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MiR-99b-5p inhibition drives apoptosis and tumor shrinkage in triple-negative breast cancer: Functional characterization through AGO2-RIP-seq and mechanistic insights

ABSTRACT: Background: Dysregulated microRNAs (miRNAs) are critical contributors to breast cancer biology, yet the functional roles of many remain incompletely understood. miR-99b-5p has been widely characterized as a tumor-suppressive miRNA in numerous cancer types, where its expression is consistently reduced in tumors compared with normal tissues. In contrast, our analyses of breast cancer datasets revealed a unique expression pattern: miR-99b-5p is significantly upregulated in breast tumors, suggesting a context-dependent oncogenic function. In this study, we identified miR-99b-5p as an oncogenic driver in triple-negative breast cancer (TNBC). Methods and Results: TCGA-based expression profiling confirmed its elevated levels in breast tumors. Functional assays demonstrated that downregulation of miR-99b-5p in TNBC cells inhibits proliferation and induces apoptosis, indicating a critical role in sustaining tumor cell survival. To elucidate the molecular mechanisms underlying this activity, we performed AGO2-RNA immunoprecipitation followed by high-throughput sequencing (AGO2-RIP-Seq), enabling unbiased identification of miR-99b-5p-associated transcripts. Pathway enrichment analyses revealed that its direct targets converge on apoptotic regulation, cell-cycle control, and ubiquitin-mediated protein degradation. Mechanistic validation through qRT-PCR, Western blotting, and luciferase assays confirmed that miR-99b-5p modulates the TRAIL-R signaling pathway via DR5 and BAK, attenuating apoptotic signaling. In vivo studies using xenograft models established with MDA-MB-231 cells stably expressing miR-99b-5p knockdown showed marked tumor regression, further supporting its oncogenic role. Conclusion: Collectively, these findings establish miR-99b-5p as a context-specific oncogenic miRNA in breast cancer and a promising therapeutic target, particularly for TNBC, where targeted treatment options remain limited.

ORGANISM(S): Homo sapiens

PROVIDER: GSE321682 | GEO | 2026/03/20

REPOSITORIES: GEO

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Project description:Background: Rosmarinic acid (RA), a natural phenolic acid, exhibits promising anti-cancer properties. The abnormal expression of microRNA (miRNA) regulates the gene expression and plays a role as an oncogenic or tumor suppressor in TNBC. However, the biological role of RA in miR-30a-5p on BCL2L11 during MDA-MB-231 induced breast cancer stem-like cells (BCSCs) progression and its regulatory mechanism have not been elucidated. Objective: To investigate whether RA inhibited the silencing effect of miR-30a-5p on the BCL2L11 gene and promoted apoptosis in BCSCs. Materials and Methods: We assessed the migration, colony formation, proliferation, cell cycle, and apoptosis of BCSCs after RA treatment using the wound-healing assay, colony formation assay, CCK-8 assay, and flow cytometry, respectively. The expression of mRNA and protein levels of BCL-2, Bax, BCL2L11, and P53 genes in BCSCs after RA treatment was obtained by real-time polymerase chain reaction and Western blot. Differential miRNA expression in BCSCs was analyzed by high-throughput sequencing. Targetscan was utilized to predict the targets of miR-30a-5p. The dual luciferase reporter system was used for validation of the miR-30a-5p target. Results: Wound-healing assay, colony formation assay, CCK-8 assay, and cell cycle assay results showed that RA inhibited migration, colony formation and viability of BCSCs, and cell cycle arrest in the G0-G1 phase. At the highest dose of RA, we noticed cell atrophy, while the arrest rate at 100 μg/mL RA surpassed that at 200 μg/mL RA. Apoptotic cells appeared early (Membrane Associated Protein V FITC+, PI-) or late (Membrane Associated Protein V FITC+, PI+) upon administration of 200 μg/mL RA, Using high-throughput sequencing to compare the differences in miRNA expression, we detected down-regulation of miR-30a-5p expression, and the results of dual luciferase reporter gene analysis indicated that BCL2L11 was a direct target of miR-30a-5p. Conclusion: RA inhibited the silencing effect of miR-30a-5p on the BCL2L11 gene and enhanced apoptosis in BCSCs. Keywords Apoptosis; miR-30a-5p; BCSCs; Rosmarinic acid; Triple-negative breast cancer

Project description:Triple negative breast cancer (TNBC) is an aggressive breast cancer subtype that promotes higher risk of metastasis and cancer reoccurrence, subsequently reduces survival rate of cancer patients. Cisplatin is one of the potential anticancer drugs for treating TNBC. However, occurrence of cisplatin resistance still remains as one of the challenges to fully eradicate TNBC. Since presence of cancer stem cells (CSCs) often known as one of the contributors of drug resistance, investigation has been conducted, suggesting sorted CSC-like subpopulation to be more resistant to cisplatin as compared to parental cells, alongside with higher self-renewability. On the other hand, plethora evidences showed the transmission of exosomal-miRNAs are capable of promoting drug resistance in breast cancers. In this study, we aim to elucidate the differential expression of exosomal-microRNAs profile and reveal the potential target genes in correlation to cisplatin resistance associated with CSC-like subpopulation by using TNBC cell line (MDA-MB-231). Utilizing next generation sequencing and Nanostring techniques, cisplatin-induced dysregulation of exosomal-miRNAs were evaluated in maximal for CSC-like subpopulation as compared to parental cells. Intriguingly, cisplatin induced a relatively oncogenic exosomal-miRNAs profile derived from treated CSC-like subpopulation as compared to treated parental cells, which may correlate to enhancement of drug resistance and maintenance of CSCs. Among the detected exosomal-miRNA profile in treated CSC-like subpopulation, unique clusters of miRNAs namely miR-221-3p, miR-196a-5p, miR-17-5p and miR-126-3p were predicted to target on six genes (ATXN1, LATS1, GSK3β, ITGA6, JAG1 and MYC), aligned with previous finding which demonstrated dysregulation of these genes in treated CSC-like subpopulation. Our results highlight the potential correlation of exosomal-miRNAs and their target genes as well as novel perspectives of the corresponding pathways that may be essential to contribute to the attenuated cytotoxicity of cisplatin in CSC-like subpopulation.

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MiR-99b-5p inhibition drives apoptosis and tumor shrinkage in triple-negative breast cancer: Functional characterization through AGO2-RIP-seq and mechanistic insights

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