Cystic fibrosis transmembrane regulator missing the first four transmembrane segments increases wild type and ΔF508 processing

We previously generated an adenoassociated viral gene therapy vector, rAAV-Δ264 cystic fibrosis transmembrane conductance regulator (CFTR), missing the first four transmembrane domains of CFTR. When infected into monkey lungs, Δ264 CFTR increased the levels of endogenous wild type CFTR protein. To understand this process, we transfected Δ264 CFTR plasmid cDNA into COS7 cells, and we noted that protein expression from the truncation mutant is barely detectable when compared with wild type or ΔF508 CFTR. Δ264 CFTR protein expression increases dramatically when cells are treated with proteasome inhibitors. Cycloheximide experiments show that Δ264 CFTR is degraded faster than ΔF508 CFTR. VCP and HDAC6, two proteins involved in retrograde translocation from endoplasmic reticulum to cytosol for proteasomal and aggresomal degradation, coimmunoprecipitate with Δ264 CFTR. In cotransfection studies in COS7 cells and in transfection of Δ264 CFTR into cells stably expressing wild type and ΔF508 CFTR, Δ264 CFTR increases wild type CFTR protein and increases levels of maturation of immature band B to mature band C of ΔF508 CFTR. Thus the adenoassociated viral vector, rAAV-Δ264 CFTR, is a highly promising cystic fibrosis gene therapy vector because it increases the amount of mature band C protein both from wild type and ΔF508 CFTR and associates with key elements in quality control mechanism of CFTR.