CFTR and SLC5A8 Associate in Thyroid Epithelial Cells

Abstract

The cystic fibrosis transmembrane conductance regulator, CFTR, is expressed at the apical membranes of many epithelial cells, where it mediates cAMP‐stimulated anion secretion. In thyroid, CFTR may indirectly and/or directly furnish iodide for hormone synthesis. CFTR functionally interacts with many membrane transporters via PSD‐Discs large homologous‐ZO‐1 (PDZ) domain‐containing scaffolding proteins, thereby forming macromolecular transport complexes. SLC5A8 is an electrogenic, sodium‐coupled monocarboxylate transporter that also is expressed at thyrocyte apical membranes. CFTR and SLC5A8 contain the identical PDZ domain interaction motif; preliminary studies utilizing overexpression systems indicate a role for PDZ adaptor proteins in linking CFTR and SLC5A8. The present studies use the Fisher rat thyroid cell line, FRTL‐5, to test the hypothesis that PDZ proteins facilitate CFTR/SLC5A8 interactions in an endogenously expressing system. Expression of CFTR (~150 kDa), SLC5A8 (~68 kDa) and NHERF‐1 (~50 kDa) in total FRTL‐5 lysates was confirmed by immunoblot analysis using anti‐CFTR (M3A7 and Cystic Fibrosis Foundation Therapeutics (CFFT) 660), anti‐SLC5A8 (Abcam) and anti‐NHERF‐1 (Alomone) antibodies. Anti‐SLC5A8‐immunoprecipitated (IPd) fractions of FRTL‐5 lysates reacted with both CFFT 660 and anti‐NHERF‐1. Fractions IPd using anti‐CFTR (M3A7) were probed with anti‐SLC5A8 and anti‐NHERF‐1. M3A7‐IPd fractions showed positive reactivity with anti‐SLC5A8, but NHERF‐1 was not detected. These data suggest that although CFTR and SLC5A8 associate in FRTL‐5 cells, the participation of NHERF‐1 is not required.
 Support: NIH/NIGMS Award 1R15GM101674‐01A1 (to PF); Office of the Director, NIH Award Number T35OD010979.