title: PMA alters folate receptor distribution in the plasma membrane and increases the rate of 5-methyltetrahydrofolate delivery in mature MA104 cells.
abstract: MA104 cells (a monkey kidney cell line) can internalize 5-methyltetrahydrofolate via a receptor mediated process termed potocytosis. Uptake is initiated by binding to an external folate receptor which cycles to an internal, but membrane bound compartment. These two pools can be measured by determining the amount of [3H]ligand removed by an acid-saline wash, i.e. acid labile and acid resistant pools. When assayed in confluent nonmitotic cells, 2/3 of the folate receptor pool is located in an internal (acid resistant) compartment, but phorbol 12-myristate 13-acetate (PMA) causes a shift such that 65-75% of the receptor pool resides on the surface of the plasma membrane. This new steady state is likely the result of an increased rate of receptor movement. In addition, PMA increases the rate of 5-methyl[3H]tetrahydrofolate delivery to the cytoplasm 1.8 fold. Using known inhibitors of potocytosis, we were able to show that the increased rate of delivery is receptor mediated. Comparison of the time courses of the PMA effects on folate receptor redistribution assessed by membrane binding of [3H]folic acid and 5-methyl[3H]tetrahydrofolate delivery to the cytoplasm suggests that PMA may be activating more than one protein kinase C independent signal transduction pathway. PMA is the first reported positive modulator of receptor mediated folate uptake.
authors.affiliation: University of Texas, Southwestern Medical Center, Dallas 75235-9063, USA.
authors.forename: C M
authors.initials: CM
authors.lastname: Lewis
authors.forename: A K
authors.initials: AK
authors.lastname: Smith
authors.forename: C
authors.initials: C
authors.lastname: Nguyen
authors.forename: B A
authors.initials: BA
authors.lastname: Kamen
mesh_terms: D000818:Animals; D002273:Carcinogens / Q000494:pharmacology*; D002352:Carrier Proteins / Q000187:drug effects* / Q000493:pharmacokinetics; D002460:Cell Line; D002462:Cell Membrane / Q000737:chemistry*; D003593:Cytoplasm / Q000737:chemistry / Q000187:drug effects; D004705:Endocytosis / Q000187:drug effects; D058973:Folate Receptors, GPI-Anchored; D005492:Folic Acid / Q000187:drug effects / Q000378:metabolism; D007700:Kinetics; D011485:Protein Binding / Q000187:drug effects; D011493:Protein Kinase C / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000187:drug effects / Q000378:metabolism; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D013763:Tetrahydrofolates / Q000378:metabolism / Q000493:pharmacokinetics*; D013997:Time Factors; D014316:Tritium
chemical_list: D002273:Carcinogens; D002352:Carrier Proteins; D058973:Folate Receptors, GPI-Anchored; D011956:Receptors, Cell Surface; D018160:Receptors, Cytoplasmic and Nuclear; D013763:Tetrahydrofolates; D014316:Tritium; D005492:Folic Acid; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate