Stimulation of amino acid efflux from cells by extracellular serine

P388 (murine) and CEM (human) leukemia cells were exposed in vitro to a serine-deprived medium. Cultivation was carried out at 37 degrees C, 5% CO2. Proliferation assay was conducted with a RPMI 1640 medium (control) and a serine-deprived medium for 3 days. The deprivation of serine reduced the proliferation of both cells, and the necessity of serine for the cell proliferation was thus recognized. The effects of the substance on the level and pattern of intracellular amino acids were observed. P388 cells exposed to serine-deprived medium for 3 h were then transferred to the control medium. The cellular amino acid levels were determined at the time of medium change and 1, 2, 3 h thereafter. Serine-deprivation improved intracellular amino acids in comparison with those from control, and the medium change to control reduced their levels. Therefore, extracellular serine appeared to regulate the efflux of amino acids from cells. This suggests that serine-deprivation may be useful for anticancer drug retention in the cells.