Late-Stage Downregulation of miR-138-5p Promotes Colorectal Cancer Progression.

Colorectal cancer (CRC) persists as a significant public health burden due to its high morbidity and mortality rates worldwide, yet the molecular events that govern its initiation and progression remain incompletely understood. We recently conducted microRNA (miRNA) profiling and identified multiple dysregulated miRNAs in CRC compared to adjacent normal tissue. Among those, miR-138-5p emerged as a potential tumor suppressor due to its marked downregulation in CRC tissue; however, the stage-specific expression of this miRNA during CRC progression and underlying molecular mechanisms remains to be unraveled. In this study, we performed differential expression profiling of healthy colon, adenomatous polyp (AP), and CRC tissues based on public datasets, revealing significant downregulation of miR-138-5p in CRC compared to controls, but not during the AP stage, suggesting a role in later stages of malignant progression. Forced expression of miR-138-5p in HCT116 and HT-29 CRC models suppressed clonogenic survival, proliferation, and migration while inducing cell death. Additionally, miR-138-5p significantly inhibited tumor formation under three-dimensional culture settings, reinforcing its tumor-suppressive function in a physiologically relevant context. Transcriptomic profiling of miR-138-5p-overexpressing CRC models revealed widespread changes in the pathways related to zinc ion binding, cilium morphogenesis, smoothened signaling, and nuclear transport. Integrated computational and experimental analyses identified 41 potential gene targets, among which