Abstract
A chemotherapeutic vitamin D analogue, EB1089, kills tumor cells via a caspase-independent pathway that results in chromatin condensation and DNA fragmentation. Employing transmission- and immunoelectronmicroscopy as well as detection of autophagosome-associated LC3-beta protein in the vacuolar structures, we show here that EB1089 also induces massive autophagy in MCF-7 cells. Interestingly, inhibition of autophagy effectively hindered apoptosis-like nuclear changes and cell death in response to EB1089. Furthermore, restoration of normal levels of beclin 1, an autophagy-inducing tumor suppressor gene that is monoallelically deleted in MCF-7 cells, greatly enhanced the EB1089-induced nuclear changes and cell death. Thus, EB1089 triggers nuclear apoptosis via a pathway involving Beclin 1-dependent autophagy. Surprisingly, tumor cells depleted for Beclin 1 failed to proliferate suggesting that even though the monoallelic depletion of beclin 1 in human cancer cells suppresses EB1089-induced autophagic death, one intact beclin 1 allele is essential for tumor cell proliferation.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Adenine / analogs & derivatives
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Adenine / pharmacology
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Antineoplastic Agents / pharmacology*
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Apoptosis Regulatory Proteins
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Autophagy / drug effects
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Beclin-1
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Breast Neoplasms / drug therapy*
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Breast Neoplasms / genetics
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Breast Neoplasms / metabolism
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Breast Neoplasms / pathology
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Cadaverine / analogs & derivatives
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Cadaverine / pharmacokinetics
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Calcitriol / analogs & derivatives*
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Calcitriol / antagonists & inhibitors
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Calcitriol / pharmacology
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Cathepsins / metabolism
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Cell Death / drug effects
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Cell Death / physiology
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Cell Growth Processes / drug effects
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Cell Growth Processes / physiology
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Cell Line, Tumor
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Cryoelectron Microscopy
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Drug Interactions
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Genes, Tumor Suppressor
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HeLa Cells
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Humans
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Immunoblotting
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Membrane Proteins
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Proteins / genetics
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Proteins / metabolism
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Proteins / physiology*
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RNA, Small Interfering / genetics
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Transfection
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Tumor Cells, Cultured
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Tumor Necrosis Factor-alpha / pharmacology
Substances
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Antineoplastic Agents
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Apoptosis Regulatory Proteins
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BECN1 protein, human
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Beclin-1
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Membrane Proteins
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Proteins
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RNA, Small Interfering
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Tumor Necrosis Factor-alpha
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3-methyladenine
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Cathepsins
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Calcitriol
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monodansylcadaverine
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Adenine
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Cadaverine
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seocalcitol