Iturin A-like lipopeptides from Bacillus subtilis trigger apoptosis, paraptosis, and autophagy in Caco-2 cells

This study revealed that iturin A-like lipopeptides produced by Bacillus subtillis induced both paraptosis and apoptosis in heterogeneous human epithelial colorectal adenocarcinoma (Caco-2) cells. Autophagy was simultaneously induced in Caco-2 cells treated with iturin A-like lipopeptides at the early stage and inhibited at the later stage. A western blot analysis showed that the lipopeptides induced apoptosis in Caco-2 cells via a mitochondrial-dependent pathway, as indicated by upregulated expression of the apoptotic genes bax and bad and downregulated expression of the antiapoptotic gene bcl-2. The induction of paraptosis in Caco-2 cells was indicated by the occurrence of many cytoplasmic vacuoles accompanied by endoplasmic reticulum (ER) dilatation and mitochondrial swelling and dysfunction. ER stress also occurred with significant increases in reactive oxygen species and Ca²⁺ levels in cells. Autophagy was detected by a transmission electron microscopy analysis and by upregulated expression of LC3-II and downregulated expression of LC3-I. The inhibition of autophagy at the later stage was shown by upregulated expression of p62. This study revealed the capability of iturin A-like B. subtilis lipopeptides to simultaneously execute antitumor potential via multiple pathways.