Cationic peroxidase from proso millet induces human colon cancer cell necroptosis by regulating autocrine TNF-α and RIPK3 demethylation.

A cationic peroxidase (POD) was purified from proso millet seeds (PmPOD) using ammonium sulfate fractionation, cation exchange, and size exclusion chromatography. The purified PmPOD showed toxicity to normal cells and tumor cells, but was more sensitive in HT29 cells. Furthermore, the mechanism driving HCT116 and HT29 cell death by PmPOD was the induction of receptor interacting protein kinase 1 (RIPK1)- and RIPK3-dependent necroptosis, independent of apoptosis. More importantly, PmPOD could induce tumor necrosis factor-α (TNF-α) production through transcriptional upregulation. In addition, PmPOD could restore RIPK3 expression in HCT116 cells via the demethylation of the RIPK3 genomic sequence. Taken together, these results suggest that two distinct mechanisms are involved in PmPOD-induced necroptosis: the autocrine production of TNF-α and the restoration of RIPK3 expression.