Myosin VI Regulates Endocytosis of the Cystic Fibrosis Transmembrane Conductance Regulator

Abstract

The cystic fibrosis transmembrane conductance regulator (CFTR) is a cyclic AMP-regulated Cl ؊ channel expressed in the apical plasma membrane in fluid-transporting epithelia. Although CFTR is rapidly endocytosed from the apical membrane of polarized epithelial cells and efficiently recycled back to the plasma membrane, little is known about the molecular mechanisms regulating CFTR endocytosis and endocytic recycling. Myosin VI, an actin-dependent, minus-end directed mechanoenzyme, has been implicated in clathrin-mediated endocytosis in epithelial cells. The goal of this study was to determine whether myosin VI regulates CFTR endocytosis. Endogenous, apical membrane CFTR in polarized human airway epithelial cells (Calu-3) formed a complex with myosin VI, the myosin VI adaptor protein Disabled 2 (Dab2), and clathrin. The tail domain of myosin VI, a dominant-negative recombinant fragment, displaced endogenous myosin VI from interacting with Dab2 and CFTR and increased the expression of CFTR in the plasma membrane by reducing CFTR endocytosis. However, the myosin VI tail fragment had no effect on the recycling of endocytosed CFTR or on fluid-phase endocytosis. CFTR endocytosis was decreased by cytochalasin D, an actin-filament depolymerizing agent. Taken together, these data indicate that myosin VI and Dab2 facilitate CFTR endocytosis by a mechanism that requires actin filaments.

Disabled-2 Protein Facilitates Assembly Polypeptide-2-independent Recruitment of Cystic Fibrosis Transmembrane Conductance Regulator to Endocytic Vesicles in Polarized Human Airway Epithelial Cells

“…Immunoprecipitation and Immunoblotting-CFTR was immunoprecipitated from cell lysates by methods described previously (12,23). Briefly, cultured cells were lysed in an immunoprecipitation buffer containing 150 mM NaCl, 50 mM Tris, pH 7.4, 1% IGEPAL (Sigma), 5 mM MgCl 2 , 5 mM EDTA, 1 mM EGTA, 30 mM NaF, 1 mM Na 3 VO 4 , Complete Protease Inhibitor Mixture and PhosSTOP (Roche Applied Sciences).…”

“…CFTR co-immunoprecipitated with Dab2 and myosin VI in human airway epithelial cells (23) and colocalized with Dab2, AP-2, and myosin VI in rat enterocytes (18). CFTR abundance was increased in the intestines of Dab2 KO mice, and CFTR endocytosis was inhibited after Dab2 depletion in human airway epithelial cells (18,19).…”

The Short Apical Membrane Half-life of Rescued ΔF508-Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) Results from Accelerated Endocytosis of ΔF508-CFTR in Polarized Human Airway Epithelial Cells

“…Fluid-phase Endocytosis-Studies were conducted to determine the cellular uptake of Alexa 647-dextran (10,000 molecular weight; Molecular Probes), a fluorescent marker of fluid phase endocytosis (33,55) in CFBE41oϪ cells stably expressing either WT-CFTR or ⌬F508-CFTR. CFBE41oϪ cells were grown on glass coverslips at 37°C for 48 h and then at 27°C for 36 h to increase trafficking and expression of ⌬F508-CFTR in the plasma membrane.…”

“…Regulation of the plasma membrane half-life of WT-CFTR is not completely understood but depends, at least in part, on the endocytic trafficking events such as endocytosis of CFTR from the plasma membrane and endocytic recycling of CFTR from endosomes to the plasma membrane. Endocytosis of WT-CFTR 1) is clathrin-dependent (27)(28)(29) and occurs in Rab5-specific endosomes (24), 2) is mediated by multiple endocytic motifs in the C terminus of CFTR (30), and 3) requires interactions with the endocytic adaptor complex, AP-2 (31), the large GTPase, dynamin (32), and myosin VI (33). Recycling of WT-CFTR from endosomes to the plasma membrane occurs in Rab11-specific recycling vesicles (24) and is facilitated by Rme-1 (34) and by PDZ domain interaction (35).…”

VIP as a Corrector of CFTR Trafficking and Membrane Stability

“…The tyrosine based motif interacts with the clathrin adapter complex AP-2 to enter into clathrin coated pits. CFTR also interacts with actin-binding proteins like myosin VI and to N-SWAP to recycle back to the plasma membrane via recycling endosomes (Okiyoneda and Lukacs, 2007;Swiatecka-Urban et al, 2004;Ganeshan et al, 2006). Conflicting results exist regarding the role of cAMP or other second messengers in CFTR recycling probably due to disparity in epithelial cells studied or the use of over-expressing systems which might saturate the normal pathway for CFTR trafficking.…”