title: Irbit mediates synergy between ca(2+) and cAMP signaling pathways during epithelial transport in mice.
abstract: OBJECTIVE
  The cyclic adenosine monophosphate (cAMP) and Ca(2+) signaling pathways synergize to regulate many physiological functions. However, little is known about the mechanisms by which these pathways interact. We investigated the synergy between these signaling pathways in mouse pancreatic and salivary gland ducts.
  
  
  METHODS
  We created mice with disruptions in genes encoding the solute carrier family 26, member 6 (Slc26a6(-/-) mice) and inositol 1,4,5-triphosphate (InsP3) receptor-binding protein released with InsP3 (Irbit(-/-)) mice. We investigated fluid secretion by sealed pancreatic ducts and the function of Slc26a6 and the cystic fibrosis transmembrane conductance regulator (CFTR) in HeLa cells and in ducts isolated from mouse pancreatic and salivary glands. Slc26a6 activity was assayed by measuring intracellular pH, and CFTR activity was assayed by measuring Cl(-) current. Protein interactions were determined by immunoprecipitation analyses.
  
  
  RESULTS
  Irbit mediated the synergistic activation of CFTR and Slc26a6 by Ca(2+) and cAMP. In resting cells, Irbit was sequestered by InsP3 receptors (IP3Rs) in the endoplasmic reticulum. Stimulation of Gs-coupled receptors led to phosphorylation of IP3Rs, which increased their affinity for InsP3 and reduced their affinity for Irbit. Subsequent weak stimulation of Gq-coupled receptors, which led to production of low levels of IP3, caused dissociation of Irbit from IP3Rs and allowed translocation of Irbit to CFTR and Slc26a6 in the plasma membrane. These processes stimulated epithelial secretion of electrolytes and fluid. These pathways were not observed in pancreatic and salivary glands from Irbit(-/-) or Slc26a6(-/-) mice, or in salivary gland ducts expressing mutant forms of IP3Rs that could not undergo protein kinase A-mediated phosphorylation.
  
  
  CONCLUSIONS
  Irbit promotes synergy between the Ca(2+) and cAMP signaling pathways in cultured cells and in pancreatic and salivary ducts from mice. Defects in this pathway could be involved in cystic fibrosis, pancreatitis, or Sjögren syndrome.
authors.affiliation: Epithelial Signaling and Transport Section, Molecular Physiology and Therapeutics Branch, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, Maryland; Department of Physiology, School of Medicine, Ewha Womans University, Seoul, Republic of Korea.
authors.forename: Seonghee
authors.initials: S
authors.lastname: Park
authors.affiliation: Epithelial Signaling and Transport Section, Molecular Physiology and Therapeutics Branch, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, Maryland.
authors.forename: Nikolay
authors.initials: N
authors.lastname: Shcheynikov
authors.affiliation: Epithelial Signaling and Transport Section, Molecular Physiology and Therapeutics Branch, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, Maryland.
authors.forename: Jeong Hee
authors.initials: JH
authors.lastname: Hong
authors.affiliation: Epithelial Signaling and Transport Section, Molecular Physiology and Therapeutics Branch, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, Maryland.
authors.forename: Changyu
authors.initials: C
authors.lastname: Zheng
authors.affiliation: Department of Physiology, School of Medicine, Ewha Womans University, Seoul, Republic of Korea.
authors.forename: Suk Hyo
authors.initials: SH
authors.lastname: Suh
authors.affiliation: Laboratory for Developmental Neurobiology, Brain Science Institute, Institute of Physical and Chemical Research (RIKEN), Saitama, Japan.
authors.forename: Katsuhiro
authors.initials: K
authors.lastname: Kawaai
authors.affiliation: Laboratory for Developmental Neurobiology, Brain Science Institute, Institute of Physical and Chemical Research (RIKEN), Saitama, Japan.
authors.forename: Hideaki
authors.initials: H
authors.lastname: Ando
authors.affiliation: Department of Pharmacotherapeutics, Showa Pharmaceutical University, Machida, Tokyo, Japan.
authors.forename: Akihiro
authors.initials: A
authors.lastname: Mizutani
authors.affiliation: Laboratory for Animal Resources and Genetic Engineering, RIKEN Center for Developmental Biology, Kobe, Japan.
authors.forename: Takaya
authors.initials: T
authors.lastname: Abe
authors.affiliation: Laboratory for Animal Resources and Genetic Engineering, RIKEN Center for Developmental Biology, Kobe, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Kiyonari
authors.affiliation: Department of Internal Medicine, Faculty of Medicine, University of Tokyo, Tokyo, Japan.
authors.forename: George
authors.initials: G
authors.lastname: Seki
authors.affiliation: Department of Pharmacology & Physiology, School of Medicine and Dentistry, University of Rochester Medical Center, Rochester, New York.
authors.forename: David
authors.initials: D
authors.lastname: Yule
authors.affiliation: Laboratory for Developmental Neurobiology, Brain Science Institute, Institute of Physical and Chemical Research (RIKEN), Saitama, Japan.
authors.forename: Katsuhiko
authors.initials: K
authors.lastname: Mikoshiba
authors.affiliation: Epithelial Signaling and Transport Section, Molecular Physiology and Therapeutics Branch, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, Maryland. Electronic address: Shmuel.muallem@nih.gov.
authors.forename: Shmuel
authors.initials: S
authors.lastname: Muallem
mesh_terms: D043383:Adenosylhomocysteinase / Q000502:physiology*; D000818:Animals; D017920:Antiporters / Q000378:metabolism; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism*; D000242:Cyclic AMP / Q000502:physiology*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000502:physiology; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000502:physiology; D004848:Epithelium / Q000378:metabolism; D015544:Inositol 1,4,5-Trisphosphate / Q000096:biosynthesis; D053496:Inositol 1,4,5-Trisphosphate Receptors / Q000502:physiology; D051379:Mice; D010183:Pancreatic Ducts / Q000378:metabolism; D010766:Phosphorylation; D018987:Salivary Ducts / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D000076988:Sulfate Transporters
chemical_list: D017920:Antiporters; D053496:Inositol 1,4,5-Trisphosphate Receptors; C466900:Slc26a6 protein, mouse; D000076988:Sulfate Transporters; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D015544:Inositol 1,4,5-Trisphosphate; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D043383:Adenosylhomocysteinase; C510392:IRBIT protein, mouse; D002118:Calcium
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