Targeting p65 to inhibit Cas3 transcription by Onjisaponin B for radiation damage therapy in p65+/- mice

Abstract

Background: In response to radiation injury, p65 becomes activated. The formation of p65 is one target of Onjisaponin B (OB), but it has not been studied in radioprotection. In addition, there is a binding site for p65 in the promoter region of Cas3. This study evaluates the use of OB as an intervention to modulate p65/Cas3 following radiation exposure.

Purpose: This study aimed to confirm that OB regulated the transcription of Cas3 via p65 to overcome radiation-induced damage.

Study design and methods: Cells and mice were exposed to X-rays at a dose of 6 Gy. Immunofluorescence was used to locate intracellular p65. For the protein and mRNA analyses, Western blotting and RT-qPCR-based assays were conducted accordingly. HE staining was used to observe pathological changes in tissues. DNA damage was detected by the comet assay and DNA ladder assay. Next, apoptosis was detected by flow cytometry and Hoechst staining.

Results: Compared with the radiation group, the expression levels of p-p65 and c-Cas3 in the drug group were significantly down-regulated by OB 20 µg/ml. When the expression of p65 was suppressed in V79 and TC cells, OB did not significantly inhibit the activation of p65 or Cas3 in response to irradiation, nor did it significantly inhibit the phosphorylation of p65 and subsequent nuclear translocation. Overexpression of p65 in V79 and MTEC-1 cells resulted in OB significantly inhibiting the activation of p65 and Cas3, and the phosphorylation and translocation of p65 into the nucleus. At 3 d for V79 cells and 24 h for MTEC-1 cells after radiation, compared with the Cas3 over plasmid transfection group, the drug transfection group had no significant effect on reducing apoptosis. In p65+/- mice, expression of the p65 gene was knocked down, leading to increased tissue apoptosis and inflammation, and serious tissue pathological changes. The inhibition of p65 activation by OB after radiation exposure was not apparent in the thymus, although it was observed in the lung.

Conclusions: OB interfered with radiation injury by targeting and regulating p65/Cas3. Therefore, it has been concluded that p65 is an important target molecule for the treatment of radiation injury.

Keywords: Caspase-3; NF-κB; Onjisaponin B; Radioprotection; p65; p65+/- Mice.