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

Pengfei Yang,Yanan Zhang,Chengyan Sheng,Nan Ding,Jinpeng He,Jin Li,Junrui Hua,Wenjun Wei,Tianyi Zhang,Heng Zhou,Xiu Feng,Jufang Wang,Liying Zhang

doi:10.1038/s41419-021-04328-w

Abstract

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.

Highlights

According to the most recent data, breast cancer has officially replaced lung cancer as the most common cancer globally [1] and its most commonplace form is estrogen receptor-positive breast cancer [2]
CYP19A is an enzyme located in the endoplasmic reticulum, which plays a critical role in estradiol synthesis, 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
MDA-MB-231 were irradiated with X-rays at different doses, and observed that the autophagic marker protein LC3B-II/I ratio was we found that 24 h after irradiation, MCF7 and MDA-MB-231 cells increased, that Beclin1 expression was upregulated, and that the expansion and proliferation slowed commensurate with the expression of P62 was downregulated by western blotting analysis increase in radiation dose (Fig. 1A)

Summary

INTRODUCTION

According to the most recent data, breast cancer has officially replaced lung cancer as the most common cancer globally [1] and its most commonplace form is estrogen receptor-positive breast cancer [2]. Studies have target for ERα and promotes ER+ breast cancer cell survival [22], shown that the EnR can degrade its accumulation through we irradiated MCF7 and T47D cells with different doses of X-rays selective autophagy, a process known as ER-phagy [15]. The expression of the above proteins was Endocrine therapy such as tamoxifen is commonly used in the upregulated in MCF7 and T47D cells by X-ray irradiation at different clinical treatment of ER+ breast cancer, but it can lead to drug doses (Fig. 3A). As numerous We further examined gene expression changes and found that investigators have demonstrated that ionizing radiation inhibits estrogen secretion in ER+ breast cancer cells [20, 21], we wished to IRE1α and XBP1 were significantly upregulated in MCF7 and T47D cells after irradiation (Fig. 3B). That the expression of IRE1α, XBP1s, and the phosphorylation of IRE1α increased in a dose-dependent manner in MCF7 and T47D cells after irradiation (Fig. 3C); the expression changes were similar in the presence of exogenous estradiol (Supplementary Fig. S2B)

RESULTS

DISCUSSION AND CONCLUSIONS

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