title: Tamm-Horsfall glycoprotein interacts with renal outer medullary potassium channel ROMK2 and regulates its function.
abstract: Tamm-Horsfall glycoprotein (THGP) or Uromodulin is a membrane protein exclusively expressed along the thick ascending limb (TAL) and early distal convoluted tubule (DCT) of the nephron. Mutations in the THGP encoding gene result in Familial Juvenile Hyperuricemic Nephropathy (FJHN), Medullary Cystic Kidney Disease type 2 (MCKD-2), and Glomerulocystic Kidney Disease (GCKD). The physicochemical and biological properties of THGP have been studied extensively, but its physiological function in the TAL remains obscure. We performed yeast two-hybrid screening employing a human kidney cDNA library and identified THGP as a potential interaction partner of the renal outer medullary potassium channel (ROMK2), a key player in the process of salt reabsorption along the TAL. Functional analysis by electrophysiological techniques in Xenopus oocytes showed a strong increase in ROMK current amplitudes when co-expressed with THGP. The effect of THGP was specific for ROMK2 and did not influence current amplitudes upon co-expression with Kir2.x, inward rectifier potassium channels related to ROMK. Single channel conductance and open probability of ROMK2 were not altered by co-expression of THGP, which instead increased surface expression of ROMK2 as determined by patch clamp analysis and luminometric surface quantification, respectively. Despite preserved interaction with ROMK2, disease-causing THGP mutants failed to increase its current amplitude and surface expression. THGP(-/-) mice exhibited increased ROMK accumulation in intracellular vesicular compartments when compared with WT animals. Therefore, THGP modulation of ROMK function confers a new role of THGP on renal ion transport and may contribute to salt wasting observed in FJHN/MCKD-2/GCKD patients.
authors.affiliation: Department of Pediatric Nephrology, Children's Hospital, Philipps University of Marburg, Baldingerstr., 35043 Marburg, Germany. renigunt@med.uni-marburg.de
authors.forename: Aparna
authors.initials: A
authors.lastname: Renigunta
authors.forename: Vijay
authors.initials: V
authors.lastname: Renigunta
authors.forename: Turgay
authors.initials: T
authors.lastname: Saritas
authors.forename: Niels
authors.initials: N
authors.lastname: Decher
authors.forename: Kerim
authors.initials: K
authors.lastname: Mutig
authors.forename: Siegfried
authors.initials: S
authors.lastname: Waldegger
mesh_terms: D000818:Animals; D006073:Gout / Q000235:genetics / Q000378:metabolism; D006801:Humans; D033461:Hyperuricemia / Q000235:genetics / Q000378:metabolism; D017136:Ion Transport / Q000235:genetics; D007668:Kidney / Q000378:metabolism*; D007674:Kidney Diseases / Q000235:genetics / Q000378:metabolism; D052177:Kidney Diseases, Cystic / Q000235:genetics / Q000378:metabolism; D008564:Membrane Potentials / Q000235:genetics; D051379:Mice; D018345:Mice, Knockout; D009154:Mutation; D009865:Oocytes; D016891:Polycystic Kidney, Autosomal Dominant; D024661:Potassium Channels, Inwardly Rectifying / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics; D020798:Two-Hybrid System Techniques; D058949:Uromodulin / Q000235:genetics / Q000378:metabolism* / Q000172:deficiency; D014982:Xenopus laevis
chemical_list: C086989:KCNJ1 protein, human; C510693:Kcnj1 protein, mouse; D024661:Potassium Channels, Inwardly Rectifying; C548612:UMOD protein, human; C548613:Umod protein, mouse; D058949:Uromodulin