Cell-Free Extracts from Probiotics Modulate miR-21 and miR-155 and Tumor Suppressors PDCD4 and PTEN in Breast Cancer

As the incidence of breast cancer continues to rise globally, understanding the molecular mechanisms by which probiotics can influence cancer cell behavior is crucial. This research explores the gene regulatory mechanism of potential anti-cancer properties of cell free supernatants derived from Bifidobacterium bifidum and Lactobacillus acidophilus on breast cancer cell lines, including MCF-7 and MDA-MB-231. We utilized a variety of experimental techniques, including MTT assays, BrdU, flow cytometry, evaluation of caspase activity and BAX/BCL-2 ratio, RT-PCR, Western blot analysis, and mimic miRNA transfection, to evaluate apoptosis induction and uncover the involved gene regulatory mechanisms throughout miRNAs. After treating the cells with probiotic supernatants for 48 hours at concentrations between 0.5 and 40 µg/ml, we observed a significant induction of apoptosis in both cell lines. Our investigation centered on four oncomiRs: miR-21-5p, miR-155-5p, miR-150-5p, and miR-223-3p, revealing notable changes in the levels of miR-155-5p and miR-21-5p. Further analysis indicated that the supernatants increased the expression of their target genes, PDCD4 and PTEN, which are essential for regulating apoptosis as tumor suppressor factors. we confirmed this gene regulatory properties by transfection of mimic miR-21-5p and miR-155-5p, the anticipated increase in these proteins was less pronounced in transfected cells. This finding suggests that probiotics can effectively downregulate certain oncomiRs and enhance their target tumor suppressor genes and protein levels. the down-regulation of oncomiRs may display positive effects of probiotics, leading to inhibition of tumor growth and anti-proliferative outcomes. Our results emphasize the intricate relationships among probiotics, miRNAs, and tumor suppressor proteins, highlighting their potential significance in cancer treatment. This study calls for further exploration of these interactions to develop improved therapeutic strategies for breast cancer through the modulation of cellular pathways by probiotics.