Babette Simon

Analysis of β-Catenin Gene Mutations in Pancreatic Tumors

Background/Aim: Mutations of the adenomatous polyposis coli (APC) tumor suppressor gene have been described in a subset of pancreatic carcinomas. The APC gene modulates the β-catenin-Tcf pathway. The major player in this pathway is the β-catenin protein encoded by the β-catenin gene. A variety of different tumors, including colon, prostate, endometrial, and hepatocellular carcinomas, carry mutations in exon 3 of the β-catenin gene. The aim of this study was to determine the role of the β-catenin gene in the genesis of exocrine and endocrine tumors of the pancreas. Methods: 78 ductal pancreatic adenocarcinomas, 14 ductal pancreatic cancer cell lines, and 33 endocrine pancreatic tumors were evaluated for mutations in exon 3 of the β-catenin gene by single-strand conformation polymorphism analysis and direct DNA sequencing. In addition, 40 ductal pancreatic adenocarcinomas were analyzed for intracellular β-catenin accumulation by immunohistochemistry, indicating alterations of the β-catenin gene. Results: Neither the 111 exocrine and endocrine pancreatic tumors nor the 14 pancreatic cancer cell lines carried mutations in exon 3 of the β-catenin gene. Intracellular β-catenin accumulation was not identified in any of the 40 pancreatic adenocarcinomas. Conclusion: These data suggest that the β-catenin gene as the major player of the β-catenin-Tcf pathway does not play an important role in the genesis of pancreatic tumors.

Management of nonfunctioning islet cell carcinomas.

Tumors arising from the pancreatic islet cells are rare and represent a heterogeneous group of benign or malignant lesions. Most tumors present with well characterized syndromes, whereas others appear to be nonfunctioning. The clinical features of 11 men and 7 women with nonfunctioning islet cell carcinomas operated on between 1983 and 1998 were reviewed. The median patient age was 53.5 years (range 26–74 years). The most frequent presenting symptoms were abdominal pain (13 patients), weight loss (7 patients), and obstructive jaundice (4 patients). Gut hormone profiles were normal in all patients. Abdominal sonography and computed tomography localized the tumor in 17 patients, and correct prediction of an endocrine tumor was achieved in 12 patients. Six of seven patients showed a hypervascular tumor upon angiograpy, and seven of eight patients preoperatively had positive somatostatin receptor scintigraphy. At operation, regional or distant metastases were present in 15 (83%) and 6 (33%) patients, respectively. Eleven patients underwent potentially curative resections, and the remaining seven patients were managed palliatively by resection (four patients) or bypass procedures (three patients). Three patients had up to three more resection for metastases. Eight patients received postoperative octreotide, interferon α therapy, or both. The overall cumulative 5- and 10-year survival rates were 65.4% and 49.1%, respectively. Of the 11 patients who underwent curative resection, 10 were alive after a median follow-up of 63 months (range 7–180 months), but only 5 are free from disease. Although surgical cure is rare in nonfunctioning islet cell carcinomas, significant long-term palliation can be achieved in a large proportion of patients with an aggressive surgical approach and, when indicated, additional medical therapy.

Frequent alterations of the tumor suppressor genes p53 and DCC in human pancreatic carcinoma

BACKGROUND/AIMS The pathogenesis of pancreatic cancer is poorly understood. The multigenetic nature of carcinogenesis has been best documented in colon cancer. The relevance of this model was suggested for other epithelial tumors. Only advanced stages of pancreatic cancer are usually detected because of late diagnosis. Analysis of accumulated, diverse genetic changes could allow further understanding of putative mechanisms involved in tumor development. Activated c-Ki-ras oncogene has been shown to be a frequent event. However, additional alterations of tumor suppressor genes are expected. Therefore, concomitant genetic changes of p53 and deleted in colon carcinoma (DCC) in pancreatic carcinoma cell lines and primary tumors were analyzed. METHODS p53 protein and transcript expression were revealed by immunocytochemistry and immunohistochemistry, immunoassay, and Northern blot analysis. p53 mutations were identified by sequence analysis. DCC expression was investigated by reverse-transcription polymerase chain reaction. RESULTS p53 overexpression was observed in 9 of 12 cell lines. p53 point mutations were confirmed in seven cell lines overexpressing p53. The majority of cell lines showed concomitant p53 and DCC alterations. Four of 6 primary tumors overexpressing p53 also showed loss of DCC expression. CONCLUSIONS p53 and DCC genetic changes are associated with pancreatic cancer and the frequently activated c-Ki-ras oncogene. Therefore, the multihit model of carcinogenesis could prove relevant for pancreatic cancer.

Low Frequency of p16INK4a Alterations in Insulinomas

Background/Aims: The molecular mechanisms contributing to the tumorigenesis of insulinomas are poorly understood. Disruption of the cell cycle due to inactivation of the p16INK4a tumor-suppressor gene was identified in a variety of human tumors, including gastrinomas and nonfunctioning endocrine pancreatic carcinomas. In this study the role of p16INK4a in the tumorigenesis of insulinomas was evaluated. Methods: Seventeen insulinomas (14 benign, 3 malignant) were analyzed for genetic alterations in the p16INK4a tumor-suppressor gene by SSCP, PCR-based deletion and methylation-specific assays. p16 expression was determined by immunohistochemistry. Results: One malignant insulinoma showed a homozygous deletion of p16INK4a and another two benign insulinomas revealed aberrant methylation of the p16INK4a promoter region. All three tumors lacked p16 expression according to immunohistochemistry. None of the insulinomas carried intragenic p16INK4a mutations. In total, 17% of insulinomas had p16INK4a alterations. Conclusions: The p16INK4a tumor-suppressor gene contributes to tumorigenesis in only a small subset of insulinomas.

The α6-integrin receptor in pancreatic carcinoma

Abstract Background/Aims: The α 6 -containing integrin was suggested to be involved in the process of tumor invasion and metastasis. Therefore, the aim of the study was to investigate the expression and function of this adhesion receptor in pancreatic carcinoma. Methods: Integrin expression was investigated in pancreatic tissue and tumor cell lines using immunohistochemistry. Radioimmunoprecipitation was used to determine the complex composition of α 6 . To analyze the function of the α 6 -containing integrin in pancreatic cancer, in vitro adhesion, migration, and invasion experiments were performed. Results: The α 6 -containing integrin was differentially expressed in normal pancreas and pancreatic carcinoma. Immunoprecipitation of different pancreatic carcinoma cell lines showed that α 6 was expressed together with the β 4 subunit as α 6 β 4 complex. However, adhesion of pancreatic cancer cells to laminin could be inhibited with anti-α 6 and anti-β 1 integrin antibodies but not by anti-β 4 integrin antibody. Migration of the cells through laminin was almost completely inhibited by anti-β 1 antibody but not by other anti-integrin antibodies. Tumor cell invasion through a reconstituted basement membrane was only slightly inhibited by anti-α 6 antibody. In contrast, a marked inhibition was observed using anti-β 1 antibodies, anti-α 2 -anti-α 5 antibodies, and RGDS. Conclusions: The α 6 -containing integrin is a laminin adhesion receptor in pancreatic carcinoma cells, possibly involved in tumor invasion through the basement membrane.

Higher frequency of DPC4/Smad4 alterations in pancreatic cancer cell lines than in primary pancreatic adenocarcinomas

The tumor suppressor gene DPC4/Smad4 at 18q21.1 is inactive in about 50% of pancreatic carcinoma xenografts and cell lines. However, the role of DPC4 in the multistep carcinogenesis of primary pancreatic adenocarcinomas remains uncertain. Therefore, we examined 45 primary human pancreatic adenocarcinomas and 12 pancreatic cancer cell lines for DPC4 alterations by single-strand conformational variant (SSCV) analysis and a PCR-based deletion assay. DPC4 was inactivated by either homozygous deletion or point mutation in 6 of 12 cell lines (50%). None of the primary pancreatic carcinomas carried a DPC4 mutation, although 66% revealed LOH of 18q21 sequences. These findings suggest that inactivation of DPC4 occurs more frequently in tumor-derived cell lines than in primary pancreatic adenocarcinomas. In addition, another, yet unidentified, tumor suppressor gene(s) may be linked with the frequent LOH of 18q21 in primary pancreatic adenocarcinomas.

Expression spectrum and methylation-dependent regulation of melanoma antigen-encoding gene family members in pancreatic cancer cells

Human MAGE and GAGE genes encode tumor-specific antigens presented by HLA I molecules recognized on tumor cells by cytolytic T lymphocytes. To determine if pancreatic cancer patients would be suitable for MAGE- or GAGE-based immunotherapy, the expression frequency of MAGE-A1, -A2, -A3, -A4, -A6 and GAGE1–8 geneswas assessed in 15 pancreatic tumor cell lines and 23 pancreatic tumor specimens using reverse transcription-polymerase chain reaction (RT-PCR). In 67% of the cell lines at least one of the MAGE-A geneswas detected, 53% revealed concomitant expression of two or more genes. GAGE1–8 expression was detected in 47% of the cell lines. In the primary pancreatic tumors, MAGE-A analysis revealed exclusive MAGE-A1 and MAGE-A2 gene expression in 26 and 30% of the specimens, respectively, independent from clinicopathologic factors. Treatment of MAGE-A expression-negative pancreatic tumor cells with the demethylating agent 5-aza-2′-deoxycytidine could activate MAGE-A1, MAGE-A2, MAGE-A3, MAGE-A4 and GAGE transcription suggesting silencing due to promoter methylation. Interestingly, a metastatic lesion to the liver revealed concomittant expression of MAGE-A1, -A2, -A3 and -A6 consistent with a more pronounced genome-wide hypomethylation in metastases. Therefore, a subset of pancreatic cancer patients could be eligible for active, specific immunotherapy directed against MAGE-A antigens and demethylating agents could increase the number of candidate patients.

Predictive Genetic Screening and Clinical Findings in Multiple Endocrine Neoplasia Type I Families

Abstract. Germline mutations of the MEN1 gene have been identified as the causative genetic defect of multiple endocrine neoplasia type I (MEN-I), an autosomal dominantly inherited condition. To establish the basis for predictive family screening we evaluated the spectrum of MEN1 gene mutations in MEN-I patients treated at our institution. Relatives at risk were subjected to predictive genetic screening after genetic counseling. Gene carriers were subjected to extensive clinical screening for MEN-I, including biochemical tests for basal hormone concentrations in blood and urine, a standardized meal stimulation test and imaging procedures (ultrasonography, computed tomography, magnetic resonance imaging). Among index patients of 15 independent MEN-I kindreds, 14 heterozygous MEN1 germline mutations were identified by single-strand conformational variant analysis (SSCV) and direct DNA sequence analysis. Of 51 individuals at risk, 26 predictively tested relatives with the wild-type MEN1 gene could be excluded from further screening procedures because they had not inherited the disease. In all previously presumed unaffected relatives with the mutant gene, our extensive clinical screening program revealed at least one manifestation of MEN-I. Furthermore, 22 additional diagnoses could be established in identified MEN-I patients. We show that mutation analysis enables predictive genetic screening for MEN-I families, providing a valuable tool for genetic counseling and clinical management. An extensive clinical screening program focusing on genetically proven individuals at risk allows detection of MEN-I manifestations at an early, asymptomatic stage of the disease. Controlled, prospective studies are now required to prove whether timely appropriate treatment on the basis of predictive screening might help improve disease-related quality of life and prolong life expectancy in MEN-I kindreds.

Transient transcriptional activation of gastrin during sodium butyrate-induced differentiation of islet cells

Transient expression of pancreatic gastrin corresponds to a period of rapid islet cell development. After birth gastrin expression silencing is coincidental with islet cell terminal differentiation, while persistent expression is accompanied with nesidioblastosis and reexpression observed in islet cell tumors. Experiments with transgenic animals suggested that gastrin might act synergistically with growth factors to stimulate islet cell development. The present study intended to establish an in vitro cell culture model to analyse the molecular events controlling gastrin gene activation and repression dependent on islet cell differentiation. Sodium butyrate, a proliferation-arresting compound has previously been shown to differentiate insulinoma cells while increasing insulin production. The present paper demonstrates concomitant transient increase in gastrin mRNA, intracellular and secreted gastrin during sodium butyrate treatment. Increased gastrin expression was due to activation or derepression of gastrin promoter activity as revealed by promoter analyses. This in vitro model mimics the expression pattern of gastrin and insulin observed during fetal islet cell development and provides an excellent tool to analyse the molecular mechanisms controlling gastrin gene activation and selective repression during islet cell differentiation.

Identification of Methylation-Associated Gene Expression in Neuroendocrine Pancreatic Tumor Cells

Background: CpG islands methylation is the main epigenetic modification found in human tumors leading to transcriptional silencing of certain tumor suppressor genes. Reacquisition of p16/CDKN2A tumor suppressor gene expression by 5-aza-2′-deoxycytidine results in concurrent growth inhibition of neuroendocrine pancreatic tumor cells. However, the growth suppressive effects of 5-aza-2′-deoxycytidine is unlikely to be solely attributable to the restored p16/CDKN2A function, but rather a consequence of re-expression of additional genes silenced by de novo methylation. In an effort to validate DNA methylation as an important mechanism in neuroendocrine tumorigenesis and metastatic spread, we attempted to isolate methylation-specific transcripts in neuroendocrine pancreatic tumor cells. Methods: Differentially expressed methylation-associated genes were identified by cDNA-representational difference analysis (cDNA-RDA). Differential expression was confirmed by semiquantitative RT-PCR using insert specific primers. Results: We identified 48 differently expressed gene fragments and methylation-associated expression was confirmed by semi-quantitative RT-PCR. 52,3% (25 of 48) showed elevated expression levels after 5-aza-2′-deoxycytidine treatment, whereas 47.7% revealed lower expression levels. 7 fragments showed homology to genes with unknown function. Interestingly, 5-aza-2′-deoxycytidine treatment led to re-expression of cofillin whereas matriptase expression levels were significantly lower. Both genes have been associated with metastastic spread and tissue invasion. The other differentially expressed genes play an unknown role in the course of neuroendocrine tumorigenesis. Conclusion: DNA methylation appears to be an important molecular mechanism in the process of neuroendocrine pancreatic tumorigenesis and metastatic spread. The definition of DNA methylation patterns associated with neuroendocrine pancreatic tumors might open up the potential for a new sensitive diagnostic tool and might serve as a new antitumor target.