Positional Mapping and Candidate Gene Analysis of the Mouse Ccs3 Locus That Regulates Differential Susceptibility to Carcinogen-Induced Colorectal Cancer

Abstract

The Ccs3 locus on mouse chromosome 3 regulates differential susceptibility of A/J (A, susceptible) and C57BL/6J (B6, resistant) mouse strains to chemically-induced colorectal cancer (CRC). Here, we report the high-resolution positional mapping of the gene underlying the Ccs3 effect. Using phenotype/genotype correlation in a series of 33 AcB/BcA recombinant congenic mouse strains, as well as in groups of backcross populations bearing unique recombinant chromosomes for the interval, and in subcongenic strains, we have delineated the maximum size of the Ccs3 physical interval to a ∼2.15 Mb segment. This interval contains 12 annotated transcripts. Sequencing of positional candidates in A and B6 identified many either low-priority coding changes or non-protein coding variants. We found a unique copy number variant (CNV) in intron 15 of the Nfkb1 gene. The CNV consists of two copies of a 54 bp sequence immediately adjacent to the exon 15 splice site, while only one copy is found in CRC-susceptible A. The Nfkb1 protein (p105/p50) expression is much reduced in A tumors compared to normal A colonic epithelium as analyzed by immunohistochemistry. Studies in primary macrophages from A and B6 mice demonstrate a marked differential activation of the NfκB pathway by lipopolysaccharide (kinetics of stimulation and maximum levels of phosphorylated IκBα), with a more robust activation being associated with resistance to CRC. NfκB has been previously implicated in regulating homeostasis and inflammatory response in the intestinal mucosa. The interval contains another positional candidate Slc39a8 that is differentially expressed in A vs B6 colons, and that has recently been associated in CRC tumor aggressiveness in humans.

CNVs Associated with Susceptibility to Cancers: A Mini-Review

“…Cancer susceptibility is different even between individuals exposed to the same carcinogen [7]. CNVs modulate (increase or decrease) the risk of sporadic cancers in individuals [38].…”

“…A question remains, however, whether genetic backgrounds have a considerable effect on the susceptibility to sporadic cancers. In a chemical carcinogenesis model, carcinogenicity depends on genotypes of a mouse; chemical carcinogens cause cancer preferentially in mice with the particular genetic backgrounds [7]. In addition, a cohort study in twins reveals that, when one of a twin is affected by cancer, the other has the same type of the cancer at high incidence [6].…”

“…The concept of CNVs associated with cancer susceptibility can explain well a difference in the frequency of sporadic cancers between individuals under the same environment. The CNVs associated with cancer susceptibility have been reported in dogs [19], mice [7] and chickens [20] as well as in human. The analysis of CNVs associated with cancer susceptibility CNVs allows us to estimate individual susceptibility to each type of cancers.…”

A New Polygenic Model for Nonfamilial Colorectal Cancer Inheritance Based on the Genetic Architecture of the Azoxymethane-Induced Mouse Model

“…approaches (Reddy 2004;Waly et al 2014;Manna et al 2015;Odun-Ayo et al 2015;Pedro et al 2016;Bi et al 2017;Md Nasir et al 2017;Wu et al 2017), and to identify genetic (Ruivenkamp et al 2003;Meunier et al 2010Meunier et al , 2011Meunier et al , 2013Eversley et al 2012;Liu et al 2012) and environmental (Bissahoyo et al 2005;Takahashi et al 2013;Piazzi et al 2019) factors that contribute to nonfamilial CRC susceptibility .…”

“…Despite the extensive use of the AOM model for experimental cancer research, few studies have evaluated the relative susceptibility to AOM-induced CRC (Nambiar et al 2003;Ruivenkamp et al 2003;Meunier et al 2010Meunier et al , 2011Meunier et al , 2013Liu et al 2012), predominantly using mice derived from commonly used strains that represent a limited pool of ancestors (Yang et al 2007). Even then, these studies used only a few mice per strain, which greatly reduces the accuracy of measuring strain response.…”