Homozygous deletion of mouse homolog of p16/CDKN2 gene on chromosome 4 in mouse liver epithelial cells in culture.

The culture of hepatocytes isolated from C3H mouse liver results in the spontaneous development of colonies of liver epithelial cells that possess some features of the hepatocytes. These liver epithelial cells frequently have a loss of chromosome 4, and become neoplasms which are hepatocellular carcinomas by transfection with the activated c-Ha-ras gene. The suppression of malignant phenotypes by mouse chromosome 4 has already been shown by fusion between normal and malignant mouse cells. We established a total of six liver epithelial cell lines from C3H mice in order to investigate the presence of a tumor suppressor gene(s) on chromosome 4 in mouse hepatocarcinogenesis, and performed an allelotype analysis in seven microsatellites on chromosome 4 by the comparative multiplex PCR method. The result of analysis revealed that three of the six liver epithelial cells had allelic imbalances in four microsatellite loci, especially, two liver epithelial cell lines showed homozygous deletion in the D4MIT77 locus. Then, we investigated the status of the mouse homolog of p16/CDKN2 gene (mouse p16) on chromosome 4 by the comparative multiplex PCR method, and detected the homozygous deletion in two liver epithelial cell lines. Our result thus supports the theory that alterations of tumor suppressor gene(s) located on chromosome 4 may play a role in mouse hepatocarcinogenesis. Mouse p16, which is an inhibitor of cyclin dependent kinase 4, may suppress the cancer development in mouse hepatocarcinogenesis, or suppress liver cell immortalization.