Side population cells in human gallbladder cancer cell line GBC-SD regulated by TGF-β-induced epithelial-mesenchymal transition

Molecular aspects of ABCB1 and ABCG2 in Gallbladder cancer and its clinical relevance

The function of ABC transporters in the body is manifold; such as maintenance of homeostasis, effect on multi-drug resistance and their role in tumor initiation & progression. Evidence pointing towards the direct or indirect role of ABC transporter genes in particular; ABCB1 and ABCG2 in cancer genesis is increasing. However, their role in gallbladder cancer is unexplored. Therefore, we investigated the methylation status and expression pattern of ABCB1 and ABCG2in gallbladder carcinogenesis. The methylation and expression study of ABCB1/MDR1 and ABCG2/BCRP was performed in tumour and normal fresh tissue samples collected from 61 histopathologically diagnosed gallbladder cancer patients. The methylation status was analysed by Methylation-Specific PCR and expression was determined by Real-Time PCR and Immunohistochemistry. Hypomethylation of ABCB1 and ABCG2 was found in 44 (72.13%) and 48 (78.6%) cases, respectively. ABCB1 hypomethylation pattern showed association with female patients (p = 0.040) and GradeII tumors (p = 0.036) while, ABCG2 hypomethylation was more frequent in early tumors (T1-T2). The mRNA expression ofABCB1 and ABCG2 was up-regulated in 33 (54.10%) and 41 (67.21%) patients with fold change of 4.7 and 5.5, respectively. The mRNA expression of both genes showed association with Grade II tumours and the increased fold change of ABCG2 was higher in (T1-T2) depth of invasion (p = 0.02) and Stage I-II disease (p = 0.08). The protein expression on IHC was strongly positive for ABCB1/MDR1and ABCG2/BCRP in 32 (52.46%) and 45 (73.77%) patients, respectively. The protein expression in ABCG2 showed association with patients age > 50 years (p = 0.04) and GradeII differentiation (p = 0.07). Interestingly, the hypomethylation of both the genes showed significant correlation with increased expression. ABCB1/MDR1 and ABCG2/BCRP hypomethylation and overexpression could have a potential role in gallbladder cancer tumorigenesis especially in early stages. The epigenetic change might be a plausible factor for altered gene expression of ABCB1 and ABCG2 in gallbladder cancer.

Hypoxia-Driven TGFβ Modulation of Side Population Cells in Breast Cancer: The Potential Role of ERα

Epithelial-to-mesenchymal transition (EMT) is known to be important in regulating the behaviour of cancer cells enabling them to acquire stem cell characteristics or by enhancing the stem cell characteristics of cancer stem cells, resulting in these cells becoming more migratory and invasive. EMT can be driven by a number of mechanisms, including the TGF-β1 signalling pathway and/or by hypoxia. However, these drivers of EMT differ in their actions in regulating side population (SP) cell behaviour, even within SPs isolated from the same tissue. In this study we examined CoCl2 exposure and TGF-β driven EMT on SP cells of the MDA-MB-231 and MCF7 breast cancer cell lines. Both TGF-β1 and CoCl2 treatment led to the depletion of MDA-MB-231 SP. Whilst TGF-β1 treatment significantly reduced the MCF7 SP cells, CoCl2 exposure led to a significant increase. Single cell analysis revealed that CoCl2 exposure of MCF7 SP leads to increased expression of ABCG2 and HES1, both associated with multi-drug resistance. We also examined the mammosphere forming efficiency in response to CoCl2 exposure in these cell lines, and saw the same effect as seen with the SP cells. We suggest that these contrasting effects are due to ERα expression and the inversely correlated expression of TGFB-RII, which is almost absent in the MCF7 cells. Understanding the EMT-mediated mechanisms of the regulation of SP cells could enable the identification of new therapeutic targets in breast cancer.

Participation of the SMAD2/3 signalling pathway in the down regulation of megalin/LRP2 by transforming growth factor beta (TGF-ß1)

Megalin/LRP2 is a receptor that plays important roles in the physiology of several organs, such as kidney, lung, intestine, and gallbladder and also in the physiology of the nervous system. Megalin expression is reduced in diseases associated with fibrosis, including diabetic nephropathy, hepatic fibrosis and cholelithiasis, as well as in some breast and prostate cancers. One of the hallmarks of these conditions is the presence of the cytokine transforming growth factor beta (TGF-ß). Although TGF-ß has been implicated in the reduction of megalin levels, the molecular mechanism underlying this regulation is not well understood. Here, we show that treatment of two epithelial cell lines (from kidney and gallbladder) with TGF-ß1 is associated with decreased megalin mRNA and protein levels, and that these effects are reversed by inhibiting the TGF-ß1 type I receptor (TGF-ßRI). Based on in silico analyses, the two SMAD-binding elements (SBEs) in the megalin promoter are located at positions -57 and -605. Site-directed mutagenesis of the SBEs and chromatin immunoprecipitation (ChIP) experiments revealed that SMAD2/3 transcription factors interact with SBEs. Both the presence of SMAD2/3 and intact SBEs were associated with repression of the megalin promoter, in the absence as well in the presence of TGF-ß1. Also, reduced megalin expression and promoter activation triggered by high concentration of albumin are dependent on the expression of SMAD2/3. Interestingly, the histone deacetylase inhibitor Trichostatin A (TSA), which induces megalin expression, reduced the effects of TGF-ß1 on megalin mRNA levels. These data show the significance of TGF-ß and the SMAD2/3 signalling pathway in the regulation of megalin and explain the decreased megalin levels observed under conditions in which TGF-ß is upregulated, including fibrosis-associated diseases and cancer.

Transforming growth factor-β decreases side population cells in hepatocellular carcinoma in vitro

Hepatocellular carcinoma (HCC) can result from hepatitis B or C infection, fibrosis or cirrhosis. Transforming growth factor-β (TGF-β) is one of the main growth factors associated with fibrosis or cirrhosis progression in the liver, but its role is controversial in hepatocarcinogenesis. In the present study, the effect of TGF-β on the HCC Huh-7 and Huh-Bat cell lines was evaluated. To study the effect of TGF-β, Huh-7 and Huh-Bat cells were treated with TGF-β and a TGF-β receptor inhibitor (SB431542). Cell survival, cell cycle, numbers of side population (SP) cells and expression of the cancer stem cell marker cluster of differentiation (CD)133, epithelial-mesenchymal transition markers (E-cadherin, α-smooth muscle actin and vimentin) and TGF-β-regulated proteins [phospho-c-Jun N-terminal kinase (p-JNK), p-c-Jun and p-smad2] were investigated. TGF-β treatment resulted in decreased cell survival with a targeted effect on SP cells. Expression of CD133 and vimentin was upregulated by treatment with the TGF-β receptor antagonist SB431542, but not with TGF-β. By contrast, TGF-β induced accumulation of cells at G0/G1, and upregulated expression of p-JNK, p-c-Jun and p-smad2. However, these effects were blocked when cells were treated with TGF-β plus SB431542, indicating the specificity of the TGF-β effect. The present results indicated that TGF-β has anticancer effects mediated by survival inhibition of cancer stem cells, which may be developed as a novel therapy for HCC.

Epithelial-to-mesenchymal transition in gallbladder cancer: from clinical evidence to cellular regulatory networks

Gallbladder cancer (GBC), with late diagnosis, rapid disease progression and early metastasis, is a highly aggressive malignant tumor found worldwide. Patients with GBC have poor survival, low curative resection rates and early recurrence. For such a lethal tumor, uncovering the mechanisms and exploring new strategies to prevent tumor progression and metastasis are critically important. Epithelial-to-mesenchymal transition (EMT) has a prominent role in the early steps of tumor progression and metastasis by initiating polarized epithelial cell transition into motile mesenchymal cells. Accumulating evidence suggests that EMT can be modulated by the cooperation of multiple mechanisms affecting common targets. Signaling pathways, transcriptional and post-transcriptional regulation and epigenetic alterations are involved in the stepwise EMT regulatory network in GBC. Loss of epithelial markers, acquisition of mesenchymal markers and dysregulation of EMT-inducing transcription factors (EMT-TFs) have been observed and are associated with the clinicopathology and prognosis of GBC patients. Therefore, EMT may be a detectable and predictable event for predicting GBC progression and metastasis in the clinic. In this review, we will provide an overview of EMT from the clinical evidence to cellular regulatory networks that have been studied thus far in clinical and basic GBC studies.

Kinetic Modeling of ABCG2 Transporter Heterogeneity: A Quantitative, Single-Cell Analysis of the Side Population Assay

The side population (SP) assay, a technique used in cancer and stem cell research, assesses the activity of ABC transporters on Hoechst staining in the presence and absence of transporter inhibition, identifying SP and non-SP cell (NSP) subpopulations by differential staining intensity. The interpretation of the assay is complicated because the transporter-mediated mechanisms fail to account for cell-to-cell variability within a population or adequately control the direct role of transporter activity on staining intensity. We hypothesized that differences in dye kinetics at the single-cell level, such as ABCG2 transporter-mediated efflux and DNA binding, are responsible for the differential cell staining that demarcates SP/NSP identity. We report changes in A549 phenotype during time in culture and with TGFβ treatment that correlate with SP size. Clonal expansion of individually sorted cells re-established both SP and NSPs, indicating that SP membership is dynamic. To assess the validity of a purely kinetics-based interpretation of SP/NSP identity, we developed a computational approach that simulated cell staining within a heterogeneous cell population; this exercise allowed for the direct inference of the role of transporter activity and inhibition on cell staining. Our simulated SP assay yielded appropriate SP responses for kinetic scenarios in which high transporter activity existed in a portion of the cells and little differential staining occurred in the majority of the population. With our approach for single-cell analysis, we observed SP and NSP cells at both ends of a transporter activity continuum, demonstrating that features of transporter activity as well as DNA content are determinants of SP/NSP identity.

PCBP1 is an important mediator of TGF-β-induced epithelial to mesenchymal transition in gall bladder cancer cell line GBC-SD

Gall bladder carcinoma (GBC) is the seventh most common cancer across the globe and the most common malignancy of the biliary tract. Most GBC related deaths occur due to secondary progression and metastasis to distant organs. Epithelial-mesenchymal transition (EMT) is an important pre-requisite for tumor metastasis, however its mechanism in GBC has not yet been defined. Using the GBC-SD cell line, we have uncovered an important mediator, poly r(C) binding protein-1 (PCBP1), of transforming growth factor-beta (TGF-β)-induced EMT in GBC. Our results show that TGF-β treatment resulted in PCBP1 phosphorylation in accordance with similar observation in other model systems. We further showed through gain- and loss-of-function assays that PCBP1 expression levels regulate the capacity of GBC-SD cells to migrate and invade in vitro. Finally, our results showed that PCBP1 expression levels also regulate generation of CD44(+)CD24(-) progenitor cell population in GBC-SD cells after TGF-β treatment. Cumulatively, our results indicate, pending further validation, that PCBP1 might be a prognostic marker for GBC metastasis.

Side populations from cervical-cancer-derived cell lines have stem-cell-like properties

The target cells for the transforming mutations caused by high-risk human papillomavirus (HPV) infection could be the stem cells of the uterine cervical epithelium, generating particular cancer stem cells (CSCs). The aim of this study was to identify and characterize the CSCs from cervical-cancer-derived cell lines. The ability of SiHa, CaLo, and C-33A cell lines to efflux Hoechst 33342 was evaluated by flow cytometry and cells from the corresponding side populations (SPs) and nonside populations (NSPs) were analyzed for their cell-cycle status (pyronin Y) and their mRNA levels of ABC transporter family members (with qPCR). Specific markers (α6-integrin(bri)/CD71(dim), CK17) of normal epithelial stem cells were evaluated by flow cytometry. The biological properties of these cells were analyzed, including their colony heterogeneity, repopulation, and anchorage-independent colony formation. We identified SPs (around 3 %) in the SiHa and CaLo cell lines, more than 70 % of which were in G0 phase and strongly expressed ABC transporters (predominantly ABCG2 and ABCB1). The SP from CaLo cells showed an α6-integrin(bri)/CD(dim) pattern, whereas the SP from the SiHa cells showed an α6-integrin(-)/CD(dim) pattern. Recultured cells from the SPs of both cell lines generated both SPs and NSPs, and had higher clonogenic potential to form mainly holoclones and greater colony-forming efficiency under anchorage-independent growth conditions than the cells from the NSPs or total cell populations. Interestingly, we identified no SP in the HPV-uninfected C-33A cell line, and it did not express ABCG2 or other members of the ABC transporters (ABCB1, ABCC1, or ABCA3).

MiR-20a triggers metastasis of gallbladder carcinoma

BACKGROUND & AIMS

The dysfunction of miRNAs has been demonstrated to participate in the development of various tumors. However, whether miRNAs are involved in metastasis and progression of gallbladder carcinoma (GBC) remains unknown.

METHODS

A new designed gain-of-function miRNA screening technology was applied to filter out pro-metastatic miRNAs in GBC. Their expression in GBC tissues was validated by real-time PCR. The biological functions of miRNAs were intensively studied by transwell, immunoblot, immunohistochemical, and in situ hybridization assays. Tumorigenicity and liver metastasis were further examined in nude mice.

RESULTS

Of 880 miRNAs, 17 were filtered out as the prominent metastatic inducers of GBCs. Among them, the upregulation of pro-metastatic miR-20a was closely associated with local invasion, distant metastasis, and poor prognosis of 67 followed-up GBC patients, clinically. Patients with higher miR-20a expression exhibited worse overall survival (OS and median OS time was 5 and 20 months, respectively) than the lower expression group. A dramatically increased TGF-β1 level was found in GBC patients, which was responsible for the elevation of miR-20a. The ectopic expression of miR-20a could induce epithelial-mesenchymal transition and enhance metastasis of GBC cells in vitro and in vivo, by directly targeting the 3' UTR of Smad7, and subsequently promoting nuclear translocation of β-catenin. Conversely, the blockage of miR-20a by specific antagomir effectively restored the expression of Smad7 and attenuated TGF-β-induced cell metastasis.

CONCLUSIONS

TGF-β1-mediated activation of the miR-20a/Smad7/β-catenin axis plays a pivotal role in the pathogenesis and worse prognosis of GBCs and may serve as a potential therapeutic target in the future.

Emodin as an effective agent in targeting cancer stem-like side population cells of gallbladder carcinoma

Side population (SP) cells are previously identified from bone marrow based on their capacity to efflux of the fluorescent dye Hoechst 33342. Recent studies demonstrate that SP cells isolated from various cancer cell lines and primary tumors possess stem-cell-like properties. Thus, targeting tumor SP cells may provide new strategies for treatment in clinic. We previously showed that 1,3,8-trihydroxy-6-methylanthraquinone (emodin), a reactive oxygen species (ROS) generator, enhanced sensitivity of gallbladder cancer SGC-996 cells to cisplatin (CDDP) via generation of ROS and downregulation of multidrug-resistance-associated protein 1 (MRP1). To determine whether emodin also acts effectively on cancer stem cells of gallbladder carcinoma, we use SP cells as a model of cancer stem-cell-like cells. Here, we found that emodin, via ROS-related mechanism and suppressing the function of ATP-binding cassette super-family G member (ABCG2), which is known to be associated with Hoechst dye efflux activity of SP cells, not only reduced the ratio, inhibited clone formation, and eliminated sphere formation of SP cells effectively, but also promoted obviously the intracellular accumulation of doxorubicin, the main substrate of the efflux pump ABCG2. In addition, emodin could sensitize CDDP, via inhibition of expression of ABCG2, to overcome chemoresistance of SP cells. Importantly, similar to the experiment in vitro, emodin/CDDP co-treatment in vivo suppressed the tumor growth derived from SP cells through downregulating ABCG2 expression. Our results suggest that emodin is an effective agent targeting cancer stem-like SP cells of gallbladder carcinoma, either alone or acts as a chemotherapy enhancer.