Estrogen promotes the brain metastatic colonization of triple negative breast cancer cells via an astrocyte-mediated paracrine mechanism

Abstract

Brain metastases (BM) are a devastating consequence of breast cancer. BM occur more frequently in patients with estrogen receptor-negative (ER−) breast cancer subtypes; HER2 overexpressing (HER2+) tumors and triple-negative (TN) (ER−, progesterone receptor-negative (PR−) and normal HER2) tumors. Young age is an independent risk factor for development of BM, thus we speculated that higher circulating estrogens in young, pre-menopausal women could exert paracrine effects through the highly estrogen-responsive brain microenvironment. Using a TN experimental metastases model, we demonstrate that ovariectomy decreased the frequency of MRI detectable lesions by 56% as compared to estrogen supplementation, and that the combination of ovariectomy and letrozole further reduced the frequency of large lesions to 14.4% of the estrogen control. Human BM expressed 4.2-48.4% ER+ stromal area, particularly ER+ astrocytes. In vitro, E2-treated astrocytes increased proliferation, migration and invasion of 231BR-EGFP cells in an ER-dependent manner. E2 upregulated EGFR ligands Egf, Ereg, and Tgfa mRNA and protein levels in astrocytes, and activated EGFR in brain metastatic cells. Co-culture of 231BR-EGFP cells with E2-treated astrocytes led to upregulation of the metastatic mediator S100 Calcium-binding protein A4 (S100A4) (1.78-fold, P<0.05). Exogenous EGF increased S100A4 mRNA levels in 231BR-EGFP cells (1.40±0.02 fold, P<0.01 compared to vehicle-control) and an EGFR/HER2 inhibitor blocked this effect, suggesting that S100A4 is a downstream effector of EGFR activation. ShRNA-mediated S100A4 silencing in 231BR-EGFP cells decreased their migration and invasion in response to E2-CM, abolished their increased proliferation in co-cultures with E2-treated astrocytes, and decreased brain metastatic colonization. Thus, S100A4 is one effector of the paracrine action of E2 in brain metastatic cells. These studies provide a novel mechanism by which estrogens, acting through ER+ astrocytes in the brain microenvironment, can promote BM of TN breast cancers, and suggests existing endocrine agents may provide some clinical benefit towards reducing and managing BM.

Role of Wnt Co-Receptor LRP6 in Triple Negative Breast Cancer Cell Migration and Invasion

“…S100A4 is up‐regulated in various types of cancers, and S100A4 expression levels in tumors are considered as a biomarker for the prognosis of both metachronous metastasis and survival of cancer patients [Garrett et al, ; Mishra et al, ; Dahlmann et al, ]. Particularly, S100A4 is able to enhance TNBC cell motility and invasion in vitro and induces lung and brain metastasis in vivo [Wang et al, ; Sartorius et al, ], and the elevated levels of S100A4 expression are associated with the poor prognosis in human patients [Platt‐Higgins et al, ; Rudland et al, ]. Importantly, S100A4 is a direct transcriptional target of the Wnt/β‐catenin signaling pathway, and a transcriptionally active β‐catenin enhances the S100A4‐induced migration and invasion of colorectal cancer cells [Stein et al, ].…”

MicroRNA-588 suppresses tumor cell migration and invasion by targeting GRN in lung squamous cell carcinoma

“…The primers were as follows: GRN, forward 5′-ATCTTTACCGTCTCAGGGACTT-3′ and reverse 5′-CCATCGACCATAACACAGCAC-3′ and β-actin, forward 5′-ATGATGATATCGCCGCGCTC-3′ and reverse 5′-CATCACGCCCTGGTGCC-3′, respectively. The relative expression levels of GRN were calculated using the ΔΔCq method as described previously ( 21 ).…”

Cancer and the metastatic substrate

“…This would explain why young patients with TN that present high levels of oestrogen have a higher risk of suffering brain metastasis. Possibly, the development of these metastasis could depend more on the hormonal profile of the patient than the intrinsic factors of the tumour cell [130]. …”