Naeem Sheik Abdul, Charlette Tiloke, Anil A. Chuturgoon, Savania Nagiah, Terisha Ghazi
Fusaric acid (FA), a common fungal contaminant of maize, is known to mediate toxicity in plants and animals; however, its mechanism of action is unclear. p53 is a tumor suppressor protein that is activated in response to cellular stress. The function of p53 is regulated by post-translational modifications—ubiquitination, phosphorylation, and acetylation. This study investigated a possible mechanism of FA induced toxicity in the human hepatocellular carcinoma (HepG2) cell line. The effect of FA on DNA integrity and post-translational modifications of p53 were investigated. Methods included: (a) culture and treatment of HepG2 cells with FA (IC50: 580.32 μM, 24 h); (b) comet assay (DNA damage); (c) Western blots (protein expression of p53, MDM2, p-Ser-15-p53, a-K382-p53, a-CBP (K1535)/p300 (K1499), HDAC1 and p-Ser-47-Sirt1); and (d) Hoechst 33342 assay (apoptosis analysis). FA caused DNA damage in HepG2 cells relative to the control (P < 0.0001). FA decreased the protein expression of p53 (0.24-fold, P = 0.0004) and increased the expression of p-Ser-15-p53 (12.74-fold, P = 0.0126) and a-K382-p53 (2.24-fold, P = 0.0096). This occurred despite the significant decrease in the histone acetyltransferase, a-CBP (K1535)/p300 (K1499) (0.42-fold, P = 0.0023) and increase in the histone deacetylase, p-Ser-47-Sirt1 (1.22-fold, P = 0.0020). The expression of MDM2, a negative regulator of p53, was elevated in the FA treatment compared to the control (1.83-fold, P < 0.0001). FA also inhibited cell proliferation and induced apoptosis in HepG2 cells as evidenced by the Hoechst assay. Together, these results indicate that FA is genotoxic and post-translationally modified p53 leading to HepG2 cell death. J. Cell. Biochem. 118: 3866–3874, 2017. © 2017 Wiley Periodicals, Inc.
FA is genotoxic and post-translationally modified p53 leading to cell growth arrest and apoptosis of HepG2 cells. The results indicate that Ser-15 phosphorylation is required for the function of p53 and this may suggest a possible universal role in promoting p53-transcriptional activity.