Fibronectin receptor internalization and AP-2 complex reorganization in potassium-depleted fibroblasts.
Potassium-depleted fibroblasts are unable to develop polarized morphology and lack coated pits. Experiments were carried out to measure internalization of fibronectin receptors (FNR) in potassium-depleted cells and possible association of FNR with AP-2 complexes after adding potassium back to the cells, which restores cell polarization. AP-2 complexes are the cell surface component of coated pits that contain both clathrin and membrane receptor binding domains. Potassium-depleted fibroblasts endocytosed antibody-tagged FNR and also internalized fluorescent fibronectin that previously had been adsorbed to the substratum. During cell polarization, antibody-tagged FNR reorganized into fibrillar structures along stress fibers beginning from nucleation sites at cell margins. Plasma membrane AP-2 complexes, which were undetectable in potassium-depleted cells, reappeared at the cell surface above the nucleus and then spread toward the cell margins. The results show that endocytosis of FNR can occur at least partially by a coated pit-independent mechanism.
Altankov
G
G
Department of Cell Biology and Neuroscience, University of Texas Southwestern Medical Center, Dallas 75235.
Grinnell
F
F
D000199:Actins / Q000378:metabolism; D033942:Adaptor Proteins, Vesicular Transport; D016764:Cell Polarity; D002478:Cells, Cultured; D004705:Endocytosis / Q000502:physiology*; D005347:Fibroblasts / Q000378:metabolism*; D005353:Fibronectins / Q000378:metabolism; D006801:Humans; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D010750:Phosphoproteins / Q000378:metabolism*; D011188:Potassium / Q000502:physiology*; D017469:Receptors, Fibronectin / Q000378:metabolism*; D012867:Skin / Q000166:cytology
D000199:Actins; D033942:Adaptor Proteins, Vesicular Transport; D005353:Fibronectins; D009419:Nerve Tissue Proteins; D010750:Phosphoproteins; D017469:Receptors, Fibronectin; D011188:Potassium