OBJECTIVE

To observe the pattern of changes in the proliferation and apoptosis at different stages of large bowel carcinoma in mice, and to explore the effects of the imbalance of apoptosis and proliferation at different stages of large-intestine carcinogenesis.

METHODS

An experimental animal model for large intestine carcinogenesis of KUNMING–strain mice was used. The carcinomas were induced by subcuteneous injection of dimethylhydrazine (DMH) and the distribution and density changes of proliferating and apoptotic cells observed through multistages toward cancer formation. The animals were killed in groups at the 12th, 18th, 24th, and 32nd weeks of carcinoma induction. The apoptotic and proliferating cells were labeled separately using TUNEL and PCNA immunohistochemical staining methods

RESULTS

In the normal mouse mucosa, all the apoptotic cells were situated in the superficial layers, however, the proliferating cells were situated in the basement layers, and the amount of both were small. In the early stage of carcinoma induction, the proliferation and the apoptotic cells slightly increased in amount, but there were no obvious changes in their ratio. In the medium stage, the densities of both distinctly increased, but there were no obvious changes in the ratio. In the late stage, the densities of the proliferating and the apoptotic cells in the non–carcinoma mucosa were higher than those at other stages. The proliferating cells in the dysplastic mucosa increased progressively with the increasing degree of the lesions. Although the apoptotic cells increased, their changes did not occur with the degree of the lesions. Their ratio showed a decreasing tendency with the degree of the lesions.

CONCLUSIONS

①The presence of an imbalance between cell proliferation and apoptosis was confirmed in the course of large intestine carcinogenesis in a mouse model. ②In the early stage of carcinoma induction both proliferation and apoptosis were at a low level; in the medium stage, they were both at a high level; and in the late stage (that is in carcinoma), proliferation was at a very high level, while apoptosis was at a low level. ③The proliferating cells increased progressively with the degree of dysplasia. There were no obvious changes in the apoptotic cells and their ratio to the proliferating cells showed a progressively increasing tendency. ④ In the stage of cancer formation, the most essential change was the excessive decrease in the ratio of apoptosis to proliferation. These results support the hypothesis of “Cell Selective Proliferation”, which was raised by authors previously in a study on human large bowel carcinoma.

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