Non-radioactive Screening of p53 Mutations in Human Oral Cancers Detected by Single Strand Conformation Polymorphism Analysis : Comparison with the Protein Accumulation

p53 gene mutation and its protein accumulation are widely detected in human cancers and have prognostic significance. To examine the relationship between p53 mutation and its protein accumulation, tumor samples from 65 oral cancer patients were analyzed using both single strand conformational polymorphism (SSCP) technique to screen the presence of p53 gene mutations and immunohisto-chemistry to detect the p53 protein accumulations. Results were simultaneously associated with clinicopathological variables of the cancers and prognoses of the patients. p53 gene mutations were found in 18 cancers (7.6%), whereas aberrant accumulations of p53 protein were present in 31 cancers (47.6%). All of the oral cancers with p53 mutation showed positive immunoreactivity, but in addition, p53 protein accumulations were still found in 13 oral cancers (20%) without detect-able gene mutations. The concordance between the protein expression and the SSCP analysis was 80%. Such p53 abnormalities were significantly correlated with lymph node metastasis and clinical stage. Patients with the detectable p53 abnormalities survived for a significantly shorter period of time. p53 abnormal-ities are reliable as an indicator for evaluating malignant potential of oral can-cers

Wild-type p53 Expression Overcomes p21-mediated G1 Arrest and Induces Apoptosis in Cancer Cells Expressing Bax

Tumor suppression by p53 is deficient in the majority of human cancers. Previous studies have suggested that expression of p53 in human cancer cells can result in either growth arrest or apoptosis. The biological and genetic de-terminants that dictate which of these two pathway - apoptosis or arrest - will be chosen by a particular cell following p53 expression are largely un-known. To investigate the basis of this difference, we evaluated the role of p21, a mediator of p53-induced growth arrest. We generated a replication-deficient adenoviral recombinant which expresses p21 and com-pared its tumor suppressive abilities with Ad-p53. Infection with Ad-p21 re-sulted in high levels of p21 expression and suppressed the growth of human cancer cells, through the Gl arrest of the cell cycle. We then examined the effects of combined infection with Ad-p21 and Ad-p53 to investigate which of these molecules had the dominant function. Introduction of exogenous p53 in RERF-LC-OK, BT549 and ZR-75-1 cells overcame p21-mediated cell cycle arrest at G1 and induced apoptosis, suggesting that this affect is a general event among human cancer cell lines. We then evaluated the role of Bax/Bcl-2 in the response to p53. A Significantly greater amount of Bax protein was pre-sent in cell lines undergoing apoptosis than in cells with arrested growth,suggesting that Bax might be an important component of the p53-mediated apoptosis of cancer cells

Methylated CpG Island Amplification of Representational Difference Analysis for Oral Cancer

CpG islands are G+C-rich regions approximately 1 kb long that are free of methylation and contain the promoters of many mammalian genes. It has been demonstrated that aberrant methylation of CpG islands is associated with gene silencing of tumor suppressor genes. To examine DNA methylation changes in oral squamous cell carcinoma (OSCC), we have applied a novel genome screening technique, methylated CpG island amplification coupled with representational difference analysis. Using DNA from an OSCC cell line as tester and DNA from normal tongue tissue as driver, DNA sequences aberrantly methylated in OSCC can be obtained. We therefore propose that MCA is a useful technique to study methylation and to isolate CpG islands differentially methylated in cancer