Analysis of cytotoxic effect of sialic binding lectin (SBL)on human breast tumor cells

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Si a lic binding lectin from Rana catesbeiana egges (SBL), which kills various tumor cells, belongs to the RNase A super-family. It has been reported that SBL-induced cell death is closely related to its catalytic activity. However, it still remains to be elucidated how SBL induces cell death by its catalytic activity. To clarify the molecular mechanism of SBL-induced cell death, this study focused on the following things ; (1) cellular localization of SBL, (2) activation of cellular proteins induced by the catalytic activity of SBL, (3) the relationship between the activated proteins and cell death induced by SBL. The results showed that SBL was internalized from early endosomes to a perinuclear region, which was independent on its catalytic activity. Furthermore, SBL catalytic activity induced both stress kinases and caspase-3 activation, and then followed by cell death. These results demonstrate the new molecular mechanism of SBL-induced cell death.