Antagonistic effect of OPN on imatinib-induced apoptosis in GIST882 by TUNEL assay. (A) Representative images indicating changes in the number of TUNEL-positive GIST882 tumor cells treated with imatinib (1 μM) with or without OPN administration (2 μg/mL). (Original magnification: ×200). (B) The number of TUNEL-positive tumor cells increased significantly in GIST882 treated with imatinib, whereas their numbers decreased significantly with simultaneous administration of OPN upon imatinib treatment, indicating an in vitro anti-apoptotic effect of OPN in GIST (Columns, mean of results in triplicate; bars, SD. *, P <0.001) . (C) Western blotting analysis of GIST882 cell lines treated with imatinib and/or OPN, corresponding to the treatment used in the TUNEL assay. (D) Quantification of the western blots indicating that significant changes in the expression of anti-apoptotic and apoptotic proteins, in response to OPN in GIST882 cell lines treated with imatinib, were similar to changes in the percentage of apoptotic cells in the TUNEL assay (Columns, mean of results in triplicate; bars, SD. *, P <0.05, one-way ANOVA).