title: Alteration of folate analogue transport inward after induced maturation of HL-60 leukemia cells. Molecular properties of the transporter in an overproducing variant and evidence for down-regulation of its synthesis in maturating cells.
abstract: Studies are described examining further the decline in folate analogue influx mediated by the one-carbon reduced-folate transport system in HL-60 cells following induction of maturation by cytodifferentiation agents. To facilitate the investigation of the underlying basis of this phenomenon, we derived a variant (HL-60/LCV) with 4-5-fold elevated influx capacity (Vmax) for folate analogues. A commensurate increase in the putative transporter for this system was documented by affinity labeling of these cells with N-hydroxysuccinimide-[3H]aminopterin. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the affinity labeled plasma membrane in HL-60/LCV cells delineated a protein peak at Mr = 75,000-80,000. This was substantially greater than the analogous transporter (Mr = 45,000-47,000) we had delineated (Yang, C.-H., Sirotnak, F.M., and Mines, L.S. (1988) J. Biol. Chem. 263, 9703-9709) with the same methodology in the L1210 cell plasma membrane. In addition, the rate of translocation of the Mr = 75,000-80,000 transporter in HL-60 and HL-60/LCV cells was 2-fold lower than the rate of translocation determined for the Mr = 45,000-47,000 transporter in L1210 cells. During induced maturation of HL-60/LCV cells toward the granulocyte pathway, [3H]methotrexate (MTX) influx capacity and the amount of the affinity labeled transporter decreased rapidly in a parallel fashion. The decrease in [3H]MTX influx and in affinity labeling and in the amount of the Mr = 75,000-80,000 transporter was 5-fold following exposure to 210 mM dimethyl sulfoxide (Me2SO) for 5 days during growth in culture. Moreover, during cycloheximide treatment, the decay in [3H]MTX influx at 37 degrees C and in amount of affinity labeled transporter was the same (t1/2 = 144-155 min) for both control and Me2SO-treated HL-60/LCV cells. These results, which reveal no difference in metabolic turnover for control and Me2SO-treated cells, suggest that the decline in folate analogue influx in HL-60/LCV influx cells is a very early event in the program of differentiation and probably occurs by down-regulation of synthesis of the transporter for the one-carbon reduced-folate transport system.
authors.affiliation: Program in Molecular Pharmacology and Therapeutics, Memorial Sloan-Kettering Cancer Center, New York, NY 10021.
authors.forename: C H
authors.initials: CH
authors.lastname: Yang
authors.forename: J
authors.initials: J
authors.lastname: Pain
authors.forename: F M
authors.initials: FM
authors.lastname: Sirotnak
mesh_terms: D000345:Affinity Labels; D001692:Biological Transport; D003513:Cycloheximide / Q000494:pharmacology; D015536:Down-Regulation; D004591:Electrophoresis, Polyacrylamide Gel; D005492:Folic Acid / Q000031:analogs & derivatives / Q000378:metabolism*; D007700:Kinetics; D008565:Membrane Proteins / Q000096:biosynthesis / Q000378:metabolism; D008727:Methotrexate / Q000378:metabolism; D014407:Tumor Cells, Cultured
chemical_list: D000345:Affinity Labels; D008565:Membrane Proteins; D005492:Folic Acid; D003513:Cycloheximide; D008727:Methotrexate