Nature Cell Biology6, 297 - 307 (2004)
Published online: 28 March 2004; | doi:10.1038/ncb1109
Delivery of raft-associated, GPI-anchored proteins to the apical surface of polarized MDCK cells by a transcytotic pathway
Roman Polishchuk1, 2, Alessio Di Pentima2
& Jennifer Lippincott-Schwartz1
1
Cell Biology and Metabolism Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA.
2
Department of Cell Biology and Oncology, Istituto di Ricerche Farmacologiche "Mario Negri", Consorzio Mario Negri Sud, 66030 Santa Maria Imbaro (Chieti), Italy.
Correspondence should be addressed to Jennifer Lippincott-Schwartz jlippin@helix.nih.gov
Epithelial cell polarity depends on mechanisms for targeting proteins to different plasma membrane domains. Here, we dissect the pathway for apical delivery of several raft-associated, glycosyl phosphatidylinositol (GPI)-anchored proteins in polarized MDCK cells using live-cell imaging and selective inhibition of apical or basolateral exocytosis. Rather than trafficking directly from the trans-Golgi network (TGN) to the apical plasma membrane as previously thought, the GPI-anchored proteins followed an indirect, transcytotic route. They first exited the TGN in membrane-bound carriers that also contained basolateral cargo, although the two cargoes were laterally segregated. The carriers were then targeted to and fused with a zone of lateral plasma membrane adjacent to tight junctions that is known to contain the exocyst. Thereafter, the GPI-anchored proteins, but not basolateral cargo, were rapidly internalized, together with endocytic tracer, into clathrin-free transport intermediates that transcytosed to the apical plasma membrane. Thus, apical sorting of these GPI-anchored proteins occurs at the plasma membrane, rather than at the TGN.
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