Escin-induced DNA damage promotes escin-induced apoptosis in human colorectal cancer cells via p62 regulation of the ATM/gamma H2AX pathway

Escin, a triterpene saponin isolated from horse chestnut seed, has been used to treat encephaledema, tissue swelling and chronic venous insufficiency. Recent studies show that escin induces cell cycle arrest, tumor proliferation inhibition and tumor cell apoptosis. But the relationship between escin-induced DNA damage and cell apoptosis in tumor cells remains unclear. In this study, we investigated whether and how escin-induced DNA damage contributed to escin-induced apoptosis in human colorectal cancer cells. Escin (5-80 mu g/mL) dose-dependently inhibited the cell viability and colony formation in HCT116 and HCT8 cells. Escin treatment induced DNA damage, leading to p-ATM and gamma H2AX upregulation. Meanwhile, escin treatment increased the expression of p62, an adaptor protein, which played a crucial role in controlling cell survival and tumorigenesis, and had a protective effect against escininduced DNA damage: knockdown of p62 apparently enhanced escin-induced DNA damage, whereas overexpression of p62 reduced escin-induced DNA damage. In addition, escin treatment induced concentration- and time-dependent apoptosis. Similarly, knockdown of p62 significantly increased escin-induced apoptosis in vitro and produced an escin-like antitumor effect in vivo. Overexpression of p62 decreased the rate of apoptosis. Further studies revealed that the functions of p62 in escin-induced DNA damage were associated with escin-induced apoptosis, and p62 knockdown combined with the ATM inhibitor KU55933 augmented escin-induced DNA damage and further increased escin-induced apoptosis. In conclusion, our results demonstrate that p62 regulates ATM/gamma H2AX pathway-mediated escin-induced DNA damage and apoptosis.