Ionizing radiation downregulates estradiol synthesis via endoplasmic reticulum stress and inhibits the proliferation of estrogen receptor-positive breast cancer cells.

Breast cancer is a major threat to women's health and estrogen receptor-positive (ER+) breast cancer exhibits the highest incidence among these cancers. As the primary estrogen, estradiol strongly promotes cellular proliferation and radiotherapy, as a standard treatment, exerts an excellent therapeutic effect on ER+ breast cancer. Therefore, we herein wished to explore the mechanism(s) underlying the inhibitory effects of radiation on the proliferation of ER+ breast cancer cells. We used the ER+ breast cancer cell lines MCF7 and T47D, and their complementary tamoxifen-resistant cell lines in our study. The aforementioned cells were irradiated at different doses of X-rays with or without exogenous estradiol. CCK8 and clone-formation assays were used to detect cellular proliferation, enzyme-linked immunosorbent assay (ELISA) to determine estradiol secretion, western immunoblotting analysis and quantitative real-time PCR to evaluate the expression of proteins, and immunofluorescence to track endoplasmic reticulum stress-related processes. Finally, BALB/C tumor-bearing nude mice were irradiated with X-rays to explore the protein expression in tumors using immunohistochemistry. We found that ionizing radiation significantly reduced the phosphorylation of estrogen receptors and the secretion of estradiol by ER+ breast cancer cells. CYP19A (aromatase) is an enzyme located in the endoplasmic reticulum, which plays a critical role in estradiol synthesis (aromatization), and we further demonstrated that ionizing radiation could induce endoplasmic reticulum stress with or without exogenous estradiol supplementation, and that it downregulated the expression of CYP19A through ER-phagy. In addition, ionizing radiation also promoted lysosomal degradation of CYP19A, reduced estradiol synthesis, and inhibited the proliferation of tamoxifen-resistant ER+ breast cancer cells. We concluded that ionizing radiation downregulated the expression of CYP19A and reduced estradiol synthesis by inducing endoplasmic reticulum stress in ER+ breast cancer cells, thereby ultimately inhibiting cellular proliferation.

Astragalus polysaccharide inhibits radiation-induced bystander effects by regulating apoptosis in Bone Mesenchymal Stem Cells (BMSCs).

The purpose of this study was to investigate the effects of astragalus polysaccharides (APS) on the proliferation and apoptosis of bone marrow mesenchymal stem cells (BMSCs) induced by X-ray radiation-induced A549 cells bystander effect (RIBE), and to explore their mechanisms. In this study, APS increased the reduced cell proliferation rate induced by RIBE and inhibiting the apoptosis of bystander cells. In terms of mechanism, APS up-regulates the proteins Bcl-2, Bcl-xl, and down-regulates the proteins Bax and Bak, which induces a decrease in mitochondrial membrane potential, which induces the release of Cyt-c and AIF, which leads to caspase-dependent and caspase-independent pathway to cause apoptosis. In addition, we believe that ROS may be the main cause of these protein changes. APS can inhibit the generation of ROS in bystander cells and thus inhibit the activation of the mitochondrial pathway, further preventing cellular damage caused by RIBE.