The genetic basis for carcinogenetic alteration is not well-known at present, but is generally thought to involve mutation or overexpression in oncogene or tumor suppressor genes as ras and p53. The purpose of this study was to clarify cell proliferation and the action of the p53 & K-ras gene in DMBA induced buccal pouch carcinogenesis in hamster. 0.5% DMBA in mineral oil was topically applied three times a week to the buccal pouch of 56 hamsters during the experimental periods. The experimental animals were subdivided into control(mineral oil only treated), and 6, 8, 10, 12, 14, 16, 18 and 20 weeks DMBA treated groups. The expression of the PCNA, pan-ras and p53 protein was evaluated by the distribution and intensity of positive cells during the carcinogenesis by immunohistochemical stains. Molecular biologic evaluation for K-ras and p53 gene was performed by reverse transcription-polymerase chain reaction (RT-PCR), Southern blot and densitometric analysis in the each experimental groups. The following results were obtained: 1. The buccal pouch epithelium of hamster was histologically changed to the dysplasia at 10 weeks, carcinoma in situ at 12 weeks, and squamous cell carcinoma at 14 weeks 2. The expression of the p53 and ras oncoprotein was restricted to the parabasal and spinous layers in the normal and dysplastic mucosa, but those positive cells were expanded to the 3. The positive index of the p53 and ras oncoprotein was markedly increased in the carcinoma compared to the CIS and dysplasia, and showed increased tendency according to DMBA treated time. 4. The mRNA of K-ras and p53 was expressed in the control and all experimental groups by RT-PCR and Southern blot analysis. But the expression of K-ras and p53 gene was increased in carcinorna stage(14-20 weeks) than control and precancerous (6-12 weeks) stage by the densitometric assay 5. PCNA positive cells were mainly mild expressed in the basal cell layer of normal oral mucosa, increased moderately, after 6 weeks. In suprabasal cell layer, control group os negative but retained moderately between weeks and 14 weeks, and decreased after 16 weeks. Inspinous cell layer, restricted only between 12 weeks and 16 weeks, other period is mild or negative. 6. PCNA Index of experimental group revealed the increased peak in 6 weeks and 20 weeks than control group, and retained between 12 weeks and 18 weeks. All experimental group expressed higher PCNA Index than control group(P.<0.05). From the above findings, expression of p53 and ras oncoprotein and their genes was the greatest in carcinoma stage, thus the mRNA for K-ras and p53 corresponded well with the pattern of protein, and overexpression of p53 and ras oncogene and cell proliferation may have important cooperative roles for the promotion of cancer.
(0)
(0)