We have previously shown that p73 isoforms are deregulated in NB tumours and that TAp73 co-operates synergistically with p53 for apoptosis of NB cells, whereas DeltaNp73 activates the expression of neuronal differentiation genes such as BTG2.
We concluded that it is unlikely that p73 is imprinted in neuroblastoma and that the methylation-dependent silencing of this gene, thus far, is a characteristic of hematologic malignancies.Oncogene (2000) 19, 4553 - 4556.
We analyzed tp73 expression in 95 sporadic neuroblastoma samples by RT-PCR and we detected the tp73 transcript in 46 cases (48.4%), without significant correlation with age, clinical stage or 3-year overall survival.
The p63 and p73 genes are rarely mutated in human cancer, although p73 loss is observed in neuroblastoma and a subtype of T-cell lymphoma. p53, p63 and p73 appear to have overlapping and distinct functions: p53 regulates the stress response to suppress tumors; p63 is essential for ectoderm development; and p73 might regulate both the stress response and development.
The p53 family proteins, p73 and p63, can also induce apoptosis, and early studies suggest that p73 may be important in neuroblastoma pathogenesis and response to treatment.
The N-myc gene was transfected into two neuroblastoma cell lines that lacked N-myc amplification to determine its effect on p73 RNA levels. p73 was detectable at low level by RT-PCR in untransfected SK-N-AS cells and became undetectable following N-myc transfection, whereas in SH-EP1 cells, p73 levels were substantially reduced following transfection but remained detectable.
Sequence analysis of the p73 coding region in the mRNAs expressed by these cell lines and tumors did not reveal inactivating mutations, suggesting that p73 is not homozygously inactivated in neuroblastoma.
Overall the data suggest that p73 may play an important role in the pathogenesis of neuroblastoma but that the true tumor suppressor gene localized to this area still remains to be identified.
In this short review, we will discuss the most relevant genomic rearrangements that define high-risk NB and the role that destabilization of p53 and p73 can have in NB aggressiveness.
In addition, p73 was expressed at higher levels in the CRC tissues than in the normal mucosa or neuroblastoma tissues, though the transcripts were detectable only by the RT-PCR method.
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.
Here, we report that cyclooxygenase (COX) inhibitors induce apoptosis independent of p53, and differentially modulate endogenous p73 isoforms in neuroblastoma and other tumors.