Anti-Proliferation Activity of Fucoidan in MKN45 Gastric Cancer Cells and Downregulation of Phosphorylated ASK1, a Cell Cycle-Regulated Kinase

BACKGROUND Fucoidan is a high-molecular polysaccharide whose main constituent is sulfated fucose. We specifically focused on the anti-proliferation activity of fucoidan and examined the underlying mechanism in MKN45 gastric cancer cells. METHODS MKN45 cell proliferation was analyzed by BrdU assay and fucoidan cytotoxicity was examined by LDH and clonogenic assays. The Agilent Human microarray kit was used to identify upregulated and downregulated genes in response to fucoidan, and western blot analyses evaluated cell cycle proteins. RESULTS Fucoidan impeded the MKN45 cell cycle by approximately 50%, and inhibited cell proliferation.LDH assays showed no immediate cytotoxic effects of fucoidan at 24 h exposure, however longer time courses revealed cell growth inhibition at 4 days in a dose-dependent manner. Microarray analysis identified MAP3K5, or ASK1 (apoptosis signal-regulating kinase),which was upregulated by 1.38-fold upon fucoidan treatment.Fucoidan increased ASK1 protein levels, while reducing phosphorylated ASK1 levels. Reduction of ASK1 by siRNA decreased proliferation of MKN45 cells. CONCLUSION Our findings show that fucoidan may suppress cellular proliferation and DNA synthesis in MKN45 cells by suppressing the ASK1-p38 signaling pathway through reduction of phosphorylated ASK1 levels.