Impairment of cell cycle progression by aflatoxin B1 in human cell lines

Aflatoxin B1 is a mycotoxin produced by Aspergillus flavus and Aspergillus parasiticum, which may be present as a food contaminant. It is known to cause acute toxic effects and act as a carcinogenic agent. The carcinogenic action has been related to its ability to form unstable adducts with DNA, which represent possible mutagenic sites. On the other hand, the primary cellular target responsible for its toxic action has not yet been clearly identified. Previous data suggested a possible correlation between cell proliferation and responsiveness to aflatoxin toxicity. These observations led us to investigate the effect of the toxin on cell cycle progression of three human cell lines (HepG2, SK-N-MC and SK-N-SH derived from liver and nervous tissue tumours); they were shown to display different responses to toxin exposure and have different growth kinetics. We performed analysis of the cell cycle, DNA synthesis and expression of p21 and p53 in the presence and absence of the toxin in all cell lines exposed. The results of cell cycle cytofluorometric analysis show significant alterations of cell cycle progression as a result of toxin treatment. In all cell lines exposure to a 24 h toxin treatment causes a dose-dependent accumulation in S phase, however, the ability to recover from impairment to traverse S phase varies in the cell lines under study. SK-N-MC cells appear more prone to resume DNA synthesis when the toxin is removed, while the other two cell lines maintain a significant inhibition of DNA synthesis, as indicated by cytofluorimetry and [(3)H]dTR incorporation. The level of p53 and p21 expression in the three cell lines was examined by western blot analysis and significant differences were detected. The ready resumption of DNA synthesis displayed by SK-N-MC cells could possibly be related to the absence of p53 control of cell cycle progression.