Mirtron Overexpression Drives Immune Modulation and Tumor Progression Through Macrophage Polarization and Oncogenic Pathway Regulation 2309835

Abstract Introduction 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. Methods 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. Results 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. Conclusion 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. Funding Source NIGMS (R16GM153648) Topic Categories Tumor Immunology: Cellular Responses and Tumor Microevironment (TIME)