title: Uptake of 5-methyltetrahydrofolate into PC-3 human prostate cancer cells is carrier-mediated.
abstract: Uptake of 5-methyltetrahydrofolate into the PC-3 human prostate cancer cells was linear for the first 60 min. There was no difference in the initial rate of uptake in cells incubated in folate-free medium for 24 or 48 hr compared to control cells grown in folate-containing medium. The initial rate of 5-methyltetrahydrofolate uptake showed little dependence on extracellular pH and it was independent of extracellular sodium ions. Transport of 5-methyltetrahydrofolate into PC-3 cells was saturable - K(m) = 0.74 micro M and V(max) = 7.78 nmol/10(9)cells/min and these kinetic constants were not different in cells incubated for 24 hr in folate-free medium (K(m) = 0.80 +/- 0.22, V(max) = 8.52 +/- 0.50; P = 0.09, N = 3). Uptake of 5-methyltetrahydrofolate was inhibited by structural analogs with the K(i) values being 0.50, 1.79, and 31.8 micro M for 5-formyltetrahydrofolate, methotrexate, and folic acid, respectively. Uptake of 5-methyltetrahydrofolate was inhibited by the energy poisons, sodium cyanide, sodium arsenate, p-chloromercuriphenylsulfonate, and sodium azide. Uptake was inhibited by increasing concentrations of sulfate and phosphate ions, suggesting that 5-methyltetrahydrofolate may be transported by an anion-exchange mechanism. These results show that 5-methyltetrahydrofolate is transported into PC-3 prostate cancer cells by a carrier-mediated process.
authors.affiliation: Medical Research Service (151), VA Medical Center, Nashville, TN 37212, USA. donald.w.horne@vanderbilt.edu
authors.forename: Donald W
authors.initials: DW
authors.lastname: Horne
authors.forename: Kathleen A
authors.initials: KA
authors.lastname: Reed
mesh_terms: D001149:Arsenates / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects; D002352:Carrier Proteins / Q000378:metabolism*; D005492:Folic Acid / Q000494:pharmacology; D006801:Humans; D006863:Hydrogen-Ion Concentration; D002955:Leucovorin / Q000494:pharmacology; D008297:Male; D008727:Methotrexate / Q000494:pharmacology; D010710:Phosphates / Q000494:pharmacology; D011471:Prostatic Neoplasms / Q000378:metabolism*; D012964:Sodium / Q000494:pharmacology; D019810:Sodium Azide / Q000494:pharmacology; D012966:Sodium Cyanide / Q000494:pharmacology; D013431:Sulfates / Q000494:pharmacology; D013763:Tetrahydrofolates / Q000378:metabolism*; D014407:Tumor Cells, Cultured
chemical_list: D001149:Arsenates; D002352:Carrier Proteins; D010710:Phosphates; D013431:Sulfates; D013763:Tetrahydrofolates; C009277:sodium arsenate; D005492:Folic Acid; D019810:Sodium Azide; D012964:Sodium; D012966:Sodium Cyanide; D002955:Leucovorin; C005984:5-methyltetrahydrofolate; D008727:Methotrexate