A PDZ-interacting domain in CFTR is an apical membrane polarization signal

TLDR

CFTR must be polarized to the apical plasma membrane to mediate chloride transport in airway, pancreas, intestine, and kidney epithelia, yet the motifs that direct this localization are unknown. The authors propose that COOH‑terminal deletions of CFTR, which account for about 10 % of CFTR mutations, impair vectorial chloride transport by disrupting CFTR’s polarized distribution. They show that the C‑terminal tripeptide T‑R‑L constitutes a PDZ‑binding motif required for apical targeting in airway and kidney cells; loss of this motif in the S1455X mutant mislocalizes CFTR to the lateral membrane, and CFTR’s interaction with the PDZ‑containing protein EBP50 confirms that PDZ domains are essential for apical polarization of ion channels.

Abstract

Polarization of the cystic fibrosis transmembrane conductance regulator (CFTR), a cAMP-activated chloride channel, to the apical plasma membrane of epithelial cells is critical for vectorial transport of chloride in a variety of epithelia, including the airway, pancreas, intestine, and kidney. However, the motifs that localize CFTR to the apical membrane are unknown. We report that the last 3 amino acids in the COOH-terminus of CFTR (T-R-L) comprise a PDZ-interacting domain that is required for the polarization of CFTR to the apical plasma membrane in human airway and kidney epithelial cells. In addition, the CFTR mutant, S1455X, which lacks the 26 COOH-terminal amino acids, including the PDZ-interacting domain, is mispolarized to the lateral membrane. We also demonstrate that CFTR binds to ezrin-radixin-moesin–binding phosphoprotein 50 (EBP50), an apical membrane PDZ domain–containing protein. We propose that COOH-terminal deletions of CFTR, which represent about 10% of CFTR mutations, result in defective vectorial chloride transport, partly by altering the polarized distribution of CFTR in epithelial cells. Moreover, our data demonstrate that PDZ-interacting domains and PDZ domain–containing proteins play a key role in the apical polarization of ion channels in epithelial cells.