title: Folate receptors targeted to clathrin-coated pits cannot regulate vitamin uptake.
abstract: Potocytosis is an endocytic process that is specialized for the internalization of small molecules. Recent studies on the uptake of 5-methyltetrahydrofolate by the folate receptor have suggested that the glycosyl-phosphatidylinositol anchor on this protein causes it to cluster and be internalized by caveolae instead of coated pits. To test this hypothesis directly, we have constructed a chimeric folate receptor that has the glycosyl-phosphatidylinositol anchor replaced with the transmembrane domain and cytoplasmic tail of the low density lipoprotein receptor. The cells with wild-type receptors delivered 5-methyltetrahydrofolate to the cytoplasm more rapidly than did cells expressing the chimeric receptor. This suggests that efficient delivery to the cytoplasm depends on caveolae. In sharp contrast to cells with wild-type folate receptors, cells internalizing folate by clathrin-coated pits were unable to decrease vitamin uptake when they were either folate replete or confluent.
authors.affiliation: Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas 75235, USA.
authors.forename: T E
authors.initials: TE
authors.lastname: Ritter
authors.forename: O
authors.initials: O
authors.lastname: Fajardo
authors.forename: H
authors.initials: H
authors.lastname: Matsue
authors.forename: R G
authors.initials: RG
authors.lastname: Anderson
authors.forename: S W
authors.initials: SW
authors.lastname: Lacey
mesh_terms: D000818:Animals; D001483:Base Sequence; D016466:CHO Cells; D002352:Carrier Proteins / Q000096:biosynthesis / Q000378:metabolism*; D002455:Cell Division; D002966:Clathrin / Q000378:metabolism*; D003034:Coated Pits, Cell-Membrane / Q000378:metabolism*; D006224:Cricetinae; D003593:Cytoplasm / Q000378:metabolism; D017931:DNA Primers; D018076:DNA, Complementary; D004705:Endocytosis; D005455:Fluorescent Antibody Technique; D058973:Folate Receptors, GPI-Anchored; D017261:Glycosylphosphatidylinositols / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D008969:Molecular Sequence Data; D010957:Plasmids; D011956:Receptors, Cell Surface; D011973:Receptors, LDL / Q000096:biosynthesis / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis / Q000378:metabolism*; D013763:Tetrahydrofolates / Q000378:metabolism*; D014162:Transfection
chemical_list: D002352:Carrier Proteins; D002966:Clathrin; D017931:DNA Primers; D018076:DNA, Complementary; D058973:Folate Receptors, GPI-Anchored; D017261:Glycosylphosphatidylinositols; D011956:Receptors, Cell Surface; D011973:Receptors, LDL; D011993:Recombinant Fusion Proteins; D013763:Tetrahydrofolates; C005984:5-methyltetrahydrofolate