CFtr-orcc regulatory interaction requires autocrine atp transport, release and signaling

CFTR regulates ORCCs through an autocrine signaling mechanism that requires CFTRand cyclic AMP-dependent ATP transport and release. ATP signaling occurs through purinergic receptors expressed on the apical membrane of the airway epithelium to stimulate ORCCs {Schwiebert et al. Celt 81:1063, 1995}. Thus, CFTR functions as a cAMP-regulated Cl channel and as a cAMP-regulated ATP channel which supplies ATP as an agonist to stimulate ORCCs. Two questions arise from these studies: (1) Which molecular domains of CFTR conduct Cl ions? and (2) which domains of CFTR transport ATP? To address these questions, we expressed a panel of mutated or truncated CFTR constructs by injecting Xenopus oocytes with CFTR cRNA and by lipofection of IB3-1 CF airway epithelial cells with RSV promoter-driven CFTR cDNA. Expression of two Nterminal truncated constructs, A259-M265, which lacks predicted a-helices 1-4 of CFTR, and A259-M265V, which lacks a-helices 1-4 with methionine 265 mutated to a valine, revealed different phenotypes. A259-M265 could conduct Cl and transport ATP to stimulate ORCCs: A259-M265V failed to conduct Cl but retained ATP transport function. TMD-1 CFTR, which contains only the first transmembrane domain of CFTR, functioned as a Cl channel but failed to transport ATP. T-N-R CFTR, which contains TMD-1, NBDI and the R domain of CFTR, retained both functions. CFTR carrying two mild CF lung disease-causing Cl conduction mutations, R334W and R347P, failed to conduct Cl but could transport ATP. Taken together, these data suggest that TMD-1 of CFTR conducts CT. while NBD-1 of CFTR is essential for ATP transport, release and signaling. These results show that the complex multi-domain structure of CFTR supports its multiple chloride channel and conductance regulator roles in epithelia. (Support: NRSA HL 08832).