Small Non-Coding RNA Profiling Identifies miR-181a-5p as a Mediator of Estrogen Receptor Beta-Induced Inhibition of Cholesterol Biosynthesis in Triple-Negative Breast Cancer

Abstract

Triple-negative breast cancer (TNBC) is a highly heterogeneous disease, representing the most aggressive breast cancer (BC) subtype with limited treatment options due to a lack of estrogen receptor alpha (ERα), progesterone receptor (PR), and Erb-B2 receptor tyrosine kinase 2 (HER2/neu) expression. Estrogen receptor beta (ERβ) is present in a fraction of TNBC patients, where its expression correlates with improved patient outcomes, supported by the fact that it exerts oncosuppressive effects in TNBC cell models in vitro. ERβ is involved in microRNA-mediated regulation of gene expression in hormone-responsive BC cells and could mediate its actions through small noncoding RNAs (sncRNAs) in TNBCs also. To verify this possibility, smallRNA sequencing was performed on three ERβ-expressing cell lines from different TNBC molecular subtypes. Several sncRNAs resulted modulated by ERβ, with a subset being regulated in a tumor subtype-independent manner. Interestingly, sncRNA profiling of 12 ERβ+and 32 ERβ− primary TNBC biopsies identified 7 microRNAs, 1 PIWI-interacting RNA (piRNA), and 1 transfer RNA (tRNA) differentially expressed in ERβ+ compared to ERβ− tumors and cell lines. Among them, miR-181a-5p was found to be overexpressed in ERβ+ tumors and predicted target key components of the cholesterol biosynthesis pathway previously found to be inhibited by ERβ in TNBC cells.

The role of estrogen receptor beta in breast cancer

“…In ERβ + TNBC, ERβ induces miR-181a-5p overexpression, which is involved in the inhibition of the cholesterol biosynthesis pathway in TNBC cells [118]. These results suggest that miRNA regulation might be a critical event in the control of the biological and clinical phenotype of breast cancer by ERβ.…”

“…Abbreviations ER: Estrogen receptor; TAM: Tamoxifen; RFS: Recurrence-free survival; PFS: Progression-free survival; DFS: Disease-free survival; OS: Overall survival; DMFS: Distant metastases-free survival; TNBC: Triple-negative breast cancer; PR: Progesterone receptor; HER2: Human epidermal growth factor receptor-2; SERM: Selective estrogen receptor modulator; ROS: Reactive oxygen species; CBP: Binding protein; NRF-1: Nuclear respiratory factor 1; BCA2: Breast cancer associated gene 2; UCP: Uncoupling protein; SIRT3: Sirtuin 3; AKT: Protein kinase B; SAPK: Stress-activated protein kinase; PI3-K: Phosphatidylinositol-3kinase; PTEN: Phosphatase and tensin homolog deleted on chromosome ten; CREB: cAMP response element-binding; ECM: Extracellular matrix; EGFR: Epidermal growth factor receptor; IGF-IR: Insulin-like growth factor-I receptor; JAK/STAT: Janus kinase/signal transducer and activator of transcription; EMT: Epithelial-mesenchymal transition; ZEB1: Zinc finger E-boxbinding homeobox 1; SIP1: Smad interacting protein; TGF-β: Transforming growth factor; VEGF: Vascular endothelial growth factor; PDGF β: Plateletderived growth factor β; HIF -1α: Hypoxia inducible factor-1α; ARNT: Aryl hydrocarbon receptor nuclear translocator; mfn2: Mitofusin2; RARβ2: Retinoic acid receptor β2; HADHB: Trifunctional protein, beta subunit; DCB1: Deleted in breast cancer 1; Id1: Inhibitor of differentiation-1; bHLH: Basic helix-loophelix; SUMO-1: Small ubiquitin-related modifier; GSK3β: Glycogen synthase kinase 3β; MicroRNAs: miRNAs; H3K4me3: Histone H3 lys4 trimethylation; BRCA1: Breast cancer 1; BRCA2: Breast cancer 2 [116] miR-30a-5p inhibition of EMT 2014 [117] miR-200a/b/429 inhibition of EMT and invasion 2012 [87] Downregulated miR-181a-5p inhibition of cholesterol biosynthesis 2020 [118] miR-10 regulation of ECM composition 2017 [116] miR-375 suppression of proliferation 2013 [115] EMT Epithelial-mesenchymal transition, ECM Extracellular matrix…”

Insights into the Role of Estrogen Receptor β in Triple-Negative Breast Cancer

“…In fact, its upregulation has been described in both TNBC cell lines, after induction of ERβ expression, and in ERβ-positive vs. -negative biopsies. Moreover, among the predicted targets of miR-181a-5p, key components of cholesterol biosynthesis were present [171]. Altogether, these results indicate the involvement of different epigenetic mechanisms in ERβ-mediated regulation of cholesterol biosynthesis in TNBC.…”

“…The most interesting mechanisms of ERβ action in TNBC are linked to the regulation of cellular metabolic programs, which takes place through ERβ-mediated downregulation of UPR in the presence of EnR stress [ 140 ], induction of OXPHOS by expression of mtDNA-encoded genes [ 156 ] and inhibition of cholesterol biosynthesis by suppression of SREBF1 gene transcription [ 32 ] or upregulation of miR-181a-5p [ 171 ]. ERβ is also able to drive expression of cystatins, that promote inhibition of TGFβ signaling leading to the reduced metastatic potential of TNBC cells in vitro and in vivo [ 83 ].…”

Perspectives on the Role of Non-Coding RNAs in the Regulation of Expression and Function of the Estrogen Receptor

“…miR-1280 has been implicated in the pathogenesis of thyroid carcinomas by targeting ERα [72]. miR-181a-5p has been identified as a mediator of ERβ-associated suppression of cholesterol production in triple-negative breast cancer [73]. ER-mediated miR-486-5p modulation of Olfactomedin 4 (OLFM4) is also implicated in ovarian cancer [74].…”