Peripheral protein quality control removes unfolded CFTR from the plasma membrane.

Therapeutic efforts to restore biosynthetic processing of the cystic fibrosis transmembrane conductance regulator lacking the F508 residue (DeltaF508CFTR) are hampered by ubiquitin-dependent lysosomal degradation of nonnative, rescued DeltaF508CFTR from the plasma membrane. Here, functional small interfering RNA screens revealed the contribution of chaperones, cochaperones, and ubiquitin-conjugating and -ligating enzymes to the elimination of unfolded CFTR from the cell surface, as part of a peripheral protein quality-control system. Ubiquitination of nonnative CFTR was required for efficient internalization and lysosomal degradation. This peripheral protein quality-control mechanism probably participates in the preservation of cellular homeostasis by degrading damaged plasma membrane proteins that have escaped from the endoplasmic reticulum quality control or are generated by environmental stresses in situ.