ABSTRACT
N-myc has proapoptotic functions, yet it acts as an oncogene in neuroblastoma. Thus, antiapoptotic mechanisms have to be operative in neuroblastoma cells that antagonize the proapoptotic effects of N-myc. We conditionally activated N-myc in SH-EP neuroblastoma cells subjected to the trophic stress of serum or nutrient deprivation while changing the expression of Bcl-2, survivin and FLIP(L), antiapoptotic molecules often overexpressed in poor prognosis neuroblastomas. Bcl-2 protected SH-EP cells from death during nutritional deprivation by activating energetically advantageous oxidative phosphorylation. N-myc overrode the metabolic protection provided by Bcl-2-induced oxidative phosphorylation by reestablishing the glycolytic phenotype and attenuated the antiapoptotic effect of Bcl-2 during metabolic stress. Survivin partially antagonized the growth suppressive function of N-myc in SH-EP neuroblastoma cells during serum deprivation whereas FLIP(L) did not. These findings advance our understanding of the functions of N-myc in neuroblastoma cells.
Subject(s)
Apoptosis/physiology , Neuroblastoma/metabolism , Oxidative Stress , Proto-Oncogene Proteins c-bcl-2/metabolism , Proto-Oncogene Proteins c-myc/metabolism , Blotting, Western , CASP8 and FADD-Like Apoptosis Regulating Protein/metabolism , Caspase Inhibitors , Caspases/metabolism , Cell Survival/physiology , Culture Media, Serum-Free/pharmacology , Gene Expression Regulation, Neoplastic , Glycolysis , Humans , Inhibitor of Apoptosis Proteins , Microtubule-Associated Proteins/antagonists & inhibitors , Microtubule-Associated Proteins/genetics , Microtubule-Associated Proteins/metabolism , Neoplasm Proteins/antagonists & inhibitors , Neoplasm Proteins/genetics , Neoplasm Proteins/metabolism , Neuroblastoma/genetics , Neuroblastoma/pathology , Phenotype , Phosphorylation , Protein Transport , Proto-Oncogene Proteins c-myc/genetics , RNA, Messenger/genetics , RNA, Messenger/metabolism , Retroviridae/genetics , Reverse Transcriptase Polymerase Chain Reaction , Survivin , Tamoxifen/analogs & derivatives , Tamoxifen/pharmacology , Tumor Cells, CulturedABSTRACT
The death ligand Apo2L/TRAIL (Apo2 ligand/tumor necrosis factor-related apoptosis-inducing ligand) eradicates many tumor types while sparing most normal tissues. However, some tumors are resistant to TRAIL. We therefore determined if TRAIL cooperates with cytosine deaminase/5-fluorocytosine (CD/5-FC) gene therapy and investigated the mechanisms involved. Transfection of human LAN-5 neuroblastoma cells with CD rendered the cells (LAN-5-CD) sensitive to 5-FC-induced, caspase-dependent apoptosis. Mediated by caspase-3, CD/5-FC and TRAIL cooperated to induce apoptosis in these TRAIL-resistant cells and to cleave X-linked inhibitor of apoptosis protein (XIAP). In established LAN-5-CD tumors growing subcutaneously in mice, intratumorally applied TRAIL did not decrease tumor growth and systemically administered 5-FC only attenuated tumor growth. In contrast, 5-FC together with TRAIL dramatically decreased tumor growth and eradicated a tumor. Assuming sufficient gene transfer of CD in situ, CD/5-FC with TRAIL may be useful for the therapy of tumors resistant to TRAIL.
Subject(s)
Cytosine Deaminase/genetics , Flucytosine/pharmacology , Genetic Therapy , TNF-Related Apoptosis-Inducing Ligand/genetics , Animals , Apoptosis/drug effects , Brain Neoplasms , Caspases/metabolism , Cell Division , Cell Line, Tumor , Cloning, Molecular , DNA-Binding Proteins/deficiency , Disease Models, Animal , Escherichia coli/enzymology , Escherichia coli/genetics , Escherichia coli Proteins/genetics , Female , Humans , Mice , Mice, Knockout , Neuroblastoma , Reverse Transcriptase Polymerase Chain ReactionABSTRACT
A modification of the sulfur dioxide (SO2)-exposed rat model proposed by Reid for the study of chronic bronchitis was employed to evaluate mucus retention and cytologic changes. Rats were exposed to from 600 to 700 ppm of SO2 for 3 hours per day, and groups were examined after 0, 9, 18, and 30 hours of cumulative exposure. Tracheal mucus retention and statistically significant increases (two- to four-fold) in the amount of solid material (cellular and mucus) recovered by bronchia lavage developed as a function of exposure time. The increase in bronchial solids was primarily due to inflammatory cells. The goblet cell population in secondary bronchi declined initially, with a significant increase after 30 hours of exposure (P less than .001). The cytologic data provide additional support to Reid's suggestion that the SO2-exposed rat may be considered as a chronic bronchitis model.
