Discovering the Biological Significance and Therapeutic Potential of miR-29b-3p in Triple-Negative Breast Cancer

The lack of estrogen or progesterone receptors and absence of HER2 amplification/overexpression in triple-negative breast cancer (TNBC) restricts therapeutic options used in clinical management. MicroRNAs (miRNAs) are small, non-coding transcripts which affect important cellular mechanisms by regulating gene expression at the post-transcriptional level. Among this class, attention was focused on miR-29b-3p with a high profile in TNBC and correlated with the overall survival rates, as TCGA data revealed. This study aims to investigate the implication of the miR-29b-3p inhibitor in TNBC cell lines by identifying a potential therapeutic transcript, improving the clinical outcomes of this disease. The experiments were performed on two TNBC cell lines (MDA-MB-231 and BT549) as in vitro models. An established dose of 50 nM was used for all functional assays performed on the miR-29b-3p inhibitor. A decreased level of miR-29b-3p determined a significant reduction in cell proliferation and colony-forming capacity. At the same time, the changes occurring at the molecular and cellular levels were highlighted. We observed that, when inhibiting the expression level of miR-29b-3p, processes such as apoptosis and autophagy were activated. Further, microarray data revealed that the miRNA expression pattern was altered after miR-29b-3p inhibition, pointing out 8 overexpressed and 11 downregulated miRNAs specific for BT549 cells and 33 upregulated and 10 downregulated miRNAs that were specific for MDA-MB-231 cells. As a common signature for both cell lines, three transcripts were observed, two downregulated, miR-29b-3p and miR-29a, and one upregulated, miR-1229-5p. According to DIANA miRPath, the main predicted targets are related to ECM (extracellular matrix) receptor interaction and TP53 signaling. An additional validation step through qRT-PCR was performed, which showed an upregulation of MCL1 and TGFB1. By inhibiting the expression level of miR-29b-3p, it was shown that complex regulatory pathways targeted this transcript in TNBC cells.

Automated summary

The lack of estrogen or progesterone receptors and absence of HER2 amplification/overexpression limit treatment options for triple-negative breast cancer (TNBC). MicroRNAs (miRNAs), particularly miR-29b-3p, have been of interest for TNBC and correlated with overall survival rates. This study explored the potential therapeutic effects of miR-29b-3p inhibition in TNBC cell lines, observing decreased cell proliferation, activation of apoptosis and autophagy, and altered miRNA expression patterns. Target analysis revealed ECM receptor interaction and TP53 signaling as the main predicted targets, with additional validation showing upregulation of MCL1 and TGFB1.