Previous reports showed inhibition of cystic fibrosis transmembrane conductance regulator (CFTR) by adenosine monophosphate dependent kinase (AMPK). AMPK is a ubiquitous energy housekeeping enzyme, which is activated by low intracellular ATP/AMP ratios. Two AMPK phosphorylation sites in CFTR were identified, S573 in the nucleotide binding fold 1 (NBF1) and S1248 in NBF2. Overexpression of CFTR in Xenopus laevis oocytes was used to functionally characterise these phosphorylation sites for AMPK dependent inhibition of CFTR. Voltage clamp experiments showed increased whole cell conductances for the two CFTR mutants S573A and S1248A, as well as for the double mutants. Incubation with the AMPK inhibitor compound C leads to a further increase in whole cell conductance. Treatment with the AMPK activators AICAR or phenformin decreased whole cell conductances generated by each mutant, but not for wt CFTR. These findings suggested that AMPK dependent inhibition of CFTR is partially due to S573 and S1248 phosphorylation. In addition other phosphorylation sites within the CFTR molecule remain to be identified.

Supported by SFB699 A6