The silencing of microRNA 148a production by DNA hypermethylation is an early event in pancreatic carcinogenesis.
BACKGROUND
The poor prognosis of pancreatic ductal adenocarcinoma (PDAC) is accounted for by the absence of early diagnostic markers and effective treatments. MicroRNAs inhibit the translation of their target mRNAs. The production of microRNAs is strongly altered in cancers, but the causes of these alterations are only partially known. DNA hypermethylation is a major cause of gene inactivation in cancer. Our aims were to identify microRNAs whose gene expression is inactivated by hypermethylation in PDAC and to determine whether this hypermethylation-mediated repression is an early event during pancreatic carcinogenesis. We also sought to investigate whether these differentially methylated regions can serve as a diagnostic marker for PDAC.


METHODS
MicroRNA production was measured by microarray hybridization and reverse-transcription quantitative PCR. The level of DNA methylation was measured by bisulfite mapping and semiquantitative methylation-specific PCR.


RESULTS
We identified 29 microRNAs encoded by genes whose expression is potentially inactivated by DNA hypermethylation. We focused our study on microRNA 148a (miR-148a) and found its production to be repressed, not only in PDAC samples but also in preneoplastic pancreatic intraepithelial neoplasia (PanIN) lesions. More importantly, we found that hypermethylation of the DNA region encoding miR-148a is responsible for its repression, which occurs in PanIN preneoplastic lesions. Finally, we show that the hypermethylated DNA region encoding miR-148a can serve as an ancillary marker for the differential diagnosis of PDAC and chronic pancreatitis (CP).


CONCLUSIONS
We show that the hypermethylation of the DNA region encoding miR-148a is responsible for its repression in PDAC precursor lesions and can be a useful tool for the differential diagnosis of PDAC and CP.
Hanoun
Naïma
N
INSERM, U858, Toulouse, France.
Delpu
Yannick
Y
Suriawinata
Arief A
AA
Bournet
Barbara
B
Bureau
Christophe
C
Selves
Janick
J
Tsongalis
Gregory J
GJ
Dufresne
Marlène
M
Buscail
Louis
L
Cordelier
Pierre
P
Torrisani
Jérôme
J
D000818:Animals; D021441:Carcinoma, Pancreatic Ductal / Q000175:diagnosis* / Q000378:metabolism / Q000473:pathology; D045744:Cell Line, Tumor; D019175:DNA Methylation; D003937:Diagnosis, Differential; D015536:Down-Regulation; D020868:Gene Silencing; D006801:Humans; D051379:Mice; D008817:Mice, Mutant Strains; D035683:MicroRNAs / Q000096:biosynthesis* / Q000235:genetics; D010190:Pancreatic Neoplasms / Q000175:diagnosis* / Q000378:metabolism / Q000473:pathology; D050500:Pancreatitis, Chronic / Q000175:diagnosis; D016133:Polymerase Chain Reaction; D011230:Precancerous Conditions / Q000175:diagnosis / Q000378:metabolism / Q000473:pathology
C550570:MIRN148 microRNA, human; D035683:MicroRNAs