N-Myc overexpression leads to decreased beta1 integrin expression and increased apoptosis in human neuroblastoma cells.
Neuroblastoma is a childhood tumor thought to arise through improper differentiation of neural crest cells. Increased N-Myc expression in neuroblastoma indicates highly malignant disease and poor patient prognosis. N-myc enhances cell growth, insulin-like growth factor type I receptor (IGF-IR) expression, and tumorigenicity in combination with Bcl-2. Despite these effects, N-Myc overexpression in SHEP neuroblastoma cells (SHEP/N-Myc cells) increases serum-withdrawal and mannitol-induced apoptosis. Although we have previously shown a protective effect of IGF-I in SHEP cells, in SHEP/N-Myc cells IGF-I rescue from mannitol-induced apoptosis is prevented. N-Myc overexpression has little effect on IGF-IR signaling pathways, but results in increased Akt phosphorylation when Bcl-2 is coexpressed. A loss of integrin-mediated adhesion promotes apoptosis in many systems. SHEP/N-Myc cells have dramatically less beta1 integrin expression than control cells, consistent with previous reports. beta1 integrin expression is decreased in more tumorigenic neuroblastoma cells lines, including IMR32 and SH-SY5Y cells. Reintroduction of beta1 integrin into the N-Myc-overexpressing cells prevents mannitol-mediated apoptosis. We speculate that N-Myc repression of beta1 integrin expression leads to a less differentiated phenotype, resulting in increased growth and tumorigenesis if properly supported or apoptosis if deprived of growth sustaining molecules.
Department of Neurology, University of Michigan, Ann Arbor, MI 48109-0588, USA.
Cynthia M
CM
van Golen
Mary E
ME
Soules
Alyssa R
AR
Grauman
Eva L
EL
Feldman
D017209:Apoptosis / Q000502:physiology*; D006801:Humans; D066298:In Vitro Techniques; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D019012:Integrin beta1 / Q000235:genetics / Q000378:metabolism*; D008353:Mannitol / Q000378:metabolism; D009447:Neuroblastoma / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*; D014407:Tumor Cells, Cultured
D019012:Integrin beta1; D019253:Proto-Oncogene Proteins c-bcl-2; D016271:Proto-Oncogene Proteins c-myc; D008353:Mannitol; D007334:Insulin-Like Growth Factor I