These results suggest that p53 levels are intimately related to an undifferentiated phenotype in neuroblastoma cells and support studies which relate p53 levels to the malignant phenotype in other tumor systems.
Our findings suggest that mutations of the p53 gene in ES might represent late genetic events related to tumor progression, and that aberrations of the p53 gene might not be involved in the development or the progression of NB.
This finding suggests that p53 mutations do not contribute to the etiology of neuroblastoma and that the chromosome 17 alterations observed in neuroblastoma involve genes which are distinct from the p53 locus.
We have concluded that although p53 expression in neuroblastoma cells is primarily localized to the cytosol, ionizing radiation induces a functional p53 protein in the nucleus and that this cytoplasmic sequestration of p53 in human neuroblastoma is not a mechanism of inactivating p53 function.
The in situ expression of Bcl-2, Rb, p21, p53 and Bax proteins, as well as the proliferation marker proliferating cell nuclear antigen (PCNA) were examined immunocytochemically in a selection of 38 stage- and outcome-identified NB tumours.
However, the demonstration that p73 is monoallelically expressed supports the notion that it is a candidate gene in neuroblastoma. p73 also has the potential to activate p53 target genes and to interact with p53.
In human neuroblastoma SH-SY5Y cells, S-nitroso-N-acetylpenicillamine (SNAP), a nitric oxide (NO)-donor, caused cell death accompanying p53 expression, nucleosomal DNA fragmentation and cell death.
The novel p73 gene is a structural and, in overexpression systems, functional p53 homologue. p73 resides on chromosome 1p36.33 within a commonly deleted region in neuroblastoma (NB) and other human tumors.
Differentiation between benign and malignant tumors of the adrenal cortex was attempted by microdissection of nine cases of adrenal cortical hyperplasia, 10 cortical adenomas, and 18 adrenal cortical carcinomas with subsequent polymerase chain reaction (PCR) amplification for loss of heterozygosity (LOH) of five microsatellites of putative tumor suppressor gene loci: p53 gene (17p), the neuroblastoma candidate gene (1p), the p16 gene (9p), the von Hippel Lindau gene (3p), and the retinoblastoma gene (13q).
Our data, therefore, suggest that the p53 protein may be differentially regulated by a neuronal cellular environment and that the sequestration of p53 in NB may be reversible.
A novel gene, termed p73, encodes a protein with a significant homology to p53 and has been mapped at chromosome 1p36.3, which is a locus of multiple suppressor genes for tumors including neuroblastoma and other cancers.
Although wild-type p53 is expressed in virtually all neuroblastoma tumors, treatment failures secondary to inadequate local control with radiotherapy are a problem in patients with advanced stage disease.
p73, a novel p53 family member, is a recently identified candidate neuroblastoma (NBL) suppressor gene mapped at chromosome 1p36.33 and was found to inhibit growth and induce apoptosis in cell lines.
This report also demonstrates that the cytoplasmic localization of p53 in neuroblastoma cells is due to its hyperactive nuclear export: p53 in these cells can be trapped in the nucleus by the export-inhibiting drug leptomycin B or by binding a p53-tetramerization domain peptide that masks the NES.
The tumor suppressor protein p53 is aberrantly localized to the cytoplasm of neuroblastoma cells, compromising the suppressor function of this protein.
Using NB cell lines as a model system to test this hypothesis, we demonstrated that the introduction of HPV E6 into two NB cell lines resulted in p53 insensitivity to HPV E6-mediated degradation.
These results suggest that molecules that efficiently disrupt GR-p53 interactions would have a therapeutic potential for the treatment of neuroblastoma and perhaps other diseases in which p53 is sequestered by GR.
This IRES was active in most transiently transfected human and nonhuman cell types, with a higher activity in p53 -/- osteosarcoma and neuroblastoma cell lines.