Colon Cancer Cells Treated with Lacticaseibacillus casei Undergo Apoptosis and Release DAMPs Indicative of Immunogenic Cell Death

Probiotic bacteria, and especially lactic acid bacteria, have long been known to wield a variety of health-beneficial effects, including antioxidant, antimicrobial, anti-inflammatory, immunomodulatory, and anticancer activities. However, our understanding of the mechanisms involved in these activities remains incomplete. In this study, we wished to investigate the processes that give rise to the anticancer activity of Lacticaseibacillus casei ATCC393 and the possibility that immunogenic cell death of cancer cells can be induced following treatment with this probiotic. In both cell lines that we have examined, we detected notable pro-apoptotic signaling, including the upregulation of death receptors, that culminated in the activation of caspase 3, the endpoint and most characteristic effector molecule of all pro-apoptotic cascades. In addition, we identified damage-associated molecular patterns associated with immunogenic cell death. Calreticulin exposure on the outer cell membrane, HMGB1 translocation outside the nucleus and depletion of intracellular ATP was evident in both cancer cell lines treated with the probiotic, while expression of type I interferons was upregulated in CT26 cells. Our findings suggest that treatment with the probiotic induced apoptosis in cancer cells, mediated by extrinsic death receptor signaling. Moreover, it resulted in the release of molecular signals related with immunogenic cell death and induction of cancer cell-specific adaptive immune responses.