells, where it may play a role in mediating or regulating ion transport in this nephron segment.

Ca2+-dependent inhibition of NHE3 requires PKC alpha which binds to E3KARP to decrease surface NHE3 containing plasma membrane complexes.

The results suggest that PKCalpha is not necessary for the Ca2+-dependent formation of the NHE3 plasma membrane complex, although it is necessary for decreasing the membrane amounts of N HE3, probably by stimulating NHE2 endocytosis.



Specific Association of Megalin and the Na+/H+ Exchanger Isoform NHE3 in the Proximal Tubule*

Findings indicate that a significant pool of NHE3 exists as a multimeric complex with megalin in the brush border of the proximal tubule.

Role of NHE3 in Mediating Renal Brush Border Na+-H+ Exchange

It is concluded that virtually all measured Na+-H+ exchange activity in brush border membranes from control and acidotic rats is mediated by NHE3 and that metabolic acidosis causes increased expression of renal brush border N HE3 protein.

Membrane Topology of NHE3

Findings indicate that epitopes within the carboxyl terminus of the Na+-H+ exchanger isoform NHE3 are exposed to the outside of the plasma membrane.

Distinct Structural Domains Confer cAMP Sensitivity and ATP Dependence to the Na/H Exchanger NHE3 Isoform (*)

It is concluded that different sites, and therefore different mechanisms, underlie inhibition of NHE3 by cAMP and by depletion of ATP, indicating that ATP dependence is conferred by a region of the molecule in or adjacent to the transmembrane domain, which is most conserved between isoforms.

The Epithelial Na+/H+ Exchanger, NHE3, Is Internalized through a Clathrin-mediated Pathway*

Results indicate that endocytosis of NHE3 occurs primarily via clathrin-coated pits and vesicles and that normal intracellular trafficking of N HE3 involves an ε-COP-dependent step.

Identification of Sites Required for Down-regulation of Na+/H+ Exchanger NHE3 Activity by cAMP-dependent Protein Kinase

Phosphorylation of Ser605 is essential for cAMP-mediated inhibition of NHE3, and Ser634 is also required for the effect of cAMP, even though this residue does not become phosphorylated upon activation of PKA.

Expression of NHE-3 in the apical membrane of rat renal proximal tubule and thick ascending limb.

NHE-3 is the isoform responsible for NaCl and NaHCO3 absorption in the proximal convoluted tubule, and NahCO absorption in a thick ascending limb and apical membrane Na/H exchange activity is likely mediated by other isoform of the NHE family.

Parathyroid hormone-induced translocation of Na-H antiporters in rat proximal tubules.

Observations suggest that PTH triggers a rapid translocation of Na-H antiporters from the microvillus membrane to a distinct membrane domain, where they are subsequently inactivated.

Modifier role of internal H+ in activating the Na+–H+ exchanger in renal microvillus membrane vesicles

The results suggest that internal H+, independent of its role as a substrate for exchange with external Na+, has an important modifier role as an allosteric activator of the Na+–H+ exchanger.