The six apoptosis inducing nucleosides (AINs), which were isolated by high performance liquid chromatography from CD57+HLA-DRbright natural suppressor (57.DR-NS) cell cultures, induced apoptosis in human gastric carcinoma (GCIY) cells demonstrating the accumulation of sub-G1 DNA content and morphological changes. By means of DNA unwinding assay, it has been revealed that DNA strand breaks were initially involved in the apoptotic cell death of GCIY cells treated with AINs followed by activation of caspase cascades, especially caspase-3. Actually, the cleavage of fluorogenic substrate for caspase-3 was identified in the reaction. Whereas, the addition of caspase-3 inhibitor into the reaction prevented the cleavage of fluorogenic substrate for caspase-3 and resulted in the blockage of the sub-G1 DNA accumulation and DNA fragmentation as apoptotic signals. Thus, it was definitely elucidated that the activation of caspase-3 displayed a key feature during AIN-induced apoptosis in GCIY cells.

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