MicroRNA expression profile of colon cancer stem-like cells in HT29 adenocarcinoma cell line

Increasing evidence has suggested cancer stem cells (CSCs) are considered to be responsible for cancer formation, recurrence, and metastasis. Recently, many studies have also revealed that microRNAs (miRNAs) strongly implicate in regulating self renewal and tumorigenicity of CSCs in human cancers. However, with respect to colon cancer, the role of miRNAs in stemness maintenance and tumorigenicity of CSCs still remains to be unknown. In the present study, we isolated a population of colon CSCs expressing a CD133 surface phenotype from human HT29 colonic adenocarcinoma cell line by Flow Cytometry Cell Sorting. The CD133⁺ cells possess a greater tumor sphere-forming efficiency in vitro and higher tumorigenic potential in vivo. Furthermore, the CD133⁺ cells are endowed with stem/progenitor cells-like property including expression of “stemness” genes involved in Wnt2, BMI1, Oct3/4, Notch1, C-myc and other genes as well as self-renewal and differentiation capacity. Moreover, we investigated the miRNA expression profile of colon CSCs using miRNA array. Consequently, we identified a colon CSCs miRNA signature comprising 11 overexpressed and 8 underexpressed miRNAs, such as miR-429, miR-155, and miR-320d, some of which may be involved in regulation of stem cell differentiation. Our results suggest that miRNAs might play important roles in stemness maintenance of colon CSCs, and analysis of specific miRNA expression signatures may contribute to potential cancer therapy.     

Integrated analysis of miRNA and mRNA expression in childhood medulloblastoma compared with neural stem cells

Medulloblastoma (MB) is the most common malignant brain tumor in children and a leading cause of cancer-related mortality and morbidity. Several molecular sub-types of MB have been identified, suggesting they may arise from distinct cells of origin. Data from animal models indicate that some MB sub-types arise from multipotent cerebellar neural stem cells (NSCs). Hence, microRNA (miRNA) expression profiles of primary MB samples were compared to CD133+ NSCs, aiming to identify deregulated miRNAs involved in MB pathogenesis. Expression profiling of 662 miRNAs in primary MB specimens, MB cell lines, and human CD133+ NSCs and CD133- neural progenitor cells was performed by qRT-PCR. Clustering analysis identified two distinct sub-types of MB primary specimens, reminiscent of sub-types obtained from their mRNA profiles. 21 significantly up-regulated and 12 significantly down-regulated miRNAs were identified in MB primary specimens relative to CD133+ NSCs (p<0.01). The majority of up-regulated miRNAs mapped to chromosomal regions 14q32 and 17q. Integration of the predicted targets of deregulated miRNAs with mRNA expression data from the same specimens revealed enrichment of pathways regulating neuronal migration, nervous system development and cell proliferation. Transient over-expression of a down-regulated miRNA, miR-935, resulted in significant down-regulation of three of the seven predicted miR-935 target genes at the mRNA level in a MB cell line, confirming the validity of this approach. This study represents the first integrated analysis of MB miRNA and mRNA expression profiles and is the first to compare MB miRNA expression profiles to those of CD133+ NSCs. We identified several differentially expressed miRNAs that potentially target networks of genes and signaling pathways that may be involved in the transformation of normal NSCs to brain tumor stem cells. Based on this integrative approach, our data provide an important platform for future investigations aimed at characterizing the role of specific miRNAs in MB pathogenesis.     

miR-30 family promotes migratory and invasive abilities in CD133<Superscript>+</Superscript> pancreatic cancer stem-like cells

Pancreatic cancer is a deadly disease with a poor prognosis. Recently, miRNAs have been reported to be abnormally expressed in several cancers and play a role in cancer development and progression. However, the role of miRNA in cancer stem cells remains unclear. Therefore, our aim was to investigate the role of miRNA in the CD133⁺ pancreatic cancer cell line Capan-1M9 because CD133 is a putative marker of pancreatic cancer stem cells. Using miRNA microarray, we found that the expression level of the miR-30 family decreased in CD133 genetic knockdown shCD133 Capan-1M9 cells. We focused on miR-30a, -30b, and -30c in the miR-30 family and created pancreatic cancer cell sublines, each transfected with these miRNAs. High expression of miR-30a, -30b, or -30c had no effect on cell proliferation and sphere forming. In contrast, these sublines were resistant to gemcitabine, which is a standard anticancer drug for pancreatic cancer, and in addition, promoted migration and invasion. Moreover, mesenchymal markers were up-regulated by these miRNAs, suggesting that mesenchymal phenotype is associated with an increase in migration and invasion. Thus, our study demonstrated that high expression of the miR-30 family modulated by CD133 promotes migratory and invasive abilities in CD133⁺ pancreatic cancer cells. These findings suggest that targeted therapies to the miR-30 family contribute to the development of novel therapies for CD133⁺ pancreatic cancer stem cells.     

MicroRNA alterations and associated aberrant DNA methylation patterns across multiple sample types in oral squamous cell carcinoma

Background

MicroRNA (miRNA) expression is broadly altered in cancer, but few studies have investigated miRNA deregulation in oral squamous cell carcinoma (OSCC). Epigenetic mechanisms are involved in the regulation of >30 miRNA genes in a range of tissues, and we aimed to investigate this further in OSCC.

Methods

TaqMan® qRT-PCR arrays and individual assays were used to profile miRNA expression in a panel of 25 tumors with matched adjacent tissues from patients with OSCC, and 8 control paired oral stroma and epithelium from healthy volunteers. Associated DNA methylation changes of candidate epigenetically deregulated miRNA genes were measured in the same samples using the MassArray® mass spectrometry platform. MiRNA expression and DNA methylation changes were also investigated in FACS sorted CD44^high oral cancer stem cells from primary tumor samples (CSCs), and in oral rinse and saliva from 15 OSCC patients and 7 healthy volunteers.

Results

MiRNA expression patterns were consistent in healthy oral epithelium and stroma, but broadly altered in both tumor and adjacent tissue from OSCC patients. MiR-375 is repressed and miR-127 activated in OSCC, and we confirm previous reports of miR-137 hypermethylation in oral cancer. The miR-200 s/miR-205 were epigenetically activated in tumors vs normal tissues, but repressed in the absence of DNA hypermethylation specifically in CD44^high oral CSCs. Aberrant miR-375 and miR-200a expression and miR-200c-141 methylation could be detected in and distinguish OSCC patient oral rinse and saliva from healthy volunteers, suggesting a potential clinical application for OSCC specific miRNA signatures in oral fluids.

Conclusions

MiRNA expression and DNA methylation changes are a common event in OSCC, and we suggest miR-375, miR-127, miR-137, the miR-200 family and miR-205 as promising candidates for future investigations. Although overall activated in OSCC, miR-200/miR-205 suppression in oral CSCs indicate that cell specific silencing of these miRNAs may drive tumor expansion and progression.     

miR-1915 and miR-1225-5p Regulate the Expression of CD133, PAX2 and TLR2 in Adult Renal Progenitor Cells

Adult renal progenitor cells (ARPCs) were recently identified in the cortex of the renal parenchyma and it was demonstrated that they were positive for PAX2, CD133, CD24 and exhibited multipotent differentiation ability. Recent studies on stem cells indicated that microRNAs (miRNAs), a class of noncoding small RNAs that participate in the regulation of gene expression, may play a key role in stem cell self-renewal and differentiation. Distinct sets of miRNAs are specifically expressed in pluripotent stem cells but not in adult tissues, suggesting a role for miRNAs in stem cell self-renewal. We compared miRNA expression profiles of ARPCs with that of mesenchymal stem cells (MSCs) and renal proximal tubular cells (RPTECs) finding distinct sets of miRNAs that were specifically expressed in ARPCs. In particular, miR-1915 and miR-1225-5p regulated the expression of important markers of renal progenitors, such as CD133 and PAX2, and important genes involved in the repair mechanisms of ARPCs, such as TLR2. We demonstrated that the expression of both the renal stem cell markers CD133 and PAX2 depends on lower miR-1915 levels and that the increase of miR-1915 levels improved capacity of ARPCs to differentiate into adipocyte-like and epithelial-like cells. Finally, we found that the low levels of miR-1225-5p were responsible for high TLR2 expression in ARPCs. Therefore, together, miR-1915 and miR-1225-5p seem to regulate important traits of renal progenitors: the stemness and the repair capacity.     

Aberrant microRNAs expression in CD133+/CD326+ human lung adenocarcinoma initiating cells from A549

Increasing evidence demonstrates that miRNAs are involved in the dysregulation of tumor initiating cells (TICs) in various tumors. Due to a lack of definitive markers, cell sorting is not an ideal separation method for lung adenocarcinoma initiating cells. In this study, we combined paclitaxel with serum-free medium cultivation (inverse-induction) to enrich TICs from A549 cells, marked by CD133/CD326, defined features of stemness. We next investigated aberrant microRNAs in this subpopulation compared to normal cells with miRNA microarray and found that 50 miRNAs exhibited a greater than 2-fold change in expression. As further validation, 10 miRNAs were chosen to perform quantitative RT-PCR on the A549 cell line and primary samples. The results suggest that aberrant expression of miRNAs such as miR-29ab, miR-183, miR-17-5p and miR-127-3P may play an important role in regulating the bio-behavior of TICs.     

miR-26b regulates cell proliferation and apoptosis of CD117+CD44+ ovarian cancer stem cells by targeting PTEN

Ovarian cancer (OC) is the one of the most common cancer in women globally. However, it still represents the most dangerous gynecologic malignancy even with the advances in detection and therapeutics. Thus, there is an urgent need in finding more effective therapeutic options for OC patients including cancer stem cells (CSC). MicroRNAs (miRNAs) are small, endogenous, and non-coding RNAs that play critical roles in the progression of various types of tumor. Our aim of this study was to find the regulatory function of microRNA-26 (miRNA- 26b) on the cell proliferation and apoptosis of ovarian CSCs. Our studies show that miR-26b is under-regulated in human CD117⁺CD44⁺ ovarian CSCs. The miR-26b overexpression inhibits the cell proliferation and promotes cell apoptosis. Moreover, phosphatase and tensin homolog (PTEN) is found to be a functional target of miR-26b. Moreover, PTEN overexpression reversed the effects of miR-26b on cell proliferation and apoptosis. PTEN overexpression remarkably accelerated cell proliferation, and inhibited cell apoptosis. These results indicate that MiR-26b regulates cell proliferation and apoptosis of CD117⁺CD44⁺ ovarian CSCs by targeting PTEN.Key words: miR-26b, PTEN, ovarian cancer stem cells (CSCs), cell proliferation, apoptosis     

New emerging roles of CD133 in cancer stem cell: Signaling pathway and miRNA regulation

Cancer stem cells (CSC) are rare immortal cells within a tumor that are able to initiate tumor progression, development, and resistance. Advances studies show that, like normal stem cells, CSCs can be both self-renewed and given rise to many cell types, therefore form tumors. A number of cell surface markers, such as CD44, CD24, and CD133 are frequently used to identify CSCs. CD133, a transmembrane glycoprotein, either alone or in collaboration with other markers, has been mainly considered to identify CSCs from different solid tumors. However, the exactness of CD133 as a cancer stem cell biomarker has not been approved yet. The clinical importance of CD133 is as a CSC marker in many cancers. Also, it contributes to shorter survival, tumor progression, and tumor recurrence. The expression of CD133 is controlled by many extracellular or intracellular factors, such as tumor microenvironment, epigenetic factors, signaling pathways, and miRNAs. In this study, it was attempted to determine: 1) CD133 function; 2) the role of CD133 in cancer; 3) CD133 regulation; 4) the therapeutic role of CD133 in cancers.     

The microRNA miR-34a inhibits prostate cancer stem cells and metastasis by directly repressing CD44

Cancer stem cells (CSCs), or tumor-initiating cells, are involved in tumor progression and metastasis. MicroRNAs (miRNAs) regulate both normal stem cells and CSCs, and dysregulation of miRNAs has been implicated in tumorigenesis. CSCs in many tumors--including cancers of the breast, pancreas, head and neck, colon, small intestine, liver, stomach, bladder and ovary--have been identified using the adhesion molecule CD44, either individually or in combination with other marker(s). Prostate CSCs with enhanced clonogenic and tumor-initiating and metastatic capacities are enriched in the CD44(+) cell population, but whether miRNAs regulate CD44(+) prostate cancer cells and prostate cancer metastasis remains unclear. Here we show, through expression analysis, that miR-34a, a p53 target, was underexpressed in CD44(+) prostate cancer cells purified from xenograft and primary tumors. Enforced expression of miR-34a in bulk or purified CD44(+) prostate cancer cells inhibited clonogenic expansion, tumor regeneration, and metastasis. In contrast, expression of miR-34a antagomirs in CD44(-) prostate cancer cells promoted tumor development and metastasis. Systemically delivered miR-34a inhibited prostate cancer metastasis and extended survival of tumor-bearing mice. We identified and validated CD44 as a direct and functional target of miR-34a and found that CD44 knockdown phenocopied miR-34a overexpression in inhibiting prostate cancer regeneration and metastasis. Our study shows that miR-34a is a key negative regulator of CD44(+) prostate cancer cells and establishes a strong rationale for developing miR-34a as a novel therapeutic agent against prostate CSCs.     

Cancer stem cells

Cancer stem cells (CSCs) are a small subpopulation of cells within tumors with capabilities of self-renewal, differentiation, and tumorigenicity when transplanted into an animal host. A number of cell surface markers such as CD44, CD24, and CD133 are often used to identify and enrich CSCs. A regulatory network consisting of microRNAs and Wnt/β-catenin, Notch, and Hedgehog signaling pathways controls CSC properties. The clinical relevance of CSCs has been strengthened by emerging evidence, demonstrating that CSCs are resistant to conventional chemotherapy and radiation treatment and that CSCs are very likely to be the origin of cancer metastasis. CSCs are believed to be an important target for novel anti-cancer drug discovery. Herein we summarize the current understanding of CSCs, with a focus on the role of miRNA and epithelial–mesenchymal transition (EMT), and discuss the clinical application of targeting CSCs for cancer treatment.     

CD90 and CD110 correlate with cancer stem cell potentials in human T-acute lymphoblastic leukemia cells

Although cancer stem cells (CSCs) have been recently identified in myeloid leukemia, published data on lymphoid malignancy have been sparse. T-acute lymphoblastic leukemia (T-ALL) is characterized by the abnormal proliferation of T-cell precursors and is generally aggressive. As CD34 is the only positive-selection marker for CSCs in T-ALL, we performed extensive analysis of CD markers in T-ALL cell lines. We found that some of the tested lines consisted of heterogeneous populations of cells with various levels of surface marker expression. In particular, a small subpopulation of CD90 (Thy-1) and CD110 (c-Mpl) were shown to correlate with stem cell properties both in vitro and in transplantation experiments. As these markers are expressed on hematopoietic stem cells, our results suggest that stem cell-like population are enriched in CD90+/CD110+ fraction and they are useful positive-selection markers for the isolation of CSCs in some cases of T-ALL.     

Transient mTOR inhibition facilitates continuous growth of liver tumors by modulating the maintenance of CD133+ cell populations

The mammalian target of the rapamycin (mTOR) pathway, which drives cell proliferation, is frequently hyperactivated in a variety of malignancies. Therefore, the inhibition of the mTOR pathway has been considered as an appropriate approach for cancer therapy. In this study, we examined the roles of mTOR in the maintenance and differentiation of cancer stem-like cells (CSCs), the conversion of conventional cancer cells to CSCs and continuous tumor growth in vivo. In H-Ras-transformed mouse liver tumor cells, we found that pharmacological inhibition of mTOR with rapamycin greatly increased not only the CD133+ populations both in vitro and in vivo but also the expression of stem cell-like genes. Enhancing mTOR activity by over-expressing Rheb significantly decreased CD133 expression, whereas knockdown of the mTOR yielded an opposite effect. In addition, mTOR inhibition severely blocked the differentiation of CD133+ to CD133- liver tumor cells. Strikingly, single-cell culture experiments revealed that CD133- liver tumor cells were capable of converting to CD133+ cells and the inhibition of mTOR signaling substantially promoted this conversion. In serial implantation of tumor xenografts in nude BALB/c mice, the residual tumor cells that were exposed to rapamycin in vivo displayed higher CD133 expression and had increased secondary tumorigenicity compared with the control group. Moreover, rapamycin treatment also enhanced the level of stem cell-associated genes and CD133 expression in certain human liver tumor cell lines, such as Huh7, PLC/PRC/7 and Hep3B. The mTOR pathway is significantly involved in the generation and the differentiation of tumorigenic liver CSCs. These results may be valuable for the design of more rational strategies to control clinical malignant HCC using mTOR inhibitors.     

Protein cross-talk in CD133+ colon cancer cells indicates activation of the Wnt pathway and upregulation of SRp20 that is potentially involved in tumorigenicity

The cancer stem cell (CSC) theory represents a breakthrough in cancer research. We characterized the protein pattern of CSCs to identify specific intracellular pathways in this subpopulation of tumor cells. We studied colon CSCs using two different colon cancer cell lines: CaCo-2 and HCT-116. Putative CSCs were separated from non-CSCs by flow cytometry using CD133 as stemness marker. Total protein extracts of CD133+ cells were then compared to protein extracts of CD133- cells by 2D DIGE. The protein spots differentially expressed in the two subpopulations of cells were analyzed by mass spectrometry. Bioinformatics analysis of the identified proteins indicated alteration of two main processes: energy metabolism and the Wnt pathway. Interestingly, we observed upregulation of the splicing factor SRp20, a newly identified target gene of the Wnt/β-catenin pathway, and we demonstrated a direct cause-effect relationship between Wnt pathway activation and the increased SRp20 expression. Our results also show that SRp20 influences cell proliferation, which suggests it plays a role in the tumorigenicity of CD133+ cells. In conclusion, activation of the Wnt pathway in CD133+ cells and upregulation of SRp20, which is implicated in tumorigenesis, raises the possibility of a sequential series of molecular events occurring in connection with this process.