PDZ-mediated interactions retain the epithelial GABA transporter on the basolateral surface of polarized epithelial cells

Abstract

The PDZ target motifs located in the C-terminal end of many receptors and ion channels mediate protein-protein interactions by binding to specific PDZ-containing proteins. These interactions are involved in the localization of surface proteins on specialized membrane domains of neuronal and epithelial cells. However, the molecular mechanism responsible for this PDZ protein-dependent polarized localization is still unclear. This study first demonstrated that the epithelial γ-aminobutyric acid (GABA) transporter (BGT-1) contains a PDZ target motif that mediates the interaction with the PDZ protein LIN-7 in Madin-Darby canine kidney (MDCK) cells, and then investigated the role of this interaction in the basolateral localization of the transporter. It was found that although the transporters from which the PDZ target motif was deleted were still targeted to the basolateral surface, they were not retained but internalized in an endosomal recycling compartment. Furthermore, an interfering BGT peptide determined the intracellular relocation of the native transporter. These data indicate that interactions with PDZ proteins determine the polarized surface localization of target proteins by means of retention and not targeting mechanisms. PDZ proteins may, therefore, act as a sort of membrane protein sorting machinery which, by recognizing retention signals (the PDZ target sequences), prevents protein internalization.

IL-1β Scavenging by the Type II IL-1 Decoy Receptor in Human Neutrophils

“…5B). Following a 10-min incubation with IL-1␤, IL-1RII receptors were found to colocalize with internalized WGA-labeled surface glycoproteins, indicating the involvement of receptor-mediated endocytosis during internalization of IL-1␤ in these cells (30,31). At later time points (results not shown), similar colocalization was also observed occurring in some cells even in the absence of IL-1␤.…”

“…This plant lectin glycoprotein is a marker of membrane transport (30) as it readily binds cell surface glycoproteins colocalizing with them upon endocytosis. Moreover, upon exposure of cells to IL-1, IL-1RII associates with the early endosome protein, EEA-1.…”

Identification of Multiple Binding Partners for the Amino-terminal Domain of Synapse-associated Protein 97

“…Movement of protein cargo along microtubules was shown to depend on the interaction of KIF17 with mLIN-10. Intriguingly, mLIN-2 binds mLIN-7 in epithelial cells where mLIN-7 acts to retain betaine-glutamate transporter 1 at the basolateral surface (10). Hence, protein complexes that include mLIN-2 seem to serve both dynamic and static functions.…”

Localization of mLin-7 at nectin-based cell–cell junctions

“…It is currently unknown how mLin-7C localizes at the nectin-based cell ± cell junctions, but the present results indicate that mLin-7C is associated with afadin or ZO-1 indirectly through an unknown molecule in an actin cytoskeleton-independent manner. mLin-7C forms a ternary complex with mLin-2 and mLin-10 (Borg et al, 1998;Butz et al, 1998) and each of these molecules interacts with many other molecules: mLin-7 with PSD-95, type 2 NMDA receptors, BGT-1, Pals, b-catenin, and VAM-1 (Jo et al, 1999;Perego et al, 1999Perego et al, , 2000Kamberov et al, 2000;Tseng et al, 2001); mLin-2 with neurexin, syndecan, protein 4.1, calcium channels, Tbr-1, hDlg, JAM, and rabphilin3A (Hata et al, 1996;Cohen et al, 1998;Hsueh et al, 1998Hsueh et al, , 2000Maximov et al, 1999;Nix et al, 2000;Martinez-Estrada et al, 2001;Zhang et al, 2001); and mLin-10 with amyloid precursor protein, Munc-18, neurexins, and KIF17 (Borg et al, 1996;Okamoto and SuÈ dhof, 1997;Biederer and SuÈ dhof, 2000;Setou et al, 2000). These earlier observations together with the present results suggest that these proteins directly or indirectly binding to mLin-7 are recruited to the nectinbased cell ± cell junctions.…”

“…mLin-7 interacts with mLin-2, which furthermore interacts with mLin-10, resulting in the formation of a heterotrimeric complex (Borg et al, 1998;Butz et al, 1998). Moreover, mLin-7 interacts with many other proteins, including PSD-95, type 2 NMDA receptors, BGT-1, Pals, b-catenin, and VAM-1 (Jo et al, 1999;Perego et al, 1999Perego et al, , 2000Kamberov et al, 2000;Tseng et al, 2001). We have previously shown that mLin-7 localizes at cell ± cell junctions including adherens junctions (AJs) in cultured Madin-Darby canine kidney (MDCK) cells, but it remains unknown how mLin-7 localizes at AJs (Irie et al, 1999).…”