title: A role for the proton-coupled folate transporter (PCFT-SLC46A1) in folate receptor-mediated endocytosis.
abstract: Recently, this laboratory identified a proton-coupled folate transporter (PCFT), with optimal activity at low pH. PCFT is critical to intestinal folate absorption and transport into the central nervous system because there are loss-of-function mutations in this gene in the autosomal recessive disorder, hereditary folate malabsorption. The current study addresses the role PCFT might play in another transport pathway, folate receptor (FR)-mediated endocytosis. FRalpha cDNA was transfected into novel PCFT(+) and PCFT(-) HeLa sublines. FRalpha was shown to bind and trap folates in vesicles but with minimal export into the cytosol in PCFT(-) cells. Cotransfection of FRalpha and PCFT resulted in enhanced folate transport into cytosol as compared with transfection of FRalpha alone. Probenecid did not inhibit folate binding to FR, but inhibited PCFT-mediated transport at endosomal pH, and blocked FRalpha-mediated transport into the cytosol. FRalpha and PCFT co-localized to the endosomal compartment. These observations (i) indicate that PCFT plays a role in FRalpha-mediated endocytosis by serving as a route of export of folates from acidified endosomes and (ii) provide a functional role for PCFT in tissues in which it is expressed, such as the choroid plexus, where the extracellular milieu is at neutral pH.
authors.affiliation: Departments of Medicine and Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
authors.forename: Rongbao
authors.initials: R
authors.lastname: Zhao
authors.forename: Sang Hee
authors.initials: SH
authors.lastname: Min
authors.forename: Yanhua
authors.initials: Y
authors.lastname: Wang
authors.forename: Estela
authors.initials: E
authors.lastname: Campanella
authors.forename: Philip S
authors.initials: PS
authors.lastname: Low
authors.forename: I David
authors.initials: ID
authors.lastname: Goldman
mesh_terms: D001693:Biological Transport, Active / Q000187:drug effects / Q000502:physiology; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism*; D004705:Endocytosis / Q000502:physiology*; D011992:Endosomes / Q000235:genetics / Q000378:metabolism*; D058973:Folate Receptors, GPI-Anchored; D005492:Folic Acid / Q000235:genetics / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007408:Intestinal Absorption / Q000187:drug effects / Q000235:genetics; D008286:Malabsorption Syndromes / Q000235:genetics / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D008661:Metabolism, Inborn Errors / Q000235:genetics / Q000378:metabolism; D011339:Probenecid / Q000494:pharmacology; D058979:Proton-Coupled Folate Transporter; D011956:Receptors, Cell Surface / Q000235:genetics / Q000378:metabolism*; D014528:Uricosuric Agents / Q000494:pharmacology
chemical_list: D002352:Carrier Proteins; D058973:Folate Receptors, GPI-Anchored; D026901:Membrane Transport Proteins; D058979:Proton-Coupled Folate Transporter; D011956:Receptors, Cell Surface; C505058:SLC46A1 protein, human; D014528:Uricosuric Agents; D005492:Folic Acid; D011339:Probenecid