| Abstract: |
Peripheral-type benzodiazepine receptors (PBR) are constituted by three protein components, the isoquinoline binding protein (IBP), the voltage-dependent anion channel (VDAC), and the adenine nucleotide transporter (ANT). Recently, we found that high levels of PBR ligand binding in glioma cell lines correlate with in vitro tumorigenicity. To study whether enhanced PBR expression is causative or in response to cancer, we genetically modified C6 glioma cells. Antisense knockdown of the IBP resulted in more than 50% reductions in PBR ligand binding both in the mitochondrial and whole cell fractions, accompanied by similar reductions in IBP levels in these respective fractions. The IBP knockdown was accompanied by a 25% increase in cell number in confluent cultures. This correlated with an 8-fold increase in in vitro tumorigenicity, as assessed by anchorage independent growth. Cell cycle analysis indicated that knockdown of the IBP resulted in a 60% reduction in the number of cells in the pre-G1 apoptosis phase. This paralleled the reduction seen in apoptosis and cell death shown by DNA fragmentation and Trypan blue assays, respectively. Furthermore, knockdown of the IBP appeared to prevent induction of apoptosis by the antineoplastic agent, erucylphosphocholine. In addition, IBP knockdown prevented processing of the caspase 3 component of the apoptosis cascade by the erucylphosphocholine congener, erucylphospho-N,N,N- trimethylammonium. In conclusion, our results suggest that enhanced IBP expression, including enhanced PBR ligand binding, such as occurring in untreated C6 glioma cells, may provide a mechanism to increase apoptotic rates of cancer cells. © 2005 American Chemical Society. |
| Keywords: |
controlled study; protein expression; unclassified drug; nonhuman; antineoplastic agent; proteins; animal cell; animals; cell death; cell cycle; apoptosis; genes; dna, antisense; caspase 3; in vitro study; caspases; cell line, tumor; transfection; blotting, western; dna; dna modification; protein processing, post-translational; tumors; glioma cell; bioassay; carrier proteins; rat; carcinogenicity; binding protein; cell count; rats; anchorage independent growth; clone cells; ligand binding; mitochondrion; cancer cells; dna fragment; phosphorylcholine; cells; benzodiazepine receptor; receptors, gaba-a; trypan blue; cell cycle analysis; glioma cells; peripheral-type benzodiazepine receptors (pbr); adenine nucleotide translocase; anion channel; erucylphospho n,n,n trimethylammonium; erucylphosphocholine; isoquinoline; isoquinoline binding protein; trimethylammonium salt derivative
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