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Over the past 20 years, huge advances have been made in modelling human diseases such as cancer using genetically modified mice. Accurate in vivo models are essential to examine the complex interaction between cancer cells, surrounding stromal cells, tumour-associated inflammatory cells, fibroblast and blood vessels, and to recapitulate all the steps involved in metastasis. Elucidating these interactions in vitro has inherent limitations, and thus animal models are a powerful tool to enable researchers to gain insight into the complex interactions between signalling pathways and different cells types. This review will focus on how advances in in vivo models have shed light on many aspects of cancer biology including the identification of oncogenes, tumour suppressors and stem cells, epigenetics, cell death and context dependent cell signalling. [ABSTRACT FROM AUTHOR]

Lower dietary vitamin D, or vitamin D receptor inactivation, compromises intestinal Lgr5+ stem cell functions and ability to initiate tumors. Mouse experiments routinely exceed vitamin D exposure levels in human populations, probably overestimating contribution of Lgr5+ cells to human intestinal homeostasis and tumor development.Lgr5+ intestinal crypt base columnar cells function as stem cells whose progeny populate the villi, and Lgr5+ cells in which Apc is inactivated can give rise to tumors. Surprisingly, these Lgr5+ stem cell properties were abrogated by the lower dietary vitamin D and calcium in a semi-purified diet that promotes both genetically initiated and sporadic intestinal tumors. Inactivation of the vitamin D receptor in Lgr5+ cells established that compromise of Lgr5 stem cell function was a rapid, cell autonomous effect of signaling through the vitamin D receptor. The loss of Lgr5 stem cell function was associated with presence of Ki67 negative Lgr5+ cells at the crypt base. Therefore, vitamin D, a common nutrient and inducer of intestinal cell maturation, is an environmental factor that is a determinant of Lgr5+ stem cell functions in vivo. Since diets used in reports that establish and dissect mouse Lgr5+ stem cell activity likely provided vitamin D levels well above the range documented for human populations, the contribution of Lgr5+ cells to intestinal homeostasis and tumor formation in humans may be significantly more limited, and variable in the population, then suggested by published rodent studies. [ABSTRACT FROM AUTHOR]

Although Apc mutation is widely considered an initiating event in colorectal cancer, little is known about the earliest stages of tumorigenesis following sporadic Apc loss. Therefore, we have utilized a novel mouse model that facilitates the sporadic inactivation of Apc via frameshift reversion of Cre in single, isolated cells and subsequently tracks the fates of Apc-deficient intestinal cells. Our results suggest that consistent with Apc being a ‘gatekeeper’, loss of Apc early in life during intestinal growth leads to adenomas or increased crypt fission, manifested by fields of mutant but otherwise normal-appearing crypts. In contrast, Apc loss occurring later in life has minimal consequences, with mutant crypts being less prone to either increased crypt fission or adenoma formation. Using the stem cell-specific Lgr5-CreER mouse, we generated different sized fields of Apc-deficient crypts via independent recombination events and found that field size correlates with progression to adenoma. To evaluate this early stage prior to adenoma formation as a therapeutic target, we examined the chemopreventive effects of sulindac on Apc-deficient occult crypt fission. We found that sulindac treatment started early in life inhibits the morphologically occult spread of Apc-deficient crypts and thus reduces adenoma numbers. Taken together these results suggest that: (i) earlier Apc loss promotes increased crypt fission, (ii) a field of Apc-deficient crypts, which can form via occult crypt fission or independent neighboring events, is an important intermediate between loss of Apc and adenoma formation and (iii) normal-appearing Apc-deficient crypts are potential unappreciated targets for cancer screening and chemoprevention. [ABSTRACT FROM AUTHOR]

Whereas aberrant activation of canonical Wnt/β-catenin signaling underlies the majority of colorectal cancer cases, the contribution of non-canonical Wnt signaling is unclear. As enhanced expression of the most extensively studied non-canonical Wnt ligand WNT5A is observed in various diseases including colon cancer, WNT5A is gaining attention nowadays. Numerous in vitro studies suggest modulating capacities of WNT5A on proliferation, differentiation, migration and invasion, affecting tumor and non-mutant cells. However, a possible contribution of WNT5A to colorectal cancer remains to be elucidated. We have analyzed WNT5A expression in colorectal cancer profiling data sets, altered WNT5A expression in colon cancer cells and used our inducible Wnt5a transgenic mouse model to gain more insight into the role of WNT5A in intestinal cancer. We observed that increased WNT5A expression is associated with poor prognosis of colorectal cancer patients. WNT5A knockdown in human colon cancer cells caused reduced directional migration, deregulated focal adhesion site formation and reduced invasion, whereas Wnt5a administration promoted the directional migration of colon cancer cells. Despite these observed protumorigenic activities of WNT5A, the induction of Wnt5a expression in intestinal tumors of Apc1638N mice was not sufficient to augment malignancy or metastasis by itself. In conclusion, WNT5A promotes adhesion sites to form in a focal fashion and promotes the directional migration and invasion of colon cancer cells. Although these activities appear insufficient by themselves to augment malignancy or metastasis in Apc1638N mice, they might explain the poor colon cancer prognosis associated with enhanced WNT5A expression. [ABSTRACT FROM PUBLISHER]

Growth arrest-specific gene (Gas) 6 is a γ-carboxyglutamic acid domain-containing protein, which shares 43% amino acid identity with protein S. Gas6 has been shown to enhance cancer cell proliferation in vitro. On the other hand, recent studies have demonstrated that Gas6 inhibits toll-like receptor-mediated immune reactions. Immune reactions are known to affect intestinal tumorigenesis. In this study, we investigated how Gas6 contributes to tumorigenesis in the intestine. Administration of recombinant Gas6 weakly, but significantly, enhanced proliferation of intestinal cancer cells (SW480 and HT29), whereas it suppressed the inflammatory responses of Lipopolysaccharide (LPS)-stimulated monocytes (THP-1). Compared with Gas6+/+ mice, Gas6–/– mice exhibited enhanced azoxymethane/dextran sulfate sodium (DSS)-induced tumorigenesis and had a shorter survival. Gas6–/– mice also exhibited more severe DSS-induced colitis. DSS-treated Gas6–/– mice showed attenuated Socs1/3 messenger RNA expression and enhanced nuclear factor-kappaB activation in the colonic stroma, suggesting that the target of Gas6 is stromal cells. Bone marrow transplantation experiments indicated that both epithelial cells and bone marrow-derived cells are Gas6 sources. Furthermore, the number of intestinal tumors in ApcMin Gas6–/– mice was higher than that in ApcMin Gas6+/+ mice, resulting in shorter survival. In a group of 62 patients with advanced colorectal cancer, Gas6 immunoreactivity in cancer tissues was positively correlated with prognosis. Thus, we revealed a unique in vivo inhibitory role of Gas6 during the progression of intestinal tumors associated with suppression of stromal immune reactions. These results suggest a novel therapeutic approach for colorectal cancer patients by regulation of stromal immune responses. [ABSTRACT FROM AUTHOR]

The causal metabolic pathways underlying associations between folate and risk for colorectal cancer (CRC) have yet to be established. Folate-mediated one-carbon metabolism is required for the de novo synthesis of purines, thymidylate and methionine. Methionine is converted to S-adenosylmethionine (AdoMet), the major one-carbon donor for cellular methylation reactions. Impairments in folate metabolism can modify DNA synthesis, genomic stability and gene expression, characteristics associated with tumorigenesis. The Mthfd1 gene product, C1-tetrahydrofolate synthase, is a trifunctional enzyme that generates one-carbon substituted tetrahydrofolate cofactors for one-carbon metabolism. In this study, we use Mthfd1gt/+ mice, which demonstrate a 50% reduction in C1-tetrahydrofolate synthase, to determine its influence on tumor development in two mouse models of intestinal cancer, crosses between Mthfd1gt/+ and Apcmin/+ mice and azoxymethane (AOM)-induced colon cancer in Mthfd1gt/+ mice. Mthfd1 hemizygosity did not affect colon tumor incidence, number or load in Apcmin/+ mice. However, Mthfd1 deficiency increased tumor incidence 2.5-fold, tumor number 3.5-fold and tumor load 2-fold in AOM-treated mice. DNA uracil content in the colon was lower in Mthfd1gt/+ mice, indicating that thymidylate biosynthesis capacity does not play a significant role in AOM-induced colon tumorigenesis. Mthfd1 deficiency-modified cellular methylation potential, as indicated by the AdoMet: S-adenosylhomocysteine ratio and gene expression profiles, suggesting that changes in the transcriptome and/or decreased de novo purine biosynthesis and associated mutability cause cellular transformation in the AOM CRC model. This study emphasizes the impact and complexity of gene–nutrient interactions with respect to the relationships among folate metabolism and colon cancer initiation and progression. [ABSTRACT FROM AUTHOR]

We have previously reported that sulindac, a non-steroidal anti-inflammatory drug, inhibited tumor formation in the small intestine but increased tumors in the colon of ApcMin/+ mice, a model of human familial adenomatous polyposis. To further explore intestinal regional responses, we studied effects of sulindac on additional gene-targeted mouse models of human intestinal tumorigenesis; these were (i) Apc1638N/+ mouse (chain termination mutation in exon 15 of the Apc gene); (ii) Mlh1+/− mouse (DNA mismatch repair deficiency, a mouse model of human hereditary non-polyposis colorectal cancer) and (iii) double-heterozygous Mlh1+/−Apc1638N/+ mutant mouse. Mice were fed AIN-76A control diet with or without 0.02% sulindac for 6 months. Intestinal regional tumor incidence, multiplicity, volume and degree of inflammation were used as end points. The results showed the following: (i) sulindac inhibited tumor development in the small intestine of Apc1638N/+ mice; (ii) in contrast, sulindac increased tumors in the small intestine of Mlh1 mutant mice, a neoplastic effect which persisted in heterozygous compound Mlh1+/−Apc1638N/+ mutant mice; (iii) sulindac increased tumors in the cecum of all mice regardless of genetic background; (iv) sulindac decreased inflammation in the small intestine of Apc1638N/+ mice, but it increased inflammation in the small intestine of Mlh1+/− mice and Mlh1+/−Apc1638N/+ mice and (v) sulindac enhanced inflammation in the cecum of all mutant mice. Findings indicate that the effects of sulindac in the intestine of these mutant mouse models are probably related to genetic background and appear to be associated with its inflammatory-inducing response. [ABSTRACT FROM PUBLISHER]

Background and aims: X-linked inhibitor of apoptosis-associated factor 1 (XAF1) was first recognized as an antagonist of X-linked inhibitor of apoptosis in suppressing caspase 3 activity. It has lower expression in cancer cells than normal tissue. Overexpression of XAF1 can inhibit cancer cell growth and sensitize tumor necrosis factor-related apoptosis-inducing ligand- or etoposide-induced apoptosis. The aim of this study is to elucidate the mechanism of XAF1 in regulating cell growth. Methods: Stable transfectants of gastrointestinal (GI) cancer cell lines AGS and SW1116 expressing XAF1 and vector control were generated. Cell growth, apoptosis, mitotic status and cell cycle distribution were assessed. The interaction between XAF1 and G2/M checkpoint proteins was evaluated by immunoblotting, kinase assay and co-immunoprecipitation assay. Mitotic catastrophe was identified by occurrence of aberrant nuclei and centrosomal amplification. Results: Our results showed that overexpression of XAF1 suppressed serum-dependent cancer cell growth, induced mitotic catastrophe and G2/M cell cycle arrest. Interestingly, XAF1 was predominantly expressed in G2/M phase after cell cycle synchronization. XAF1 interacted with and activated checkpoint kinase 1 (Chk1), inactivated Cdc25C and lead to inactivation of Cdc2–cyclin B complex. Suppression of Chk1 abrogated XAF1-induced G2/M arrest. Conclusions: Our findings implicate XAF1 as a novel cell cycle modulator that is recruited in G2/M phase and thus unravel a novel function pathway of XAF1, suggesting the potential role of XAF1 as the target for the management of GI cancers. [ABSTRACT FROM PUBLISHER]