Mesenchymal stem cells in the colorectal tumor microenvironment: recent progress and implications

Mesenchymal stem cells (MSCs) are nonhematopoietic multipotent adult stem cells. They have been shown to have a natural tropism for many tumors types, including colorectal, and are capable of escaping host immune surveillance. MSCs are known to engraft at tumors and integrate into their architecture, potentially as carcinoma-associated fibroblasts. In contrast with other malignancies, our understanding of the interactions between colorectal cancer cells and MSCs remains limited. Considering the established importance of inflammation in the colorectal cancer primary tumor microenvironment and the role of stromal cells in this process, there is a potential wealth of information to be gleaned from further investigation of interactions between these cell populations. Epithelial-mesenchymal transition is central to colorectal cancer progression and MSCs have also been implicated in this process. This review explores the current knowledge (both in vitro and in vivo) of interactions between colorectal cancer cells and MSCs. It highlights potential effects of cell source, number and ratio on outcome of in vivo studies and explores strategies to more accurately explore their role in the primary tumor microenvironment. As our understanding of the underlying molecular processes in colorectal cancer develops, elucidation of these interactions will be central to development of novel therapeutic strategies for this prevalent disease.     

Co-culturing human prostate carcinoma cells with hepatocytes leads to increased expression of E-cadherin

Metastasis is a multi-step process wherein tumour cells detach from the primary mass, migrate through barrier matrices, gain access to conduits to disseminate, and subsequently survive and proliferate in an ectopic site. During the initial invasion stage, prostate carcinoma cells undergo epithelial-mesenchymal-like transition with gain of autocrine signalling and loss of E-cadherin, hallmarks that appear to enable invasion and dissemination. However, some metastases express E-cadherin, and we found close connections between prostate carcinoma cells and hepatocytes in a liver microtissue bioreactor. We hypothesise that phenotypic plasticity occurs late in prostate cancer progression at the site of ectopic seeding. Immunofluorescence staining for E-cadherin in co-cultures of hepatocytes and DU-145 prostate cancer cells revealed E-cadherin upregulation at peripheral sites of contact by day 2 of co-culture; E-cadherin expression also increased in PC-3 cells in co-culture. These carcinoma cells bound to hepatocytes in an E-cadherin-dependent manner. Although the signals by which the hepatocytes elicited E-cadherin expression remain undetermined, it appeared related to downregulation of epidermal growth factor receptor (EGFR) signalling. Inhibition of autocrine EGFR signalling increased E-cadherin expression and cell-cell heterotypic adhesion; further, expression of a downregulation-resistant EGFR variant prevented E-cadherin upregulation. These findings were supported by finding E-cadherin and catenins but not activated EGFR in human prostate metastases to the liver. We conclude that the term epithelial-mesenchymal transition only summarises the transient downregulation of E-cadherin for invasion with re-expression of E-cadherin being a physiological consequence of metastatic seeding.     

大肠癌细胞HCT-15肿瘤干细胞样细胞分离及成瘤性比较

目的:依据人大肠癌细胞HCT-15的表面标志物,分离其中的干细胞亚群。建立裸鼠体内原代大肠癌荷瘤模型,比较各亚群肿瘤体积和质量。方法:利用免疫磁珠分选技术,分离其中CD133/CD44干细胞亚群。分选得到CD133+CD44+、CD133+CD44-亚群分别接种于裸鼠体内,并观察肿瘤大小和质量。结果:CD133+CD44+和CD133+CD44-细胞亚群成功的从HCT-15细胞中分离出来。接种CD133+CD44+细胞的裸鼠形成的肿瘤体积［（2.76±0.22）cm3］和质量［（5.2±0.21）g］明显高于接种CD133+CD44-细胞裸鼠的肿瘤体积与质量［（1.56±0.34）cm3,（3.4±0.18）g］（P＜0.05）。结论:CD44阳性的大肠癌肿瘤干细胞成瘤能力明显高于CD44阴性的大肠癌肿瘤干细胞。     

MicroRNA expression profiling identifies miR-328 regulates cancer stem cell-like SP cells in colorectal cancer

Background:

Side population (SP) cells and their relationship to stem cell-like properties have been insufficiently studied in colorectal cancer (CRC). MicroRNAs (miRNAs) have attracted much attention but their roles in the maintenance of SP phenotype remain unclear.

Methods:

The SPs from CRC cell lines and primary cell cultures were analysed for stem cell-like properties. MiRNA microarray analysis identified miR-328 as a potential stemness miRNA of SP phenotype. The level of miR-328 expression in clinical samples and its correlation with SP fraction were determined. Gain-of-function and loss-of-function studies were performed to examine its roles in cancer stem-like SP cells. Furthermore, bioinformatics prediction and experimental validation were used to identify miR-328 target genes.

Results:

The SP cells sorted from CRC possess cancer stem cell (CSC)-like properties, including self-renewal, differentiation, resistance to chemotherapy, invasive and strong tumour formation ability. MiR-328 expression was significantly reduced in SP cells compared with Non-SP cells (P<0.05). Moreover, miR-328 expression was downregulated in CRC (n=33, P<0.05) and low miR-328 expression tend to correlate with high SP fraction (n=15, r=0.6559, P<0.05, Pearson''s correlation). Functional studies indicated that miR-328 expression affects the number of SP cells. In addition, miR-328 overexpression reversed drug resistance and inhibited cell invasion of SP cells. Furthermore, luciferase reporter assay demonstrated that miR-328 directly targets ABCG2 and MMP16 and affects the levels of mRNA and protein expression in SP cells.

Conclusion:

These findings indicate that CRC contain cancer stem-like SP cells. MiR-328 has an important role in maintaining cancer stem-like SP phenotype that may be a potential target for effective CRC therapy.     

Tumour-suppressive function of SIRT4 in human colorectal cancer

Background:

SIRT4, which is localised in the mitochondria, is one of the least characterised members of the sirtuin family of nicotinamide adenine dinucleotide-dependent enzymes that play key roles in multiple cellular processes such as metabolism, stress response and longevity. There are only a few studies that have characterised its function and assessed its clinical significance in human cancers.

Methods:

We established colorectal cancer cell lines (SW480, HCT116, and HT29) overexpressing SIRT4 and investigated their effects on proliferation, migration and invasion, as well as E-cadherin expression, that negatively regulates tumour invasion and metastases. The associations between SIRT4 expression in colorectal cancer specimens and clinicopathological features including prognosis were assessed by immunohistochemistry.

Results:

SIRT4 upregulated E-cadherin expression and suppressed proliferation, migration and invasion through inhibition of glutamine metabolism in colorectal cancer cells. Moreover, SIRT4 expression in colorectal cancer decreased with the progression of invasion and metastasis, and a low expression level of SIRT4 was correlated with a worse prognosis.

Conclusions:

SIRT4 has a tumour-suppressive function and may serve as a novel therapeutic target in colorectal cancer.     

脂肪间充质干细胞分泌的Exosome促进结肠癌细胞系上皮间质转化

目的：研究间充质干细胞（mesenchymal stem cell,MSC）来源的Exosome对结肠癌细胞系HCT8上皮间质转化（epithelial mesenchymal transition,EMT）的影响。方法从人脂肪组织中分离出MSC后,对MSC进行培养并传代,并对MSC的分化能力进行鉴定。在人脂肪来源的MSC中提取Exosome后,用透射电子显微镜观察并拍照,并用蛋白质印迹法检测其抗原表达情况。在HCT8培养体系中加入人脂肪来源的MSC分泌的Exosome ,定量PCR和蛋白质印迹法检测上皮和间质转化相关标志物的表达,细胞侵袭和迁移实验检测人脂肪来源的MSC分泌的Exosome对HCT8迁移和侵袭的影响。结果人脂肪来源的MSC具有多系分化能力,人脂肪来源的Exosome直径为40～100 nm ,表达CD63、HSP70和HSP90,下调HCT8上皮相关标志E-cadherin和ZO-1的表达,上调间质相关标志Fibronectin的表达,促进HCT8的迁移和侵袭。结论人脂肪来源的MSC分泌的Exosome可促进结肠癌细胞系HCT8的EMT。     

Cell cycle heterogeneity and plasticity of colorectal cancer stem cells

Cancer stem cells (CSCs) are a long-lived and self-renewing cancer cell population that drives tumor propagation and maintains cancer heterogeneity. They are also implicated in the therapeutic resistance of various types of cancer. Recent studies of CSCs in colorectal cancer (CRC) have uncovered fundamental paradigms that have increased understanding of CSC systems in solid tumors. Colorectal CSCs share multiple biological properties with normal intestinal stem cells (ISCs), including expression of the stem cell marker Lgr5. New evidence suggests that colorectal CSCs manifest substantial heterogeneity, as exemplified by the existence of both actively cycling Lgr5⁺ CSCs as well as quiescent Lgr5⁺ CSCs that are resistant to conventional anticancer therapies. The classical view of a rigid cell hierarchy and irreversible cell differentiation trajectory in normal and neoplastic tissues is now challenged by the finding that differentiated cells have the capacity to revert to stem cells through dynamic physiological reprogramming events. Such plasticity of CSC systems likely underlies both carcinogenesis and therapeutic resistance in CRC. Further characterization of the mechanisms underpinning the heterogeneity and plasticity of CSCs should inform future development of eradicative therapeutic strategies for CRC.     

Bone marrow-derived mesenchymal stem cell-secreted IL-8 promotes the angiogenesis and growth of colorectal cancer

Mesenchymal stem cells (MSCs) have recently been shown to home to tumors and contribute to the formation of the tumor-associated stroma. In addition, MSCs can secrete paracrine factors to facilitate tumor progression. However, the involvement of MSC-derived cytokines in colorectal cancer (CRC) angiogenesis and growth has not been clearly addressed. In this study, we report that interleukin-8 (IL-8) was the most highly upregulated pro-angiogenic factor in MSCs co-cultured with CRC cells and was expressed at substantially higher levels in MSCs than CRC cells. To evaluate the effect of MSC-derived IL-8 on CRC angiogenesis and growth, we used MSCs that expressed small hairpin (interfering) RNAs (shRNA) targeting IL-8 (shIL-8-MSCs). We found that MSC-secreted IL-8 promoted human umbilical vein endothelial cell (HUVEC) proliferation and migration, tube-formation ability and CRC cell proliferation. Additionally, in vivo studies showed that MSCs promoted tumor angiogenesis partially through IL-8. Taken together, these findings suggest that IL-8 secreted by MSCs promotes CRC angiogenesis and growth and can therefore serve as a potential novel therapeutic target.     

Ciprofloxacin induces apoptosis and inhibits proliferation of human colorectal carcinoma cells

Efficacy of chemotherapy in advanced stages of colorectal tumours is limited. The quinolone antibiotic ciprofloxacin was recently shown to inhibit growth and to induce apoptosis in human bladder carcinomas cells. We investigated the effect of ciprofloxacin on colon carcinoma lines in vitro. CC-531, SW-403 and HT-29 colon carcinoma and HepG2 hepatoma cells (control cells) were exposed to ciprofloxacin. Proliferation was assessed by bromodeoxyuridine-incorporation into DNA and apoptosis was measured by flow cytometry after propidium iodide or JC-1 staining. Expression of anti-apoptotic Bcl-2 and pro-apoptotic Bax was analyzed by semiquantitative Western blot analysis and activity of caspases 3, 8 and 9 by substrate-cleavage assays. Ciprofloxacin suppressed DNA synthesis of all colon carcinoma cells time- and dose-dependently, whereas the hepatoma cells remained unaffected. Apoptosis reached its maximum between 200 and 500 microg ml(-1). This was accompanied by an upregulation of Bax and of the activity of caspases 3, 8 and 9, and paralleled by a decrease of the mitochondrial membrane potential. Ciprofloxacin decreases proliferation and induces apoptosis of colon carcinoma cells, possibly in part by blocking mitochondrial DNA synthesis. Therefore, qualification of ciprofloxacin as adjunctive agent for colorectal cancer should be evaluated.     

CD44s signals the acquisition of the mesenchymal phenotype required for anchorage-independent cell survival in hepatocellular carcinoma

Background:

Circulating tumour cells (CTCs) have an important role in metastatic processes, but details of their basic characteristics remain elusive. We hypothesised that CD44-expressing CTCs show a mesenchymal phenotype and high potential for survival in hepatocellular carcinoma (HCC).

Methods:

Circulating CD44⁺CD90⁺ cells, previously shown to be tumour-initiating cells, were sorted from human blood and their genetic characteristics were compared with those of tumour cells from primary tissues. The mechanism underlying the high survival potential of CD44-expressing cells in the circulatory system was investigated in vitro.

Results:

CD44⁺CD90⁺ cells in the blood acquired epithelial–mesenchymal transition, and CD44 expression remarkably increased from the tissue to the blood. In Li7 and HLE cells, the CD44^high population showed higher anoikis resistance and sphere-forming ability than did the CD44^low population. This difference was found to be attributed to the upregulation of Twist1 and Akt signal in the CD44^high population. Twist1 knockdown showed remarkable reduction in anoikis resistance, sphere formation, and Akt signal in HLE cells. In addition, mesenchymal markers and CD44s expression were downregulated in the Twist1 knockdown.

Conclusions:

CD44s symbolises the acquisition of a mesenchymal phenotype regulating anchorage-independent capacity. CD44s-expressing tumour cells in peripheral blood are clinically important therapeutic targets in HCC.     

Lenti-TK介导间充质干细胞对鼻咽癌CD133+干细胞的靶向迁移及杀伤作用

目的： 观察慢病毒-胸苷激酶（lentivirus-thymidine kinase,Lenti-TK)/间充质干细胞(mesenchymal stem cell,MSC）对鼻咽癌CD133+干细胞的靶向迁移及杀伤作用。 方法： 构建包含TK基因的重组慢病毒表达载体Lenti-TK,感染MSC后得到Lenti-TK-MSC,RT-PCR及Western blotting检测Lenti-TK-MSC中HA-TK的表达。免疫磁珠法从鼻咽癌5-8F细胞中分选CD133+细胞;Transwell小室迁移实验检测Lenti-TK-MSC对CD133+5-8F细胞的趋向性;Lenti-TK-MSC联合更昔洛韦（ganciclovir,Lenti-TK-MSC/GCV）与CD133+5-8F细胞共培养,CCK-8试剂盒检测其对细胞的杀伤作用和旁观者效应。 结果： 成功构建重组慢病毒载体Lenti-TK,其滴度为1×108UT/ml,Lenti-TK（MOI=50）感染MSC 72 h时,感染效率达（95.1±01）%。Lenti-TK-MSC迁移至CD133+5-8F细胞组的细胞数明显多于CD133-5-8F细胞组、未分选5-8F细胞组\[（83.0±8.7） vs （29.6±53）、（38.3±5.2）,P=0.000\]。Lenti-TK-MSC/GCV处理组与单独GCV处理组、Lenti-TK-MSC/GCV条件培养液（即Lenti-TK-MSC加入1 mg/L GCV培养48 h的培养上清）处理组相比,CD133+5-8F细胞的存活率明显降低\[（37.2±2.3）% vs （98.5±3.1）%、（83.8±34）%,P=0.000\]。Lenti-TK-MSC数量达到混合细胞总数（Lenti-TK-MSC和CD133+5-8F细胞)的20%时,CD133+5-8F细胞存活率为（68.2±2.3）%,表现出明显的旁观者杀伤效应。 结论： Lenti-TK感染后MSC对鼻咽癌CD133+5-8F细胞具有靶向迁移及杀伤作用。     

The requirement for freshly isolated human colorectal cancer (CRC) cells in isolating CRC stem cells

Background:

Isolation of colorectal cancer (CRC) cell populations enriched for cancer stem cells (CSCs) may facilitate target identification. There is no consensus regarding the best methods for isolating CRC stem cells (CRC-SCs). We determined the suitability of various cellular models and various stem cell markers for the isolation of CRC-SCs.

Methods:

Established human CRC cell lines, established CRC cell lines passaged through mice, patient-derived xenograft (PDX)-derived cells, early passage/newly established cell lines, and cells directly from clinical specimens were studied. Cells were FAC-sorted for the CRC-SC markers CD44, CD133, and aldehyde dehydrogenase (ALDH). Sphere formation and in vivo tumorigenicity studies were used to validate CRC-SC enrichment.

Results:

None of the markers studied in established cell lines, grown either in vitro or in vivo, consistently enriched for CRC-SCs. In the three other cellular models, CD44 and CD133 did not reliably enrich for stemness. In contrast, freshly isolated PDX-derived cells or early passage/newly established CRC cell lines with high ALDH activity formed spheres in vitro and enhanced tumorigenicity in vivo, whereas cells with low ALDH activity did not.

Conclusions:

PDX-derived cells, early passages/newly established CRC cell lines and cells from clinical specimen with high ALDH activity can be used to identify CRC-SC-enriched populations. Established CRC cell lines should not be used to isolate CSCs.     

Epstein-Barr Virus latent membrane protein 1 induces Snail and epithelial-mesenchymal transition in metastatic nasopharyngeal carcinoma

Background:

Epstein-Barr Virus (EBV)-associated nasopharyngeal carcinoma (NPC) is distinctive among head-and-neck cancers in its undifferentiated histopathology and highly metastatic character. We have recently investigated the involvement of epithelial–mesenchymal transition (EMT) in NPC. In a previous study, we found a close association of expression of LMP1, the principal EBV oncoprotein, with expression of Twist and induction of EMT.

Methods:

We analysed expression of Snail in 41 NPC tissues by immunohistochemistry. The role of Twist as well as Snail in EMT of NPC was investigated by using NP69SV40T human nasopharyngeal cells.

Results:

In NPC tissues, overexpression of Snail is associated with expression of LMP1 in carcinomatous cells. In addition, expression of Snail positively correlated with metastasis and independently correlated inversely with expression of E-cadherin. Expression of Twist had no association with expression of E-cadherin. Further, in a human nasopharyngeal cell line, LMP1 induces EMT and its associated cellular motility and invasiveness. Expression of Snail is induced by LMP1 in these cells, and small hairpin RNA (shRNA) to Snail reversed the cellular changes. By contrast, Twist did not produce EMT in these nasopharyngeal cells.

Conclusions:

This study strengthens the association of EMT with the metastatic behaviour of NPC. These results suggest that induction of Snail by the EBV oncoprotein LMP1 has a pivotal role in EMT in NPC.     

Oxidized high mobility group B‐1 enhances metastability of colorectal cancer via modification of mesenchymal stem/stromal cells

High mobility group box‐1 (HMGB1) is known to be a chemotactic factor for mesenchymal stem/stromal cells (MSCs), but the effect of post‐translational modification on its function is not clear. In this study, we hypothesized that differences in the oxidation state of HMGB1 would lead to differences in the function of MSCs in cancer. In human colorectal cancer, MSCs infiltrating into the stroma were correlated with liver metastasis and serum HMGB1. In animal models, oxidized HMGB1 mobilized three‐fold fewer MSCs to subcutaneous tumors compared with reduced HMGB1. Reduced HMGB1 inhibited the proliferation of mouse bone marrow MSCs (BM‐MSCs) and induced differentiation into osteoblasts and vascular pericytes, whereas oxidized HMGB1 promoted proliferation and increased stemness, and no differentiation was observed. When BM‐MSCs pretreated with oxidized HMGB1 were co‐cultured with syngeneic cancer cells, cell proliferation and stemness of cancer cells were increased, and tumorigenesis and drug resistance were promoted. In contrast, co‐culture with reduced HMGB1‐pretreated BM‐MSCs did not enhance stemness. In an animal orthotopic transplantation colorectal cancer model, oxidized HMGB1, but not reduced HMGB1, promoted liver metastasis with intratumoral MSC chemotaxis. Therefore, oxidized HMGB1 reprograms MSCs and promotes cancer malignancy. The oxidized HMGB1–MSC axis may be an important target for cancer therapy.     

结直肠癌干细胞及靶向治疗研究进展

肿瘤干细胞是一类未分化的原始肿瘤细胞,是肿瘤转移,复发和耐药的根源。研究结直肠癌干细胞及标志物对于寻求针对肿瘤干细胞的治疗措施将是肿瘤治疗研究的新方向,针对性的靶向治疗将成为肿瘤治疗的研究热点。     

CD133-positive tumor cell content is a predictor of early recurrence in colorectal cancer

Background

The aims of this study were to demonstrate the tumorigenicity of CD133+ colon cancer cells in vitro, analyze the correlations between spheroid formation and clinicopathologic variables, and screen for overexpressed genes in CD133+ colon cancer stem cells. Moreover, the aim of this study was to establish a living tumor tissue bank using surgically resected specimens.

Methods

Using LoVo cell line, we isolated CD133+ cells and performed clonogenic assay and animal experiment to test tumorigenicity of CD133+ cells. Twenty-nine surgical samples were freshly collected from 27 patients who received curative or palliative surgery, and the samples were mechanically and enzymatically dissociated into single cells.

Results

We confirmed the enhanced tumorigenicity of CD133+ cells isolated from LoVo cell line both in vitro and in vivo. Of these 29 samples, 8 (28%) contained >3% CD133+ cells. Sphere formation was significantly higher in samples from patients with lymphatic invasion than in those without lymphatic invasion [54.5% (6/11) vs. 12.5% (2/16); P=0.033] and in samples containing >3% of CD133+ cells than in those containing ≤3% of CD133+ cells [36.4% (4/11) vs. 0% (0/16); P=0.019].

Conclusions

These findings indicate that CD133 is a valid marker for identifying cancer stem cells from fresh surgically resected colorectal cancer tissues. Furthermore, we successfully established a living tumor tissue bank using surgically resected colorectal tissues with a viability of >70%.     

Breast tumour cell-induced down-regulation of type I collagen mRNA in fibroblasts

This study investigated the modulation of type I collagen gene expression in normal fibroblasts by breast tumour cells. Northern analysis of total RNA extracted from stages I, II and III breast tumour tissue revealed that collagen mRNA levels were elevated in stage I tumours compared to the adjacent normal breast tissues, whereas they were decreased in stages II and III breast tumours. This aberrant collagen gene expression was confirmed by non-radioactive RNA:RNA in situ hybridization analysis of 30 breast carcinomas which localized the production of type I collagen mRNA to the stromal fibroblasts within the vicinity of the tumour cells. In order to determine whether the tumour cells were directly responsible for this altered collagen production by the adjacent fibroblasts, breast tumour cell lines were co-cultured with normal fibroblasts for in vitro assessment of collagen and steady-state collagen RNA levels. Co-culture of tumour cells and normal fibroblasts in the same dish resulted in down-regulation of collagen mRNA and protein. Treatment of the fibroblasts with tumour-cell conditioned medium also resulted in decreased collagen protein levels but the mRNA levels, however, remained unaltered. These results suggested that the tumour cells either secrete a labile 'factor', or express a cell surface protein requiring direct contact with the fibroblasts, resulting in down-regulation of collagen gene expression. Modulation of the ECM is a common characteristic of invading tumour cells and usually involves increased production of collagenases by the tumour cells or stromal fibroblasts. This study showed that tumour cells were also able to modulate collagen mRNA production by stromal fibroblasts, which may facilitate tumour cell invasion and metastasis.