Frequent loss of heterozygosity at chromosome 3p14.2-3p21 in human pancreatic islet cell tumours

Nuclear BAP1 loss is common in intrahepatic cholangiocarcinoma and a subtype of hepatocellular carcinoma but rare in pancreatic ductal adenocarcinoma

Deletion in the 3p21 region, the chromosomal location of BAP1, has been reported in a subset of hepatocellular carcinoma (HCC), biliary and pancreatic cancers. This suggests that BAP1 could play a role in the pathogenesis of these tumors. We assessed the frequency of BAP1 loss by immunohistochemistry in 103 hepatic, biliary and pancreatic cancers. We also assessed chromosomal alterations in the BAP1 region in the same tumors by genotyping. We identified high frequency 4/8 (50%) of BAP1 loss in intrahepatic cholangicarcinoma (ICC). However the frequency was lower in HCC 9/51 (17.6%), pancreatic 1/42(2.4%) and extrahepatic biliary cancers (0/2). Loss of heterozygosity of at least one marker from the 3p21 region was observed in 75% of ICC, 52.9% of HCC and 45.2% of pancreatic cancers. Expression of hepatocytic (HepPar1) and bile duct (cytokeratin 7) markers were common (7/9, 77.8%) in the HCC tumors with loss or decrease of BAP1 compared with those with preserved BAP1 (18/42, 42.9%), (Fisher exact p = 0.0751). Our results confirm the high frequency of BAP1 alterations in ICC and low frequency in pancreatic cancers. It also suggests that BAP1 is commonly altered in a subtype of HCC with both hepatocytic and biliary differentiation. Further studies of the therapeutic implications of our findings are warranted.

Surgical and molecular pathology of pancreatic neoplasms

BACKGROUND

Histologic characteristics have proven to be very useful for classifying different types of tumors of the pancreas. As a result, the major tumor types in the pancreas have long been classified based on their microscopic appearance.

MAIN BODY

Recent advances in whole exome sequencing, gene expression profiling, and knowledge of tumorigenic pathways have deepened our understanding of the underlying biology of pancreatic neoplasia. These advances have not only confirmed the traditional histologic classification system, but also opened new doors to early diagnosis and targeted treatment.

CONCLUSION

This review discusses the histopathology, genetic and epigenetic alterations and potential treatment targets of the five major malignant pancreatic tumors - pancreatic ductal adenocarcinoma, pancreatic neuroendocrine tumor, solid-pseudopapillary neoplasm, acinar cell carcinoma and pancreatoblastoma.

Molecular pathology and genetics of pancreatic endocrine tumours

Pancreatic neuroendocrine tumours (PETs) are the second most frequent pancreatic neoplasms. Their poor chemosensitivity, high rate of metastatic disease and relatively long survival make PETs an ideal field to be explored for novel therapies based on specific molecular changes. PETs are generally sporadic but can also arise within hereditary syndromes, such as multiple endocrine neoplasia type 1, von Hippel-Lindau, neurofibromatosis type 1 and tuberous sclerosis complex, which represent a model for sporadic cases too. Among allelic imbalances, main genomic changes involve gain of 17q, 7q and 20q and loss of 11q, 6q and 11p, which identify regions of putative candidate oncogenes or tumour suppressor genes (TSGs), respectively, sometime with potential prognostic significance. Overexpression of Src-like kinases and cyclin D1 (CCND1) oncogene has been described. As for TSGs, P53 (TP53), DPC4/SMAD4 and RB (RB1) are not implicated in PET tumorigenesis, while for p16INK4a (CDKN2A), TIMP3, RASSF1A and hMLH1, more data are available, suggesting a role for methylation as a silencing mechanism. In the last decade, gene expression profile studies, analysis of microRNAs and, more recently, large-scale mutational analysis have highlighted commonly altered molecular pathways in the pathology of PETs. The roles of the mammalian target of rapamycin pathway, and its connection with Src kinases, and the activity of a number of tyrosine kinase receptors seem to be pivotal, as confirmed by the results of recent clinical trials with targeted agents. Mutations of DAXX and ATRX are common and related to altered telomeres but not to prognosis.

Chromosome 3p alterations in pancreatic endocrine neoplasia

Pancreatic endocrine tumors (PET) are rare neoplasms classified as functioning (F-PET) or non-functioning (NF-PET) according to the presence of a clinical syndrome due to hormonal hypersecretion. PETs show variable degrees of clinical aggressiveness and loss of chromosome 3p has been suggested to be associated with an advanced stage of disease. We assessed chromosome 3p copy number in 113 primary PETs and 32 metastases by fluorescence in situ hybridization (FISH) using tissue microarrays. The series included 56 well-differentiated endocrine tumors (WDET), 62 well-differentiated endocrine carcinomas (WDEC), and 6 poorly differentiated endocrine carcinomas (PDEC). Chromosome 3p alterations were found in 23/113 (20%) primary tumors, with losses being predominant over gains (14% vs. 6%). Loss of 3p was found in 5/55 (9%) WDET, 11/52 (21%) WDEC, and never in PDEC. Gains of 3p were detected in 4/55 (7%) WDET, no WDEC, but notably in 3/6 (50%) PDEC (OR 23.6; P = 0.003). Metastases were more frequently monosomic for 3p compared to primary tumors (OR 3.6; P = 0.005). Monosomy was significantly associated with larger tumor size, more advanced tumor stage, and metastasis. No association was found with survival. Chromosome 3p copy number alterations are frequent events in advanced stage PET, with gains prevailing in PDEC while losses are more frequent in WDEC, supporting the view that a specific pattern of alterations are involved in these diverse disease subtypes.

Molecular testing in solid tumors: an overview

Molecular testing in anatomic pathology is going to become more and more important during the next decade as we develop assays that can aid in diagnosis, prognosis, and predicting response to therapy. The anatomic pathologist needs to be familiar with the different assays available but also needs to be able to discern which are going to become standard of care and which will not. Three different types of tumors are reviewed: thyroid cancer, oligodendroglioma, and lung carcinoma. Molecular assays that are currently in use or on the near horizon, including translocation analyses for RET-PTC and PPARgamma-PAX8, point mutation analysis for BRAF and epidermal growth factor receptor, and genetic loss for 1p and 19q, are discussed.

Transplantable tumor lines generated in clonal zebrafish

Transplantable zebrafish tumors are a novel and very promising model in cancer research. However, further progress in this field has been contained by a lack of true inbred lines in zebrafish. To overcome this problem, we generated two lines of homozygous diploid clonal zebrafish lines (i.e., CB1 and CW1), which allowed us to carry out transplantation of any tissue, including tumors, from one fish to another within a line without rejection of the graft. The primary tumors in CB1 fish were induced by N-nitrosodiethylamine (DEN). The histologic analysis of these tumors revealed different types of hepatocellular carcinomas, hepatoblastomas, hepatoma, cholangiocarcinoma, and pancreatic carcinoma. Four spontaneous acinar cell carcinomas of pancreas were also found in 10- to 18-month-old CB1 fish. Small pieces of tissue or cell suspensions of either DEN-induced or spontaneous tumors were serially transplanted into the peritoneal cavity of syngeneic fish at different stages of development from 5-day-old larvae to adult fish. The development of grossly visible tumors occurred from 2 weeks to 3 months after tumor grafting and grew either as solitary smooth nodules or as an amorphous jelly-like mass infiltrating abdominal organs. The majority of tumors were also successfully transplanted to isogeneic (F1 generation from crossing CB1 x CW1) fish. At the present time, 19 transplantable zebrafish tumor lines have been generated and maintained for as long as 3 to 25 passages. This model provides a novel tool for studying experimental tumor biology and therapy and will become a cost effective system for high throughput screening of anticancer drugs.

The molecular genetics of gastroenteropancreatic neuroendocrine tumors

The pathobiology of neuroendocrine tumors (NETs) is hampered by the lack of scientific tools that define their mechanisms of secretion, proliferation, and metastasis; and, currently, there are no accurate means to assess tumor behavior and disease prognosis. Molecular biologic techniques and genetic analysis may facilitate the delineation of the molecular pathology of NETs and provide novel insights into their cellular mechanisms. The current status and recent advances in assessment of the molecular basis of tumorigenesis of gastroenteropancreatic neuroendocrine tumors (GEP-NETs) were reviewed (1981-2004). The objectives of this retrospective study were to provide a cohesive overview of the current state of knowledge and to develop a molecular understanding of these rare tumor entities to facilitate the establishment of therapeutic targets and rational management strategies. Multiple differences in chromosomal aberration patterns were noted between gastrointestinal (GI) neuroendocrine and pancreatic endocrine tumors (PETs). Divergence in gene expression patterns in the development of GI carcinoids and PETs was identified, whereas examination of the PET and GI carcinoid data demonstrated only few areas of overlap in the accumulation of genetic aberrations. These data suggest that the recent World Health Organization classification of GEP-NETs may require updating. In addition, previous assumptions of tumor similarity (pancreatic vs. GI) may be unfounded when they are examined at a molecular level. On the basis of the evolution of genetic information, enteric neuroendocrine lesions (carcinoids) and PETs may need to be classified as two distinct entities rather than grouped together as the single entity "GEP-NETs."

Chromosome 1q loss of heterozygosity frequently occurs in sporadic insulinomas and is associated with tumor malignancy

The pathogenesis of sporadic insulinomas is not clear, and there are no reliable genetic determinants that are useful to distinguish malignant and benign forms of this tumor. It was reported that 1q LOH might contribute to pathogenesis in gastrinomas and was correlated with tumor progression. However, little data are available on 1q LOH in sporadic insulinomas. In our study, we determine whether 1q LOH occurs in sporadic insulinomas and is associated with tumor malignancy by performing 1q allelotyping with 17 markers in 40 tumors and pair normal DNA. Thirty-five (88%) insulinomas had 1q LOH. Of the 35 insulinomas with 1q LOH, 14 (40%) had 1q21.3-23.2 LOH over a 7.5 cM region (SRO-1), whereas LOH in 21 tumors (60%) occurred at 1q31.3 over an 11.4 cM area (SRO-2). Of 24 tumors without MEN1 LOH, 20 had either SRO-1 or SRO-2 LOH (83%), whereas in 16 tumors with MEN1 LOH, 9 were shown to have LOH at either SRO-1 or SRO-2 (56%) (p = 0.065). This result suggests that LOH at 2 SRO might be MEN1 gene independent and may contribute to the pathogenesis in a subset of insulinomas without MEN1 gene LOH. The presence of 1q21.3-23.2 LOH is significantly associated with malignancy of insulinomas (p = 0.014). The high frequency of LOH at 1q 21.3-23.2 and 1q31.3 suggests these 2 areas may harbor putative tumor suppressor genes that may play an important role in the tumorigenesis of a subset of insulinomas. LOH at 1q21.3-23.2, which was associated with tumor malignancy, could be one of the genetic markers for identifying malignancy in sporadic insulinomas.

Xq25 and Xq26 identify the common minimal deletion region in malignant gastroenteropancreatic endocrine carcinomas

Loss of heterozygosity (LOH) for markers on X chromosome are associated with malignancy in endocrine tumors of the stomach and pancreas. The aim of this work is to investigate low-grade, well-differentiated endocrine carcinomas (WDEC) vs high-grade, poorly differentiated endocrine carcinomas (PDEC) of the gastroenteropancreatic (GEP) tract for common deletion regions on X chromosome. We performed a comparative allelotyping analysis with 24 highly polymorphic markers for the X chromosome in 12 WDECs and 5 PDECs. Overall, the LOH frequency in all informative loci investigated was 59% in primary and 61% in metastasis, with a significantly higher rate in PDECs than in WDECs (p<0.015 for primary and p<0.00005 for metastasis). In both WDECs and PDECs, the small Xq25 region as defined by DXS8059, DXS8098, and DXS8009 markers showed higher LOH rate as compared to the rest of the chromosome markers (p<0.04). In addition, LOH was very frequently elevated also in DXS294 and in DXS102 loci mapping the chromosomal region Xq26. In no instances differences were found between primary tumors and metastases. Methylation analysis revealed that Xq25 loss preferentially occurred on the inactive X chromosome, a feature in agreement with findings from other human cancers suggesting escape of tumor suppressor genes to X chromosome inactivation at this region. Overall, our data indicate that the two chromosomal regions, Xq25 and Xq26, may participate to the malignant progression of GEP endocrine carcinomas.

RASSF1A promoter methylation and 3p21.3 loss of heterozygosity are features of foregut, but not midgut and hindgut, malignant endocrine tumours

The Ras-association domain family 1A (RASSF1A) tumour suppressor gene is inactivated in a variety of solid tumours, usually by epigenetic silencing of the promoter and/or allelic loss of its locus at 3p21.3. RASSF1A induces cell cycle arrest through inhibition of cyclin D1 accumulation. In this work, 62 endocrine tumours from different sites in the gut were investigated for methylation of the RASSF1A promoter using the polymerase chain reaction, the presence of 3p21.3 deletions by loss of heterozygosity analysis, and cyclin D1 expression by immunohistochemistry. Methylation was found in 20/62 (32%) cases and was restricted to foregut tumours; deletion at 3p21.3 was found in 15/58 (26%) informative cases and restricted to malignant foregut tumours; cyclin D1 hyper-expression was found in 31/58 (53%) cases and correlated with RASSF1A methylation. Our data suggest that RASSF1A is involved in the development of endocrine tumours derived from the foregut only, and that the presence of both RASSF1A methylation and 3p21.3 deletion is associated with malignancy. These results may provide a rationale for foregut-targeted therapy for aggressive endocrine carcinomas entailing the use of demethylating agents.

Mutational analysis of PPARG as a candidate tumour suppressor gene in enteropancreatic endocrine tumours

OBJECTIVES

Loss of heterozygosity (LOH) or deletion of chromosome 3p is a frequent finding in enteropancreatic endocrine tumours (EPETs), suggesting the pathogenetic involvement of one or more tumour suppressor genes on 3p. PPARG, the gene encoding the gamma isoform of the peroxisome proliferator-activated receptor (PPARgamma), is highly expressed in normal human pancreatic islet cells, is located at 3p25, and has been reported to sustain loss-of-function mutations in human colorectal carcinomas. Additionally, the development of islet cell hyperplasia in an islet cell-specific pparg knockout mouse has further emphasized the attractiveness of PPARG as a candidate gene important in the pathogenesis of EPETs. Therefore, we sought to examine PPARG for intragenic inactivating mutations, the evidence needed to rigorously establish it as a tumour suppressor in EPETs.

PATIENTS AND DESIGN

Twenty-three EPETs from 20 patients were examined for coding region mutations in PPARG and for LOH on 3p at microsatellite markers flanking PPARG.

RESULTS

LOH on 3p was detected in tumours from six patients (30%), but no intragenic mutations were detected in PPARG, whether or not LOH was present.

CONCLUSION

These findings strongly suggest that PPARG does not commonly function as a classical tumour suppressor gene in the pathogenesis of EPETs.

Different molecular profiles characterize well-differentiated endocrine tumors and poorly differentiated endocrine carcinomas of the gastroenteropancreatic tract

PURPOSE

The molecular pathogenesis of gastroenteropancreatic endocrine tumors (ETs) is still largely unknown. The purpose of this work was a molecular characterization of 38 gastroenteropancreatic ETs with respect to the primary site and to the morphofunctional profile, pointing out useful diagnostic or prognostic molecular markers.

EXPERIMENTAL DESIGN

Twenty-four well-differentiated ETs or carcinomas (WDET/Cs; 11 pancreatic, 3 gastric, and 10 intestinal) and 14 poorly differentiated endocrine carcinomas (1 pancreatic, 6 gastric, and 7 colorectal) were microallelotyped using 38 polymorphic microsatellite markers covering chromosomes 1, 3, 5q, 6, 11, 17, and 18.

RESULTS

Regardless of the primary site, a significantly higher percentage of allelic imbalances (AIs) was observed in poorly differentiated endocrine carcinomas than in WDET/Cs (P = 0.012), except for 3 of 8 nonfunctioning pancreatic endocrine tumors and 1 colorectal WDEC, exhibiting multiple AIs on chromosomes 1, 3, 6, and 11. A strong positive correlation between AI percentage and Ki-67 proliferation index was detected considering both the whole series of ETs (P = 0.004) and the group of WDET/Cs alone (P = 0.011). The survival analysis showed a positive correlation between low percentage of AI and longer survival (P = 0.01). No recurrent AIs at specific chromosomal regions were identifiable with respect to the primary site.

CONCLUSIONS

The malignant progression of endocrine tumors seems to be associated with complex allelotypes and chromosomal instability. Although no specific molecular markers of malignancy can be defined with certainty, the ploidy status and the degree of chromosomal derangements appear to be the most informative genetic factors with prognostic significance.

Targeted elimination of peroxisome proliferator-activated receptor gamma in beta cells leads to abnormalities in islet mass without compromising glucose homeostasis

The nuclear hormone receptor peroxisome proliferator-activated receptor gamma (PPAR gamma) is an important regulator of lipid and glucose homeostasis and cellular differentiation. Studies of many cell types in vitro and in vivo have demonstrated that activation of PPAR gamma can reduce cellular proliferation. We show here that activation of PPAR gamma is sufficient to reduce the proliferation of cultured insulinoma cell lines. We created a model with mice in which the expression of the PPARG gene in beta cells was eliminated (beta gamma KO mice), and these mice were found to have significant islet hyperplasia on a chow diet. Interestingly, the normal expansion of beta-cell mass that occurs in control mice in response to high-fat feeding is markedly blunted in these animals. Despite this alteration in beta-cell mass, no effect on glucose homeostasis in beta gamma KO mice was noted. Additionally, while thiazolidinediones enhanced insulin secretion from cultured wild-type islets, administration of rosiglitazone to insulin-resistant control and beta gamma KO mice revealed that PPAR gamma in beta cells is not required for the antidiabetic actions of these compounds. These data demonstrate a critical physiological role for PPAR gamma function in beta-cell proliferation and also indicate that the mechanisms controlling beta-cell hyperplasia in obesity are different from those that regulate baseline cell mass in the islet.

Molecular insights into gastrointestinal neuroendocrine tumours: importance and recent advances

A subset of gastrointestinal neuroendocrine tumours (carcinoids and pancreatic endocrine tumours) show aggressive growth. Early identification of this subset is essential for management; however, clinical, laboratory and histologic features frequently fail to achieve this. Currently, there is an increased understanding of the molecular pathogenesis/changes in neuroendocrine tumours and this may identify important prognostic factors and possibly, new treatments. Recent findings and progress in this area are briefly reviewed in this article.

Frequent deletion of chromosome 3 in malignant sporadic pancreatic endocrine tumors

Pancreatic endocrine tumors (PETs) arise from neuroendocrine cells in and around the pancreas. As loss of heterozygosity (LOH) of chromosome 3 has been reported in sporadic PETs, we examined 16 sporadic PETs for LOH of 10 polymorphic DNA markers spanning both arms of chromosome 3. LOH was demonstrated in 4 of 8 (50%) sporadic PETs with hepatic metastasis, but in none of 8 sporadic PETs without hepatic involvement. The smallest common-deleted region (SCDR) mapped to 3q27-qter. Analysis of this data with the status of markers on chromosomes 1, 11, and MEN1 mutations in these 16 sporadic PETs revealed that chromosome 3q loss may be a late event in sporadic PET tumorigenesis. These data, combined with reports from other investigators, indicate that chromosome 3q27-qter may contain a tumor suppressor gene that's important in the tumorigenesis of sporadic PETs.

A novel insulinoma tumor suppressor gene locus on chromosome 22q with potential prognostic implications

The molecular mechanisms contributing to the tumorigenesis of insulinomas are still poorly understood. As moderate to high rates of LOH have been found on chromosome 22q in gastrinomas, we performed a finer deletion mapping study of chromosome 22q with 8 microsatellite markers in 15 insulinomas (4 malignant and 11 benign). Fourteen of 15 (93%) insulinomas revealed LOH on chromosome 22q, whereas the shortest region of overlap implicated a deletion of approximately 700 kb at 22q12.1-q12.2 with an LOH rate of up to 57% (8 of 14). Although the expressed sequence tag marker A006E25 that is localized in the hSNF5/INI1 gene on 22q11.2 revealed LOH in 50% of informative cases (7 of 14), no alterations in this gene could be identified by single strand conformational polymorphism analysis, direct DNA sequencing, or RNA expression analysis. Remarkably, the four malignant tumors showed a common deleted region between markers D22S345 and D22S1144 compared with none of the 11 benign insulinomas. The observed high frequency of chromosome 22q12 deletions in insulinomas is suggestive for a region compatible with harboring a tumor suppressor gene. The hSNF5/INI1 gene is most likely not the candidate gene, because no alterations could be identified. The distinct pattern of allelic loss identified in this chromosomal region appears to be an attractive candidate marker for further evaluation with regard to the discrimination between benign and malignant insulinomas.

MCG10, a novel p53 target gene that encodes a KH domain RNA-binding protein, is capable of inducing apoptosis and cell cycle arrest in G(2)-M

p53, a tumor suppressor, inhibits cell proliferation by inducing cellular genes involved in the regulation of the cell cycle. MCG10, a novel cellular p53 target gene, was identified in a cDNA subtraction assay with mRNA isolated from a p53-producing cell line. MCG10 can be induced by wild-type but not mutant p53 and by DNA damage via two potential p53-responsive elements in the promoter of the MCG10 gene. The MCG10 gene contains 10 exons and is located at chromosome 3p21, a region highly susceptible to aberrant chromosomal rearrangements and deletions in human neoplasia. The MCG10 gene locus encodes at least two alternatively spliced transcripts, MCG10 and MCG10as. The MCG10 and MCG10as proteins contain two domains homologous to the heterogeneous nuclear ribonucleoprotein K homology (KH) domain. By generating cell lines that inducibly express either wild-type or mutated forms of MCG10 and MCG10as, we found that MCG10 and MCG10as can suppress cell proliferation by inducing apoptosis and cell cycle arrest in G(2)-M. In addition, we found that MCG10 and MCG10as, through their KH domains, can bind poly(C) and that their RNA-binding activity is necessary for inducing apoptosis and cell cycle arrest. Furthermore, we found that the level of the poly(C) binding MCG10 protein is increased in cells treated with the DNA-damaging agent camptothecin in a p53-dependent manner. These results suggest that the MCG10 RNA-binding protein is a potential mediator of p53 tumor suppression.