Interaction of the type IIa Na/Pi cotransporter with PDZ proteins.
The type IIa Na(+)-dependent inorganic phosphate (Na/P(i)) cotransporter is localized in the apical membrane of proximal tubular cells and is regulated by an endocytotic pathway. Because molecular processes such as apical sorting, internalization, or subsequent degradation might be assisted by associated proteins, a yeast two-hybrid screen against the C-terminal, cytosolic tail of type IIa cotransporter was designed. Most of the potential proteins found belonged to proteins with multiple PDZ modules and were either identical/related to PDZK1 or identical to NHERF-1. Yeast trap truncation assays confined the peptide-protein association to the C-terminal amino acid residues TRL of type IIa cotransporter and to single PDZ domains of each identified protein, respectively. The specificity of these interactions were confirmed in yeast by testing other apical localized transmembraneous proteins. Moreover, the type IIa protein was recovered in vitro by glutathione S-transferase-fused PDZ proteins from isolated renal brush border membranes or from type IIa-expressing oocytes. Further, these PDZ proteins are immunohistochemically detected either in the microvilli or in the subapical compartment of proximal tubular cells. Our results suggest that the type IIa Na/P(i) cotransporter interacts with various PDZ proteins that might be responsible for the apical sorting, parathyroid hormone controlled endocytosis or the lysosomal sorting of internalized type IIa cotransporter.
Gisler
S M
SM
Institute of Physiology, Veterinary Biochemistry, and Anatomy, University of Zürich-Irchel, CH-8057 Zürich, Switzerland.
Stagljar
I
I
Traebert
M
M
Bacic
D
D
Biber
J
J
Murer
H
H
D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism*; D000818:Animals; D001483:Base Sequence; D002352:Carrier Proteins / Q000378:metabolism*; D017931:DNA Primers; D005982:Glutathione Transferase / Q000378:metabolism; D006801:Humans; D007687:Kidney Tubules, Proximal / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism*; D051379:Mice; D008969:Molecular Sequence Data; D011485:Protein Binding; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D050608:Sodium-Phosphate Cotransporter Proteins; D050613:Sodium-Phosphate Cotransporter Proteins, Type IIa; D027981:Symporters
D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D017931:DNA Primers; D008565:Membrane Proteins; C515735:PDZK2 protein, mouse; D011993:Recombinant Fusion Proteins; C493554:SLC34A1 protein, human; C493555:Slc34a1 protein, mouse; C493556:Slc34a1 protein, rat; D050608:Sodium-Phosphate Cotransporter Proteins; D050613:Sodium-Phosphate Cotransporter Proteins, Type IIa; D027981:Symporters; D005982:Glutathione Transferase