Overexpression of CD90 (Thy-1) in Pancreatic Adenocarcinoma Present in the Tumor Microenvironment

CD90 (Thy-1) plays important roles in oncogenesis and shows potential as a candidate marker for cancer stem cells (CSCs) in various malignancies. Herein, we investigated the expression of CD90 in pancreatic adenocarcinoma (PDAC), with a comparison to normal pancreas and non-malignant pancreatic disease, by immunohistochemical (IHC) analysis of tissue microarrays containing 183 clinical tissue specimens. Statistical analysis was performed to evaluate the correlation between CD90 expression and the major clinicopathological factors after adjustment of age and gender. The IHC data showed that CD90 was significantly overexpressed in PDAC and its metastatic cancers as compared to chronic pancreatitis and benign islet tumors, while it was negative in normal pancreas and 82.7% of adjacent normal pancreas tissues. The abundant CD90 expression was predominantly present in PDAC stroma, such as fibroblasts and vascular endothelial cells, which could serve as a promising marker to distinguish pancreatic adenocarcinoma from normal pancreas and non-malignant pancreatic diseases. Double immunostaining of CD90 with CD24, a CSC marker for PDAC, showed that there was little overlap between these two markers. However, CD90⁺ fibroblast cells were clustered around CD24⁺ malignant ducts, suggesting that CD90 may be involved in the tumor-stroma interactions and promote pancreatic cancer development. Furthermore, CD90 mostly overlapped with α-smooth muscle actin (αSMA, a marker of activated pancreatic stellate cells (PSCs)) in PDAC stroma, which demonstrated that CD90⁺ stromal cells consist largely of activated PSCs. Double immunostaining of CD90 and a vascular endothelial cell marker CD31 demonstrated that CD90 expression on vascular endothelial cells was significantly increased in PDACs as compared to normal pancreas and non-malignant pancreatic diseases. Our findings suggest that CD90 could serve as a promising marker for pancreatic adenocarcinoma where desmoplastic stroma plays an important role in tumor growth and angiogenesis.     

CD95 promotes metastatic spread via Sck in pancreatic ductal adenocarcinoma

Cancer stem cells (CSCs) have been implicated in the initiation and maintenance of tumour growth as well as metastasis. Recent reports link stemness to epithelial–mesenchymal transition (EMT) in cancer. However, there is still little knowledge about the molecular markers of those events. In silico analysis of RNA profiles of 36 pancreatic ductal adenocarcinomas (PDAC) reveals an association of the expression of CD95 with EMT and stemness that was validated in CSCs isolated from PDAC surgical specimens. CD95 expression was also higher in metastatic pancreatic cells than in primary PDAC. Pharmacological inhibition of CD95 activity reduced PDAC growth and metastasis in CSC-derived xenografts and in a murine syngeneic model. On the mechanistic level, Sck was identified as a novel molecule indispensable for CD95''s induction of cell cycle progression. This study uncovers CD95 as a marker of EMT and stemness in PDAC. It also addresses the molecular mechanism by which CD95 drives tumour growth and opens tantalizing therapeutic possibilities in PDAC.Recent analysis of the cellular heterogeneity within the tumour mass revealed the existence of cells that share characteristics with stem cells of the tissue of origin.¹ These cells are responsible for the tumour''s resistance to current therapies and therefore provide new perspectives in cancer treatment. Cancer stem cells (CSCs) or tumour-initiating cells (TICs) are characterized by their self-renewal and differentiation capacity, which are assessed by their ability to generate a heterogeneous tumour in immunocompromised mice in serial transplantations.² In pancreatic cancer, those properties were initially shown by cells expressing CD24, CD44 and ESA (epithelial surface antigen).³Pancreatic cancer is the fourth leading cause of cancer-related death in the United States of America.⁴ The highly malignant phenotype of pancreatic ductal adenocarcinoma (PDAC) results from aggressive invasion and early metastatic potential. Epithelial–mesenchymal transition (EMT) is considered to be the first step of metastatic spread. During this process, the tumour cells master the ability to detach from their neighbours and gain motile and invasive properties enabling them to spread via blood or lymph vessels.⁵ As cells undergo EMT, they lose their epithelial features including sheet-like architecture, polarity and E-cadherin expression and gradually gain motility and expression of mesenchymal markers such as N-cadherin, fibronectin and vimentin. Recent studies have uncovered a link between the EMT and the acquisition of stem cell characteristics.^{6, 7} Most growth factors such as TGF-β, HGF, EGF, IGF and FGF are known to trigger EMT.⁸ Interestingly, there is growing evidence that the so-called ‘death receptor'' CD95 (Fas/Apo-1) behaves like a growth factor receptor in cancer cells.^{9, 10, 11}CD95 was first discovered as the initiator of programmed cell death by forming death-inducing signalling complex (DISC, including Fas-associated death domain, FADD and caspase-8/10) upon stimulation with CD95 ligand (CD95L).¹² However, mitogen-activated protein kinases (MAPKs), leading to p38, JNK or extracellular signal-regulated kinase (ERK) 1/2 activation, were also reported to be driven by CD95.^{13, 14} In glioblastoma multiforme (GBM), CD95-induced migration depends on the formation of the so-called phosphatidyl-inositol 3-kinase (PI3K) activation complex (PAC),^{11, 12} consisting of the Src family kinase (SFK), Yes and p85, the regulatory subunit of PI3K. PAC components, however, differ between cell types, encompassing also other SFKs or the Syk tyrosine kinase.^{15, 16}Here, we show that the expression of CD95 increases in primary PDACs as compared with non-tumour-bearing pancreas and is higher in metastatic pancreatic cells than in primary PDAC. In CSCs isolated from primary PDAC surgical specimens, the expression of CD95 positively correlates with EMT markers. We also identified Sck as the molecular link between CD95 and activation of the PI3K and MAPK pathways. Neutralization of the CD95L reduces PDAC growth and metastasis. The present study defines CD95 and its downstream signalling pathway components as new targets for PDAC therapy.     

ALDH activity selectively defines an enhanced tumor-initiating cell population relative to CD133 expression in human pancreatic adenocarcinoma

Background

Multiple studies in recent years have identified highly tumorigenic populations of cells that drive tumor formation. These cancer stem cells (CSCs), or tumor-initiating cells (TICs), exhibit properties of normal stem cells and are associated with resistance to current therapies. As pancreatic adenocarcinoma is among the most resistant human cancers to chemo-radiation therapy, we sought to evaluate the presence of cell populations with tumor-initiating capacities in human pancreatic tumors. Understanding which pancreatic cancer cell populations possess tumor-initiating capabilities is critical to characterizing and understanding the biology of pancreatic CSCs towards therapeutic ends.

Methodology/Principal Findings

We have isolated populations of cells with high ALDH activity (ALDH^high) and/or CD133 cell surface expression from human xenograft tumors established from multiple patient tumors with pancreatic adenocarcinoma (direct xenograft tumors) and from the pancreatic cancer cell line L3.6pl. Through fluorescent activated cell sorting (FACs)-mediated enrichment and depletion of selected pancreatic cancer cell populations, we sought to discriminate the relative tumorigenicity of cell populations that express the pancreatic CSC markers CD133 and aldehyde dehydrogenase (ALDH). ALDH^high and ALDH^low cell populations were further examined for co-expression of CD44 and/or CD24. We demonstrate that unlike cell populations demonstrating low ALDH activity, as few as 100 cells enriched for high ALDH activity were capable of tumor formation, irrespective of CD133 expression. In direct xenograft tumors, the proportions of total tumor cells expressing ALDH and/or CD133 in xenograft tumors were unchanged through a minimum of two passages. We further demonstrate that ALDH expression among patients with pancreatic adenocarcinoma is heterogeneous, but the expression is constant in serial generations of individual direct xenograft tumors established from bulk human pancreatic tumors in NOD/SCID mice.

Conclusions/Significance

We conclude that, in contrast to some previous studies, cell populations enriched for high ALDH activity alone are sufficient for efficient tumor-initiation with enhanced tumorigenic potential relative to CD133⁺ and ALDH^low cell populations in some direct xenograft tumors. Although cell populations enriched for CD133 expression may alone possess tumorigenic potential, they are significantly less tumorigenic than ALDH^high cell populations. ALDH^high/CD44⁺/CD24⁺ or ALDH^low/CD44⁺/CD24⁺ phenotypes do not appear to significantly contribute to tumor formation at low numbers of inoculated tumor cells. ALDH expression broadly varies among patients with pancreatic adenocarcinoma and the apparent expression is recapitulated in serial generations of direct xenograft tumors in NOD/SCID. We have thus identified a distinct population of TICs that should lead to identification of novel targets for pancreatic cancer therapy.     

Coexpression of EpCAM,CD44 Variant Isoforms and Claudin-7 in Anaplastic Thyroid Carcinoma

Background

Anaplastic thyroid cancer is considered to be one of the most aggressive human malignancies, and the mean survival time after diagnosis is approximately six months, regardless of treatments. This study aimed to examine how EpCAM and its related molecules are involved in the characteristics of anaplastic thyroid carcinoma.

Methodology/Principal Findings

Two differentiated thyroid cancer cell lines (TPC-1 and FTC-133), and two anaplastic thyroid cancer cell lines (FRO, ACT-1) were analyzed for expression of CD44 standard isoform (CD44s), CD44 variant isoforms, and EpCAM, and human aldehyde dehydrogenase-1 (ALDH1) enzymatic activity using flow cytometry. CD44s expression was higher in TPC-1 and FTC-133 than in the FRO and ACT-1, whereas ALDH1 activities were higher in FRO and ACT-1 than in TPC-1 and FTC-133. An inverse correlation between CD44s expression and ALDH1 activity was observed in all thyroid cancer cell lines. As for the expressions of CD44 variant isoforms, ACT-1 showed higher and FRO showed moderate CD44v6 expressions, whereas either TPC-1 or FTC-133 showed negative CD44v6 expression. EpCAM expressions in FRO and ACT-1 were higher than those in TPC-1 and FTC-133, and EpCAM expressions inversely correlated with those of CD44s. A positive correlation was observed between EpCAM expression and ALDH1 activity in thyroid cancer cell lines. In the RT-PCR analysis, the expression levels of EpCAM, caludin-7 and ALDH1 in FRO and ATC-1 cells were significantly higher than those in TPC-1 and FTC-133 cells. In clinical specimens of thyroid cancers, nuclear expression of EpCAM and high expression of CD44v6 were detected significantly more frequently in anaplastic carcinomas.

Conclusions/Significance

Our study suggests the possibility that EpCAM, together with CD44v6 and claudin-7 as well as ALDH1, may be involved in the development of the aggressive phenotype of anaplastic thyroid carcinoma. Our findings may suggest a novel therapeutic strategy for treatment of anaplastic thyroid carcinoma.