Sea cucumber-derived holotoxin A1 and B1 induce β-defensin 2 and β-defensin 3 in oral epithelial cells

Holotoxins (HTXs) derived from sea cucumber ( Apostichopus armata and japonicus ) are known natural fungicides and inducers of apoptosis in carcinoma cells. This study examined the novel activity of HTXs as immunostimulants, with a focus on inducing antimicrobial peptides from oral epithelial cells TR146. At subtoxic concentration, Holotoxin A 1 and B 1 (HTX-A1 and HTX-B1) induced β -defensins (hBDs), hBD-2 and -3, in TR146 cells. HTXs exhibited cytotoxicity in TR146 cells. However, cytotoxicity was reduced in WI-38 and layered TR146 cells compared with the TR146 cells in the growth phase. Notably, defensin expression levels by HTXs were enhanced in the layered cells, which were closer to oral epithelial tissue than cells in the proliferative phase. Reactive oxygen species (ROS) are primary antifungal and anticancer compounds produced by the stimulation of sea cucumber saponins. ROS are also common signaling molecules in immune responses, but we did not confirm their involvement in this study. In contrast, inhibiting epidermal growth factor receptor (EGFR) signaling suppressed hBDs expressions, suggesting that EGFR signaling is involved in TR146 cell responses to HTXs. These findings suggest that HTX-A1 and -B1 act as the immunostimulatory agents on oral epithelial cells to induce β -defensins.