Aberrant methylation of CpG islands in intraductal papillary mucinous neoplasms of the pancreas.
OBJECTIVE
The functional abrogation of several tumor suppressor genes, including p16, DPC4, and p53, is a major mechanism underlying pancreatic ductal carcinogenesis. However, mutational inactivation of these genes is relatively uncommon in intraductal papillary mucinous neoplasms (IPMNs) of the pancreas. We hypothesized that an alternative mechanism for gene inactivation (notably, transcriptional silencing by promoter methylation) could be important in the pathogenesis of IPMNs.


METHODS
Using methylation-specific polymerase chain reaction, we analyzed the methylation status of 7 CpG islands previously identified as aberrantly methylated in pancreatic adenocarcinoma (including preproenkephalin [ppENK], p16, and thrombospondin 1) in 51 IPMNs of different histologic grades. The relationship between methylation status and expression was evaluated using reverse-transcription polymerase chain reaction for ppENK and immunohistochemistry for p16.


RESULTS
We found that more than 80% of the IPMNs exhibited hypermethylation of at least one of these CpG islands. Hypermethylation of ppENK and p16 was detected at a significant higher frequency in high-grade (in situ carcinoma) IPMNs than in low-grade (adenoma/borderline) IPMNs (ppENK, 82% vs. 28%, P = 0.0002; p16, 21% vs. 0%, P = 0.04). Furthermore, the average number of methylated loci was significantly higher in high-grade IPMNs than in low-grade IPMNs (2.4 vs. 0.9; P = 0.0008). Aberrant methylation of ppENK and p16 was associated with loss of expression.


CONCLUSIONS
These results suggest that de novo methylation of multiple CpG islands is one of the critical pathways that contributes to the malignant progression of IPMNs.
Sato
Norihiro
N
Department of Pathology, The Johns Hopkins Medical Institutions, Baltimore, Maryland 21205, USA.
Ueki
Takashi
T
Fukushima
Noriyoshi
N
Iacobuzio-Donahue
Christine A
CA
Yeo
Charles J
CJ
Cameron
John L
JL
Hruban
Ralph H
RH
Goggins
Michael
M
D002288:Adenocarcinoma, Mucinous / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D000231:Adenocarcinoma, Papillary / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D000236:Adenoma / Q000235:genetics / Q000378:metabolism; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002278:Carcinoma in Situ / Q000235:genetics / Q000378:metabolism; D021441:Carcinoma, Pancreatic Ductal / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D018899:CpG Islands / Q000235:genetics*; D019175:DNA Methylation; D004745:Enkephalins / Q000235:genetics / Q000378:metabolism; D005260:Female; D019942:Genes, p16 / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D010190:Pancreatic Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D011498:Protein Precursors / Q000235:genetics / Q000378:metabolism
D004745:Enkephalins; D011498:Protein Precursors; C033660:preproenkephalin