Background: Colorectal Cancer (CRC) remains a major health challenge, with perturbation in the cell cycle playing a crucial role in its progression. Hsa-miR-16-5p (miR-16-5p) is a crucial tumor suppressor, but its precise role in modulating cell cycle genes, particularly in the presence of ionizing radiation, is not fully understood. Objective: This study investigated the role of miR-16-5p in modulating the expression of cell cycle genes in colorectal cancer cells exposed to ionizing radiation. Material and Methods: In this experimental study, HT-29 cells were transfected with miR-16-5p using the polyfectamine transfection reagent. Expression levels of miR-16-5p, Cyclin-Dependent Kinase 4 (CDK4), Cyclin E1 (CCNE1), and Cyclin D1 (CCND1) were quantified by real-time Polymerase Chain Reaction (PCR). To assess the changes after irradiation, cells were exposed to 4 Gy. Results: Ionizing radiation significantly downregulated miR-16-5p compared to controls, while transfection of miR-16-5p significantly increased its expression level. However, irradiation of 4 Gy did not significantly alter CCND1 or CCNE1, but decreased CDK4 expression. The miR-16-5p transfection significantly suppressed CCND1, CCNE1 and CDK4 compared to controls. The expression of CCND1, CCNE1, and CDK4 significantly decreased when miR-16-5p transfection was performed before 4 Gy irradiation compared to both 4 Gy irradiation alone and the control group. Conclusion: Our results highlight the role of miR-16-5p in modulating key cell cycle genes in CRC. Increasing miR-16-5p expression could improve radiosensitivity and represent a therapeutic strategy for the treatment of CRC.

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