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Apical Cargo Traverses Endosomal Compartments on the Passage to the Cell Surface
Author(s) -
CrammBehrens Catharina I.,
Dienst Martina,
Jacob Ralf
Publication year - 2008
Publication title -
traffic
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.677
H-Index - 130
eISSN - 1600-0854
pISSN - 1398-9219
DOI - 10.1111/j.1600-0854.2008.00829.x
Subject(s) - endosome , biology , microbiology and biotechnology , vesicle , golgi apparatus , transport protein , apical membrane , lipid raft , intracellular , biochemistry , endoplasmic reticulum , membrane , signal transduction
Epithelial polarity is based on intracellular sorting machinery that maintains the asymmetric distribution of lipids and proteins to the cell surface. Dependent on their lipid raft affinity, newly synthesized apical polypeptides are segregated into distinct vesicle populations subsequent to the passage through the Golgi apparatus. Using a combined fluorescence microscopic and biochemical approach, we found that lipid raft‐associated sucrase‐isomaltase (SI) as well as non‐raft‐associated lactase‐phlorizin hydrolase (LPH) traverse endosomal compartments before entering the apical membrane. Fluorescent fusion proteins of both hydrolases were co‐stained with Rab4‐, Rab8‐ and Rab11‐positive endosomes in polarized Madin–Darby canine kidney and non‐polarized COS‐1 cells. Immunoisolation of post‐Golgi vesicles subsequent to different times of TGN release revealed that LPH and SI navigate in chronological order through Rab4‐, Rab8‐ and Rab11‐positive endosomes. Thereafter, the two hydrolases are segregated into distinct vesicle populations. In addition, apical membrane traffic could be significantly inhibited by RNA interference‐mediated depletion of these guanosine triphosphatases. These results suggest that in epithelial cells, lipid raft‐dependent and ‐independent apical cargo follow a transendosomal route.