Cross-talk Between Autophagy And Apoptosis In Crotoxin-induced Death Of K562 And MCF-7 Cells

Objective: To study the cross-talk between autophagy and apoptosis in crotoxin-induced death of K562 (with high constutive tyrosine kinase activity) and MCF-7 (with no caspase-3 activity) cells and the mechanism involved in it. Methods: MTT assay and LDH leakage were used to select sensitive tumor cell lines and to determine inhibitory effects of crotoxin after various inhibitors were added. MDC staining and TEM were applied to identify autophagy, apoptosis and ultrastructural changes after crotoxin treatment. ApoAlert? kit, western blot analysis and immunofluorescence were used to study the mechanism involved in apoptotic and autophagic death of K562 and MCF-7 cells.Results: The proliferation of K562 and MCF-7 was inhibited as well as autophagy and apoptosis were induced after crotoxin treatment. Caspase inhibitors attenuated crotoxin-induced death of K562 cells. Inhibition of autophagy by 3-methyladenine (3-MA) and NH₄Cl potentiated crotoxin's cytotoxicitiy in K562 cells, whereas it reduced crotoxin-induced death of MCF-7 cells. And more, in K562 cells, mitochondrial membrane potential collapsed and cyto-c release was induced after crotoxin treatment and activation of caspase-3 was accelerated when pretreated with 3-MA. In MCF-7 cells, AIF nuclear localization and increased protein levels of cathepsin B, D, L were also found following crotoxin administration. Conclusions: Autophagy and apoptosis have differential contribution to crotoxin-induced death of K562 and MCF-7 cells. An apoptotic mechanism is a leading cause of death of K562 cells, while an autophagic mechanism is a main contributor to death of MCF-7 cells induced by crotoxin. There is a mutual regulation between apoptosis and autophagy in death signaling process mediated by mitochondria.