SYNTAXIN 1A INHIBITS CFTR CHLORIDE CHANNELS BY MEANS OF DOMAIN-SPECIFIC PROTEIN-PROTEIN INTERACTIONS

Previously we showed that the functional activity of the epithelial ch loride channel that is encoded by the cystic fibrosis gene (CFTR) is r eciprocally modulated by two components of the vesicle fusion machiner y, syntaxin 1A and Munc-18, Here we report that syntaxin LA inhibits C FTR chloride channels by means of direct and domain-specific protein-p rotein interactions. Syntaxin 1A stoichiometrically binds to the N-ter minal cytoplasmic tail of CFTR, and this binding is blocked by Munc-18 , The modulation of CFTR currents by syntaxin 1A is eliminated either by deletion of this tail or by injecting this tail as a blocking pepti de into coexpressing Xenopus oocytes, The CFTR binding site on syntaxi n 1A maps to the third predicted helical domain (H3) of this membrane protein, Moreover, CFTR Cl- currents are effectively inhibited by a mi nimal syntaxin 1A construct (i.e., the membrane-anchored H3 domain) th at cannot fully substitute for wild-type syntaxin 1A in membrane fusio n reactions. We also show that syntaxin 1A binds to and inhibits the a ctivities of disease-associated mutants of CFTR, and that the chloride current activity of recombinant Delta F508 CFTR (i.e., the most commo n cystic fibrosis mutant) can be potentiated by disrupting its interac tion with syntaxin 1A in cultured epithelial cells. Our results provid e evidence for a direct physical interaction between CFTR and syntaxin 1A that limits the functional activities of normal and disease-associ ated forms of this chloride channel.