Retroviral transfer of the ?-nerve growth factor gene into murine neuroectodermal tumor cells modulates cell proliferation rate, neurite formation, and NGF binding site expression

The role of nerve growth factor in caspase-dependent apoptosis in human BE(2)C neuroblastoma

PURPOSE

The purpose of the study was to determine if nerve growth factor (NGF) stimulation induces apoptosis in the BE(2)C neuroblastoma cell line in vitro.

METHODS

The LPCX retroviral vector was used to achieve stable transduction of NGF complementary DNA into BE(2)C neuroblastoma cells. Wild-type and NGF-transduced cells were then incubated with varying concentrations of NGF for varying periods. A laddering assay was performed to determine the presence of DNA fragments characteristic of apoptosis. The expression of various cleaved and total caspases was determined by Western immunoblotting.

RESULTS

p75 receptor expression in the NGF-transduced cell line was equivalent to that in the wild-type cell line, but Trk A receptor expression was significantly decreased in BE(2)C-NGF cells. DNA laddering assay demonstrated that only BE(2)C-NGF cells underwent apoptosis after stimulation with exogenous NGF. BE(2)C-NGF cells have increased expression of cleaved caspase-3 when compared with wild-type cells. Cleaved caspase-3 expression is further increased with exogenous NGF stimulation in the transduced cells.

CONCLUSION

This study confirms that NGF stimulation of BE(2)C neuroblastoma cells can induce apoptosis through activation of the caspase cascade in vitro. The differential expression of the receptors Trk A and p75 between the wild-type and NGF-transduced cell lines may explain the differing effects observed.

Down-regulation of growth factor-stimulated MAP kinase signaling in cytotoxic drug-resistant human neuroblastoma cells

The mitogen-activated protein kinase (MAPk) signaling pathway, which plays a critical role in the proliferation of mammalian cells, is frequently up-regulated in human tumors and may contribute to the transformed phenotype. Since a major limitation of current cancer chemotherapy is prevalent resistance to cytotoxic drugs, this study determined whether alterations in growth factor signaling through MAPk may contribute to this phenomenon in human neuroblastoma cell lines. Drug-resistant SKNSH cell lines were established by long-term incubation with increasing concentrations to 10(-6) M doxorubicin (SKNSH rDOX6) or MDL 28842 (SKNSH rMDL6). The expression of epidermal growth factor receptor (EGFR) and epidermal growth factor (EGF)-induced EGFR tyrosine phosphorylation were lower in drug-resistant SKNSH cells than their wild-type counterparts. In SKNSH rDOX6 cells, decreased activation and reduced nuclear translocation of MAPk in response to EGF, or lysophosphatidic acid (LPA), or phorbol 12-myristate 13-acetate (PMA), were observed. In SKNSH rMDL6 cells, although MAPk could be activated to wild-type levels by ligand stimulation, the translocation of active MAPk to the nucleus was also reduced. These results suggest that resistance to cytotoxic drugs in human neuroblastoma cell lines is associated with a decrease in growth factor signaling through the MAPk pathway.