The glycophospholipid-linked folate receptor internalizes folate without entering the clathrin-coated pit endocytic pathway

J Cell Biol. 1990 Mar;110(3):637-49. doi: 10.1083/jcb.110.3.637.

Abstract

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.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Carrier Proteins / metabolism*
  • Carrier Proteins / ultrastructure
  • Cell Line
  • Coated Pits, Cell-Membrane / metabolism*
  • Coated Pits, Cell-Membrane / ultrastructure
  • Endocytosis*
  • Endosomes / metabolism*
  • Fluorescent Antibody Technique
  • Folate Receptors, GPI-Anchored
  • Folic Acid / metabolism*
  • Freeze Etching
  • Glycolipids / metabolism*
  • Glycosylphosphatidylinositols
  • Humans
  • KB Cells
  • Microscopy, Electron
  • Phosphatidylinositols / metabolism*
  • Receptors, Cell Surface / metabolism

Substances

  • Carrier Proteins
  • Folate Receptors, GPI-Anchored
  • Glycolipids
  • Glycosylphosphatidylinositols
  • Phosphatidylinositols
  • Receptors, Cell Surface
  • Folic Acid