Downregulation of miR-199b is associated with distant metastasis in colorectal cancer via activation of SIRT1 and inhibition of CREB/KISS1 signaling

Exploring the Role of Hypoxia-Inducible Carbonic Anhydrase IX (CAIX) in Circulating Tumor Cells (CTCs) of Breast Cancer

Circulating tumor cells (CTCs) in the peripheral blood are believed to be the source of metastasis and can be used as a liquid biopsy to monitor cancer progression and therapeutic response. However, it has been challenging to accurately detect CTCs because of their low frequency and the heterogeneity of the population. In this study, we have developed an in vitro model of CTCs by using non-adherent suspension culture. We used this model to study a group of breast cancer cell lines with distinct molecular subtypes (TNBC, HER2⁺, and ER⁺/PR⁺). We found that, when these breast cancer cell lines lost their attachment to the extracellular matrix, they accumulated a subtype of cancer stem cells (CSC) that expressed the surface markers of stem cells (e.g., CD44⁺CD24^-). These stem-like CTCs also showed high expressions of hypoxia-inducible gene products, particularly the hypoxia-inducible carbonic anhydrase IX (CAIX). Inhibition of CAIX activity was found to reduce CAIX expression and stem cell phenotypes in the targeted CTCs. Further studies are needed, using CTC samples from breast cancer patients, to determine the role of CAIX in CTC survival, CSC transition, and metastasis. CAIX may be a useful surface marker for the detection of CSCs in the blood, and a potential target for treating metastatic breast cancers.

A Comprehensive Characterization of Stemness in Cell Lines and Primary Cells of Pancreatic Ductal Adenocarcinoma

The aim of this study is to provide a comprehensive characterization of stemness in pancreatic ductal adenocarcinoma (PDAC) cell lines. Seventeen cell lines were evaluated for the expression of cancer stem cell (CSC) markers. The two putative pancreatic CSC phenotypes were expressed heterogeneously ranging from 0 to 99.35% (median 3.46) for ESA+CD24+CD44+ and 0 to 1.94% (median 0.13) for CXCR4+CD133+. Cell lines were classified according to ESA+CD24+CD44+ expression as: Low-Stemness (LS; <5%, n = 9, median 0.31%); Medium-Stemness (MS; 6−20%, n = 4, median 12.4%); and High-Stemness (HS; >20%, n = 4, median 95.8%) cell lines. Higher degree of stemness was associated with in vivo tumorigenicity but not with in vitro growth kinetics, clonogenicity, and chemo-resistance. A wide characterization (chemokine receptors, factors involved in pancreatic organogenesis, markers of epithelial−mesenchymal transition, and secretome) revealed that the degree of stemness was associated with KRT19 and NKX2.2 mRNA expression, with CD49a and CA19.9/Tie2 protein expression, and with the secretion of VEGF, IL-7, IL-12p70, IL-6, CCL3, IL-10, and CXCL9. The expression of stem cell markers was also evaluated on primary tumor cells from 55 PDAC patients who underwent pancreatectomy with radical intent, revealing that CXCR4+/CD133+ and CD24+ cells, but not ESA+CD24+CD44+, are independent predictors of mortality.

The plasticity of pancreatic cancer stem cells: implications in therapeutic resistance

The ever-growing perception of cancer stem cells (CSCs) as a plastic state rather than a hardwired defined entity has evolved our understanding of the functional and biological plasticity of these elusive components in malignancies. Pancreatic cancer (PC), based on its biological features and clinical evolution, is a prototypical example of a CSC-driven disease. Since the discovery of pancreatic CSCs (PCSCs) in 2007, evidence has unraveled their control over many facets of the natural history of PC, including primary tumor growth, metastatic progression, disease recurrence, and acquired drug resistance. Consequently, the current near-ubiquitous treatment regimens for PC using aggressive cytotoxic agents, aimed at ‘‘tumor debulking’’ rather than eradication of CSCs, have proven ineffective in providing clinically convincing improvements in patients with this dreadful disease. Herein, we review the key hallmarks as well as the intrinsic and extrinsic resistance mechanisms of CSCs that mediate treatment failure in PC and enlist the potential CSC-targeting ‘natural agents’ that are gaining popularity in recent years. A better understanding of the molecular and functional landscape of PCSC-intrinsic evasion of chemotherapeutic drugs offers a facile opportunity for treating PC, an intractable cancer with a grim prognosis and in dire need of effective therapeutic advances.

CD24, A Review of its Role in Tumor Diagnosis, Progression and Therapy

CD24, is a mucin-like GPI-anchored molecules. By immunohistochemistry, it is widely detected in many solid tumors, such as breast cancers, genital system cancers, digestive system cancers, neural system cancers and so on. The functional roles of CD24 are either fulfilled by combination with ligands or participate in signal transduction, which mediate the initiation and progression of neoplasms. However, the character of CD24 remains to be intriguing because there are still opposite voices about the impact of CD24 on tumors. In preclinical studies, CD24 target therapies, including monoclonal antibodies, target silencing by RNA interference and immunotherapy, have shown us brighten futures on the anti-tumor application. Nevertheless, evidences based on clinical studies are urgently needed. Here, with expectancy to spark new ideas, we summarize the relevant studies about CD24 from a tumor perspective.

Identification of CD24 as a potential diagnostic and therapeutic target for malignant pleural mesothelioma

Malignant pleural mesothelioma (MPM) is an aggressive malignancy of the pleura that is currently incurable due to the lack of an effective early diagnostic method and specific medication. The CDKN2A (p16) and NF2 genes are both frequently mutated in MPM. To understand how these mutations contribute to MPM tumor growth, we generated NF2/p16 double-knockout (DKO) cell clones using human MeT-5A and HOMC-B1 mesothelial cell lines. Cell growth and migration activities were significantly increased in DKO compared with parental cells. cDNA microarray analysis revealed differences in global gene expression profiles between DKO and parental cells. Quantitative PCR and western blot analyses showed upregulation of CD24 concomitant with increased phosphorylation of AKT, p70S6K, and c-Jun in DKO clones. This upregulation was abrogated by exogenous expression of NF2 and p16. CD24 knockdown in DKO cells significantly decreased TGF-β1 expression and increased expression of E-cadherin, an epithelial-mesenchymal transition marker. CD24 was highly expressed in human mesothelioma tissues (28/45 cases, 62%) and associated with the loss of NF2 and p16. Public data analysis revealed a significantly shorter survival time in MPM patients with high CD24 gene expression levels. These results strongly indicate the potential use of CD24 as a prognostic marker as well as a novel diagnostic and therapeutic target for MPM.

Novel insights into the function of CD24: A driving force in cancer

CD24 is a highly glycosylated protein with a small protein core that is linked to the plasma membrane via a glycosyl-phosphatidylinositol anchor. CD24 is primarily expressed by immune cells but is often overexpressed in human tumors. In cancer, CD24 is a regulator of cell migration, invasion and proliferation. Its expression is associated with poor prognosis and it is used as cancer stemness marker. Recently, CD24 on tumor cells was identified as a phagocytic inhibitor ("do not eat me" signal) having a suppressive role in tumor immunity via binding to Siglec-10 on macrophages. This finding is reminiscent of the demonstration that soluble CD24-Fc can dampen the immune system in autoimmune disease. In the present review, we summarize recent progress on the role of the CD24-Siglec-10 binding axis at the interface between tumor cells and the immune system, and the role of CD24 genetic polymorphisms in cancer. We describe the specific function of cytoplasmic CD24 and discuss the presence of CD24 on tumor-released extracellular vesicles. Finally, we evaluate the potential of CD24-based immunotherapy.

Characterization of the metastatic potential of the floating cell component of MIA PaCa-2, a human pancreatic cancer cell line

In pancreatic cancer, morphologically and functionally heterogeneous cancer cells reside within the same patient. The heterogeneity is believed to promote metastasis and resistance to chemoradiotherapy. MIA PaCa-2, an established human pancreatic ductal adenocarcinoma (PDAC) cell line, contains round and spindle-shaped adherent cells, as well as, round floating cells. In this study, we aimed to assess if the floating cells might have greater metastatic potential and/or be more resistant to drug-induced apoptosis compared to adherent cells. Time-lapse analysis revealed that the two types of adherent cells transformed bilaterally, and some of the adherent, round cells converted to floating cells. Flow cytometry and electron microscopy showed that approximately 90% of the floating cells were viable. qRT-PCR analysis revealed that floating cells expressed lower levels of integrins and ATP-binding cassette (ABC) transporters than adherent cells. In contrast, except for vimentin, floating cells expressed more epithelial to mesenchymal transition markers than adherent cells. Floating cells included a larger population of G2/M-phase cells, and migration assays revealed a decreased migration ability by floating cells relative to adherent cells. A cell aggregation assay showed that the aggregative properties of the floating cells were lower than those of the adherent cells. In 3D culture, spheres derived from floating cells were more sensitive to anti-cancer drugs, including gemcitabine, 5-FU, and abraxane, than those derived from adherent cells. Expression levels of stemness markers in the spheres derived from floating cells were lower than those derived from adherent cells. Morphological characterization of human PDAC cell lines may help to clarify the series of alterations cancer cells undergo during the metastatic process and may contribute to the development of new PDAC diagnostics and more patient-specific treatments for those with PDAC.

Fetal bovine serum enlarges the size of human pancreatic cancer spheres accompanied by an increase in the expression of cancer stem cell markers

Pancreatic ductal adenocarcinoma (PDAC) is a major histological type of pancreatic cancer and remains one of the most lethal cancers with a high mortality rate owing to its aggressive growth, high metastatic rate, and recurrence. Recent studies on cancer stem cells (CSCs) have suggested that the aggressive growth, high metastatic rate, and recurrence might be caused by the ability of CSCs to self-renew, differentiate, and drive tumorigenesis. Thus, CSCs are expected to be a therapeutic target for PDAC. Sphere forming assay of cancer cells, including PDAC cells, is commonly performed using epidermal growth factor and fibroblast growth factor-2 containing serum-free medium to identify and isolate the enriched CSCs. Recently, we observed that PDAC spheres cultured in fetal bovine serum containing medium are morphologically similar to spheres cultured in the growth factor containing medium. In this study, we cultured two PDAC cell lines, PANC-1 and PK-1, in growth factor containing serum-free medium or serum containing medium, and compared the morphology of the spheres formed in detail by electron microscopy and examined the expression of major CSC marker genes. Both the PDAC cells formed larger spheres in the serum containing medium than in the growth factor containing medium. PK-1 cells formed more morphologically differentiated spheres, with peripheral flat lining cells, in the serum containing medium. Expression levels of most of the CSC markers were higher in the spheres of the two PDAC cells in both the culture mediums than in the cells cultured under adherent conditions. The expression levels of CSC markers in PDAC spheres cultured in the growth factor containing medium were not necessarily higher than that in the spheres cultured in the serum containing medium. These findings suggest that sphere forming assay using serum containing medium, by which large PDAC spheres with enriched CSCs are formed, may be useful for deciphering the characteristics of CSCs and for developing anti-CSC therapies for PDAC.

The natural anticancer agent cantharidin alters GPI-anchored protein sorting by targeting Cdc1-mediated remodeling in endoplasmic reticulum

Cantharidin (CTD) is a potent anticancer small molecule produced by several species of blister beetle. It has been a traditional medicine for the management of warts and tumors for many decades. CTD suppresses tumor growth by inducing apoptosis, cell cycle arrest, and DNA damage and inhibits protein phosphatase 2 phosphatase activator (PP2A) and protein phosphatase 1 (PP1). CTD also alters lipid homeostasis, cell wall integrity, endocytosis, adhesion, and invasion in yeast cells. In this study, we identified additional molecular targets of CTD using a Saccharomyces cerevisiae strain that expresses a cantharidin resistance gene (CRG1), encoding a SAM-dependent methyltransferase that methylates and inactivates CTD. We found that CTD specifically affects phosphatidylethanolamine (PE)-associated functions that can be rescued by supplementing the growth media with ethanolamine (ETA). CTD also perturbed endoplasmic reticulum (ER) homeostasis and cell wall integrity by altering the sorting of glycosylphosphatidylinositol (GPI)-anchored proteins. A CTD-dependent genetic interaction profile of CRG1 revealed that the activity of the lipid phosphatase cell division control protein 1 (Cdc1) in GPI-anchor remodeling is the key target of CTD, independently of PP2A and PP1 activities. Moreover, experiments with human cells further suggested that CTD functions through a conserved mechanism in higher eukaryotes. Altogether, we conclude that CTD induces cytotoxicity by targeting Cdc1 activity in GPI-anchor remodeling in the ER.

H19 long non-coding RNA contributes to sphere formation and invasion through regulation of CD24 and integrin expression in pancreatic cancer cells

The long non-coding RNA H19 is highly expressed in several cancers, and the functions of H19 vary among cancer cell types. Recently, we reported that H19 contributes to the metastasis of pancreatic ductal adenocarcinoma (PDAC) cells and that inhibition of H19 reduces metastasis in vivo. However, the molecular mechanisms underlying the metastasis-promoting role of H19 in PDAC cells remain poorly elucidated. In this study, we clarified the mechanisms by which H19 regulates PDAC metastasis, with a focus on cancer stem cells (CSCs), by using H19-overexpressing and knockdown PDAC cells. Whereas the sphere-formation and invasion abilities of PDAC cells depended on H19 expression levels, other CSC characteristics of the cells, including stemness-marker expression and anticancer-drug resistance, were unaffected by H19 levels. Furthermore, metalloproteinase activity, a key mediator of invasion, was also independent of H19 expression. By contrast, H19 promoted cell adhesion through regulation of integrin and CD24 expression. Notably, the increased adhesion of H19-overexpressing cells was blocked by an anti-β1-integrin antibody, and this resulted in the inhibition of sphere formation and invasion. Thus, H19 plays critical roles in the CSC self-renewal and cell adhesion of PDAC that lead to invasion and metastasis. Our findings suggest that H19 represents a novel therapeutic target for the metastasis of pancreatic cancer.

MicroRNAs in the prognosis and therapy of colorectal cancer: From bench to bedside

MicroRNAs (miRNAs) are small, single-stranded, noncoding RNAs that can post-transcriptionally regulate the expression of various oncogenes and tumor suppressor genes. Dysregulated expression of many miRNAs have been shown to mediate the signaling pathways critical in the multistep carcinogenesis of colorectal cancer (CRC). MiRNAs are stable and protected from RNase-mediated degradation, thereby enabling its detection in biological fluids and archival tissues for biomarker studies. This review focuses on the role and application of miRNAs in the prognosis and therapy of CRC. While stage II CRC is potentially curable by surgical resection, a significant percentage of stage II CRC patients do develop recurrence. MiRNA biomarkers may be used to stratify such high-risk population for adjuvant chemotherapy to provide better prognoses. Growing evidence also suggests that miRNAs are involved in the metastatic process of CRC. Certain of these miRNAs may thus be used as prognostic biomarkers to identify patients more likely to have micro-metastasis, who could be monitored more closely after surgery and/or given more aggressive adjuvant chemotherapy. Intrinsic and acquired resistance to chemotherapy severely hinders successful chemotherapy in CRC treatment. Predictive miRNA biomarkers for response to chemotherapy may identify patients who will benefit the most from a particular regimen and also spare the patients from unnecessary side effects. Selection of patients to receive the new targeted therapy is becoming possible with the use of predictive miRNA biomarkers. Lastly, forced expression of tumor suppressor miRNA or silencing of oncogenic miRNA in tumors by gene therapy can also be adopted to treat CRC alone or in combination with other chemotherapeutic drugs.

Histone deacetylase class-I inhibition promotes epithelial gene expression in pancreatic cancer cells in a BRD4- and MYC-dependent manner

Pancreatic ductal adenocarcinoma (PDAC) is a highly aggressive cancer with a particularly dismal prognosis. Histone deacetylases (HDAC) are epigenetic modulators whose activity is frequently deregulated in various cancers including PDAC. In particular, class-I HDACs (HDAC 1, 2, 3 and 8) have been shown to play an important role in PDAC. In this study, we investigated the effects of the class I-specific HDAC inhibitor (HDACi) 4SC-202 in multiple PDAC cell lines in promoting tumor cell differentiation. We show that 4SC-202 negatively affects TGFβ signaling and inhibits TGFβ-induced epithelial-to-mesenchymal transition (EMT). Moreover, 4SC-202 markedly induced p21 (CDKN1A) expression and significantly attenuated cell proliferation. Mechanistically, genome-wide studies revealed that 4SC-202-induced genes were enriched for Bromodomain-containing Protein-4 (BRD4) and MYC occupancy. BRD4, a well-characterized acetyllysine reader, has been shown to play a major role in regulating transcription of selected subsets of genes. Importantly, BRD4 and MYC are essential for the expression of a subgroup of genes induced by class-I HDACi. Taken together, our study uncovers a previously unknown role of BRD4 and MYC in eliciting the HDACi-mediated induction of a subset of genes and provides molecular insight into the mechanisms of HDACi action in PDAC.

Nuclear CD24 Drives Tumor Growth and Is Predictive of Poor Patient Prognosis

Elevated tumor expression of the cell surface GPI-linked CD24 protein signals poor patient prognosis in many tumor types. However, some cancer cells selected to be negative for surface CD24 (surCD24-) still retain aggressive phenotypes in vitro and in vivo Here, we resolve this apparent paradox with the discovery of biologically active, nuclear CD24 (nucCD24) and finding that its levels are unchanged in surCD24- cells. Using the complementary techniques of biochemical cellular fractionation and immunofluorescence, we demonstrate a signal for CD24 in the nucleus in cells from various histologic types of cancer. Nuclear-specific expression of CD24 (NLS-CD24) increased anchorage-independent growth in vitro and tumor formation in vivo Immunohistochemistry of patient tumor samples revealed the presence of nucCD24, whose signal intensity correlated positively with the presence of metastatic disease. Analysis of gene expression between cells expressing CD24 and NLS-CD24 revealed a unique nucCD24 transcriptional signature. The median score derived from this signature was able to stratify overall survival in four patient datasets from bladder cancer and five patient datasets from colorectal cancer. Patients with high scores (more nucCD24-like) had reduced survival. These findings define a novel and functionally important intracellular location of CD24; they explain why surCD24- cells can remain aggressive, and they highlight the need to consider nucCD24 in both fundamental research and therapeutic development. Cancer Res; 77(18); 4858-67. ©2017 AACR.

Epigenetic Regulation of ZBTB18 Promotes Glioblastoma Progression

Glioblastoma (GBM) comprises distinct subtypes characterized by their molecular profile. Mesenchymal identity in GBM has been associated with a comparatively unfavorable prognosis, primarily due to inherent resistance of these tumors to current therapies. The identification of molecular determinants of mesenchymal transformation could potentially allow for the discovery of new therapeutic targets. Zinc Finger and BTB Domain Containing 18 (ZBTB18/ZNF238/RP58) is a zinc finger transcriptional repressor with a crucial role in brain development and neuronal differentiation. Here, ZBTB18 is primarily silenced in the mesenchymal subtype of GBM through aberrant promoter methylation. Loss of ZBTB18 contributes to the aggressive phenotype of glioblastoma through regulation of poor prognosis-associated signatures. Restitution of ZBTB18 expression reverses the phenotype and impairs tumor-forming ability. These results indicate that ZBTB18 functions as a tumor suppressor in GBM through the regulation of genes associated with phenotypically aggressive properties.Implications: This study characterizes the role of the putative tumor suppressor ZBTB18 and its regulation by promoter hypermethylation, which appears to be a common mechanism to silence ZBTB18 in the mesenchymal subtype of GBM and provides a new mechanistic opportunity to specifically target this tumor subclass. Mol Cancer Res; 15(8); 998-1011. ©2017 AACR.