Promoter methylation precedes chromosomal alterations in colorectal cancer development.
BACKGROUND
Colorectal cancers are characterized by genetic and epigenetic alterations. This study aimed to explore the timing of promoter methylation and relationship with mutations and chromosomal alterations in colorectal carcinogenesis.


METHODS
In a series of 47 nonprogressed adenomas, 41 progressed adenomas (malignant polyps), 38 colorectal carcinomas and 18 paired normal tissues, we evaluated promoter methylation status of hMLH1, O6MGMT, APC, p14ARF, p16INK4A, RASSF1A, GATA-4, GATA-5, and CHFR using methylation-specific PCR. Mutation status of TP53, APC and KRAS were studied by p53 immunohistochemistry and sequencing of the APC and KRAS mutation cluster regions. Chromosomal alterations were evaluated by comparative genomic hybridization.


RESULTS
Our data demonstrate that nonprogressed adenomas, progressed adenomas and carcinomas show similar frequencies of promoter methylation for the majority of the genes. Normal tissues showed significantly lower frequencies of promoter methylation of APC, p16INK4A, GATA-4, and GATA-5 (P-values: 0.02, 0.02, 1.1x10(-5) and 0.008 respectively). P53 immunopositivity and chromosomal abnormalities occur predominantly in carcinomas (P values: 1.1x10(-5) and 4.1x10(-10)).


CONCLUSIONS
Since promoter methylation was already present in nonprogressed adenomas without chromosomal alterations, we conclude that promoter methylation can be regarded as an early event preceding TP53 mutation and chromosomal abnormalities in colorectal cancer development.
Derks
Sarah
S
Department of Pathology, Research Institute GROW, University Maastricht, The Netherlands.
Postma
Cindy
C
Moerkerk
Peter T M
PT
van den Bosch
Sandra M
SM
Carvalho
Beatriz
B
Hermsen
Mario A J A
MA
Giaretti
Walter
W
Herman
James G
JG
Weijenberg
Matty P
MP
de Bruïne
Adriaan P
AP
Meijer
Gerrit A
GA
van Engeland
Manon
M
D000236:Adenoma / Q000235:genetics / Q000473:pathology; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002869:Chromosome Aberrations; D015179:Colorectal Neoplasms / Q000235:genetics* / Q000473:pathology*; D019175:DNA Methylation; D018450:Disease Progression; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011230:Precancerous Conditions / Q000235:genetics* / Q000473:pathology; D011401:Promoter Regions, Genetic / Q000235:genetics*; D013997:Time Factors