title: Convergence of IRBIT, phosphatidylinositol (4,5) bisphosphate, and WNK/SPAK kinases in regulation of the Na+-HCO3- cotransporters family.
abstract: Fluid and HCO3(-) secretion is a vital function of secretory epithelia, involving basolateral HCO3(-) entry through the Na(+)-HCO3(-) cotransporter (NBC) NBCe1-B, and luminal HCO3(-) exit mediated by cystic fibrosis transmembrane conductance regulator (CFTR) and solute carrier family 26 (SLC26) Cl(-)/HCO3(-) exchangers. HCO3(-) secretion is highly regulated, with the WNK/SPAK kinase pathway setting the resting state and the IRBIT/PP1 pathway setting the stimulated state. However, we know little about the relationships between the WNK/SPAK and IRBIT/PP1 sites in the regulation of the transporters. The first 85 N-terminal amino acids of NBCe1-B function as an autoinhibitory domain. Here we have identified a positively charged module within NBCe1-B(37-65) that is conserved in NBCn1-A and all 20 members of the NBC superfamily except NBCe1-A. This module is required for the interaction and activation of NBCe1-B and NBCn1-A by IRBIT and their regulation by phosphatidylinositol 4,5-bisphosphate (PIP2). Activation of the transporters by IRBIT and PIP2 is nonadditive but complementary. Phosphorylation of Ser65 mediates regulation of NBCe1-B by SPAK, and phosphorylation of Thr49 is required for regulation by IRBIT and SPAK. Sequence searches using the NBCe1-B regulatory module as a template identified a homologous sequence in the CFTR R domain and Slc26a6 sulfat transporter and antisigma factor antagonist (STAS) domain. Accordingly, the R and STAS domains bind IRBIT, and the R domain is required for activation of CFTR by IRBIT. These findings reveal convergence of regulatory modalities in a conserved domain of the NBC that may be present in other HCO3(-) transporters and thus in the regulation of epithelial fluid and HCO3(-) secretion.
authors: Epithelial Signaling and Transport Section, Molecular Physiology and Therapeutics Branch, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD 20892, USA.
authors: Jeong Hee
authors: JH
authors: Hong
authors: Dongki
authors: D
authors: Yang
authors: Nikolay
authors: N
authors: Shcheynikov
authors: Ehud
authors: E
authors: Ohana
authors: Dong Min
authors: DM
authors: Shin
authors: Shmuel
authors: S
authors: Muallem
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D037181:Lectins, C-Type / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000378:metabolism*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D027982:Sodium-Bicarbonate Symporters / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: C505032:CFTR protein, human; C470184:CLECL1 protein, human; D037181:Lectins, C-Type; D008565:Membrane Proteins; D019269:Phosphatidylinositol 4,5-Diphosphate; D011994:Recombinant Proteins; C498898:SLC4A4 protein, human; D027982:Sodium-Bicarbonate Symporters; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D017346:Protein Serine-Threonine Kinases; C486409:STK39 protein, human