Regulation of the cytoplasmic accumulation of 5-methyltetrahydrofolate in MA104 cells is independent of folate receptor regulation.
To better understand how the folate receptor (also known as the membrane folate binder) is able to deliver 5-methyltetrahydrofolic acid to the cytoplasm of folate-depleted MA104 cells, we have examined the kinetics of movement from the cell surface into the cytoplasm. Bound 5-methyltetrahydrofolic acid was transferred into an acid-resistant membrane compartment at the rate of 0.9-1.0 pmol/10(6) cells per h. This folate appeared in the cytoplasm at the same rate. Furthermore, cytoplasmic 5-methyltetrahydrofolic acid became polyglutamated at the rate of 0.6-0.7 pmol/10(6) cells per h. As soon as intracellular 5-methyltetrahydrofolate reached 5-7 pmol/10(6) cells, however, cytoplasmic accumulation was markedly inhibited even though the folate receptor remained functional. Therefore, the acute regulation of 5-methyltetrahydrofolic acid accumulation appears to be achieved by controlling the movement of the vitamin from the receptor into the cytoplasm of the cell.
Kamen
B A
BA
Department of Pediatrics, University of Texas, Southwestern Medical Center, Dallas 75235.
Johnson
C A
CA
Wang
M T
MT
Anderson
R G
RG
D000818:Animals; D001692:Biological Transport; D002352:Carrier Proteins / Q000502:physiology*; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism*; D058973:Folate Receptors, GPI-Anchored; D006863:Hydrogen-Ion Concentration; D007668:Kidney; D007700:Kinetics; D011099:Polyglutamic Acid / Q000378:metabolism; D011956:Receptors, Cell Surface; D013763:Tetrahydrofolates / Q000378:metabolism*
D002352:Carrier Proteins; D058973:Folate Receptors, GPI-Anchored; D011956:Receptors, Cell Surface; D013763:Tetrahydrofolates; D011099:Polyglutamic Acid; C005984:5-methyltetrahydrofolate