Michael Kersting

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.

p16INK4a is a Prognostic Marker in Resected Ductal Pancreatic Cancer: An Analysis of p16INK4a, p53, MDM2, an Rb

ObjectiveTo identify the prognostic relevance of the G1/S cell cycle regulator genes p16INK4a, p53, MDM2, and Rb in patients with resected ductal pancreatic cancer (PC). Summary Background DataThe tumor suppressor genes p16INK4a, p53, and Rb are altered in PC in 27% to 95%, 40% to 70%, and 5%, respectively. The role of MDM2 is not clearly defined in PC. The prognostic value of these cell cycle regulators has not been clarified. MethodsSixty-two patients with PC with complete follow-up who underwent potentially curative resections were included in the study. An extreme group analysis was performed including the 20 patients with the shortest survival and the 20 patients with the longest survival. Protein expression of p16, p53, MDM2, and Rb was investigated, and mutation analysis of p16INK4a and p53 was performed. p16INK4a promoter hypermethylation was examined by methylation-specific polymerase chain reaction. ResultsSignificantly more tumors in the shortest-surviving patients had p16INK4a alterations compared with tumors of the longest-surviving patients. In contrast, the frequency of p53 alterations was not significantly higher in the shortest-surviving versus the longest-surviving groups. Stabilization of MDM2 and loss of Rb expression were identified in a minority of tumors, independent of survival length. ConclusionsThe presence of p16INK4a alterations in resected tumors of patients with PC is connected with a worse prognosis, indicating patients that might benefit from adjuvant therapy regimens. p53 alterations, MDM2 overexpression, and loss of Rb expression could not be identified as prognostic markers from this study, but a larger study with greater statistical power might show a different result with regard to p53.

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.

Tumor-suppressing pathways in cystic pancreatic tumors.

Introduction and Aims Serous and mucinous cystic pancreatic tumors have different clinical behavior. We evaluated whether they also have genotypic differences by analyses of the tumor suppressor genes p16INK4a, p53, and DPC4. Methodology Seven serous cystadenomas (SCA) and seven malignant mucinous cystadenocarcinomas (MCC) were analyzed for alterations in the tumor suppressor genes p16INK4a, p53, and DPC4 by single-strand conformational variant analysis, direct sequencing, and immunohistochemical analysis. Methylation-specific polymerase chain reaction analysis was performed to identify p16INK4a promoter hypermethylation. Clinical data were compared with genetic data. Results None of the seven patients with SCAs but five of the seven patients with MCCs died of the tumor after a median follow-up of 44.5 months (range, 4–169 months). All seven MCCs had alterations in at least one tumor suppressor gene compared with none of the seven SCAs. Of the seven MCCs, three had inactivating p16INK4a promoter hypermethylation, five had p53 alterations, and three had DPC4 mutations. Conclusions The tumor suppressor genes p16INK4a, p53, and DPC4 appear to play an important role in the tumorigenesis of MCCs but not SCAs. These molecular data underscore the clinical and histologic differences of serous and mucinous cystic pancreatic tumors.

The p16/Cdkn2a/Ink4a Gene Is Frequently Deleted in Nitrosourea-Induced Rat Glial Tumors

The present study investigates nitrosourea-induced rat (Rattus norvegicus) glioma cell lines for the functional status of the p16/Cdkn2a/Ink4a gene, which encodes the p16 cdk4 inhibitor and the alternative reading frame protein, p19ARF. We detected homozygous deletions of the p16/Cdkn2a/Ink4a gene locus in 4 of 5 glioma cell lines (C6, F98, RG2, and RGL.3), but not in the 9L gliosarcoma cell line or in a rat primary fibroblast cell line. RT-PCR demonstrated expression of the p16 and p19ARF mRNAs only in 9L cells and in rat fibroblasts. Comparative genomic in situ hybridization showed that the copy number of rat chromosome RNO5 was not altered in any of the glioma cell lines investigated, indicating that the deletions result from a discrete loss in the region of the p16/Cdkn2a/Ink4a locus. This is the first report of p16/Cdkn2a/Ink4a deletions present in nitrosourea-induced rat glioma cell lines. Since this genetic alteration is also commonly observed in human malignant glial tumors, our results validate the use of chemically induced rat glioma cell lines as an experimental model in the development of gene therapy strategies.

Multiple primary tumors as an indicator for p16INK4a germline mutations in pancreatic cancer patients

Multiple primary tumors in pancreatic cancer patients might indicate a genetic predisposition to the development of malignancies. In this study we evaluated whether the mutation rate of the TP53 and p16INK4a genes of pancreatic cancers differs in pancreatic cancer patients with and without multiple primaries. Furthermore, we investigated whether pancreatic cancer patients with multiple primaries carry germline mutations in either p16INK4a, TP53, or BRCA2 tumor suppressor genes to detect a genetic alteration that predisposes to the development of different primaries. Fourteen (23%) of 60 pancreatic cancer patients developed histologically verified additional primaries during their lifetimes. Normal constitutional and tumor DNA of the 14 patients with a positive cancer history, but negative family history, were analyzed for p16INK4a, TP53, and BRCA2 mutations by single-strand conformational variant (SSCV) analysis and direct sequencing. Hypermethylation of the p16INK4a promoter region in pancreatic cancers was identified by methylation-specific polymerase chain reaction (PCR; MSP). Four of 14 pancreatic carcinomas carried somatic intragenic p16INK4a mutations, and another four tumors revealed hypermethylation of the p16INK4a promoter region. Somatic intragenic TP53 mutations were identified in six of 14 tumors. None of the pancreatic cancer patients carried TP53 or BRCA2 germline mutations. In contrast, one of 14 pancreatic cancer patients with multiple primaries carried the p16INK4a mutation A68V in his germline. This mutation was localized in the conserved second ankyrin repeat of p16INK4a and did not occur in 100 control patients. The frequency of somatic TP53 and p16INK4a mutations in pancreatic cancer is similar in patients with and without multiple primaries. TP53 and BRCA2 germline mutations seem not to be significantly associated with the occurrence of multiple primaries in pancreatic cancer patients. However, p16INK4a germline mutations might be causative for tumor development in some pancreatic cancer patients with multiple primaries. The genetic investigation of patients with accumulation of different cancers even without a positive family history may be a new approach for the understanding of the relation of different cancers.

p16 INK4a -Alterationen in Gastrinomen und nicht-funktionellen neuroendokrinen Inselzellkarzinomen

Endokrine Pankreastumoren sind selten und machen etwa 1–5% a11er Pankreastumoren aus. 90% der endokrinen Pankreastumoren, vor allem Insulinome und Gastrinome, sind durch eine extensive Hormonsekretion charakterisiert. Bei 10 % der endokrinen Pankreastumoren handelt es sich um nicht-funktionelle Tumoren ohne Hormonsekretion [1]. Etwa 10–20% der endokrinen Pankreastumoren sind mit der autosomal dominant vererbten Multiplen Endokrinen Neoplasie Typ 1 assoziiert [2]. Das Wissen um genetische Veranderungen, die mit der Initiierung and Progression der Inselzelltumoren einhergehen, ist sehr beschrankt und die vorliegenden Daten basieren auf sehr kleinen Fallzahlen. Das p16 INK4a Tumorsuppressorgen auf Chromosom 9p21 ist bei einer Vielzahl humaner Tumoren, einschlieslich denen des exokrinen Pankreas, durch Mutation, homozygote Deletion oder aberrante Promotorhypermethylierung inaktiviert [3, 4]. Aufgrund der engen anatomischen Beziehung zwischen endokrinem und exokrinem Pankreas haben wir 10 nicht-funktionelle Inselzellkarzinome und 8 Gastrinome auf Alterationen im p16 INK4a Tumorsuppressorgen untersucht.