Frequent loss of heterozygosity on chromosome 4 in diethylnitrosamine-induced C3H/MSM mouse hepatocellular carcinomas in culture.

Genetic changes, in particular the loss of heterozygosity (LOH) and the presence of c-Ha-ras codon 61 point mutations, were investigated in diethylnitrosamine-induced hepatocellular carcinomas (HCCs) in C3H/MSM F1 mice. (MSM are wild mice.) LOH analysis of 48 primary tumors with microsatellite probes covering at least one proximal and one distal site of each autosome revealed no obvious positive results for LOH. Analysis of 23 cell lines established from seven of these HCCs, however, showed LOH on chromosome 4 in all (seven of seven), even in early passages (G2-G3). With regard to other chromosomes, LOH was observed only rarely on chromosomes 16 and 19. These allelotype features were maintained in later passages (G11-G14), with only a few additional occurrences of LOH appearing on chromosomes 1, 6, and 8. Extensive analyses with multiple microsatellite probes from chromosome 4 and with 52 cell lines established from 24 HCCs of 18 mice revealed LOH in 22 of the tumors (92%), with the shortest region about 10 cM distal to the alpha-interferon gene. No c-Ha-ras oncogene activation in codon 61 was observed. These data indicate that loss of tumor suppressor genes on chromosome 4 may play an important role in mouse hepatocarcinogenesis in progression in vivo or in immortalization in vitro or both.