|Budget Amount *help
¥1,600,000 (Direct Cost : ¥1,600,000)
Fiscal Year 1991 : ¥300,000 (Direct Cost : ¥300,000)
Fiscal Year 1990 : ¥1,300,000 (Direct Cost : ¥1,300,000)
Origin of cerebellar medulloblastoma, and mechanism of oncogenesis of this malignant tumor in childhood remain unknown, largely because of a lack of suitable animal models. We have successfully induced medulloblastoma in hamster cerebellum by inoculating a human papovavirus JC. Using this animal model, we examined the origin of medulloblastoma in the cerebellum, the molecular basis of viral tissue tropism, the putative mechanism of transformation, and the possible relation of this virus to human brain tumors.
First, by in-situ hybridization" it could be demonstrated that the cells migrating from the external granular layer to the internal granular layer contained the JC virus large T protein mRNA, and that transformed cells in the internal granular layer also contained this mRNA. Thus, the cells in the neonatal external granular layer may be the original cells responsible for the medulloblastoma.
Second, to clarify the mechanism of JC virus neurotropism, we carried out a CAT assay, and w
ere able to demonstrate that JC virus enhancer became active in neuroblastoma cells, but was inactive in Hela cells and glio-ma cells. This showed that JC virus enhancer plays an important role in tissue tropism.
Third, in the studies of possible mechanism of transformation by JC virus, immunoprecipitation methods demonstrated that JC virus large T protein could bind onto both anti-oncogene products, the retinoblastoma protein and the protein p53. Thus, the association between JC virus large T protein and anti-oncogene products seemed to be an essential step in transformation by JC virus.
Finally, we investigated using DNA amplification methods whether human brain tumors in childhood contain JC virus genome. Zinc finger domain of JC virus T region was not detected in PCR products from paraffin sections of 3 human brain tumors of childhood, compared to positive hamster brain tumors. Although we are still in progress of this study, DNA amplification extracted from paraffin section seemed not to be suitable method to answer the final question. Thus, it becomes more important to examine more cases of fresh brain tumors and cell lines using JC virus probes encompassing regulatory region, RB domain, p53 domain, and ATP domain. Less