Most
cancer cells have an increased synthesis of
purine nucleotides to fulfil their enhanced division rate. The de novo synthesis of
purines requires
folic acid in the form of N10-formyltetrahydrofolate (10-formyl-THF). However, regular cell
culture media contain very high, non-physiological concentrations of
folic acid, which may have an impact on cell metabolism. Using cell
culture media with physiological levels of
folic acid (25 nM), we uncover
purine alterations in several human cell lines. HEK293T, Jurkat, and A549 cells accumulate 5'-aminoimidazole-4-carboxamide
ribonucleotide (
ZMP), an intermediary of the de novo biosynthetic pathway, at physiological levels of
folic acid, but not with the artificially high levels (2200 nM) present in regular media. Interestingly, HEK293T and Jurkat cells do not accumulate high levels of
ZMP when
AICAr, the precursor of
ZMP, is added to medium containing 2200 nM
folate; instead,
ATP levels are increased, suggesting an enhanced de novo synthesis. On the other hand, HeLa and EHEB cells do not accumulate
ZMP at physiological levels of
folic acid, but they do accumulate in medium containing
AICAr plus 2200 nM
folate. Expression of SLC19A1, which encodes the
reduced folate carrier (RFC), is increased in HEK293T and Jurkat cells compared with HeLa and EHEB, and it is correlated with the total
purine nucleotide content at high levels of
folic acid or with
ZMP accumulation at physiological levels of
folic acid. In conclusion, tumoral cell lines show a heterogenous response to
folate changes in the media, some of them accumulating
ZMP at physiological levels of
folic acid. Further research is needed to clarify the
ZMP downstream targets and their impact on cell function.