Predominant modifier of extreme liver cancer susceptibility in C57BR/cdJ female mice localized to 6 Mb on chromosome 17

Abstract

Sex hormones influence the susceptibility of inbred mice to liver cancer. C57BR/cdJ (BR) females are extremely susceptible to spontaneous and chemically induced liver tumors, in part due to a lack of protection against hepatocarcinogenesis normally offered by ovarian hormones. BR males are also moderately susceptible, and the susceptibility of both sexes of BR mice to liver tumors induced with N,N-diethylnitrosamine relative to the resistant C57BL/6J (B6) strain is caused by two loci designated Hcf1 and Hcf2 (hepatocarcinogenesis in females) located on chromosomes 17 and 1, respectively. The Hcf1 locus on chromosome 17 is the predominant modifier of liver cancer in BR mice. To validate the existence of this locus and investigate its potential interaction with Hcf2, congenic mice for each region were generated. Homozygosity for the B6.BR(D17Mit164-D17Mit2) region resulted in a 4-fold increase in liver tumor multiplicity in females and a 4.5-fold increase in males compared with B6 controls. A series of 16 recombinants covering the entire congenic region was developed to further narrow the area containing Hcf1. Susceptible heterozygous recombinants demonstrated a 3- to 7-fold effect in females and a 1.5- to 2-fold effect in males compared with B6 siblings. The effect in susceptible lines completely recapitulated the susceptibility of heterozygous full-length chromosome 17 congenics and furthermore narrowed the location of the Hcf1 locus to a single region of the chromosome from 30.05 to 35.83 Mb.

Fig. 1.

Ordered series of 16 recombinant lines for chromosome 17. Sixteen ordered recombinant lines were bred, each containing a segment of chromosome 17 from the susceptible BR strain on a resistant B6 background. Microsatellite markers used for genotyping and their positions are indicated at the top. Additional sequencing markers used to further refine breakpoint locations are indicated at the bottom. Black regions indicate an area inherited from the B6 strain, white regions indicate a portion inherited from the BR strain and gray regions are areas of unknown genotype where recombinations have occurred.

Fig. 2.

Haplotype analysis of chromosome 17 minimal susceptibility region. The top line in each panel indicates the positions of the SNPs. For each strain, SNP alleles are indicated by both the shading of the vertical tic and its position with respect to the horizontal line. Sequences identical to those in B6 are indicated in dark gray (above the horizontal line), sequences different from B6 but identical in C3H and BR are in light gray (across the line) and sequences unique to BR are in black (below the line). Closely spaced SNPs may not be individually distinguishable in the representations for each strain. (A) SNPs with alleles in B6, C3H and BR were compiled from the Mouse Phenome Database. The data show two areas unique to BR at ∼30.05 and 35.74 Mb. (B) Segments of 3′-untranslated regions or the most 3′-introns of genes were sequenced. These data identify two additional areas unique to BR at ∼33.04 and 34.50 Mb.