miR-526b enhances glucose metabolism in breast cancer cells, an effect reversed by targeting the COX-2/EP4 pathway.

INTRODUCTION: Cancer cells reprogram metabolic pathways to meet energy demands and sustain rapid growth, a hallmark of malignancy. Identifying molecular signatures underlying these changes can aid in early detection and inform targeted therapies. miR-526b has been shown to promote migration, invasion, angiogenesis, and metastasis, yet its role in dysregulated glucose metabolism remains underexplored. METHODS: We used MCF7 (Luminal A) and SKBR3 (HER2-Enriched) breast cancer cell lines, which exhibit distinct metabolic characteristics, to study miR-526b's impact on metabolic marker expression, ATP production, oxygen consumption rate, and extracellular acidification. Cells were treated with glycolysis inhibitor 2 Deoxy-D-Glucose (2DG) or ox-phos inhibitor Oligomycin (OM) to measure dependence on glycolysis or oxidative phosphorylation. Stable transfection was used to overexpress miR-526b in MCF7 and SKBR3 cell lines, and miRNA inhibitors were used to inhibit miR-526b in MCF7-COX2 cells, comparing its effects across subtypes. Targeted inhibition of EP4 with a specific antagonist (EP4A) RQ-15986 (CJ-042794) was done in aggressive MCF7-COX2 cells to test the involvement of COX-2/EP4. RESULTS: SKBR3 exhibits an enhanced glycolytic phenotype, while MCF7 demonstrates increased ox-phos metabolism. Overexpression of miR-526b amplified these inherent metabolic properties, increasing ATP production and proliferation in both cell lines. miR-526b enhanced ox-phos activity in MCF7, reducing sensitivity to glycolysis inhibition, whereas it amplified glycolytic metabolism in SKBR3, reducing sensitivity to ox-phos inhibition. Overexpression of COX-2 in MCF7 replicated the metabolic effects of miR-526b. Inhibition of miR-526b in MCF7-COX2 cells enhances HK2 and GLUT1 expression, but did not significantly alter cell proliferation or cell viability. Targeting the COX-2/EP4 axis with a selective EP4A reversed the transcriptomic changes induced by miR-526b, but did not reduce the increased proliferation observed in MCF7-COX2. CONCLUSION: miR-526b enhances inherent metabolic characteristics of breast cancer cell lines, increasing ATP production, proliferation, and resistance to metabolic inhibitors. Targeting the COX-2/EP4 axis mitigated some of the effects induced by miR-526b, but it did not normalize cell behavior, highlights the complex regulation of glucose metabolism in breast cancer and underscores the need for combination therapy strategies.