CFTR anion channel regulation by phosphorylation of focal adhesion kinase at tyrosine 407 in osmosensing mitochondria‐rich ion transporting cells of killifish (Fundulus heteroclitus)

Abstract

Focal adhesion kinase (FAK) is a tyrosine kinase with multiple Y sites and an ezrin/radixin/moesin binding site. Antibodies to the phosphorylated form of FAK at Y407 and Y587 are colocalized with the Cl− channel CFTR in the apical membrane of mitochondria‐rich (MR) cells of seawater‐acclimated euryhaline killifish opercular epithelium. Hypotonic treatment (80%, 224 mOsm/kg) causes rapid, reversible cell swelling (observed via confocal microscopy of living cells in situ), inhibition of Cl− secretion and dephosphorylation of FAK pY407 but no effect on FAK phosphorylated at Y576. Re‐phosphorylation of FAK at Y407 specifically in the apical membrane of MR cells was immunohistochemically detected following 10‐min treatments with forskolin (10 μM), 3‐isobutyl‐1‐methylxanthine (IBMX, 0.1 mM) and isoproterenol (1.0 μM), all known to increase cAMP and activate CFTR. There is parallel recovery of Cl− secretion by MR cells in the isolated epithelium, detected electrophysiologically. These results suggest involvement of phosphorylation of FAK pY407 but not pY576 in cell signaling pathways regulating the Cl− transport function of CFTR. (Supported by NSERC Canada)