Quiescent stem cells in intestinal homeostasis and cancer

Abstract

Adult stem cell niches are characterized by a dichotomy of cycling and quiescent stem cells: while the former are responsible for tissue turnover, their quiescent counterparts are thought to become active upon tissue injury thus underlying the regenerative response. Moreover, quiescence prevents adult stem cells from accumulating mutations thus ensuring a reservoir of unaltered stem cells. In the intestine, while cycling stem cells were shown to give rise to the main differentiated lineages, the identity of their quiescent equivalents remains to date elusive. This is of relevance for conditions such as Crohn's disease and ulcerative colitis where quiescent stem cells may underlie metaplasia and the increased cancer risk associated with chronic inflammation. Tumours are thought to share a comparable hierarchical structure of adult tissues with pluripotent and self-renewing cancer stem cells (CSCs) giving rise to more differentiated cellular types. As such, neoplastic lesions may encompass both cycling and quiescent CSCs. Because of their infrequent cycling, quiescent CSCs are refractory to chemo- and radiotherapy and are likely to play a role in tumour dissemination, dormancy and recurrence.     

Metformin protects against intestinal barrier dysfunction via AMPKα1‐dependent inhibition of JNK signalling activation

Disruption of the intestinal epithelial barrier, that involves the activation of C‐Jun N‐terminal kinase (JNK), contributes to initiate and accelerate inflammation in inflammatory bowel disease. Metformin has unexpected beneficial effects other than glucose‐lowering effects. Here, we provided evidence that metformin can protect against intestinal barrier dysfunction in colitis. We showed that metformin alleviated dextran sodium sulphate (DSS)‐induced decreases in transepithelial electrical resistance, FITC‐dextran hyperpermeability, loss of the tight junction (TJ) proteins occludin and ZO‐1 and bacterial translocation in Caco‐2 cell monolayers or in colitis mice models. Metformin also improved TJ proteins expression in ulcerative colitis patients with type 2 diabetes mellitus. We found that metformin ameliorated the induction of colitis and reduced the levels of pro‐inflammatory cytokines IL‐6, TNF‐a and IL‐1β. In addition, metformin suppressed DSS‐induced JNK activation, an effect dependent on AMP‐activated protein kinase α1 (AMPKα1) activation. Consistent with this finding, metformin could not maintain the barrier function of AMPKα1‐silenced cell monolayers after DSS administration. These findings highlight metformin protects against intestinal barrier dysfunction. The potential mechanism may involve in the inhibition of JNK activation via an AMPKα1‐dependent signalling pathway.     

Lymphatics and fibroblasts support intestinal stem cells in homeostasis and injury

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Innate immune signalling at the intestinal epithelium in homeostasis and disease

The intestinal epithelium-which constitutes the interface between the enteric microbiota and host tissues-actively contributes to the maintenance of mucosal homeostasis and defends against pathogenic microbes. The recognition of conserved microbial products by cytosolic or transmembrane pattern recognition receptors in epithelial cells initiates signal transduction and influences effector cell function. However, the signalling pathways, effector molecules and regulatory mechanisms involved are not yet fully understood, and the functional outcome is poorly defined. This review analyses the complex and dynamic role of intestinal epithelial innate immune recognition and signalling, on the basis of results in intestinal epithelial cell-specific transgene or gene-deficient animals. This approach identifies specific epithelial cell functions within the diverse cellular composition of the mucosal tissue, in the presence of the complex and dynamic gut microbiota. These insights have thus provided a more comprehensive understanding of the role of the intestinal epithelium in innate immunity during homeostasis and disease.     

Selective inhibitors for JNK signalling: a potential targeted therapy in cancer

Abstract

c-Jun N-terminal kinase (JNK) signalling regulates both cancer cell apoptosis and survival. Emerging evidence show that JNK promoted tumour progression is involved in various cancers, that include human pancreatic-, lung-, and breast cancer. The pro-survival JNK oncoprotein functions in a cell context- and cell type-specific manner to affect signal pathways that modulate tumour initiation, proliferation, and migration. JNK is therefore considered a potential oncogenic target for cancer therapy. Currently, designing effective and specific JNK inhibitors is an active area in the cancer treatment. Some ATP-competitive inhibitors of JNK, such as SP600125 and AS601245, are widely used in vitro; however, this type of inhibitor lacks specificity as they indiscriminately inhibit phosphorylation of all JNK substrates. Moreover, JNK has at least three isoforms with different functions in cancer development and identifying specific selective inhibitors is crucial for the development of targeted therapy in cancer. Some selective inhibitors of JNK are identified; however, their clinical studies in cancer are relatively less conducted. In this review, we first summarised the function of JNK signalling in cancer progression; there is a focus on the discussion of the novel selective JNK inhibitors as potential targeting therapy in cancer. Finally, we have offered a future perspective of the selective JNK inhibitors in the context of cancer therapies. We hope this review will help to further understand the role of JNK in cancer progression and provide insight into the design of novel selective JNK inhibitors in cancer treatment.     

Human umbilical cord mesenchymal stem cells suppress breast cancer tumourigenesis through direct cell-cell contact and internalization

The purpose of this study was to investigate how human umbilical cord mesenchymal stem cells (HUMSCs) affect breast cancer tumourigenesis. To observe the influence of HUMSCs on tumourigenesis in vitro, we performed a co-culture of MDA MB-231 breast cancer cells with HUMSCs, and a result of HUMSCs on tumourigenesis in vivo was achieved by injection of HUMSCs into nonobese diabetic/severe combined immunodeficient mice following tumour establishment with MDA-MB231. During the co-culture, apoptosis of MDA-MB231 was noted, which was driven either by binding with HUMSC through direct cell-cell contact or by formation of a novel cell-in-cell phenomenon after internalization of HUMSC. Also, treatment with HUMSC injection was efficacious in both in situ and metastatic breast cancers in the animal models. Since HUMSCs were proved to efficaciously suppress breast cancer tumourigenesis both in vitro and in vivo, it is our expectation that treatment with HUMSCs can be a viable therapy for breast cancer in the near future. In addition, we share a new point of view on the role of HUMSCs in foetal development during pregnancy.     

A JNK inhibitor SP600125 induces defective cytokinesis and enlargement in P19 embryonal carcinoma cells

While analyzing the role of c‐Jun NH₂‐terminal kinase (JNK) in neurogenesis in P19 embryonal carcinoma cells, we noticed that treatment with SP600125, a JNK inhibitor, increased the cell size markedly. SP600125‐induced enlargement of P19 cells was time‐ and dose‐dependent. The increased cell size in response to SP600125 was also detected in B6mt‐1 embryonic stem cells. SP600125 treatment inhibited cell growth and increased DNA contents, indicating the inhibition of cell proliferation resulting from endoreduplication. Concurrently, the gene expression of p21, a regulator of G2/M arrest as well as G1 arrest, was increased in cells treated with SP600125. The increased cell size in response to SP600125 was detected even in P19 cells treated with colcemide, an inhibitor of cell cycle progression at the metaphase. The present study suggests that treatment with SP600125 progresses the cell cycle, skipping cytokinesis in P19 cells. Copyright © 2009 John Wiley & Sons, Ltd.     

Hippo pathway in intestinal homeostasis and tumorigenesis

The Hippo pathway plays a crucial role in controlling organ size by inhibiting cell proliferation and promoting cell death. Recent findings implicate that this pathway is involved in the process of intestinal regeneration and tumorigenesis. Here we summarize current studies for the function of the Hippo signaling pathway in intestinal homeostasis, regeneration and tumorigenesis, and the crosstalk between the Hippo signaling pathway and other major signaling pathways, i.e. Wnt, Notch and Jak/Stat signaling pathways in intestinal compartment.     

ATG4B/autophagin-1 regulates intestinal homeostasis and protects mice from experimental colitis

The identification of inflammatory bowel disease (IBD) susceptibility genes by genome-wide association has linked this pathology to autophagy, a lysosomal degradation pathway that is crucial for cell and tissue homeostasis. Here, we describe autophagy-related 4B, cysteine peptidase/autophagin-1 (ATG4B) as an essential protein in the control of inflammatory response during experimental colitis. In this pathological condition, ATG4B protein levels increase in parallel with the induction of autophagy. Moreover, ATG4B expression is significantly reduced in affected areas of the colon from IBD patients. Consistently, atg4b^−/− mice present Paneth cell abnormalities, as well as an increased susceptibility to DSS-induced colitis. atg4b-deficient mice exhibit significant alterations in proinflammatory cytokines and mediators of the immune response to bacterial infections, which are reminiscent of those found in patients with Crohn disease or ulcerative colitis. Additionally, antibiotic treatments and bone marrow transplantation from wild-type mice reduced colitis in atg4b^−/− mice. Taken together, these results provided additional evidence for the importance of autophagy in intestinal pathologies and describe ATG4B as a novel protective protein in inflammatory colitis. Finally, we propose that atg4b-null mice are a suitable model for in vivo studies aimed at testing new therapeutic strategies for intestinal diseases associated with autophagy deficiency.     

Emerging roles of the FBW7 tumour suppressor in stem cell differentiation

FBW7 is a ubiquitin E3 ligase substrate adaptor that targets many important oncoproteins-such as Notch, c-Myc, cyclin E and c-Jun-for ubiquitin-dependent proteolysis. By doing so, it plays crucial roles in many cellular processes, including cell cycle progression, cell growth, cellular metabolism, differentiation and apoptosis. Loss of FBW7 has been observed in many types of human cancer, and its role as a tumour suppressor was confirmed by genetic ablation of FBW7 in mice, which leads to the induction of tumorigenesis. How FBW7 exerts its tumour suppression function, and whether loss of FBW7 leads to de-differentiation or acquisition of stemness-a process frequently seen in human carcinomas-remains unclear. Emerging evidence shows that FBW7 controls stem cell self-renewal, differentiation, survival and multipotency in various stem cells, including those of the haematopoietic and nervous systems, liver and intestine. Here, we focus on the function of FBW7 in stem cell differentiation, and its potential relevance to human disease and therapeutics.     

Berberine potently attenuates intestinal polyps growth in ApcMin mice and familial adenomatous polyposis patients through inhibition of Wnt signalling

As a traditional anti‐inflammatory Chinese herbal medicine, Alkaloid berberine has been recently reported to exhibit anti‐tumour effects against a wide spectrum of cancer. However, the mechanism was largely unknown. Gene chip array reveals that with berberine treatment, c‐Myc, the target gene of Wnt pathway, was down‐regulated 5.3‐folds, indicating that berberine might inhibit Wnt signalling. TOPflash analysis revealed that Wnt activity was significantly reduced after berberine treatment, and the mechanism of which might be that berberine disrupted β‐catenin transfer to nucleus through up‐regulating the expression of adenomatous polyposis coli (APC) gene and stabilized APC‐β‐catenin complex. Berberine administration in ApcMin/+ mice exhibited fewer and smaller polyps in intestine, along with reduction in cyclin D1 and c‐Myc expression. In clinical practice, oral administration of berberine also significantly reduced the familial adenomatous polyposis patients' polyp size along with the inhibition of cyclin D1 expression in polyp samples. These observations indicate that berberine inhibits colon tumour formation through inhibition of Wnt/β‐catenin signalling and berberine might be a promising drug for the prevention of colon cancer.     

Adult lung stem cells and their contribution to lung tumourigenesis

The isolation and characterization of lung stem and progenitor cells represent an important step towards the understanding of lung repair after injury, lung disease pathogenesis and the identification of the target cells of transformation in lung carcinogenesis. Different approaches using prospective isolation of progenitor cells by flow cytometry or lineage-tracing experiments in mouse models of lung injury have led to the identification of distinct progenitor subpopulations in different morphological regions of the adult lung. Genetically defined mouse models of lung cancer are offering new perspectives on the cells of origin of different subtypes of lung cancer. These mouse models pave the way to further investigate human lung progenitor cells at the origin of lung cancers, as well as to define the nature of the lung cancer stem cells. It will be critical to establish the link between oncogenic driver mutations recently discovered in lung cancers, target cells of transformation and subtypes of lung cancers to enable better stratification of patients for improved therapeutic strategies.     

Compound K protects MIN6N8 pancreatic β‐cells against palmitate‐induced apoptosis through modulating SAPK/JNK activation

Chronic elevation of NEFAs (non‐esterified fatty acids) due to insulin resistance and obesity has been shown to be associated with increased β‐cell apoptosis and with the aetiology of the reduced β‐cell mass of Type 2 diabetes. SAPK (stress‐activated protein kinase)/JNK (c‐Jun N‐terminal kinase) have been implicated in the control of apoptosis. C‐K [compound K; 20‐O‐β‐d ‐glucopyranosyl‐20(S)‐protopanaxadiol] is the main intestinal bacterial metabolite of protopanaxadiol ginsenosides. Currently, little is known about the effects of C‐K on β‐cells with the presence of NEFAs. The aim of the present study was to investigate the in vitro protective effect of C‐K on MIN6N8 mouse insulinoma β‐cells against NEFA‐induced apoptosis, as well as the modulating effect on SAPK/JNK activation. Our results have shown that C‐K inhibited the palmitate‐induced apoptosis through modulating SAPK/JNK activation. We conclude that C‐K protects against β‐cell death and that, by anti‐apoptotic activity, C‐K may contribute to the previously reported anti‐diabetic actions of ginseng.     

Role of c-Jun N-terminal kinase activation in blastema formation during planarian regeneration

The robust regenerative abilities of planarians absolutely depend on a unique population of pluripotent stem cells called neoblasts, which are the only mitotic somatic cells in adult planarians and are responsible for blastema formation after amputation. Little is known about the molecular mechanisms that drive blastema formation during planarian regeneration. Here we found that treatment with the c-Jun N-terminal kinase (JNK) inhibitor SP600125 blocked the entry of neoblasts into the M-phase of the cell cycle, while allowing neoblasts to successfully enter S-phase in the planarian Dugesia japonica. The rapid and efficient blockage of neoblast mitosis by treatment with the JNK inhibitor provided a method to assess whether temporally regulated cell cycle activation drives blastema formation during planarian regeneration. In the early phase of blastema formation, activated JNK was detected prominently in a mitotic region (the "postblastema") proximal to the blastema region. Furthermore, we demonstrated that undifferentiated mitotic neoblasts in the postblastema showed highly activated JNK at the single cell level. JNK inhibition by treatment with SP600125 during this period caused a severe defect of blastema formation, which accorded with a drastic decrease of mitotic neoblasts in regenerating animals. By contrast, these animals still retained many undifferentiated neoblasts near the amputation stump. These findings suggest that JNK signaling plays a crucial role in feeding into the blastema neoblasts for differentiation by regulating the G2/M transition in the cell cycle during planarian regeneration.     

结肠癌中NGX6抑制EGFR/K-ras/JNK/c-Jun/cyclin D1信号通路的研究

候选抑瘤基因NGX6具有抑制结肠癌增殖和转移的作用,研究表明其为表皮生长因子受体(epidermal growth factor receptor, EGFR)的负性调控因子,并可下调JNK通路中重要分子MADD (MAP-kinase activating death domain)的表达,其抑瘤机制是否与抑制EGFR介导的JNK信号通路的活性有关?在已建立的转染NGX6的细胞模型基础上,借助蛋白质印迹(Western blot)和免疫组化方法在细胞和组织水平检测NGX6转染前后EGFR/K-ras/JNK/c-Jun/cyclin D1信号通路中重要蛋白质的表达.结果表明,NGX6转染后结肠癌细胞HT-29在裸鼠体内成瘤明显受抑,差异有统计学意义.Western blot结果显示,在结肠癌细胞中NGX6可明显下调EGFR、K-ras、p-JNK、c-Jun和cyclin D1的表达;进一步采用Western blot和免疫组化法验证NGX6在体内对上述关键分子表达的影响,发现NGX6可抑制裸鼠移植瘤组织中EGFR、K-ras、p-JNK、c-Jun和cyclin D1的表达,与体外结果一致.上述研究表明,NGX6在结肠癌中主要通过抑制EGFR介导的JNK通路的活性而发挥其抑瘤作用,该研究为深入探讨NGX6的机制提供了重要的实验依据.