title: NHERF2 is necessary for basal activity, second messenger inhibition, and LPA stimulation of NHE3 in mouse distal ileum.
abstract: To test the hypothesis that Na(+)/H(+) exchanger (NHE) regulatory factor 2 (NHERF2) is necessary for multiple aspects of acute regulation of NHE3 in intact mouse small intestine, distal ileal NHE3 activity was determined using two-photon microscopy/SNARF-4F in a NHERF2-null mouse model. The NHERF2-null mouse ileum had shorter villi, deeper crypts, and decreased epithelial cell number. Basal rates of NHE3 activity were reduced in NHERF2-null mice, which was associated with a reduced percentage of NHE3 in the apical domain and an increase in intracellular NHE3 amount but no change in total level of NHE3 protein. cAMP, cGMP, and elevated Ca(2+) due to apical exposure to UTP all inhibited NHE3 activity in wild-type mouse ileum but not in NHERF2-null mice, while inhibition by hyperosmolarity occurred normally. The cAMP-increased phosphorylation of NHE3 at aa 552; levels of PKAIIα and cGMP-dependent protein kinase II (cGKII); and elevation of Ca(2+) were similar in wild-type and NHERF2-null mouse ileum. Luminal lysophosphatidic acid (LPA) stimulated NHE3 in wild-type but not in NHERF2-null ileum. In conclusion, 1) there are subtle structural abnormalities in the small intestine of NHERF2-null mouse which include fewer villus epithelial cells; 2) the decreased basal NHE3 activity and reduced brush border NHE3 amount in NHERF2-null mice show that NHERF2 is necessary for normal basal trafficking or retention of NHE3 in the apical domain; 3) hyperosmolar inhibition of NHE3 occurs similarly in wild-type and NHERF2-null ileum, demonstrating that some inhibitory mechanisms of NHE3 are not NHERF2 dependent; 4) cAMP inhibition of NHE3 is NHERF2 dependent at a step downstream of cAMP/PKAII phosphorylation of NHE3 at aa 552; 5) cGMP- and UTP-induced inhibition of NHE3 are NHERF2 dependent at steps beyond cGKII and the UTP-induced increase of intracellular Ca(2+); and 6) LPA stimulation of NHE3 is also NHERF2 dependent.
authors: Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland 21287, USA.
authors: Rakhilya
authors: R
authors: Murtazina
authors: Olga
authors: O
authors: Kovbasnjuk
authors: Tian-E
authors: TE
authors: Chen
authors: Nicholas C
authors: NC
authors: Zachos
authors: Yeuping
authors: Y
authors: Chen
authors: Hetal S
authors: HS
authors: Kocinsky
authors: Boris M
authors: BM
authors: Hogema
authors: Ursula
authors: U
authors: Seidler
authors: Hugo R
authors: HR
authors: de Jonge
authors: Mark
authors: M
authors: Donowitz
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D049109:Cell Proliferation; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism; D006152:Cyclic GMP / Q000378:metabolism; D004847:Epithelial Cells / Q000378:metabolism; D007082:Ileum / Q000166:cytology / Q000378:metabolism*; D008246:Lysophospholipids / Q000378:metabolism*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008871:Microvilli / Q000378:metabolism; D009994:Osmolar Concentration; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism*; D021381:Protein Transport; D015290:Second Messenger Systems; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers / Q000235:genetics / Q000378:metabolism*
chemical_list: D008246:Lysophospholipids; D010750:Phosphoproteins; C000613386:Slc9a3 protein, mouse; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers; C093376:sodium-hydrogen exchanger regulatory factor; D000242:Cyclic AMP; D006152:Cyclic GMP; C032881:lysophosphatidic acid; D002118:Calcium