Figure 2.

Requirement for folate correlates with polyamine biosynthesis. A) Intracellular folate stores are depleted in cell lines grown in zero-folate medium by PD 8. B) Intracellular folate levels are directly proportional to folate in the medium. The higher the folate concentration in medium, the slower the depletion of intracellular folate. C) Comparison of folate-dependent growth rates. Graphical representation of growth rates of the different cell lines grown with different amounts of FA. Data are averages + sd of 2 biological replicates per point. D) Inverse correlation between polyamine pools (intracellular plus secreted) and folate-dependent growth rates. Each cell line is represented according to its levels of polyamine pools (Table 1) on the x axis and its growth rate in limiting amounts of folate (50 nM) (as calculated in panel C) on the y axis. There is a significant (P<0.001) inverse correlation between polyamine pools and growth rates with 50 nM folate, as calculated by a 1-tailed Pearson correlation test. Significant correlation was also found when cells were grown at 100 nM folate (figure shows only the correlation as a dashed line, but not the actual experimental points, which can be inferred by Table 1 and panel C). E) Significant (P<0.05) inverse correlation between ODC activity and folate-dependent growth rates. Experimental points on graph correspond to growth rates of cells grown in 50 nM folate. Significant correlation was also found when cells were grown at 100 nM folate, shown as in panel D.