TGF-β stimulation of EMT programs elicits non-genomic ER-α activity and anti-estrogen resistance in breast cancer cells

Abstract

Aim Estrogen receptor-α (ER-α) activation drives the progression of luminal breast cancers. Signaling by transforming growth factor-β (TGF-β) typically opposes the actions of ER-α; it also induces epithelial-mesenchymal transition (EMT) programs that promote breast cancer dissemination, stemness, and chemoresistance. The impact of EMT programs on nongenomic ER-α signaling remains unknown and was studied herein. Methods MCF-7 and BT474 cells were stimulated with TGF-β to induce EMT programs, at which point ER-α expression, localization, and nongenomic interactions with receptor tyrosine kinases and MAP kinases (MAPKs) were determined. Cell sensitivity to anti-estrogens both before and after traversing the EMT program was also investigated. Results TGF-β stimulated MCF-7 and BT474 cells to acquire EMT phenotypes, which enhanced cytoplasmic accumulation of ER-α without altering its expression. Post-EMT cells exhibited (i) elevated expression of EGFR and IGF1R, which together with Src formed cytoplasmic complexes with ER-α; (ii) enhanced coupling of EGF, IGF-1 and estrogen to the activation of MAPKs; and (iii) reduced sensitivity to tamoxifen, an event reversed by administration of small molecule inhibitors against the receptors for TGF-β, EGF, and IGF-1, as well as those against MAPKs. Conclusion EMT stimulated by TGF-β promotes anti-estrogen resistance by activating EGFR-, IGF1R-, and MAPK-dependent nongenomic ER-α signaling.

Epithelial–Mesenchymal Transition Programs and Cancer Stem Cell Phenotypes: Mediators of Breast Cancer Therapy Resistance

“…Accordingly, the administration of neutralizing anti-TGFb antibodies was sufficient to restore the antiproliferative activities of tamoxifen on xenografts derived from tamoxifen-resistant human breast carcinoma cells (127). Along these lines, EMT programs stimulated by TGFb also elicit tamoxifen resistance by promoting receptor tyrosine kinase-dependent (e.g., EGFR and IGF1R) activation of SRC and MAPKs, which coalesce in mediating the cytoplasmic accumulation of ERa and its ability to engage in nongenomic signaling (128). Regardless of the cause and effect relationship between tamoxifen resistance and EMT programs, it is abundantly clear that endocrine resistance is highly associated with the invasive and metastatic characteristics afforded by EMT, as evidenced by the high degree of crosstalk between the effector pathways of EMT and tamoxifen resistance (Fig.…”

Endocrine Resistance in Hormone Receptor Positive Breast Cancer–From Mechanism to Therapy

“…A recent study demonstrated the effect of TGF-β, where it promoted epithelial mesenchymal transition (EMT) and expression of the EGFR and IGF-IR. These RTKs (EGFR and IGF-IR) formed complexes with ERα and SRC, thereby supporting endocrine resistance in BC (324). Furthermore, c-SRC phosphorylates the ER and has been shown to regulate ER localization (325, 326).…”

ER and PI3K Pathway Activity in Primary ER Positive Breast Cancer Is Associated with Progression-Free Survival of Metastatic Patients under First-Line Tamoxifen

“…Based on this connection, the samples were divided into three subgroups: (1) low PI3K pathway activity, as defined by high FOXO activity and low SOD2; (2) high PI3K pathway activity, defined by low FOXO activity; (3) putative PI3K pathway activity with cellular oxidative stress, defined by high FOXO activity and high SOD2, in the presence of high NFκB pathway activity. In the oxidative stress group, 17 (68%) patients had low ER pathway activity, five of which with high TGFβ and two with high HH pathway activity, suggesting a tumor subtype with some characteristics of epithelial mesenchymal transition [31][32][33]. On the other hand, in the PI3K pathway active subgroup without oxidative stress, the PI3K pathway seemed to be mostly the single tumor-driving pathway.…”

“…The third group (putative PI3K pathway activity with cellular oxidative stress), despite eight (32%) samples with a high ER pathway activity, shows distinct features that have been described in triple-negative tumors, i.e., TGFβ activity and oxidative stress [4,29,35]. TGFβ is thought to exert its tumor promoting effects through induction of EMT in cancer cells, a process which may be promoted by cellular oxidative stress, and associated with aggressive tumor pathology and bad prognosis [4,[29][30][31]33,36,37].…”