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BAMLET activates a lysosomal cell death program in cancer cells.
Paul Rammer1, Line Groth-Pedersen, Thomas Kirkegaard
1Apoptosis Department and Centre for Genotoxic Stress Response, Institute for Cancer Biology, Danish Cancer Society, Copenhagen, Denmark.
Molecular Cancer Therapeutics
|January 8, 2010
Summary
Bovine alpha-lactalbumin and oleic acid (BAMLET) kills cancer cells by damaging lysosomes. This protein-lipid complex targets tumor cells, offering a new pathway for cancer therapy by inducing lysosomal cell death.
Area of Science:
- Biochemistry
- Cell Biology
- Oncology
Background:
- Human alpha-lactalbumin and oleic acid (HAMLET) is a potent anticancer agent derived from human milk.
- HAMLET and similar protein-lipid complexes kill transformed cells while sparing healthy cells.
- The precise mechanism of cell death induced by these complexes remains largely unknown.
Purpose of the Study:
- To investigate the mechanism by which bovine alpha-lactalbumin and oleic acid (BAMLET) induces cancer cell death.
- To determine if BAMLET utilizes a similar mechanism to HAMLET in its cytotoxic activity.
Main Methods:
- Assessing BAMLET's cytotoxic activity against various cancer cell lines and nontransformed fibroblasts.
- Tracking BAMLET's cellular localization and its effect on the endolysosomal compartment.
- Investigating the role of lysosomal stability proteins (Hsp70, Hsp70-2, LEDGF) and other cellular factors (Bcl-2, caspase, autophagy) in BAMLET-induced cell death.
Main Results:
- BAMLET demonstrated potent cytotoxicity against eight cancer cell lines but was less effective against nontransformed NIH-3T3 fibroblasts.
- BAMLET rapidly accumulated in the endolysosomal compartment of tumor cells, leading to lysosomal membrane permeabilization.
- Leakage of lysosomal cathepsins into the cytosol and subsequent Bax activation were observed.
- Stabilizing proteins of the lysosomal compartment conferred protection against BAMLET, while Bcl-2, caspase inhibition, and autophagy inhibition did not.
Conclusions:
- BAMLET induces cancer cell death through a mechanism involving lysosomal membrane permeabilization and subsequent release of cathepsins.
- This study clarifies that alpha-lactalbumin:oleate complexes can trigger a lysosomal cell death pathway, explaining their efficacy against apoptosis-resistant tumors.
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