Identification of novel carcinogen‐mediated mammary tumor susceptibility loci in the rat using the chromosome substitution technique

Abstract

We here report the genetic basis for susceptibility and resistance to carcinogen-mediated (7,12-Dimethylbenz[a]anthracene (DMBA)) mammary tumorigenesis using the full panel of SS/BN consomic rat strains, in which substitutions of individual chromosomes from the resistant BN strain onto the genomic background of the susceptible SS strain were made. Analysis of 252 consomic females identified rat mammary Quantitative Trait Loci (QTLs) affecting tumor incidence on chromosomes 3 and 5, latency on chromosomes 3, 9, 14 and 19, and multiplicity on chromosomes 13, 16 and 19. In addition, we unexpectedly identified a novel QTL on chromosome 6 controlling a lethal toxic phenotype in response to DMBA. Upon further investigation with chromosomes 6 and 13 congenic lines, in which an additional 114 rats were investigated, we mapped 1) a novel mammary tumor QTL to a region of 27.1 Mbp in the distal part of RNO6, a region that is entirely separated from the toxicity phenotype, and 2) a novel and powerful mammary tumor susceptibility locus of 4.5 Mbp that mapped to the proximal q-arm of RNO13. Comparison of genetic strain differences using existing rat genome databases enabled us to further construct priority lists containing single breast cancer candidate genes within the defined QTLs, serving as potential functional variants for future testing.

CXM: A New Tool for Mapping Breast Cancer Risk in the Tumor Microenvironment

“…Compared with SS plugs (14 ± 3 vessels/mm 2 ; n = 9 rats), the BVD in SS.BN3 consomic rats was ~2-fold higher (23 ± 4 vessels/mm 2 ; P < 0.05; n = 19 rats) (Figure 4A, B). Likewise, BVD of SS.BN3 mammary tumors (n = 9) from the DMBA-inducible model showed a ~2-fold ( P < 0.01) increase relative to SS tumors (n = 9) from the same study (16) (Figure 4C, D), collectively demonstrating that SS.BN3 has increased angiogenic potential (i.e., the ability to form new blood vessels), despite having decreased tumor growth, vascular invasion, and hematogenous metastasis (Figures 2 and 3). …”

“…In most cases, BVD is positively correlated with tumor growth and hematogenous metastasis(33), prompting us to validate whether the paradoxical angiogenesis phenotype seen in SS.BN3 IL2Rγ (Figure 3B) is present in the unmodified parental SS and SS.BN3 consomic strains using two independent methods: a matrigel plug angiogenesis assay (34) and reanalysis of the DMBA-inducible mammary tumors from Adamovic et al (16). For the matrigel plug angiogenesis assay, female SS and SS.BN3 consomic rats were implanted with 500 μl of matrigel supplemented with 500 ng/ml of recombinant rat VEGF 164 .…”

“…Previously we showed that the SS.BN3 consomic rat has significantly reduced tumorigenicity in a DMBA-inducible model of breast cancer(16). We postulated that this could be at least partially due to genetic differences in the tumor microenvironment, rather than inherent differences in the malignant tumor cells only.…”

“…Acquisition of DMBA-induced mammary tumors from the SS.BN3 consomic (n = 9) and SS (n = 9) rats were previously described by Adamovic et al (16). These tumors were previously formalin fixed and paraffin embedded, precluding us from using the traditional anti-CD31 antibody that does not recognize formalin-fixed antigens.…”

“…We first generated and characterized an IL2Rγ mutant parental SS strain (SS IL2Rγ ), which was then selectively bred onto the SS.BN3 consomic background to generate the SS.BN3 IL2Rγ consomic. The parental SS (SS/JrHsdMcwi) rat strain is susceptible to mammary tumors, whereas the BN (BN/NHsdMcwi) rat strain is highly resistant to mammary tumors (16). Our rationale for choosing SS (parental) and SS.BN3 consomic (i.e., BN chromosome 3 introgressed onto the isogenic SS background) was based on prior data demonstrating a 64% reduction in breast cancer incidence in the SS.BN3 consomic compared with the SS (16) and other evidence that multiple overlapping protective loci exist on rat chromosome 3 (16–19).…”