ΔF508 CFTR pool in the endoplasmic reticulum is increased by calnexin overexpression

The most common cystic fibrosis transmembrane conductance regulator (CFTR) mutant in cystic fibrosis patients, DeltaF508 CFTR, is retained in the endoplasmic reticulum (ER) and is consequently degraded by the ubiquitin-proteasome pathway known as ER-associated degradation (ERAD). Because the prolonged interaction of DeltaF508 CFTR with calnexin, an ER chaperone, results in the ERAD of DeltaF508 CFTR, calnexin seems to lead it to the ERAD pathway. However, the role of calnexin in the ERAD is controversial. In this study, we found that calnexin overexpression partially attenuated the ERAD of DeltaF508 CFTR. We observed the formation of concentric membranous bodies in the ER upon calnexin overexpression and that the DeltaF508 CFTR but not the wild-type CFTR was retained in the concentric membranous bodies. Furthermore, we observed that calnexin overexpression moderately inhibited the formation of aggresomes accumulating the ubiquitinated DeltaF508 CFTR. These findings suggest that the overexpression of calnexin may be able to create a pool of DeltaF508 CFTR in the ER.