Cellular proliferation is an intricately regulated process mediated by the coordinated interactions of critical growth control genes.
Two of these factors in mammalian cells are the p53 and mdm-2 genes. A protein product of the mem-2 oncogene has been recently shown to associate with the protein encoded by the tumor suppressor gene p53
The p53 tumor suppressor protein is stabilized in response to DNA damage and other stress signals and causes the cell to undergo growth arrest or apoptosis, thus preventing the establishment of mutations in future cellular generations. Mutation or loss of p53 is a very common event in tumor progression. It otters in about 50% of all tumors analysed including of colon, lung, breast and liver.
The cellular mdm-2 gene, which has potential transforming activity that can be activated by overexpression, is amplified in a significant percentage of human sarcoma and in other mammalian tumors. Proteins encoded by the mdm-2 gene are able to bind to the p53 protein and, when overexpressed, can inhibit p53´s transcriptional activation function, thus mdm-2 can act as a negative regulator of p53 function.
Experimental study was performed to observe the relationship between p53 gene mutation and mdm-2 protein expression and apply the results to the clinical activity.
36 golden synan hamster each weighing 6080g were used and painted with 0.5% DMBA by 3 times weekly on the right buccal cheek(experimental side) for 6, 8, 10, 12, 14 and 16 weeks. Left buccal cheek(control side) was treated with mineral oil as the same manner to the right side. The hamsters were sacrificed on the 6, 8, 10, 12, 14 & 16 weeks.
Normal and tumor tissues from paraffin block were examined for histology and immunohistochemistry observation, and were completely dissected by microdissection and DNA from both tissue were isolated by proteins K/phenoVchloroform extraction. Segments of the hamstci p53 exons 5, 6, 7 and 8 were amplified by PCR using the oligonucleotide primers, and then confirmational change was observed by SSCP respectively.
The results were as follows :
1. Dysplasia at 6 weeks, carcinoma in situ at 8 weeks and invasive carcinoma from 10 weeks could be observed in experimental groups.
2. p53 mutations were detected in 10 of the 36(28%) and the exons 6(6 of the 10 : 60%) was the most hot spot area among the highy conserved region(exons 5, 6, 7 & 8).
3. Immunohistochemical study confirmed 22 of the 36(61%) of p53 expression involving 10 of p53 mutations.
4. mdm-2 expression of was showed in 3 of the 36(8%) involving 1 of the 22 of p53 expression and 2 of the 14 of p53 non-expression.
From the above results, mutation of p53 gene or expression of p53 protein may have the influence of the DMBA induced carcinoma of hamster buccal pouch but the expression of mdm-2 protein may not have relationship with tumorigenesis.
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