IR-induced BACE-1 mediates cleavage of ST6Gal I, and inhibits sialylation of cell surface molecules and colon cancer cell migration. A. Following irradiation of SW480 and CT26 cells, BACE1 expression levels were determined by RT-PCR and immunoblotting. CT26 vector control cells and cells stably expressing ST6Gal I were exposed to 10 Gy of IR. B. The soluble form of ST6Gal I was analyzed after co-transfection with WT ST6Gal I and BACE1, or after exposure of IR (10 Gy, 48 h) to WT ST6Gal I -transfected cells. C. SW480 and CT26 colorectal carcinoma cell lines were stably transfected with ST6Gal I and exposed to 10 Gy of IR. After 24 hours, culture media were harvested and ST6Gal I activity was assayed by ELISA. Data are presented as means ± SDs from three replicates. CT26 vector control cells and cells stably expressing ST6Gal I were exposed to 10 Gy of IR. After 24, α2,6 sialylation of cell surface was analyzed by flow cytometry. Data are presented as means ± SDs of three replicates. *p < 0.05. n.s., not significant. (D). Cell migration was determined using Transwell migration assays (E). Upper: images of migrated cells captured by phase-contrast microscopy; lower: migration measured by counting cells. Data are presented as means ± SDs of three replicates (*p < 0.05 vs. the corresponding control).