A composition of bractatin and neobractatin from the fruits of Garciniabracteatainduces apoptosis in throat cancer through the endoplasmic reticulum stress, mitochondrial apoptotic and Akt pathways

The natural compound from Garcinia bracteata mainly induces GSDME-mediated pyroptosis in esophageal cancer cells

BACKGROUND

Pyroptosis, an inflammatory form of programmed cell death (PCD), is reported to play important roles in the treatment of tumors. In our previous studies, we found that neobractatin (NBT), a caged prenylxanthone isolated from edible fruits of Garcinia bracteata C. Y. Wu ex Y. H. Li, showed anticancer effects against different cancer cells. However, the effect of NBT on pyroptosis is not well understood.

PURPOSE

This study aims to investigate whether and how GSDME-mediated pyroptosis contributes to NBT-induced antitumor effects in esophageal cancer (EC) cells.

METHODS

Cell viability assay and colony formation assay were used to determine the anticancer effects of NBT in esophageal cancer cells. Lactate dehydrogenase (LDH) release assay and microscopy imaging were used to detect the main characteristic of pyroptosis. CRISPR-Cas9 knockout and siRNA knockdown were performed to verify the roles of GSDME and caspase-3 in NBT-induced pyroptosis. Flow cytometry was used to measure the reactive oxygen species (ROS) level and cell apoptosis. The changes of related protein level were detected by Western blot. Furthermore, animal experiments were used to verify the in vivo effect of NBT.

RESULTS

The results showed that NBT reduced the viability of EC cells mainly through GSDME-mediated pyroptosis. Morphologically, NBT induced cell swelling and formed large bubbles emerging from plasma membrane in wild type EC cells. Furthermore, NBT induced the cleavage of GSDME by activating caspase-3 in EC cells. On the other hand, caspase-3 activated by NBT also induced apoptosis especially at high dosage. Knocking down GSDME switched NBT-induced cell death from mainly pyroptosis to apoptosis in vivo and in vitro. Mechanistic studies indicated that NBT led to accumulation of ROS, which then regulated the phosphorylation of both JNK and MEK/ERK. In the absence of ROS or caspase-3, NBT-induced pyroptosis and apoptosis were completely reversed. Moreover, NBT showed a significant antitumor effect in both the KYSE150 and GSDME knockout KYSE150-/- xenograft models by inducing pyroptosis and apoptosis, respectively.

CONCLUSION

Our results indicated that natural compound NBT could induce GSDME-mediated pyroptosis and apoptosis in esophageal cancer cells, making it a potential therapeutic drug in clinical treatment.

The natural compound neobractatin inhibits cell proliferation mainly by regulating the RNA binding protein CELF6

The fruits of Garcinia bracteata can be eaten raw or processed into spices, which are considered to possess nutritional and medicinal value. Neobractatin (NBT) is a natural compound isolated from Garcinia bracteate. This study showed that NBT showed antitumor effect by upregulation of CELF6. CELF6, an RNA-binding protein of the CELF family, is involved in cancer cell proliferation. However, the role of CELF6 in human cervical cancer remains unknown. Here, we showed that CELF6 overexpression significantly suppressed HeLa cell proliferation. Mechanistically, the RNA immunoprecipitation sequencing (RIP-seq) results suggested that CELF6 physically targeted the cyclin D1 transcript, affecting protein stability. Overexpression of CELF6 increased the degradation of cyclin D1. Consistent results were obtained for the effect of NBT, which increased the expression of CELF6 at both the mRNA and protein levels. An in vivo study further confirmed the regulatory effect of NBT on CELF6 and cyclin D1 levels in a HeLa xenograft model. Similar effects of NBT on CELF6 were also shown in K562 cells in vitro and in vivo. In conclusion, our findings identified CELF6 as a tumor suppressor and a novel therapeutic target in cervical cancer. The upregulation of CELF6 expression by NBT and its antiproliferative effect on HeLa cells indicated that NBT from G. bracteata might be a small-molecule compound targeting CELF6.