Isoform-Specific Transcriptomic Effects of miR-133A1, miR-133A2, and miR-133B in a Colorectal Cancer Cell Line

Background: MicroRNA-133 (miR-133) has been implicated in diverse cancers as a tumor suppressor, yet the isoform-specific contributions of miR-133A1, miR-133A2, and miR-133B in colorectal cancer (CRC) remain unclear. Methods: We established stable colorectal cancer cell lines expressing each miR-133 isoform and performed isoform-level transcriptomic profiling. Differentially expressed genes (DEGs) were identified relative to parental cells and subjected to gene ontology (GO) and KEGG enrichment analyses. Comparative analyses highlighted both shared and distinct biological pathways regulated by each isoform. Results: Venn diagram and clustering analyses revealed that all three isoforms shared a core regulatory program, with 34 genes consistently upregulated and 195 genes downregulated across all isoforms, while also displaying isoform-specific DEGs. miR-133A1, miR-133A2, and miR-133B showed predominantly convergent transcriptional programs, with subtle quantitative differences observed primarily in KI133B. Heatmap analysis of representative genes confirmed both overlapping and isoform-specific expression changes, with survival- and proliferation-associated genes more strongly upregulated in miR-133A2 and miR-133B. Conclusion: These findings suggest that miR-133 isoforms exert both shared and subtly divergent regulatory functions in colorectal cancer, coordinating apoptosis, proliferation, migration, and signaling network modulation. Isoform-specific transcriptional regulation of miR-133 may contribute to tumor progression and represents a potential biomarker and therapeutic target in CRC.