Genetic control of renal tumorigenesis by the mouse Rtm1 locus

Abstract

Background: The genetic basis of susceptibility to renal tumorigenesis has not yet been established in mouse strains. Mouse lines derived by bidirectional phenotypic selection on the basis of their maximal (AIRmax) or minimal (AIRmin) acute inflammatory responsiveness differ widely in susceptibility to spontaneous and urethane-induced renal tumorigenesis. To map the functional loci modulating renal tumor susceptibility in these mice, we carried out a genome-wide genetic linkage study, using SNP arrays, in an (AIRmax x AIRmin)F2 intercross population treated with a single urethane dose at 1 week of age and phenotyped for renal tumors at 35 weeks of age.

Results: AIRmax mice did not develop renal tumors spontaneously nor in response to urethane, whereas in AIRmin mice renal tumors formed spontaneously (in 52% of animals) and after urethane induction (89%). The tumors had a papillary morphology and were positive for alpha-methylacyl-CoA racemase and negative for CD10. By analysis of 879 informative SNPs in 662 mice, we mapped a single quantitative trait locus modulating the incidence of renal tumors in the (AIRmax x AIRmin)F2 intercross population. This locus, which we named Renal tumor modifier QTL 1 (Rtm1), mapped to chromosome 17 at 23.4 Mb (LOD score = 15.8), with SNPs rs3696835 and rs3719497 flanking the LOD score peak. The A allele of rs3719497 from AIRmin mice was associated with a 2.5-fold increased odds ratio for renal tumor development. The LOD score peak included the Tuberous sclerosis 2 (Tsc2) gene which has already been implicated in kidney disease: loss of function by germline retroviral insertion is associated with spontaneous renal tumorigenesis in the Eker rat, and heterozygous-null Tsc2(+/-) mice develop renal cystadenomas.

Conclusions: We mapped Rtm1 as a single major locus modulating renal tumorigenesis in a murine intercross population. Thus, the AIR mouse lines can be considered a new genetic model for studying the role of germline and somatic molecular alterations in kidney neoplastic disease.

Figure 1

Percent incidence of renal tumors in AIRmax (n = 15) and AIRmin (n = 9) mice and their F1 hybrid (n = 31) and F2 intercross (n = 662) offspring. Mice were treated with 300 mg/kg urethane at 1 week of age and then followed until 35 weeks of age, when animals were sacrificed.

Figure 2

Histological section of a papillary neoplastic proliferation of a kidney from an (AIRmax x AIRmin)F2 mouse. Panel A, hematoxylin and eosin stained section, 40X magnification. Panel B, same section at 250X magnification. The renal tumor resulted positive for racemase (AMACR) immunostaining (panel C, 250X magnification) and negative for CD10 immunostaining (panel D, 250X magnification).

Figure 3

Genome-wide genetic linkage analysis of renal tumor susceptibility in 662 (AIRmax x AIRmin)F2 intercross mice. Panel A, above the genome-wide threshold value of LOD score = 3.67 for α=0.05 (horizontal red line), a single locus on chromosome 17 was detected. Panel B, details of chromosome 17 showing the mapping of the Rtm1 locus, with LOD score peak of 15.8, at 23.4 Mb distance from the centromere.

Figure 4

Odds ratios (ORs) of renal tumor incidence of (AIRmax x AIRmin)F2 mice by genotype at rs3719497 on chromosome 17, located near the peak LOD score of genetic linkage between renal tumor incidence and genomic variants. At the reference genotype GG, carried by AIRmax mice, renal tumors were observed in 4 of 163 F2 mice (2.5% incidence, reference category). At the GA genotype, renal tumors were seen in 110 of 361 mice (30.5%; OR = 14.4; 95% CI, 6.0 – 56.6), while at the AA genotype renal tumors were observed in 54 of 138 mice (39.1%; OR = 25.5; 95% CI, 8.5 – 86.1). ORs and 95% CIs are reported on a logarithmic scale.