High mobility group box-1 protects against Aflatoxin G1-induced pulmonary epithelial cell damage in the lung inflammatory environment

Aflatoxin G(1) (AFG1) is a member of the carcinogenic aflatoxin family. Our previous studies indicated that oral administration of AFG(1) caused tumor necrosis factor (TNF)-alpha-dependent inflammation that enhanced oxidative DNA damage in alveolar epithelial cells, which may be related to AFG(1)-induced lung carcinogenesis. High mobility group box-1 (HMGB1) is a nuclear DNA-binding protein; the intracellular and extracellular roles of HMGB1 have been shown to contribute to DNA repair and sterile inflammation. The role of HMGB1 in DNA damage in an aflatoxin-induced lung inflammatory environment was investigated in this study. Upregulation of HMGB1, TLR2, and RAGE was observed in AFG(1)-induced lung inflamed tissues and adenocarcinoma. Blocking AFG(1)-induced inflammation by neutralization of TNF-alpha inhibited the upregulation of HMGB1 in mouse lung tissues, suggesting that AFG(1)-induced TNF-alpha-dependent inflammation regulated HMGB1 expression. In the in vitro human pulmonary epithelial cell line model, Beas-2b, AFG(1) directly enhanced the cytosolic translocation of HMGB1 and its extracellular secretion. The addition of extracellular soluble HMGB1 protected AFG(1)-induced DNA damage through the TLR2/NF-kappa B pathway in Beas-2b cells. In addition, blockade of endogenous HMGB1 by siRNA significantly enhanced AFG(1)-induced damage. Thus, our findings showed that both extracellularly-released and nuclear and cytosolic HMGB1 could protect the cell from AFG(1)-induced cell damage in a TNF-alpha-dependent lung inflammatory environment.