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1.  Krüppel-like factor 5 is a crucial mediator of intestinal tumorigenesis in mice harboring combined ApcMin and KRASV12 mutations 
Molecular Cancer  2010;9:63.
Background
Both mutational inactivation of the adenomatous polyposis coli (APC) tumor suppressor gene and activation of the KRAS oncogene are implicated in the pathogenesis of colorectal cancer. Mice harboring a germline ApcMin mutation or intestine-specific expression of the KRASV12 gene have been developed. Both mouse strains develop spontaneous intestinal tumors, including adenoma and carcinoma, though at a different age. The zinc finger transcription factor Krüppel-like factor 5 (KLF5) has previously been shown to promote proliferation of intestinal epithelial cells and modulate intestinal tumorigenesis. Here we investigated the in vivo effect of Klf5 heterozygosity on the propensity of ApcMin/KRASV12 double transgenic mice to develop intestinal tumors.
Results
At 12 weeks of age, ApcMin/KRASV12 mice had three times as many intestinal tumors as ApcMin mice. This increase in tumor number was reduced by 92% in triple transgenic ApcMin/KRASV12/Klf5+/- mice. The reduction in tumor number in ApcMin/KRASV12/Klf5+/- mice was also statistically significant compared to ApcMin mice alone, with a 75% decrease. Compared with ApcMin/KRASV12, tumors from both ApcMin/KRASV12/Klf5+/- and ApcMin mice were smaller. In addition, tumors from ApcMin mice were more distally distributed in the intestine as contrasted by the more proximal distribution in ApcMin/KRASV12 and ApcMin/KRASV12/Klf5+/- mice. Klf5 levels in the normal-appearing intestinal mucosa were higher in both ApcMin and ApcMin/KRASV12 mice but were attenuated in ApcMin/KRASV12/Klf5+/- mice. The levels of β-catenin, cyclin D1 and Ki-67 were also reduced in the normal-appearing intestinal mucosa of ApcMin/KRASV12/Klf5+/- mice when compared to ApcMin/KRASV12 mice. Levels of pMek and pErk1/2 were elevated in the normal-appearing mucosa of ApcMin/KRASV12 mice and modestly reduced in ApcMin/KRASV12/Klf5+/- mice. Tumor tissues displayed higher levels of both Klf5 and β-catenin, irrespective of the mouse genotype from which tumors were derived.
Conclusions
Results of the current study confirm the cumulative effect of Apc loss and oncogenic KRAS activation on intestinal tumorigenesis. The drastic reduction in tumor number and size due to Klf5 heterozygosity in ApcMin/KRASV12 mice indicate a critical function of KLF5 in modulating intestinal tumor initiation and progression.
doi:10.1186/1476-4598-9-63
PMCID: PMC2856552  PMID: 20298593
2.  Fas/CD95 Deficiency in ApcMin/+ Mice Increases Intestinal Tumor Burden 
PLoS ONE  2010;5(2):e9070.
Background
Fas, a member of the tumor necrosis family, is responsible for initiating the apoptotic pathway when bound to its ligand, Fas-L. Defects in the Fas-mediated apoptotic pathway have been reported in colorectal cancer.
Methodology/Principal Findings
In the present study, a variant of the ApcMin/+ mouse, a model for the human condition, Familial Adenomatous Polyposis (FAP), was generated with an additional deficiency of Fas (ApcMin/+/Faslpr) by cross-breeding ApcMin/+ mice with Fas deficient (Faslpr) mice. One of the main limitations of the ApcMin/+ mouse model is that it only develops benign polyps. However, ApcMin/+/Faslpr mice presented with a dramatic increase in tumor burden relative to ApcMin/+ mice and invasive lesions at advanced ages. Proliferation and apoptosis markers revealed an increase in cellular proliferation, but negligible changes in apoptosis, while p53 increased at early ages. Fas-L was lower in ApcMin/+/Faslpr mice relative to ApcMin/+ cohorts, which resulted in enhanced inflammation.
Conclusions/Significance
This study demonstrated that imposition of a Fas deletion in an ApcMin/+ background results in a more aggressive phenotype of the ApcMin/+ mouse model, with more rapid development of invasive intestinal tumors and a decrease in Fas-L levels.
doi:10.1371/journal.pone.0009070
PMCID: PMC2816700  PMID: 20140201
3.  Identification of Mom12 and Mom13, two novel modifier loci of ApcMin-mediated intestinal tumorigenesis 
Cell Cycle  2011;10(7):1092-1099.
Colorectal cancer is a heterogeneous disease resulting from a combination of genetic and environmental factors. The C57BL/6J (B6) ApcMin/+ mouse develops polyps throughout the gastrointestinal tract and has been a valuable model for understanding the genetic basis of intestinal tumorigenesis. ApcMin/+ mice have been used to study known oncogenes and tumor suppressor genes on a controlled genetic background. These studies often utilize congenic knockout alleles, which can carry an unknown amount of residual donor DNA. The ApcMin model has also been used to identify modifer loci, known as Modifier of Min (Mom) loci, which alter ApcMin-mediated intestinal tumorigenesis. B6 mice carrying a knockout allele generated in WW6 embryonic stem cells were crossed to B6 ApcMin/+ mice to determine the effect on polyp multiplicity. The newly generated colony developed significantly more intestinal polyps than ApcMin/+ controls. Polyp multiplicity did not correlate with inheritance of the knockout allele, suggesting the presence of one or more modifier loci segregating in the colony. Genotyping of simple sequence length polymorphism (SSLP) markers revealed residual 129X1/SvJ genomic DNA within the congenic region of the parental knockout line. An analysis of polyp multiplicity data and SSLP genotyping indicated the presence of two Mom loci in the colony: (1) Mom12, a dominant modifier linked to the congenic region on chromosome 6 and (2) Mom13, which is unlinked to the congenic region and whose effect is masked by Mom12. The identification of Mom12 and Mom13 demonstrates the potential problems resulting from residual heterozygosity present in congenic lines.
doi:10.4161/cc.10.7.15089
PMCID: PMC3100885  PMID: 21386660
adenomatous polyposis coli; modifier of min; congenic mice; caveolin-1; cancer susceptibility
4.  SPDEF Functions as a Colorectal Tumor Suppressor by Inhibiting β-Catenin Activity 
Gastroenterology  2013;144(5):1012-1023.e6.
BACKGROUND & AIMS
Expression of the SAM pointed domain containing ETS transcription factor (SPDEF or prostate-derived ETS factor) is regulated by Atoh1 and is required for the differentiation of goblet and Paneth cells. SPDEF has been reported to suppress the development of breast, prostate, and colon tumors. We analyzed levels of SPDEF in colorectal tumor samples from patients and its tumor-suppressive functions in mouse models of colorectal cancer (CRC).
METHODS
We analyzed levels of SPDEF messenger RNA and protein in more than 500 human CRC samples and more than 80 nontumor controls. Spdef−/− and wild-type mice (controls) were either bred with ApcMin/+ mice, or given azoxymethane (AOM) and dextran sodium sulfate (DSS), or 1,2-dimethylhydrazine and DSS, to induce colorectal tumors. Expression of Spdef also was induced transiently by administration of tetracycline to Spdefdox-intestine mice with established tumors, induced by the combination of AOM and DSS or by breeding with ApcMin/+ mice. Colon tissues were collected and analyzed for tumor number, size, grade, and for cell proliferation and apoptosis. We also analyzed the effects of SPDEF expression in HCT116 and SW480 human CRC cells.
RESULTS
In colorectal tumors from patients, loss of SPDEF was observed in approximately 85% of tumors and correlated with progression from normal tissue, to adenoma, to adenocarcinoma. Spdef−/−; ApcMin/+ mice developed approximately 3-fold more colon tumors than Spdef+/+; ApcMin/+ mice. Likewise, Spdef−/− mice developed approximately 3-fold more colon tumors than Spdef+/+ mice after administration of AOM and DSS. After administration of 1,2-dimethylhydrazine and DSS, invasive carcinomas were observed exclusively in Spdef−/− mice. Conversely, expression of SPDEF was sufficient to promote cell-cycle exit in cells of established adenomas from Spdefdox-intestine; ApcMin/+ mice and in Spdefdox-intestine mice after administration of AOM + DSS. SPDEF inhibited the expression of β-catenin–target genes in mouse colon tumors, and interacted with β-catenin to block its transcriptional activity in CRC cell lines, resulting in lower levels of cyclin D1 and c-MYC.
CONCLUSIONS
SPDEF is a colon tumor suppressor and a candidate therapeutic target for colon adenomas and adenocarcinoma.
doi:10.1053/j.gastro.2013.01.043
PMCID: PMC3738069  PMID: 23376423
Notch Signaling; Differentiation Factor; Colon Cancer; Colitis-Associated Cancer
5.  The pro-apoptotic K-Ras 4A proto-oncoprotein does not affect tumorigenesis in the ApcMin/+ mouse small intestine 
BMC Gastroenterology  2008;8:24.
Background
Alterations in gene splicing occur in human sporadic colorectal cancer (CRC) and may contribute to tumour progression. The K-ras proto-oncogene encodes two splice variants, K-ras 4A and 4B, and K-ras activating mutations which jointly affect both isoforms are prevalent in CRC. Past studies have established that splicing of both the K-ras oncogene and proto-oncogene is altered in CRC in favour of K-ras 4B. The present study addressed whether the K-Ras 4A proto-oncoprotein can suppress tumour development in the absence of its oncogenic allele, utilising the ApcMin/+ (Min) mouse that spontaneously develops intestinal tumours that do not harbour K-ras activating mutations, and the K-rastmΔ4A/tmΔ4A mouse that can express the K-ras 4B splice variant only. By this means tumorigenesis in the small intestine was compared between ApcMin/+, K-ras+/+ and ApcMin/+, K-rastmΔ4A/tmΔ4A mice that can, and cannot, express the K-ras 4A proto-oncoprotein respectively.
Methods
The relative levels of expression of the K-ras splice variants in normal small intestine and small intestinal tumours were quantified by real-time RT-qPCR analysis. Inbred (C57BL/6) ApcMin/+, K-ras+/+ and ApcMin/+, K-rastmΔ4A/tmΔ4A mice were generated and the genotypes confirmed by PCR analysis. Survival of stocks was compared by the Mantel-Haenszel test, and tumour number and area compared by Student's t-test in outwardly healthy mice at approximately 106 and 152 days of age. DNA sequencing of codons 12, 13 and 61 was performed to confirm the intestinal tumours did not harbour a K-ras activating mutation.
Results
The K-ras 4A transcript accounted for about 50% of K-ras expressed in the small intestine of both wild-type and Min mice. Tumours in the small intestine of Min mice showed increased levels of K-ras 4B transcript expression, but no appreciable change in K-ras 4A transcript levels. No K-ras activating mutations were detected in 27 intestinal tumours derived from Min and compound mutant Min mice. K-Ras 4A deficiency did not affect mouse survival, or tumour number, size or histopathology.
Conclusion
The K-Ras 4A proto-oncoprotein does not exhibit tumour suppressor activity in the small intestine, even though the K-ras 4A/4B ratio is reduced in adenomas lacking K-ras activating mutations.
doi:10.1186/1471-230X-8-24
PMCID: PMC2442095  PMID: 18554389
6.  Five Quantitative Trait Loci Control Radiation-Induced Adenoma Multiplicity in Mom1R ApcMin/+ Mice 
PLoS ONE  2009;4(2):e4388.
Ionising radiation is a carcinogen capable of inducing tumours, including colorectal cancer, in both humans and animals. By backcrossing a recombinant line of ApcMin/+ mice to the inbred BALB/c mouse strain, which is unusually sensitive to radiation–induced tumour development, we obtained panels of 2Gy-irradiated and sham-irradiated N2 ApcMin/+ mice for genotyping with a genome-wide panel of microsatellites at ∼15 cM density and phenotyping by counting adenomas in the small intestine. Interval and composite interval mapping along with permutation testing identified five significant susceptibility quantitative trait loci (QTLs) responsible for radiation induced tumour multiplicity in the small intestine. These were defined as Mom (Modifier of Min) radiation-induced polyposis (Mrip1-5) on chromosome 2 (log of odds, LOD 2.8, p = 0.0003), two regions within chromosome 5 (LOD 5.2, p<0.00001, 6.2, p<0.00001) and two regions within chromosome 16 respectively (LOD 4.1, p  = 4×10−5, 4.8, p<0.00001). Suggestive QTLs were found for sham-irradiated mice on chromosomes 3, 6 and 13 (LOD 1.7, 1.5 and 2.0 respectively; p<0.005). Genes containing BALB/c specific non-synonymous polymorphisms were identified within Mrip regions and prediction programming used to locate potentially functional polymorphisms. Our study locates the QTL regions responsible for increased radiation-induced intestinal tumorigenesis in ApcMin/+ mice and identifies candidate genes with predicted functional polymorphisms that are involved in spindle checkpoint and chromosomal stability (Bub1b, Casc5, and Bub1), DNA repair (Recc1 and Prkdc) or inflammation (Duox2, Itgb2l and Cxcl5). Our study demonstrates use of in silico analysis in candidate gene identification as a way of reducing large-scale backcross breeding programmes.
doi:10.1371/journal.pone.0004388
PMCID: PMC2633613  PMID: 19194513
7.  Long-lived Min Mice Develop Advanced Intestinal Cancers through a Genetically Conservative Pathway 
Cancer research  2009;69(14):5768-5775.
C57BL/6J mice carrying the Min allele of Adenomatous polyposis coli (Apc) develop numerous adenomas along the entire length of the intestine and consequently die at an early age. This short lifespan would prevent the accumulation of somatic genetic mutations or epigenetic alterations necessary for tumor progression. To overcome this limitation, we generated F1 ApcMin/+ hybrids by crossing C57BR/cdcJ and SWR/J females to B6 ApcMin/+ males. These hybrids developed few intestinal tumors and often lived longer than 1 year. Many of the tumors (24–87%) were invasive adenocarcinomas, in which neoplastic tissue penetrated through the muscle wall into the mesentery. In a few cases (3%), lesions metastasized by extension to regional lymph nodes. The development of these familial cancers does not require chromosomal gains or losses, a high level of microsatellite instability, or the presence of Helicobacter. To test whether genetic instability might accelerate tumor progression, we generated ApcMin/+ mice homozygous for the hypomorphic allele of the Nijmegen breakage syndrome gene (Nbs1ΔB) and also treated ApcMin/+ mice with a strong somatic mutagen. These imposed genetic instabilities did not reduce the time required for cancers to form, nor increase the percentage of cancers, nor drive progression to the point of distant metastasis. In summary, we have found that the ApcMin/+ mouse model for familial intestinal cancer can develop frequent invasive cancers in the absence of overt genomic instability. Possible factors that promote invasion include age-dependent epigenetic changes, conservative somatic recombination, or direct effects of alleles in the F1 hybrid genetic background.
doi:10.1158/0008-5472.CAN-09-0446
PMCID: PMC2775466  PMID: 19584276
Intestinal neoplasia; invasive adenocarcinomas; local metastasis; microsatellite instability; chromosomal instability
8.  Cables1 is a tumor suppressor gene that regulates intestinal tumor progression in ApcMin mice 
Cancer Biology & Therapy  2013;14(7):672-678.
The transformation of colonic mucosal epithelium to adenocarcinoma requires progressive oncogene activation and tumor suppressor gene inactivation. Loss of chromosome 18q is common in colon cancer but not in precancerous adenomas. A few candidate tumor suppressor genes have been identified in this region, including CABLES1 at 18q11.2−12.1. This study investigates the role of CABLES1 in an in vivo mouse model of intestinal adenocarcinoma and in human colon cancer cell culture. ApcMin/+ mice were crossed with mice harboring targeted inactivation of the Cables1 gene (Cables1−/−). The intestinal tumor burden and tumor expression of β-catenin and PCNA was compared in Cables1+/+ApcMin/+ and Cables1−/−ApcMin/+ mice. β-catenin activity in human colon cancer cells with CABLES1 inactivation and intestinal progenitor cell function in Cables1−/− mice were assayed in vitro. The mean number of small intestinal tumors per mouse was 3.1 ± 0.6 in Cables1+/+ ApcMin/+ mice, compared with 32.4 ± 3.5 in the Cables1−/−ApcMin/+ mice (P < 0.0001). Fewer colonic tumors were observed in Cables1+/+ApcMin/+ mice (mean 0.6 ± 0.1) compared with the Cables1−/−ApcMin/+ mice (mean 1.3 ± 0.3, P = 0.01). Tumors from Cables1−/−ApcMin/+ mice demonstrated increased nuclear expression of β-catenin and an increased number of PCNA-positive cells. In vitro studies revealed that CABLES1 deficiency increased β-catenin dependent transcription and increased intestinal progenitor cell activity. Loss of Cables1 enhances tumor progression in the ApcMin/+ mouse model and activates the Wnt/β-catenin signaling pathway. Cables1 is a tumor suppressor gene on chromosome 18q in this in vivo mouse model and likely has a similar role in human colon cancer.
doi:10.4161/cbt.25089
PMCID: PMC3742496  PMID: 23792637
ApcMinmice; Cables1; adenocarcinoma; chromosome 18q; colorectal cancer; tumor suppressor gene; β-catenin
9.  Colorectal Cancer Screening for Average-Risk North Americans: An Economic Evaluation 
PLoS Medicine  2010;7(11):e1000370.
An economic analysis of different screening methods for detection of colorectal cancers suggests that in US or Canadian settings, screening with fecal immunochemical testing results in lower health-care costs as compared with other screening approaches.
Background
Colorectal cancer (CRC) fulfills the World Health Organization criteria for mass screening, but screening uptake is low in most countries. CRC screening is resource intensive, and it is unclear if an optimal strategy exists. The objective of this study was to perform an economic evaluation of CRC screening in average risk North American individuals considering all relevant screening modalities and current CRC treatment costs.
Methods and Findings
An incremental cost-utility analysis using a Markov model was performed comparing guaiac-based fecal occult blood test (FOBT) or fecal immunochemical test (FIT) annually, fecal DNA every 3 years, flexible sigmoidoscopy or computed tomographic colonography every 5 years, and colonoscopy every 10 years. All strategies were also compared to a no screening natural history arm. Given that different FIT assays and collection methods have been previously tested, three distinct FIT testing strategies were considered, on the basis of studies that have reported “low,” “mid,” and “high” test performance characteristics for detecting adenomas and CRC. Adenoma and CRC prevalence rates were based on a recent systematic review whereas screening adherence, test performance, and CRC treatment costs were based on publicly available data. The outcome measures included lifetime costs, number of cancers, cancer-related deaths, quality-adjusted life-years gained, and incremental cost-utility ratios. Sensitivity and scenario analyses were performed. Annual FIT, assuming mid-range testing characteristics, was more effective and less costly compared to all strategies (including no screening) except FIT-high. Among the lifetimes of 100,000 average-risk patients, the number of cancers could be reduced from 4,857 to 1,782 and the number of CRC deaths from 1,393 to 457, while saving CAN$68 per person. Although screening patients with FIT became more expensive than a strategy of no screening when the test performance of FIT was reduced, or the cost of managing CRC was lowered (e.g., for jurisdictions that do not fund expensive biologic chemotherapeutic regimens), CRC screening with FIT remained economically attractive.
Conclusions
CRC screening with FIT reduces the risk of CRC and CRC-related deaths, and lowers health care costs in comparison to no screening and to other existing screening strategies. Health policy decision makers should consider prioritizing funding for CRC screening using FIT.
Please see later in the article for the Editors' Summary
Editors' Summary
Background
Colorectal (bowel) cancer is the second leading cause of cancer deaths for both men and women in North America. Colorectal cancer screening is an important means for reducing morbidity and mortality and fulfils the World Health Organization criteria for mass screening. However, a variety of CRC screening approaches are available. Colonoscopy is viewed as the gold standard of colorectal cancer screening as it has a high sensitivity for identifying adenomas and cancer and polyps can be removed during the screening examination. However, colonoscopy is associated with a number of complications and there are also barriers to access. Another type of test, the guaiac fecal occult blood test, has been shown to reduce mortality from colorectal cancer but this test has low sensitivity for identifying colorectal neoplasia, particularly adenomas. Fecal immunochemical tests, which also detect blood in the stool, have improved test performance characteristics (high sensitivity and specificity) and the potential to improve participation rates compared to guaiac fecal occult blood test and flexible sigmoidoscopy. Fecal DNA (a stool test, based on the detection of DNA shed by cancerous tissue) is another screening option, as is computed tomographic colonography (“virtual” colonoscopy), that might rival colonoscopy in detecting advanced adenomas and colorectal cancer but is expensive and requires a full colonic preparation.
Why Was This Study Done?
In the absence of firm comparative evidence to guide the selection of any one screening modality and given the varied test performance characteristics and the significant differences in costs and resources associated with each, a robust cost-effectiveness analysis might help health policy makers in deciding whether or not to offer screening and if so, in selecting the most appropriate and cost effective screening modality. In this study the researchers conducted a full economic evaluation of all relevant colorectal cancer screening modalities in North America.
What Did the Researchers Do and Find?
The researchers used an incremental cost-utility analysis, a sophisticated modeling technique, and two hypothetical patient cohorts (individuals with an “average risk,” i.e., no family history of colorectal cancer, aged 50–64 and 65–75) to compare guaiac-based fecal occult blood test or fecal immunochemical test annually (the researchers considered three distinct fecal immunochemical testing strategies on the basis of assays and collection methods taken from studies that have reported “low,” “mid,” and “high” test performance characteristics), fecal DNA every three years, flexible sigmoidoscopy or computed tomographic colonography every 5 years, and colonoscopy every 10 years. The researchers also included a no screening natural history arm as a comparison to each screening approach. For the baseline data of their model, the researchers used adenoma and colorectal prevalence rates from a recent systematic review and based screening adherence, test performance, and colorectal treatment costs on available data. The researchers found that annual fecal immunochemical testing with mid-range testing characteristics, was more effective and less costly compared to all strategies (including no screening). Using this screening modality, among the lifetimes of 100,000 average-risk patients, the number of cancers could be reduced from 4,857 to 1,393 and the number of deaths from colorectal cancer from 1,782 to 457, while saving CAN$68 per person. Although in the sensitivity and scenario analysis, screening patients using fecal immunochemical testing became more expensive than a strategy of no screening when the test performance of fecal immunochemical testing was reduced, or the cost of managing colorectal cancers was lowered, the researchers found that screening for colorectal cancer with fecal immunochemical testing remained the most economically attractive screening option.
What Do These Findings Mean?
This model-based economic analysis found that fecal immunochemical testing is more effective and less costly than all other colorectal screening strategies, including the most commonly-used stool-based screening test, guaiac-based fecal occult blood testing, and no screening. Furthermore, this study suggests that annual screening with fecal immunochemical testing (assuming mid-range test performance characteristics) reduces the risk of colorectal cancer and colorectal cancer–related deaths, and lowers health care costs in comparison to all other screening strategies and to no screening. Therefore, health policy makers should consider prioritizing funding for fecal immunochemical testing as the screening modality for colorectal cancer.
Additional Information
Please access these Web sites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.1000370.
Cancer.org has information for patients on colorectal cancer
The US Centers for Disease Control (CDC) list colorectal screening guidelines
The CDC also provides patient information on colorectal cancer Screening
doi:10.1371/journal.pmed.1000370
PMCID: PMC2990704  PMID: 21124887
10.  The Myc 3′ Wnt-Responsive Element Suppresses Colonic Tumorigenesis 
Molecular and Cellular Biology  2014;34(9):1659-1669.
Mutations in components of the Wnt/β-catenin signaling pathway are commonly found in colorectal cancers, and these mutations cause aberrant expression of genes controlled by Wnt-responsive DNA elements (WREs). While the c-Myc proto-oncogene (Myc) is required for intestinal phenotypes associated with pathogenic Wnt/β-catenin signaling in vivo, the WREs that control Myc expression in this setting have yet to be fully described. Previously, we demonstrated that the Myc 3′ WRE was required for intestinal homeostasis and intestinal repair in response to damage. Here, we tested the role of the Myc 3′ WRE in intestinal tumorigenesis using two independent mouse models. In comparison to ApcMin/+ mice, ApcMin/+ Myc 3′ WRE−/− mice contained 25% fewer tumors in the small intestine. Deletion of the Myc 3′ WRE−/− in the ApcMin/+ background resulted in 4-fold more colonic tumors. In a model of colitis-associated colorectal cancer, the Myc 3′ WRE suppressed colonic tumorigenesis, most notably within the cecum. Using chromatin immunoprecipitation and transcript analysis of purified colonic crypts, we found that the Myc 3′ WRE is required for the transcriptional regulation of Myc expression in vivo. These results emphasize the critical role of the Myc 3′ WRE in maintaining homeostatic Myc expression.
doi:10.1128/MCB.00969-13
PMCID: PMC3993608  PMID: 24567369
11.  Vitamin D Receptor Deficiency Enhances Wnt/β-Catenin Signaling and Tumor Burden in Colon Cancer 
PLoS ONE  2011;6(8):e23524.
Aberrant activation of the Wnt/β-catenin pathway is critical for the initiation and progression of most colon cancers. This activation provokes the accumulation of nuclear β-catenin and the induction of its target genes. Apcmin/+ mice are the most commonly used model for colon cancer. They harbor a mutated Apc allele and develop intestinal adenomas and carcinomas during the first months of life. This phenotype is caused by the mutation of the second Apc allele and the consequent accumulation of nuclear β-catenin in the affected cells. Here we describe that vitamin D receptor (VDR) is a crucial modulator of nuclear β-catenin levels in colon cancer in vivo. By appropriate breeding of Apcmin/+ mice and Vdr+/− mice we have generated animals expressing a mutated Apc allele and two, one, or none Vdr wild type alleles. Lack of Vdr increased the number of colonic Aberrant Crypt Foci (ACF) but not that of adenomas or carcinomas in either small intestine or colon. Importantly, colon ACF and tumors of Apcmin/+Vdr-/- mice had increased nuclear β-catenin and the tumors reached a larger size than those of Apcmin/+Vdr+/+. Both ACF and carcinomas in Apcmin/+Vdr-/- mice showed higher expression of β-catenin/TCF target genes. In line with this, VDR knock-down in cultured human colon cancer cells enhanced β-catenin nuclear content and target gene expression. Consistently, VDR depletion abrogated the capacity of 1,25(OH)2D3 to promote the relocation of β-catenin from the nucleus to the plasma membrane and to inhibit β-catenin/TCF target genes. In conclusion, VDR controls the level of nuclear β-catenin in colon cancer cells and can therefore attenuate the impact of oncogenic mutations that activate the Wnt/β-catenin pathway.
doi:10.1371/journal.pone.0023524
PMCID: PMC3156234  PMID: 21858154
12.  Characterization of hERG1 channel role in mouse colorectal carcinogenesis 
Cancer Medicine  2013;2(5):583-594.
The human ether-à-go-go-related gene (hERG)1 K+ channel is upregulated in human colorectal cancer cells and primary samples. In this study, we examined the role of hERG1 in colorectal carcinogenesis using two mouse models: adenomatous polyposis coli (Apcmin/+) and azoxymethane (AOM)-treated mice. Colonic polyps of Apcmin/+ mice overexpressed mERG1 and their formation was reverted by the hERG1 blocker E4031. AOM was applied to either hERG1-transgenic (TG) mice, which overexpress hERG1 in the mucosa of the large intestine, or wild-type mice. A significant increase of both mucin-depleted foci and polyps in the colon of hERG1-TG mice was detected. Both the intestine of TG mice and colonic polyps of Apcmin/+ showed an upregulation of phospho-Protein Kinase B (pAkt)/vascular endothelial growth factor (VEGF-A) and an increased angiogenesis, which were reverted by treatment with E4031. On the whole, this article assigns a relevant role to hERG1 in the process of in vivo colorectal carcinogenesis.
doi:10.1002/cam4.72
PMCID: PMC3892791  PMID: 24403225
Apcmin/+ mice; azoxymethane; colorectal cancer; hERG1 channel; VEGF-A
13.  Roles of Arrest-Defective Protein 1225 and Hypoxia-Inducible Factor 1α in Tumor Growth and Metastasis 
Background
Vascular endothelial growth factor A (VEGFA), a critical mediator of tumor angiogenesis, is a well-characterized target of hypoxia-inducible factor 1 (HIF-1). Murine arrest-defective protein 1A (mARD1A225) acetylates HIF-1α, triggering its degradation, and thus may play a role in decreased expression of VEGFA.
Methods
We generated ApcMin/+/mARD1A225 transgenic mice and quantified growth of intestinal polyps. Human gastric MKN74 and murine melanoma B16F10 cells overexpressing mARD1A225 were injected into mice, and tumor growth and metastasis were measured. VEGFA expression and microvessel density in tumors were assessed using immunohistochemistry. To evaluate the role of mARD1A225 acetylation of Lys532 in HIF-1α, we injected B16F10-mARD1A225 cell lines stably expressing mutant HIF-1α/K532R into mice and measured metastasis. All statistical tests were two-sided, and P values less than .05 were considered statistically significant.
Results
ApcMin/+/mARD1A225 transgenic mice (n = 25) had statistically significantly fewer intestinal polyps than ApcMin/+ mice (n = 21) (number of intestinal polyps per mouse: ApcMin/+ mice vs ApcMin/+/mARD1A225 transgenic mice, mean = 83.4 vs 38.0 polyps, difference = 45.4 polyps, 95% confidence interval [CI] = 41.8 to 48.6; P < .001). The growth and metastases of transplanted tumors were also statistically significantly reduced in mice injected with mARD1A225-overexpressing cells than in mice injected with control cells (P < .01). Moreover, overexpression of mARD1A225 decreased VEGFA expression and microvessel density in tumor xenografts (P < .04) and ApcMin/+ intestinal polyps (P = .001). Mutation of lysine 532 of HIF-1α in B16F10-mARD1A225 cells prevented HIF-1α degradation and inhibited the antimetastatic effect of mARD1A225 (P < .001).
Conclusion
mARD1A225 may be a novel upstream target that blocks VEGFA expression and tumor-related angiogenesis.
doi:10.1093/jnci/djq026
PMCID: PMC2841038  PMID: 20194889
14.  Haploinsufficiency of Krüppel-Like Factor 4 Promotes Adenomatous Polyposis Coli–Dependent Intestinal Tumorigenesis 
Cancer research  2007;67(15):7147-7154.
The zinc finger transcription factor Krüppel-like factor 4 (KLF4) is frequently down-regulated in colorectal cancer. Previous studies showed that the expression of KLF4 was activated by the colorectal cancer tumor suppressor adeno-matous polyposis coli (APC) and that KLF4 repressed the Wnt/β-catenin pathway. Here, we examined whether KLF4 plays a role in modulating intestinal tumorigenesis by comparing the tumor burdens in mice heterozygous for the ApcMin allele (ApcMin/+) and those heterozygous for both the ApcMin and Klf4 alleles (Klf4+/−/ApcMin/+). Between 10 and 20 weeks of age, Klf4+/−/ApcMin/+ mice developed, on average, 59% more intestinal adenomas than ApcMin/+ mice (P < 0.0001). Immunohistochemical staining showed that Klf4 protein levels were lower in the normal-appearing intestinal tissues of Klf4+/−/ApcMin/+ mice compared with wild-type, Klf4+/−, or ApcMin/+ mice. In contrast, the levels of β-catenin and cyclin D1 were higher in the normal-appearing intestinal tissues of Klf4+/−/ApcMin/+ mice compared with the other three genotypes. Klf4 levels were further decreased in adenomas from both ApcMin/+ and Klf4+/−/ApcMin/+ mice compared with their corresponding normal-appearing tissues. Reverse transcription-PCR showed an inverse correlation between adenoma size and Klf4 mRNA levels in both Klf4+/−/ApcMin/+ and ApcMin/+ mice. There was also a progressive loss of heterozygosity of the wild-type Apc allele in adenomas with increasing size from Klf4+/−/ApcMin/+ and ApcMin/+ mice. Results from this study show that KLF4 plays an important role in promoting the development of intestinal adenomas in the presence of ApcMin mutation.
doi:10.1158/0008-5472.CAN-07-1302
PMCID: PMC2373271  PMID: 17671182
15.  Muscarinic receptor subtype-3 gene ablation and scopolamine butylbromide treatment attenuate small intestinal neoplasia in Apcmin/+ mice 
Carcinogenesis  2011;32(9):1396-1402.
M3 subtype muscarinic receptors (CHRM3) are over-expressed in colon cancer. In this study, we used Apcmin/+ mice to identify the role of Chrm3 expression in a genetic model of intestinal neoplasia, explored the role of Chrm3 in intestinal mucosal development and determined the translational potential of inhibiting muscarinic receptor activation. We generated Chrm3-deficient Apcmin/+ mice and compared intestinal morphology and tumor number in 12-week-old Apcmin/+Chrm3−/− and Apcmin/+Chrm3+/+ control mice. Compared with Apcmin/+Chrm3+/+ mice, Apcmin/+Chrm3−/− mice showed a 70 and 81% reduction in tumor number and volume, respectively (P < 0.01). In adenomas, β-catenin nuclear staining was reduced in Apcmin/+Chrm3−/− compared with Apcmin/+Chrm3+/+ mice (P < 0.02). Whereas Apc gene mutation increased the number of crypt and Paneth cells and decreased villus goblet cells, these changes were absent in Apcmin/+Chrm3−/− mice. To determine whether pharmacological inhibition of muscarinic receptor activation attenuates intestinal neoplasia, we treated 6-week-old Apcmin/+ mice with scopolamine butylbromide, a non-subtype-selective muscarinic receptor antagonist. After 8 weeks of continuous treatment, scopolamine butylbromide-treated mice showed a 22% reduction in tumor number (P = 0.027) and a 36% reduction in tumor volume (P = 0.004) as compared with control mice. Compared with Chrm3 gene ablation, the muscarinic antagonist was less efficacious, most probably due to shorter duration of treatment and incomplete blockade of muscarinic receptors. Overall, these findings indicate that interplay of Chrm3 and β-catenin signaling is important for intestinal mucosal differentiation and neoplasia and provide a proof-of-concept that pharmacological inhibition of muscarinic receptor activation can attenuate intestinal neoplasia in vivo.
doi:10.1093/carcin/bgr118
PMCID: PMC3165126  PMID: 21705482
16.  Candidate serum biomarkers for early intestinal cancer using 15N metabolic labeling and quantitative proteomics in the Apcmin/+ mouse 
Journal of proteome research  2013;12(9):4152-4166.
Current screening procedures for colorectal cancer are imperfect, highly invasive and result in increased mortality rates due to low compliance. The goal of the experiments reported herein is to identify potential blood-based biomarkers indicative of early-stage intestinal cancers using the ApcMin/+ mouse model of intestinal cancer as an experimental system. Serum proteins from tumor-bearing ApcMin/+ mice were quantitatively compared to tumor-free Apc+/+ wild-type mice via in anima metabolic labeling with 14N/15N labeled Spirulina algae and an LTQ Orbitrap mass spectrometer. Out of 1116 total serum proteins quantified, this study identified 40 that were differentially expressed and correlated with the increase in intestinal neoplasms. A subset of these differentially expressed proteins underwent a secondary quantitative screen using selected reaction monitoring-mass spectrometry with stable isotope-labeled peptides. Using both quantitative techniques, we identified MGAM and COL1A1 as downregulated and ITIH3 and F5 as upregulated in serum. All but COL1A1 were similarly differentially expressed in the mRNA of neoplastic colonic tissues of ApcMin/+ mice compared to normal wild-type tissue. These differentially expressed proteins identified in the ApcMin/+ mouse model have provided a set of candidate biomarkers for future validation screens in humans.
doi:10.1021/pr400467c
PMCID: PMC3792563  PMID: 23924158
Blood protein biomarkers; Intestinal cancer; Colon cancer; ApcMin/+ mouse; 14N/15N metabolic labeling; Tandem mass spectrometry; Selected Reaction Monitoring-Mass Spectrometry; mRNA Microarray
17.  Leptin stimulates the proliferation of human colon cancer cells in vitro but does not promote the growth of colon cancer xenografts in nude mice or intestinal tumorigenesis in ApcMin/+ mice 
Gut  2005;54(8):1136-1145.
Background and aims: Leptin, the product of the ob gene, has been suggested to increase the risk of colon cancer. However, we have shown that although leptin stimulates epithelial cell proliferation it reduces the development of carcinogen induced preneoplastic lesions in the rat colon. Here, we explored the effect of leptin in vitro on proliferation of human colon cancer cells, and in vivo on the growth of HT-29 xenografts in nude mice and the development of intestinal tumours in ApcMin/+ mice.
Methods: Proliferation of HT-29, LoVo, Caco2, and SW 480 cells was assessed in the absence or presence of leptin (20–500 ng/ml) by 3H-thymidine incorporation and cell count. Leptin (800 µg/kg/day) or its vehicle was delivered for four weeks to nude mice, inoculated with HT-29 cells on day 0, and for six weeks to ApcMin/+ mice.
Results: Leptin dose dependently stimulated cell DNA synthesis and growth in all cell lines. In nude mice, leptin caused a 4.3-fold increase in plasma leptin levels compared with pair fed controls. This hyperleptinaemia, despite leptin receptor expression in tumours, did not induce significant variation in tumour volume or weight. Tumour Ki-67 index was even inhibited. In leptin treated ApcMin/+ mice, a 2.4-fold increase in plasma leptin levels did not modify the number, size, or distribution of intestinal adenomas compared with pair fed controls.
Conclusions: Leptin acts as a growth factor on colon cancer cells in vitro but does not promote tumour growth in vivo in the two models tested. These findings do not support a pivotal role for hyperleptinaemia in intestinal carcinogenesis.
doi:10.1136/gut.2004.060533
PMCID: PMC1774895  PMID: 15857934
hormone; carcinogenesis; animal models; cell lines; TdT, terminal deoxynucleotidyl transferase; TUNEL, terminal deoxynucleotidyl transferase mediated dUTP nick end labelling
18.  Fecal Lipocalin 2, a Sensitive and Broadly Dynamic Non-Invasive Biomarker for Intestinal Inflammation 
PLoS ONE  2012;7(9):e44328.
Inflammation has classically been defined histopathologically, especially by the presence of immune cell infiltrates. However, more recent studies suggest a role for "low-grade" inflammation in a variety of disorders ranging from metabolic syndrome to cancer, which is defined by modest elevations in pro-inflammatory gene expression. Consequently, there is a need for cost-effective, non-invasive biomarkers that, ideally, would have the sensitivity to detect low-grade inflammation and have a dynamic range broad enough to reflect classic robust intestinal inflammation. Herein, we report that, for assessment of intestinal inflammation, fecal lipocalin 2 (Lcn-2), measured by ELISA, serves this purpose. Specifically, using a well-characterized mouse model of DSS colitis, we observed that fecal Lcn-2 and intestinal expression of pro-inflammatory cytokines (IL-1β, CXCL1, TNFα) are modestly but significantly induced by very low concentrations of DSS (0.25 and 0.5%), and become markedly elevated at higher concentrations of DSS (1.0 and 4.0%). As expected, careful histopathologic analysis noted only modest immune infiltrates at low DSS concentration and robust colitis at higher DSS concentrations. In accordance, increased levels of the neutrophil product myeloperoxidase (MPO) was only detected in mice given 1.0 and 4.0% DSS. In addition, fecal Lcn-2 marks the severity of spontaneous colitis development in IL-10 deficient mice. Unlike histopathology, MPO, and q-RT-PCR, the assay of fecal Lcn-2 requires only a stool sample, permits measurement over time, and can detect inflammation as early as 1 day following DSS administration. Thus, assay of fecal Lcn-2 by ELISA can function as a non-invasive, sensitive, dynamic, stable and cost-effective means to monitor intestinal inflammation in mice.
doi:10.1371/journal.pone.0044328
PMCID: PMC3434182  PMID: 22957064
19.  CCR6, the Sole Receptor for the Chemokine CCL20, Promotes Spontaneous Intestinal Tumorigenesis 
PLoS ONE  2014;9(5):e97566.
Interactions between the inflammatory chemokine CCL20 and its receptor CCR6 have been associated with colorectal cancer growth and metastasis, however, a causal role for CCL20 signaling through CCR6 in promoting intestinal carcinogenesis has not been demonstrated in vivo. In this study, we aimed to determine the role of CCL20-CCR6 interactions in spontaneous intestinal tumorigenesis. CCR6-deficient mice were crossed with mice heterozygous for a mutation in the adenomatous polyposis coli (APC) gene (APCMIN/+ mice) to generate APCMIN/+ mice with CCR6 knocked out (CCR6KO-APCMIN/+ mice). CCR6KO-APCMIN/+ mice had diminished spontaneous intestinal tumorigenesis. CCR6KO-APCMIN/+ also had normal sized spleens as compared to the enlarged spleens found in APCMIN/+ mice. Decreased macrophage infiltration into intestinal adenomas and non-tumor epithelium was observed in CCR6KO-APCMIN/+ as compared to APCMIN/+ mice. CCL20 signaling through CCR6 caused increased production of CCL20 by colorectal cancer cell lines. Furthermore, CCL20 had a direct mitogenic effect on colorectal cancer cells. Thus, interactions between CCL20 and CCR6 promote intestinal carcinogenesis. Our results suggest that the intestinal tumorigenesis driven by CCL20-CCR6 interactions may be driven by macrophage recruitment into the intestine as well as proliferation of neoplastic epithelial cells. This interaction could be targeted for the treatment or prevention of malignancy.
doi:10.1371/journal.pone.0097566
PMCID: PMC4035256  PMID: 24866282
20.  eRapa Restores A Normal Life Span in a FAP Mouse Model 
Mutation of a single copy of the adenomatous polyposis coli (APC) gene results in familial adenomatous polyposis (FAP), which confers an extremely high risk for colon cancer. ApcMin/+ mice exhibit multiple intestinal neoplasia (MIN) that causes anemia and death from bleeding by 6 months. Mechanistic target of rapamycin complex 1 (mTORC1) inhibitors were shown to improve ApcMin/+ mouse survival when administered by oral gavage or added directly to the chow, but these mice still died from neoplasia well short of a natural life span. The National Institute of Aging Intervention Testing Program showed that enterically targeted rapamycin (eRapa) extended life span for wild type genetically heterogeneous mice in part by inhibiting age-associated cancer. We hypothesized that eRapa would be effective in preventing neoplasia and extend survival of ApcMin/+ mice. We show that eRapa improved survival for ApcMin/+ mice in a dose-dependent manner. Remarkably, and in contrast to previous reports, most of the ApcMin/+ mice fed 42 ppm eRapa lived beyond the median life span reported for wild type syngeneic mice. Furthermore, chronic eRapa did not cause detrimental immune effects in mouse models of cancer, infection or autoimmunity; thus, assuaging concerns that chronic rapamycin treatment suppresses immunity. Our studies suggest that a novel formulation (enteric targeting) of a well-known and widely used drug (rapamycin) can dramatically improve its efficacy in targeted settings. eRapa or other mTORC1 inhibitors could serve as effective cancer preventatives for people with FAP without suppressing the immune system, thus reducing the dependency on surgery as standard therapy.
doi:10.1158/1940-6207.CAPR-13-0299
PMCID: PMC4058993  PMID: 24282255
21.  Deletion of Gpr128 results in weight loss and increased intestinal contraction frequency 
AIM: To generate a Gpr128 gene knockout mouse model and to investigate its phenotypes and the biological function of the Gpr128 gene.
METHODS: Bacterial artificial chromosome-retrieval methods were used for constructing the targeting vector. Using homologous recombination and microinjection technology, a Gpr128 knockout mouse model on a mixed 129/BL6 background was generated. The mice were genotyped by polymerase chain reaction (PCR) analysis of tail DNA and fed a standard laboratory chow diet. Animals of both sexes were used, and the phenotypes were assessed by histological, biochemical, molecular and physiological analyses. Semi-quantitative reverse transcription-PCR and Northern blotting were used to determine the tissue distribution of Gpr128 mRNA. Beginning at the age of 4 wk, body weights were recorded every 4 wk. Food, feces, blood and organ samples were collected to analyze food consumption, fecal quantity, organ weight and constituents of the blood and plasma. A Trendelenburg preparation was utilized to examine intestinal motility in wild-type (WT) and Gpr128-/- mice at the age of 8 and 32 wk.
RESULTS: Gpr128 mRNA was highly and exclusively detected in the intestinal tissues. Targeted deletion of Gpr128 in adult mice resulted in reduced body weight gain, and mutant mice exhibited an increased frequency of peristaltic contraction and slow wave potential of the small intestine. The Gpr128+/+ mice gained more weight on average than the Gpr128-/- mice since 24 wk, being 30.81 ± 2.84 g and 25.74 ± 4.50 g, respectively (n = 10, P < 0.01). The frequency of small intestinal peristaltic contraction was increased in Gpr128-/- mice. At the age of 8 wk, the frequency of peristalsis with an intraluminal pressure of 3 cmH2O was 6.6 ± 2.3 peristalsis/15 min in Gpr128-/- intestine (n = 5) vs 2.6 ± 1.7 peristalsis/15 min in WT intestine (n = 5, P < 0.05). At the age of 32 wk, the frequency of peristaltic contraction with an intraluminal pressure of 2 and 3 cmH2O was 4.6 ± 2.3 and 3.1 ± 0.8 peristalsis/15 min in WT mice (n = 8), whereas in Gpr128-/- mice (n = 8) the frequency of contraction was 8.3 ± 3.0 and 7.4 ± 3.1 peristalsis/15 min, respectively (2 cmH2O: P < 0.05 vs WT; 3 cmH2O: P < 0.01 vs WT). The frequency of slow wave potential in Gpr128-/- intestine (35.8 ± 4.3, 36.4 ± 4.2 and 37.1 ± 4.8/min with an intraluminal pressure of 1, 2 and 3 cmH2O, n = 8) was also higher than in WT intestine (30.6 ± 4.2, 31.4 ± 3.9 and 31.9 ± 4.5/min, n = 8, P < 0.05).
CONCLUSION: We have generated a mouse model with a targeted deletion of Gpr128 and found reduced body weight and increased intestinal contraction frequency in this animal model.
doi:10.3748/wjg.v20.i2.498
PMCID: PMC3923024  PMID: 24574718
G-protein-coupled receptors; Gpr128; Knockout mouse; Weight loss; Intestinal contraction frequency
22.  The proprotein convertase PC5/6 is protective against intestinal tumorigenesis: in vivo mouse model 
Molecular Cancer  2009;8:73.
Background
The secretory basic amino acid-specific proprotein convertases (PCs) have often been associated with cancer/metastasis. By controlling the cleavage of cancer-associated proteins, PCs play key roles in multiple steps of cancer development. Most analyses of the implication of PCs in cancer/metastasis relied on the use of in vitro overexpression systems or inhibitors that can affect more than one PC. Aside from the role of furin in salivary gland tumorigenesis, no other in vivo genetic model of PC-knockout was reported in relation to cancer development.
Results
Since PC5/6 is highly expressed in the small intestine, the present study examined its in vivo role in intestinal tumorigenesis. Analysis of human intestinal tumors at various stages showed a systematic down-regulation of PC5/6 expression. Since gene inactivation of PC5/6 leads to lethality at birth, we generated mice lacking PC5/6 in enterocytes and analyzed the impact of the presence or absence of this PC in the mouse ApcMin/+ model that develops numerous adenocarcinomas along the intestinal tract. This resulted in viable mice with almost no expression of PC5/6 in small intestine, but with no overt phenotype. The data showed that by themselves ApcMin/+ tumors express lower levels of PC5/6 mRNA, and that the lack of PC5/6 in enterocytes results in a significantly higher tumor number in the duodenum, with a similar trend in other intestinal segments. Finally, the absence of PC5/6 is also associated with a premature mortality of ApcMin/+ mice.
Conclusion
Overall, these data suggest that intestinal PC5/6 is protective towards tumorigenesis, especially in mouse duodenum, and possibly in human colon.
doi:10.1186/1476-4598-8-73
PMCID: PMC2746178  PMID: 19737405
23.  The Ets dominant repressor En/Erm enhances intestinal epithelial tumorigenesis in ApcMin mice 
BMC Cancer  2009;9:197.
Background
Ets transcription factors have been widely implicated in the control of tumorigenesis, with most studies suggesting tumor-promoting roles. However, few studies have examined Ets tumorigenesis-modifying functions in vivo using model genetic systems.
Methods
Using mice expressing a previously characterized Ets dominant repressor transgene in the intestinal epithelium (Villin-En/Erm), we examined the consequences of blocking endogenous Ets-mediated transcriptional activation on tumorigenesis in the ApcMin model of intestinal carcinoma.
Results
En/Erm expression in the intestine, at levels not associated with overt crypt-villus dysmorphogenesis, results in a marked increase in tumor number in ApcMin animals. Moreover, when examined histologically, tumors from En/Erm-expressing animals show a trend toward greater stromal invasiveness. Detailed analysis of crypt-villus homeostasis in these En/Erm transgenic animals suggests increased epithelial turnover as one possible mechanism for the enhanced tumorigenesis.
Conclusion
Our findings provide in vivo evidence for a tumor-restricting function of endogenous Ets factors in the intestinal epithelium.
doi:10.1186/1471-2407-9-197
PMCID: PMC2714157  PMID: 19545444
24.  Cited1 Deficiency Suppresses Intestinal Tumorigenesis 
PLoS Genetics  2013;9(8):e1003638.
Conditional deletion of Apc in the murine intestine alters crypt-villus architecture and function. This process is accompanied by multiple changes in gene expression, including upregulation of Cited1, whose role in colorectal carcinogenesis is unknown. Here we explore the relevance of Cited1 to intestinal tumorigenesis. We crossed Cited1 null mice with ApcMin/+ and AhCre+Apcfl/fl mice and determined the impact of Cited1 deficiency on tumour growth/initiation including tumour multiplicity, cell proliferation, apoptosis and the transcriptome. We show that Cited1 is up-regulated in both human and murine tumours, and that constitutive deficiency of Cited1 increases survival in ApcMin/+ mice from 230.5 to 515 days. However, paradoxically, Cited1 deficiency accentuated nearly all aspects of the immediate phenotype 4 days after conditional deletion of Apc, including an increase in cell death and enhanced perturbation of differentiation, including of the stem cell compartment. Transcriptome analysis revealed multiple pathway changes, including p53, PI3K and Wnt. The activation of Wnt through Cited1 deficiency correlated with increased transcription of β-catenin and increased levels of dephosphorylated β-catenin. Hence, immediately following deletion of Apc, Cited1 normally restrains the Wnt pathway at the level of β-catenin. Thus deficiency of Cited1 leads to hyper-activation of Wnt signaling and an exaggerated Wnt phenotype including elevated cell death. Cited1 deficiency decreases intestinal tumourigenesis in ApcMin/+ mice and impacts upon a number of oncogenic signaling pathways, including Wnt. This restraint imposed by Cited1 is consistent with a requirement for Cited1 to constrain Wnt activity to a level commensurate with optimal adenoma formation and maintenance, and provides one mechanism for tumour repression in the absence of Cited1.
Author Summary
Colorectal cancer is the fourth leading cause of cancer related deaths worldwide, and a key genetic change associated with this disease is mutation of the gene APC. APC encodes a protein which plays a regulatory role in the Wnt signalling pathway. To better understand the mechanisms leading to colorectal cancer after APC loss, we have used a mouse model in which we deleted Apc in the bowel and which developed several characteristics of early stage cancers. Here, we show that after Apc loss, the expression of another gene, Cited1, is increased in mice and human colorectal tumours. To study the role of Cited1 in bowel cancer after loss of Apc, we generated mice mutant for Apc (Min) or mutant for Apc and Cited1 (MinCited1). We observed that MinCited1 mice developed fewer intestinal tumours and lived longer than Min mice suggesting that Cited1 is pro-tumourigenic. However, we also observed that Cited1 deficiency actually increased many of the aspects associated with loss of Apc, including deregulation of the Wnt pathway and cell death. To explain this apparent paradox, we propose a model whereby loss of Cited1, in the context of deregulated Wnt signalling, ‘over-stimulates’ the Wnt pathway, the net effect of which is to inhibit tumourigenesis.
doi:10.1371/journal.pgen.1003638
PMCID: PMC3731217  PMID: 23935526
25.  Inhibition of CXCR2 profoundly suppresses inflammation-driven and spontaneous tumorigenesis 
The Journal of Clinical Investigation  2012;122(9):3127-3144.
The chemokine receptor CXCR2 is a key mediator of neutrophil migration that also plays a role in tumor development. However, CXCR2 influences tumors through multiple mechanisms and might promote or inhibit tumor development depending on context. Here, we used several mouse models of spontaneous and inflammation-driven neoplasia to define indispensable roles for CXCR2 in benign and malignant tumors. CXCR2-activating chemokines were part of the secretome of cultured primary benign intestinal adenomas (ApcMin/+) and highly expressed by all tumors in all models. CXCR2 deficiency profoundly suppressed inflammation-driven tumorigenesis in skin and intestine as well as spontaneous adenocarcinoma formation in a model of invasive intestinal adenocarcinoma (AhCreER;Apcfl/+;Ptenfl/fl mice). Pepducin-mediated CXCR2 inhibition reduced tumorigenesis in ApcMin/+ mice. Ly6G+ neutrophils were the dominant source of CXCR2 in blood, and CXCR2 deficiency attenuated neutrophil recruitment. Moreover, systemic Ly6G+ cell depletion purged CXCR2-dependent tumor-associated leukocytes, suppressed established skin tumor growth and colitis-associated tumorigenesis, and reduced ApcMin/+ adenoma formation. CXCR2 is thus a potent protumorigenic chemokine receptor that directs recruitment of tumor-promoting leukocytes into tissues during tumor-inducing and tumor-driven inflammation. Similar leukocyte populations were also found in human intestinal adenomas, which suggests that CXCR2 antagonists may have therapeutic and prophylactic potential in the treatment of cancer.
doi:10.1172/JCI61067
PMCID: PMC3428079  PMID: 22922255

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