title: Down regulation of small intestinal ion transport in PDZK1- (CAP70/NHERF3) deficient mice.
abstract: The PDZ-binding protein PDZK1 (CAP70/PDZ-dc-1/NHERF3) in vitro binds to cystic fibrosis transmembrane conductance regulator (CFTR), the anion exchangers SLC26A3 and SLC26A6 and the Na(+)/H(+) exchanger NHE3, all of which are major transport proteins for intestinal anion secretion and salt absorption. This study was undertaken to search for a role of PDZK1 in regulating electrolyte transport in native murine small intestine. Short circuit current (I (SC)) and HCO-(3) secretory rate (J(HCO-)(3)) were measured to assess electrogenic anion secretion; (22)Na(+) fluxes to assess sodium absorption in isolated small intestine. NHE3, CFTR, as well as NHERF1, NHERF2, and PDZK1 messenger RNA (mRNA) expression levels, and NHE3 total enterocyte and brush border membrane (BBM) protein abundance were determined by quantitative polymerase chain reaction (PCR) and Western analysis. NHE3 localization was performed by immunohistochemistry. In pdzk1 -/- jejunal mucosa, basal net Na(+) absorption as well as the inhibition of Na(+) absorption by forskolin was significantly reduced. In pdzk1 -/- duodenal mucosa, identical basal I (SC) and (J(HCO-)(3)) but a significant, yet mild, reduction of forskolin-stimulated Delta(J(HCO-)(3)) and DeltaI (SC) was observed compared to +/+ tissue. Tissue conductance, morphological features, and the DeltaI (SC) and increase in (22)Na(+) absorption in response to luminal glucose was identical in pdzk1 +/+ and -/- small intestine, ruling out a general absorptive defect. While CFTR mRNA expression levels were unchanged, NHE3 mRNA expression levels were significantly increased in small intestinal mucosa of pdzk1 -/- mice. Total enterocyte and BBM abundance was not significantly different, suggesting an increased NHE3 turnover, possibly due to reduced NHE3 membrane retention time. Lack of the PDZ-adapter protein PDZK1 in murine small intestine causes a mild reduction in maximal CFTR activation, but a severe defect in electroneutral Na(+) absorption.
authors.affiliation: Department of Gastroenterology, Hepatology, and Endocrinology, Hannover Medical School, Carl-Neuberg-Strasse 1, 30625 Hannover, Germany.
authors.forename: Jutta
authors.initials: J
authors.lastname: Hillesheim
authors.forename: Brigitte
authors.initials: B
authors.lastname: Riederer
authors.forename: Biguang
authors.initials: B
authors.lastname: Tuo
authors.forename: Mingmin
authors.initials: M
authors.lastname: Chen
authors.forename: Michael
authors.initials: M
authors.lastname: Manns
authors.forename: Jürg
authors.initials: J
authors.lastname: Biber
authors.forename: Chris
authors.initials: C
authors.lastname: Yun
authors.forename: Olivier
authors.initials: O
authors.lastname: Kocher
authors.forename: Ursula
authors.initials: U
authors.lastname: Seidler
mesh_terms: D000818:Animals; D001639:Bicarbonates / Q000378:metabolism; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000502:physiology; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000235:genetics / Q000378:metabolism; D015536:Down-Regulation / Q000502:physiology*; D005786:Gene Expression Regulation; D007408:Intestinal Absorption / Q000187:drug effects / Q000502:physiology; D007421:Intestine, Small / Q000502:physiology*; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism*; D017136:Ion Transport / Q000502:physiology*; D008565:Membrane Proteins; D051379:Mice; D018345:Mice, Knockout; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012964:Sodium / Q000378:metabolism; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers / Q000235:genetics / Q000378:metabolism
chemical_list: D001639:Bicarbonates; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; C514896:PDZK1 protein, mouse; D010750:Phosphoproteins; D012333:RNA, Messenger; C000613386:Slc9a3 protein, mouse; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers; C093376:sodium-hydrogen exchanger regulatory factor; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D005576:Colforsin; D012964:Sodium; D000242:Cyclic AMP