Transgenic mice were generated by microinjection into fertilized one-cell mouse embryos a plasmid DNA containing the SV40 large T antigen(Tag) gene fused with the mouse albumin promoter/enhancer sequences to establish animal models of human liver canc...
Transgenic mice were generated by microinjection into fertilized one-cell mouse embryos a plasmid DNA containing the SV40 large T antigen(Tag) gene fused with the mouse albumin promoter/enhancer sequences to establish animal models of human liver cancers.
Among eleven founder transgenic animals, four developed hepatocellular carcinoma, two showed kidney cancer and one developed skin and brain tumors. Three stable transgenic lines, #1-2, #1-6 and #1-11 were established
Members of the lines #1-6 and #1-11 reproducibly developed liver tumors by 8 to 10 weeks of age but did not exhibit any phenotypic changes in other tissues. Histrlogical changes leading to liver tumor formation occurred with predictable kinetics and could be classified into three distinct stages; (a) newborn to 3 weeks of age, characterized by hyperplastic hepatocytes with reduced amounts of cytoplasm without any nuclear alterations, (b) between 4 to 8 weeks of age, characterized by diffuse liver cell dysplasia without observable tumor nodules, and (c) 9 weeks of age and thereafter, characterized by hepatocellular carcinomas in the background of extensive liver dysplasia. Metastasis in the lung from a liver carcinoma was observed in #1-11 founder animal.
Molecular studies were carried out for primary and secondary tumor nodules from the #1-11 transgenic nice at 28 weeks of age and for tumor cell lines established from the same transgenic mouse to investigate the expression of the tumor suppressor genes p53 and Rb and the oncogene c-myc and cell cycle checkpoint genes cyclin Dl, cyclin A and cyclin B. The results indicated that SV40 Tag induced overexpression of the oncogene c-myc and cell cycle cheekpoint genes cyclin Dl, cyclin A and cyclin B. These results suggest that aberrant expression of these regulatory genes can play important roles in the hepatocellular carcinogenesis.
This transgenic mouse system disp]ays similarities with human liver cancers in a number of aspects and provides a useful model for the dissection of molecular events involved in the hepatocarcinogenesis.