Role of SALL4 in HER2+ Breast Cancer Progression: Regulating PI3K/AKT Pathway

Treatment for the HER2+ breast cancer subtype is still unsatisfactory, despite breakthroughs in research. The discovery of various new molecular mechanisms of transcription factors may help to make treatment regimens more effective. The transcription factor SALL4 has been related to aggressiveness and resistance therapy in cancer. Its molecular mechanisms and involvement in various signaling pathways are unknown in the HER2+ breast cancer subtype. In this study, we have evaluated the implication of SALL4 in the HER2+ subtype through its expression in patients' samples and gain and loss of function in HER2+ cell lines. We found higher SALL4 expression in breast cancer tissues compared to healthy tissue. Interestingly, high SALL4 expression was associated with disease relapse and poor patient survival. In HER2+ cell lines, transient overexpression of SALL4 modulates PI3K/AKT signaling through regulating PTEN expression and BCL2, which increases cell survival and proliferation while reducing the efficacy of trastuzumab. SALL4 has also been observed to regulate the epithelial-mesenchymal transition and stemness features. SALL4 overexpression significantly reduced the epithelial markers E-cadherin, while it increased the mesenchymal markers β-catenin, vimentin and fibronectin. Furthermore, it has been also observed an increased expression of MYC, an essential transcription factor for regulating epithelial-mesenchymal transition and/or cancer stem cells. Our study demonstrates, for the first time, the importance of SALL4 in the HER2+ subtype and partial regulation of trastuzumab sensitivity. It provides a viable molecular mechanism-driven therapeutic strategy for an important subset of HER2-overexpressing patients whose malignancies are mediated by SALL4 expression.

Comparative Proteomic Profiling of Secreted Extracellular Vesicles from Breast Fibroadenoma and Malignant Lesions: A Pilot Study

Extracellular vesicles (EVs) shuttle proteins, RNA, DNA, and lipids crucial for cell-to-cell communication. Recent findings have highlighted that EVs, by virtue of their cargo, may also contribute to breast cancer (BC) growth and metastatic dissemination. Indeed, EVs are gaining great interest as non-invasive cancer biomarkers. However, little is known about the biological and physical properties of EVs from malignant BC lesions, and even less is understood about EVs from non-malignant lesions, such as breast fibroadenoma (FAD), which are clinically managed using conservative approaches. Thus, for this pilot study, we attempted to purify and explore the proteomic profiles of EVs from benign breast lesions, HER2+ BCs, triple–negative BCs (TNBCs), and continuous BC cell lines (i.e., BT-549, MCF–10A, and MDA-MB-231), combining experimental and semi-quantitative approaches. Of note, proteome-wide analyses showed 49 common proteins across EVs harvested from FAD, HER2+ BCs, TNBCs, and model BC lines. This is the first feasibility study evaluating the physicochemical composition and proteome of EVs from benign breast cells and primary and immortalized BC cells. Our preliminary results hold promise for possible implications in precision medicine for BC.

MicroRNAs as a clue to overcome breast cancer treatment resistance

Breast cancer is the most frequent cancer in women worldwide. Despite the improvement in diagnosis and treatments, the rates of cancer relapse and resistance to therapies remain higher than desirable. Alterations in microRNAs have been linked to changes in critical processes related to cancer development and progression. Their involvement in resistance or sensitivity to breast cancer treatments has been documented by different in vivo and in vitro experiments. The most significant microRNAs implicated in modulating resistance to breast cancer therapies are summarized in this review. Resistance to therapy has been linked to cellular processes such as cell cycle, apoptosis, epithelial-to-mesenchymal transition, stemness phenotype, or receptor signaling pathways, and the role of microRNAs in their regulation has already been described. The modulation of specific microRNAs may modify treatment response and improve survival rates and cancer patients' quality of life. As a result, a greater understanding of microRNAs, their targets, and the signaling pathways through which they act is needed. This information could be useful to design new therapeutic strategies, to reduce resistance to the available treatments, and to open the door to possible new clinical approaches.

miR-503-5p induces doxorubicin resistance in triple-negative breast cancer

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Background: Triple-negative breast cancer (TNBC) is an aggressive breast cancer (BC) subtype comprising approximately 15% of BC. Conventional cytotoxic chemotherapies continue to be the mainstay for treatment of this BC, which lacks targetable markers. In this context, microRNAs have been described to have an important role. The aim of this work was to elucidate the function of miR-503-5p in doxorubicin resistance in TNBC. Methods: miR-503-5p expression was evaluated in the TNBC cell line with acquired resistance to doxorubicin (MDA-MB-231R) and its parental cell line (MDA-MB-231), by qRT-PCR. Studies of gain/loss of function of miR-503-5p were carried out in MDA-MB-231 and MDA-MB-231R cells by transient transfection of mimics and inhibitors. Cells were treated with doxorubicin, and viability was measured by flow cytometry and MTT assay. The role of miR-503-5p was also evaluated in vivo by Chicken Chorioallantoic Membrane (CAM) assay. MDA-MB-231 cells transfected with miR-503-5p mimic or scramble miRNA were inoculated onto the CAM of fertilized chicken eggs. After 48 hours, tumours were treated with doxorubicin or supplemented media for 48 hours and tumour growth was measured. miR-503-5p expression was quantified by qRT-PCR in a retrospective cohort of 74 TNBC patients treated with anthracycline + taxane regimens. Overall survival analysis for miR-503-5p in TNBC patients from METABRIC dataset was evaluated by the KM plotter online tool. Results: miR-503-5p was significantly upregulated in the resistant MDA-MB-231R TNBC cell line when compared to its parental cell line MDA-MB-231 (̃3.5-fold; p< 0.0001). Then, gain/loss function assays showed that upregulation of miR-503-5p in MDA-MB-231 cells increased resistance to doxorubicin ( p< 0.0001) and its downregulation in MDA-MB-231R cells had the opposite effect ( p< 0.0001). Moreover, the role of miR-503-5p was also confirmed in the CAM assay in vivo model, where miR-503-5p overexpression inhibited the effect of doxorubicin. In our cohort of patients, miR-503-5p expression levels in core biopsies sampled before preoperative chemotherapy were associated with residual cancer burden (RCB). miR-503-5p expression was significantly higher in patients with poor response to chemotherapy (RCB II and III; median, 95% CI: 0.00055, 0.00024 - 0.00136) than in patients with good response (RCB 0 and I; median, 95% CI: 0.00018, 0.00011 - 0.00034; p = 0.036). Moreover, we confirmed that TNBC patients with high expression of miR-503-5p had worse overall survival than patients with low expression ( p= 0.016). Conclusions: We identified miR-503-5p as a modulator of doxorubicin resistance in TNBC. Our in vitro findings are supported by the clinical data of TNBC patients and in vivo assays. Hence, the inhibition of miR-503-5p may be a promising strategy to improve chemotherapeutic efficacy. Moreover, the expression levels of miR-503-5p may be used as a biomarker for therapy response in TNBC.

MicroRNA-33b Suppresses Epithelial-Mesenchymal Transition Repressing the MYC-EZH2 Pathway in HER2+ Breast Carcinoma

Downregulation of miR-33b has been documented in many types of cancers and is being involved in proliferation, migration, and epithelial–mesenchymal transition (EMT). Furthermore, the enhancer of zeste homolog 2-gene (EZH2) is a master regulator of controlling the stem cell differentiation and the cell proliferation processes. We aim to evaluate the implication of miR-33b in the EMT pathway in HER2+ breast cancer (BC) and to analyze the role of EZH2 in this process as well as the interaction between them. miR-33b is downregulated in HER2+ BC cells vs healthy controls, where EZH2 has an opposite expression in vitro and in patients’ samples. The upregulation of miR-33b suppressed proliferation, induced apoptosis, reduced invasion, migration and regulated EMT by an increase of E-cadherin and a decrease of ß-catenin and vimentin. The silencing of EZH2 mimicked the impact of miR-33b overexpression. Furthermore, the inhibition of miR-33b induces cell proliferation, invasion, migration, EMT, and EZH2 expression in non-tumorigenic cells. Importantly, the Kaplan–Meier analysis showed a significant association between high miR-33b expression and better overall survival. These results suggest miR-33b as a suppressive miRNA that could inhibit tumor metastasis and invasion in HER2+ BC partly by impeding EMT through the repression of the MYC–EZH2 loop.