Estrogen receptor β inhibits breast cancer cells migration and invasion through CLDN6-mediated autophagy

Abstract

Background Estrogen receptor β (ERβ) has been reported to play an anti-cancer role in breast cancer, but the regulatory mechanism by which ERβ exerts this effect is not clear. Claudin-6 (CLDN6), a tight junction protein, acts as a tumor suppressor gene in breast cancer. Our previous studies have found that 17β-estradiol (E2) induces CLDN6 expression and inhibits MCF-7 cell migration and invasion, but the underlying molecular mechanisms are still unclear. In this study, we aimed to investigate the role of ERβ in this process and the regulatory mechanisms involved. Methods Polymerase chain reaction (PCR) and western blot were used to characterize the effect of E2 on the expression of CLDN6 in breast cancer cells. Chromatin immunoprecipitation (ChIP) assays were carried out to confirm the interaction between ERβ and CLDN6. Dual luciferase reporter assays were used to detect the regulatory role of ERβ on the promoter activity of CLDN6. Wound healing and Transwell assays were used to examine the migration and invasion of breast cancer cells. Western blot, immunofluorescence and transmission electron microscopy (TEM) were performed to detect autophagy. Xenograft mouse models were used to explore the regulatory effect of the CLDN6-beclin1 axis on breast cancer metastasis. Immunohistochemistry (IHC) was used to detect ERβ/CLDN6/beclin1 expression in breast cancer patient samples. Results Here, E2 upregulated the expression of CLDN6, which was mediated by ERβ. ERβ regulated CLDN6 expression at the transcriptional level. ERβ inhibited the migration and invasion of breast cancer cells through CLDN6. Interestingly, this effect was associated with CLDN6-induced autophagy. CLDN6 positively regulated the expression of beclin1, which is a key regulator of autophagy. Beclin1 knockdown reversed CLDN6-induced autophagy and the inhibitory effect of CLDN6 on breast cancer metastasis. Moreover, ERβ and CLDN6 were positively correlated, and the expression of CLDN6 was positively correlated with beclin1 in breast cancer tissues. Conclusion Overall, this is the first study to demonstrate that the inhibitory effect of ERβ on the migration and invasion of breast cancer cells was mediated by CLDN6, which induced the beclin1-dependent autophagic cascade. Electronic supplementary material The online version of this article (10.1186/s13046-019-1359-9) contains supplementary material, which is available to authorized users.

The Effects of Trifolium pratense L. Sprouts’ Phenolic Compounds on Cell Growth and Migration of MDA-MB-231, MCF-7 and HUVEC Cells

“…Still, comparison of both cell lines relative levels of ERα/β expression shows that nuclear estrogen receptors are rather insignificantly involved in the MDA-MB-231 cellular response to red clover isoflavones, but they may be involved in other non-genomic intracellular action. These results are consistent with data presented in other studies, where a low-invasive MCF-7 cell line reported as an ER-positive cellular model expressed both types of estrogen receptors, whereas highly-invasive MDA-MB-231, known as ER-negative one, expressed ERβ [50,51]. As it is shown in Figure 8; Figure 9C,D, red clover extracts revealed no significant influence on ERβ and ERα mRNA expression and protein levels.…”

“…Since estrogenicity is connected with cell proliferation, we evaluated indirectly estrogenic-like effects of T. pratense phenolics at dosages lower than IC0 through the measurement of MCF-7 cells with crystal violet staining. Figure 9C presents the ratios of the proliferative effects of extracts and 17 β-estradiol described by the RPE parameter, where total agonist induces RPE between 80% and 100%, partial agonists induce 25% to 80% and a weak agonist induces between 10% and 25% These results are consistent with data presented in other studies, where a low-invasive MCF-7 cell line reported as an ER-positive cellular model expressed both types of estrogen receptors, whereas highly-invasive MDA-MB-231, known as ER-negative one, expressed ERβ [50,51]. As it is shown in Figure 8; Figure 9C,D, red clover extracts revealed no significant influence on ERβ and ERα mRNA expression and protein levels.…”

Claudins: New Players in Human Fertility and Reproductive System Cancers

“…Lu et al demonstrated that SMAD2 causes downregulation of claudin-6 by DNA (cytosine-5)-methyltransferase 1 (DNMT1)-mediated DNA methylation, which results in increased migration and invasion of breast cancer cells [105]. In addition, research has shown that estrogen receptor β (ERβ) plays an anti-cancer role in breast cancer, and Song et al demonstrated that this effect is mediated by claudin-6 [106]. On the other hand, Yang et al demonstrated that claudin-6 affects chemo-resistance in MDA-MB-231 cells in response to adriamycin (ADM) by reducing the drug-induced apoptosis [107].…”

Combination of an Autophagy Inducer and an Autophagy Inhibitor: A Smarter Strategy Emerging in Cancer Therapy

“…Many natural compounds and synthetic agents exhibit their anticancer effects through triggering autophagic cell death (Law et al, 2017;Xu et al, 2019;Kiruthiga et al, 2020;Pellerito et al, 2020). Moreover, the activation of autophagy-related signaling may implicate the suppression of certain other cancer therapeutic target to help against cancer, such as tumor invasion and migration and tumor angiogenesis Jiang et al, 2019;Song et al, 2019).…”