May 1, 1988

Influence on immunoreactive folate-binding proteins of extracellular folate concentration in cultured human cells

The Journal of Clinical Investigation
M A KaneJ F Kolhouse

Abstract

The influence of extracellular folate concentration on cellular levels of the folate transport protein and its soluble product was studied directly in cultured human nasopharyngeal carcinoma (KB) cells. As determined by radioimmunoassay, levels of the folate transport protein and the soluble folate-binding protein were 58 +/- 17 (mean +/- SD) and 5 +/- 2 pmol/mg cell protein, respectively, in KB cells maintained in standard medium (containing 2,300 nM folic acid). These levels significantly increased to 182 +/- 34 and 26 +/- 6 pmol/mg cell protein, respectively, in KB cells serially passaged in low folate medium (containing 2-10 nM 5-methyltetrahydrofolate). Increases in folate-binding protein levels occurred more rapidly in KB cells serially passaged in very low folate medium containing less than 2 nM folate and were prevented by the addition of 100 nM 5-methyltetrahydrofolate or 0.1-1 microM 5-formyltetrahydrofolate to this medium. When KB cells which had been passaged in low folate medium were passaged back into either standard medium or low folate medium supplemented with reduced folates, the levels of both folate-binding proteins fell linearly towards the levels in KB cells continuously maintained in standard medium. The f...Continue Reading

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Mentioned in this Paper

Cancer of Nasopharynx
Nasopharyngeal Carcinoma
Hormone Receptors, Cell Surface
Lymphoid Cells
Folr1
Folate
Squamous Cell Carcinoma
Fibroblasts
FOLR1
Mammary Neoplasms, Human

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