Regulation of the cytoplasmic accumulation of 5-methyltetrahydrofolate in MA104 cells is independent of folate receptor regulation.

B A Kamen; C A Johnson; M T Wang; R G Anderson

doi:10.1172/JCI114310

Department of Pediatrics, University of Texas, Southwestern Medical Center, Dallas 75235.

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Department of Pediatrics, University of Texas, Southwestern Medical Center, Dallas 75235.

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Department of Pediatrics, University of Texas, Southwestern Medical Center, Dallas 75235.

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Department of Pediatrics, University of Texas, Southwestern Medical Center, Dallas 75235.

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Published in Volume 84, Issue 5 on November 1, 1989
J Clin Invest. 1989;84(5):1379–1386. https://doi.org/10.1172/JCI114310.
© 1989 The American Society for Clinical Investigation

Published November 1, 1989 - Version history

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.