CpG island methylation profile of pancreatic intraepithelial neoplasia

Abstract

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 ¼ 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 ¼ 0.0008), and from PanIN-2 to PanIN-3 for SARP2 (P ¼ 0.001), Reprimo (P ¼ 0.01), and LHX1 (P ¼ 0.03). These results suggest that aberrant CpG island hypermethylation begins in early stages of PanINs, and its prevalence progressively increases during neoplastic progression. Keywords: PanIN; pancreatic cancer; methylation specific PCR; DNA methylation Accumulating evidence supports the hypothesis that infiltrating adenocarcinoma of the pancreas develops from noninvasive precursor lesions in the small ducts and ductules, called pancreatic intraductal neoplasia (PanIN). 1,2 Characterization of molecular basis for these precursor lesions may refine our understanding of pancreatic ductal carcinogenesis and also provide important insight into early pancreatic cancer detection strategies and novel targets for chemoprevention. 3 Many of the genetic abnormalities observed in invasive pancreatic cancer have also been observed in PanIN lesions. The reported genetic alterations in PanINs include activating point mutations in the KRAS2 oncogene 4 and inactivation of p16/CDKN2A, 5 TP53, 6 SMAD4/DPC4, 6,7 and BRCA2. 2,8,9 Most of these genetic alterations have been detected in the histologically more advanced PanIN lesions (PanIN-2 and PanIN-3), and the initiating events in neoplastic progression within the pancreatic ducts remains unknown. In addition, telomere shortening is a common genetic abnormality observed in all stages of PanINs including the vast majority of earliest lesions (PanIN-1A). 10 PanIN lesions may be particularly important in patients with a strong family history of pancreatic cancer. [11][12][13] Pancreata in patients with a strong family history of pancreatic cancer are remarkable for the presence of multifocal PanIN lesions, and these PanIN lesions are characteristi...

Early Epigenetic Downregulation of microRNA-192 Expression Promotes Pancreatic Cancer Progression

“…Emerging studies support that dysregulation of miRNA expression in cancer is also mediated by DNA methylation (8,9). Interestingly, aberrant changes in DNA methylation and miRNA expression were shown to be early events in PDAC (10), as well as in other cancers (11) and have been linked to the initiation and progression of cancer. For example, miR-148a was reported to be downregulated in multiple cancers like colon, melanoma, lung cancer (12), and PDAC (13).…”

Genome-wide profiling at methylated promoters in pancreatic adenocarcinoma

“…This altered gene function arises from both gene silencing associated with aberrant hypermethylation of promoter CpG islands and induction of gene expression associated with gene hypomethylation. 1 Aberrant DNA methylation contributes to pancreatic cancer development and progression [2][3][4][5][6][7][8][9][10] and the detection of aberrant DNA methylation is being evaluated as a strategy to improve the diagnosis of pancreatic cancer. 11 While the causes of aberrant CpG island methylation during the cancer development are not well understood, [12][13][14][15][16] the identification of differentially methylated CpG islands in cancer relative to normal tissues may lead to the development of cancer-specific markers of cancer and may also identify important pathways that merit therapeutic targeting.…”

Genome-wide profiling of methylated promoters in pancreatic adenocarcinoma: defining the pancreatic cancer epigenome

“…[13][14][15] The feasibility of using methylation-specific PCR to diagnose pancreatic cancer in "juice" collected endoscopically from the pancreatic duct has already shown promise. 16,17 One of the present research challenges is to identify candidate methylated genes that will perform with the best sensitivity and specificity in diagnosing pancreatic cancer at the earliest possibility.…”