Cathepsins and BID are involved in the molecular switch between apoptosis and autophagy in breast cancer MCF-7 cells exposed to camptothecin

The details of molecular switching points between apoptosis and autophagy in tumor cells have still not been fully elucidated. This study focused on the role of cathepsin B and its substrate, BID as molecular links between apoptosis and autophagy in human breast cancer MCF-7 cells exposed to camptothecin. Apoptosis occurred rapidly with a peak in 60 min after drug administration, whereas autophagy developed at a much slower rate with continuous progression during 24 h of cell exposure to the drug. CPT induced very rapid activation of cathepsin B. Inhibition of cathepsins by E64d prevented CPT-induced BAX and BID aggregation on mitochondria and reduced significantly reduced apoptotic cell number. The above effects were accompanied by an increase in autophagosome formation, measured by expression of MAP I LC3. BID knock down resulted in strong suppression of CPT-induced apoptosis and a shift of cell death towards autophagy, manifesting with an increase of Beclin 1 and MAP I LC3 cellular content.