Abstract
Progress in molecular medicine has resulted in novel cancer therapies, with microRNAs (miRNAs) recognized as promising instruments for cancer detection and treatment. MicroRNAs are tiny non-coding RNA sequences that manipulate gene expression at the post-transcriptional stage and are involved in cellular differentiation and death. miR-32-5p demonstrates oncogenic activity in several cancers, while c-MYC oncogene is a well-known driver of cancer, promoting tumor growth by stimulating cell proliferation, blocking apoptosis, and suppressing immune responses. This study aimed to examine how inhibiting miR-32-5p affected the behavior of breast tumor cells (MCF-7), particularly focusing on changes in cellular apoptosis and proliferation, and to investigate its relationship with c-MYC expression. A locked nucleic acid (LNA)-based inhibitor was used to knock down miR-32-5p in MCF-7 breast cancer cells. Cell viability was assessed using MTT assays at 24, 48, and 72 h post-transfection. Apoptotic and necrotic cell populations were differentiated using Annexin-V labeling with Propidium iodide. Expression levels of miR-32-5p and c-MYC were evaluated using quantitative Real-Time PCR before and after transfection with the miR-32-5p inhibitor. Inhibition of miR-32-5p significantly reduced MCF-7 cell viability at 48 h post-transfection (P < 0.002) and increased apoptotic cells to approximately 17% (vs. 0.3% in controls, P < 0.05), concomitant with significant downregulation of c-MYC mRNA (P < 0.006). The lowest level of miR-32-5p expression was observed at 48 h following transfection, with levels gradually increasing by 72 h. This study is the first to demonstrate a plausible regulatory relationship between miR-32-5p and c-MYC in breast tumor cells. The significant reduction in cell viability and increase in apoptosis following miR-32-5p inhibition, likely mediated through c-MYC downregulation, suggests a plausible pathway that may be targeted for therapeutic intervention in breast cancer.