Endocytosis of junctional cadherins in bovine kidney epithelial (MDBK) cells cultured in low Ca2+ ion medium.
The release of intercellular contacts in MDBK cells, initiated by the depletion of Ca2+ ions from the culture medium, results in the endocytotic uptake of membrane vesicles containing specific membrane constituents of the zonula adhaerens (ZA). During this process the junction-derived, endocytosed vesicles remain associated with the ZA plaque components, while the plaque and its attached actin filaments retract as a whole in a ring-like fashion from the plasma membrane, often accumulating, usually in fragments, in the juxtanuclear cytoplasm. Double-label immunofluorescence microscopy with antiplakoglobin and antivinculin has indicated that both plaque proteins colocalize with the hallmark membrane glycoprotein of this junction type, E-cadherin (uvomorulin). When HRP used as a fluid phase marker is applied to the culture medium, simultaneously with the Ca2+ ion-chelator EGTA, numerous HRP-positive vesicles are found in close association with the dislocated plaque material, suggesting that the HRP is contained in the vesicles formed upon EGTA-induced junction splitting. Immunoelectron microscopy with various cadherin-specific antibodies revealed vesicle-associated labeling, confirming the derivation of these plaque-associated vesicles from the ZA. As the desmosome-specific cadherin, desmoglein, is recovered in another type of junction-derived vesicle, which is characterized by its association with a desmoplakin-plaque, we conclude that the membrane domains of both kinds of junction are endocytosed during Ca2+ depletion but stay in different vesicle populations, emphasizing the selective interaction of the specific cadherins with their respective plaque and filament partners.
Kartenbeck
J
J
Institute of Cell and Tumor Biology, German Cancer Research Center, Heidelberg.
Schmelz
M
M
Franke
W W
WW
Geiger
B
B
D000199:Actins / Q000378:metabolism; D000818:Animals; D015820:Cadherins / Q000378:metabolism*; D002118:Calcium / Q000502:physiology*; D002417:Cattle; D002448:Cell Adhesion; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D003896:Desmosomes / Q000378:metabolism / Q000648:ultrastructure; D004705:Endocytosis; D005455:Fluorescent Antibody Technique; D007124:Immunoenzyme Techniques; D066298:In Vitro Techniques; D007365:Intercellular Junctions / Q000378:metabolism* / Q000648:ultrastructure; D007425:Intracellular Membranes / Q000378:metabolism; D007668:Kidney / Q000166:cytology; D008854:Microscopy, Electron
D000199:Actins; D015820:Cadherins; D002118:Calcium