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Updated: Aug 2, 2025
Profiling of Estrogen-regulated MicroRNAs in Breast Cancer Cells
Published on: February 21, 2014
miRNA-128 and miRNA-223 regulate cholesterol-mediated drug resistance in breast cancer
Gabriella Bianca Henriques Palma1, Mandeep Kaur1
1School of Molecular and Cell Biology, University of the Witwatersrand, Johannesburg, South Africa.
Background:
Breast cancer is the second most common malignancy worldwide and 70% of all breast cancer cases are estrogen receptor-positive (ER+). Endocrine therapy, Tamoxifen (TAM), is a popular treatment for ER+ breast cancer patients; however, despite its success in reducing breast cancer mortality, cancer drug resistance remains a significant challenge. A major contributor to this resistance is the dysregulation of cholesterol homeostasis, where breast cancer cells have elevated cholesterol levels. MicroRNAs (miRNAs) are master regulators of cholesterol-related and cancer drug resistance pathways, and their aberrant expression often confers resistance. Therefore, we aimed to investigate the roles of miRNA-128 and miRNA-223 in cholesterol-mediated TAM resistance.
Methods:
Three breast cancer cell lines were treated with a combination of 1 μM TAM and 10 μM of a cholesterol depleting agent (Acetyl Plumbagin: AP) following transfection with a miR-128 inhibitor or a miR-223 mimic. Cell viability and cholesterol levels were assessed using an MTT assay and fluorescence staining, respectively. In addition, expression levels of several genes and proteins involved in cancer drug resistance and cholesterol homeostasis were also assessed using RT-qPCR and western blotting.
Results:
The combination treatment with altered miRNA expression led to reduced cell viability due to a reduction in free cholesterol and lipid rafts in MCF-7, MDA-MB-231, and long-term estrogen-deprived cells (resistant breast cancer cells). Moreover, reduced miR-128 expression was favoured in all breast cancer cell lines as this alteration lowered the expression of genes involved in cholesterol synthesis and transport, drug resistance, and cell signalling.
Conclusions:
Investigating the gene expression profiles in different breast cancer cell lines was important to elucidate further the molecular mechanisms involved in miRNA-regulated cholesterol homeostasis and cancer drug resistance. Therefore, our findings demonstrated that miR-128 and miR-223 could be potential targets in reducing TAM resistance through the depletion of excess cholesterol.
Insights
MicroRNAs miR-128 and miR-223 can overcome Tamoxifen resistance in breast cancer by reducing cholesterol levels. Targeting these microRNAs offers a new strategy to combat drug resistance in ER+ breast cancer.
Area of Science:
- Oncology
- Molecular Biology
- Biochemistry
Background:
- Breast cancer is a prevalent malignancy, with 70% of cases being estrogen receptor-positive (ER+).
- Tamoxifen (TAM) is a standard endocrine therapy for ER+ breast cancer, but drug resistance is a major clinical challenge.
- Elevated cholesterol levels and dysregulated cholesterol homeostasis contribute significantly to TAM resistance in breast cancer cells, often linked to aberrant microRNA (miRNA) expression.
Purpose of the Study:
- To investigate the role of miR-128 and miR-223 in cholesterol-mediated Tamoxifen (TAM) resistance in breast cancer.
- To explore the potential of modulating these miRNAs to overcome TAM resistance.
Main Methods:
- Breast cancer cell lines were treated with TAM and a cholesterol-depleting agent (Acetyl Plumbagin), with concurrent manipulation of miR-128 and miR-223 expression.
- Cell viability was assessed using MTT assays, and cholesterol levels were measured via fluorescence staining.
- Gene and protein expression related to drug resistance and cholesterol homeostasis were analyzed using RT-qPCR and western blotting.
Main Results:
- Combined treatment with altered miRNA expression reduced cell viability and free cholesterol levels in various breast cancer cell lines, including resistant ones.
- Downregulation of miR-128 was particularly effective, decreasing the expression of genes involved in cholesterol synthesis, transport, drug resistance, and cell signaling.
- Cholesterol depletion and lipid raft reduction were observed in conjunction with altered miRNA expression.
Conclusions:
- miR-128 and miR-223 are implicated in regulating cholesterol homeostasis and mediating Tamoxifen (TAM) resistance in breast cancer.
- Modulating miR-128 and miR-223, alongside cholesterol depletion, presents a promising therapeutic strategy to overcome TAM resistance.
- Further investigation into miRNA-gene expression profiles is crucial for understanding these mechanisms in breast cancer treatment.
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