The folate receptor, also known as the membrane folate-binding protein, is maximally expressed on the surface of folate-depleted tissue culture cells and mediates the high affinity accumulation of 5-methyltetrahydrofolic acid in the cytoplasm of these cells. Recent evidence suggests that this receptor recycles during folate internalization and that it is anchored in the membrane by a glycosyl-phosphatidylinositol linkage. Using quantitative immunocytochemistry, we now show that (a) this receptor is highly clustered on the cell surface; (b) these clusters are preferentially associated with uncoated membrane invaginations rather than clathrin-coated pits; and (c) the receptor is not present in endosomes or lysosomes. This receptor appears to physically move in and out of the cell using a novel uncoated pit pathway that does not merge with the clathrin-coated pit endocytic machinery.
The glycophospholipid-linked folate receptor internalizes folate without entering the clathrin-coated pit endocytic pathway.
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K G Rothberg, Y S Ying, J F Kolhouse, B A Kamen, R G Anderson; The glycophospholipid-linked folate receptor internalizes folate without entering the clathrin-coated pit endocytic pathway.. J Cell Biol 1 March 1990; 110 (3): 637–649. doi: https://doi.org/10.1083/jcb.110.3.637
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