Despite advances in treatment, invasive breast cancer remains among the deadliest cancers in women, driven by limited therapeutic options that precisely target their molecular drivers. Mirtrons, an emerging class of intron-derived microRNAs, may represent unrecognized regulators of tumor progression and invasion. This study examines how mirtron-5010 influences cancer stemness and iron accumulation in triple negative MDA-MB-231 breast cancer.
MDA-MB-231 bulk and stem cell populations were engineered to upregulate mirtron-5010. Classical stemness markers (SOX2, OCT4, NANOG, and KLF4) as well as the regulatory subunit PPP2R2D, were analyzed using quantitative PCR and immunohistochemistry. Intracellular iron levels were measured using FerroOrange fluorescence quantification.
Across bulk cultures, mirtron-5010 upregulation elevated SOX2, OCT4, and NANOG expression, indicating enhanced stem-like characteristics. When looking into tumor stem cell population, mirtron-5010 upregulation further increased SOX2 and NANOG expression. Consistent with this, both bulk and tumor stem cells with mirtron-5010 upregulation showed greater labile iron pool determined by FerroOrange fluorescence, signifying an altered preference in iron metabolic pathways than controls. Interestingly, the subunit PPP2R2D of the PP2A enzyme complex was downregulated in mirtron-5010 upregulated cells.
In conclusion, mirtron-5010 enhances stemness and promotes iron accumulation in invasive breast cancer cells, highlighting its potential as a molecular target for therapy-resistant subtypes. Through modulation of the PP2A enzyme complex, mirtron-5010 also dampens IL-2—driven T-cell activation and proliferation, suggesting a role in shaping the tumor immune microenvironment. Future studies will further delineate the functional consequences of mirtron-5010 expression in both cancer and immune cell contexts across diverse breast cancer models.
NIGMS (R16GM153648)
Tumor Immunology: Cellular Responses and Tumor Microevironment (TIME)
Reagan Farrell, Noah Padilla, A. Ruíz et al.· Journal of Immunology· 0 citations
Mirtrons, a specialized subclass of intron-derived microRNAs (miRNAs), bypass canonical Drosha-dependent processing by undergoing splicing and debranching to form pre-miRNA hairpins directly processed by Dicer. This alternative pathway imparts high structural stability and resistance to exonucleolytic degradation, supporting their persistence in the tumor microenvironment. This study investigates the expression of specific human mirtrons and their influence on macrophage proliferation and polarization within cancer-associated conditions.
Human cancer cell lines (T47D, MDA-MB-231, PC-3, and MCF-7) and normal HEK cells were cultured to assess mirtron expression. Quantitative RT-PCR was performed to measure levels of human mirtrons such as miR-5010, miR-1228, miR-1224, miR-6756, miR-7110, and uc002mxv.2. Exosomes isolated from mirtron-overexpressing cancer cells were co-cultured with THP-1 and U937 macrophage models. Cell proliferation assays evaluated macrophage growth following exposure, while qRT-PCR quantified polarization markers to distinguish M1 and M2 phenotypes.
All tested mirtrons showed marked overexpression in cancer cell lines relative to normal HEK controls. Exosome-mediated delivery of these mirtrons to macrophages significantly reduced proliferation rates. Expression analysis revealed downregulation of M1-associated markers (TNFα, IL-6, ARG2) and upregulation of M2-associated markers (CD206, IL-10, TGFβ), indicating polarization toward an immunosuppressive phenotype.
These results suggest that mirtrons modulate macrophage fate through post-transcriptional regulation of inflammatory pathways, linking RNA processing mechanisms to tumor—immune crosstalk. Their overexpression in cancer cells promotes M2 macrophage polarization and suppresses macrophage proliferation, thereby supporting immune evasion and tumor progression. These findings highlight mirtrons as potential diagnostic biomarkers and RNA-based therapeutic targets in molecular oncology.
NIGMS (R16GM153648)
Tumor Immunology: Cellular Responses and Tumor Microevironment (TIME)
Md Shakil Ahmed Khan, K. Chen· Journal of Immunology· 0 citations
Immunofluorescence imaging demonstrated that mirtrons carried by tumor-derived exosomes are taken up by human monocyte U937 cells and are predominantly localized to the cytoplasm, consistent with the behavior of conventional miRNAs.
Mei Li, Arya Sreenivas, Santosh Poudel et al.· Journal of Immunology· 0 citations