seocalcitol and 3-methyladenine

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.

Topics: Adenine; Antineoplastic Agents; Apoptosis Regulatory Proteins; Autophagy; Beclin-1; Breast Neoplasms; Cadaverine; Calcitriol; Cathepsins; Cell Death; Cell Growth Processes; Cell Line, Tumor; Cryoelectron Microscopy; Drug Interactions; Genes, Tumor Suppressor; HeLa Cells; Humans; Immunoblotting; Membrane Proteins; Proteins; RNA, Small Interfering; Transfection; Tumor Cells, Cultured; Tumor Necrosis Factor-alpha