title: The identification of Histidine 712 as a critical residue for constitutive TRPV5 internalization.
abstract: The epithelial Ca(2+) channel TRPV5 constitutes the apical entry gate for Ca(2+) transport in renal epithelial cells. Ablation of the trpv5 gene in mice leads to a reduced Ca(2+) reabsorption. TRPV5 is tightly regulated by various calciotropic hormones, associated proteins, and other factors, which mainly affect channel activity via the C terminus. To further identify the role of the C terminus in TRPV5 regulation, we expressed channels harboring C-terminal deletions and studied channel activity by measuring intracellular Ca(2+) concentration ([Ca(2+)](i)) using fura-2 analysis. Removal of amino acid His(712) elevated the [Ca(2+)](i), indicating enlarged TRPV5 activity. In addition, substitution of the positively charged His(712) for a negative (H712D) or neutral (H712N) amino acid also stimulated TRPV5 activity. This critical role of His(712) was confirmed by patch clamp analysis, which demonstrates increased Na(+) and Ca(2+) currents for TRPV5-H712D. Cell surface biotinylation studies revealed enhanced plasma membrane expression of TRPV5-H712D as compared with wild-type (WT) TRPV5. This elevated plasma membrane presence also was observed with the Ca(2+)-impermeable TRPV5-H712D and TRPV5-WT pore mutants, demonstrating that the elevation is not due to the increased [Ca(2+)](i). Finally, using an internalization assay, we demonstrated a delayed cell surface retrieval for TRPV5-H712D, likely causing the increase in plasma membrane expression. Together, these results demonstrate that His(712) plays an essential role in plasma membrane regulation of TRPV5 via a constitutive endocytotic mechanism.
authors.affiliation: Department of Physiology, Radboud University Nijmegen Medical Centre, 6500 HB Nijmegen, The Netherlands.
authors.forename: Theun
authors.initials: T
authors.lastname: de Groot
authors.forename: Sjoerd
authors.initials: S
authors.lastname: Verkaart
authors.forename: Qi
authors.initials: Q
authors.lastname: Xi
authors.forename: René J M
authors.initials: RJ
authors.lastname: Bindels
authors.forename: Joost G J
authors.initials: JG
authors.lastname: Hoenderop
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D002460:Cell Line; D002462:Cell Membrane / Q000235:genetics / Q000378:metabolism*; D004705:Endocytosis / Q000502:physiology; D006801:Humans; D051379:Mice; D020125:Mutation, Missense; D011188:Potassium / Q000378:metabolism*; D011817:Rabbits; D017384:Sequence Deletion; D012964:Sodium / Q000378:metabolism*; D050916:TRPV Cation Channels / Q000235:genetics / Q000378:metabolism*
chemical_list: D050916:TRPV Cation Channels; D012964:Sodium; D011188:Potassium