PDZK1: I. a major scaffolder in brush borders of proximal tubular cells

Kidney Int. 2003 Nov;64(5):1733-45. doi: 10.1046/j.1523-1755.2003.00266.x.

Abstract

Background: In proximal tubular cells, PDZK1 (NaPi-Cap1) has been implicated in apical expression of the Na+-dependent phosphate cotransporter (NaPi-IIa) via interaction with its C-terminus. PDZK1 represents a multidomain protein consisting of four PDZ domains and thus is believed to have a broader specificity besides NaPi-IIa.

Methods: We subjected single PDZ domains derived from PDZK1 either to yeast two-hybrid screens or yeast trap assays. Different pull-down assays and blot overlays were applied to corroborate the PDZK1-mediated interactions in vitro. Co-localization of interacting proteins with PDZK1 in proximal tubular cells was assessed by immunohistochemistry.

Results: In the yeast screens, the most abundant candidate protein to interact with PDZK1 was the membrane-associated protein of 17 kD (MAP17). Besides MAP17, C-terminal parts of following transporters were also identified: NaPi-IIa, solute carrier SLC17A1 (NaPi-I), Na+/H+ exchanger (NHE-3), organic cation transporter (OCTN1), chloride-formate exchanger (CFEX), and urate-anion exchanger (URAT1). In addition, other regulatory factors were found among the clones, such as a protein kinase A (PKA)-anchoring protein (D-AKAP2) and N+/H+ exchanger regulator factor (NHERF-1). All interactions of itemized proteins with PDZK1 were affirmed by in vitro techniques. Apart from PDZK1, strong in vitro interactions of NHERF-1 were also observed with the solute transporters (excluding MAP17) and D-AKAP2. All identified proteins were immunolocalized in proximal tubular cells, wherein all membrane proteins co-localized with PDZK1 in brush borders.

Conclusion: We hypothesize that PDZK1 and NHERF-1 establish an extended network beneath the apical membrane to which membrane proteins and regulatory components are anchored.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Glycosylphosphatidylinositols / metabolism
  • Immunohistochemistry
  • Kidney Tubules, Proximal / cytology
  • Kidney Tubules, Proximal / metabolism*
  • Membrane Proteins / genetics
  • Membrane Proteins / metabolism*
  • Mice
  • Microvilli / metabolism
  • Phosphoproteins / metabolism*
  • Protein Binding / physiology
  • Sodium-Hydrogen Exchangers
  • Two-Hybrid System Techniques
  • Yeasts

Substances

  • Glycosylphosphatidylinositols
  • Membrane Proteins
  • Phosphoproteins
  • Sodium-Hydrogen Exchangers
  • sodium-hydrogen exchanger regulatory factor