TGF-beta receptor inactivation and mutant Kras induce intestinal neoplasms in mice via a beta-catenin-independent pathway

Establishment, characterization, and biobanking of 36 pancreatic cancer organoids: prediction of metastasis in resectable pancreatic cancer

PURPOSE

Early dissemination of primary pancreatic ductal adenocarcinoma (PDAC) is the main cause of dismal prognosis as it highly limits possible treatment options. A number of PDAC patients experience distant metastasis even after treatment due to the metastatic clones. We aimed to demonstrate the molecular architecture of borderline resectable PDAC manifests cancer dissemination of PDAC.

METHODS

Here, 36 organoids isolated from primary tumor masses of PDAC patients with diverse metastatic statues are presented. Whole-exome sequencing and RNA sequencing were performed and drug responses to clinically relevant 18 compounds were assessed.

RESULTS

Our results revealed that borderline resectable PDAC organoids exhibited distinct patterns according to their metastatic potency highlighted by multiple genetic and transcriptional factors and strong variances in drug responses.

CONCLUSIONS

These data suggest that the presence of metastatic PDAC can be identified by integrating molecular compositions and drug responses of borderline resectable PDAC.

Molecular mechanisms of microRNA-301a during tumor progression and metastasis

Cancer is known as one of the leading causes of human deaths globally. Late diagnosis is considered as one of the main reasons for the high mortality rate among cancer patients. Therefore, the introduction of early diagnostic tumor markers can improve the efficiency of therapeutic modalities. MicroRNAs (miRNAs) have a key role in regulation of cell proliferation and apoptosis. MiRNAs deregulation has been frequently reported during tumor progressions. Since, miRNAs have a high stability in body fluids; they can be used as the reliable non-invasive tumor markers. Here, we discussed the role of miR-301a during tumor progressions. MiR-301a mainly functions as an oncogene via the modulation of transcription factors, autophagy, epithelial-mesenchymal transition (EMT), and signaling pathways. This review paves the way to suggest miR-301a as a non-invasive marker for the early tumor diagnosis. MiR-301a can also be suggested as an effective target in cancer therapy.

Ferroptosis in colorectal cancer: a future target?

Colorectal cancer (CRC) is the third leading cause of cancer deaths worldwide and is characterised by frequently mutated genes, such as APC, TP53, KRAS and BRAF. The current treatment options of chemotherapy, radiation therapy and surgery are met with challenges such as cancer recurrence, drug resistance, and overt toxicity. CRC therapies exert their efficacy against cancer cells by activating biological pathways that contribute to various forms of regulated cell death (RCD). In 2012, ferroptosis was discovered as an iron-dependent and lipid peroxide-driven form of RCD. Recent studies suggest that therapies which target ferroptosis are promising treatment strategies for CRC. However, a greater understanding of the mechanisms of ferroptosis initiation, propagation, and resistance in CRC is needed. This review provides an overview of recent research in ferroptosis and its potential role as a therapeutic target in CRC. We also propose future research directions that could help to enhance our understanding of ferroptosis in CRC.

The immunomodulatory role of matrix metalloproteinases in colitis-associated cancer

Matrix metalloproteinases (MMPs) are an important class of enzymes in the body that function through the extracellular matrix (ECM). They are involved in diverse pathophysiological processes, such as tumor invasion and metastasis, cardiovascular diseases, arthritis, periodontal disease, osteogenesis imperfecta, and diseases of the central nervous system. MMPs participate in the occurrence and development of numerous cancers and are closely related to immunity. In the present study, we review the immunomodulatory role of MMPs in colitis-associated cancer (CAC) and discuss relevant clinical applications. We analyze more than 300 pharmacological studies retrieved from PubMed and the Web of Science, related to MMPs, cancer, colitis, CAC, and immunomodulation. Key MMPs that interfere with pathological processes in CAC such as MMP-2, MMP-3, MMP-7, MMP-9, MMP-10, MMP-12, and MMP-13, as well as their corresponding mechanisms are elaborated. MMPs are involved in cell proliferation, cell differentiation, angiogenesis, ECM remodeling, and the inflammatory response in CAC. They also affect the immune system by modulating differentiation and immune activity of immune cells, recruitment of macrophages, and recruitment of neutrophils. Herein we describe the immunomodulatory role of MMPs in CAC to facilitate treatment of this special type of colon cancer, which is preceded by detectable inflammatory bowel disease in clinical populations.

Epithelial TGFβ engages growth-factor signalling to circumvent apoptosis and drive intestinal tumourigenesis with aggressive features

The pro-tumourigenic role of epithelial TGFβ signalling in colorectal cancer (CRC) is controversial. Here, we identify a cohort of born to be bad early-stage (T1) colorectal tumours, with aggressive features and a propensity to disseminate early, that are characterised by high epithelial cell-intrinsic TGFβ signalling. In the presence of concurrent Apc and Kras mutations, activation of epithelial TGFβ signalling rampantly accelerates tumourigenesis and share transcriptional signatures with those of the born to be bad T1 human tumours and predicts recurrence in stage II CRC. Mechanistically, epithelial TGFβ signalling induces a growth-promoting EGFR-signalling module that synergises with mutant APC and KRAS to drive MAPK signalling that re-sensitise tumour cells to MEK and/or EGFR inhibitors. Together, we identify epithelial TGFβ signalling both as a determinant of early dissemination and a potential therapeutic vulnerability of CRC's with born to be bad traits.

Comprehensive microRNA analysis across genome-edited colorectal cancer organoid models reveals miR-24 as a candidate regulator of cell survival

Somatic mutations drive colorectal cancer (CRC) by disrupting gene regulatory mechanisms. Distinct combinations of mutations can result in unique changes to regulatory mechanisms leading to variability in the efficacy of therapeutics. MicroRNAs are important regulators of gene expression, and their activity can be altered by oncogenic mutations. However, it is unknown how distinct combinations of CRC-risk mutations differentially affect microRNAs. Here, using genetically-modified mouse intestinal organoid (enteroid) models, we identify 12 different modules of microRNA expression patterns across different combinations of mutations common in CRC. We also show that miR-24-3p is aberrantly upregulated in genetically-modified mouse enteroids irrespective of mutational context. Furthermore, we identify an enrichment of miR-24-3p predicted targets in downregulated gene lists from various mutational contexts compared to WT. In follow-up experiments, we demonstrate that miR-24-3p promotes CRC cell survival in multiple cell contexts. Our novel characterization of genotype-specific patterns of miRNA expression offer insight into the mechanisms that drive inter-tumor heterogeneity and highlight candidate microRNA therapeutic targets for the advancement of precision medicine for CRC.

Mouse models of Kras activation in gastric cancer

Gastric cancer has one of the highest incidence rates and is one of the leading causes of cancer-related mortality worldwide. Sequential steps within the carcinogenic process are observed in gastric cancer as well as in pancreatic cancer and colorectal cancer. Kirsten rat sarcoma viral oncogene homolog (KRAS) is the most well-known oncogene and can be constitutively activated by somatic mutations in the gene locus. For over 2 decades, the functions of Kras activation in gastrointestinal (GI) cancers have been studied to elucidate its oncogenic roles during the carcinogenic process. Different approaches have been utilized to generate distinct in vivo models of GI cancer, and a number of mouse models have been established using Kras-inducible systems. In this review, we summarize the genetically engineered mouse models in which Kras is activated with cell-type and/or tissue-type specificity that are utilized for studying carcinogenic processes in gastric cancer as well as pancreatic cancer and colorectal cancer. We also provide a brief description of histological phenotypes and characteristics of those mouse models and the current limitations in the gastric cancer field to be investigated further.

Loss of MMR and TGFBR2 Increases the Susceptibility to Microbiota-Dependent Inflammation-Associated Colon Cancer

BACKGROUND AND AIMS

Mutations in DNA mismatch repair (MMR) genes are causative in Lynch syndrome and a significant proportion of sporadic colorectal cancers (CRCs). MMR-deficient (dMMR) CRCs display increased mutation rates, with mutations frequently accumulating at short repetitive DNA sequences throughout the genome (microsatellite instability). The TGFBR2 gene is one of the most frequently mutated genes in dMMR CRCs. Therefore, we generated an animal model to study how the loss of both TGFBR2 signaling impacts dMMR-driven intestinal tumorigenesis in vivo and explore the impact of the gut microbiota.

METHODS

We generated VCMsh2/Tgfbr2 mice in which Msh2loxP and Tgfbr2loxP alleles are inactivated by Villin-Cre recombinase in the intestinal epithelium. VCMsh2/Tgfbr2 mice were analyzed for their rate of intestinal cancer development and for the mutational spectra and gene expression profiles of tumors. In addition, we assessed the impact of chemically induced chronic inflammation and gut microbiota composition on colorectal tumorigenesis.

RESULTS

VCMsh2/Tgfbr2 mice developed small intestinal adenocarcinomas and CRCs with histopathological features highly similar to CRCs in Lynch syndrome patients. The CRCs in VCMsh2/Tgfbr2 mice were associated with the presence of colitis and displayed genetic and histological features that resembled inflammation-associated CRCs in human patients. The development of CRCs in VCMsh2/Tgfbr2 mice was strongly modulated by the gut microbiota composition, which in turn was impacted by the TGFBR2 status of the tumors.

CONCLUSIONS

Our results demonstrate a synergistic interaction between MMR and TGFBR2 inactivation in inflammation-associated colon tumorigenesis and highlight the crucial impact of the gut microbiota on modulating the incidence of inflammation-associated CRCs.

2-Pyridin-4-yl-methylene-beta-boswellic Acid-A Potential Candidate for Targeting O6-Methylguanine-DNA Methyltransferase Epi-transcriptional Reprogramming in KRAS G13D-Microsatellite Stable, G12V-Microsatellite Instable Mutant Colon Cancer

PMBA (2-Pyridin-4-yl-methylene-beta-boswellic acid), screened from among the 21 novel series of semisynthetic analogues of β-boswellic acid, is being presented as a lead compound for integrative management of KRAS mutant colorectal cancer (CRC), upon testing and analysis for its anticancerous activity on a panel of NCI-60 cancer cell lines and in vivo models of the disease. PMBA (1.7-29 μM) exhibited potent proliferation inhibition on the cell lines and showed sensitivity in microsatellite instability and microsatellite stable (GSE39582 and GSE92921) subsets of KRAS gene (Kirsten rat sarcoma viral oncogene homolog)-mutated colon cell lines, as revealed via flow cytometry analysis. A considerable decrease in mitogen-activated protein kinase pathway downstream effectors was observed in the treated cell lines via the western blot and STRING (Search tool for the retrieval of interacting genes/proteins) analysis. PMBA was further found to target KRAS at its guanosine diphosphate site. Treatment of the cell lines with PMBA showed significant reduction in MGMT promoter methylation but restored MGMT (O⁶-methylguanine-DNA methyltransferase) messenger ribonucleic acid expression via significant demethylation of the hypermethylated CpG (Cytosine phosphate guanine) sites in the MGMT promoter. A significant decrease in dimethylated H3K9 (Dimethylation of lysine 9 on histone 3) levels in the MGMT promoter in DNA hypo- and hypermethylated HCT-116^G13D and SW-620^G12V cells was observed after treatment. In the MNU (N-methyl-N-nitrosourea)-induced CRC in vivo model, PMBA instillation restricted and repressed polyp formation, suppressed tumor proliferation marker Ki67 (Marker of proliferation), ablated KRAS-associated cytokine signaling, and decreased mortality. Clinical trial data for the parent molecule revealed its effectiveness against the disease, oral bioavailability, and system tolerance. Comprehensively, PMBA represents a new class of KRAS inhibitors having a therapeutic window in the scope of a drug candidate. The findings suggest that the PMBA analogue could inhibit the growth of human CRC in vivo through downregulation of cancer-associated biomarkers as well as reactivate expression of the MGMT gene associated with increased H3K9 acetylation and H3K4 methylation with facilitated transcriptional activation, which might be important in silencing of genes associated with upregulation in the activity of KRAS.

Sequestration of Intestinal Acidic Toxins by Cationic Resin Attenuates Pancreatic Cancer Progression through Promoting Autophagic Flux for YAP Degradation

Simple Summary

Annually, more than 450,000 people are diagnosed with pancreatic cancer worldwide with over 430,000 mortalities. Pancreatic ductal carcinoma (PDAC) accounts for around 80% of pancreatic cancer cases with an extremely high mortality rate. Emerging research has demonstrated that gut dysbiosis is closely associated with pancreatic cancer, while the underlying mechanisms remain elusive. In this study, we found that elevated levels of endotoxin (LPS) and bile acids were associated with malignant progression in Kras-driven pancreatic cancer mice. Importantly, oral administration of cationic resins to sequestrate intestinal endotoxins and bile acids efficiently attenuated tumor progression. Thus, sequestration of intestinal acidic toxins by oral administration of cationic resins may have potential as an intervention strategy for pancreatic malignancy.

Abstract

Pancreatic cancer is driven by risk factors such as diabetes and chronic pancreatic injury, which are further associated with gut dysbiosis. Intestinal toxins such as bile acids and bacterial endotoxin (LPS), in excess and persistence, can provoke chronic inflammation and tumorigenesis. Of interest is that many intestinal toxins are negatively charged acidic components in essence, which prompted us to test whether oral administration of cationic resin can deplete intestinal toxins and ameliorate pancreatic cancer. Here, we found that increased plasma levels of endotoxin and bile acids in Pdx1-Cre: LSL-Kras^G12D/+ mice were associated with the transformation of the pancreatic ductal carcinoma (PDAC) state. Common bile-duct-ligation or LPS injection impeded autolysosomal flux, leading to Yap accumulation and malignant transformation. Conversely, oral administration of cholestyramine to sequestrate intestinal endotoxin and bile acids resumed autolysosomal flux for Yap degradation and attenuated metastatic incidence. Conversely, chloroquine treatment impaired autolysosomal flux and exacerbated malignance, showing jeopardization of p62/ Sqxtm1 turnover, leading to Yap accumulation, which is also consistent with overexpression of cystatin A (CSTA) in situ with pancreatic cancer cells and metastatic tumor. At cellular levels, chenodeoxycholic acid or LPS treatment activated the ligand–receptor-mediated AKT-mTOR pathway, resulting in autophagy-lysosomal stress for YAP accumulation and cellular dissemination. Thus, this work indicates a potential new strategy for intervention of pancreatic metastasis through sequestration of intestinal acidic toxins by oral administration of cationic resins.

Epigenetic basis of oncogenic-Kras-mediated epithelial-cellular proliferation and plasticity

Oncogenic Kras induces a hyper-proliferative state that permits cells to progress to neoplasms in diverse epithelial tissues. Depending on the cell of origin, this also involves lineage transformation. Although a multitude of downstream factors have been implicated in these processes, the precise chronology of molecular events controlling them remains elusive. Using mouse models, primary human tissues, and cell lines, we show that, in Kras-mutant alveolar type II cells (AEC2), FOSL1-based AP-1 factor guides the mSWI/SNF complex to increase chromatin accessibility at genomic loci controlling the expression of genes necessary for neoplastic transformation. We identified two orthogonal processes in Kras-mutant distal airway club cells. The first promoted their transdifferentiation into an AEC2-like state through NKX2.1, and the second controlled oncogenic transformation through the AP-1 complex. Our results suggest that neoplasms retain an epigenetic memory of their cell of origin through cell-type-specific transcription factors. Our analysis showed that a cross-tissue-conserved AP-1-dependent chromatin remodeling program regulates carcinogenesis.

TGF-β Signaling in Liver, Pancreas, and Gastrointestinal Diseases and Cancer

Genetic alterations affecting transforming growth factor-β (TGF-β) signaling are exceptionally common in diseases and cancers of the gastrointestinal system. As a regulator of tissue renewal, TGF-β signaling and the downstream SMAD-dependent transcriptional events play complex roles in the transition from a noncancerous disease state to cancer in the gastrointestinal tract, liver, and pancreas. Furthermore, this pathway also regulates the stromal cells and the immune system, which may contribute to evasion of the tumors from immune-mediated elimination. Here, we review the involvement of the TGF-β pathway mediated by the transcriptional regulators SMADs in disease progression to cancer in the digestive system. The review integrates human genomic studies with animal models that provide clues toward understanding and managing the complexity of the pathway in disease and cancer.

Role of TGF-Beta and Smad7 in Gut Inflammation, Fibrosis and Cancer

The human gastrointestinal tract contains the largest population of immune cells in the body and this is a reflection of the fact that it is continuously exposed to a myriad of dietary and bacterial antigens. Although these cells produce a variety of inflammatory cytokines that could potentially promote tissue damage, in normal conditions the mucosal immune response is tightly controlled by counter-regulatory factors, which help induce and maintain gut homeostasis and tolerance. One such factor is transforming growth factor (TGF)-β1, a cytokine produced by multiple lineages of leukocytes, stromal cells and epithelial cells, and virtually targets all the gut mucosal cell types. Indeed, studies in animals and humans have shown that defects in TGF-β1 production and/or signaling can lead to the development of immune-inflammatory pathologies, fibrosis and cancer in the gut. Here, we review and discuss the available evidence about the role of TGF-β1 and Smad7, an inhibitor of TGF-β1 activity, in gut inflammation, fibrosis and cancer with particular regard to the contribution of these two molecules in the pathogenesis of inflammatory bowel diseases and colon cancer.

Roles of Src family kinase, Ras, and mTOR signaling in intestinal epithelial homeostasis and tumorigenesis

The turnover of intestinal epithelial cells (IECs) is relatively rapid (3-5 days in mouse and human), and this short existence and other aspects of the homeostasis of IECs are tightly regulated by various signaling pathways including Wnt-β-catenin signaling. Dysregulation of IEC homeostasis likely contributes to the development of intestinal inflammation and intestinal cancer. The roles of receptor protein tyrosine kinases and their downstream signaling molecules such as Src family kinases, Ras, and mTOR in homeostatic regulation of IEC turnover have recently been evaluated. These signaling pathways have been found to promote not only the proliferation of IECs but also the differentiation of progenitor cells into secretory cell types such as goblet cells. Of note, signaling by Src family kinases, Ras, and mTOR has been shown to oppose the Wnt-β-catenin signaling pathway and thereby to limit the number of Lgr5⁺ intestinal stem cells or of Paneth cells. Such cross-talk of signaling pathways is important not only for proper regulation of IEC homeostasis but for the development of intestinal tumors and potentially for anticancer therapy.

Erk and MAPK signaling is essential for intestinal development through Wnt pathway modulation

Homeostasis of intestinal stem cells (ISCs) is maintained by the orchestration of niche factors and intrinsic signaling networks. Here, we have found that deletion of Erk1 and Erk2 (Erk1/2) in intestinal epithelial cells at embryonic stages resulted in an unexpected increase in cell proliferation and migration, expansion of ISCs, and formation of polyp-like structures, leading to postnatal death. Deficiency of epithelial Erk1/2 results in defects in secretory cell differentiation as well as impaired mesenchymal cell proliferation and maturation. Deletion of Erk1/2 strongly activated Wnt signaling through both cell-autonomous and non-autonomous mechanisms. In epithelial cells, Erk1/2 depletion resulted in loss of feedback regulation, leading to Ras/Raf cascade activation that transactivated Akt activity to stimulate the mTor and Wnt/β-catenin pathways. Moreover, Erk1/2 deficiency reduced the levels of Indian hedgehog and the expression of downstream pathway components, including mesenchymal Bmp4 - a Wnt suppressor in intestines. Inhibition of mTor signaling by rapamycin partially rescued Erk1/2 depletion-induced intestinal defects and significantly prolonged the lifespan of mutant mice. These data demonstrate that Erk/Mapk signaling functions as a key modulator of Wnt signaling through coordination of epithelial-mesenchymal interactions during intestinal development.

Acceleration of BRAFV600E-induced thyroid carcinogenesis by TGFβ signal deficiency in mice

PURPOSE

Transforming growth factor-β (TGFβ) has pleiotropic actions, including both anti- and pro-tumorigenic abilities. We have previously shown no tumor development in the thyroid-specific TGFβ receptor type II knockout (Tgfβr2 KO) mice, indicating the insufficiency of defective TGFβ signal itself for thyroid cancer initiation. In the current study, we evaluated whether defective TGFβ signal accelerates BRAF^V600E-mediated thyroid carcinogenesis in our mouse model, in which intrathyroidal injection of adenovirus expressing Cre under thyroglobulin (TG) promoter (Ad-TgP-Cre) into thyroid lobes of conditional Braf^V600E knock-in mice (Braf^CA) induces thyroid cancers 12 months later.

METHODS

Braf^CA/wt;Tgfbr2^{floxE2/floxE2} mice were generated by crossing Tgfbr2^{floxE2/floxE2} and Braf^CA mice, and Ad-TgP-Cre was injected into the left lobes of 4-6-week-old mice. Mice were sacrificed at 6 and 12 months, and the thyroid tissues were subjected to H&E and immune-histochemistry and -fluorecence.

RESULTS

Thyroid tumors were observed in 8 of 10 mice at 6 months and 4 of 7 mice at 12 months. These tumors were judged to be malignant by H&E staining, because of the presence of papillary growth of atypical follicular cells, intranuclear cytoplasmic inclusions and so on. Immunohistochemical analyses using thyroid cancer tissues obtained at 6 months demonstrated variable levels of TG but steady levels of Paired Box-8 expression and higher Ki67 positivity. The degree of epithelial-to-mesenchymal transition could not be evaluated because normal thyroid tissues and thyroid cancers developed in Braf^CA and Braf^CA/wt;Tgfbr2^{floxE2/floxE2} mice were all E-cadherin⁺/vimentin^-, that is, epithelial type.

CONCLUSION

In a mouse model, defective TGFβ signaling pathway accelerates BRAF^V600E-induced thyroid cancer development, which is occasionally accompanied by reduced TG expression implying dedifferentiation. The former finding is consistent with anti-tumorigenic ability of TGFβ in early tumorigenic process, but the latter is contradictory to generally accepted concept for TGFβ-induction of dedifferentiation.

Mouse models of colorectal cancer: Past, present and future perspectives

Colorectal cancer (CRC) is the third most common diagnosed malignancy among both sexes in the United States as well as in the European Union. While the incidence and mortality rates in western, high developed countries are declining, reflecting the success of screening programs and improved treatment regimen, a rise of the overall global CRC burden can be observed due to lifestyle changes paralleling an increasing human development index. Despite a growing insight into the biology of CRC and many therapeutic improvements in the recent decades, preclinical in vivo models are still indispensable for the development of new treatment approaches. Since the development of carcinogen-induced rodent models for CRC more than 80 years ago, a plethora of animal models has been established to study colon cancer biology. Despite tenuous invasiveness and metastatic behavior, these models are useful for chemoprevention studies and to evaluate colitis-related carcinogenesis. Genetically engineered mouse models (GEMM) mirror the pathogenesis of sporadic as well as inherited CRC depending on the specific molecular pathways activated or inhibited. Although the vast majority of CRC GEMM lack invasiveness, metastasis and tumor heterogeneity, they still have proven useful for examination of the tumor microenvironment as well as systemic immune responses; thus, supporting development of new therapeutic avenues. Induction of metastatic disease by orthotopic injection of CRC cell lines is possible, but the so generated models lack genetic diversity and the number of suited cell lines is very limited. Patient-derived xenografts, in contrast, maintain the pathological and molecular characteristics of the individual patient’s CRC after subcutaneous implantation into immunodeficient mice and are therefore most reliable for preclinical drug development – even in comparison to GEMM or cell line-based analyses. However, subcutaneous patient-derived xenograft models are less suitable for studying most aspects of the tumor microenvironment and anti-tumoral immune responses. The authors review the distinct mouse models of CRC with an emphasis on their clinical relevance and shed light on the latest developments in the field of preclinical CRC models.

Epithelial NOTCH Signaling Rewires the Tumor Microenvironment of Colorectal Cancer to Drive Poor-Prognosis Subtypes and Metastasis

The metastatic process of colorectal cancer (CRC) is not fully understood and effective therapies are lacking. We show that activation of NOTCH1 signaling in the murine intestinal epithelium leads to highly penetrant metastasis (100% metastasis; with >80% liver metastases) in KrasG12D-driven serrated cancer. Transcriptional profiling reveals that epithelial NOTCH1 signaling creates a tumor microenvironment (TME) reminiscent of poorly prognostic human CRC subtypes (CMS4 and CRIS-B), and drives metastasis through transforming growth factor (TGF) β-dependent neutrophil recruitment. Importantly, inhibition of this recruitment with clinically relevant therapeutic agents blocks metastasis. We propose that NOTCH1 signaling is key to CRC progression and should be exploited clinically.

The Molecular Basis of Metastatic Colorectal Cancer

PURPOSE OF REVIEW

Metastatic colorectal cancer (CRC) is a vexing clinical problem. In contrast to early stage disease, once CRC metastasizes to other organs, long-term survival is compromised. We seek to review the molecular pathogenesis, animal models, and functional genomics for an enhanced understanding of how CRC metastasizes and how this can be exploited therapeutically.

RECENT FINDINGS

Mouse models may recapitulate certain aspects of metastatic human CRC and allow for studies to identify regulators of metastasis. Modulation of transcription factors, onco-proteins, or tumor suppressors have been identified to activate known metastatic pathways. CD44 variants, microRNAs and RNA binding proteins are emerging as metastatic modulators.

SUMMARY

CRC metastasis is a multi-faceted and heterogeneous disease. Despite common pathways contributing to metastatic development, there are numerous variables that modulate metastatic signals in subsets of patients. It is paramount that studies continue to investigate metastatic drivers, enhancers and inhibitors in CRC to develop therapeutic targets and improve disease outcomes.

KLF5 mediates the hyper-proliferative phenotype of the intestinal epithelium in mice with intestine-specific endogenous K-RasG12D expression

Oncogenic K-Ras activation is a common mutational event in colorectal cancer. We previously showed that transcription factor, Krüppel-like factor 5 (KLF5), contributes to intestinal polyposis in mice with K-Ras activation. At 14 months of age, Villin-Cre/LSL-K-Ras^G12D mice developed small intestinal and colonic hyperplastic polyps while LSL-K-Ras^G12D had none. The intestinal crypts of Villin-Cre/LSL-K-Ras^G12D mice contained a higher number of mitotic figures and increased crypt heights compared to controls. The intestinal epithelium of Villin-Cre/LSL-K-Ras^G12D mice showed prolific KLF5 expression throughout and above the elongated crypts. In contrast, KLF5 expression was limited to the upper crypt region in the controls. The levels of K-Ras effectors were significantly increased in Villin-Cre/LSL-K-Ras^G12D as compared to controls. The Villin-Cre/LSL-K-Ras^G12D mice showed decreased survival upon treatment with azoxymethane (AOM) as compared to controls. Furthermore, loss of one of Klf5 alleles reduced levels of K-Ras effector proteins and prevented mortality of Villin-Cre/LSL-K-Ras^G12D mice upon AOM treatment. The Villin-Cre/LSL-K-Ras^G12D mice spontaneously develop hyperplastic intestinal polyps and display a hyper-proliferative intestinal phenotype with elongated crypts, increased numbers of mitotic figures, elevated expression of KLF5, and other pro-proliferative targets. Induction of colonic tumorigenesis with AOM is detrimental to Villin-Cre/LSL-K-Ras^G12D mice that is in part dependent of KLF5.

Molecular challenges of neuroendocrine tumors

Neuroendocrine tumors (NETs) are a very heterogeneous group that are thought to originate from the cells of the endocrine and nervous systems. These tumors develop in a number of organs, predominantly in the gastrointestinal and pulmonary systems. Clinical detection and diagnosis are reliable at the late stages when metastatic spread has occurred. However, traditional conventional therapies such as radiation and chemotherapy are not effective. In the majority of cases even surgical resection at that stage is unlikely to produce promising reusults. NETs present a serious clinical challenge, as the survival rates remain low, and as these rare tumors are very difficult to study, novel approaches and therapies are required. This review will highlight the important points of accumulated knowledge covering the molecular aspects of the role of neuroendocrine cells, hormonal peptides, the reasons for ectopic hormone production in NET, neuropeptides and epigenetic regulation as well as the other challenging questions that require further understanding.

Associations of TGFBR1 and TGFBR2 gene polymorphisms with the risk of hypospadias: a case-control study in a Chinese population

This case-control study investigated the association of transforming growth factor-β (TGF-β) receptor type I and II (TGFBR1 and TGFBR2) gene polymorphisms with the risk of hypospadias in a Chinese population. One hundred and sixty two patients suffering from hypospadias were enrolled as case group and 165 children who underwent circumcision were recruited as control group. Single nucleotide polymorphisms (SNPs) in TGFBR1 and TGFBR2 genes were selected on the basis of genetic data obtained from HapMap. PCR-restriction fragment length polymorphism (PCR-RFLP) was performed to identify TGFBR1 and TGFBR2 gene polymorphisms and analyze genotype distribution and allele frequency. Logistic regression analysis was conducted to estimate the risk factors for hypospadias. No significant difference was found concerning the genotype and allele frequencies of TGFBR1 rs4743325 polymorphism between the case and control groups. However, genotype and allele frequencies of TGFBR2 rs6785358 in the case group were significantly different in contrast with those in the control group. Patients carrying the G allele of TGFBR2 rs6785358 polymorphism exhibited a higher risk of hypospadias compared with the patients carrying the A allele (P<0.05). The TGFBR2 rs6785358 genotype was found to be significantly related to abnormal pregnancy and preterm birth (both P<0.05). The frequency of TGFBR2 rs6785358 GG genotype exhibited significant differences amongst patients suffering from four different pathological types of hypospadias. Logistic regression analysis revealed that preterm birth, abnormal pregnancy, and TGFBR2 rs6785358 were the independent risk factors for hypospadias. Our study provides evidence that TGFBR2 rs6785358 polymorphism might be associated with the risk of hypospadias.

TGFβ pathway limits dedifferentiation following WNT and MAPK pathway activation to suppress intestinal tumourigenesis

Recent studies have suggested increased plasticity of differentiated cells within the intestine to act both as intestinal stem cells (ISCs) and tumour-initiating cells. However, little is known of the processes that regulate this plasticity. Our previous work has shown that activating mutations of Kras or the NF-κB pathway can drive dedifferentiation of intestinal cells lacking Apc. To investigate this process further, we profiled both cells undergoing dedifferentiation in vitro and tumours generated from these cells in vivo by gene expression analysis. Remarkably, no clear differences were observed in the tumours; however, during dedifferentiation in vitro we found a marked upregulation of TGFβ signalling, a pathway commonly mutated in colorectal cancer (CRC). Genetic inactivation of TGFβ type 1 receptor (Tgfbr1/Alk5) enhanced the ability of KrasG12D/+ mutation to drive dedifferentiation and markedly accelerated tumourigenesis. Mechanistically this is associated with a marked activation of MAPK signalling. Tumourigenesis from differentiated compartments is potently inhibited by MEK inhibition. Taken together, we show that tumours arising in differentiated compartments will be exposed to different suppressive signals, for example, TGFβ and blockade of these makes tumourigenesis more efficient from this compartment.

Defining key concepts of intestinal and epithelial cancer biology through the use of mouse models

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.

Musashi-1 promotes a cancer stem cell lineage and chemoresistance in colorectal cancer cells

Colorectal cancers (CRCs) are a critical health issue worldwide. Cancer stem cell (CSC) lineages are associated with tumour transformation, progression, and malignant transformation. However, how lineages are transformed and how chemoresistance is acquired by CRCs remain largely unknown. In this report, we demonstrated that the RNA-binding protein Musashi-1 enhanced the development of CD44⁺ colorectal CSCs and triggered the formation of anti-apoptotic stress granules (SGs). Our results indicated that CD44⁺ CSC lineage-specific induction of tumour malignancies was controlled by Musashi-1. In addition, Musashi-1 formed SGs when CRC cell lines were treated with 5-fluorouracil. The C-terminal domain of Musashi-1 was critical for recruitment of Musashi-1 into SGs. Intracellular Musashi-1 SGs enhanced the chemoresistance of CRCs. Analysis of clinical CRC samples indicated that Musashi-1 expression was prominent in CRC stage IIA and IIB. In summary, we demonstrated that Musashi-1, a stemness gene, is a critical modulator that promotes the development of CD44⁺ colorectal CSCs and also enhances CRC chemoresistance via formation of SGs. Our findings elucidated a novel mechanism of CRC chemoresistance through increased anti-apoptotic effects via Musashi-1-associated SGs.

Multiple components of PKA and TGF-β pathways are mutated in pseudomyxoma peritonei

Pseudomyxoma peritonei (PMP) is a subtype of mucinous adenocarcinoma mainly restricted to the peritoneal cavity and most commonly originating from the appendix. The genetic background of PMP is poorly understood and no targeted treatments are currently available for this fatal disease. While RAS signaling pathway is affected in most if not all PMP cases and over half of them also have a mutation in the GNAS gene, other genetic alterations and affected pathways are, to a large degree, poorly known. In this study, we sequenced whole coding genome of nine PMP tumors and paired normal tissues in order to identify additional, commonly mutated genes and signaling pathways affected in PMP. These exome sequencing results were validated with an ultra-deep amplicon sequencing method, leading to 14 validated variants. The validated results contain seven genes that contribute to the protein kinase A (PKA) pathway. PKA pathway, which also contains GNAS, is a major player of overproduction of mucin, which is the characteristic feature of PMP. In addition to PKA pathway, we identified mutations in six genes that belong to the transforming growth factor beta (TGF-β) pathway, which is a key regulator of cell proliferation. Since either GNAS mutation or an alternative mutation in the PKA pathway was identified in 8/9 patients, inhibition of the PKA pathway might reduce mucin production in most of the PMP patients and potentially suppress disease progression.

TGFβ engages MEK/ERK to differentially regulate benign and malignant pancreas cell function

While TGFβ signals are anti-proliferative in benign and well-differentiated pancreatic cells, TGFβ appears to promote the progression of advanced cancers. To better understand dysregulation of the TGFβ pathway, we first generated mouse models of neoplastic disease with TGFβ receptor deficiencies. These models displayed reduced levels of pERK irrespective of KRAS mutation. Furthermore, exogenous TGFβ led to rapid and sustained TGFBR1-dependent ERK phosphorylation in benign pancreatic duct cells. Similar to results that our group has published in colon cancer cells, inhibition of ERK phosphorylation in duct cells mitigated TGFβ-induced upregulation of growth suppressive pSMAD2 and p21, prevented downregulation of the pro-growth signal CDK2 and ablated TGFβ-induced EMT. These observations suggest that ERK is a key factor in growth suppressive TGFβ signals, yet may also contribute to detrimental TGFβ signaling such as EMT. In neoplastic PanIN cells, pERK was not necessary for either TGFβ-induced pSMAD2 phosphorylation or CDK2 repression, but was required for upregulation of p21 and EMT indicating a partial divergence between TGFβ and MEK/ERK in early carcinogenesis. In cancer cells, pERK had no effect on TGFβ-induced upregulation of pSMAD2 and p21, suggesting the two pathways have completely diverged with respect to the cell cycle. Furthermore, inhibition of pERK both reduced levels of CDK2 and prevented EMT independent of exogenous TGFβ, consistent with most observations identifying pERK as a tumor promoter. Combined, these data suggest that during carcinogenesis pERK initially facilitates and later antagonizes TGFβ-mediated cell cycle arrest, yet remains critical for the pathological, EMT-inducing arm of TGFβ signaling.

No back seat for a progression event-K-RAS as a therapeutic target in CRC

In this Outlook, Poulin and Haigis discuss a study from Boutin et al. that presents a new mouse model of CRC in which the expression of oncogenic K-RAS is regulated by doxycycline.

KRAS is the most frequently mutated oncogene in human cancer and plays a central, although poorly understood, role in colorectal cancer (CRC) progression. In this issue of Genes & Development, Boutin and colleagues (pp. 370–382) present a new mouse model of CRC in which the expression of oncogenic K-RAS is regulated by doxycycline. Using this model, they demonstrate that continued expression of oncogenic K-RAS is required for the survival of primary and metastatic colon cancers and that oncogenic K-RAS activates TGF-β signaling to promote tumor invasion and metastasis.

Gasdermin C Is Upregulated by Inactivation of Transforming Growth Factor β Receptor Type II in the Presence of Mutated Apc, Promoting Colorectal Cancer Proliferation

Mutations in TGFBR2, a component of the transforming growth factor (TGF)-β signaling pathway, occur in high-frequency microsatellite instability (MSI-H) colorectal cancer (CRC). In mouse models, Tgfbr2 inactivation in the intestinal epithelium accelerates the development of malignant intestinal tumors in combination with disruption of the Wnt-β-catenin pathway. However, no studies have further identified the genes influenced by TGFBR2 inactivation following disruption of the Wnt-β-catenin pathway. We previously described CDX2P-G19Cre;Apc^flox/flox mice, which is stochastically null for Apc in the colon epithelium. In this study, we generated CDX2P-G19Cre;Apc^flox/flox;Tgfbr2^flox/flox mice, with simultaneous loss of Apc and Tgfbr2. These mice developed tumors, including adenocarcinoma in the proximal colon. We compared gene expression profiles between tumors of the two types of mice using microarray analysis. Our results showed that the expression of the murine homolog of GSDMC was significantly upregulated by 9.25-fold in tumors of CDX2P-G19Cre;Apc^flox/flox;Tgfbr2^flox/flox mice compared with those of CDX2P-G19Cre;Apc^flox/flox mice. We then investigated the role of GSDMC in regulating CRC tumorigenesis. The silencing of GSDMC led to a significant reduction in the proliferation and tumorigenesis of CRC cell lines, whereas the overexpression of GSDMC enhanced cell proliferation. These results suggested that GSDMC functioned as an oncogene, promoting cell proliferation in colorectal carcinogenesis. In conclusion, combined inactivation of both Apc and Tgfbr2 in the colon epithelium of a CRC mouse model promoted development of adenocarcinoma in the proximal colon. Moreover, GSDMC was upregulated by TGFBR2 mutation in CRC and promoted tumor cell proliferation in CRC carcinogenesis, suggesting that GSDMC may be a promising therapeutic target.

Transposon mutagenesis identifies candidate genes that cooperate with loss of transforming growth factor-beta signaling in mouse intestinal neoplasms

Colorectal cancer (CRC) results from the accumulation of gene mutations and epigenetic alterations in colon epithelial cells, which promotes CRC formation through deregulating signaling pathways. One of the most commonly deregulated signaling pathways in CRC is the transforming growth factor β (TGF-β) pathway. Importantly, the effects of TGF-β signaling inactivation in CRC are modified by concurrent mutations in the tumor cell, and these concurrent mutations determine the ultimate biological effects of impaired TGF-β signaling in the tumor. However, many of the mutations that cooperate with the deregulated TGF-β signaling pathway in CRC remain unknown. Therefore, we sought to identify candidate driver genes that promote the formation of CRC in the setting of TGF-β signaling inactivation. We performed a forward genetic screen in mice carrying conditionally inactivated alleles of the TGF-β receptor, type II (Tgfbr2) using Sleeping Beauty (SB) transposon mediated mutagenesis. We used TAPDANCE and Gene-centric statistical methods to identify common insertion sites (CIS) and, thus, candidate tumor suppressor genes and oncogenes within the tumor genome. CIS analysis of multiple neoplasms from these mice identified many candidate Tgfbr2 cooperating genes and the Wnt/β-catenin, Hippo and MAPK pathways as the most commonly affected pathways. Importantly, the majority of candidate genes were also found to be mutated in human CRC. The SB transposon system provides an unbiased method to identify Tgfbr2 cooperating genes in mouse CRC that are functionally relevant and that may provide further insight into the pathogenesis of human CRC.

A recellularized human colon model identifies cancer driver genes

Refined cancer models are needed to bridge the gaps between cell line, animal and clinical research. Here we describe the engineering of an organotypic colon cancer model by recellularization of a native human matrix that contains cell-populated mucosa and an intact muscularis mucosa layer. This ex vivo system recapitulates the pathophysiological progression from APC-mutant neoplasia to submucosal invasive tumor. We used it to perform a Sleeping Beauty transposon mutagenesis screen to identify genes that cooperate with mutant APC in driving invasive neoplasia. We identified 38 candidate invasion-driver genes, 17 of which, including TCF7L2, TWIST2, MSH2, DCC, EPHB1 and EPHB2 have been previously implicated in colorectal cancer progression. Six invasion-driver genes that have not, to our knowledge, been previously described were validated in vitro using cell proliferation, migration and invasion assays and ex vivo using recellularized human colon. These results demonstrate the utility of our organoid model for studying cancer biology.

TGF-β signaling in liver and gastrointestinal cancers

Transforming Growth Factor-β (TGF-β) plays crucial and complex roles in liver and gastrointestinal cancers. These include a multitude of distinct functions, such as maintaining stem cell homeostasis, promoting fibrosis, immune modulating, as a tumor suppressor and paradoxically, as a tumor progressor. However, key mechanisms for the switches responsible for these distinct actions are poorly understood, and remain a challenge. The Cancer Genome Atlas (TCGA) analyses and genetically engineered mouse models now provide an integrated approach to dissect these multifaceted and context-dependent driving roles of the TGF-β pathway. In this review, we will discuss the molecular mechanisms of TGF-β signaling, focusing on colorectal, gastric, pancreatic, and liver cancers. Novel drugs targeting the TGF-β pathway have been developed over the last decade, and some have been proven effective in clinical trials. A better understanding of the TGF-β pathway may improve our ability to target it, thus providing more tools to the armamentarium against these deadly cancers.

Mouse models of intestinal cancer

Murine models of intestinal cancer are powerful tools to recapitulate human intestinal cancer, understand its biology and test therapies. With recent developments identifying the importance of the tumour microenvironment and the potential for immunotherapy, autochthonous genetically engineered mouse models (GEMMs) will remain an important part of preclinical studies for the foreseeable future. This review will provide an overview of the current mouse models of intestinal cancer, from the Apc(Min/+) mouse, which has been used for over 25 years, to the latest 'state-of-the-art' organoid models. We discuss here how these models have been used to define fundamental processes involved in tumour initiation and the attempts to generate metastatic models, which is the ultimate cause of cancer mortality. Together these models will provide key insights to understand this complex disease and hopefully will lead to the discovery of new therapeutic strategies.

From mice to men: Murine models of colorectal cancer for use in translational research

Colorectal cancer (CRC) is the third most common carcinoma worldwide and despite advances in treatment, survival for patients with metastatic disease remains poor. With nearly 50% of patients developing metastases, in vivo investigation is essential to improve outcomes for these patients and numerous murine models of CRC have been developed to allow the study of chemoprevention and chemotherapy, in addition to improving our understanding of the pathogenesis of CRC. Selecting the most appropriate murine model for a specific application will maximize the conversion of potential therapies from the laboratory to clinical practice and requires an understanding of the various models available. This review will provide an overview of the murine models currently used in CRC research, discussing the limitations and merits of each and their most relevant application. It is aimed at the developing researcher, acting as a guide to prompt further reading in planning a specific study.

Colorectal cancer models for novel drug discovery

INTRODUCTION

Despite increased screening rates and advances in targeted therapy, colorectal cancer (CRC) remains the third leading cause of cancer-related mortality. CRC models that recapitulate key features of human disease are essential to the development of novel and effective therapeutics. Classic methods of modeling CRC such as human cell lines and xenograft mice, while useful for many applications, carry significant limitations. Recently developed in vitro and in vivo models overcome some of these deficiencies and thus can be utilized to better model CRC for mechanistic and translational research.

AREAS COVERED

The authors review established models of in vitro cell culture and describe advances in organoid culture for studying normal and malignant intestine. They also discuss key features of classic xenograft models and describe other approaches for in vivo CRC research, including patient-derived xenograft, carcinogen-induced, orthotopic transplantation and transgenic mouse models. We also describe mouse models of metastatic CRC.

EXPERT OPINION

No single model is optimal for drug discovery in CRC. Genetically engineered models overcome many limitations of xenograft models. Three-dimensional organoids can be efficiently derived from both normal and malignant tissue for large-scale in vitro and in vivo (transplantation) studies and are thus a significant advance in CRC drug discovery.

Suppressing TGFβ signaling in regenerating epithelia in an inflammatory microenvironment is sufficient to cause invasive intestinal cancer

Genetic alterations in the TGFβ signaling pathway in combination with oncogenic alterations lead to cancer development in the intestines. However, the mechanisms of TGFβ signaling suppression in malignant progression of intestinal tumors have not yet been fully understood. We have examined Apc(Δ716) Tgfbr2(ΔIEC) compound mutant mice that carry mutations in Apc and Tgfbr2 genes in the intestinal epithelial cells. We found inflammatory microenvironment only in the invasive intestinal adenocarcinomas but not in noninvasive benign polyps of the same mice. We thus treated simple Tgfbr2(ΔIEC) mice with dextran sodium sulfate (DSS) that causes ulcerative colitis. Importantly, these Tgfbr2(ΔIEC) mice developed invasive colon cancer associated with chronic inflammation. We also found that TGFβ signaling is suppressed in human colitis-associated colon cancer cells. In the mouse invasive tumors, macrophages infiltrated and expressed MT1-MMP, causing MMP2 activation. These results suggest that inflammatory microenvironment contributes to submucosal invasion of TGFβ signaling-repressed epithelial cells through activation of MMP2. We further found that regeneration was impaired in Tgfbr2(ΔIEC) mice for intestinal mucosa damaged by DSS treatment or X-ray irradiation, resulting in the expansion of undifferentiated epithelial cell population. Moreover, organoids of intestinal epithelial cells cultured from irradiated Tgfbr2(ΔIEC) mice formed "long crypts" in Matrigel, suggesting acquisition of an invasive phenotype into the extracellular matrix. These results, taken together, indicate that a simple genetic alteration in the TGFβ signaling pathway in the inflamed and regenerating intestinal mucosa can cause invasive intestinal tumors. Such a mechanism may play a role in the colon carcinogenesis associated with inflammatory bowel disease in humans.

MicroRNA-301a promotes migration and invasion by targeting TGFBR2 in human colorectal cancer

BACKGROUND

MicroRNAs (miRNAs) have been reported to play crucial roles in regulating a variety of genes pivotal for tumor metastasis. MicroRNA-301a (miR-301a) is overexpressed and displays oncogenic activity in many cancers. However, little is known about the potential roles of miR-301a in colorectal cancer (CRC).

METHODS

Taqman probe stem-loop real-time PCR was used to quantitatively measure the expression level of miR-301a in 48 cases of CRC tissues and the matched adjacent non-tumor mucosa as well as in CRC cell lines. miR-301a mimics and inhibitors were used to up-regulate and down-regulate miR-301a in CRC cells, respectively; lentivirus was used to construct miR-301a stably up- and down-regulated CRC cell lines. Metastasis ability was evaluated by transwell and wound healing assays while invasion was measured by transwell coated with matrix gel in vitro; in vivo metastasis was performed on nude mice model. The target of miR-301a was predicted by TargetScan software and validated by qRT-PCR, immunohistochemistry, western blot and luciferase reporter gene assay.

RESULTS

The expression of miR-301a was significantly higher in lymph node metastasis positive CRC samples compared with negative ones. Downregulation of miR-301a significantly inhibited the migration and invasion both in vitro and in vivo while forced up-regulation of miR-301a promoted migration and invasion. TGFBR2 was identified to be the downstream target of miR-301a. Knockdown of TGFBR2 in cells treated by miR-301a inhibitor elevated the previously abrogated migration and invasion.

CONCLUSIONS

Our data indicated that miR-301a correlated with the metastatic and invasive ability in human colorectal cancers and miR-301a exerted its role as oncogene by targeting TGFBR2.

Role of MTA1 in head and neck cancers

Head and neck cancers usually originate in the squamous cells that line the inner mucosal surfaces of the oral and the neck region. These cancers follow multifocal steps for progression that include risk of developing metastasis. Although therapeutics has advanced in the past decades, head and neck cancers continue to cause much morbidity and mortality. Even with the promising effect of targeted therapies, there is a need for a better evaluation of patients with head and neck cancers. Metastasis-associated tumour antigen 1 (MTA1), a chromatin modifier, is found as an integral part of nucleosome remodelling and histone deacetylation (NuRD) complex. MTA1 is a biomarker for several solid tumours, and the overexpression of which have been documented in various cancers such as breast, ovarian, colon, prostrate etc. Interestingly also, a set of head and neck cancers shows MTA1 overexpression. However, recent evidences from clinical data raise a critical question on the role of MTA1 in head and neck cancers. This calls for a detailed review to the role of MTA1 in oral cancer. This review gives a brief account on the existing biological and molecular data in the context of head and neck cancer invasion and metastasis in relation to MTA1.

The utility of Apc-mutant rats in modeling human colon cancer

Prior to the advent of genetic engineering in the mouse, the rat was the model of choice for investigating the etiology of cancer. Now, recent advances in the manipulation of the rat genome, combined with a growing recognition of the physiological differences between mice and rats, have reignited interest in the rat as a model of human cancer. Two recently developed rat models, the polyposis in the rat colon (Pirc) and Kyoto Apc Delta (KAD) strains, each carry mutations in the intestinal-cancer-associated adenomatous polyposis coli (Apc) gene. In contrast to mouse models carrying Apc mutations, in which cancers develop mainly in the small intestine rather than in the colon and there is no gender bias, these rat models exhibit colonic predisposition and gender-specific susceptibility, as seen in human colon cancer. The rat also provides other experimental resources as a model organism that are not provided by the mouse: the structure of its chromosomes facilitates the analysis of genomic events, the size of its colon permits longitudinal analysis of tumor growth, and the size of biological samples from the animal facilitates multiplexed molecular analyses of the tumor and its host. Thus, the underlying biology and experimental resources of these rat models provide important avenues for investigation. We anticipate that advances in disease modeling in the rat will synergize with resources that are being developed in the mouse to provide a deeper understanding of human colon cancer.

Concomitant Notch activation and p53 deletion trigger epithelial-to-mesenchymal transition and metastasis in mouse gut

Epithelial-to-mesenchymal transition-like (EMT-like) is a critical process allowing initiation of metastases during tumour progression. Here, to investigate its role in intestinal cancer, we combine computational network-based and experimental approaches to create a mouse model with high metastatic potential. Construction and analysis of this network map depicting molecular mechanisms of EMT regulation based on the literature suggests that Notch activation and p53 deletion have a synergistic effect in activating EMT-like processes. To confirm this prediction, we generate transgenic mice by conditionally activating the Notch1 receptor and deleting p53 in the digestive epithelium (NICD/p53(-/-)). These mice develop metastatic tumours with high penetrance. Using GFP lineage tracing, we identify single malignant cells with mesenchymal features in primary and metastatic tumours in vivo. The development of such a model that recapitulates the cellular features observed in invasive human colorectal tumours is appealing for innovative drug discovery.

The landscape of somatic chromosomal copy number aberrations in GEM models of prostate carcinoma

Human prostate cancer is known to harbor recurrent genomic aberrations consisting of chromosomal losses, gains, rearrangements, and mutations that involve oncogenes and tumor suppressors. Genetically engineered mouse (GEM) models have been constructed to assess the causal role of these putative oncogenic events and provide molecular insight into disease pathogenesis. While GEM models generally initiate neoplasia by manipulating a single gene, expression profiles of GEM tumors typically comprise hundreds of transcript alterations. It is unclear whether these transcriptional changes represent the pleiotropic effects of single oncogenes, and/or cooperating genomic or epigenomic events. Therefore, it was determined whether structural chromosomal alterations occur in GEM models of prostate cancer and whether the changes are concordant with human carcinomas. Whole genome array-based comparative genomic hybridization (CGH) was used to identify somatic chromosomal copy number aberrations (SCNA) in the widely used TRAMP, Hi-Myc, Pten-null, and LADY GEM models. Interestingly, very few SCNAs were identified and the genomic architecture of Hi-Myc, Pten-null, and LADY tumors were essentially identical to the germline. TRAMP neuroendocrine carcinomas contained SCNAs, which comprised three recurrent aberrations including a single copy loss of chromosome 19 (encoding Pten). In contrast, cell lines derived from the TRAMP, Hi-Myc, and Pten-null tumors were notable for numerous SCNAs that included copy gains of chromosome 15 (encoding Myc) and losses of chromosome 11 (encoding p53).

IMPLICATIONS

Chromosomal alterations are not a prerequisite for tumor formation in GEM prostate cancer models and cooperating events do not naturally occur by mechanisms that recapitulate changes in genomic integrity as observed in human prostate cancer.

Animal models of gastrointestinal and liver diseases. New mouse models for studying dietary prevention of colorectal cancer

Colorectal cancer is a heterogeneous disease that is one of the major causes of cancer death in the U.S. There is evidence that lifestyle factors like diet can modulate the course of this disease. Demonstrating the benefit and mechanism of action of dietary interventions against colon cancer will require studies in preclinical models. Many mouse models have been developed to study colon cancer but no single model can reflect all types of colon cancer in terms of molecular etiology. In addition, many models develop only low-grade cancers and are confounded by development of the disease outside of the colon. This review will discuss how mice can be used to model human colon cancer and it will describe a variety of new mouse models that develop colon-restricted cancer as well as more advanced phenotypes for studies of late-state disease.

Vicious cycle of TGF-β signaling in tumor progression and metastasis

TGF-β is an important biological mediator. It regulates a wide range of functions including embryonic development, wound healing, organ development, immuno-modulation, and cancer progression. Interestingly, TGF-β is known to inhibit cell growth in benign cells but promote progression in cancer cells, a phenomenon known as TGF-β paradox. TGF-β stimulation in cancer cells leads to a differential Erk activation, which srves as the basis of TGF-β paradox between benign and cancer cells. The critical events of TGF-β mediated Erk activation are suppressed TBRs and elevated TGF-β in tumor cells but not in benign cells. These events form the basis of the "vicious cycle of TGF-β signaling". The term "vicious cycle", implies that, with each advancing cycle of TGF-β signaling, the tumor will accumulate more TGF-β and will be more "aggressive" than that of the previous cycle. Understanding this vicious cycle of TGF-β signaling in tumor progression and metastasis will help us to predict indolent from aggressive cancers and will help us to develop novel anti-cancer strategies.

Mysteries of TGF-β Paradox in Benign and Malignant Cells

TGF-β regulates a wide range of biological functions including embryonic development, wound healing, organogenesis, immune modulation, and cancer progression. Interestingly, TGF-β is known to inhibit cell growth in benign cells but promote progression in cancer cells; this phenomenon is known as TGF-β paradox. To date, the mechanism of this paradox still remains a scientific mystery. In this review, we present our experience, along with the literature, in an attempt to answer this mystery. First, we observed that, on TGF-β engagement, there is a differential activation of Erk between benign and cancer cells. Since activated Erk is a major mediator in tumor progression and metastasis, a differentially activated Erk represents the answer to this mystery. Second, we identified a key player, PP2A-B56α, which is differentially recruited by the activated type I TGF-β receptor (TBRI) in benign and tumor cells, resulting in differential Erk activation. Finally, TGF-β stimulation leads to suppressed TBRs in tumor cells but not in benign cells. This differentially suppressed TBRs triggers differential recruitment of PP2A-B56α and, thus, differential activation of Erk. The above three events explain the mysteries of TGF-β paradox. Understanding the mechanism of TGF-β paradox will help us to predict indolent from aggressive cancers and develop novel anti-cancer strategies.

Inactivation of TGF-β signaling and loss of PTEN cooperate to induce colon cancer in vivo

The accumulation of genetic and epigenetic alterations mediates colorectal cancer (CRC) formation by deregulating key signaling pathways in cancer cells. In CRC, one of the most commonly inactivated signaling pathways is the transforming growth factor-beta (TGF-β) signaling pathway, which is often inactivated by mutations of TGF-β type II receptor (TGFBR2). Another commonly deregulated pathway in CRC is the phosphoinositide-3-kinase (PI3K)-AKT pathway. Phosphatase and tensin homolog deleted on chromosome 10 (PTEN) is an important negative regulator of PI3K-AKT signaling and is silenced in ∼30% of CRC. The combination of TGFBR2 inactivation and loss of PTEN is particularly common in microsatellite-unstable CRCs. Consequently, we determined in vivo if deregulation of these two pathways cooperates to affect CRC formation by analyzing tumors arising in mice that lack Tgfbr2 and/or Pten specifically in the intestinal epithelium. We found that lack of Tgfbr2 (Tgfbr2(IEKO)) alone is not sufficient for intestinal tumor formation and lack of Pten (Pten(IEKO)) alone had a weak effect on intestinal tumor induction. However, the combination of Tgfbr2 inactivation with Pten loss (Pten(IEKO);Tgfbr2(IEKO)) led to malignant tumors in both the small intestine and colon in 86% of the mice and to metastases in 8% of the tumor-bearing mice. Moreover, these tumors arose via a β-catenin-independent mechanism. Inactivation of TGF-β signaling and loss of Pten in the tumors led to increased cell proliferation, decreased apoptosis and decreased expression of cyclin-dependent kinase inhibitors. Thus, inactivation of TGF-β signaling and loss of PTEN cooperate to drive intestinal cancer formation and progression by suppressing cell cycle inhibitors.