Actin filament organization is required for proper cAMP-dependent activation of CFTR

Previous studies have indicated a role of the actin cytoskeleton in the reg ulation of the cystic fibrosis transmembrane conductance regulator (CFTR) i on channel. However, the exact molecular nature of this regulation is still largely unknown. In this report human epithelial CFTR was expressed in hum an melanoma cells genetically devoid of the filamin homologue act-in-cross- linking protein ABP-280 [ABP(-)]. cAMP stimulation of ABP(-) cells or cells genetically rescued with ABP-280 cDNA [ABP(+)] was without effect on whole cell Cl- currents. In ABP(-) cells expressing CFTR, cAMP was also without effect on Cl- conductance. In contrast, cAMP induced a 10-fold increase in the diphenylamine-2-carboxylate (DPC)-sensitive whole cell Cl- currents of ABP(+)/CFTR(+) cells. Further, in cells expressing both CFTR and a truncate d form of ABP-280 unable to cross-link actin filaments, cAMP was also witho ut effect on CFTR activation. Dialysis of ABP-280 or filamin through the pa tch pipette, however, resulted in a DPC-inhibitable increase in the whole c ell currents of ABP(-)/CFTR(+) cells. At the single-channel let el, protein kinase A plus ATP activated single Cl- channels only in excised patches fi om ABP(+)/CFTR(+) cells. Furthermore, filamin alone also induced Cl- chann el activity in excised patches of ABP( - )/CFTR( +) cells. The present data indicate that an organized actin cytoskeletan is required for cAMP-depende nt activation of CFTR.