Peritumoral fibroblast SPARC expression and patient outcome with resectable pancreatic adenocarcinoma

Pancreatic cancer associated fibroblasts display normal allelotypes

BACKGROUND

Recent studies have reported widespread copy number alterations and p53 mutations arising in cancer associated stromal cells. The aim of this study was to determine if pancreatic cancer associated fibroblasts display similar genetic alterations.

DESIGN

Cancer-associated fibroblast cultures were established from 7 primary pancreatic adenocarcinomas. These fibroblasts and corresponding normal tissues when available were analyzed for genome-wide copy number changes using Affymetrix 250K SNP microarrays. Evidence of p53 protein expression, an indicator of p53 mutation was determined by immunohistochemical labeling of tissue microarrays containing 117 pancreatic ductal adenocarcinomas.

RESULTS

Pancreatic cancer associated fibroblasts did not show any evidence of somatic copy number gains or losses. p53 protein expression was confined to invasive pancreatic adenocarcinoma cells and was not expressed in cancer-associated fibroblasts.

CONCLUSIONS

We find no evidence that pancreatic cancer associated fibroblasts harbor somatic copy number changes or immunohistochemical evidence of p53 mutations.

CpG island methylation profile of pancreatic intraepithelial neoplasia

Infiltrating adenocarcinoma of the pancreas is thought to develop through well-defined precursor lesions called pancreatic intraductal neoplasia (PanIN). Despite the exponential growth in our understanding of genetic events that characterize the progression of PanINs to invasive carcinoma, little is known about the role of epigenetic alterations in these precursor lesions. To define the timing and prevalence of methylation abnormalities during early pancreatic carcinogenesis, we investigated the CpG island methylation profile in the various grades of PanINs. Using methylation-specific PCR, we analyzed DNA samples from 65 PanIN lesions for methylation status of eight genes recently identified by microarray approach as aberrantly hypermethylated in invasive pancreatic cancer. Aberrant methylation at any of the eight genes was identified in 68% of all the PanIN lesions examined, and, notably, aberrant methylation was identified in more than 70% of the earliest lesions (PanIN-1A). The average number of methylated loci was 1.1 in PanIN-1A, 0.8 in PanIN-1B, 1.1 in PanIN-2, and 2.9 in PanIN-3 lesions (P=0.01 for PanIN -3 vs earlier PanINs). Among the genes analyzed, NPTX2 demonstrated an increase in methylation prevalence from PanIN-1 to PanIN-2 (P=0.0008), and from PanIN-2 to PanIN-3 for SARP2 (P=0.001), Reprimo (P=0.01), and LHX1 (P=0.03). These results suggest that aberrant CpG island hypermethylation begins in early stages of PanINs, and its prevalence progressively increases during neoplastic progression.

Mechanotransduction from the ECM to the genome: Are the pieces now in place?

A multitude of biochemical signaling processes have been characterized that affect gene expression and cellular activity. However, living cells often need to integrate biochemical signals with mechanical information from their microenvironment as they respond. In fact, the signals received by shape alone can dictate cell fate. This mechanotrasduction of information is powerful, eliciting proliferation, differentiation, or apoptosis in a manner dependent upon the extent of physical deformation. The cells internal "prestressed" structure and its "hardwired" interaction with the extra-cellular matrix (ECM) appear to confer this ability to filter biochemical signals and decide between divergent cell functions influenced by the nature of signals from the mechanical environment. In some instances mechanical signaling through the tissue microenvironment has been shown to be dominant over genomic defects, imparting a normal phenotype on cells that otherwise have transforming genetic lesions. This mechanical control of phenotype is postulated to have a central role in embryogenesis, tissue physiology as well as the pathology of a wide variety of diseases, including cancer. We will briefly review studies showing physical continuity between the external cellular microenvironment and the interior of the cell nucleus. Newly characterized structures, termed nuclear envelope lamina spanning complexes (NELSC), and their interactions will be described as part of a model for mechanical transduction of extracellular cues from the ECM to the genome.

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 overexpression 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 overexpressed in non-neoplastic stromal cells in 171 (96.6%) of the 177 evaluable pancreatic cancers. By contrast, the overexpression 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 overexpression 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 overexpressed in most pancreatic cancer cells, the overexpression of palladin is not likely to be responsible for pancreatic cancer cells invasive and migratory abilities.

Pancreatic cancer

Pancreatic cancer remains a major unsolved health problem, with conventional cancer treatments having little impact on disease course. Almost all patients who have pancreatic cancer develop metastases and die. The main risk factors are smoking, age, and some genetic disorders, although the primary causes are poorly understood. Advances in molecular biology have, however, greatly improved understanding of the pathogenesis of pancreatic cancer. Many patients have mutations of the K-ras oncogene, and various tumour-suppressor genes are also inactivated. Growth factors also play an important part. However, disease prognosis is extremely poor. Around 15-20% of patients have resectable disease, but only around 20% of these survive to 5 years. For locally advanced, unresectable, and metastatic disease, treatment is palliative, although fluorouracil chemoradiation for locally advanced and gemcitabine chemotherapy for metastatic disease can provide palliative benefits. Despite pancreatic cancer's resistance to currently available treatments, new methods are being investigated. Preoperative chemoradiation is being advocated, with seemingly sound reasoning, and a wider role for gemcitabine is being explored. However, new therapeutic strategies based on the molecular biology of pancreatic cancer seem to hold the greatest promise.