Characterization of a major colon cancer susceptibility locus (Ccs3) on mouse chromosome 3

Short chain fatty acids prime colorectal cancer cells to activate antitumor immunity

Introduction

Colorectal cancer (CRC) is a leading cause of death worldwide and its growth can either be promoted or inhibited by the metabolic activities of intestinal microbiota. Short chain fatty acids (SCFAs) are microbial metabolites with potent immunoregulatory properties yet there is a poor understanding of how they directly regulate immune modulating pathways within the CRC cells.

Methods

We used engineered CRC cell lines, primary organoid cultures, orthotopic in vivo models, and patient CRC samples to investigate how SCFA treatment of CRC cells regulates their ability to activate CD8+ T cells.

Results

CRC cells treated with SCFAs induced much greater activation of CD8+ T cells than untreated CRC cells. CRCs exhibiting microsatellite instability (MSI) due to inactivation of DNA mismatch repair were much more sensitive to SCFAs and induced much greater CD8+ T cell activation than chromosomally instable (CIN) CRCs with intact DNA repair, indicating a subtype-dependent response to SCFAs. This was due to SCFA-induced DNA damage that triggered upregulation of chemokine, MHCI, and antigen processing or presenting genes. This response was further potentiated by a positive feedback loop between the stimulated CRC cells and activated CD8+ T cells in the tumor microenvironment. The initiating mechanism in the CRCs was inhibition of histone deacetylation by the SCFAs that triggered genetic instability and led to an overall upregulation of genes associated with SCFA signaling and chromatin regulation. Similar gene expression patterns were found in human MSI CRC samples and in orthotopically grown MSI CRCs independent of the amount of SCFA producing bacteria in the intestine.

Discussion

MSI CRCs are widely known to be more immunogenic than CIN CRCs and have a much better prognosis. Our findings indicate that a greater sensitivity to microbially produced SCFAs contributes to the successful activation of CD8+ T cells by MSI CRCs, thereby identifying a mechanism that could be therapeutically targeted to improve antitumor immunity in CIN CRCs.

Anti-tumor immunity in mismatch repair-deficient colorectal cancers requires type I IFN-driven CCL5 and CXCL10

Colorectal cancers (CRCs) deficient in DNA mismatch repair (dMMR) contain abundant CD8+ tumor-infiltrating lymphocytes (TILs) responding to the abundant neoantigens from their unstable genomes. Priming of such tumor-targeted TILs first requires recruitment of CD8+ T cells into the tumors, implying that this is an essential prerequisite of successful dMMR anti-tumor immunity. We have discovered that selective recruitment and activation of systemic CD8+ T cells into dMMR CRCs strictly depend on overexpression of CCL5 and CXCL10 due to endogenous activation of cGAS/STING and type I IFN signaling by damaged DNA. TIL infiltration into orthotopic dMMR CRCs is neoantigen-independent and followed by induction of a resident memory-like phenotype key to the anti-tumor response. CCL5 and CXCL10 could be up-regulated by common chemotherapies in all CRCs, indicating that facilitating CD8+ T cell recruitment underlies their efficacy. Induction of CCL5 and CXCL10 thus represents a tractable therapeutic strategy to induce TIL recruitment into CRCs, where local priming can be maximized even in neoantigen-poor CRCs.

TIAM2S Mediates Serotonin Homeostasis and Provokes a Pro-Inflammatory Immune Microenvironment Permissive for Colorectal Tumorigenesis

The short isoform of human TIAM2 has been shown to promote proliferation and invasion in various cancer cells. However, the roles of TIAM2S in immune cells in relation to tumor development have not been investigated. To characterize the effects of TIAM2S, we generated TIAM2S-overexpressing mouse lines and found that aged TIAM2S-transgenic (TIAM2S-TG) developed significantly higher occurrence of lymphocytic infiltration and tumorigenesis in various organs, including colon. In addition, TIAM2S-TG is more sensitized to AOM-induced colon tumor development, suggesting a priming effect toward tumorigenesis. In the light of our recent findings that TIAM2S functions as a novel regulator of cellular serotonin level, we found that serotonin, in addition to Cox2, is a unique inflammation marker presented in the colonic lesion sites in the aged TG animals. Furthermore, our results demonstrated that ectopic TIAM2S altered immunity via the expansion of T lymphocytes; this was especially pronounced in CD8⁺ T cells in combination with CXCL13/BCA-1 pro-inflammatory chemokine in the serum of TIAM2S-TG mice. Consequently, T lymphocytes and B cells were recruited to the lesion sites and stimulated IL-23/IL17A expression to form the tertiary lymphoid organs. Collectively, our research suggests that TIAM2S provokes a pro-inflammatory immune microenvironment permissive to colorectal tumorigenesis through the serotonin-induced immunomodulatory effects.

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

The azoxymethane model of colorectal cancer (CRC) was used to gain insights into the genetic heterogeneity of nonfamilial CRC. We observed significant differences in susceptibility parameters across 40 mouse inbred strains, with 6 new and 18 of 24 previously identified mouse CRC modifier alleles detected using genome-wide association analysis. Tumor incidence varied in F1 as well as intercrosses and backcrosses between resistant and susceptible strains. Analysis of inheritance patterns indicates that resistance to CRC development is inherited as a dominant characteristic genome-wide, and that susceptibility appears to occur in individuals lacking a large-effect, or sufficient numbers of small-effect, polygenic resistance alleles. Our results suggest a new polygenic model for inheritance of nonfamilial CRC, and that genetic studies in humans aimed at identifying individuals with elevated susceptibility should be pursued through the lens of absence of dominant resistance alleles rather than for the presence of susceptibility alleles.

Inactivation of Interferon Regulatory Factor 1 Causes Susceptibility to Colitis-Associated Colorectal Cancer

The mechanisms linking chronic inflammation of the gut (IBD) and increased colorectal cancer susceptibility are poorly understood. IBD risk is influenced by genetic factors, including the IBD5 locus (human 5q31), that harbors the IRF1 gene. A cause-to-effect relationship between chronic inflammation and colorectal cancer, and a possible role of IRF1 were studied in Irf1^-/- mice in a model of colitis-associated colorectal cancer (CA-CRC) induced by azoxymethane and dextran sulfate. Loss of Irf1 causes hyper-susceptibility to CA-CRC, with early onset and increased number of tumors leading to rapid lethality. Transcript profiling (RNA-seq) and immunostaining of colons shows heightened inflammation and enhanced enterocyte proliferation in Irf1^−/− mutants, prior to appearance of tumors. Considerable infiltration of leukocytes is seen in Irf1^−/− colons at this early stage, and is composed primarily of proinflammatory Gr1⁺ Cd11b⁺ myeloid cells and other granulocytes, as well as CD4⁺ lymphoid cells. Differential susceptibility to CA-CRC of Irf1^−/− vs. B6 controls is fully transferable through hematopoietic cells as observed in bone marrow chimera studies. Transcript signatures seen in Irf1^−/− mice in response to AOM/DSS are enriched in clinical specimens from patients with IBD and with colorectal cancer. In addition, IRF1 expression in the colon is significantly decreased in late stage colorectal cancer (stages 3, 4) and is associated with poorer prognosis. This suggests that partial or complete loss of IRF1 expression alters the type, number, and function of immune cells in situ during chronic inflammation, possibly via the creation of a tumor-promoting environment.

The p53 status can influence the role of Sam68 in tumorigenesis

The expression and activities of RNA binding proteins are frequently dysregulated in human cancer. Their roles, however, appears to be complex, with reports indicating both pro-tumorigenic and tumor suppressive functions. Here we show, using two classical mouse cancer models, that the role of KH-type RNA binding protein, Sam68, in tumor development can be influenced by the status of the p53 tumor suppressor. We demonstrate that in mice expressing wild type p53, Sam68-deficiency resulted in a higher incidence and malignancy of carcinogen-induced tumors, suggesting a tumor suppressive role for Sam68. In marked contrast, Sam68-haploinsufficiency significantly delayed the onset of tumors in mice lacking p53 and prolonged their survival, indicating that Sam68 accelerates the development of p53-deficient tumors. These findings provide considerable insight into a previously unknown relationship between Sam68 and the p53 tumor suppressor in tumorigenesis.

Inflammation-induced tumorigenesis in mouse colon is caspase-6 independent

Caspases play an important role in maintaining tissue homeostasis. Active Caspase-6 (Casp6) is considered a novel therapeutic target against Alzheimer disease (AD) since it is present in AD pathological brain lesions, associated with age-dependent cognitive decline, and causes age-dependent cognitive impairment in the mouse brain. However, active Casp6 is highly expressed and activated in normal human colon epithelial cells raising concerns that inhibiting Casp6 in AD may promote colon carcinogenesis. Furthermore, others have reported rare mutations of Casp6 in human colorectal cancers and an effect of Casp6 on apoptosis and metastasis of colon cancer cell lines. Here, we investigated the role of Casp6 in inflammation-associated azoxymethane/dextran sulfate sodium (AOM/DSS) colon cancer in Casp6-overexpressing and -deficient mice. In wild-type mice, AOM/DSS-induced tumors had significantly higher Casp6 mRNA, protein and activity levels compared to normal adjacent colon tissues. Increased human Casp6 or absence of Casp6 expression in mice colon epithelial cells did not change colonic tumor multiplicity, burden or distribution. Nevertheless, the incidence of hyperplasia was slightly reduced in human Casp6-overexpressing colons and increased in Casp6 null colons. Overexpression of Casp6 did not affect the grade of the tumors while all tumors in heterozygous or homozygous Casp6 null colons were high grade compared to only 50% high grade in wild-type mice. Casp6 levels did not alter cellular proliferation and apoptosis. These results suggest that Casp6 is unlikely to be involved in colitis-associated tumors.

Neonatal Fc receptor expression in dendritic cells mediates protective immunity against colorectal cancer

Cancers arising in mucosal tissues account for a disproportionately large fraction of malignancies. Immunoglobulin G (IgG) and the neonatal Fc receptor for IgG (FcRn) have an important function in the mucosal immune system that we have now shown extends to the induction of CD8(+) T cell-mediated antitumor immunity. We demonstrate that FcRn within dendritic cells (DCs) was critical for homeostatic activation of mucosal CD8(+) T cells that drove protection against the development of colorectal cancers and lung metastases. FcRn-mediated tumor protection was driven by DCs activation of endogenous tumor-reactive CD8(+) T cells via the cross-presentation of IgG complexed antigens (IgG IC), as well as the induction of cytotoxicity-promoting cytokine secretion, particularly interleukin-12, both of which were independently triggered by the FcRn-IgG IC interaction in murine and human DCs. FcRn thus has a primary role within mucosal tissues in activating local immune responses that are critical for priming efficient anti-tumor immunosurveillance.

TLR4 activates the β-catenin pathway to cause intestinal neoplasia

Colonic bacteria have been implicated in the development of colon cancer. We have previously demonstrated that toll-like receptor 4 (TLR4), the receptor for bacterial lipopolysaccharide (LPS), is over-expressed in humans with colitis-associated cancer. Genetic epidemiologic data support a role for TLR4 in sporadic colorectal cancer (CRC) as well, with over-expression favoring more aggressive disease. The goal of our study was to determine whether TLR4 played a role as a tumor promoter in sporadic colon cancer. Using immunofluorescence directed to TLR4, we found that a third of sporadic human colorectal cancers over-express this marker. To mechanistically investigate this observation, we used a mouse model that over-expresses TLR4 in the intestinal epithelium (villin-TLR4 mice). We found that these transgenic mice had increased epithelial proliferation as measured by BrdU labeling, longer colonic crypts and an expansion of Lgr5+ crypt cells at baseline. In addition, villin-TLR4 mice developed spontaneous duodenal dysplasia with age, a feature that is not seen in any wild-type (WT) mice. To model human sporadic CRC, we administered the genotoxic agent azoxymethane (AOM) to villin-TLR4 and WT mice. We found that villin-TLR4 mice showed an increased number of colonic tumors compared to WT mice as well as increased β-catenin activation in non-dysplastic areas. Biochemical studies in colonic epithelial cell lines revealed that TLR4 activates β-catenin in a PI3K-dependent manner, increasing phosphorylation of β-catenin(Ser552), a phenomenon associated with activation of the canonical Wnt pathway. Our results suggest that TLR4 can trigger a neoplastic program through activation of the Wnt/β-catenin pathway. Our studies highlight a previously unexplored link between innate immune signaling and activation of oncogenic pathways, which may be targeted to prevent or treat CRC.

Positional mapping and candidate gene analysis of the mouse Ccs3 locus that regulates differential susceptibility to carcinogen-induced colorectal cancer

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.

Identification of five novel modifier loci of Apc(Min) harbored in the BXH14 recombinant inbred strain

Every year thousands of people in the USA are diagnosed with small intestine and colorectal cancers (CRC). Although environmental factors affect disease etiology, uncovering underlying genetic factors is imperative for risk assessment and developing preventative therapies. Familial adenomatous polyposis is a heritable genetic disorder in which individuals carry germ-line mutations in the adenomatous polyposis coli (APC) gene that predisposes them to CRC. The Apc ( Min ) mouse model carries a point mutation in the Apc gene and develops polyps along the intestinal tract. Inbred strain background influences polyp phenotypes in Apc ( Min ) mice. Several Modifier of Min (Mom) loci that alter tumor phenotypes associated with the Apc ( Min ) mutation have been identified to date. We screened BXH recombinant inbred (RI) strains by crossing BXH RI females with C57BL/6J (B6) Apc ( Min ) males and quantitating tumor phenotypes in backcross progeny. We found that the BXH14 RI strain harbors five modifier loci that decrease polyp multiplicity. Furthermore, we show that resistance is determined by varying combinations of these modifier loci. Gene interaction network analysis shows that there are multiple networks with proven gene-gene interactions, which contain genes from all five modifier loci. We discuss the implications of this result for studies that define susceptibility loci, namely that multiple networks may be acting concurrently to alter tumor phenotypes. Thus, the significance of this work resides not only with the modifier loci we identified but also with the combinations of loci needed to get maximal protection against polyposis and the impact of this finding on human disease studies.

Ginsenoside compound K, not Rb1, possesses potential chemopreventive activities in human colorectal cancer

Ginsenoside compound K (C-K) is an intestinal microbiota metabolite of ginsenoside Rb1, a major constituent in American ginseng. However, previous ginseng anti-cancer observations were largely focused on ginseng parent compounds but not metabolites, and anti-colorectal cancer studies on C-K were limited. This study investigated the anti-proliferative effects of C-K when compared to those of Rb1, and the related mechanisms of action, in HCT-116 and SW-480 colorectal cancer cells. The effects of Rb1 and C-K on the proliferation of HCT-116 and SW-480 human colorectal cancer cells were compared using an MTS assay. Cell cycle and cell apoptosis were assayed using flow cytometry. Enzymatic activities of caspases were determined by colorimetric assay, and interactions of C-K and caspases were explored by docking analysis. C-K showed significant anti-proliferative effects in HCT-116 and SW-480 cells at concentrations of 30-50 µM. At the same concentrations, Rb1 did not show any effects, while C-K arrested the cells in the G1 phase, and significantly induced cell apoptosis. Compared to HCT-116 (p53 wild-type), the p53 mutant cell line SW-480 was more sensitive to C-K as assessed by cell cycle regulation and apoptosis induction. C-K activated expression of caspases 8 and 9, consistent with docking analysis. The docking data suggested that C-K forms hydrogen bonds with Lys253, Thr904 and Gly362 in caspase 8, and with Thr62, Ser63 and Arg207 in caspase 9. C-K, but not its parent ginsenoside Rb1, showed significant anti-proliferative and pro-apoptotic effects in human colorectal cancer cells. These results suggest that C-K could be a potentially effective anti-colorectal cancer agent.

Identification of loci controlling restriction of parasite growth in experimental Taenia crassiceps cysticercosis

Human neurocysticercosis (NC) caused by Taenia solium is a parasitic disease of the central nervous system that is endemic in many developing countries. In this study, a genetic approach using the murine intraperitoneal cysticercosis caused by the related cestode Taenia crassiceps was employed to identify host factors that regulate the establishment and proliferation of the parasite. A/J mice are permissive to T. crassiceps infection while C57BL/6J mice (B6) are comparatively restrictive, with a 10-fold difference in numbers of peritoneal cysticerci recovered 30 days after infection. The genetic basis of this inter-strain difference was explored using 34 AcB/BcA recombinant congenic strains derived from A/J and B6 progenitors, that were phenotyped for T. crassiceps replication. In agreement with their genetic background, most AcB strains (A/J-derived) were found to be permissive to infection while most BcA strains (B6-derived) were restrictive with the exception of a few discordant strains, together suggesting a possible simple genetic control. Initial haplotype association mapping using >1200 informative SNPs pointed to linkages on chromosomes 2 (proximal) and 6 as controlling parasite replication in the AcB/BcA panel. Additional linkage analysis by genome scan in informative [AcB55xDBA/2]F1 and F2 mice (derived from the discordant AcB55 strain), confirmed the effect of chromosome 2 on parasite replication, and further delineated a major locus (LOD = 4.76, p<0.01; peak marker D2Mit295, 29.7 Mb) that we designate Tccr1 (T. crassiceps cysticercosis restrictive locus 1). Resistance alleles at Tccr1 are derived from AcB55 and are inherited in a dominant fashion. Scrutiny of the minimal genetic interval reveals overlap of Tccr1 with other host resistance loci mapped to this region, most notably the defective Hc/C5 allele which segregates both in the AcB/BcA set and in the AcB55xDBA/2 cross. These results strongly suggest that the complement component 5 (C5) plays a critical role in early protective inflammatory response to infection with T. crassiceps.

Infection with the cestode Taenia solium causes cysticercosis in humans and pigs. Neurocysticercosis is a severe manifestation of T. solium infection that constitutes an important health concern in developing countries. Studies in humans living in areas of endemic disease and in pigs experimentally infected have suggested a large spectrum of permissiveness to T. solium multiplication, with the possible contribution of genetic factors. In the present report, we have used an experimental mouse model of intraperitoneal infection with Taenia crassiceps to study the potential role of genetic factors in regulating replication of this parasite. Our study focused on two inbred mouse strains A/J and C57BL/6J that are respectively permissive and non-permissive to intraperitoneal multiplication of T. crassiceps. We have used a set of AcB/BcA recombinant congenic strains of mice along with standard F2 crosses to decipher the complexity and nature of the genetic component of the A/J vs. C57BL/6J interstrain difference in permissiveness. Our results point to a major role of the complement component 5 (C5) in early response and protection against T. crassiceps infection.

Most lung and colon cancer susceptibility genes are pair-wise linked in mice, humans and rats

Genetic predisposition controlled by susceptibility quantitative trait loci (QTLs) contributes to a large proportion of common cancers. Studies of genetics of cancer susceptibility, however, did not address systematically the relationship between susceptibility to cancers in different organs. We present five sets of data on genetic architecture of colon and lung cancer susceptibility in mice, humans and rats. They collectively show that the majority of genes for colon and lung cancer susceptibility are linked pair-wise and are likely identical or related. Four CcS/Dem recombinant congenic strains, each differing from strain BALB/cHeA by a different small random subset of ±12.5% of genes received from strain STS/A, suggestively show either extreme susceptibility or extreme resistance for both colon and lung tumors, which is unlikely if the two tumors were controlled by independent susceptibility genes. Indeed, susceptibility to lung cancer (Sluc) loci underlying the extreme susceptibility or resistance of such CcS/Dem strains, mapped in 226 (CcS-10×CcS-19)F2 mice, co-localize with susceptibility to colon cancer (Scc) loci. Analysis of additional Sluc loci that were mapped in OcB/Dem strains and Scc loci in CcS/Dem strains, respectively, shows their widespread pair-wise co-localization (P = 0.0036). Finally, the majority of published human and rat colon cancer susceptibility genes map to chromosomal regions homologous to mouse Sluc loci. 12/12 mouse Scc loci, 9/11 human and 5/7 rat colon cancer susceptibility loci are close to a Sluc locus or its homologous site, forming 21 clusters of lung and colon cancer susceptibility genes from one, two or three species. Our data shows that cancer susceptibility QTLs can have much broader biological effects than presently appreciated. It also demonstrates the power of mouse genetics to predict human susceptibility genes. Comparison of molecular mechanisms of susceptibility genes that are organ-specific and those with trans-organ effects can provide a new dimension in understanding individual cancer susceptibility.

A two-locus system controls susceptibility to colitis-associated colon cancer in mice

We have previously shown that the differential susceptibility of A/J (susceptible) and C57BL/6J (B6, resistant) mouse strains to azoxymethane (AOM)-induced colorectal cancer (CRC) is controlled by the chromosome 3 locus, Ccs3. We report that A/J and B6 mice also show differential susceptibility to colitis-associated colorectal cancer (CA-CRC) induced by combined administration of AOM and dextran sulfate. This differential susceptibility is not controlled by Ccs3, but is under distinct genetic control. Linkage analyses in (A/J x B6)F2 mice detected a major CA-CRC susceptibility locus on chromosome 9 (Ccs4) which controls tumor multiplicity and tumor surface area. Susceptibility alleles at Ccs4 are inherited in a recessive fashion, with A/J alleles being associated with susceptibility. We also detected a second locus on chromosome 14 that acts in an additive fashion with Ccs4. Strikingly, F2 mice homozygous for A/J alleles at both loci (Ccs4 and chromosome 14) are as susceptible to CA-CRC as the A/J controls while mice homozygous for B6 alleles are as resistant as the B6 controls, thus supporting the role of two interacting loci in this CA-CRC model. This indicates that susceptibility to chemically-induced CRC and susceptibility to CA-CRC are under distinct genetic control in mice, and probably involve distinct cellular pathways.