S100A8 and S100A9 induction is involved in inflammation-associated hepatocarcinogenesis under hypoxic conditions via the JNK pathway

Abstract

Background: S100A8 and S100A9 are two heterodimeric members of the cytoplasmic S100 Ca2+ signaling protein family. They act as proinflammatory signals and play a role in tumorigenesis as they affect inflammation, proliferation, and invasion of tumor cells in various types of cancer, including hepatocellular carcinoma (HCC). Hypoxia plays an important role in inflammation-associated tumorigenesis, but the direct role of S100A8 and S100A9 in hepatocarcinogenesis has not yet been elucidated, particularly with regard to the impact of hypoxia. The present study investigated the role of S100A8 and S100A9 in HCC under hypoxic conditions. Methods: The expression of S100A8 and S100A9 was quantified using real-time polymerase chain reaction. Human HCC cells (SNU-761 and SNU-3058) were grown with either S100A8/A9 treatment or control, under either normoxic or hypoxic conditions. MTS and invasion assays were performed to evaluate the role of S100A8 and S100A9 in HCC. Immunoblot analyses were performed to investigate the signaling pathway that is involved in the activity of S100A8 and S100A9. Results: S100A8 and S100A9 mRNA expression increased under hypoxic conditions compared with normoxic conditions. S100A8 and S100A9 treatment significantly increased the invasion of HCC cells, especially under hypoxic conditions, whereas no significant changes in HCC cell proliferation were observed. S100A8 treatment significantly enhanced the expression of interleukin-8 (IL-8), an inflammatory cytokine that is involved in tumor progression, under hypoxic conditions. IL-8 siRNA transfection attenuated the S100A8-induced invasion of HCC cells. S100A8 treatment attenuated bile acid-induced HCC cell apoptosis under hypoxic conditions. Moreover, S100A8 increased the protein expression of mesenchymal markers, including vimentin, matrix metalloproteinase 9 (MMP-9), and MMP-2, which were attenuated by a c-Jun N-terminal kinase (JNK) inhibitor. Conclusion: Hypoxia-induced S100A8/A9 expression increased the invasion of HCC cells and attenuated bile acid-induced HCC apoptosis by increasing IL-8 under hypoxic conditions. Considering the enhanced expression of epithelial-mesenchymal transition (EMT) markers, the JNK pathway may be involved in controlling the activity of S100A8 and S100A9. These results indicate that S100A8 and S100A9 may serve as therapeutic targets for the treatment of HCC under hypoxic conditions.