AST modulates calpain activity (A) and calpain protein expression on HCT116 colon cancer cells (B). HCT116 colon cancer cells were treated with AST (80 μg/ml) for different time intervals (4–96 h). Calpain activity was measured by employing the calpain activity assay using fluorescent calpain substrate Ac-LLY-AFC. Calpain I and II protein levels in AST-treated cells were assessed by Western immunoblotting using specific antibodies. Data shown are representative immunoblots with similar findings, normalized by β-actin. Blots were scanned and optical densities were determined using the Quantity One software. Each histogram represents mean ± SEM of four independent experiments. *p <0.05 compared with the protein level at zero time.