Article

IRBIT governs epithelial secretion in mice by antagonizing the WNK/SPAK kinase pathway.

The Epithelial Signaling and Transport Section, Molecular Physiology and Therapeutics Branch, National Institute of Dental and Craniofacial Research, NIH, Bethesda, Maryland 20892, USA.
The Journal of clinical investigation (impact factor: 15.39). 03/2011; 121(3):956-65. DOI:10.1172/JCI43475 pp.956-65
Source: PubMed

ABSTRACT Fluid and HCO(3)(-) secretion are fundamental functions of epithelia and determine bodily fluid volume and ionic composition, among other things. Secretion of ductal fluid and HCO(3)(-) in secretory glands is fueled by Na(+)/HCO(3)(-) cotransport mediated by basolateral solute carrier family 4 member 4 (NBCe1-B) and by Cl(-)/HCO(3)(-) exchange mediated by luminal solute carrier family 26, member 6 (Slc26a6) and CFTR. However, the mechanisms governing ductal secretion are not known. Here, we have shown that pancreatic ductal secretion in mice is suppressed by silencing of the NBCe1-B/CFTR activator inositol-1,4,5-trisphosphate (IP(3)) receptor-binding protein released with IP(3) (IRBIT) and by inhibition of protein phosphatase 1 (PP1). In contrast, silencing the with-no-lysine (WNK) kinases and Ste20-related proline/alanine-rich kinase (SPAK) increased secretion. Molecular analysis revealed that the WNK kinases acted as scaffolds to recruit SPAK, which phosphorylated CFTR and NBCe1-B, reducing their cell surface expression. IRBIT opposed the effects of WNKs and SPAK by recruiting PP1 to the complex to dephosphorylate CFTR and NBCe1-B, restoring their cell surface expression, in addition to stimulating their activities. Silencing of SPAK and IRBIT in the same ducts rescued ductal secretion due to silencing of IRBIT alone. These findings stress the pivotal role of IRBIT in epithelial fluid and HCO(3)(-) secretion and provide a molecular mechanism by which IRBIT coordinates these processes. They also have implications for WNK/SPAK kinase-regulated processes involved in systemic fluid homeostasis, hypertension, and cystic fibrosis.

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Keywords

bodily fluid volume
 
cell surface expression
 
cystic fibrosis
 
dephosphorylate CFTR
 
ductal fluid
 
ductal secretion
 
epithelial fluid
 
ionic composition
 
luminal solute carrier family 26
 
member 6
 
NBCe1-B
 
NBCe1-B/CFTR activator inositol-1,4,5-trisphosphate
 
pancreatic ductal secretion
 
phosphorylated CFTR
 
pivotal role
 
protein phosphatase 1
 
recruit SPAK
 
secretory glands
 
systemic fluid homeostasis
 
WNK/SPAK kinase-regulated processes