title: PTH-Induced downregulation of the type IIa Na/P(i)-cotransporter is independent of known endocytic motifs.
abstract: Parathyroid hormone (PTH)-induced inhibition of renal proximal tubular Na/P(i) cotransport involves two consecutive steps: endocytosis followed by lysosomal degradation of the type IIa Na/P(i) cotransporter. Tyrosine-, dileucine-, and diacidic-based motifs are suggested to be involved in endocytosis and/or lysosomal targeting of different plasma membrane proteins. The rat type IIa cotransporter (NaPi2) contains two cytoplasmic tyrosine residues (Y) within sequences highly homologous to tyrosine-based motifs (GY(402)FAM and Y(509)RWF), three cytoplasmic dileucine (LL(101), LL(374), and LI(591)) and two cytoplasmic diacidic motifs (EE(81) and EE(616)). We studied the role of these motifs on the PTH-induced retrieval and lysosomal degradation of the NaPi2 cotransporter. To follow its trafficking in vivo, the NaPi2 protein was fused to the carboxyl-terminal end of the enhanced green fluorescence protein. This fusion did not impair the apical targeting or the PTH-induced endocytosis of the wild-type cotransporter when transfected in opossum kidney cells. Single and multiple Y and LL mutants retained the apical targeting and the PTH-induced degradation. Mutations of the diacidic motifs were also without effect. These data suggest that the above three motifs are not required for the PTH-induced internalization and/or degradation of the cotransporter.
authors.affiliation: Institute of Physiology, University of Zürich, Switzerland.
authors.forename: Nati
authors.initials: N
authors.lastname: Hernando
authors.affiliation: Institute of Physiology, University of Zürich, Switzerland.
authors.forename: Jutka
authors.initials: J
authors.lastname: Forgo
authors.affiliation: Institute of Physiology, University of Zürich, Switzerland.
authors.forename: Jürg
authors.initials: J
authors.lastname: Biber
authors.affiliation: Institute of Physiology, University of Zürich, Switzerland.
authors.forename: Heini
authors.initials: H
authors.lastname: Murer
mesh_terms: D020816:Amino Acid Motifs / Q000502:physiology; D000818:Animals; D002352:Carrier Proteins / Q000235:genetics* / Q000378:metabolism*; D002460:Cell Line; D015536:Down-Regulation; D004705:Endocytosis / Q000502:physiology*; D049452:Green Fluorescent Proteins; D007202:Indicators and Reagents; D008164:Luminescent Proteins / Q000235:genetics; D009893:Opossums; D010281:Parathyroid Hormone / Q000502:physiology*; D020033:Protein Isoforms / Q000378:metabolism; D051381:Rats; D011993:Recombinant Fusion Proteins; D050608:Sodium-Phosphate Cotransporter Proteins; D050613:Sodium-Phosphate Cotransporter Proteins, Type IIa; D027981:Symporters
chemical_list: D002352:Carrier Proteins; D007202:Indicators and Reagents; D008164:Luminescent Proteins; D010281:Parathyroid Hormone; D020033:Protein Isoforms; D011993:Recombinant Fusion Proteins; C493556:Slc34a1 protein, rat; D050608:Sodium-Phosphate Cotransporter Proteins; D050613:Sodium-Phosphate Cotransporter Proteins, Type IIa; D027981:Symporters; D049452:Green Fluorescent Proteins