Phosphoinositide binding differentially regulates NHE1 Na+/H+ exchanger-dependent proximal tubule cell survival

  • J Biol Chem. 2011 Dec 9;286(49):42435-42445. doi: 10.1074/jbc.M110.212845.
Bassam G Abu Jawdeh  1 ,  Shenaz Khan  1 ,  Isabelle Deschênes  2 ,  Malcolm Hoshi  3 ,  Monu Goel  3 ,  Jeffrey T Lock  3 ,  Krekwit Shinlapawittayatorn  3 ,  Gerald Babcock  2 ,  Sujata Lakhe-Reddy  1 ,  Garren DeCaro  1 ,  Satya P Yadav  4 ,  Maradumane L Mohan  4 ,  Sathyamangla V Naga Prasad  4 ,  William P Schilling  2 ,  Eckhard Ficker  1 ,  Jeffrey R Schelling  5
Affiliations
  • 1. Department of Medicine, Case Western Reserve University, Cleveland, Ohio 44109.
  • 2. Department of Medicine, Case Western Reserve University, Cleveland, Ohio 44109; Departments of Physiology and Biophysics, Lerner Research Institute, Case Western Reserve University, Cleveland, Ohio 44109.
  • 3. Departments of Physiology and Biophysics, Lerner Research Institute, Case Western Reserve University, Cleveland, Ohio 44109.
  • 4. Department of Cleveland Clinic Foundation, Case Western Reserve University, Cleveland, Ohio 44109.
  • 5. Department of Medicine, Case Western Reserve University, Cleveland, Ohio 44109. Electronic address: [email protected].
PMID: 22020933 DOI: 10.1074/jbc.M110.212845
Abstract

Tubular atrophy predicts chronic kidney disease progression, and is caused by proximal tubular epithelial cellcaused by proximal tubular epithelial cell (PTC) Apoptosis. The normally quiescent Na(+)/H(+) exchanger-1 (NHE1) defends against PTC Apoptosis, and is regulated by PI(4,5)P(2) binding. Because of the vast array of plasma membrane lipids, we hypothesized that NHE1-mediated cell survival is dynamically regulated by multiple anionic inner leaflet Phospholipids. In membrane overlay and surface plasmon resonance assays, the NHE1 C terminus bound Phospholipids with low affinity and according to valence (PIP(3) > PIP(2) > PIP = PA > PS). NHE1-phosphoinositide binding was enhanced by acidic pH, and abolished by NHE1 Arg/Lys to Ala mutations within two juxtamembrane domains, consistent with electrostatic interactions. PI(4,5)P(2)-incorporated vesicles were distributed to apical and lateral PTC domains, increased NHE1-regulated Na(+)/H(+) exchange, and blunted Apoptosis, whereas NHE1 activity was decreased in cells enriched with PI(3,4,5)P(3), which localized to basolateral membranes. Divergent PI(4,5)P(2) and PI(3,4,5)P(3) effects on NHE1-dependent Na(+)/H(+) exchange and Apoptosis were confirmed by selective phosphoinositide sequestration with pleckstrin homology domain-containing Phospholipase Cδ and Akt peptides, PI 3-kinase, and Akt inhibition in wild-type and NHE1-null PTCs. The results reveal an on-off switch model, whereby NHE1 toggles between weak interactions with PI(4,5)P(2) and PI(3,4,5)P(3). In response to apoptotic stress, NHE1 is stimulated by PI(4,5)P(2), which leads to PI 3-kinase activation, and PI(4,5)P(2) phosphorylation. The resulting PI(3,4,5)P(3) dually stimulates sustained, downstream Akt survival signaling, and dampens NHE1 activity through competitive inhibition and depletion of PI(4,5)P(2).