Immunohistochemical demonstration of p63 in DMBA-induced hamster buccal pouch squamous cell carcinogenesis

Abnormalities in the p53 gene are regarded as the most consistent genetic abnormalities detected in head and neck squamous cell carcinogenesis. Two new members of the p53 gene family, p73 at the 1p36 region and p63 at the 3q27-29 region, have recently been identified. They share considerable sequence homology with p53 in the transactivation, DNA binding, and oligomerization domains, indicating possible involvement in carcinogenesis. To our knowledge, however, p63 expression in experimental oral carcinogenesis has not been studied.

Immunohistochemical analysis of p63 protein expression was performed in 7,12-dimethylbenz[a]anthracene (DMBA)-induced hamster buccal pouch squamous cell carcinogenesis. Fifty outbred, young (6 weeks), male, Syrian golden hamsters (Mesocricatus auratus) were randomly divided into three experimental groups (each consisting of 10 3-, 9- and 15-week DMBA treated animals), and two control groups (with 10 animals in each). The pouches of the three experimental groups were painted bilaterally with a 0.5% DMBA solution three times a week. The treatment protocol for animals in one of the control groups was identical with only mineral oil applied, while the other control group remained untreated throughout the experiment.

In all of the untreated and mineral oil-treated pouch mucosa, nuclear positivity for p63 was mainly observed in the basal/parabasal cell layers. The p63 nuclear positivity extended from the basal/parabasal layers to the whole epithelial layers in the 3- and 9-week DMBA-treated pouch mucosa. Furthermore, the positive nuclear-stain cells were randomly distributed throughout the entire epithelial layers in the 3- and 9-week DMBA-treated pouch-mucosa specimens. In carcinomas from 15-week DMBA-treated pouch specimens, p63 staining was more uniform and homogeneous for the less-differentiated tumor areas. By contrast, p63 expression was noted mainly in the peripheral cells of tumor nests in the well-differentiated tumor areas.

The results of this study are consistent with those from previous analyses of p63 expression in human oral mucosa, suggesting that p63 may be associated with the regulation of epithelial differentiation and proliferation in DMBA-induced hamster buccal pouch squamous cell carcinogenesis. Further study is required to investigate which p63 isoform(s) is/are involved in hamster buccal pouch carcinogenesis.