Transient Receptor Potential Canonical Channel 6 Links Ca2+ Mishandling to Cystic Fibrosis Transmembrane Conductance Regulator Channel Dysfunction in Cystic Fibrosis

In cystic fibrosis (CF), abnormal control of cellular Ca2+ homeostasis is observed. We hypothesized that transient receptor potential canonical (TRPC) channels could be a link between the abnormal Ca2+ concentrations in CF cells and cystic fibrosis transmembrane conductance regulator (CFTR) dysfunction. We measured the TRPC and CFTR activities (using patch clamp and fluorescent probes) and interactions (using Western blotting and co-immunoprecipitation) in CF and non-CF human epithelial cells treated with specific and scrambled small interfering RNA(siRNA). The TRPC6-mediated Ca2+ influx was abnormally increased in CF compared with non-CF cells. After correction of abnormal F508 deletion (del)-CFTR trafficking in CF cells, the level of TRPC6-dependent Ca2+ influx was also normalized. In CF cells, siRNA-TRPC6 reduced this abnormal Ca2+ influx. In non-CF cells, siRNA-TRPC6 reduced the Ca2+ influx and activity wild-type (wt)-CFTR. Co-immunoprecipitation experiments revealed TRPC6/CFTR and TRPC6/F508 del-CFTR interactions in CF or non-CF epithelial cells. Although siRNA-CFTR reduced the activity of wt-CFTR in non-CF cells and of F508 del-CFTR in corrected CF cells, it also enhanced TRPC6-dependent Ca2+ influx in non-CF cells, mimicking the results obtained in CF cells. Finally, this functional and reciprocal coupling between CFTR and TRPC6 was also detected in non-CF ciliated human epithelial cells freshly isolated from lung samples. These data indicate that TRPC6 and CFTR are functionally and reciprocally coupled within a molecular complex in airway epithelial human cells. Because this functional coupling is lost in CF cells, the TRPC6-dependent Ca2+ influx is abnormal.