Abstract
Abnormalities in the p53 gene are regarded as the most consistent of the genetic abnormalities associated with oral squamous-cell carcinoma. Two related members of the p53 gene family, p73 and p63, have shown remarkable structural similarity to p53, suggesting possible functional and biological interactions. The purpose of this study was to investigate the differential expression of p73, p63 and p53 genes for DMBA-induced hamster buccal-pouch squamous-cell carcinoma. Immunohistochemical analysis for protein expression and reverse transcriptase-polymerase chain reaction (RT-PCR) for mRNA expression were performed for 40 samples of hamster buccal pouches, the total being separated into one experimental group (15-week DMBA-treated; 20 animals) and two control groups (untreated and mineral oil-treated; 10 animals each). Using immunohistochemical techniques, nuclear staining of p53 and p73 proteins was detected in a subset of hamster buccal-pouch tissue specimens treated with DMBA for a period of 15 weeks, whereas p63 proteins were noted for all of the 20 hamster buccal-pouch tissue specimens treated with DMBA for 15 weeks as well as for all of the untreated and mineral oil-treated hamster buccal-pouch tissue specimens. Differential expression of p63, p73 and p53 protein for the experimental group was as follows: p63+/p73+/p53+ (n = 14; 70%); p63+/p73+/p53- (n = 2; 10%); p63+/p73-/p53- (n = 4; 20%) and p63+/p73-/p53- (untreated [n = 10] and mineral oil-treated mucosa [n = 10]; 100% each). Upon RT-PCR, DeltaNp63mRNA was detected within all of the 20 hamster buccal-pouch tissue specimens treated with DMBA for 15 weeks, whereas expression of TAp63 was not detected. Furthermore, p73 mRNA was identified for 16 of the hamster buccal-pouch tissue specimens treated with DMBA for 15 weeks, whereas p53 mRNA was noted for 14 15-week DMBA-treated pouches. The proportional (percentage) expression of DeltaNp63, p73 and p53 mRNA for the hamster buccal-pouch tissue specimens treated with DMBA for 15 weeks was noted to be consistent with the findings using immunohistochemical techniques. A significant correlation between p53, p63 and p73 expression (protein and mRNA) was demonstrated for the hamster buccal-pouch carcinoma samples. Our results indicate that both p73 and p63 may be involved in the development of chemically induced hamster buccal-pouch carcinomas, perhaps in concert with p53.