Allelotype analysis in mouse hepatocellular carcinomas; frequent homozygous deletion of mouse homolog of p16/CDKN2 gene on chromosome 4 in culture.

Because allelotype analysis of many tumors has been important in the identification of new tumor suppressor genes, here we have analyzed hepatocellular carcinomas (HCCs) derived from F1 hybrid mice between C3H and MSM in detail. The analysis showed no allelic loss in primary HCCs, while the loss was detected in tumor cell lines established from HCCs. Recently, a candidate tumor suppressor gene termed p16/CDKN2, which was located near the interferon gene cluster on human chromosome 9p21, was identified by virtue of its frequent homozygous deletion in cell lines derived from many different tumor types. Since frequent allelic imbalances in the D4MIT9 locus and loss of heterozygosity in the alpha-interferon gene which was located near the mouse homolog of p16/CDKN2 (mouse p16) gene were detected in tumor cell lines, we investigated homozygous deletion of the mouse p16 gene by the comparative multiplex PCR method. The analysis revealed frequent homozygous deletion of the gene in thirteen of the tumor cell lines (13/25, 52%), but not in primary HCCs (0/25, 0%). These data indicate that gene deletions including the mouse p16 gene on chromosome 4 in tumor cell lines occur during the culture and that allelic imbalances are uncommon in mouse primary HCCs. Our results suggest that mouse p16 plays an important role in mouse hepatocarcinogenesis in vivo in progression or immortalization in vitro.