Loss of the epithelial marker CDX1 predicts poor prognosis in early-stage CRC patients

BACKGROUND

We have previously shown that non-curative chemotherapy imposes fetal conversion and high metastatic capacity to cancer cells. From the set of genes differentially expressed in Chemotherapy Resistant Cells, we obtained a characteristic fetal intestinal cell signature that is present in a group of untreated tumors and is sufficient to predict patient prognosis. A feature of this fetal signature is the loss of CDX1.

METHODS

We have analyzed transcriptomic data in public datasets and performed immunohistochemistry analysis of paraffin embedded tumor samples from two cohorts of colorectal cancer patients.

RESULTS

We demonstrated that low levels of CDX1 are sufficient to identify patients with poorest outcome at the early tumor stages II and III. Presence tumor areas that are negative for CDX1 staining in stage I cancers is associated with tumor relapse.

CONCLUSIONS

Our results reveal the actual possibility of incorporating CDX1 immunostaining as a valuable biomarker for CRC patients.

Revisiting ameloblastin; addressing the EMT-ECM axis above and beyond oral biology

Ameloblastin (AMBN) is best characterized for its role in dental enamel formation, regulating cell differentiation and mineralization, and cell matrix adhesion. However, AMBN has also been detected in mesenchymal stem cells in addition to bone, blood, and adipose tissue. Using immunofluorescence in a pilot scheme, we identified that AMBN is expressed in different parts of the gastrointestinal (GI) tract. AMBN mRNA and protein detection in several tissues along the length of the GI tract suggests a role for AMBN in the structure and tissue integrity of the extracellular matrix (ECM). Intracellular AMBN expression in subsets of cells indicates a potential alternative role in signaling processes. Of note, our previous functional AMBN promoter analyses had shown that it contains epithelial-mesenchymal transition (EMT) regulatory elements. ΑΜΒΝ is herein presented as a paradigm shift of the possible associations and the spatiotemporal regulation of the ECM regulating the EMT and vice versa, using the example of AMBN expression beyond oral biology.

Technological advances define shifting pathway signaling from normal to primary and metastatic colorectal cancer

Adoption of organoid/tumoroid propagation of normal and malignant intestinal epithelia has provided unparalleled opportunities to compare cell growth factor and signaling dependencies. These 3D structures recapitulate tumours in terms of gene expression regarding the tumor cells but also allow deeper insights into the contribution of the tumour microenvironment (TME). Elements of the TME can be manipulated or added back in the form of infiltrating cytotoxic lymphocytes and/or cancer associated fibroblasts. The effectiveness of chemo-, radio- and immunotherapies can be explored within weeks of deriving these patient-derived tumour avatars informing treatment of these exact patients in a timely manner. Entrenched paths to colorectal cancer (CRC) from the earliest steps of conventional adenoma or serrated lesion formation, and the recognition of further sub-categorisations embodied by consensus-molecular-subtypes (CMS), provide genetic maps allowing a molecular form of pathologic taxonomy. Recent advances in organoid propagation and scRNAseq are reshaping our understanding of CMS and CRC.

CDK8 and CDK19 regulate intestinal differentiation and homeostasis via the chromatin remodeling complex SWI/SNF

Initiation and maintenance of transcriptional states are critical for controlling normal tissue homeostasis and differentiation. The cyclin dependent kinases CDK8 and CDK19 (Mediator kinases) are regulatory components of Mediator, a highly conserved complex that orchestrates enhancer-mediated transcriptional output. While Mediator kinases have been implicated in the transcription of genes necessary for development and growth, its function in mammals has not been well defined. Using genetically defined models and pharmacological inhibitors, we showed that CDK8 and CDK19 function in a redundant manner to regulate intestinal lineage specification in humans and mice. The Mediator kinase module bound and phosphorylated key components of the chromatin remodeling complex switch/sucrose non-fermentable (SWI/SNF) in intestinal epithelial cells. Concomitantly, SWI/SNF and MED12-Mediator colocalized at distinct lineage-specifying enhancers in a CDK8/19-dependent manner. Thus, these studies reveal a transcriptional mechanism of intestinal cell specification, coordinated by the interaction between the chromatin remodeling complex SWI/SNF and Mediator kinase.

Molecular regulation after mucosal injury and regeneration in ulcerative colitis

Ulcerative colitis (UC) is a chronic nonspecific inflammatory disease with a complex etiology. Intestinal mucosal injury is an important pathological change in individuals with UC. Leucine-rich repeat-containing G protein-coupled receptor 5 (LGR5+) intestinal stem cells (ISCs) exhibit self-renewal and high differentiation potential and play important roles in the repair of intestinal mucosal injury. Moreover, LGR5+ ISCs are intricately regulated by both the Wnt/β-catenin and Notch signaling pathways, which jointly maintain the function of LGR5+ ISCs. Combination therapy targeting multiple signaling pathways and transplantation of LGR5+ ISCs may lead to the development of new clinical therapies for UC.

BIX-01294 enhances the effect of chemotherapy on colorectal cancer by inhibiting the expression of stemness genes

During the development of colorectal cancer, tumor cells will generate some cancer stem cells with self-renewal ability because they adapt to the environment. Therefore, in the treatment of colorectal cancer, it has certain potential clinical application value to effectively inhibit cancer stem cells. A small molecule EHMT-2 inhibitor, BIX-01294, was evaluated for its activity in inhibiting cancer stem cells in human colorectal cancer by in vitro and in vivo experiments. Transcriptome analysis was performed on BIX-01294 treated cells for holistic analysis to elucidate how BIX-01294 inhibits the expression of genes related to cancer stem cells. The results show that BIX-01294 significantly inhibited the proliferative phenotype of human colorectal cancer in vivo and in vitro, reduced the proportion of cancer stem cells, and inhibited some stemness-related gene. Morever, it is synergistic with 5-fluorouracil in inhibiting the proliferation of colorectal cancer. In summary, EHMT-2 is a novel target of anti-tumor drugs. The combination of BIX-01294 and 5-fluorouracil has a synergistic therapeutic effect on human colorectal cancer.

Chromatin occupancy and target genes of the haematopoietic master transcription factor MYB

The transcription factor MYB is a master regulator in haematopoietic progenitor cells and a pioneer factor affecting differentiation and proliferation of these cells. Leukaemic transformation may be promoted by high MYB levels. Despite much accumulated molecular knowledge of MYB, we still lack a comprehensive understanding of its target genes and its chromatin action. In the present work, we performed a ChIP-seq analysis of MYB in K562 cells accompanied by detailed bioinformatics analyses. We found that MYB occupies both promoters and enhancers. Five clusters (C1-C5) were found when we classified MYB peaks according to epigenetic profiles. C1 was enriched for promoters and C2 dominated by enhancers. C2-linked genes were connected to hematopoietic specific functions and had GATA factor motifs as second in frequency. C1 had in addition to MYB-motifs a significant frequency of ETS-related motifs. Combining ChIP-seq data with RNA-seq data allowed us to identify direct MYB target genes. We also compared ChIP-seq data with digital genomic footprinting. MYB is occupying nearly a third of the super-enhancers in K562. Finally, we concluded that MYB cooperates with a subset of the other highly expressed TFs in this cell line, as expected for a master regulator.

Long noncoding RNAs in intestinal homeostasis, regeneration, and cancer

Signaling pathways that regulate homeostasis and regeneration are found to be deregulated in various human malignancies. Accordingly, attempts have been made to target them at the protein level with little success. However, studies using high-throughput sequencing technologies suggest that only about 2% of the genome translates into proteins, whereas about 75% of the genome is transcribed into noncoding RNAs. Among noncoding RNAs, long noncoding RNAs (lncRNAs) have received tremendous attention in recent years as a crucial player in the regulation of almost all cellular processes involved in tissue homeostasis as well as in the development of various malignancies, including intestinal cancer. Emerging evidence suggests that lncRNAs play an instrumental role in the regulation of intestinal stem cells, injury-induced regeneration, and initiation and progression of intestinal tumors. Here, we summarize the recently discovered lncRNAs during intestinal homeostasis, regeneration, and tumorigenesis. We further present lncRNAs as diagnostic and therapeutic markers in intestinal pathologies.

Regulation of gene transcription of B lymphoma Mo-MLV insertion region 1 homolog (Review)

B lymphoma Mo-MLV insertion region 1 homolog (Bmi-1) is a core protein component of the polycomb repressive complex 1 that inhibits cell senescence and maintains the self-renewal ability of stem cells via downregulation of p16Ink4a and p19Arf expression. Bmi-1 serves an important role in hematopoietic stem cell maintenance and neurodevelopment during embryonic development, and it has been shown to enhance tumorigenesis by promoting cancer stem cell self-renewal and epithelial to mesenchymal transition. Emerging evidence suggests that Bmi-1 overexpression is closely related to the development and progression of various types of cancer, and that downregulation of Bmi-1 expression can inhibit the proliferation, invasion and metastasis of cancer cells. It is therefore important to elucidate the mechanisms underlying the regulation of Bmi-1 expression both under normal growth conditions and in malignant tissues. In the present review, the current body of knowledge pertaining to the transcriptional and post-transcriptional regulation of the BMI-1 gene is discussed, and the potential mechanisms by which Bmi-1 is dysregulated in various types of cancer are highlighted. Bmi-1 expression is primarily controlled via transcriptional regulation, and is regulated by the transcription https://www.ushuaia.pl/hyphen/?ln=en factors of the Myc family, including Myb, Twist1, SALL4 and E2F-1. Post-transcriptionally, regulation of Bmi-1 expression is inhibited by several microRNAs and certain small-molecule drugs. Thus, regulatory transcriptional factors are potential therapeutic targets to reduce Bmi-1 expression in cancer cells. Thus, the present review provides an up-to-date review on the regulation of BMI-1 gene expression at the transcriptional and post-transcriptional level.

The cellular niche for intestinal stem cells: a team effort

The rapidly self-renewing epithelium in the mammalian intestine is maintained by multipotent intestinal stem cells (ISCs) located at the bottom of the intestinal crypt that are interspersed with Paneth cells in the small intestine and Paneth-like cells in the colon. The ISC compartment is also closely associated with a sub-epithelial compartment that contains multiple types of mesenchymal stromal cells. With the advances in single cell and gene editing technologies, rapid progress has been made for the identification and characterization of the cellular components of the niche microenvironment that is essential for self-renewal and differentiation of ISCs. It has become increasingly clear that a heterogeneous population of mesenchymal cells as well as the Paneth cells collectively provide multiple secreted niche signals to promote ISC self-renewal. Here we review and summarize recent advances in the regulation of ISCs with a main focus on the definition of niche cells that sustain ISCs.

Chromatin Dynamics in Intestinal Epithelial Homeostasis: A Paradigm of Cell Fate Determination versus Cell Plasticity

The rapid renewal of intestinal epithelium is mediated by a pool of stem cells, located at the bottom of crypts, giving rise to highly proliferative progenitor cells, which in turn differentiate during their migration along the villus. The equilibrium between renewal and differentiation is critical for establishment and maintenance of tissue homeostasis, and is regulated by signaling pathways (Wnt, Notch, Bmp…) and specific transcription factors (TCF4, CDX2…). Such regulation controls intestinal cell identities by modulating the cellular transcriptome. Recently, chromatin modification and dynamics have been identified as major actors linking signaling pathways and transcriptional regulation in the control of intestinal homeostasis. In this review, we synthesize the many facets of chromatin dynamics involved in controlling intestinal cell fate, such as stemness maintenance, progenitor identity, lineage choice and commitment, and terminal differentiation. In addition, we present recent data underlying the fundamental role of chromatin dynamics in intestinal cell plasticity. Indeed, this plasticity, which includes dedifferentiation processes or the response to environmental cues (like microbiota’s presence or food ingestion), is central for the organ’s physiology. Finally, we discuss the role of chromatin dynamics in the appearance and treatment of diseases caused by deficiencies in the aforementioned mechanisms, such as gastrointestinal cancer, inflammatory bowel disease or irritable bowel syndrome.

Role of Apelin/APJ axis in cancer development and progression

Apelin is an endogenous peptide, which is expressed in a vast board of organs such as the brain, placenta, heart, lungs, kidneys, pancreas, testis, prostate and adipose tissues. The apelin receptor, called angiotensin-like-receptor 1 (APJ), is also expressed in the brain, spleen, placenta, heart, liver, intestine, prostate, thymus, testis, ovary, lungs, kidneys, stomach, and adipose tissue. The apelin/APJ axis is involved in a number of physiological and pathological processes. The apelin expression is increased in various kinds of cancer and the apelin/APJ axis plays a key role in the development of tumors through enhancing angiogenesis, metastasis, cell proliferation and also through the development of cancer stem cells and drug resistance. The apelin also stops the apoptosis of cancer cells. The apelin/APJ axis was considered in this review as an attractive therapeutic target for cancer treatment.

The Tumor Suppressor Roles of MYBBP1A, a Major Contributor to Metabolism Plasticity and Stemness

The MYB binding protein 1A (MYBBP1A, also known as p160) acts as a co-repressor of multiple transcription factors involved in many physiological processes. Therefore, MYBBP1A acts as a tumor suppressor in multiple aspects related to cell physiology, most of them very relevant for tumorigenesis. We explored the different roles of MYBBP1A in different aspects of cancer, such as mitosis, cellular senescence, epigenetic regulation, cell cycle, metabolism plasticity and stemness. We especially reviewed the relationships between MYBBP1A, the inhibitory role it plays by binding and inactivating c-MYB and its regulation of PGC-1α, leading to an increase in the stemness and the tumor stem cell population. In addition, MYBBP1A causes the activation of PGC-1α directly and indirectly through c-MYB, inducing the metabolic change from glycolysis to oxidative phosphorylation (OXPHOS). Therefore, the combination of these two effects caused by the decreased expression of MYBBP1A provides a selective advantage to tumor cells. Interestingly, this only occurs in cells lacking pVHL. Finally, the loss of MYBBP1A occurs in 8%–9% of renal tumors. tumors, and this subpopulation could be studied as a possible target of therapies using inhibitors of mitochondrial respiration.

Loss of MYBBP1A Induces Cancer Stem Cell Activity in Renal Cancer

Tumors are cellular ecosystems where different populations and subpopulations of cells coexist. Among these cells, cancer stem cells (CSCs) are considered to be the origin of the tumor mass, being involved in metastasis and in the resistance to conventional therapies. Furthermore, tumor cells have an enormous plasticity and a phenomenon of de-differentiation of mature tumor cells to CSCs may occur. Therefore, it is essential to identify genetic alterations that cause the de-differentiation of mature tumor cells to CSCs for the future design of therapeutic strategies. In this study, we characterized the role of MYBBP1A by experiments in cell lines, xenografts and human tumor samples. We have found that MYBBP1A downregulation increases c-MYB (Avian myeloblastosis viral oncogene homolog) activity, leading to a rise in the stem-like cell population. We identified that the downregulation of MYBBP1A increases tumorigenic properties, in vitro and in vivo, in renal carcinoma cell lines that express high levels of c-MYB exclusively. Moreover, in a cohort of renal tumors, MYBBP1A is downregulated or lost in a significant percentage of tumors correlating with poor patient prognosis and a metastatic tendency. Our data support the role of MYBBP1A as a tumor suppressor by repressing c-MYB, acting as an important regulator of the plasticity of tumor cells.

Using 3D epigenomic maps of primary olfactory neuronal cells from living individuals to understand gene regulation

As part of PsychENCODE, we developed a three-dimensional (3D) epigenomic map of primary cultured neuronal cells derived from olfactory neuroepithelium (CNON). We mapped topologically associating domains and high-resolution chromatin interactions using Hi-C and identified regulatory elements using chromatin immunoprecipitation and nucleosome positioning assays. Using epigenomic datasets from biopsies of 63 living individuals, we found that epigenetic marks at distal regulatory elements are more variable than marks at proximal regulatory elements. By integrating genotype and metadata, we identified enhancers that have different levels corresponding to differences in genetic variation, gender, smoking, and schizophrenia. Motif searches revealed that many CNON enhancers are bound by neuronal-related transcription factors. Last, we combined 3D epigenomic maps and gene expression profiles to predict enhancer-target gene interactions on a genome-wide scale. This study not only provides a framework for understanding individual epigenetic variation using a primary cell model system but also contributes valuable data resources for epigenomic studies of neuronal epithelium.

LncGata6 maintains stemness of intestinal stem cells and promotes intestinal tumorigenesis

The intestinal epithelium harbours remarkable self-renewal capacity that is driven by Lgr5⁺ intestinal stem cells (ISCs) at the crypt base. However, the molecular mechanism controlling Lgr5⁺ ISC stemness is incompletely understood. We show that a Gata6 long noncoding RNA (lncGata6) is highly expressed in ISCs. LncGata6 knockout or conditional knockout in ISCs impairs the stemness of ISCs and epithelial regeneration. Mechanistically, lncGata6 recruits the NURF complex onto the Ehf promoter to induce its transcription, which promotes the expression of Lgr4/5 to enhance Wnt signalling activation. Moreover, the human orthologue lncGATA6 is highly expressed in the cancer stem cells of colorectal cancer and promotes tumour initiation and progression. Antisense oligonucleotides against lncGATA6 exhibit strong therapeutic efficacy on colorectal cancer. Thus, targeting lncGATA6 will have potential clinical applications in colorectal cancer treatment as an ideal therapeutic target.

Colorectal Cancer Stem Cells Acquire Chemoresistance Through the Upregulation of F-Box/WD Repeat-Containing Protein 7 and the Consequent Degradation of c-Myc

The cancer stem cell (CSC) paradigm suggests that tumors are organized hierarchically. Chugai previously established an LGR5⁺ human colorectal cancer (CRC) stem-cell-enriched cell line (colorectal CSCs) that expresses well-accepted colorectal CSC markers and that can dynamically switch between proliferative and drug-resistant noncycling states. We performed this study to elucidate the molecular mechanisms responsible for evading cell death in colorectal CSCs mediated by anticancer agents. During the cell cycle arrest caused by anticancer agents, we found that c-Myc expression was substantially decreased in colorectal CSCs. The c-Myc expression alterations were mediated by upregulation of F-box/WD repeat-containing protein 7 (FBXW7), as evidenced through FBXW7-small interfering RNA knockdown experiments that resulted in enhanced cell sensitivity to anticancer agents. Upregulation of FBXW7 following drug treatment was not evident in commercially available cancer cell lines. Colorectal CSCs were induced to differentiation by Matrigel and fetal bovine serum. Differentiated CSCs treated with anticancer agents did not show upregulation of FBXW7 and were more sensitive to irinotecan (CPT-11), highlighting the potential CSC-specific nature of our data. The FBXW7 over-expression was further validated in resected liver metastatic sites in CRC patients after chemotherapy. In conclusion, our study revealed that a CSC-specific FBXW7-regulatory mechanism is strongly associated with resistance to chemotherapeutic agents. Inhibition of FBXW7-upregulation in CSCs following chemotherapy may enhance the response to anticancer agents and represents an attractive strategy for the elimination of colorectal CSCs. Stem Cells 2017;35:2027-2036.

Identification of FERM domain-containing protein 5 as a novel target of β-catenin/TCF7L2 complex

Deregulation of the canonical Wnt signaling pathway plays an important role in human tumorigenesis through the accumulation of β‐catenin and subsequent transactivation of TCF7L2. Although some of the consequences associated with the accumulated β‐catenin have been clarified, the comprehensive effect of activated β‐catenin/TCF7L2 transcriptional complex on tumorigenesis remains to be elucidated. To understand the precise molecular mechanisms underlying colorectal cancer, we searched for genes regulated by the complex in colorectal tumors. We performed expression profile analysis of HCT116 and SW480 colon cancer cells treated with β‐catenin siRNAs, and ChIP‐sequencing using anti‐TCF7L2 antibody. Combination of these data with public microarray data of LS174 cells with a dominant‐negative form of TCF7L2 identified a total of 11 candidate genes. In this paper, we focused on FERM domain‐containing protein 5 (FRMD5), and confirmed that it is regulated by both β‐catenin and TCF7L2. An additional reporter assay disclosed that a region in intron1 transcriptionally regulated the expression of FRMD5. ChIP assay also corroborated that TCF7L2 associates with this region. These data suggested that FRMD5 is a novel direct target of the β‐catenin/TCF7L2 complex.

The oncoprotein HBXIP up-regulates YAP through activation of transcription factor c-Myb to promote growth of liver cancer

The oncoprotein Yes-associated protein (YAP) in Hippo pathway plays crucial roles in the development of cancer. However, the mechanism of YAP regulation in cancer remains poorly understood. Here, we supposed that the oncoprotein hepatitis B X-interacting protein (HBXIP) might be involved in the modulation of YAP in liver cancer. Interestingly, our data showed that the expression levels of HBXIP were positively associated with those of YAP in clinical hepatocellular carcinoma (HCC) samples by immunohistochemistry (IHC) staining and real-time PCR assays. HBXIP was able to up-regulate YAP in hepatoma cells at the levels of promoter, mRNA and protein. Mechanistically, we identified that HBXIP up-regulated YAP through co-activating the transcription factor c-Myb in hepatoma cells. Functionally, silencing YAP abolished the proliferation of hepatoma cells mediated by HBXIP in vitro. Moreover, knockdown of YAP strongly blocked the HBXIP-enhanced tumor growth in mice. Thus, we conclude that HBXIP up-regulates YAP expression via activating transcription factor c-Myb to facilitate the growth of hepatoma cells. Our finding provides new insights into the mechanism of YAP regulation. Therapeutically, the oncoprotein HBXIP and YAP might serve as targets in liver cancer.

Enhancer decommissioning by Snail1-induced competitive displacement of TCF7L2 and down-regulation of transcriptional activators results in EPHB2 silencing

Transcriptional silencing is a major cause for the inactivation of tumor suppressor genes, however, the underlying mechanisms are only poorly understood. The EPHB2 gene encodes a receptor tyrosine kinase that controls epithelial cell migration and allocation in intestinal crypts. Through its ability to restrict cell spreading, EPHB2 functions as a tumor suppressor in colorectal cancer whose expression is frequently lost as tumors progress to the carcinoma stage. Previously we reported that EPHB2 expression depends on a transcriptional enhancer whose activity is diminished in EPHB2 non-expressing cells. Here we investigated the mechanisms that lead to EPHB2 enhancer inactivation. We show that expression of EPHB2 and SNAIL1 - an inducer of epithelial-mesenchymal transition (EMT) - is anti-correlated in colorectal cancer cell lines and tumors. In a cellular model of Snail1-induced EMT, we observe that features of active chromatin at the EPHB2 enhancer are diminished upon expression of murine Snail1. We identify the transcription factors FOXA1, MYB, CDX2 and TCF7L2 as EPHB2 enhancer factors and demonstrate that Snail1 indirectly inactivates the EPHB2 enhancer by downregulation of FOXA1 and MYB. In addition, Snail1 induces the expression of Lymphoid enhancer factor 1 (LEF1) which competitively displaces TCF7L2 from the EPHB2 enhancer. In contrast to TCF7L2, however, LEF1 appears to repress the EPHB2 enhancer. Our findings underscore the importance of transcriptional enhancers for gene regulation under physiological and pathological conditions and show that SNAIL1 employs a combinatorial mechanism to inactivate the EPHB2 enhancer based on activator deprivation and competitive displacement of transcription factors.

c-Myb regulates NOX1/p38 to control survival of colorectal carcinoma cells

The c-Myb transcription factor is important for maintenance of immature cells of many tissues including colon epithelium. Overexpression of c-Myb occurring in colorectal carcinomas (CRC) as well as in other cancers often marks poor prognosis. However, the molecular mechanism explaining how c-Myb contributes to progression of CRC has not been fully elucidated. To address this point, we investigated the way how c-Myb affects sensitivity of CRC cells to anticancer drugs. Using CRC cell lines expressing exogenous c-myb we show that c-Myb protects CRC cells from the cisplatin-, oxaliplatin-, and doxorubicin-induced apoptosis, elevates reactive oxygen species via up-regulation of NOX1, and sustains the pro-survival p38 MAPK pathway. Using pharmacological inhibitors and gene silencing of p38 and NOX1 we found that these proteins are essential for the protective effect of c-Myb and that NOX1 acts upstream of p38 activation. In addition, our result suggests that transcription of NOX1 is directly controlled by c-Myb and these genes are strongly co-expressed in human tumor tissue of CRC patients. The novel c-Myb/NOX1/p38 signaling axis that protects CRC cells from chemotherapy described in this study could provide a new base for design of future therapies of CRC.

Models of human core transcriptional regulatory circuitries

A small set of core transcription factors (TFs) dominates control of the gene expression program in embryonic stem cells and other well-studied cellular models. These core TFs collectively regulate their own gene expression, thus forming an interconnected auto-regulatory loop that can be considered the core transcriptional regulatory circuitry (CRC) for that cell type. There is limited knowledge of core TFs, and thus models of core regulatory circuitry, for most cell types. We recently discovered that genes encoding known core TFs forming CRCs are driven by super-enhancers, which provides an opportunity to systematically predict CRCs in poorly studied cell types through super-enhancer mapping. Here, we use super-enhancer maps to generate CRC models for 75 human cell and tissue types. These core circuitry models should prove valuable for further investigating cell-type–specific transcriptional regulation in healthy and diseased cells.

Myb permits multilineage airway epithelial cell differentiation

The epithelium of the pulmonary airway is specially differentiated to provide defense against environmental insults, but also subject to dysregulated differentiation that results in lung disease. The current paradigm for airway epithelial differentiation is a one-step program whereby a p63(+) basal epithelial progenitor cell generates a ciliated or secretory cell lineage, but the cue for this transition and whether there are intermediate steps are poorly defined. Here, we identify transcription factor Myb as a key regulator that permits early multilineage differentiation of airway epithelial cells. Myb(+) cells were identified as p63(-) and therefore distinct from basal progenitor cells, but were still negative for markers of differentiation. Myb RNAi treatment of primary-culture airway epithelial cells and Myb gene deletion in mice resulted in a p63(-) population with failed maturation of Foxj1(+) ciliated cells as well as Scbg1a1(+) and Muc5ac(+) secretory cells. Consistent with these findings, analysis of whole genome expression of Myb-deficient cells identified Myb-dependent programs for ciliated and secretory cell differentiation. Myb(+) cells were rare in human airways but were increased in regions of ciliated cells and mucous cell hyperplasia in samples from subjects with chronic obstructive pulmonary disease. Together, the results show that a p63(-) Myb(+) population of airway epithelial cells represents a distinct intermediate stage of differentiation that is required under normal conditions and may be heightened in airway disease.

Novel regenerative peptide TP508 mitigates radiation-induced gastrointestinal damage by activating stem cells and preserving crypt integrity

In recent years, increasing threats of radiation exposure and nuclear disasters have become a significant concern for the United States and countries worldwide. Exposure to high doses of radiation triggers a number of potentially lethal effects. Among the most severe is the gastrointestinal (GI) toxicity syndrome caused by the destruction of the intestinal barrier, resulting in bacterial translocation, systemic bacteremia, sepsis, and death. The lack of effective radioprotective agents capable of mitigating radiation-induced damage has prompted a search for novel countermeasures that can mitigate the effects of radiation post exposure, accelerate tissue repair in radiation-exposed individuals, and prevent mortality. We report that a single injection of regenerative peptide TP508 (rusalatide acetate, Chrysalin) 24 h after lethal radiation exposure (9 Gy, LD100/15) appears to significantly increase survival and delay mortality by mitigating radiation-induced intestinal and colonic toxicity. TP508 treatment post exposure prevents the disintegration of GI crypts, stimulates the expression of adherens junction protein E-cadherin, activates crypt cell proliferation, and decreases apoptosis. TP508 post-exposure treatment also upregulates the expression of DCLK1 and LGR5 markers of stem cells that have been shown to be responsible for maintaining and regenerating intestinal crypts. Thus, TP508 appears to mitigate the effects of GI toxicity by activating radioresistant stem cells and increasing the stemness potential of crypts to maintain and restore intestinal integrity. These results suggest that TP508 may be an effective emergency nuclear countermeasure that could be delivered within 24 h post exposure to increase survival and delay mortality, giving victims time to reach clinical sites for advanced medical treatment.

Intestinal-specific activatable Myb initiates colon tumorigenesis in mice

Transcription factor Myb is overexpressed in most colorectal cancers (CRC). Patients with CRC expressing the highest Myb are more likely to relapse. We previously showed that mono-allelic loss of Myb in an Adenomatous polyposis coli (APC)-driven CRC mouse model (Apc^Min/+) significantly improves survival. Here we directly investigated the association of Myb with poor prognosis and how Myb co-operates with tumor suppressor genes (TSGs) (Apc) and cell cycle regulator, p27. Here we generated the first intestinal-specific, inducible transgenic model; a MybER transgene encoding a tamoxifen-inducible fusion protein between Myb and the estrogen receptor-α ligand-binding domain driven by the intestinal-specific promoter, Gpa33. This was to mimic human CRC with constitutive Myb activity in a highly tractable mouse model. We confirmed that the transgene was faithfully expressed and inducible in intestinal stem cells (ISCs) before embarking on carcinogenesis studies. Activation of the MybER did not change colon homeostasis unless one p27 allele was lost. We then established that MybER activation during CRC initiation using a pro-carcinogen treatment, azoxymethane (AOM), augmented most measured aspects of ISC gene expression and function and accelerated tumorigenesis in mice. CRC-associated symptoms of patients including intestinal bleeding and anaemia were faithfully mimicked in AOM-treated MybER transgenic mice and implicated hypoxia and vessel leakage identifying an additional pathogenic role for Myb. Collectively, the results suggest that Myb expands the ISC pool within which CRC is initiated while co-operating with TSG loss. Myb further exacerbates CRC pathology partly explaining why high MYB is a predictor of worse patient outcome.

Defective Myb Function Ablates Cyclin E1 Expression and Perturbs Intestinal Carcinogenesis

Cyclin E1 is essential for the reentry of quiescent cells into the cell cycle. When hypomorphic mutant Myb mice (Myb(Plt4)) were examined, it was noted that Cyclin E1 (Ccne1) expression was reduced. Furthermore, the induction of Ccne1 in recovering intestinal epithelia following radiation-induced damage was ablated in Myb-mutant mice. These data prompted us to investigate whether Myb directly regulated Ccne1 and to examine whether elevated Myb in colorectal cancer is responsible for Cyclin E1-driven tumor growth. Here, it was found that Myb/MYB and Ccne1/CCNE1 expressions were coupled in both mouse and human adenomas. In addition, the low molecular weight Cyclin E1 was the predominant form in intestinal crypts and adenomatous polyposis coli (Apc)-mutant adenomas. Chromatin immunoprecipitation (ChIP) analysis confirmed that Myb bound directly to the Ccne1 promoter and regulated its endogenous expression. In contrast, Myb(Plt4) served as a dominant-negative factor that inhibited wild-type Myb and this was not apparently compensated for by the transcription factor E2F1 in intestinal epithelial cells. Myb(Plt4/Plt4) mice died prematurely on an Apc(Min/) (+) background associated with hematopoietic defects, including a myelodysplasia; nevertheless, Apc(Min/) (+) mice were protected from intestinal tumorigenesis when crossed to Myb(Plt4/) (+) mice. Knockdown of CCNE1 transcript in murine colorectal cancer cells stabilized chromosome ploidy and decreased tumor formation. These data suggest that Cyclin E1 expression is Myb dependent in normal and transformed intestinal epithelial cells, consistent with a cell-cycle progression and chromosome instability role in cancer.

IMPLICATIONS

This study demonstrates that Myb regulates Cyclin E1 expression in normal gastrointestinal tract epithelial cells and is required during intestinal tumorigenesis.

MYB elongation is regulated by the nucleic acid binding of NFκB p50 to the intronic stem-loop region

MYB transcriptional elongation is regulated by an attenuator sequence within intron 1 that has been proposed to encode a RNA stem loop (SLR) followed by a polyU tract. We report that NFκBp50 can bind the SLR polyU RNA and promote MYB transcriptional elongation together with NFκBp65. We identified a conserved lysine-rich motif within the Rel homology domain (RHD) of NFκBp50, mutation of which abrogated the interaction of NFκBp50 with the SLR polyU and impaired NFκBp50 mediated MYB elongation. We observed that the TAR RNA-binding region of Tat is homologous to the NFκBp50 RHD lysine-rich motif, a finding consistent with HIV Tat acting as an effector of MYB transcriptional elongation in an SLR dependent manner. Furthermore, we identify the DNA binding activity of NFκBp50 as a key component required for the SLR polyU mediated regulation of MYB. Collectively these results suggest that the MYB SLR polyU provides a platform for proteins to regulate MYB and reveals novel nucleic acid binding properties of NFκBp50 required for MYB regulation.

Naphthol AS-E Phosphate Inhibits the Activity of the Transcription Factor Myb by Blocking the Interaction with the KIX Domain of the Coactivator p300

The transcription factor c-Myb is highly expressed in hematopoietic progenitor cells and controls the transcription of genes important for lineage determination, cell proliferation, and differentiation. Deregulation of c-Myb has been implicated in the development of leukemia and certain other types of human cancer. c-Myb activity is highly dependent on the interaction of the c-Myb with the KIX domain of the coactivator p300, making the disruption of this interaction a reasonable strategy for the development of Myb inhibitors. Here, we have used bacterial Autodisplay to develop an in vitro binding assay that mimics the interaction of Myb and the KIX domain of p300. We have used this binding assay to investigate the potential of Naphthol AS-E phosphate, a compound known to bind to the KIX domain, to disrupt the interaction between Myb and p300. Our data show that Naphthol AS-E phosphate interferes with the Myb-KIX interaction in vitro and inhibits Myb activity in vivo. By using several human leukemia cell lines, we demonstrate that Naphthol AS-E phosphate suppresses the expression of Myb target genes and induces myeloid differentiation and apoptosis. Our work identifies Naphthol AS-E phosphate as the first low molecular weight compound that inhibits Myb activity by disrupting its interaction with p300, and suggests that inhibition of the Myb-KIX interaction might be a useful strategy for the treatment of leukemia and other tumors caused by deregulated c-Myb.

c-MYB regulates cell growth and DNA damage repair through modulating MiR-143

Radiotherapy is the most successful nonsurgical treatment for nasopharyngeal carcinoma (NCP). Although NPCs initially respond well to a full course of radiation, recurrence and metastasis are frequent. In this study, we found that down-regulated c-MYB expression was associated with increased radiation resistance and DNA damage repair ability. Interestingly, c-MYB was over-expressed in cancer tissues but not in the adjacent tissues. Down-regulation of c-MYB expression inhibited cell proliferation, and led to cell cycle arrest at the M phase in NPC cells. Luciferase and chromatin immunoprecipitation assays demonstrated that c-MYB transactivated miR-143 through direct binding to its promoter. Based on these results, c-MYB might target miR-143 in order to regulate stem cell properties, cell growth, apoptosis, and DNA damage repair.

Therapeutic DNA vaccination against colorectal cancer by targeting the MYB oncoprotein

Cancers can be addicted to continued and relatively high expression of nuclear oncoproteins. This is evident in colorectal cancer (CRC) where the oncoprotein and transcription factor MYB is over expressed and essential to continued proliferation and tumour cell survival. Historically, targeting transcription factors in the context of cancer has been very challenging. Nevertheless, we formulated a DNA vaccine to generate a MYB-specific immune response in the belief MYB peptides might be aberrantly presented on the cell surface of CRC cells. MYB, like many tumour antigens, is weakly immunogenic as it is a 'self' antigen and is subject to tolerance. To break tolerance, a fusion vaccine was generated comprising a full-length MYB complementary DNA (cDNA) flanked by two potent CD4-epitopes derived from tetanus toxoid. Vaccination was achieved against tumours initiated by two distinct highly aggressive, syngeneic cancer cell lines (CT26 and MC38) that express MYB. This was done in BALB/c and C57BL/6 mouse strains respectively. We introduced multiple inactivating mutations into the oncogene sequence for safety and sub-cloned the cDNA into a Food and Drug Administration (FDA)-compliant vector. We used low dose cyclophosphamide (CY) to overcome T-regulatory cell immune suppression, and anti-program cell death receptor 1 (anti-PD-1) antibodies to block T-cell exhaustion. Anti-PD-1 administered alone slightly delayed tumour growth in MC38 and more effectively in CT26 bearing mice, while CY treatment alone did not. We found that therapeutic vaccination elicits protection when MC38 tumour burden is low, mounts tumour-specific cell killing and affords enhanced protection when MC38 and CT26 tumour burden is higher but only in combination with anti-PD-1 antibody or low dose CY, respectively.

Brief report: Dclk1 deletion in tuft cells results in impaired epithelial repair after radiation injury

The role of Dclk1(+) tuft cells in the replacement of intestinal epithelia and reestablishing the epithelial barrier after severe genotoxic insult is completely unknown. Successful restoration requires precise coordination between the cells within each crypt subunit. While the mechanisms that control this response remain largely uncertain, the radiation model remains an exceptional surrogate for stem cell-associated crypt loss. Following the creation of Dclk1-intestinal-epithelial-deficient Villin-Cre;Dclk1(flox/flox) mice, widespread gene expression changes were detected in isolated intestinal epithelia during homeostasis. While the number of surviving crypts was unaffected, Villin-Cre;Dclk1(flox/flox) mice failed to maintain tight junctions and died at approximately 5 days, where Dclk1(flox/flox) mice lived until day 10 following radiation injury. These findings suggest that Dclk1 plays a functional role critical in the epithelial restorative response.

Situational awareness: regulation of the myb transcription factor in differentiation, the cell cycle and oncogenesis

This review summarizes the mechanisms that control the activity of the c-Myb transcription factor in normal cells and tumors, and discusses how c-Myb plays a role in the regulation of the cell cycle. Oncogenic versions of c-Myb contribute to the development of leukemias and solid tumors such as adenoid cystic carcinoma, breast cancer and colon cancer. The activity and specificity of the c-Myb protein seems to be controlled through changes in protein-protein interactions, so understanding how it is regulated could lead to the development of novel therapeutic strategies.

Tripartite interactions between Wnt signaling, Notch and Myb for stem/progenitor cell functions during intestinal tumorigenesis

Deletion studies confirm Wnt, Notch and Myb transcriptional pathway engagement in intestinal tumorigenesis. Nevertheless, their contrasting and combined roles when activated have not been elucidated. This is important as these pathways are not ablated but rather are aberrantly activated during carcinogenesis. Using ApcMin/+ mice as a source of organoids we documented their transition, on a clone-by-clone basis, to cyst-like spheres with constitutively activated Wnt pathway, increased self-renewal and growth and reduced differentiation. We then looked at this transition when Myb and/or Notch1 are activated. Activated Notch promoted cyst-like organoids. Conversely growth and propagation of cyst-like, but not normal organoids were Notch-independent. Activated Myb promoted normal, but not cyst-like organoids. Interestingly the Wnt, Notch and Myb pathways were all involved in regulating the expression of the intestinal stem cell (ISC) gene Lgr5 in organoids, while ISC gene and Notch target Olfm4 was dominantly repressed by Wnt. These findings parallel mouse intestinal adenoma formation where Notch promoted the initiation, but not growth, of Wnt-driven Olfm4-repressed colon tumors. Also Myb was essential for colon tumor initiation and collateral mouse pathologies. These data reveal the complex interplay and hierarchy of transcriptional networks that operate in ISCs and uncover a shift in pathway-dependencies during tumor initiation.

Mybs in mouse hair follicle development

The Myb transcription factors are involved in essential cellular processes, such as cell proliferation, differentiation and cell death. Biological functions carried out by specific Myb proteins are distinct. Hair follicles are ectodermal-derived organs with cycling character of the growth resulting from the presence of somatic stem cells. In this study, we followed the expression of the Myb proteins in developing hair follicles and in the hair follicle stem cell niche by immunofluorescence staining. During hair follicle development, B-Myb was present in a few cells located in the area of cell division; c-Myb was abundant postanally in dividing cells but also in keratinizing zone. In addition, c-Myb was also detected in cells under the hair follicle bulge. These findings indicate possible involvement of c-Myb in regulation of activated stem cells leaving the niche.

Wnt inhibitory factor 1 suppresses cancer stemness and induces cellular senescence

Hyperactivation of the Wingless-type (Wnt)/β-catenin pathway promotes tumor initiation, tumor growth and metastasis in various tissues. Although there is evidence for the involvement of Wnt/β-catenin pathway activation in salivary gland tumors, the precise mechanisms are unknown. Here we report for the first time that downregulation of the Wnt inhibitory factor 1 (WIF1) is a widespread event in salivary gland carcinoma ex-pleomorphic adenoma (CaExPA). We also show that WIF1 downregulation occurs in the CaExPA precursor lesion pleomorphic adenoma (PA) and indicates a higher risk of progression from benign to malignant tumor. Our results demonstrate that diverse mechanisms including WIF1 promoter hypermethylation and loss of heterozygosity contribute to WIF1 downregulation in human salivary gland tumors. In accordance with a crucial role in suppressing salivary gland tumor progression, WIF1 re-expression in salivary gland tumor cells inhibited cell proliferation, induced more differentiated phenotype and promoted cellular senescence, possibly through upregulation of tumor-suppressor genes, such as p53 and p21. Most importantly, WIF1 significantly diminished the number of salivary gland cancer stem cells and the anchorage-independent cell growth. Consistent with this observation, WIF1 caused a reduction in the expression of pluripotency and stemness markers (OCT4 and c-MYC), as well as adult stem cell self-renewal and multi-lineage differentiation markers, such as WNT3A, TCF4, c-KIT and MYB. Furthermore, WIF1 significantly increased the expression of microRNAs pri-let-7a and pri-miR-200c, negative regulators of stemness and cancer progression. In addition, we show that WIF1 functions as a positive regulator of miR-200c, leading to downregulation of BMI1, ZEB1 and ZEB2, with a consequent increase in downstream targets such as E-cadherin. Our study emphasizes the prognostic and therapeutic potential of WIF1 in human salivary gland CaExPA. Moreover, our findings demonstrate a novel mechanism by which WIF1 regulates cancer stemness and senescence, which might have major implications in the field of cancer biology.

Pharmaceutical drugs supporting regeneration of small-intestinal mucosa severely damaged by ionizing radiation in mice

Accidental exposure of the abdomen to high-dose radiation leads to severe consequences initiated by disruption of the mucosa in the small intestine. Therapeutic options are limited, even though various treatments have been investigated, particularly in the field of regenerative therapy. In order to identify readily available treatment methods, we included several current pharmaceutical drugs, for which the clinical trials have already been completed, in tests on mice that had undergone severe mucosal damage by radiation. The drugs were injected into mice 24 h after exposure to 15.7 Gy X-rays. The effects of the drugs on the damaged mucosa of the small intestine were evaluated using early regeneration indices [the expression of c-myb mRNA, and proliferation of epithelial cells in the form of microcolonies (MCs) by Days 4 and 5 post-irradiation] and the survival rate of the mice. Enhancement of mucosal regeneration at Day 4 (c-myb: P < 0.01, MC: P < 0.05) and improvement of the survival rate (P < 0.05) were observed when a clinical dose of gonadotropin, a stimulator of androgen, was injected. Similarly, a clinical dose of thiamazole (which prevents secretion of thyroid hormone) stimulated mucosal growth by Day 5 (c-myb: P < 0.01, MC: P < 0.05) and also improved the survival rate (P < 0.05). The nonclinical drugs histamine and high-dose octreotide (a growth hormone antagonist) also gave significant survival-enhancing benefits (P < 0.01 and P < 0.05, respectively). These results can be used to construct therapeutic programs and applied in various experimental studies to control the regeneration of damaged mucosa.

Pax7 is regulated by cMyb during early neural crest development through a novel enhancer

The neural crest (NC) is a migratory population of cells unique to vertebrates that generates many diverse derivatives. NC cells arise during gastrulation at the neural plate border (NPB), which is later elevated as the neural folds (NFs) form and fuse in the dorsal region of the closed neural tube, from where NC cells emigrate. In chick embryos, Pax7 is an early marker, and necessary component of NC development. Unlike other early NPB markers, which are co-expressed in lateral ectoderm, medial neural plate or posterior-lateral mesoderm, Pax7 early expression seems more restricted to the NPB. However, the molecular mechanisms controlling early Pax7 expression remain poorly understood. Here, we identify a novel enhancer of Pax7 in avian embryos that replicates the expression of Pax7 associated with early NC development. Expression from this enhancer is found in early NPB, NFs and early emigrating NC, but unlike Pax7, which is also expressed in mesodermal derivatives, this enhancer is not active in somites. Further analysis demonstrates that cMyb is able to interact with this enhancer and modulates reporter and endogenous early Pax7 expression; thus, cMyb is identified as a novel regulator of Pax7 in early NC development.

Lessons learned about human stem cell responses to ionizing radiation exposures: a long road still ahead of us

Human stem cells (hSC) possess several distinct characteristics that set them apart from other cell types. First, hSC are self-renewing, capable of undergoing both asymmetric and symmetric cell divisions. Second, these cells can be coaxed to differentiate into various specialized cell types and, as such, hold great promise for regenerative medicine. Recent progresses in hSC biology fostered the characterization of the responses of hSC to genotoxic stresses, including ionizing radiation (IR). Here, we examine how different types of hSC respond to IR, with a special emphasis on their radiosensitivity, cell cycle, signaling networks, DNA damage response (DDR) and DNA repair. We show that human embryonic stem cells (hESCs) possess unique characteristics in how they react to IR that clearly distinguish these cells from all adult hSC studied thus far. On the other hand, a manifestation of radiation injuries/toxicity in human bodies may depend to a large extent on hSC populating corresponding tissues, such as human mesenchymal stem cells (hMSC), human hematopoietic stem cells (hHSC), neural hSC, intestine hSC, etc. We discuss here that hSC responses to IR differ notably across many types of hSC which may represent the distinct roles these cells play in development, regeneration and/or maintenance of homeostasis.

Grape exosome-like nanoparticles induce intestinal stem cells and protect mice from DSS-induced colitis

Food-derived exosome-like nanoparticles pass through the intestinal tract throughout our lives, but little is known about their impact or function. Here, as a proof of concept, we show that the cells targeted by grape exosome-like nanoparticles (GELNs) are intestinal stem cells whose responses underlie the GELN-mediated intestinal tissue remodeling and protection against dextran sulfate sodium (DSS)-induced colitis. This finding is further supported by the fact that coculturing of crypt or sorted Lgr5⁺ stem cells with GELNs markedly improved organoid formation. GELN lipids play a role in induction of Lgr5⁺ stem cells, and the liposome-like nanoparticles (LLNs) assembled with lipids from GELNs are required for in vivo targeting of intestinal stem cells. Blocking β-catenin-mediated signaling pathways of GELN recipient cells attenuates the production of Lgr5⁺ stem cells. Thus, GELNs not only modulate intestinal tissue renewal processes, but can participate in the remodeling of it in response to pathological triggers.

The Myb-p300-CREB axis modulates intestine homeostasis, radiosensitivity and tumorigenesis

The gastrointestinal (GI) epithelium is constantly renewing, depending upon the intestinal stem cells (ISC) regulated by a spectrum of transcription factors (TFs), including Myb. We noted previously in mice with a p300 mutation (plt6) within the Myb-interaction-domain phenocopied Myb hypomorphic mutant mice with regard to thrombopoiesis, and here, changes in GI homeostasis. p300 is a transcriptional coactivator for many TFs, most prominently cyclic-AMP response element-binding protein (CREB), and also Myb. Studies have highlighted the importance of CREB in proliferation and radiosensitivity, but not in the GI. This prompted us to directly investigate the p300–Myb–CREB axis in the GI. Here, the role of CREB has been defined by generating GI-specific inducible creb knockout (KO) mice. KO mice show efficient and specific deletion of CREB, with no evident compensation by CREM and ATF1. Despite complete KO, only modest effects on proliferation, radiosensitivity and differentiation in the GI under homeostatic or stress conditions were evident, even though CREB target gene pcna (proliferating cell nuclear antigen) was downregulated. creb and p300 mutant lines show increased goblet cells, whereas a reduction in enteroendocrine cells was apparent only in the p300 line, further resembling the Myb hypomorphs. When propagated in vitro, crebKO ISC were defective in organoid formation, suggesting that the GI stroma compensates for CREB loss in vivo, unlike in MybKO studies. Thus, it appears that p300 regulates GI differentiation primarily through Myb, rather than CREB. Finally, active pCREB is elevated in colorectal cancer (CRC) cells and adenomas, and is required for the expression of drug transporter, MRP2, associated with resistance to Oxaliplatin as well as several chromatin cohesion protein that are relevant to CRC therapy. These data raise the prospect that CREB may have a role in GI malignancy as it does in other cancer types, but unlike Myb, is not critical for GI homeostasis.

CSF-1 receptor-dependent colon development, homeostasis and inflammatory stress response

The colony stimulating factor-1 (CSF-1) receptor (CSF-1R) directly regulates the development of Paneth cells (PC) and influences proliferation and cell fate in the small intestine (SI). In the present study, we have examined the role of CSF-1 and the CSF-1R in the large intestine, which lacks PC, in the steady state and in response to acute inflammation induced by dextran sulfate sodium (DSS). As previously shown in mouse, immunohistochemical (IHC) analysis of CSF-1R expression showed that the receptor is baso-laterally expressed on epithelial cells of human colonic crypts, indicating that this expression pattern is shared between species. Colons from Csf1r null and Csf1(op/op) mice were isolated and sectioned for IHC identification of enterocytes, enteroendocrine cells, goblet cells and proliferating cells. Both Csf1r(-/-) and Csf1(op/op) mice were found to have colon defects in enterocytes and enteroendocrine cell fate, with excessive goblet cell staining and reduced cell proliferation. In addition, the gene expression profiles of the cell cycle genes, cyclinD1, c-myc, c-fos, and c-myb were suppressed in Csf1r(-/-) colonic crypt, compared with those of WT mice and the expression of the stem cell marker gene Lgr5 was markedly reduced. However, analysis of the proliferative responses of immortalized mouse colon epithelial cells (lines; Immorto-5 and YAMC) indicated that CSF-1R is not a major regulator of colonocyte proliferation and that its effects on proliferation are indirect. In an examination of the acute inflammatory response, Csf1r(+/-) male mice were protected from the adverse affects of DSS-induced colitis compared with WT mice, while Csf1r(+/-) female mice were significantly less protected. These data indicate that CSF-1R signaling plays an important role in colon homeostasis and stem cell gene expression but that the receptor exacerbates the response to inflammatory challenge in male mice.

Activation of two distinct Sox9-EGFP-expressing intestinal stem cell populations during crypt regeneration after irradiation

Recent identification of intestinal epithelial stem cell (ISC) markers and development of ISC reporter mice permit visualization and isolation of regenerating ISCs after radiation to define their functional and molecular phenotypes. Previous studies in uninjured intestine of Sox9-EGFP reporter mice demonstrate that ISCs express low levels of Sox9-EGFP (Sox9-EGFP Low), whereas enteroendocrine cells (EEC) express high levels of Sox9-EGFP (Sox9-EGFP High). We hypothesized that Sox9-EGFP Low ISCs would expand after radiation, exhibit enhanced proliferative capacities, and adopt a distinct gene expression profile associated with rapid proliferation. Sox9-EGFP mice were given 14 Gy abdominal radiation and studied between days 3 and 9 postradiation. Radiation-induced changes in number, growth, and transcriptome of the different Sox9-EGFP cell populations were determined by histology, flow cytometry, in vitro culture assays, and microarray. Microarray confirmed that nonirradiated Sox9-EGFP Low cells are enriched for Lgr5 mRNA and mRNAs enriched in Lgr5-ISCs and identified additional putative ISC markers. Sox9-EGFP High cells were enriched for EEC markers, as well as Bmi1 and Hopx, which are putative markers of quiescent ISCs. Irradiation caused complete crypt loss, followed by expansion and hyperproliferation of Sox9-EGFP Low cells. From nonirradiated intestine, only Sox9-EGFP Low cells exhibited ISC characteristics of forming organoids in culture, whereas during regeneration both Sox9-EGFP Low and High cells formed organoids. Microarray demonstrated that regenerating Sox9-EGFP High cells exhibited transcriptomic changes linked to p53-signaling and ISC-like functions including DNA repair and reduced oxidative metabolism. These findings support a model in which Sox9-EGFP Low cells represent active ISCs, Sox9-EGFP High cells contain radiation-activatable cells with ISC characteristics, and both participate in crypt regeneration.

Regulation of intestinal cancer stem cells

Colorectal tumours harbour a sub-population of cells with stem like properties termed 'cancer stem cells', which are believed to ultimately drive cancer growth. This review discusses recent advances in our understanding of both normal and cancer intestinal stem cells, with emphasis on similarities and differences. Specifically we discuss the role of the Wnt, Notch and BMP pathways and their roles in both stem cell proliferation and differentiation. Furthermore we discuss the emerging role of microRNA and the influence of environmental factors such as tumour associated myofibroblasts and hypoxia on cancer stem cell regulation.

Colorectal cancer mouse models: integrating inflammation and the stroma

Sequences of molecular events that initiate and advance the progression of human colorectal cancer (CRC) are becoming clearer. Accepting that these events, once they are in place, accumulate over time, rapid disease progression might be expected. Yet CRC usually develops slowly over decades. Emerging insights suggest that the tumor cell microenvironment encompassing fibroblasts and endothelial and immune cells dictate when, whether, and how malignancies progress. Signaling pathways that affect the microenvironment and the inflammatory response seem to play a central role in CRC. Indeed, some of these pathways directly regulate the stem/progenitor cell niche at the base of the crypt; it now appears that the survival and growth of neoplastic cells often relies upon their subverted engagement of these pathways. Spurned on by the use of gene manipulation technologies in the mouse, dissecting and recapitulating these complex molecular interactions between the tumor and its microenvironment in the gastrointestinal (GI) tract is a reality. In parallel, our ability to isolate and grow GI stem cells in vitro enables us, for the first time, to complement reductionist in vitro findings with complex in vivo observations. Surprisingly, data suggest that the large number of signaling pathways underpinning the reciprocal interaction between the neoplastic epithelium and its microenvironment converge on a small number of common transcription factors. Here, we review the separate and interactive roles of NFκB, Stat3, and Myb, transcription factors commonly overexpressed or excessively activated in CRC. They confer molecular links between inflammation, stroma, the stem cell niche, and neoplastic cell growth.