Molecular mechanisms underlying endoplasmic reticulum stress-triggered apoptosis induced by <i>Trichoderma pseudokoningii</i> exopolysaccharide in WEHI-3 mouse myeloid leukemic cells

In this work, the anticancer activities of an exopolysaccharide (EPS) from <i>Trichoderma pseudokoningii</i>, as well as its influence on WEHI-3 mouse myeloid leukemia cells, were investigated. This EPS not only inhibited the proliferation of WEHI-3 cells in a time- and concentration-dependent manner but also altered the morphology of WEHI-3 cells in a manner similar to that of apoptotic cells, as demonstrated by fluorescence staining experiments. Moreover, flow cytometry analysis also revealed that the EPS induced apoptosis in WEHI-3 cells. Additionally, the results indicated that the endoplasmic reticulum (ER) stress may be involved in this apoptotic process. Apoptotic factors related to the ER pathway were assessed subsequently. The results revealed that after treatment with the EPS for 48 h, the concentration of intracellular calcium in WEHI-3 cells increased. Exposure of WEHI-3 cells to different concentrations of the EPS (0.25, 0.50, and 1.0 mg/mL) resulted in decreased GRP78 mRNA transcription and increased CHOP mRNA expression in relation to the ER pathway. In addition, the Western blot results revealed that EPS significantly increased the p-PERK/PERK ratio, decreased the protein levels of GRP78 and Bcl-2, and increased the protein levels of CHOP and Bax. Caspase activity analysis also revealed that EPS treatment of WEHI-3 cells resulted in a dose-dependent increase in the activities of caspase-4 and caspase-3. Taking all together, these results provide evidence that the endoplasmic reticulum pathway is one of the potential pathways for the EPS-induced apoptosis in WEHI-3 cells.