Stromal Niche Signals That Orchestrate Intestinal Regeneration

Stromal cell populations have a central role in providing signals that support the maintenance, differentiation, and function of the intestinal epithelium. The behavior and fate of epithelial cells is directed by the spatial organization of stromal cells that either sustain stem and progenitor cell identity or drive differentiation. A combination of single-cell analyses, mouse models, and organoid coculture assays have provided insight into the diversity of signals delivered by stromal cells. Signaling gradients are established and fine-tuned by the expression of signaling agonists and antagonists along the crypt-villus axis. On epithelial injury, there are disruptions to the abundance and organization of stromal populations. There are also distinct changes in the signals originating from these cells that impact remodeling of the epithelium. How these signals coordinate to mediate epithelial repair or sustain tissue injury in inflammatory bowel diseases is beginning to emerge. Understanding of these processes may lead to opportunities to target stromal cell populations as a strategy to modify disease states.

SRSF3 shapes the structure of miR-17-92 cluster RNA and promotes selective processing of miR-17 and miR-20a

MicroRNA (miRNA) biogenesis is tightly regulated to maintain distinct miRNA expression patterns. Almost half of mammalian miRNAs are generated from miRNA clusters, but this process is not well understood. We show here that Serine-arginine rich splicing factor 3 (SRSF3) controls the processing of miR-17-92 cluster miRNAs in pluripotent and cancer cells. SRSF3 binding to multiple CNNC motifs downstream of Drosha cleavage sites within miR-17-92 is required for the efficient processing of the cluster. SRSF3 depletion specifically compromises the processing of two paralog miRNAs, miR-17 and miR-20a. In addition to SRSF3 binding to the CNNC sites, the SRSF3 RS-domain is essential for miR-17-92 processing. SHAPE-MaP probing demonstrates that SRSF3 binding disrupts local and distant base pairing, resulting in global changes in miR-17-92 RNA structure. Our data suggest a model where SRSF3 binding, and potentially its RS-domain interactions, may facilitate an RNA structure that promotes miR-17-92 processing. SRSF3-mediated increase in miR-17/20a levels inhibits the cell cycle inhibitor p21, promoting self-renewal in normal and cancer cells. The SRSF3-miR-17-92-p21 pathway operates in colorectal cancer, linking SRSF3-mediated pri-miRNA processing and cancer pathogenesis.

Modeling Intestinal Carcinogenesis Using In Vitro Organoid Cultures

Mouse models of intestinal carcinogenesis are very powerful tools for studying the impact of specific mutations on tumor initiation and progression. Mutations can be studied both singularly and in combination using conditional alleles that can be induced in a temporal manner. The steps in intestinal carcinogenesis are complex and can be challenging to image in live animals at a cellular level. The ability to culture intestinal epithelial tissue in three-dimensional organoids in vitro provides an accessible system that can be genetically manipulated and easily visualized to assess specific biological impacts in living tissue. Here, we describe methodology for conditional mutation of genes in organoids from genetically modified mice via induction of Cre recombinase induced by tamoxifen or by transient exposure to TAT-Cre protein and subsequent phenotyping of the organoids. This methodology provides a rapid platform for assessing the cellular changes induced by specific mutations in intestinal tissue.

Intestinal stem cell aging signature reveals a reprogramming strategy to enhance regenerative potential

The impact of aging on intestinal stem cells (ISCs) has not been fully elucidated. In this study, we identified widespread epigenetic and transcriptional alterations in old ISCs. Using a reprogramming algorithm, we identified a set of key transcription factors (Egr1, Irf1, FosB) that drives molecular and functional differences between old and young states. Overall, by dissecting the molecular signature of aged ISCs, our study identified transcription factors that enhance the regenerative capacity of ISCs.

Modeling colorectal cancer: A bio-resource of 50 patient-derived organoid lines

BACKGROUND AND AIM

Colorectal cancer (CRC) is the second leading cause of cancer death worldwide. To improve outcomes for these patients, we need to develop new treatment strategies. Personalized cancer medicine, where patients are treated based on the characteristics of their own tumor, has gained significant interest for its promise to improve outcomes and reduce unnecessary side effects. The purpose of this study was to examine the potential utility of patient-derived colorectal cancer organoids (PDCOs) in a personalized cancer medicine setting.

METHODS

Patient-derived colorectal cancer organoids were derived from tissue obtained from treatment-naïve patients undergoing surgical resection for the treatment of CRC. We examined the recapitulation of key histopathological, molecular, and phenotypic characteristics of the primary tumor.

RESULTS

We created a bio-resource of PDCOs from primary and metastatic CRCs. Key histopathological features were retained in PDCOs when compared with the primary tumor. Additionally, a cohort of 12 PDCOs, and their corresponding primary tumors and normal sample, were characterized through whole exome sequencing and somatic variant calling. These PDCOs exhibited a high level of concordance in key driver mutations when compared with the primary tumor.

CONCLUSIONS

Patient-derived colorectal cancer organoids recapitulate characteristics of the tissue from which they are derived and are a powerful tool for cancer research. Further research will determine their utility for predicting patient outcomes in a personalized cancer medicine setting.

Evaluation of FGFR targeting in breast cancer through interrogation of patient-derived models

BACKGROUND

Particular breast cancer subtypes pose a clinical challenge due to limited targeted therapeutic options and/or poor responses to the existing targeted therapies. While cell lines provide useful pre-clinical models, patient-derived xenografts (PDX) and organoids (PDO) provide significant advantages, including maintenance of genetic and phenotypic heterogeneity, 3D architecture and for PDX, tumor-stroma interactions. In this study, we applied an integrated multi-omic approach across panels of breast cancer PDXs and PDOs in order to identify candidate therapeutic targets, with a major focus on specific FGFRs.

METHODS

MS-based phosphoproteomics, RNAseq, WES and Western blotting were used to characterize aberrantly activated protein kinases and effects of specific FGFR inhibitors. PDX and PDO were treated with the selective tyrosine kinase inhibitors AZD4547 (FGFR1-3) and BLU9931 (FGFR4). FGFR4 expression in cancer tissue samples and PDOs was assessed by immunohistochemistry. METABRIC and TCGA datasets were interrogated to identify specific FGFR alterations and their association with breast cancer subtype and patient survival.

RESULTS

Phosphoproteomic profiling across 18 triple-negative breast cancers (TNBC) and 1 luminal B PDX revealed considerable heterogeneity in kinase activation, but 1/3 of PDX exhibited enhanced phosphorylation of FGFR1, FGFR2 or FGFR4. One TNBC PDX with high FGFR2 activation was exquisitely sensitive to AZD4547. Integrated 'omic analysis revealed a novel FGFR2-SKI fusion that comprised the majority of FGFR2 joined to the C-terminal region of SKI containing the coiled-coil domains. High FGFR4 phosphorylation characterized a luminal B PDX model and treatment with BLU9931 significantly decreased tumor growth. Phosphoproteomic and transcriptomic analyses confirmed on-target action of the two anti-FGFR drugs and also revealed novel effects on the spliceosome, metabolism and extracellular matrix (AZD4547) and RIG-I-like and NOD-like receptor signaling (BLU9931). Interrogation of public datasets revealed FGFR2 amplification, fusion or mutation in TNBC and other breast cancer subtypes, while FGFR4 overexpression and amplification occurred in all breast cancer subtypes and were associated with poor prognosis. Characterization of a PDO panel identified a luminal A PDO with high FGFR4 expression that was sensitive to BLU9931 treatment, further highlighting FGFR4 as a potential therapeutic target.

CONCLUSIONS

This work highlights how patient-derived models of human breast cancer provide powerful platforms for therapeutic target identification and analysis of drug action, and also the potential of specific FGFRs, including FGFR4, as targets for precision treatment.

Source and Impact of the EGF Family of Ligands on Intestinal Stem Cells

Epidermal Growth Factor (EGF) has long been known for its role in promoting proliferation of intestinal epithelial cells. EGF is produced by epithelial niche cells at the base of crypts in vivo and is routinely added to the culture medium to support the growth of intestinal organoids ex vivo. The recent identification of diverse stromal cell populations that reside underneath intestinal crypts has enabled the characterization of key growth factor cues supplied by these cells. The nature of these signals and how they are delivered to drive intestinal epithelial development, daily homeostasis and tissue regeneration following injury are being investigated. It is clear that aside from EGF, other ligands of the family, including Neuregulin 1 (NRG1), have distinct roles in supporting the function of intestinal stem cells through the ErbB pathway.

Mesenchymal Niche-Derived Neuregulin-1 Drives Intestinal Stem Cell Proliferation and Regeneration of Damaged Epithelium

Epidermal growth factor (EGF) maintains intestinal stem cell (ISC) proliferation and is a key component of organoid growth media yet is dispensable for intestinal homeostasis, suggesting roles for multiple EGF family ligands in ISC function. Here, we identified neuregulin 1 (NRG1) as a key EGF family ligand that drives tissue repair following injury. NRG1, but not EGF, is upregulated upon damage and is expressed in mesenchymal stromal cells, macrophages, and Paneth cells. NRG1 deletion reduces proliferation in intestinal crypts and compromises regeneration capacity. NRG1 robustly stimulates proliferation in crypts and induces budding in organoids, in part through elevated and sustained activation of mitogen-activated protein kinase (MAPK) and AKT. Consistently, NRG1 treatment induces a proliferative gene signature and promotes organoid formation from progenitor cells and enhances regeneration following injury. These data suggest mesenchymal-derived NRG1 is a potent mediator of tissue regeneration and may inform the development of therapies for enhancing intestinal repair after injury.

Personalized Medicine-Current and Emerging Predictive and Prognostic Biomarkers in Colorectal Cancer

Colorectal cancer (CRC) is the third most common cancer diagnosed worldwide and is heterogeneous both morphologically and molecularly. In an era of personalized medicine, the greatest challenge is to predict individual response to therapy and distinguish patients likely to be cured with surgical resection of tumors and systemic therapy from those resistant or non-responsive to treatment. Patients would avoid futile treatments, including clinical trial regimes and ultimately this would prevent under- and over-treatment and reduce unnecessary adverse side effects. In this review, the potential of specific biomarkers will be explored to address two key questions—1) Can the prognosis of patients that will fare well or poorly be determined beyond currently recognized prognostic indicators? and 2) Can an individual patient’s response to therapy be predicted and those who will most likely benefit from treatment/s be identified? Identifying and validating key prognostic and predictive biomarkers and an understanding of the underlying mechanisms of drug resistance and toxicity in CRC are important steps in order to personalize treatment. This review addresses recent data on biological prognostic and predictive biomarkers in CRC. In addition, patient cohorts most likely to benefit from currently available systemic treatments and/or targeted therapies are discussed in this review.

Molecular signature of interleukin-22 in colon carcinoma cells and organoid models

Interleukin (IL)-22 activates STAT (signal transducer and activator of transcription) 3 and antiapoptotic and proproliferative pathways; but beyond this, the molecular mechanisms by which IL-22 promotes carcinogenesis are poorly understood. Characterizing the molecular signature of IL-22 in human DLD-1 colon carcinoma cells, we observed increased expression of 26 genes, including NNMT (nicotinamide N-methyltransferase, ≤10-fold) and CEA (carcinoembryonic antigen, ≤7-fold), both known to promote intestinal carcinogenesis. ERP27 (endoplasmic reticulum protein-27, function unknown, ≤5-fold) and the proinflammatory ICAM1 (intercellular adhesion molecule-1, ≤4-fold) were also increased. The effect on CEA was partly STAT3-mediated, as STAT3-silencing reduced IL-22-induced CEA by ≤56%. Silencing of CEA or NNMT inhibited IL-22-induced proliferation/migration of DLD-1, Caco-2, and SW480 colon carcinoma cells. To validate these results in primary tissues, we assessed IL-22-induced gene expression in organoids from human healthy colon and colon cancer patients, and from normal mouse small intestine and colon. Gene regulation by IL-22 was similar in DLD-1 cells and human and mouse healthy organoids. CEA was an exception with no induction by IL-22 in organoids, indicating the 3-dimensional organization of the tissue may produce signals absent in 2D cell culture. Importantly, augmentation of NNMT was 5-14-fold greater in human cancerous compared to normal organoids, supporting a role for NNMT in IL-22-mediated colon carcinogenesis. Thus, NNMT and CEA emerge as mediators of the tumor-promoting effects of IL-22 in the intestine. These data advance our understanding of the multifaceted role of IL-22 in the gut and suggest the IL-22 pathway may represent a therapeutic target in colon cancer.

Patient-Derived Colorectal Cancer Organoids Upregulate Revival Stem Cell Marker Genes following Chemotherapeutic Treatment

Colorectal cancer stem cells have been proposed to drive disease progression, tumour recurrence and chemoresistance. However, studies ablating leucine rich repeat containing G protein-coupled receptor 5 (LGR5)-positive stem cells have shown that they are rapidly replenished in primary tumours. Following injury in normal tissue, LGR5+ stem cells are replaced by a newly defined, transient population of revival stem cells. We investigated whether markers of the revival stem cell population are present in colorectal tumours and how this signature relates to chemoresistance. We examined the expression of different stem cell markers in a cohort of patient-derived colorectal cancer organoids and correlated expression with sensitivity to 5-fluorouracil (5-FU) treatment. Our findings revealed that there was inter-tumour variability in the expression of stem cell markers. Clusterin (CLU), a marker of the revival stem cell population, was significantly enriched following 5-FU treatment and expression correlated with the level of drug resistance. Patient outcome data revealed that CLU expression is associated with both lower patient survival and an increase in disease recurrence. This suggests that CLU is a marker of drug resistance and may identify cells that drive colorectal cancer progression.

Modelling Intestinal Carcinogenesis Using In Vitro Organoid Cultures

Mouse models of intestinal carcinogenesis are very powerful for studying the impact of specific mutations on tumour initiation and progression. Mutations can be studied both singularly and in combination using conditional alleles that can be induced in a temporal manner. The steps in intestinal carcinogenesis are complex and can be challenging to image in live animals at a cellular level. The ability to culture intestinal epithelial tissue in three-dimensional organoids in vitro provides an accessible system that can be genetically manipulated and easily visualised to assess specific biological impacts in living tissue. Here, we describe methodology for conditional mutation of genes in organoids from genetically modified mice via induction of Cre recombinase induced by tamoxifen or by transient exposure to TAT-Cre protein. This methodology provides a rapid platform for assessing the cellular changes induced by specific mutations in intestinal tissue.

Wnt and Neuregulin1/ErbB signalling extends 3D culture of hormone responsive mammary organoids

The development of in vitro culture systems quantitatively and qualitatively recapitulating normal breast biology is key to the understanding of mammary gland biology. Current three-dimensional mammary culture systems have not demonstrated concurrent proliferation and functional differentiation ex vivo in any system for longer than 2 weeks. Here, we identify conditions including Neuregulin1 and R-spondin 1, allowing maintenance and expansion of mammary organoids for 2.5 months in culture. The organoids comprise distinct basal and luminal compartments complete with functional steroid receptors and stem/progenitor cells able to reconstitute a complete mammary gland in vivo. Alternative conditions are also described that promote enrichment of basal cells organized into multiple layers surrounding a keratinous core, reminiscent of structures observed in MMTV-Wnt1 tumours. These conditions comprise a unique tool that should further understanding of normal mammary gland development, the molecular mechanism of hormone action and signalling events whose deregulation leads to breast tumourigenesis.

A Versatile Strategy for Isolating a Highly Enriched Population of Intestinal Stem Cells

The isolation of pure populations of mouse intestinal stem cells (ISCs) is essential to facilitate functional studies of tissue homeostasis, tissue regeneration, and intestinal diseases. However, the purification of ISCs has relied predominantly on the use of transgenic reporter alleles in mice. Here, we introduce a combinational cell surface marker-mediated strategy that allows the isolation of an ISC population transcriptionally and functionally equivalent to the gold standard Lgr5-GFP ISCs. Used on reporter-free mice, this strategy allows the isolation of functional, transcriptionally distinct ISCs uncompromised by Lgr5 haploinsufficiency.

•

Reporter-free method to purify intestinal stem cells (ISCs)

•

Cells share molecular signature with gold standard Lgr5-GFP high cells

•

Multidimensional FACS data analysis reveals structure of intestinal crypt

•

Lgr5 haploinsufficiency with functional consequences in ISCs from reporter mice

ERBB3 Positively Correlates with Intestinal Stem Cell Markers but Marks a Distinct Non Proliferative Cell Population in Colorectal Cancer

Several studies have suggested ERBB3/HER3 may be a useful prognostic marker for colorectal cancer. Tumours with an intestinal stem cell signature have also been shown to be more aggressive. Here, we investigate whether ERBB3 is associated with intestinal stem cell markers in colorectal cancer and if cancer stem cells within tumours are marked by expression of ERBB3. Expression of ERBB3 and intestinal stem cell markers (LGR5, EPHB2, CD44s and CD44v6) was assessed by qRT-PCR in primary colorectal tumours (stages 0 to IV) and matched normal tissues from 53 patients. The localisation of ERBB3, EPHB2 and KI-67 within tumours was investigated using co-immunofluorescence. Expression of ERBB3 and intestinal stem cell markers were significantly elevated in adenomas and colorectal tumours compared to normal tissue. Positive correlations were found between ERBB3 and intestinal stem cell markers. However, co-immunofluorescence analysis showed that ERBB3 and EPHB2 marked specific cell populations that were mutually exclusive within tumours with distinct proliferative potentials, the majority of ERBB3+ve cells being non-proliferative. This pattern resembles cellular organisation within normal colonic epithelium where EPHB2 labelled proliferative cells reside at the crypt base and ERBB3+ve cells mark differentiated cells at the top of crypts. Our results show that ERBB3 and intestinal stem cell markers correlate in colorectal cancers. ERBB3 localises to differentiated cell populations within tumours that are non-proliferative and distinct from cancer stem cells. These data support the concept that tumours contain discrete stem, proliferative and differentiation compartments similar to that present in normal crypts.

Microarray profiling to analyze the effect of Snai1 loss in mouse intestinal epithelium

Epithelial stem cells from a variety of tissues have been shown to express genes linked to mesenchymal cell states. The Snail family of transcriptional factors has long been regarded as a marker of mesenchymal cells, however recent studies have indicated an involvement in regulation of epithelial stem cell populations. Snai1 is expressed in the stem cell population found at the base of the mouse small intestinal crypt that is responsible for generating all differentiated cell types of the intestinal epithelium. We utilized an inducible Cre recombinase approach in the intestinal epithelium combined with a conditional floxed Snai1 allele to induce knockout of gene function in the stem cell population. Loss of Snai1 resulted in loss of crypt base columnar cells and a failure to induce a proliferative response following radiation damage. We induced Snai1 loss in cultured organoids that had been derived from epithelial cells and compared gene expression to organoids with functional Snai1. Here we describe in detail the methods for generation of knockout organoids and analysis of microarray data that has been deposited in Gene Expression Omnibus (GEO):GSE65005.

Snai1 regulates cell lineage allocation and stem cell maintenance in the mouse intestinal epithelium

Snail family members regulate epithelial-to-mesenchymal transition (EMT) during invasion of intestinal tumours, but their role in normal intestinal homeostasis is unknown. Studies in breast and skin epithelia indicate that Snail proteins promote an undifferentiated state. Here, we demonstrate that conditional knockout of Snai1 in the intestinal epithelium results in apoptotic loss of crypt base columnar stem cells and bias towards differentiation of secretory lineages. In vitro organoid cultures derived from Snai1 conditional knockout mice also undergo apoptosis when Snai1 is deleted. Conversely, ectopic expression of Snai1 in the intestinal epithelium in vivo results in the expansion of the crypt base columnar cell pool and a decrease in secretory enteroendocrine and Paneth cells. Following conditional deletion of Snai1, the intestinal epithelium fails to produce a proliferative response following radiation-induced damage indicating a fundamental requirement for Snai1 in epithelial regeneration. These results demonstrate that Snai1 is required for regulation of lineage choice, maintenance of CBC stem cells and regeneration of the intestinal epithelium following damage.

Leptin induces a proliferative response in breast cancer cells but not in normal breast cells

Obesity is a risk factor for breast cancer in postmenopausal women. Leptin, a hormone excessively produced during obesity, is suggested to be involved in breast cancer. The aim of the study was to investigate procarcinogenic potential of leptin by evaluating influence of leptin on cell proliferation, cell cycle, apoptosis, and signaling on numerous breast cells lines, including 184B5 normal cells, MCF10A fibrocystic cells and MCF-7, MDA-MB-231, and T47D cancer cells. Expressions of leptin and Ob-R were analyzed using qRT-PCR and immunohistochemistry, proliferation using fluorimetric resazurin reduction test and xCELLigence system, apoptosis and cell cycle by flow cytometry, and effect of leptin on different signalling pathways using qRT-PCR and Western blot. Cells were exposed to increasing concentrations of leptin. All cell lines expressed mRNA and protein of leptin and Ob-R. Leptin stimulated proliferation of all cell lines except for 184B5 and MDA-MB-231 cells. Leptin inhibited apoptosis but didn't alter proportion of cells within cell cycle in MCF7 cells. Leptin induced overexpression of leptin, Ob-R, estrogen receptor, and aromatase mRNA in MCF-7 and T47D cells. Autoregulation induced by leptin, relationship with estrogen pathway, and proliferative and antiapoptic activity in breast cancer cells may explain that obesity-associated hyperleptinemia may be a breast cancer risk factor.

Brg1 is required for stem cell maintenance in the murine intestinal epithelium in a tissue-specific manner

Brg1 is a chromatin remodeling factor involved in mediation of a plethora of signaling pathways leading to its participation in various physiological processes both during development and in adult tissues. Among other signaling pathways, the Wnt pathway has been proposed to require Brg1 for transactivation of its target genes. Given the pivotal role of the Wnt pathway in the maintenance of normal intestinal homeostasis, we aimed to investigate the effects of Brg1 loss on the intestinal physiology. To this end, we deleted Brg1 in the murine small and large intestinal epithelia using a range of transgenic approaches. Pan-epithelial loss of Brg1 in the small intestine resulted in crypt ablation, while partial Brg1 deficiency led to gradual repopulation of the intestinal mucosa with wild-type cells. In contrast, Brg1 loss in the large intestinal epithelium was compensated by upregulation of Brm. We propose that while Brg1 is dispensable for the survival and function of the progenitor and differentiated cells in the murine intestinal epithelium, it is essential for the maintenance of the stem cell population in a tissue-specific manner.

Adiponectin, an anti-carcinogenic hormone? A systematic review on breast, colorectal, liver and prostate cancer

Adiponectin is an adipose tissue-derived hormone, expressed almost exclusively in adipose tissue, with significant antidiabetic, anti-atherosclerotic, anti-inflammatory and anti-proliferative properties. The anti-carcinogenic effects of adiponectin result from two main mechanisms: a modulation in the signaling pathways involved in proliferation process and a subtle regulation of the apoptotic response. In this review, we present recent findings on the association of adiponectin with the risk of several malignancies (breast, colorectal, liver and prostate cancers), as well as data on underlying molecular mechanisms by which adiponectin plays a substantial role in cancer pathogenesis.

In vivo and in vitro models for the therapeutic targeting of Wnt signaling using a Tet-OΔN89β-catenin system

Although significant progress has been made in understanding the importance of Wnt signaling in the initiation of colorectal cancer, less is known about responses that accompany the reversal of oncogenic Wnt signaling. The aim of this study was to analyze in vivo and in vitro responses to an 'ideal' Wnt pathway inhibitor as a model for the therapeutic targeting of the pathway. A tetracycline-inducible transgenic mouse model expressing truncated β-catenin (ΔN89β-catenin) that exhibited a strong intestinal hyperplasia was analyzed during the removal of oncogenic β-catenin expression both in 3D 'crypt culture' and in vivo. Oncogenic Wnt signaling was rapidly and completely reversed. The strongest inhibition of Wnt target gene expression occurred within 24 h of doxycycline removal at which time the target genes Ascl2, Axin2 and C-myc were downregulated to levels below that in the control intestine. In vitro, the small molecule Wnt inhibitor CCT036477 induced a response within 4 h of treatment. By 7 days following doxycycline withdrawal, gene expression, cell proliferation and tissue morphology were undistinguishable from control animals.In conclusion, these results demonstrate that the reversal of Wnt signaling by inhibitors should ideally be studied within hours of treatment. The reversible system described, involving medium throughput in vitro approaches and rapid in vivo responses, should allow the rapid advance of early stage compounds into efficacy models that are more usually considered later in the drug discovery pipeline.

Conditional disruption of Axin1 leads to development of liver tumors in mice

BACKGROUND & AIMS

Mutations in components of the Wnt signaling pathway, including β-catenin and AXIN1, are found in more than 50% of human hepatocellular carcinomas (HCCs). Disruption of Axin1 causes embryonic lethality in mice. We generated mice with conditional disruption of Axin1 to study its function specifically in adult liver.

METHODS

Mice with a LoxP-flanked allele of Axin1 were generated by homologous recombination. Mice homozygous for the Axin1fl/fl allele were crossed with AhCre mice; in offspring, Axin1 was disrupted in liver following injection of β-naphthoflavone (Axin1fl/fl/Cre mice). Liver tissues were collected and analyzed by quantitative real-time polymerase chain reaction and immunoprecipitation, histology, and immunoblot assays.

RESULTS

Deletion of Axin1 from livers of adult mice resulted in an acute and persistent increase in hepatocyte cell volume, proliferation, and transcription of genes that induce the G(2)/M transition in the cell cycle and cytokinesis. A subset of Wnt target genes was activated, including Axin2, c-Myc, and cyclin D1. However, loss of Axin1 did not increase nuclear levels of β-catenin or cause changes in liver zonation that have been associated with loss of the adenomatous polyposis coli (APC) or constitutive activation of β-catenin. After 1 year, 5 of 9 Axin1fl/fl/Cre mice developed liver tumors with histologic features of HCC.

CONCLUSIONS

Hepatocytes from adult mice with conditional disruption of Axin1 in liver have a transcriptional profile that differs from that associated with loss of APC or constitutive activation of β-catenin. It might be similar to a proliferation profile observed in a subset of human HCCs with mutations in AXIN1. Axin1fl/fl mice could be a useful model of AXIN1-associated tumorigenesis and HCC.

Intestinal renin-angiotensin system is stimulated after deletion of Lkb1

BACKGROUND AND AIMS

LKB1 is a serine-threonine kinase, mutation of which can lead to the development of multiple benign intestinal hamartomas (Peutz-Jeghers syndrome). In this study, the authors investigate the mechanisms underlying this phenotype by exploring the transcriptional changes associated with Lkb1 deletion in intestinal epithelium.

METHODS

The authors used mice with Lkb1 deleted in the intestinal epithelium using a Cyp1a1-specific inducible Cre recombinase and used Affymetrix (Santa Clara, California, USA) microarray analysis to examine the transcriptional changes occurring immediately after Lkb1 loss. The authors also generated crypt-villus organoid culture to analyse Lkb1 role in intestinal responses to exogenous stimuli.

RESULTS

Affymetrix analysis identified the most significant change to be in Ren1 expression, a gene encoding a protease involved in angiotensinogen processing. Lkb1 deletion also enhanced ACE expression and subsequently angiotensin II (AngII) production in the mouse intestine. Intestinal apoptosis induced by Lkb1 deficiency was suppressed by ACE inhibitor captopril. Lkb1-deficient intestinal epithelium showed dynamic changes in AngII receptor type 1, suggesting a possible compensatory response to elevated AngII levels. A similar reduction in epithelial AngII receptor type 1 was also observed in human Peutz-Jeghers syndrome tumours contrasting with high expression of the receptor in the tumour stroma. Mechanistically, the authors showed two pieces of data that position Lkb1 in renin expression regulation, and they implied the importance of Lkb1 in linking cell responses with nutrient levels. First, the authors showed that Lkb1 deletion in isolated epithelial organoid culture resulted in renin upregulation only when the organoids were challenged with external cues such as AngII; second, that renin upregulation was dependent upon the MEK/ERK pathway in a circadian fashion and corresponded to active feeding time when nutrient levels were high.

CONCLUSIONS

Taken together, these data reveal a novel role for Lkb1 in regulation of the gastrointestinal renin-angiotensin system.

Wnt signalling in murine postnatal mammary gland development

The mammary gland undergoes numerous developmental processes postnatally, from the elongation of the ductal tree-like structure to pregnancy-induced lobulo-alveolar development. Mammary epithelial stem cells have been suggested to be central to the control of enormous tissue expansion and remodelling during phases of mammary development. The Wnt signalling pathway plays a critical role in these biological steps and is suggested to be involved in the maintenance of the stem cell population. This review provides insight into recent findings on the activity of Wnt signalling during ductal and lobular mammary development and discusses the potential interplay between Wnt signals and mammary stem cells in mice.

New insights into anticarcinogenic properties of adiponectin: a potential therapeutic approach in breast cancer?

Obesity is a recognized breast cancer risk factor in postmenopausal women. A recent hypothesis suggests a major role for adipose tissue in carcinogenesis. During many years, the adipose tissue was only considered as a fat storage of energy. This tissue is now described as an endocrine organ secreting a large range of molecules called adipokines. Among these adipokines, adiponectin may play a major role in breast cancer. Plasma adiponectin levels were found to be decreased in cases of breast cancer and in obese patients. Adiponectin may act directly on breast cancer cells by inhibiting proliferation and angiogenesis or by stimulating apoptosis. Increasing adiponectin levels may be of major importance in the prevention and/or the treatment of breast cancer. This therapeutic approach may be of particular significance for obese patients. The beneficial effects of adiponectin and its possible therapeutic applications will be discussed in this review.

Molecular mechanisms of leptin and adiponectin in breast cancer

Obesity is associated with an increased risk of breast cancer in postmenopausal women. Accumulating evidence suggests that adipose tissue, which is an endocrine organ producing a large range of factors, may interfere with breast cancer development. Leptin and adiponectin are two major adipocyte-secreted hormones. The pro-carcinogenic effect of leptin and conversely, the anti-carcinogenic effect of adiponectin result from two main mechanisms: a modulation in the signalling pathways involved in proliferation process and a subtle regulation of the apoptotic response. This review provides insight into recent findings on the molecular mechanisms of leptin and adiponectin in mammary tumours, and discusses the potential interplay between these two adipokines in breast cancer.

Involvement of adiponectin and leptin in breast cancer: clinical and in vitro studies

Obesity is a risk factor for breast cancer development. A recent hypothesis suggests that the adipokines, adiponectin and leptin, are involved in breast cancer development. This prompted us to investigate the role of adiponectin and leptin in mammary carcinogenesis. Adiponectin receptors (AdipoR1 and AdipoR2) and leptin receptor (Ob-Rt, representing all the isoforms of Ob-R) proteins were detected by immunohistochemistry in in situ ductal carcinoma, invasive ductal malignancy, and healthy adjacent tissue. In addition, mRNA expression of adiponectin, AdipoR1, AdipoR2, leptin, Ob-Rt, and Ob-Rl (the long isoform of Ob-R) was observed in MCF-7 breast cancer cells. Interestingly, leptin mRNA expression was 34.7-fold higher than adiponectin mRNA expression in the MCF-7 cell line. Moreover, adiponectin (10 microg/ml) tended to decrease the mRNA expression of leptin (-36%) and Ob-Rl (-28%) and significantly decreased Ob-Rt mRNA level (-26%). In contrast, leptin treatment (1 microg/ml) significantly decreased AdipoR1 mRNA (-23%). Adiponectin treatment (10 microg/ml) inhibited the proliferation of MCF-7 cells, whereas leptin (1 microg/ml) stimulated the growth of cancer cells. In addition, adiponectin inhibited leptin-induced cell proliferation (both 1 microg/ml). Using microarray analysis, we found that adiponectin reduced the mRNA levels of genes involved in cell cycle regulation (mitogen-activated protein kinase 3 and ATM), apoptosis (BAG1, BAG3, and TP53), and potential diagnosis/prognosis markers (ACADS, CYP19A1, DEGS1, and EVL), whereas leptin induced progesterone receptor mRNA expression. In conclusion, the current study indicates an interaction of leptin- and adiponectin-signaling pathways in MCF-7 cancer cells whose proliferation is stimulated by leptin and suppressed by adiponectin.

Leptin and leptin receptor involvement in cancer development: a study on human primary breast carcinoma

Obesity is associated with an increased risk of breast cancer. Leptin, a hormone synthesised essentially by adipose tissue, may be involved in cancer development. We examined the expression of leptin and leptin receptor (Ob-R) in human primary breast cancer and adjacent non-cancerous tissue. We also analysed their relationships with histological variables such as the oestrogen and progesterone receptors, Ki67 proliferation factor and tumour size. The expressions of leptin and Ob-R were investigated by immunohistochemical staining in 35 primary breast cancers and 17 adjacent non-cancerous tissues. Samples and histological features were obtained from the Anti-Cancer Centre. Expressions of leptin and Ob-R were detected in, respectively, 85 and 75% of the primary breast cancer cases studied. The expression of leptin was significantly correlated with Ob-R detection (p=0.008). In addition, Ob-R expression in primary breast carcinoma was positively correlated with oestrogen receptor expression (p=0.028) and tumour size (p=0.045) but not with Ki67 or progesterone receptor expressions. However, the expression of leptin showed no statistical correlation with these variables. First, the co-expression of leptin and Ob-R in primary breast cancer shows that leptin acts on mammary tumour cells via an autocrine pathway. Second, the co-expression of Ob-R and oestrogen receptors suggests a possible interaction between leptin and oestrogen systems to promote breast carcinogenesis. Finally, the fact that Ob-R expression was positively correlated with tumour size may point to a potential role of leptin as a growth factor and of Ob-R as a new prognostic factor.