We have evaluated transcytotic routes in MDCK cells for their ability to generate a polarized surface distribution of trafficking proteins by following the intracellular sorting of transferrin receptors (TRs). We find that the selective basolateral expression of TRs is maintained in the face of extensive trafficking between the apical and basolateral surfaces. Biochemical studies of receptors loaded with tracer under conditions approaching steady state indicate that TRs internalized from the two surfaces are extensively colocalized within MDCK cells and that both populations of receptors are selectively delivered to the basolateral surface. Tailless TRs in which the cytoplasmic domain has been deleted display an unpolarized cell surface distribution and recycle in an unpolarized fashion. We show by EM that wild-type receptors internalized from each surface are colocalized within endosomal elements distributed throughout the cytoplasm. By preloading endosomal elements directly accessible from the basolateral surface with transferrin (Tf)-HRP, we show that apically internalized TRs rapidly enter the same compartment. We also show that both transcytosing (apically internalized) and recycling (basolaterally internalized) TRs are delivered to the basolateral border by a distinctive subset of exocytotic, 60-nm-diam vesicles. Together, the biochemical and morphological data show that apical and basolateral endosomes of MDCK cells are interconnected and contain a signal-dependent polarized sorting mechanism. We propose a dynamic model of polarized sorting in MDCK cells in which a single endosome-based, signal-dependent sorting step is sufficient to maintain the polarized phenotype.
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1 October 1996
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October 01 1996
Apical and basolateral endosomes of MDCK cells are interconnected and contain a polarized sorting mechanism.
G Odorizzi,
G Odorizzi
Department of Cancer Biology, Salk Institute for Biological Studies, San Diego, California 92186-5800, USA.
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A Pearse,
A Pearse
Department of Cancer Biology, Salk Institute for Biological Studies, San Diego, California 92186-5800, USA.
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D Domingo,
D Domingo
Department of Cancer Biology, Salk Institute for Biological Studies, San Diego, California 92186-5800, USA.
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I S Trowbridge,
I S Trowbridge
Department of Cancer Biology, Salk Institute for Biological Studies, San Diego, California 92186-5800, USA.
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C R Hopkins
C R Hopkins
Department of Cancer Biology, Salk Institute for Biological Studies, San Diego, California 92186-5800, USA.
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G Odorizzi
Department of Cancer Biology, Salk Institute for Biological Studies, San Diego, California 92186-5800, USA.
A Pearse
Department of Cancer Biology, Salk Institute for Biological Studies, San Diego, California 92186-5800, USA.
D Domingo
Department of Cancer Biology, Salk Institute for Biological Studies, San Diego, California 92186-5800, USA.
I S Trowbridge
Department of Cancer Biology, Salk Institute for Biological Studies, San Diego, California 92186-5800, USA.
C R Hopkins
Department of Cancer Biology, Salk Institute for Biological Studies, San Diego, California 92186-5800, USA.
Online ISSN: 1540-8140
Print ISSN: 0021-9525
J Cell Biol (1996) 135 (1): 139–152.
Citation
G Odorizzi, A Pearse, D Domingo, I S Trowbridge, C R Hopkins; Apical and basolateral endosomes of MDCK cells are interconnected and contain a polarized sorting mechanism.. J Cell Biol 1 October 1996; 135 (1): 139–152. doi: https://doi.org/10.1083/jcb.135.1.139
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