Basolateral sorting of the cation-dependent mannose 6-phosphate receptor in Madin-Darby canine kidney cells. Identification of a basolateral determinant unrelated to clathrin-coated pit localization signals.
Abstract
In polarized Madin-Darby canine kidney (MDCK) cells, sorting of membrane proteins in the trans-Golgi network for basolateral delivery depends on the presence of cytoplasmic determinants that are related or unrelated to clathrin-coated pit localization signals. Whether these signals mediate basolateral protein sorting through common or distinct pathways is unknown. The cytoplasmic domain of the cation-dependent mannose 6-phosphate receptor (CD-MPR) contains clathrin-coated pit localization signals that are necessary for endocytosis and lysosomal enzyme targeting. In this study, we have addressed the function of these signals in polarized sorting of the CD-MPR. A chimeric protein, made of the luminal domain of the influenza virus hemagglutinin fused to the transmembrane and cytoplasmic domains of the CD-MPR was stably expressed in MDCK cells. This chimera (HCD) is able to interact with the AP-1 Golgi-specific assembly proteins and is detected on the basolateral plasma membrane of MDCK cells where it is endocytosed. Deletion analysis and site-directed mutagenesis of the cytoplasmic domain of the CD-MPR indicate that HCD chimeras devoid of clathrin-coated pit localization signals are still transported to the basolateral membrane wh...Continue Reading
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