['To investigate the effect of knocking-down microRNA-221 (miR-221) expression on the radiosensitivity of human colorectal carcinoma cells.', 'Human colorectal carcinoma-derived cell line Caco2 was transfected with miR-221 antisense oligonucleotides (anti-miR-221) via Lipofectamine 2000. Real-time quantitative PCR was performed to detect the expression of miR-221 and PTEN mRNA in Caco2 cells. The changes in the protein expression of PTEN in the transfected cells were detected by Western blotting. The cell death after transfection and irradiation was detected by flow cytometry.', 'Transfection with anti-miR-221 caused a significant reduction in miR-221 expression (P<0.05) and up-regulated PTEN protein expression (P<0.05) in Caco2 cells. The percentage of cell death was significantly increased in anti-miR-221 group and anti-miR-221 with irradiation group (P<0.01). Anti-miR-221 significantly enhanced the radiosensitivity of Caco2 cells, which was partially reversed by PTEN-siRNA.'] Does [ Anti-microRNA-221 enhance radiosensitivity of colorectal carcinoma cells by up-regulating PTEN ]?