EZH2 inhibition stimulates repetitive element expression and viral mimicry in resting splenic B cells

Mammalian cells repress expression of repetitive genomic sequences by forming heterochromatin. However, the consequences of ectopic repeat expression remain unclear. Here we demonstrate that inhibitors of EZH2, the catalytic subunit of the Polycomb repressive complex 2 (PRC2), stimulate repeat misexpression and cell death in resting splenic B cells. B cells are uniquely sensitive to these agents because they exhibit high levels of histone H3 lysine 27 trimethylation (H3K27me3) and correspondingly low DNA methylation at repeat elements. We generated a pattern recognition receptor loss-of-function mouse model, called RIC, with mutations in Rigi (encoding for RIG-I), Ifih1 (MDA5), and Cgas. In both wildtype and RIC mutant B cells, EZH2 inhibition caused loss of H3K27me3 at repetitive elements and upregulated their expression. However, NF-κB-dependent expression of inflammatory chemokines and subsequent cell death was suppressed by the RIC mutations. We further show that inhibition of EZH2 in cancer cells requires the same pattern recognition receptors to activate an interferon response. Together, the results reveal chemokine expression induced by EZH2 inhibitors in B cells as a novel inflammatory response to genomic repeat expression. Given the overlap of genes induced by EZH2 inhibitors and Epstein-Barr virus infection, this response can be described as a form of viral mimicry.

Tff2 defines transit-amplifying pancreatic acinar progenitors that lack regenerative potential and are protective against Kras-driven carcinogenesis

While adult pancreatic stem cells are thought not to exist, it is now appreciated that the acinar compartment harbors progenitors, including tissue-repairing facultative progenitors (FPs). Here, we study a pancreatic acinar population marked by trefoil factor 2 (Tff2) expression. Long-term lineage tracing and single-cell RNA sequencing (scRNA-seq) analysis of Tff2-DTR-CreERT2-targeted cells defines a transit-amplifying progenitor (TAP) population that contributes to normal homeostasis. Following acute and chronic injury, Tff2+ cells, distinct from FPs, undergo depopulation but are eventually replenished. At baseline, oncogenic KrasG12D-targeted Tff2+ cells are resistant to PDAC initiation. However, KrasG12D activation in Tff2+ cells leads to survival and clonal expansion following pancreatitis and a cancer stem/progenitor cell-like state. Selective ablation of Tff2+ cells prior to KrasG12D activation in Mist1+ acinar or Dclk1+ FP cells results in enhanced tumorigenesis, which can be partially rescued by adenoviral Tff2 treatment. Together, Tff2 defines a pancreatic TAP population that protects against Kras-driven carcinogenesis.

F4/80+Ly6Chigh Macrophages Lead to Cell Plasticity and Cancer Initiation in Colitis

BACKGROUND & AIMS

Colorectal cancer is a leading cause of cancer death, and a major risk factor is chronic inflammation. Despite the link between colitis and cancer, the mechanism by which inflammation leads to colorectal cancer is not well understood.

METHODS

To investigate whether different forms of inflammation pose the same risk of cancer, we compared several murine models of colitis (dextran sodium sulfate [DSS], 2,4,6-trinitrobenzene sulfonic acid, 4-ethoxylmethylene-2-phenyloxazol-5-one, Citrobacter rodentium, Fusobacterium nucleatum, and doxorubicin) with respect to their ability to lead to colonic tumorigenesis. We attempted to correlate the severity of colitis and inflammatory profile with the risk of tumorigenesis in both azoxymethane-dependent and Dclk1/APCfl/fl murine models of colitis-associated cancer.

RESULTS

DSS colitis reproducibly led to colonic tumors in both mouse models of colitis-associated cancer. In contrast, all other forms of colitis did not lead to cancer. When compared with the colitis not associated with tumorigenesis, DSS colitis was characterized by significantly increased CD11b+F4/80+Ly6Chigh macrophages and CD11b+Ly6G+ neutrophils. Interestingly, depletion of the CD11b+F4/80+Ly6Chigh macrophages inhibited tumorigenesis, whereas depletion of CD11b+Ly6G+ neutrophils had no effect on tumorigenesis. Furthermore, the macrophage-derived cytokines interleukin-1β, tumor necrosis factor-α, and interleukin-6 were significantly increased in DSS colitis and promoted stemness of Dclk1+ tuft cells that serve as the cellular origin of cancer.

CONCLUSIONS

We have identified CD11b+F4/80+Ly6Chigh macrophages as key mediators of cancer initiation in colitis-associated cancer. Development of new therapies that target these cells may provide an effective preventative strategy for colitis-associated cancer.

A86 CANNABIS USE IN PATIENTS WITH INFLAMMATORY BOWEL DISEASE IS HIGHER FOLLOWING LEGALIZATION OF CANNABIS IN CANADA AND IS ASSOCIATED WITH LOWER QUALITY OF LIFE

Background

Patients with inflammatory bowel disease (IBD), including Crohn’s disease (CD) and ulcerative colitis (UC), often experience fluctuating and unpredictable symptoms. Most individuals require chronic therapy with immunomodulators or novel biologics to maintain disease remission. In addition to conventional medical therapy, many patients also seek out alternative therapies such as cannabis. Reports in the USA suggest that cannabis is used by ~12% of UC and ~16% of CD patients, despite it being legally prohibited.

Purpose

The aim of our study is to evaluate the use of cannabis in a cohort of patients with IBD following its legalization in Canada, and to assess its effects on IBD disease severity.

Method

We conducted a prospective cohort study of adult IBD patients seen in clinic at a tertiary care center in London, ON. Patients completed an online 40-question survey that collected data on demographics, IBD disease history, cannabis use, and included the Short Inflammatory Bowel Disease Questionnaire (SIBDQ). The survey was distributed and collected by the REDCap platform maintained by Western University. The study was approved by the Western University Ethics Committee.

Result(s)

Completed surveys were obtained from 254 individuals (148 individuals with CD, 90 with UC and 16 with indeterminate colitis). Over half of participants were between 35-64 years of age and female. Fifty-three percent of participants reported life-time cannabis use and 51% of users started using cannabis only in the preceding 3 years. Individuals with CD had higher rates of recent use, defined as use within the past 6 months, when compared with UC (41% vs 31%). Cannabis was taken multiple times per week by 57% of users. Cannabis was used to treat GI symptoms by 30% of users, as well as to help with sleep (26%) and for recreation (27%). Despite side effects such as dry mouth, anxiety and concentration issues, 79% of users felt the benefits of cannabis outweighed its harms. Interestingly, only 46% of cannabis users discussed their use with their family physician or gastroenterologist. Recent cannabis users did not differ in the use of IBD medication or self-reported rates of GI symptoms. Furthermore, recent users did not differ in the rates of surgical procedures for IBD (recent 35% vs non-recent 32%). Recent cannabis users did have a significantly lower quality of life as indicated by SIBDQ scores when compared to non-recent users (recent use 37 vs non-recent use 40).

Conclusion(s)

Cannabis use among patients with IBD after its legalization is more than double the rate previously reported in the literature. Importantly, physicians are likely to be unaware of its prevalence in their practice. Cannabis was used by patients to treat GI and non-GI symptoms, and it was associated with lower SIBDQ scores. Our results suggest that physicians should inquire about Cannabis use amongst their patients with IBD, and that further studies are required to determine its effects on disease severity.

Please acknowledge all funding agencies by checking the applicable boxes below

CIHR

Disclosure of Interest

None Declared

A222 EFFECT OF CLINICAL FACTORS ON IBD TREATMENT RESPONSE: FINDINGS FROM A NOVEL SINGLE CENTER PATIENT REGISTRY

Background

Inflammatory bowel disease (IBD), comprising both Crohn’s disease as well as ulcerative colitis, has shown heterogenous response to therapy. Over the past decades, targeted biologic therapies have become the mainstay of treatment. Even with the rapid pace of progress in this field, roughly a third of patients do not show an initial response to these treatments. The ability to accurately predict treatment response to therapy would both improve patient safety and satisfaction as well as decrease costs from ineffective therapies.

Purpose

The primary aim of this project is to identify clinical factors predictive of disease response to induction biologic therapy in inflammatory bowel disease through the creation of a novel single center patient registry.

Method

Initially, a single center tissue biopsy registry of IBD patients receiving colonoscopy was created. Retrospective clinical data was subsequently collected on patients identified to have initiated or changed biologic therapy after entry into the registry. Clinical data regarding age, sex, comorbidities, lifestyle factors, time since initial diagnosis, extra intestinal manifestations, serum markers, prior IBD treatments, planned treatment, clinical response, as well as endoscopic response were collected. A Pilot study of the first 30 patients identified was undertaken. Individual clinical factors were compared between patients with a documented clinical response to biologic therapy and non-responders at the group level as well as by biologic therapy initiated.

Result(s)

No statistically significant differences in collected clinical data parameters were observed between treatment responders and non responders in aggregate as well as when sub selected by individual biologic therapy initiated, bio-naive status, and steroid dependence.

Conclusion(s)

This project has demonstrated that clinical factors alone do not adequately predict disease response in inflammatory bowel disease. Future work will expand this data registry to further clinical factors and continue patient enrolment. Next steps also include the addition of tissue level data, in particular tissue level RNA data. It is hoped that these parameters, either individually or in combination, will provide a robust and accessible predictor of response to biologic therapy in inflammatory bowel disease.

Please acknowledge all funding agencies by checking the applicable boxes below

Other

Please indicate your source of funding below:

Western University Department of Medicine

Disclosure of Interest

None Declared

A27 DNA HYPOMETHYLATION INDUCED BY 5-AZA-CDR OR LOSS OF DNMT1 INHIBITS COLITIS-ASSOCIATED COLORECTAL CANCER

Background

Colorectal cancer is the second leading cause of cancer death in Canada. A major risk factor for the development of colorectal cancer is chronic inflammation leading to colitis-associated cancer (CAC). We previously described a CAC mouse model in which tumors arise from DCLK1+ tuft cells following loss of the tumor suppressor adenomatous polyposis coli (APC) and induction of colitis. Interestingly, both colitis and CAC display epigenetic changes that modulate gene expression. However, the impact of DNA methylation changes on colonic tumorigenesis is not known. Thus, we hypothesize that inhibition of DNA methylation in DCLK1+ tuft cells reduces colonic tumorigenesis.

Purpose

In this study, we aim to investigate the role of DNA methylation in CAC by inhibiting DNA methylation using genetic and pharmacologic means.

Method

Using a publicly available dataset (GSE75214) of gene expression data analyzed by microarray from colonic biopsies of patients with ulcerative colitis and Crohn’s Disease with active disease, we examined the expression of DNA methyltransferases (DNMTs). Expression of DNMTs in mice with colitis was additionally examined by RT-qPCR and global DNA methylation levels measured by 5-mC ELISA. In separate experiments, Dclk1-CreERT2/Apc^f/f mice were crossed to DNMT1^f/f mice to knock-out the DNA methyltransferase DNMT1 in DCLK1+ tuft cells. Dclk1/Apc^f/f and Dclk1/Apc^f/f/DNMT1^f/f mice were then administered three doses of tamoxifen followed by 2.5% dextran sodium sulfate (DSS) for five days to induce colitis. Fourteen weeks later, we assessed colonic tumor number and size. In a separate cohort of Dclk1/Apc^f/f mice, we induced colitis and treated the mice with six doses of the DNA de-methylating drug 5-AZA-2’-deoxycytidine (5-AZA) or vehicle, and assessed colonic tumor number. To examine DNA methylation changes, we then treated WT mice with 5-AZA and DSS and isolated intestinal epithelial cells. From the intestinal epithelial cell, we isolated DNA and ran the Infinium MouseMethylation BeadChip Array.

Result(s)

Patients with IBD were found to have increased expression of DNMT1 compared to healthy controls. Mice treated with DSS similarly had increased DNMT1 expression, as well as, global methylation levels compared to controls. Deletion of DNMT1 in DCLK1+ cells significantly inhibited the number and size of colonic tumors. Treatment of mice with 5-AZA decreased global and gene specific DNA methylation levels, and significantly reduced both the number of mice with tumors, and the average colonic tumor number and size per mouse.

Conclusion(s)

Our findings demonstrate that colitis in both patients and mice is associated with DNA methylation. Furthermore, DNA hypomethylation by 5-AZA treatment or loss of DNMT1 reduces CAC formation suggesting that altered DNA methylation plays a critical role in colonic tumorigenesis.

Disclosure of Interest

None Declared

The Origin and Contribution of Cancer-Associated Fibroblasts in Colorectal Carcinogenesis

BACKGROUND & AIMS

Cancer-associated fibroblasts (CAFs) play an important role in colorectal cancer (CRC) progression and predict poor prognosis in CRC patients. However, the cellular origins of CAFs remain unknown, making it challenging to therapeutically target these cells. Here, we aimed to identify the origins and contribution of colorectal CAFs associated with poor prognosis.

METHODS

To elucidate CAF origins, we used a colitis-associated CRC mouse model in 5 different fate-mapping mouse lines with 5-bromodeoxyuridine dosing. RNA sequencing of fluorescence-activated cell sorting-purified CRC CAFs was performed to identify a potential therapeutic target in CAFs. To examine the prognostic significance of the stromal target, CRC patient RNA sequencing data and tissue microarray were used. CRC organoids were injected into the colons of knockout mice to assess the mechanism by which the stromal gene contributes to colorectal tumorigenesis.

RESULTS

Our lineage-tracing studies revealed that in CRC, many ACTA2⁺ CAFs emerge through proliferation from intestinal pericryptal leptin receptor (Lepr)⁺ cells. These Lepr-lineage CAFs, in turn, express melanoma cell adhesion molecule (MCAM), a CRC stroma-specific marker that we identified with the use of RNA sequencing. High MCAM expression induced by transforming growth factor β was inversely associated with patient survival in human CRC. In mice, stromal Mcam knockout attenuated orthotopically injected colorectal tumoroid growth and improved survival through decreased tumor-associated macrophage recruitment. Mechanistically, fibroblast MCAM interacted with interleukin-1 receptor 1 to augment nuclear factor κB-IL34/CCL8 signaling that promotes macrophage chemotaxis.

CONCLUSIONS

In colorectal carcinogenesis, pericryptal Lepr-lineage cells proliferate to generate MCAM⁺ CAFs that shape the tumor-promoting immune microenvironment. Preventing the expansion/differentiation of Lepr-lineage CAFs or inhibiting MCAM activity could be effective therapeutic approaches for CRC.

A35 DNA HYPOMETHYLATION INHIBITS TUFT CELL-DERIVED COLITIS-ASSOCIATED CANCER

Background

Colorectal cancer is the second leading cause of cancer death in Canada. A major risk factor for the development of colorectal cancer is chronic inflammation leading to colitis-associated cancer (CAC). We previously described a CAC mouse mode in which tumors arise from DCLK1+ tuft cells following loss of the tumor suppressor adenomatous polyposis coli (APC) and induction of colitis. Interestingly, both colitis and CAC display epigenetic changes that modulate gene expression. Specifically, DNA methylation is altered in colitis, but its role in colonic tumorigenesis is not known. We hypothesize that inhibition of DNA methylation in DCLK1+ tuft cells reduces colonic tumorigenesis.

Aims

In this study, we aim to investigate the role of DNA methylation in CAC by inhibiting DNA methylation by genetic and pharmacologic means.

Methods

We crossed our Dclk1-CreERT2/Apc^f/f mice to DNMT1^f/f mice to delete the DNA methyltransferase DNMT1 in DCLK1+ tuft cells. We induced CAC in Dclk1/Apc^f/f and Dclk1/Apc^f/f/DNMT1^f/f mice by administering three doses of tamoxifen followed by 2.5% dextran sodium sulfate (DSS) for five days. Fourteen weeks later we assessed colonic tumor number and size. Lineage tracing of Dclk1+ cells was also examined in colonic tissues from all mice. In a separate cohort of Dclk1/Apc^f/f mice, we induced colitis and treated the mice with six doses of the DNA de-methylating drug 5-AZA-2’-deoxycytidine (5-AZA) or vehicle. Ki67 immunostaining was additionally performed to assess cellular proliferation in the colon.

Results

Deletion of DNMT1 in DCLK1+ cells significantly inhibited the number and size of colonic tumors. Treatment of mice with 5-AZA similarly reduced the overall number of mice with tumors, as well as, the number and size of tumors per mouse. Interestingly, 5-AZA treatment was associated with reduced colonic proliferation as assessed by fewer Ki67+ cells, and quiescent DCLK1+ cells that did not lineage trace. Furthermore, deletion of DNMT1 or treatment with 5-AZA reduced the number of lineage tracing events detected upon exposure to low DSS.

Conclusions

Our findings demonstrate that loss of Dnmt1 or 5-AZA treatment reduces CAC formation. Furthermore, 5-AZA appears to exert its anti-tumor effects by reducing proliferation and preventing tuft cell stemness. Our data demonstrates that altering DNA methylation plays an important role in CAC.

Funding Agencies

CIHR

A166 CANNABIS USE IN CANADIAN INDIVIDUALS WITH INFLAMMATORY BOWEL DISEASE FOLLOWING LEGALIZATION OF CANNABIS

Background

Inflammatory bowel disease (IBD), including Crohn’s disease (CD) and ulcerative colitis (UC), are characterized by remitting and relapsing symptoms of abdominal pain, diarrhea, nausea, fatigue, and poor sleep. Most patients with IBD require chronic immunosuppressive therapy to maintain their disease in remission. Due to their disease chronicity, individuals often seek additional complementary or alternative medicines such as cannabis to treat their symptoms. Reports from the US show cannabis use in 12% of UC and 16% of CD patients. However, these numbers are likely underestimates given that cannabis remains illegal in many states.

Aims

The aim of our study is to evaluate the use of cannabis in a cohort of patients with IBD and to assess its association with IBD disease severity.

Methods

We conducted a prospective cohort survey of adult patients with IBD seen in tertiary care in London Health Sciences Centre. A 40-question online survey was completed by consenting patients and collected data on demographics, IBD disease history, cannabis use, and included the Short Inflammatory Bowel Disease Questionnaire (SIBDQ) as a measure of disease severity. The study was approved by the Western University Ethics Committee. Statistical analyses was performed using a Chi squared test for categorical data, and a two-tailed t-test for continuous data.

Results

Completed surveys were obtained from 210 individuals (135 individuals with CD and 75 with UC) and demographics were similar between the CD and UC cohort. Fifty-six percent of participants reported cannabis use at least once in their lifetime, with 38% of participants reporting cannabis use in the preceding 6 months. Interestingly, 46 percent of life-time cannabis users did not divulge their cannabis use to their physicians. In patients with UC, those who actively used cannabis were less likely to be on 5-ASA therapy (9 active users vs 22 non-users, p<0.05). Medical therapy was otherwise similar between cannabis users and non-users. Surgical rates were similar between cannabis users and non-users amongst both IBD subtypes. With respect to the burden of disease, patients with CD reported higher rates of abdominal pain if they were active users, however, overall SIBDQ scores were not altered by cannabis use (21 user vs 20 non-user). Similarly, SIBDQ scores were similar amongst patients with UC who were cannabis users and non-users (20 user vs 16 non-user).

Conclusions

Cannabis use in patients with IBD is very common and much higher than previously reported prior to the legalization in Canada, but its use is not associated with lower disease severity based on patient reported outcomes. Our study also reveals that patients often do not report this use to their doctors so physicians must be aware of its prevalence amongst their IBD patient population.

Funding Agencies

None

A1 F4/80+LY6CHI MACROPHAGES ARE KEY TO CANCER INITIATION IN COLITIS

Background

Colorectal cancer (CRC) is the third leading cause of cancer death, with a major risk factor being chronic inflammation. Thus, patients with inflammatory bowel disease (IBD) are at an increased risk of CRC. Despite the clear association between inflammation and cancer, the mechanism by which colitis leads to CRC is still not well understood.

Aims

In this study, we aim to explore the mechanism by which inflammation contributes to the initiation of colitis-associated cancer (CAC). We hypothesize that dextran sodium sulfate (DSS)-induced colitis leads to the infiltration of a specific immune cell type associated with tumorigenesis.

Methods

Following an injection of azoxymethane (AOM), mice were treated with the colitis-inducing agents DSS, trinitrobenzene sulfonic acid (TNBS), oxazolone (oxa), Citrobacter rodentium, or Doxorubicin (Doxo). The tumor studies were repeated using our published Cre-dependent murine model of CAC. To generate tamoxifen-inducible Cre transgenic mice that allow for Dclk1+ cell lineage tracing and cell-specific knock-out of the tumor suppressor adenomatous polyposis coli (APC), we crossed our Dclk1CreERT2 mice to both ROSA26tdTomato and APCfl/fl mice (Dclk1/APCfl/fl).

Results

Treatment with DSS, TNBS, oxa, C. rodentium, or Doxo induced colonic inflammation as detected by increased myeloperoxidase (MPO) activity and histologic analysis. DSS administration led to colonic tumors, whereas TNBS, oxa, C. rodentium, or Doxo did not lead to tumorigenesis up to 52 weeks following colitis induction. Upon flow cytometric analysis of several types of immune cells in the colonic tissue, we observed no difference in the number of T and B cells between mice treated with various colitis inducing agents. We did, however, detect significantly increased levels of Ly6G+ neutrophils and F4/80+Ly6Chi macrophages in the DSS-treated mice when compared to mice in the other models of colitis. mRNA and protein array analyses of the colonic tissue, as well as analysis of the RNA-seq data from 206 UC patients (GSE109142), revealed upregulated expression of genes associated with macrophages and neutrophils. Addition of macrophage-produced cytokines, such as IL-1β, TNF-α, or IL-6, induced lineage tracing of Dclk1+ tuft cells in intestinal organoids. Clodronate liposome-mediated depletion of F4/80+Ly6Chi macrophages significantly reduced the number of colonic tumors but did not affect tumor size in Dclk1/APCfl/fl mice.

Conclusions

Our data suggest that infiltration of F4/80+Ly6Chi macrophages, unique to DSS-induced colitis, leads to colonic tumor formation. This demonstrates that specific immune cell types, rather than the presence of colonic inflammation, plays an important role in the initiation of CAC.

Funding Agencies

CAG, CIHR

Abstract 5089: The origin and contribution of the tumor stroma in colorectal cancer

Cancer-associated fibroblasts (CAFs) are a major constituent of the tumor microenvironment and play a critical part in cancer progression. However, the precise origin of the tumor stroma remains unknown, making it challenging to effectively target the cancer mesenchyme. Here, employing 4 different genetic fate mapping mouse models and a bone marrow transplantation model in combination with BrdU labeling, we uncovered a key contributor to the tumor stroma in colorectal cancer (CRC). We found that approximately half of a-smooth muscle actin (aSMA)+ CAFs emerge through proliferation in an AOM/DSS mouse model of CRC. Lineage tracing experiments revealed that intestinal leptin receptor (Lepr)-lineage stromal cells expanded and contributed to 75% of the aSMA+ proliferating CAFs. Notably, no aSMA+ CAFs in the tumor were derived from Krt19-lineage epithelial cells or bone marrow-transplanted cells, indicating no involvement of epithelial-mesenchymal transition and bone marrow recruitment to the tumor in this model. Moreover, RNA-sequencing of FACS-purified CRC mesenchymal cells identified MCAM (also known as CD146) as a CRC stroma-specific marker, which is expressed by Lepr-lineage cells. Analysis of human CRC samples showed that high MCAM expression was associated with a mesenchymal subtype of CRC and was independently prognostic of poor overall survival. Our data identify Lepr-lineage cells as a major source of the tumor stroma in CRC and suggest that targeting MCAM+ cells may serve as a novel therapeutic approach to restrain CRC progression.

Citation Format: Hiroki Kobayashi, Krystyna A. Gieniec, Tamsin RM Lannagan, Tongtong Wang, Samuel Asfaha, Yoku Hayakawa, Simon J. Leedham, Nicholas Arpaia, Siddhartha Mukherjee, Timothy C. Wang, Atsushi Enomoto, Masahide Takahashi, Susan L. Woods, Daniel L. Worthley. The origin and contribution of the tumor stroma in colorectal cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5089.

A29 HOPX LABELS A COLONIC STEM CELL THAT CONTRIBUTES TO COLONIC REGENERATION BUT NOT COLONIC TUMORS

Background

Colorectal cancer is the 2nd leading cause of cancer death in Canada. In rapidly dividing tissues such as the intestine or colon, only long-lived, multipotent, self-renewing tissue stem cells have longevity to accumulate mutations and serve as the cellular origin of cancer. In the small intestine, genetic fate mapping studies have demonstrated that there are at least two principal stem cell pools: actively cycling, crypt base cells expressing Lgr5, and quiescent cells situated above the crypt base. Clevers and colleagues have previously shown that Lgr5-expressing cells can give rise to cancer upon mutation. Interestingly, when Lgr5+ stem cells are selectively “killed”, intestinal integrity remains intact and other stem cells restore homeostasis. To determine whether another stem cell population can give rise to cancer in the colon, we examined whether the atypical homeobox protein Hopx, marks stem cells in the colon and whether these cells can give rise to colon cancer.

Aims

In the present study, we aim to determine whether Hopx-expressing cells are colonic stem cells that contribute to gut healing and can give rise to colonic tumours following the loss of APC.

Methods

To determine whether Hopx expressing cells show stemness, we crossed Hopx-CreERT mice to R26-TdTomato reporter mice. We then conducted genetic lineage tracing studies in the colon during homeostasis and following dextran sodium sulphate (DSS)-induced colitis. To test the function of Hopx expressing cells, Hopx-CreERT mice were also crossed to R26DTR mice and treated with diphtheria toxin (DT) following tamoxifen. These mice were then exposed to either normal drinking water or DSS to determine the role of Hopx+ cells in colonic regeneration. To test whether Hopx expressing cells can serve as a cellular origin for colon cancer, Hopx-CreERT mice were crossed to Apcf/f (floxed) mice.

Results

Consistent with the labeling of a stem cell, following tamoxifen, Hopx+ cells expressing tdTomato expanded to lineage trace full colonic crypts within 7 days, and labelling was persistent for greater than 6 months. Interestingly, ablation of Hopx+ cells with DT did not alter weight, histological damage or survival during normal homeostasis, however, Hopx+ cell ablation in mice treated with DSS resulted in increased histological damage. Surprisingly, loss of APC in Hopx-expressing cells did not induce colonic adenomas even after 8 months following tamoxifen administration.

Conclusions

These findings prove that Hopx expressing cells identify a novel colonic stem cell pool that is redundant in homeostasis, but in the context of injury, are essential for epithelial regeneration. Interestingly, Hopx+ cells do not have the capacity to give rise to colorectal adenomas upon loss of the APC gene.

Funding Agencies

CIHR

A30 INHIBITION OF NF-KB SIGNALING IN DCLK1+ CELLS PROMOTES COLONIC INFLAMMATION AND COLITIS-ASSOCIATED CANCER

Background

Colorectal cancer (CRC) is the 2nd leading cause of cancer death in Canada. A major risk factor for this disease is chronic inflammation. Despite the clear link between inflammation and cancer, the exact mechanism by which colitis leads to cancer is unknown. Our group has previously shown that a rare cell type in the gut marked by the expression of doublecortin-like kinase-1 (Dclk1) and known as a tuft cell, is quiescent, long-lived, and resistant to proliferation even upon mutation of the tumor suppressor APC. Interestingly, in the setting of colitis, these APC-mutated tuft cells become powerful cancer-initiating cells, but the mechanism by which this occurs is not known. NF-kB signaling is a major inflammatory pathway active in colitis and that has been linked to colorectal cancer. Inhibition of the NF-kB pathway in intestinal epithelial cells has also been shown to inhibit tumor initiation in a mouse model of colitis-associated cancer (Greten et al., 2004).

Aims

In the present study, we aim to examine the effect of NF-kB inhibition in tuft cells on colitis-associated cancer.

Methods

Dclk1CreERT2/APCf/f mice were crossed to IKK-β f/f mice and administered tamoxifen to conditionally knockout the function of both APC and IKK-β in tuft cells. Mice were then exposed to the colitis-inducing agent dextran sodium sulfate (DSS) to induce tumorigenesis. Approximately 16 weeks post-tamoxifen, colonic tumor number and size were analyzed to determine the effect of NF-kB pathway inhibition on tumor initiation and growth, respectively. Extent of inflammation was assessed by myeloperoxidase (MPO) activity and histological damage, and colonic tissue was collected for measurement of inflammatory mediators by qRT-PCR at both acute and long-term time points.

Results

Interestingly, at baseline we detected increased MPO activity in Dclk1CreERT2/APCf/f/IKK-β f/f mice compared to control mice, suggesting that inhibition of NF-kB in Dclk1+ cells may increase basal colonic inflammation. Consistent with this observation, inhibition of the NF-kB pathway also resulted in an increased number of tuft cell-derived tumors, with no observed change in tumor size. Acutely, we also observed an exacerbation of DSS-colitis in Dclk1CreERT2/APCf/f/IKK-β f/f mice, as detected by elevated MPO activity, increased histological damage, and reduced colon length compared to wildtype (IKK-β +/+) controls.

Conclusions

These data suggest that Dclk1+ cell-specific NF-kB signaling plays a key protective role against colitis and colitis-associated tumorigenesis. Targeting the NF-kB pathway may reduce the severity of colitis and the incidence of colitis-associated cancer.

Funding Agencies

CIHR

A16 ROLE OF MYELOID CELLS IN THE INITIATION OF COLITIS-ASSOCIATED COLON CANCER

Background

Colorectal cancer (CRC) is the second leading cause of cancer death, with a major risk factor being chronic inflammation. Despite the clear association between inflammation and cancer, the mechanism by which colitis leads to CRC is not well understood. We recently showed that the presence of inflammation does not always correlate with colonic tumorigenesis, as the type of colitis (i.e. colitis-inducing agent) appears to be important for tumor initiation.

Aims

In this study, we aim to explore the mechanism by which inflammation contributes to the initiation of colitis-associated cancer. We hypothesized that dextran sodium sulfate (DSS)-induced colitis leads to the infiltration of a specific immune cell type that is associated with colonic tumorigenesis.

Methods

To generate tamoxifen-inducible Cre transgenic mice that allow for Dclk1+ cell lineage tracing and cell-specific knock-out of the tumor suppressor adenomatous polyposis coli (APC), we first crossed our transgenic Dclk1CreERT2 mice to both ROSA26tdTomato and APCfl/fl mice (Dclk1/APCfl/fl). Following Tamoxifen induction, mice were treated with the colitis-inducing agents DSS, trinitrobenzene sulfonic acid (TNBS), oxazolone, or Citrobacter rodentium. The tumor studies were repeated using azoxymethane (AOM)-DSS induced colitis-associated cancer model.

Results

Treatment with any of the four colitis-inducing agents (DSS, TNBS, oxazolone, or C. rodentium) induced colonic inflammation as detected by increased myeloperoxidase (MPO) activity and histologic analysis. Interestingly, DSS administration led to colonic tumors, whereas TNBS, oxazolone, or C. rodentium did not, even up to 52 weeks following colitis induction. FACS analysis of immune cells in the colon revealed no difference in the number of T or B cells in mice treated with any of the colitis-inducing agents. We did, however, detect significantly increased levels of Ly6G+ neutrophils and F4/80+ macrophages in DSS-treated mice compared to mice in any of the other three models of colitis. Consistent with this myeloid cell infiltration, significantly upregulated protein levels of G-CSF, IL-6, TNF-α, and CXCL1 were detected in DSS-treated mice compared to the other three models of colitis. IL-1α, IL-1β, IL-4, IL-10, and TGF-β levels were unchanged.

Conclusions

Our data suggest that infiltration of Ly6G+ neutrophils and pro-inflammatory F4/80+ macrophages, unique to DSS-induced colitis, contributes to colonic tumor formation. These data demonstrate that specific immune cell types, rather than the presence of colonic inflammation, play a critical role in the initiation of colitis-associated CRC.

Funding Agencies

CAG, CIHR

CDK4 Inhibitors Thwart Immunity by Inhibiting Phospho-RB-NF-κB Complexes

PD-L1 plays a central role in immune recognition of cancer cells. In this issue of Molecular Cell, Jin et al. (2019) report that a phosphorylated retinoblastoma protein contacts the DNA-binding domain of p65 NF-κB, thereby blocking transcription of PD-L1.

BHLHA15-Positive Secretory Precursor Cells Can Give Rise to Tumors in Intestine and Colon in Mice

BACKGROUND & AIMS

The intestinal epithelium is maintained by long-lived intestinal stem cells (ISCs) that reside near the crypt base. Above the ISC zone, there are short-lived progenitors that normally give rise to lineage-specific differentiated cell types but can dedifferentiate into ISCs in certain circumstances. However, the role of epithelial dedifferentiation in cancer development has not been fully elucidated.

METHODS

We performed studies with Bhlha15-CreERT, Lgr5-DTR-GFP, Apc^flox/flox, LSL-Notch (IC), and R26-reporter strains of mice. Some mice were given diphtheria toxin to ablate Lgr5-positive cells, were irradiated, or were given 5-fluorouracil, hydroxyurea, doxorubicin, or dextran sodium sulfate to induce intestinal or colonic tissue injury. In intestinal tissues, we analyzed the fate of progeny that expressed Bhlha15. We used microarrays and reverse-transcription PCR to analyze gene expression patterns in healthy and injured intestinal tissues and in tumors. We analyzed gene expression patterns in human colorectal tumors using The Cancer Genome Atlas data set.

RESULTS

Bhlha15 identified Paneth cells and short-lived secretory precursors (including pre-Paneth label-retaining cells) located just above the ISC zone in the intestinal epithelium. Bhlha15⁺ cells had no plasticity after loss of Lgr5-positive cells or irradiation. However, Bhlha15⁺ secretory precursors started to supply the enterocyte lineage after doxorubicin-induced epithelial injury in a Notch-dependent manner. Sustained activation of Notch converts Bhlha15⁺ secretory precursors to long-lived enterocyte progenitors. Administration of doxorubicin and expression of an activated form of Notch resulted in a gene expression pattern associated with enterocyte progenitors, whereas only sustained activation of Notch altered gene expression patterns in Bhlha15⁺ precursors toward those of ISCs. Bhlha15⁺ enterocyte progenitors with sustained activation of Notch formed intestinal tumors with serrated features in mice with disruption of Apc. In the colon, Bhlha15 marked secretory precursors that became stem-like, cancer-initiating cells after dextran sodium sulfate-induced injury, via activation of Src and YAP signaling. In analyses of human colorectal tumors, we associated activation of Notch with chromosome instability-type tumors with serrated features in the left colon.

CONCLUSIONS

In mice, we found that short-lived precursors can undergo permanent reprogramming by activation of Notch and YAP signaling. These cells could mediate tumor formation in addition to traditional ISCs.

Atoh1+ secretory progenitors possess renewal capacity independent of Lgr5+ cells during colonic regeneration

During homeostasis, the colonic epithelium is replenished every 3-5 days by rapidly cycling Lgr5 ⁺ stem cells. However, various insults can lead to depletion of Lgr5 ⁺ stem cells, and colonic epithelium can be regenerated from Lgr5-negative cells. While studies in the small intestine have addressed the lineage identity of the Lgr5-negative regenerative cell population, in the colon this question has remained unanswered. Here, we set out to identify which cell(s) contribute to colonic regeneration by performing genetic fate-mapping studies of progenitor populations in mice. First, using keratin-19 (Krt19) to mark a heterogeneous population of cells, we found that Lgr5-negative cells can regenerate colonic crypts and give rise to Lgr5 ⁺ stem cells. Notch1 ⁺ absorptive progenitor cells did not contribute to epithelial repair after injury, whereas Atoh1 ⁺ secretory progenitors did contribute to this process. Additionally, while colonic Atoh1 ⁺ cells contributed minimally to other lineages during homeostasis, they displayed plasticity and contributed to epithelial repair during injury, independent of Lgr5 ⁺ cells. Our findings suggest that promotion of secretory progenitor plasticity could enable gut healing in colitis.

Bone marrow-derived epithelial cells and hair follicle stem cells contribute to development of chronic cutaneous neoplasms

We used allogeneic bone marrow transplantation (BMT) and a mouse multistage cutaneous carcinogenesis model to probe recruitment of bone marrow-derived epithelial cells (BMDECs) in skin tumors initiated with the carcinogen, dimethylbenz[a]anthracene (DMBA), and promoted with 12-O-tetradecanolyphorbol-13-acetate (TPA). BMDECs clustered in the lesional epithelium, expressed cytokeratins, proliferated, and stratified. We detected cytokeratin induction in plastic-adherent bone marrow cells (BMCs) cultured in the presence of filter-separated keratinocytes (KCs) and bone morphogenetic protein 5 (BMP5). Lineage-depleted BMCs migrated towards High Mobility Group Box 1 (HMGB1) protein and epidermal KCs in ex vivo invasion assays. Naive female mice receiving BMTs from DMBA-treated donors developed benign and malignant lesions after TPA promotion alone. We conclude that BMDECs contribute to the development of papillomas and dysplasia, demonstrating a systemic contribution to these lesions. Furthermore, carcinogen-exposed BMCs can initiate benign and malignant lesions upon tumor promotion. Ultimately, these findings may suggest targets for treatment of non-melanoma skin cancers.

Bone Marrow Myeloid Cells Regulate Myeloid-Biased Hematopoietic Stem Cells via a Histamine-Dependent Feedback Loop

Myeloid-biased hematopoietic stem cells (MB-HSCs) play critical roles in recovery from injury, but little is known about how they are regulated within the bone marrow niche. Here we describe an auto-/paracrine physiologic circuit that controls quiescence of MB-HSCs and hematopoietic progenitors marked by histidine decarboxylase (Hdc). Committed Hdc⁺ myeloid cells lie in close anatomical proximity to MB-HSCs and produce histamine, which activates the H₂ receptor on MB-HSCs to promote their quiescence and self-renewal. Depleting histamine-producing cells enforces cell cycle entry, induces loss of serial transplant capacity, and sensitizes animals to chemotherapeutic injury. Increasing demand for myeloid cells via lipopolysaccharide (LPS) treatment specifically recruits MB-HSCs and progenitors into the cell cycle; cycling MB-HSCs fail to revert into quiescence in the absence of histamine feedback, leading to their depletion, while an H₂ agonist protects MB-HSCs from depletion after sepsis. Thus, histamine couples lineage-specific physiological demands to intrinsically primed MB-HSCs to enforce homeostasis.

CXCR4-expressing Mist1+ progenitors in the gastric antrum contribute to gastric cancer development

Mist1 was recently shown to identify a discrete population of stem cells within the isthmus of the oxyntic gland within the gastric corpus. Chief cells at the base of the gastric corpus also express Mist1. The relevance of Mist1 expression as a marker of specific cell populations within the antral glands of the distal stomach, however, is unknown. Using Mist1-CreERT mice, we revealed that Mist1⁺ antral cells, distinct from the Mist1⁺ population in the corpus, comprise long-lived progenitors that reside within the antral isthmus above Lgr5⁺ or CCK2R⁺ cells. Mist1⁺ antral progenitors can serve as an origin of antral tumors induced by loss of Apc or MNU treatment. Mist1⁺ antral progenitors, as well as other antral stem/progenitor population, express Cxcr4, and are located in close proximity to Cxcl12 (the Cxcr4 ligand)-expressing endothelium. During antral carcinogenesis, there is an expansion of Cxcr4⁺ epithelial cells as well as the Cxcl12⁺ perivascular niche. Deletion of Cxcl12 in endothelial cells or pharmacological blockade of Cxcr4 inhibits antral tumor growth. Cxcl12/Cxcr4 signaling may be a potential therapeutic target.

Abstract LB-144: Tff2 labels pancreatic progenitors that lack proliferative potential during tissue regeneration but can serve as the origin of pancreatic cancer

While controversy over the existence of adult pancreatic stem cells persists, it is now appreciated that the acinar compartment of the pancreas harbors heterogeneous progenitors. Recent single-cell analysis also demonstrated the presence of molecularly distinct, albeit morphologically identical, acinar cell sub-lineages. Previously, using lineage-tracing approach, we reported the Dclk1+ facultative progenitors that are critical for pancreatic regeneration. Here, we identified a different pancreatic progenitor-like subpopulation which is labelled by trefoil factor 2 (Tff2), a known progenitor marker and capable of tracing multiple cell lineages in the stomach. In addition, Tff2 molecules have been shown to play a suppressive role in PDAC progression. We utilized constitutive Tff2Cre and inducible Tff2CreERT2-DTR mice which were generated through modification of a BAC allele. We crossed Tff2CreERT2-DTR with reporter mice (R26R-mTmG, -tdTomato) to trace Tff2 labeled cells, and found that Tff2 labels ~2 % of the overall population in the adult acinar compartment, which showed slow proliferation (1 year, descendants <5%) with a proliferative peak at around 6 months. Analysis of Cre recombination of both Tff2CreERT2-DTR and Cre mice revealed proliferative heterogeneity among Tff2+ acinar cells. Interestingly, following caerulein-induced injury, pancreatic ductal ligation and partial pancreatectomy, Tff2 labeled cells, distinct from Dclk1+ acinar cells, did not show increased proliferation but remained unchanged or decreased in the number of clones, suggesting that Tff2+ progenitors are not the major drivers of acinar regeneration in response to injurious stimuli. Quantitative RT-PCR analysis revealed higher expression of Sox9 and c-Met in Tff2+ acinar progenitor-like cells vs. Tff2- acinar cells. Targeted expression of KRasG12D in Tff2+ cells in the adult pancreas through crosses to LSL-KRasG12D mice led to a spectrum of mPanIN formation from 6 to 12 months, but no progression to PDAC within 12 months. Upon caerulein treatment, the progression of PanIN lesions was dramatically accelerated, with approximately 30% of the mice developing aggressive PDAC. Embryonic activation of KRasG12D in Tff2+ cells in Tff2cre mice spontaneously initiated a robust PDAC in the absence of cerulein. Clonal expansion labeled by a multicolor reporter (R26R-Brainbow2.1) showed that PDACs were polyclonal, derived from multiple Tff2+ progenitor cells. Acute pancreatitis induced by caeruelein accelerated tumor development, and significantly shortened the survival of Tff2cre;LSL-Kras mice. Altogether, Tff2 labels a subpopulation of the larger acinar progenitor pool. Tff2+ acinar cells are not facultative progenitors but can serve as a cell of origin for PDAC.

Citation Format: Zhengyu Jiang, Bernhard W. Renz, Marina Macchini, Tanaka Takayuki, Ryota Takahashi, Giovanni Valenti, Woosook Kim, Wenju Chang, Yoku Hayakawa, Kosuke Sakitani, Moritz Middelhoff, Zinaida Dubeykovskaya, Timothy Chu, Karan Nagar, Yagnesh Tailor, Chythra R. Chandregowda, Akanksha Anand, Samuel Asfaha, Alina C. Iuga, Timothy C. Wang. Tff2 labels pancreatic progenitors that lack proliferative potential during tissue regeneration but can serve as the origin of pancreatic cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr LB-144. doi:10.1158/1538-7445.AM2017-LB-144

Performance report cards increase adenoma detection rate

BACKGROUND AND STUDY AIMS

Adenoma detection rate (ADR) is an important measure of colonoscopy quality, as are polyp, advanced ADR, and adenocarcinoma detection rates. We investigated whether performance report cards improved these outcome measures.

PATIENTS AND METHODS

Endoscopists were given report cards comparing their detection rates to the institutional mean on an annual basis. Detection rates were evaluated at baseline, 1 year after report cards (Year 1), and 2 years after report cards (Year 2). Endoscopists were unaware of the study and received no other interventions. The primary outcome was ADR and secondary outcomes were polyp detection rate (PDR), advanced ADR, and adenocarcinoma detection rate. Multivariate regression was performed to adjust for temporal trends in patient, endoscopists, and procedural factors.

RESULTS

 Seventeen physicians performed 3,118 screening colonoscopies in patients with positive FOBT or family history of colon cancer. The ADR increased from 34.5 % (baseline) to 39.4 % (Year 1) and 41.2 % (Year 2) ( P  = 0.0037). The PDR increased from 45 % (baseline) to 48.8 % (Year 1) and 51.8 % (Year 2) ( P  = 0.011). There was no significant improvement in advanced ADR or adenocarcinoma detection rates. On multivariate analysis, the ADR increased by 22 % in Year 1 ( P  = 0.03) and 30 % in Year 2 ( P  = 0.008). Among physicians with a baseline ADR < 25 %, improvement in ADR was even greater, increasing 2.2 times by the end of the study ( P  = 0.004). Improvements in ADR were not correlated with specialty although gastroenterologists were 52 % more likely to find an adenoma than general surgeons.

CONCLUSIONS

 Annual performance report cards increased adenoma detection rates, especially among physicians with low ADR < 25 %.

Nerve Growth Factor Promotes Gastric Tumorigenesis through Aberrant Cholinergic Signaling

Within the gastrointestinal stem cell niche, nerves help to regulate both normal and neoplastic stem cell dynamics. Here, we reveal the mechanisms underlying the cancer-nerve partnership. We find that Dclk1⁺ tuft cells and nerves are the main sources of acetylcholine (ACh) within the gastric mucosa. Cholinergic stimulation of the gastric epithelium induced nerve growth factor (NGF) expression, and in turn NGF overexpression within gastric epithelium expanded enteric nerves and promoted carcinogenesis. Ablation of Dclk1⁺ cells or blockade of NGF/Trk signaling inhibited epithelial proliferation and tumorigenesis in an ACh muscarinic receptor-3 (M3R)-dependent manner, in part through suppression of yes-associated protein (YAP) function. This feedforward ACh-NGF axis activates the gastric cancer niche and offers a compelling target for tumor treatment and prevention.

Dclk1 Defines Quiescent Pancreatic Progenitors that Promote Injury-Induced Regeneration and Tumorigenesis

The existence of adult pancreatic progenitor cells has been debated. While some favor the concept of facultative progenitors involved in homeostasis and repair, neither a location nor markers for such cells have been defined. Using genetic lineage tracing, we show that Doublecortin-like kinase-1 (Dclk1) labels a rare population of long-lived, quiescent pancreatic cells. In vitro, Dclk1+ cells proliferate readily and sustain pancreatic organoid growth. In vivo, Dclk1+ cells are necessary for pancreatic regeneration following injury and chronic inflammation. Accordingly, their loss has detrimental effects after cerulein-induced pancreatitis. Expression of mutant Kras in Dclk1+ cells does not affect their quiescence or longevity. However, experimental pancreatitis converts Kras mutant Dclk1+ cells into potent cancer-initiating cells. As a potential effector of Kras, Dclk1 contributes functionally to the pathogenesis of pancreatic cancer. Taken together, these observations indicate that Dclk1 marks quiescent pancreatic progenitors that are candidates for the origin of pancreatic cancer.

Macrophage-derived extracellular vesicle-packaged WNTs rescue intestinal stem cells and enhance survival after radiation injury

WNT/β-catenin signalling is crucial for intestinal homoeostasis. The intestinal epithelium and stroma are the major source of WNT ligands but their origin and role in intestinal stem cell (ISC) and epithelial repair remains unknown. Macrophages are a major constituent of the intestinal stroma. Here, we analyse the role of macrophage-derived WNT in intestinal repair in mice by inhibiting their release using a macrophage-restricted ablation of Porcupine, a gene essential for WNT synthesis. Such Porcn-depleted mice have normal intestinal morphology but are hypersensitive to radiation injury in the intestine compared with wild-type (WT) littermates. Porcn-null mice are rescued from radiation lethality by treatment with WT but not Porcn-null bone marrow macrophage-conditioned medium (CM). Depletion of extracellular vesicles (EV) from the macrophage CM removes WNT function and its ability to rescue ISCs from radiation lethality. Therefore macrophage-derived EV-packaged WNTs are essential for regenerative response of intestine against radiation.

The intestinal stroma secretes WNT ligands but the role of WNT in intestinal repair is unclear. Here, the authors show that when WNT synthesis is ablated from stromal macrophages, the intestine morphology is normal but hypersensitive to radiation injury, implicating macrophage-derived WNT in intestinal repair.

Abstract 912: Mist1+ secretory progenitor cells can give rise to cancer in the intestine and colon

Intestinal crypts are maintained by long-lived intestinal stem cells (ISCs) which reside near the base of glands. Above the ISC pool, there are short-lived progenitors that can supply lineage-specific differentiated cell types into the villus. Notch and Wnt pathways play a key role for determining the stem/progenitor cell function and their cell fate, and regulating cancer development in the gastrointestine. Although it has been well established that ISCs are a major origin of intestinal cancer, it remains unknown whether intestinal progenitor population can give rise to cancer. We use Mist1-CreERT mice and induce Notch and Wnt activation by mating with LSL-Notch1-IC mice and/or Apc flox mice. We found that a bHLH transcriptional factor Mist1 is expressed in Paneth cells (Lysozyme+CD24high) as well as short-lived secretory progenitors (Lysozyme-CD24low) in the intestine. Mist1+ secretory progenitors are radio- and chemo-resistant, but do not show stem cell interconversion even after intestinal injury or Lgr5 ablation. However, aberrant Notch activation changes Mist1+ cells to Lgr5+ long-lived enterocyte progenitors, with loss of secretory lineage differentiation. Mist1+CD24low progenitor population can form intestinal organoids with Notch activation in vitro. Mist1+ secretory progenitors can give rise to intestinal cancer by simultaneous Notch and Wnt activation by loss of Apc gene, while loss of Apc in Mist1 lineage alone does not develop cancer. In the colon, Mist1 marks colonic secterory progenitors that become to lineage trace and can be a cancer-initiating cell after Notch activation or DSS-induced colonic injury. These results provide the clear evidence of cellular plasticity dependent on Notch signaling in the gut, and suggest short-lived progenitors as another cellular origin of cancer besides ISC pool.

Citation Format: Yoku Hayakawa, Kosuke Sakitani, Woosook Kim, Yagnesh Tailor, Karan Nagar, Kazuhiko Koike, Samuel Asfaha, Timothy C. Wang. Mist1+ secretory progenitor cells can give rise to cancer in the intestine and colon. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 912.

Abstract 1721: Desmoplasia stem and progenitor cells within the tumor microenvironment

All developing and adult organs are supported by connective tissues. We recently demonstrated that Gremlin 1 expressing cells in the bone (osteochondroreticular stem cells) and the bowel (intestinal reticular stem cells) are connective tissue stem cells, during development and healing. The contribution of these stem cells to the desmoplasia surrounding gastrointestinal and skeletal cancers, however, is unknown. In this study we first established that typical markers of bone marrow skeletal stem cells, also identify colony forming unit-fibroblasts (CFU-Fs) in the tumour microenvironment (identified by CD45-Ter-119-CD31-CD1040a+CD105+). Next we tested the local origins of alpha-smooth muscle actin (Acta2) expressing cancer-associated fibroblasts in orthotopic (colonoscopically delivered MC38 and carcinogenesis AOM/DSS) mouse models of colorectal cancer. Using transgenic mouse models to lineage trace and report the connective tissues in the bone and bowel, including Grem1-creERT;R26-LSL-ZsGreen; Acta2-RFP and our Acta2-CreERT line, we found that normal Grem1-expressing and Acta2-expressing cells each contribute to some, but not all, of the reactive cancer-associated fibroblasts surrounding our mouse models of cancer. Whilst, neoplastic cells appear to make a significant contribution to cancer-associated fibroblasts in some other cancers, using an epithelial specific Cre (K19-cre) there was no contribution of epithelium to Acta2-expressing cells in our AOM-DSS colorectal cancer models. We investigated Grem1 and Acta2 derived cells from the tumor microenvironment and found that these cells were clonagenic. Finally, we compared their capacity to support the in vitro growth of colorectal normal and neoplastic organoids compared to other colonic mesenchymal cell types. We are currently examining the role of these cells on expanding intestinal stem cells in normal and neoplastic gastrointestinal glands and examining the secreted factors from these cells that are relevant to tumor initiation and spread.

Citation Format: Tamsin Lannagan, Susan Woods, Laura Vrbanac, Miao Yang, Jia Ng, Tongtong Wang, Yagnesh Tailor, Samuel Asfaha, Timothy Wang, Daniel L. Worthley. Desmoplasia stem and progenitor cells within the tumor microenvironment. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1721.

Neural innervation stimulates splenic TFF2 to arrest myeloid cell expansion and cancer

CD11b⁺Gr-1⁺ myeloid-derived suppressor cells (MDSCs) expand in the spleen during cancer and promote progression through suppression of cytotoxic T cells. An anti-inflammatory reflex arc involving the vagus nerve and memory T cells is necessary for resolution of acute inflammation. Failure of this neural circuit could promote procarcinogenic inflammation and altered tumour immunity. Here we show that splenic TFF2, a secreted anti-inflammatory peptide, is released by vagally modulated memory T cells to suppress the expansion of MDSCs through CXCR4. Splenic denervation interrupts the anti-inflammatory neural arc, resulting in the expansion of MDSCs and colorectal cancer. Deletion of Tff2 recapitulates splenic denervation to promote carcinogenesis. Colorectal carcinogenesis could be suppressed through transgenic overexpression of TFF2, adenoviral transfer of TFF2 or transplantation of TFF2-expressing bone marrow. TFF2 is important to the anti-inflammatory reflex arc and plays an essential role in arresting MDSC proliferation. TFF2 offers a potential approach to prevent and to treat cancer.

During colorectal inflammation and cancer, myeloid cells accumulate in the spleen and suppress the host immunity response. In this study, the authors use a mouse model of colitis to demonstrate that upon vagus stimulation splenic memory T cells release TFF2, which suppresses the expansion of myeloid cells and cancer progression.

Nkx2.2 is expressed in a subset of enteroendocrine cells with expanded lineage potential

There are two major stem cell populations in the intestinal crypt region that express either Bmi1 or Lgr5; however, it has been shown that other populations in the crypt can regain stemness. In this study, we demonstrate that the transcription factor NK2 homeobox 2 (Nkx2.2) is expressed in enteroendocrine cells located in the villus and crypt of the intestinal epithelium and is coexpressed with the stem cell markers Bmi1 and Lgr5 in a subset of crypt cells. To determine whether Nkx2.2-expressing enteroendocrine cells display cellular plasticity and stem cell potential, we performed genetic lineage tracing of the Nkx2.2-expressing population using Nkx2.2(Cre/+);R26RTomato mice. These studies demonstrated that Nkx2.2+ cells are able to give rise to all intestinal epithelial cell types in basal conditions. The proliferative capacity of Nkx2.2-expressing cells was also demonstrated in vitro using crypt organoid cultures. Injuring the intestine with irradiation, systemic inflammation, and colitis did not enhance the lineage potential of Nkx2.2-expressing cells. These findings demonstrate that a rare mature enteroendocrine cell subpopulation that is demarcated by Nkx2.2 expression display stem cell properties during normal intestinal epithelial homeostasis, but is not easily activated upon injury.

Mist1 Expressing Gastric Stem Cells Maintain the Normal and Neoplastic Gastric Epithelium and Are Supported by a Perivascular Stem Cell Niche

The regulation and stem cell origin of normal and neoplastic gastric glands are uncertain. Here, we show that Mist1 expression marks quiescent stem cells in the gastric corpus isthmus. Mist1(+) stem cells serve as a cell-of-origin for intestinal-type cancer with the combination of Kras and Apc mutation and for diffuse-type cancer with the loss of E-cadherin. Diffuse-type cancer development is dependent on inflammation mediated by Cxcl12(+) endothelial cells and Cxcr4(+) gastric innate lymphoid cells (ILCs). These cells form the perivascular gastric stem cell niche, and Wnt5a produced from ILCs activates RhoA to inhibit anoikis in the E-cadherin-depleted cells. Targeting Cxcr4, ILCs, or Wnt5a inhibits diffuse-type gastric carcinogenesis, providing targets within the neoplastic gastric stem cell niche.

Intestinal stem cells and inflammation

The intestinal epithelium is renewed every 3-5 days from at least two principal stem cell pools. Actively cycling crypt based columnar (CBC) Lgr5(+) cells and slower cycling Bmi1-expressing or Krt19-expressing cells maintain the small intestinal and colonic epithelium in homeostasis and injury. Following acute epithelial damage, Lgr5+ stem cells are susceptible to injury and a reserve stem cell or progenitor pool is responsible for regeneration of the epithelium. Current data suggests that intestinal stem cells respond to inflammatory signals to modulate their expansion during epithelial regeneration. Here, we review how inflammation and injury affect intestinal and colonic stem cells.

Abstract B73: Adrenergic signaling promotes pancreatic tumor initiation and progression

Background/Aims: There is increasing evidence that chronic sympathetic nervous system activation can lead to increased noradrenaline levels in the tumor microenvironment. This process has been associated with proliferative signals largely mediated by beta-adrenergic signaling. However, the mechanisms by which adrenergic neurotransmitters are delivered to the tumor microenvironment are not well understood. In this study we aimed to investigate the role of locally and systemically delivered catecholamines to the tumor microenvironment in a well-established genetically engineered pancreatic cancer mouse model (PDx1-Cre/KRasG12D (KC) and PDx1-Cre/KRasG12D/Trp53R172H (KPC)).

Methods: Adrenergic signaling was induced or inhibited in KC or KPC mice or 3D pancreatic spheres in culture using specific non-selective and selective agonists or antagonists. Adrenergic receptor expression was assessed by RT-PCR, Western blot and immunohistochemistry. Adrenergic signaling was also modeled in vivo applying restraint stress. To elucidate the crosstalk between nerve and cancer cells, pancreatic spheres and pancreatic cancer cells were co-cultured with dorsal root ganglia and neuronal plasticity was quantified by evaluating neurite outgrowth and number of branches. Denervation of the pancreas was performed using surgical or chemical neural ablation.

Results: Adrenergic signaling receptors, in particular ADRB2, is upregulated during pancreatic cancer development. Furthermore, in vitro stimulation of cells harboring an oncogenic KRas mutation displayed a significantly increased sphere forming efficiency. This effect was blocked by the non-specific beta-blocker propranolol and the selective beta2-blocker ICI 188,551. Stimulation of pancreatic sphere formation from KC mice induced by adrenergic signaling from dorsal root ganglia in vitro was also prevented by selective blockage of the beta2-adrenergic signaling pathway. While surgical or chemical (Botulinum toxin A) denervation of the pancreas appeared not to retard the development precancerous lesions in KC mice, denervation significantly increased the survival when performed in mice after a tumor (3-5mm) was detected by high–resolution ultrasound imaging. In contrast, stress accelerated pancreatic cancer development in KC mice. The effects of stress were prevented by treatment with the selective ADRB2 antagonist ICI 188,551.

Conclusions: Taken together, our data suggests that an increased level of stress and an increased level of systemic catecholamines may promote pancreatic carcinogenesis in its early stages. During this phase, patients might benefit from pharmacological inhibition of stress-induced signaling. The progression of pancreatic cancer seems to depend on the local delivery of catecholamines to the microenvironment, and thus patients might also benefit by additional targeting of the ADRB2 signaling pathway.

Citation Format: Bernhard W. Renz, Christoph B. Westphalen, Xiaowei Chen, Yoku Hayakawa, Yoshihiro Takemoto, Marina Macchini, Daniel L. Worthley, Samuel Asfaha, Axel Kleespies, Helen Remotti, Kenneth P. Olive, Timothy C. Wang. Adrenergic signaling promotes pancreatic tumor initiation and progression. [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Innovations in Research and Treatment; May 18-21, 2014; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2015;75(13 Suppl):Abstract nr B73.

Gremlin 1 identifies a skeletal stem cell with bone, cartilage, and reticular stromal potential

The stem cells that maintain and repair the postnatal skeleton remain undefined. One model suggests that perisinusoidal mesenchymal stem cells (MSCs) give rise to osteoblasts, chondrocytes, marrow stromal cells, and adipocytes, although the existence of these cells has not been proven through fate-mapping experiments. We demonstrate here that expression of the bone morphogenetic protein (BMP) antagonist gremlin 1 defines a population of osteochondroreticular (OCR) stem cells in the bone marrow. OCR stem cells self-renew and generate osteoblasts, chondrocytes, and reticular marrow stromal cells, but not adipocytes. OCR stem cells are concentrated within the metaphysis of long bones not in the perisinusoidal space and are needed for bone development, bone remodeling, and fracture repair. Grem1 expression also identifies intestinal reticular stem cells (iRSCs) that are cells of origin for the periepithelial intestinal mesenchymal sheath. Grem1 expression identifies distinct connective tissue stem cells in both the bone (OCR stem cells) and the intestine (iRSCs).

CCK2R identifies and regulates gastric antral stem cell states and carcinogenesis

OBJECTIVE

Progastrin is the incompletely cleaved precursor of gastrin that is secreted by G-cells in the gastric antrum. Both gastrin and progastrin bind to the CCK2 receptor (Cckbr or CCK2R) expressed on a subset of gastric epithelial cells. Little is known about how gastrin peptides and CCK2R regulate gastric stem cells and carcinogenesis. Interconversion among progenitors in the intestine is documented, but the mechanisms by which this occurs are poorly defined.

DESIGN

We generated CCK2R-CreERT mice and performed inducible lineage tracing experiments. CCK2R+ antral cells and Lgr5+ antral stem cells were cultured in a three-dimensional in vitro system. We crossed progastrin-overexpressing mice with Lgr5-GFP-CreERT mice and examined the role of progastrin and CCK2R in Lgr5+ stem cells during MNU-induced carcinogenesis.

RESULTS

Through lineage tracing experiments, we found that CCK2R defines antral stem cells at position +4, which overlapped with an Lgr5(neg or low) cell population but was distinct from typical antral Lgr5(high) stem cells. Treatment with progastrin interconverts Lgr5(neg or low) CCK2R+ cells into Lgr5(high) cells, increases CCK2R+ cell numbers and promotes gland fission and carcinogenesis in response to the chemical carcinogen MNU. Pharmacological inhibition or genetic ablation of CCK2R attenuated progastrin-dependent stem cell expansion and carcinogenesis.

CONCLUSIONS

CCK2R labels +4 antral stem cells that can be activated and expanded by progastrin, thus identifying one hormonal trigger for gastric stem cell interconversion and a potential target for gastric cancer chemoprevention and therapy.

Abstract 4795: CCK2R marks gastric antral stem cell and mediates antral carcinogenesis

Gastrin is a hormone that binds to the CCK2 receptor and promotes proximal gastric cancer, but inhibits distal gastric cancer development. However, the precise roles of the CCK2 receptor, and its alternative ligand, progastrin, in gastric carcinogenesis have not been clarified. In this study, we found that progastrin accelerated antral proliferation and carcinogenesis through CCK2R+ antral stem cell expansion, using mouse gastric cancer models and transgenic mice lines including human progastrin-overexpressing (hGAS) mice, CCK2R knockout mice, Lgr5-CreERT-IRES-GFP knockin mice, and newly generated CCK2R-BAC-CreERT mice. Progastrin promoted gastric antral cancer development induced by MNU and/or H. felis. During carcinogenesis, progastrin increased the expression of Lgr5 and gland fission in response to the chemical carcinogen MNU. Genetic ablation of CCK2R diminished these progastrin-mediated effects. In vitro 3D culture experiments revealed that progastrin, but not amidated gastrin, significantly increased gastric organoid formation and growth in Noggin-free condition, effects that were ablated by a CCK2R inhibitor YF-476 or CCK2R gene deletion. In the antrum, CCK2R was expressed in an Lgr5low cell population that displayed stemness, which could be enhanced by progastrin. In the presence of progastrin, Lgr5lowCCK2R+ cells interconverted to Lgr5hi cells. Finally, we generated a new BAC-transgenic CCK2R-CreERT murine line, and lineage tracing experiments showed that CCK2R+ cells, which reside slightly above the base of the antrum, contained long-lived stem cells in vivo and in vitro. Chemical inhibition of CCK2R attenuated progastrin-dependent cancer development in mice. In conclusion, CCK2R labels Lgr5low antral stem cells that can be activated and expanded by progastrin. These findings may help the understanding of the underlying mechanism in gastric stem cell regulation by a CCK2R signal.

Citation Format: Hayakawa Yoku, Guanchun Jin, Hongshan Wang, Xiaowei Chen, Christoph B. Westphalen, Samuel Asfaha, Daniel L. Worthley, Bernhard Renz, Hiroshi Ariyama, Zinaida A. Dubeykovskaya, Yoshihiro Takemoto, Ashlesha Mulay, Yagnesh Tailor, Duan Chen, Sureshkumar Muthupalani, James G. Fox, Shigeo Takaishi, Timothy C. Wang. CCK2R marks gastric antral stem cell and mediates antral carcinogenesis. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4795. doi:10.1158/1538-7445.AM2014-4795

Abstract 4092: Long-lived Dclk1+ cells serve as colon cancer initiating cells

Introduction: In the rapidly proliferating gastrointestinal epithelium, long-lived tissue stem cells, characterized by multipotentiality and self-renewing ability, remain the most likely cellular origin for cancer. Previous studies have suggested actively cycling Lgr5+ stem cells are one cellular origin for intestinal adenomas. However, it has also recently been suggested that non-Lgr5+ cells may also contribute to the cellular origin of colorectal cancer. Doublecortin-like kinase 1 (Dclk1) protein is a gastrointestinal tuft cell marker that has been proposed to identify quiescent stem cells and cancer stem cells that sustain tumor growth. The role of Dclk1+ tuft cells within the gastrointestinal epithelium and their potential to function as cancer-initiating cells, however, remain poorly understood. Here, we used Dclk1(BAC)-CreERT;ROSA26rLacZ mice crossed to APCff mice to examine whether Dclk1+ cells contribute to colonic tumor formation.

Methods: To recapitulate the endogenous expression pattern of Dclk1, we used a BAC strategy and generated a transgenic mouse with a Tamoxifen inducible Cre under the control of the Dclk1 promoter (Dclk1-BAC-Cre-ERT). Dclk1-CreERT mice were crossed to both ROSA26rLacZ and APCff mice and treated with tamoxifen (6 mg p.o.). Dclk1+ lineage tracing was assessed by X-gal staining. To examine the contribution of the Dclk1+ cells to colonic tumorigenesis, we treated Dclk1(BAC)-CreERT;ROSA26rLacZ; APCff mice with DSS (3% in drinking water) to induce colitis. Mice were sacrificed 3-4 months after DSS weeks to assess for tumor formation and X-gal staining performed to stain for the Dclk1+ cell lineage.

Results: Dclk1-BAC-CreERT genetic lineage tracing demonstrated that a subpopulation of Dclk1+ cells is extremely long-lived and shows rare stem cell abilities. Moreover, genetic ablation reveals a pivotal role for Dclk1+ tuft cells in the response to intestinal and colonic injury. Surprisingly, conditional loss of APC in Dclk1+ cells is not sufficient to drive colonic carcinogenesis, whereas induction of DSS colitis in Dclk1-CreERT; APCflox/flox mice leads to the development of poorly differentiated colonic adenocarcinoma. Importantly, colonic tumor formation occurs even when the onset of colitis is delayed for up to 3 months after APC loss in Dclk1+ cells.

Conclusions. Thus, our data define a novel intestinal Dclk1+ tuft cell population that is long-lived, quiescent and important for intestinal homeostasis and regeneration. Long-lived Dclk1+ cells maintain quiescence even following oncogenic mutation, but are activated by tissue injury and can serve as a potent cellular origin of colon cancer.

Citation Format: Samuel Asfaha, Christoph Benedikt Westphalen, Yoku Hayakawa, Yoshihiro Takemoto, Dana J. Lukin, Wanda Setlik, Helen Remotti, Ashlesha Muley, Xiaowei Chen, Randal May, Courtney W. Houchen, James G. Fox, Michael D. Gershon, Michael Quante, Timothy Wang. Long-lived Dclk1+ cells serve as colon cancer initiating cells. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4092. doi:10.1158/1538-7445.AM2014-4092

Long-lived intestinal tuft cells serve as colon cancer-initiating cells

Doublecortin-like kinase 1 protein (DCLK1) is a gastrointestinal tuft cell marker that has been proposed to identify quiescent and tumor growth-sustaining stem cells. DCLK1⁺ tuft cells are increased in inflammation-induced carcinogenesis; however, the role of these cells within the gastrointestinal epithelium and their potential as cancer-initiating cells are poorly understood. Here, using a BAC-CreERT-dependent genetic lineage-tracing strategy, we determined that a subpopulation of DCLK1⁺ cells is extremely long lived and possesses rare stem cell abilities. Moreover, genetic ablation of Dclk1 revealed that DCLK1⁺ tuft cells contribute to recovery following intestinal and colonic injury. Surprisingly, conditional knockdown of the Wnt regulator APC in DCLK1⁺ cells was not sufficient to drive colonic carcinogenesis under normal conditions; however, dextran sodium sulfate-induced (DSS-induced) colitis promoted the development of poorly differentiated colonic adenocarcinoma in mice lacking APC in DCLK1⁺ cells. Importantly, colonic tumor formation occurred even when colitis onset was delayed for up to 3 months after induced APC loss in DCLK1⁺ cells. Thus, our data define an intestinal DCLK1⁺ tuft cell population that is long lived, quiescent, and important for intestinal homeostasis and regeneration. Long-lived DCLK1⁺ cells maintain quiescence even following oncogenic mutation, but are activated by tissue injury and can serve to initiate colon cancer.

Progastrin stimulates colonic cell proliferation via CCK2R- and β-arrestin-dependent suppression of BMP2

BACKGROUND & AIMS

Progastrin stimulates colonic mucosal proliferation and carcinogenesis through the cholecystokinin 2 receptor (CCK2R)-partly by increasing the number of colonic progenitor cells. However, little is known about the mechanisms by which progastrin stimulates colonic cell proliferation. We investigated the role of bone morphogenetic proteins (BMPs) in progastrin induction of colonic cell proliferation via CCK2R.

METHODS

We performed microarray analysis to compare changes in gene expression in the colonic mucosa of mice that express a human progastrin transgene, gastrin knockout mice, and C57BL/6 mice (controls); the effects of progastrin were also determined on in vitro colonic crypt cultures from cholecystokinin 2 receptor knockout and wild-type mice. Human colorectal and gastric cancer cells that expressed CCK2R were incubated with progastrin or Bmp2; levels of β-arrestin 1 and 2 were knocked down using small interfering RNAs. Cells were analyzed for progastrin binding, proliferation, changes in gene expression, and symmetric cell division.

RESULTS

The BMP pathway was down-regulated in the colons of human progastrin mice compared with controls. Progastrin suppressed transcription of Bmp2 through a pathway that required CCK2R and was mediated by β-arrestin 1 and 2. In mouse colonic epithelial cells, down-regulation of Bmp2 led to decreased phosphorylation of Smads1/5/8 and suppression of inhibitor of DNA binding 4. In human gastric and colorectal cancer cell lines, CCK2R was necessary and sufficient for progastrin binding and induction of proliferation; these effects were blocked when cells were incubated with recombinant Bmp2. Incubation with progastrin increased the number of CD44(+), bromodeoxyuridine+, and NUMB(+) cells, indicating an increase in symmetric divisions of putative cancer stem cells.

CONCLUSIONS

Progastrin stimulates proliferation in colons of mice and cultured human cells via CCK2R- and β-arrestin 1 and 2-dependent suppression of Bmp2 signaling. This process promotes symmetric cell division.

Stromal cell-derived factor-1 overexpression induces gastric dysplasia through expansion of stromal myofibroblasts and epithelial progenitors

OBJECTIVE

Stromal cell-derived factor-1 (SDF-1/CXCL12), the main ligand for CXCR4, is overexpressed in human cancer. This study addressed the precise contribution of SDF-1 to gastric carcinogenesis.

DESIGN

SDF-1 transgenic mice were created and a Helicobacter-induced gastric cancer model was used in combination with H/K-ATPase-IL-1β mice. Gastric tissue was analysed by histopathology and cells isolated from the stomach were analysed by molecular biological methods.

RESULTS

Analysis of the H/K-ATPase/SDF-1 transgenic (SDF-Tg) mice showed that SDF-1 overexpression results in significant gastric epithelial hyperproliferation, mucous neck cell hyperplasia and spontaneous gastric dysplasia (wild-type mice 0/15 (0%) vs SDF-Tg mice 4/14 (28.6%), p=0.042, Fisher exact test) but has minimal effects on inflammation. SDF-Tg mice also showed a dramatic expansion of α-smooth muscle actin-positive myofibroblasts and CXCR4-expressing gastric epithelial cells in the progenitor zone, both of which preceded the development of significant gastritis or dysplasia. Gremlin 1-expressing mesenchymal stem cells, the putative precursors of myofibroblasts, were also increased within the dysplastic stomachs of SDF-Tg mice and showed chemotaxis in response to SDF-1 stimulation. SDF-1 overexpression alone resulted in minimal recruitment of haematopoietic cells to the gastric mucosa, although macrophages were increased late in the disease. When SDF-Tg mice were crossed with H/K-ATPase-IL-1β mice or infected with Helicobacter felis, however, there were dramatic synergistic effects on recruitment of bone marrow-derived cells and progression to preneoplasia.

CONCLUSION

Activation of the SDF-1/CXCR4 axis can contribute to early stages of carcinogenesis primarily through recruitment of stromal cells and modulation of the progenitor niche.

Mice that express human interleukin-8 have increased mobilization of immature myeloid cells, which exacerbates inflammation and accelerates colon carcinogenesis

BACKGROUND & AIMS

Interleukin (IL)-8 has an important role in initiating inflammation in humans, attracting immune cells such as neutrophils through their receptors CXCR1 and CXCR2. IL-8 has been proposed to contribute to chronic inflammation and cancer. However, mice do not have the IL-8 gene, so human cancer cell lines and xenograft studies have been used to study the role of IL-8 in colon and gastric carcinogenesis. We generated mice that carry a bacterial artificial chromosome that encompasses the entire human IL-8 gene, including its regulatory elements (IL-8Tg mice).

METHODS

We studied the effects of IL-8 expression in APCmin(+/-) mice and IL-8Tg mice given azoxymethane and dextran sodium sulfate (DSS). We also examined the effects of IL-8 expression in gastric cancer in INS-GAS mice that overexpress gastrin and IL-8Tg mice infected with Helicobacter felis.

RESULTS

In IL-8Tg mice, expression of human IL-8 was controlled by its own regulatory elements, with virtually no messenger RNA or protein detectable under basal conditions. IL-8 was strongly up-regulated on systemic or local inflammatory stimulation, increasing mobilization of immature CD11b(+)Gr-1(+) myeloid cells (IMCs) with thioglycolate-induced peritonitis, DSS-induced colitis, and H. felis-induced gastritis. IL-8 was increased in colorectal tumors from patients and IL-8Tg mice compared with nontumor tissues. IL-8Tg mice developed more tumors than wild-type mice following administration of azoxymethane and DSS. Expression of IL-8 increased tumorigenesis in APCmin(+/-) mice compared with APCmin(+/-) mice that lack IL-8; this was associated with increased numbers of IMCs and angiogenesis in the tumors.

CONCLUSIONS

IL-8 contributes to gastrointestinal carcinogenesis by mobilizing IMCs and might be a therapeutic target for gastrointestinal cancers.

Abstract 2969: Gremlin 1 labels a mesenchymal progenitor cell in the gastrointestinal tract, bone marrow and cancer microenvironment

The gastrointestinal tract is supported by myofibroblasts (MF) that regulate epithelial homeostasis. In cancer the physiological stroma is replaced by activated cells including bone marrow (BM)-derived cancer-associated fibroblasts (CAFs) that drive carcinogenesis. MFs and a significant proportion of CAFs express αSMA. The origin of these cells and their relation to the stem cell niche in cancer, however, is unclear. We examined gene expression to determine markers of the MSC niche, from which MFs and CAFs develop, and then generated three transgenic mouse models to trace and examine the kinetics of the physiological and cancer stroma. MSC cultures from whole BM of αSMA-RFP transgenic reporter mice consist of a heterogeneous population of αSMA-RFP (+) and (-) cells (FACS). The αSMA-RFP (-) population contained the true MSC (CFU-F and differentiation). The BMP-antagonist, Grem1, was specifically upregulated in the combined RFP+/− population but not RFP+ cells suggesting that Grem1 may mark the MSC within its niche. Additionally, we confirmed the expansion of BM-derived Grem1 cells in the gastric peritumoral stroma supporting our hypothesis that the mesenchymal niche is recruited to the cancer microenvironment. In order to confirm that Grem1 labels MSCs, we developed a Grem1-BAC-CreER transgenic mouse to lineage trace this cell. 24 hours after tamoxifen induction single recombined cells were evident throughout the gastrointestinal stroma adjacent to the epithelial stem cell zone. By 3 months post-induction the recombined cells had expanded giving rise to αSMA+ MFs. Importantly, Grem1(+) cells were identified within BM-derived MSC cultures, where they also gave rise to αSMA(+) MFs and adipocytes, and are currently being differentiated into osteocytes and chondrocytes. Furthermore, in a syngeneic tumor model, subcutaneous injection of MC38 cells into Grem1-BAC-CreER mice, yielded infiltrating CAFs derived from Grem1 cells, suggesting that Grem1 marks the cellular origin of both physiological and pathological mesenchyme. Gastrointestinal carcinogenesis models (AOM/DSS, MNU/H. felis), metastasis models (splenic injection MC38) and longer term lineage tracing are proceeding. We also developed αSMA-BAC-CreER and Vimentin-BAC-CreER transgenic mice to characterize the cellular kinetics of the stroma and further refine markers co-expressed by MSCs. These studies have confirmed the turnover of intestinal MFs. In summary, Grem1 expressing stromal cells co-localize with the epithelial stem cell niche within the gastrointestinal tract and specifically label a mesenchymal cell that gives rise to αSMA+ MFs. Furthermore, syngeneic tumor models suggest that Grem1 cells also give rise to peritumoral mesenchyme. Grem1 expression identifies a likely progenitor to gastrointestinal MFs/CAFs in health and cancer. Grem1 is a promising marker of the MSC in health in cancer.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2969. doi:1538-7445.AM2012-2969

Abstract 3301: Multiple cytokeratin-19 positive stem cells contribute to the clonal origin of colonic tumors in mice

Introduction: The clonal origin of tumors is not well understood. Previous studies using chimeric mice have suggested that the origin of tumors in the mammalian small intestine may be polyclonal, with 2 or more progenitor cells contributing to intestinal adenomas. In the intestine, tissue stem cells are believed to be present in small numbers, and either quiescent or actively dividing, as previously shown with Lgr-5+ cells. Cytokeratin 19 (K19) is a potential progenitor marker expressed in the intestinal isthmus. Using the K19 gene promoter to drive Cre recombinase expression, we tracked the lineage of K19+ cells in an inducible fashion. Here, we used K19-CreERT2;ROSA26rLacZ mice to examine whether K19+ cells contribute to colonic tumor formation. Methods: In order to recapitulate the endogenous expression pattern of K19, we used a BAC strategy and generated a transgenic mouse with a Tamoxifen inducible Cre under the control of the K19 promoter (K19-BAC-Cre-ERT2). K19CreERT2 mice were crossed to ROSA26rLacZ (or GFP) reporter mice and treated with tamoxifen (6 mg/ day p.o. for 3 days) to assess K19+ lineage tracing by X-gal or GFP staining. To examine the contribution of the K19+ cells to colonic tumorigenesis, we used the AOM/DSS inflammation-associated model of colonic carcinogenesis. Mice were sacrificed 20 weeks following AOM induction and X-gal staining performed to stain for the K19+ cell lineage. Results: Treatment of control K19CreERT2/Rosa26r mice with tamoxifen resulted in the stochastic labelling of about 20-50% of colonic and intestinal glands, respectively. Consistent with the labeling of stem cells, marked glands stained positive beyond 52 weeks following tamoxifen induction. K19CreERT2/Rosa26r mice treated with AOM or DSS alone following tamoxifen labelling of K19+ glands displayed evidence of K19+ cell expansion and crypt fission, as determined by increased labelling of contiguous X-gal positive glands. K19CreERT2/Rosa26r mice were then treated with a single dose of AOM followed by DSS. When K19+ cells were labelled by tamoxifen administration prior to AOM, we observed that ∼10% tumors were entirely X-gal positive, suggesting derivation from a single K19+ cell. Interestingly, when K19+ cells were labelled by tamoxifen shortly after tumor initiation with AOM, some tumors were derived from both K19 recombined and non-recombined cells in a clonal fashion, suggesting a model whereby a K19+ cell gives rise to multiple K19+ daughter cells that each contribute to the tumor. Conclusions. Using K19CreERT2/Rosa26r mice, we show that K19 marks stem cells within the intestinal isthmus of the small intestine and colon. Using a carcinogen induced model of inflammation-associated carcinogenesis, we demonstrate that K19 expressing cells contribute to tumor formation in a manner consistent with tumor initiation following division of K19+ cells.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3301. doi:1538-7445.AM2012-3301

Abstract 5202: Bone marrow-derived epithelial cells contribute to chronic skin inflammation and skin tumor formation in the mouse

Although a stem cell origin for tumors was postulated nearly 200 years ago, a critical role of keratin-15 expressing hair follicle stem cells in skin tumorigenesis has only recently been established. In addition to tissue stem cells, bone marrow cells can play a reparative function in damaged organs and contribute to cancer development as recently demonstrated in a gastric cancer model of Helicobacter felis-induced chronic inflammation. We report here that bone marrow derived cells (BMDCs) are an exogenous source of epithelial cells in tumor development in the multistage skin carcinogenesis model following gender mismatched allogeneic bone marrow transplantation. First, clusters of BMDCs were detected in the epithelium of 37.78% papilloma samples with a genetic marker (EGFP) indicating their bone marrow donor origin. Second, clusters of keratin immunoreactive BMDCs were located primarily in the basal epithelium of the papillomas. Third, a subset of BMDCs in the basal epithelium was found to be highly proliferative as measured by incorporation of BrdU and expression of Ki67. Furthermore, a significant contribution of BMDCs was identified in 53.06% of ulcer-associated dysplastic skin samples by immunostaining and confirmed by presence of a Y chromosome. Moreover, an enhanced contribution of bone marrow-derived epithelial cells was observed in the dysplastic epidermis. Therefore, these results demonstrate that a subset of BMDCs participates as a new epithelial cell source in chronically damaged skin lesions including papillomas and ulcers.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 5202. doi:1538-7445.AM2012-5202