Immortal human pancreatic duct epithelial cell lines with near normal genotype and phenotype

RPL38, FOSL1, and UPP1 are predominantly expressed in the pancreatic ductal epithelium

OBJECTIVES

Establishing more effective treatment of pancreatic cancer requires an understanding of the molecular events leading to the onset and progression of this disease. The biology of tumorigenesis may be better understood if cell type-specific genes in the pancreas are more recognized. This recognition may be as important as discovering a disease-responsible gene. Identification of a ductal epithelium-specific gene can contribute not only to our knowledge of pancreatic tumorigenesis, tumor marker discovery, and effective drug targeting but also is crucial for making a reliable animal model.

METHODS

We used the x-Profiler engine online to compare the SAGE (Serial Analysis of Gene Expression) libraries derived from 2 short-term cultures of normal human ductal epithelial cells from the pancreas against 34 other SAGE libraries generated from other normal human tissues to identify the best candidate gene specific for the ductal epithelium of the pancreas.

RESULTS

We identified 3 genes, ribosomal protein L38 (RPL38), uridine phosphorylase (UPP1), and FOS-like antigen-1 (FOSL1), predominantly expressed in the pancreatic ductal epithelium. The expression patterns of these 3 genes were confirmed by virtual Northern analysis, semi-quantitative RT-PCR, and in situ hybridization.

CONCLUSION

Although the expressions of these 3 genes are not completely restricted to the ductal epithelium of the pancreas, we showed that they have more specific expression patterns than CK19 and MUC1. We also demonstrated that all 3 genes are highly expressed in a panel of pancreatic cancer cell lines and can potentially be useful in tumor targeting or as tumor markers.

Increased survival, proliferation, and migration in metastatic human pancreatic tumor cells expressing functional CXCR4

In this study, we have evaluated 11 pancreatic tumor cell lines and tumor cells from surgical samples of patients with pancreatic adenocarcinoma for expression of the chemokine receptor CXCR4. Six of 11 cell lines expressed detectable mRNA of CXCR4, with three cell lines (AsPC1, Capan1, and Hs766T) having substantial amounts of transcripts. Expression was higher in lines derived from metastatic lesions compared with those derived from primary tumors. Different inflammatory cytokines did not modify expression, whereas IFN-gamma down-regulated and hypoxia up-regulated CXCR4 transcripts. Transcript expression was associated with surface expression in pancreatic carcinoma cell lines. All surgical carcinoma samples tested expressed higher levels of CXCR4 than normal pancreatic ducts, which were used as reference tissue. The chemokine CXCL12 induced chemotaxis in CXCR4-positive pancreatic carcinoma cell lines, which was inhibited by anti-CXCR4 monoclonal antibody and by the antagonist AMD3100. Transendothelial migration, Matrigel invasion, and activation of matrix metalloproteases were also enhanced by CXCL12. In CXCR4-positive cell lines, CXCL12 stimulated cell proliferation. The cell line Hs766T produces high levels of CXCL12, and addition of the CXCR4 antagonist AMD3100 partially inhibited proliferation, indicating an autocrine loop. Moreover, the addition of exogenous CXCL12 inhibited apoptosis induced by serum starvation. These results indicate that the CXCR4 receptor is frequently expressed in metastatic pancreatic tumor cells. CXCR4 not only stimulates cell motility and invasion but also promotes survival and proliferation. Strategies to target CXCR4 expressed on tumor cells may be of benefit in patients with pancreatic cancer.

Epithelial-cadherin and beta-catenin expression changes in pancreatic intraepithelial neoplasia

PURPOSE

Cadherins and associated catenins are important mediators of epithelial cell-cell adhesion, as well as the Wnt-signaling pathway. Significant changes in their expression or structure have been implicated in malignancy. This study aimed to investigate the epithelial-cadherin (E-cadherin) and beta-catenin expression changes during multistage, pancreatic ductal carcinogenesis.

EXPERIMENTAL DESIGN

Ninety-four Whipple resection specimens were retrieved from the surgical pathology files of the University Health Network (Toronto, Canada), from which tissue microarray blocks containing 36 pancreatic ductal adenocarcinomas, 34 PanIN-1A lesions, 28 PanIN-1B lesions, 27 PanIN-2 lesions, 16 PanIN-3 lesions, and 32 normal ducts were constructed. The E-cadherin, beta-catenin, and the phosphorylated glycogen synthase kinase-3beta of the Wnt/beta-catenin pathway were immunohistochemically evaluated in these duct/PanIN lesions.

RESULTS

There was marked increase in the cytoplasmic E-cadherin expression in PanIN lesions (P < 0.0001) and adenocarcinoma (P = 0.005) compared with normal pancreatic ducts. In contrast, reduced/loss of E-cadherin membranous expression was also significant in ductal adenocarcinoma compared with both the PanIN lesions (P < 0.0001) and normal ducts (P = 0.05). The beta-catenin expression showed significantly more frequent aberrant nuclear localization in high-grade PanIN lesions, particularly PanIN2 and in adenocarcinoma compared with normal ducts or low grade PanIN lesions (P < 0.0001). However, there was a lack of correlation between phospho(Ser9)-glycogen synthase kinase-3beta cytoplasmic expression and beta-catenin aberrant nuclear expression (P = 0.07).

CONCLUSIONS

Aberration in the expression of E-cadherin and its associated beta-catenin is evident in pre-invasive (PanIN) neoplastic pancreatic duct cells, suggesting involvement of pathways leading to beta-catenin stabilization during pancreatic duct cell carcinogenesis.

Proendocrine genes coordinate the pancreatic islet differentiation program in vitro

In the developing pancreas, the basic helix-loop-helix (bHLH) protein Neurogenin3 (Ngn3) specifies which precursor cells ultimately will become endocrine cells and initiates the islet differentiation program. NeuroD1, a closely related bHLH protein and a downstream target of Ngn3, maintains the differentiation program initiated by Ngn3. We have developed an in vitro model of Ngn3-dependent differentiation by infecting pancreatic duct cell lines with an Ngn3-expressing adenovirus. We found that both Ngn3 and its downstream target NeuroD1 activated the islet differentiation program in these cells by inducing the expression of genes with early roles in the differentiation cascade, as well as genes characteristic of fully differentiated islet cells. Induction of these genes, as exemplified by the insulin1 gene, involved alteration of the local chromatin structure. Interestingly, the subsets of genes activated by Ngn3 and NeuroD1 were not completely overlapping, indicating that these two bHLH proteins serve specific functions in the development of the endocrine pancreas. In addition, microarray gene expression analysis identified a previously uncharacterized group of Ngn3-induced genes with potentially important roles in islet development and function. These studies demonstrate how Ngn3 initiates islet differentiation and provide us with a model for testing methods for producing islet cells for people with diabetes.

Successful growth and characterization of mouse pancreatic ductal cells: functional properties of the Ki-RAS(G12V) oncogene

BACKGROUND & AIMS

The Ki-RAS oncogene is altered in pancreatic ductal neoplasms. Pancreatic ductal cells (PDCs) were purified from cytokeratin 19 (K19)-Ki-RAS(G12V) transgenic mice and control littermates to identify properties of Ki-Ras activation in a cell-type-specific context. Because Ki-RAS mutation has prognostic significance in patients treated with radiation, we studied the influence of Ki-RAS status on radiation survival.

METHODS

Pancreatic ductal fragments from mice with Ki-RAS(G12V) mutation or wild-type (WT)-Ki-RAS were cultured. Growth curves, electron microscopy, flow cytometry, and analysis of signaling and cell-cycle proteins were established. Farnesyltransferase inhibitor (FTI) treatment with R115777 before and after irradiation was used to determine the effect of Ki-Ras farnesylation on cell survival.

RESULTS

PDCs from WT and K19-Ki-RAS(G12V) mice had features of ductal cells with formation of 3-dimensional structures on collagen without differences in morphology, growth, and cell-cycle distribution. This may result from up-regulation of p16INK4 and p27(Kip1) and lack of hyperstimulation of the mitogen-activated protein kinase pathway in Ki-RAS(G12V) PDCs. No differences in radiation survival between Ki-RAS(G12V) PDCs and WT PDCs were observed. However, Ki-RAS(G12V) PDCs expressing mutant p53(V143A) had enhanced survival compared with WT PDCs transduced with p53(V143A). R115777 treatment sensitized Ki-RAS(G12V) PDCs and Ki-RAS(G12V)/p53(V143A) PDCs, but not WT PDCs.

CONCLUSIONS

Novel characterization of murine WT PDCs and Ki-RAS(G12V) PDCs is described. Induction of cell-cycle regulators and lack of mitogen-activated protein kinase hyperstimulation likely are responsible for constraining activated Ki-RAS(G12V)-mediated proliferation. Because its activation was required for sensitization by an FTI, R115777 may be useful against pancreatic tumors expressing oncogenic Ki-Ras.

Conditional transformation of mouse pancreatic epithelial cells: an in vitro model for analysis of genetic events in pancreatocarcinogenesis

Pancreatic ductal adenocarcinomas arise through the accumulation of certain genetic alterations including ras, p16, p53, and DPC4. We found that activation of ras and inactivation of p53 could cooperatively induce in vitro tumorigenicity in conditionally immortalized pancreatic epithelial (IMPE) cells. IMPE cells were established from transgenic mice bearing a temperature-sensitive mutant SV40 Large T (LT) antigen. IMPE cells grew continuously under permissive conditions (33 degrees C with interferon-gamma), but rapidly suffered growth arrest under non-permissive conditions (39 degrees C without interferon-gamma). The cells showed strong expression of E-cadherin and beta-catenin as epithelial markers, and cytokeratin 19, a specific ductal cell marker. Cell proliferation under permissive conditions was associated with down-regulation of p21 expression through inactivation of p53 after overexpression of LT antigen. Intriguingly, the shift from the permissive to non-permissive culture conditions caused G2/M arrest of IMPE cells. Although the cells did not form colonies when cultured in soft agar without activation of ras, cells with ras activation via an adenovirus vector formed colonies under permissive conditions. These findings suggest that activation of ras and inactivation of p53 can cooperatively induce anchorage-independent growth of IMPE cells. This cell line might be useful for studying the processes involved in pancreatocarcinogenesis.

Identification of human polo-like kinase 1 as a potential therapeutic target in pancreatic cancer

Pancreas cancer is the fourth leading cause of cancer-related death in adults in the United States. New molecular targets for diagnosis and therapy of this disease are desperately needed. In this study, we report on the mitotic serine-threonine kinase polo-like kinase 1 (Plk1) in pancreatic cancer. Plk1 mRNA was found to be overexpressed in 9 of 10 tested pancreatic cancer cell lines and in 4 of 4 tested human tumors. Immunohistochemical staining of a pancreatic tissue microarray showed that 26 of the 35 tumors taken directly from patients overexpressed Plk1. We also examined the effects of depleting Plk1 in pancreatic cancer cells by the use of antisense oligonucleotides. Antisense-treated pancreatic cancer cells showed cell cycle arrest in G2-M as well as a drastic reduction in proliferation rates. These data suggest that Plk1 is a potential therapeutic target in devising a treatment for patients with pancreatic cancer.

Pancreatic carcinoma cells express neuropilins and vascular endothelial growth factor, but not vascular endothelial growth factor receptors

BACKGROUND

Neuropilins (NRPs) are characterized as coreceptors of vascular endothelial growth factor (VEGF). In the current study, the authors assessed the expression of NRPs, VEGF, and vascular endothelial growth factor receptors (VEGFRs), as well as VEGF-induced cell proliferation, in pancreatic carcinoma cell lines and tissue specimens.

METHODS

Human pancreatic carcinoma cell lines (Panc-1 and MIA PaCa-2), normal human pancreatic ductal epithelial cells (HPDE), and human umbilical vein endothelial cells (HUVECs) were cultured. Human pancreatic adenocarcinoma tissue specimens were also studied. Expression levels of NRPs, VEGFRs, and VEGF were determined by real-time polymerase chain reaction analysis and immunostaining. Cell proliferation was examined using a [3H]thymidine incorporation assay.

RESULTS

Both NRP-1 and NRP-2 were expressed in Panc-1 cells, HPDE cells, and HUVECs but were expressed minimally in MIA PaCa-2 cells. Panc-1 expressed 30 times more NRP-1 mRNA than NRP-2 mRNA. NRP-1 levels in Panc-1 cells were 5.3 times higher than in HPDE cells but were similar to NRP-1 levels in HUVECs. NRP-2 levels in Panc-1 cells were similar to NRP-2 levels in HPDE cells but lower than NRP-2 levels in HUVECs. Expression of all three VEGFRs was observed only in HUVECs. However, VEGF mRNA was detected in all cell types except for HUVECs. NRP-1 immunoreactivity levels were much higher than NRP-2 immunoreactivity levels in Panc-1 and human pancreatic adenocarcinoma tissue specimens, whereas VEGFRs were not detected in either of these two settings. In response to VEGF165, [3H]thymidine incorporation in Panc-1 cells increased significantly (by 61%; P < 0.01). A monoclonal antibody against human NRP-1 significantly blocked VEGF-induced cell proliferation in Panc-1 cells.

CONCLUSIONS

The pancreatic carcinoma cell line Panc-1 and adenocarcinoma tissue specimens expressed high levels of NRP-1 and VEGF, but not VEGFRs, and exogenous VEGF significantly increased NRP-1-mediated, but not VEGFR-mediated, Panc-1 cell proliferation. These data suggested that NRP-1 may be involved in the pathogenesis of pancreatic carcinoma.

Characterization of gap junctional intercellular communication in immortalized human pancreatic ductal epithelial cells with stem cell characteristics

INTRODUCTION

Gap junctional intercellular communication has been implicated in the homeostatic regulation of cell growth, differentiation, and apoptosis. Cancer cells, which have been viewed as "partially blocked stem cells," and which lack the ability for growth control, terminal differentiation, and apoptosis, also lack functional gap junctional communication.

AIMS AND METHODOLOGY

A clone of a human pancreatic ductal epithelial cell line, H6c7, derived after immortalization with human papilloma virus, was used to examine gap junctional intercellular communication and the ability to differentiate under different growth conditions.

RESULTS

The cells showed characteristic epithelial morphology on standard tissue culture dishes. When placed on Matrigel they showed phenotypical changes with extensive ductal organization and budding structures. In growth medium containing hormones and growth factors, these cells were gap junctional intercellular communication (GJIC)-incompetent. In the presence of c-AMP elevating agents, isobutylmethylxanthine, and forskolin, in basal medium that did not contain the hormones and growth factors, the cells became GJIC-competent and expressed connexin43 gap junction protein within 48 hours after treatment. RT-PCR analyses of the cells under different growth conditions showed that the cells expressed, and genes when cultured in the basal medium with c-AMP elevating agents. They also expressed the gene that did not change with c-AMP treatment. H6c7 cells also have the capacity to turn on an ectopic insulin promoter reporter gene.

CONCLUSION

Our data suggest that the immortalized H6c7 cells retain stem-like characteristics and have the potential to differentiate into duct-like structures and perhaps insulin-producing cells.

Characterization of gene expression profiles in intraductal papillary-mucinous tumors of the pancreas

The molecular pathology of precursor lesions leading to invasive pancreatic ductal adenocarcinomas remains relatively unknown. We have applied cDNA microarray analysis to characterize gene expression profiles in a series of intraductal papillary-mucinous tumors (IPMTs) of the pancreas, which represents one of the alternative routes of intraepithelial progression to full malignancy in the pancreatic duct system. Using a cDNA microarray containing 4992 human genes, we screened a total of 13 IPMTs including nine noninvasive and four invasive cases. Expression change in more than half of the tumors was observed for 120 genes, ie, 62 up-regulated and 58 down-regulated genes. Some of the up-regulated genes in this study have been previously described in classical pancreatic carcinomas such as lipocalin 2, galectin 3, claudin 4, and cathepsin E. The most highly up-regulated genes in IPMTs corresponded to three members of the trefoil factor family (TFF1, TFF2, and TFF3). Immunohistochemistry performed on five genes found to be differentially expressed at the RNA level (TFF1, TFF2, TFF3, lipocalin 2, and galectin 3) showed a good concordance between transcript level and protein abundance, except for TFF2. Hierarchical clustering organized the cases according to the dysplastic and invasive phenotype of theIPMTs. This analysis has permitted us to implicate several genes (caveolin 1, glypican 1, growth arrest-specific 6 protein, cysteine-rich angiogenic inducer 61) in tumor progression. The observation that several genes are differentially expressed both in IPMTs and pancreatic carcinomas suggests that they may be involved at an early stage of pancreatic carcinogenesis.

Peptide differential display of serum-free conditioned medium from cancer cell lines

Conditioned medium (CM) from cultured cells is a source for screening small peptides of therapeutic or diagnostic value in cancer research. Mass spectrometry has recently enabled the profiling of peptides present in biological samples. We report a single-step extraction method to increase a chance to discover small peptides with a starting volume of 750 microl of serum-free CM. In combination with protein chip mass spectrometry, our protocol will contribute to the discovery of target peptides.