Cystic fibrosis (CF) is caused by mutation in the single gene coding for the cystic fibrosis transmembrane conductance regulator (CFTR), an apical membrane Cl- channel. Despite extensive study, there are significant gaps in our understanding of how CFTR is synthesized and processed and how CFTR is regulated and functions at the apical membrane. CFTR associates with a number of proteins that facilitate its trafficking or function, but our understanding of these interactions and how they are altered in CF is relatively poor. We find that the actin binding proteins filamin A (FLN-A) and FLN-B associate directly with residues 1-25 of human CFTR. This interaction enhances receptor-stimulated activation of CFTR and a known disease-causing mutation in the N-terminus of CFTR (S13F) decreases the affinity of the interaction. In addition, the half-life of S13F CFTR is significantly decreased when compared to CFTR proteins that can bind FLN. We also find that a novel sorting nexin, SNX27, associates with CFTR. SNX27 accumulates on subapical endosomes and RNA interference-mediated depletion of SNX27 significantly decreased the levels of cell surface-associated CFTR. Since FLNs and SNX27 associate with CFTR at the cell surface or in endosomal compartments, we hypothesize that these novel CFTR-interacting proteins modulate aspects of CFTR internalization and recycling in polarized cells. Therefore, we propose to fully characterize the biological significance of the CFTR-FLN and CFTR-SNX27 interactions using biochemical, cellular, and functional assays in airway epithelial cells. Our data suggest that CFTR is tethered to the actin cytoskeleton via two distinct linkages - an N-terminal interaction with FLN and C-terminal interaction with actin-associated PDZ proteins. Therefore we will test the hypothesis that these two cytoskeletal anchors work in concert to stabilize CFTR at the apical membrane of polarized cells. The characterization of protein interactions that modulate CFTR trafficking, stability and/or function provide one prospect for new therapies for CF and will increase our understanding of the trafficking and regulation of this complex epithelial ion channel. Lay Summary: Mutations in CFTR cause the lethal childhood disease, cystic fibrosis;our experiments address the question of how other proteins that bind CFTR alter its function in the human lung.

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Research Project (R01)
Project #
5R01HL080561-04
Application #
7666029
Study Section
Lung Cellular, Molecular, and Immunobiology Study Section (LCMI)
Program Officer
Banks-Schlegel, Susan P
Project Start
2006-08-01
Project End
2010-07-31
Budget Start
2009-08-01
Budget End
2010-07-31
Support Year
4
Fiscal Year
2009
Total Cost
$317,782
Indirect Cost
Name
University of North Carolina Chapel Hill
Department
Physiology
Type
Schools of Medicine
DUNS #
608195277
City
Chapel Hill
State
NC
Country
United States
Zip Code
27599
Kota, Pradeep; Garcia-Caballero, Agustin; Dang, Hong et al. (2012) Energetic and structural basis for activation of the epithelial sodium channel by matriptase. Biochemistry 51:3460-9
Gentzsch, Martina; Dang, Hong; Dang, Yan et al. (2010) The cystic fibrosis transmembrane conductance regulator impedes proteolytic stimulation of the epithelial Na+ channel. J Biol Chem 285:32227-32
Cholon, Deborah M; O'Neal, Wanda K; Randell, Scott H et al. (2010) Modulation of endocytic trafficking and apical stability of CFTR in primary human airway epithelial cultures. Am J Physiol Lung Cell Mol Physiol 298:L304-14
Rollins, Brett M; Garcia-Caballero, Agustin; Stutts, M Jackson et al. (2010) SPLUNC1 expression reduces surface levels of the epithelial sodium channel (ENaC) in Xenopus laevis oocytes. Channels (Austin) 4:255-9
Gaillard, Erol A; Kota, Pradeep; Gentzsch, Martina et al. (2010) Regulation of the epithelial Na+ channel and airway surface liquid volume by serine proteases. Pflugers Arch 460:1-17
Thelin, William R; Chen, Yun; Gentzsch, Martina et al. (2007) Direct interaction with filamins modulates the stability and plasma membrane expression of CFTR. J Clin Invest 117:364-74