PIKfyve upregulates CFTR activity

Abstract The cystic fibrosis transmembrane conductance regulator (CFTR) is a cAMP-activated Cl − channel critically important in Cl − secreting epithelia. Mutations in the CFTR gene, such as ΔF508 CFTR leads to cystic fibrosis, a severe disease with defective Cl − secretion. CFTR is stimulated by the serum and glucocorticoid-inducible kinase SGK1. The SGK1 dependent regulation of several carriers and channels involves the phosphatidylinositol-3-phosphate-5-kinase PIKfyve, which similarly mediates the regulation of glucose carriers by PKB/Akt. The present study was thus performed to elucidate whether PKB/Akt and PIKfyve are regulators of CFTR. To this end CFTR or ΔF508 CFTR were expressed in Xenopus oocytes alone or together with PKB, PIKfyve or the SGK1/PKB resistant mutant S318A PIKfyve, and the current generated by cAMP upregulation with 10 μM forskolin + 1 mM IBMX determined utilizing dual electrode voltage clamp. As a result, forskolin/IBMX treatment triggered a current ( I cAMP ) in CFTR-expressing Xenopus oocytes, but not in oocytes expressing ΔF508 CFTR. Coexpression of PKB/Akt and PIKfyve, but not of S318A PIKfyve, stimulated I cAMP in CFTR-expressing (≈2- to 3-fold) but not in ΔF508 CFTR - expressing or water injected Xenopus oocytes. Immunohistochemistry revealed that the coexpression of PIKfyve, but not of S318A PIKfyve, enhanced the CFTR protein abundance but not the ΔF508 CFTR protein abundance in CFTR or ΔF508 CFTR-expressing oocytes. The present observations reveal a novel powerful regulator of intact but not of defective CFTR.