Abstract for presentation at Australia and New Zealand Society of Nephrology Annual Scientific Conference

The roles of Na-H Exchanger Regulatory Factor 2 (NHERF-2) and Serum and glucocorticoid inducible kinase (SGK-1) in albumin uptake by the proximal tubule

  • Deanne Hryciw, The University of Queensland, Australia
  • Dr Jenny Ekberg, The University of Queensland, Australia
  • Dr Aven Lee, The University of Queensland, Australia
  • Dr Dongsheng Wang, Emory University, United States
  • Prof Carol Pollock, University of Sydney, Australia
  • Prof Chris Yun, Emory University, United States
  • Dr Philip Poronnik, The University of Queensland, Australia

    • The constitutive reuptake of albumin from the glomerular filtrate by receptor-mediated endocytosis is a key function of the renal proximal tubule. The Cl- channel ClC-5 is a critical component of the macromolecular endocytic complex that is required for albumin uptake. The epithelial PDZ scaffold NHERF2 can facilitate the formation of complexes by acting as a scaffold. Therefore we investigated its role in albumin uptake using opossum kidney (OK) cells. We found that ClC-5 co-immunoprecipitates with NHERF2 from OK cell lysate and using fusion proteins, we demonstrated that this interaction was between an internal binding site in the C-terminus of ClC-5 and the PDZ2 module of NHERF2. Silencing NHERF2 reduced both cell surface levels of ClC-5 and albumin uptake. Surface biotinylation experiments revealed that NHERF2 was associated with the plasma membrane and that NHERF2 was recruited to the membrane in the presence of albumin. PDZ1 of NHERF2 binds to SGK-1, a kinase that regulates the activity of proteins present in the macromolecular complex. Therefore, we investigated the role of SGK-1 in albumin endocytosis. Overexpression of SGK-1 increased albumin endocytosis while overexpression of a dominant negative SGK-1 reduced albumin endocytosis. Further we found that ClC 5 immunoprecipitates with SGK-1, however this interaction does not involve the C-terminus of the channel. Therefore, the interaction between ClC-5 and SGK-1 is likely to regulate endocytosis via a novel mechanism that does not involve NHERF-2.

    Conference Organiser - ICMS Pty Ltd