Michel M. Ouellette

Absence of cancer-associated changes in human fibroblasts immortalized with telomerase

The ectopic expression of telomerase in normal human cells results in an extended lifespan, indicating that telomere shortening regulates the timing of cellular senescence. As telomerase expression is a hallmark of cancer, we investigated the long–term effects of forced expression of human telomerase catalytic component (hTERT) in normal human fibroblasts. In vitro growth requirements, cell–cycle checkpoints and karyotypic stability in telomerase–expressing cells are similar to those of untransfected controls. In addition, co–expression of telomerase, the viral oncoproteins HPV16 E6/E7 (which inactivate p53 and pRB) and oncogenic HRAS does not result in growth in soft agar. Thus, although ectopic expression of telomerase in human fibroblasts is sufficient for immortalization, it does not result in changes typically associated with malignant transformation.

Sonic hedgehog promotes desmoplasia in pancreatic cancer

Purpose: We investigated the contribution of Sonic hedgehog (SHH) to pancreatic cancer progression. Experimental Design: We expressed SHH in a transformed primary ductal-derived epithelial cell line from the human pancreas, transformed hTert-HPNE (T-HPNE), and evaluated the effects on tumor growth. We also directly inhibited the activity of SHH in vivo by administering a blocking antibody to mice challenged orthotopically with the Capan-2 pancreatic cancer cell line, which is known to express SHH and form moderately differentiated tumors in nude mice. Results: Our data provide evidence that expression of SHH influences tumor growth by contributing to the formation of desmoplasia in pancreatic cancer. We further show that SHH affects the differentiation and motility of human pancreatic stellate cells and fibroblasts. Conclusions: These data suggest that SHH contributes to the formation of desmoplasia in pancreatic cancer, an important component of the tumor microenvironment.

K-Ras Promotes Growth Transformation and Invasion of Immortalized Human Pancreatic Cells by Raf and Phosphatidylinositol 3-Kinase Signaling

Mutational activation of the K-Ras oncogene is well established as a key genetic step in the development and growth of pancreatic adenocarcinomas. However, the mechanism by which aberrant Ras signaling promotes uncontrolled pancreatic tumor cell growth remains to be fully elucidated. The recent use of primary human cells to study Ras-mediated oncogenesis provides important model cell systems to dissect this mechanism. We have used a model of telomerase-immortalized human pancreatic duct-derived cells (E6/E7/st) to study mechanisms of Ras growth transformation. First, we found that human papillomavirus E6 and E7 oncogenes, which block the function of the p53 and Rb tumor suppressors, respectively, and SV40 small t antigen were required to allow mutant K-Ras(12D) growth transformation. Second, K-Ras(12D) caused growth transformation in vitro, including enhanced growth rate and loss of density dependency for growth, anchorage independence, and invasion through reconstituted basement membrane proteins, and tumorigenic transformation in vivo. Third, we determined that the Raf, phosphatidylinositol 3-kinase (PI3K), and Ral guanine nucleotide exchange factor effector pathways were activated, although extracellular signal-regulated kinase (ERK) activity was not up-regulated persistently. Finally, pharmacologic inhibition of Raf/mitogen-activated protein kinase/ERK and PI3K signaling impaired K-Ras-induced anchorage-independent growth and invasion. In summary, our studies established, characterized, and validated E6/E7/st cells for the study of Ras-induced oncogenesis.

Early diagnosis of pancreatic cancer: neutrophil gelatinase-associated lipocalin as a marker of pancreatic intraepithelial neoplasia.

Pancreatic cancer is a highly lethal malignancy with a dismal 5-year survival of less than 5%. The scarcity of early biomarkers has considerably hindered our ability to launch preventive measures for this malignancy in a timely manner. Neutrophil gelatinase-associated lipocalin (NGAL), a 24-kDa glycoprotein, was reported to be upregulated nearly 27-fold in pancreatic cancer cells compared to normal ductal cells in a microarray analysis. Given the need for biomarkers in the early diagnosis of pancreatic cancer, we investigated the expression of NGAL in tissues with the objective of examining if NGAL immunostaining could be used to identify foci of pancreatic intraepithelial neoplasia, premalignant lesions preceding invasive cancer. To examine a possible correlation between NGAL expression and the degree of differentiation, we also analysed NGAL levels in pancreatic cancer cell lines with varying grades of differentiation. Although NGAL expression was strongly upregulated in pancreatic cancer, and moderately in pancreatitis, only a weak expression could be detected in the healthy pancreas. The average composite score for adenocarcinoma (4.26±2.44) was significantly higher than that for the normal pancreas (1.0) or pancreatitis (1.0) (P<0.0001). Further, although both well- and moderately differentiated pancreatic cancer were positive for NGAL, poorly differentiated adenocarcinoma was uniformly negative. Importantly, NGAL expression was detected as early as the PanIN-1 stage, suggesting that it could be a marker of the earliest premalignant changes in the pancreas. Further, we examined NGAL levels in serum samples. Serum NGAL levels were above the cutoff for healthy individuals in 94% of pancreatic cancer and 62.5% each of acute and chronic pancreatitis samples. However, the difference between NGAL levels in pancreatitis and pancreatic cancer was not significant. A ROC curve analysis revealed that ELISA for NGAL is fairly accurate in distinguishing pancreatic cancer from non-cancer cases (area under curve=0.75). In conclusion, NGAL is highly expressed in early dysplastic lesions in the pancreas, suggesting a possible role as an early diagnostic marker for pancreatic cancer. Further, serum NGAL measurement could be investigated as a possible biomarker in pancreatitis and pancreatic adenocarcinoma.

Two Inactive Fragments of the Integral RNA Cooperate To Assemble Active Telomerase with the Human Protein Catalytic Subunit (hTERT) In Vitro

ABSTRACT We have mapped the 5′ and 3′ boundaries of the region of the human telomerase RNA (hTR) that is required to produce activity with the human protein catalytic subunit (hTERT) by using in vitro assembly systems derived from rabbit reticulocyte lysates and human cell extracts. The region spanning nucleotides +33 to +325 of the 451-base hTR is the minimal sequence required to produce levels of telomerase activity that are comparable with that made with full-length hTR. Our results suggest that the sequence approximately 270 bases downstream of the template is required for efficient assembly of active telomerase in vitro; this sequence encompasses a substantially larger portion of the 3′ end of hTR than previously thought necessary. In addition, we identified two fragments of hTR (nucleotides +33 to +147 and +164 to +325) that cannot produce telomerase activity when combined separately with hTERT but can function together to assemble active telomerase. These results suggest that the minimal sequence of hTR can be divided into two sections, both of which are required for de novo assembly of active telomerase in vitro.

Nicotine/cigarette smoke promotes metastasis of pancreatic cancer through α7nAChR-mediated MUC4 upregulation

Despite evidence that long-term smoking is the leading risk factor for pancreatic malignancies, the underlying mechanism(s) for cigarette-smoke (CS)-induced pancreatic cancer (PC) pathogenesis has not been well established. Our previous studies revealed an aberrant expression of the MUC4 mucin in PC as compared with the normal pancreas, and its association with cancer progression and metastasis. Interestingly, here we explore a potential link between MUC4 expression and smoking-mediated PC pathogenesis and report that both cigarette smoke extract and nicotine, which is the major component of CS, significantly upregulates MUC4 in PC cells. This nicotine-mediated MUC4 overexpression was via the α7 subunit of nicotinic acetylcholine receptor (nAChR) stimulation and subsequent activation of the JAK2/STAT3 downstream signaling cascade in cooperation with the MEK/ERK1/2 pathway; this effect was blocked by the α7nAChR antagonists, α-bungarotoxin and mecamylamine, and by specific siRNA-mediated STAT3 inhibition. In addition, we demonstrated that nicotine-mediated MUC4 upregulation promotes the PC cell migration through the activation of the downstream effectors, such as HER2, c-Src and FAK; this effect was attenuated by shRNA-mediated MUC4 abrogation, further implying that these nicotine-mediated pathological effects on PC cells are MUC4 dependent. Furthermore, the in vivo studies showed a marked increase in the mean pancreatic tumor weight (low dose (100 mg/m3 total suspended particulate (TSP)), P=0.014; high dose (247 mg/m3 TSP), P=0.02) and significant tumor metastasis to various distant organs in the CS-exposed mice, orthotopically implanted with luciferase-transfected PC cells, as compared with the sham controls. Moreover, the CS-exposed mice had elevated levels of serum cotinine (low dose, 155.88±35.96 ng/ml; high dose, 216.25±29.95 ng/ml) and increased MUC4, α7nAChR and pSTAT3 expression in the pancreatic tumor tissues. Altogether, our findings revealed for the first time that CS upregulates the MUC4 mucin in PC via the α7nAChR/JAK2/STAT3 downstream signaling cascade, thereby promoting metastasis of PC.

Targeting telomerase-expressing cancer cells

•  Targeting telomerase‐expressing cancer cells •  Human telomeres act as a mitotic clock •  Telomerase expression and cellular lifespan ‐  Telomerase inhibition to block tumour growth •  Telomerase‐targeted immunotherapy •  Targeting telomerase‐expressing cells with oncolytic viruses •  Concluding remarks

Class III β-tubulin, a marker of resistance to paclitaxel, is overexpressed in pancreatic ductal adenocarcinoma and intraepithelial neoplasia

Aims:  Class III β‐tubulin (TUBB3) reduces microtubule stability and confers resistance to microtubule‐stabilizing taxanes, including paclitaxel and docetaxel. Pancreatic ductal adenocarcinomas show limited responsiveness to taxanes, but little is known of the underlying mechanisms. The aim of this study was to examine TUBB3 expression in pancreatic cancer cell lines, invasive pancreatic adenocarcinoma and pancreatic intraepithelial neoplasia (PanIN).

Palladin is overexpressed in the non-neoplastic stroma of infiltrating ductal adenocarcinomas of the pancreas, but is only rarely overexpressed in neoplastic cells

Background: It has recently been suggested that over expression of palladin in sporadic pancreatic cancer may contribute to pancreatic cancer’s invasive and migratory abilities. This hypothesis was based on reverse transcriptase-polymerase chain reaction analyses of bulk pancreatic tissue, yet pancreatic cancer is a complex admixture of neoplastic epithelial cells and desmoplastic stroma. Design: Immunohistochemical labeling of tissue microarrays was used to define the patterns of palladin protein expression in 177 ductal adenocarcinomas of the pancreas. Western blot analysis was used to determine the epitope(s) of palladin recognized by the antibody as well as the relative levels of palladin expression in short-term cultures of stromal fibroblasts, non-neoplastic ductal cells and pancreatic cancer cell lines. Results: Immunolabeling revealed that the palladin protein was strongly over expressed in non-neoplastic stromal cells in 171 (96.6%) of the 177 evaluable pancreatic cancers. By contrast, the over expression of palladin protein by the neoplastic epithelial cells relative to normal pancreatic epithelium was observed in only 22 (12.4%) of the 177 cancers. Western blot analysis confirmed that the antibody recognizes the ~90 kDa isoform of palladin, and demonstrated that fibroblast cell lines had higher expression of palladin than pancreatic cancer cell lines. Conclusions: The over expression of palladin relative to normal pancreas in the majority of pancreatic cancers is limited to non-neoplastic stromal cells. This observation highlights the limitations of relying on bulk tissues when analyzing gene expression. Since palladin is not over expressed in most pancreatic cancer cells, the over expression of palladin is not likely to be responsible for pancreatic cancer cells invasive and migratory abilities.

Notch2-positive progenitors with the intrinsic ability to give rise to pancreatic ductal cells

Pancreatic adenocarcinomas display foci of duct-like structures that are positive for markers of pancreatic ductal cells. The development of these tumors is promoted by conditions leading to acinar-to-ductal metaplasia, a process by which acinar cells are replaced by ductal cells. Acinar-to-ductal metaplasia has recently been shown to proceed through intermediary cells expressing Nestin. To create an in vitro system to study pancreatic adenocarcinomas, we had used an hTERT cDNA to immortalize primary cells of the human pancreas. In this report, we show that the immortalized cells, termed hTERT-HPNE cells, have the ability to differentiate to pancreatic ductal cells. Exposing hTERT-HPNE cells to sodium butyrate and 5-aza-2′-deoxycytidine lead to the formation of pancreatic ductal cells marked by the expression of MDR-1, carbonic anhydrase II, and the cytokeratins 7, 8, and 19. hTERT-HPNE cells were found to have properties of the intermediary cells formed during acinar-to-ductal metaplasia, which included their undifferentiated phenotype, expression of Nestin, evidence of active Notch signaling, and ability to differentiate to pancreatic ductal cells. These results provide further evidence for the presence in the adult pancreas of a precursor of ductal cells. hTERT-HPNE cells should provide a useful model to study acinar-to-ductal metaplasia and the role played by this process in pancreatic cancer development.