Colorectal cancer with mutation in BRAF, KRAS, and wild-type with respect to both oncogenes showing different patterns of DNA methylation.
OBJECTIVE
BRAF mutations are common in sporadic colorectal cancers (CRCs) with a DNA mismatch repair (MMR) deficiency that results from promoter methylation of hMLH1, whereas KRAS mutations are common in MMR proficient CRCs associated with promoter methylation of MGMT. The aim of this study was to further investigate the link between genetic alterations in the RAS/RAF/ERK pathway and an underlying epigenetic disorder.


METHODS
Activating mutations of BRAF and KRAS were identified and correlated with promoter methylation of 11 loci, including MINT1, MINT2, MINT31, CACNA1G, p16(INK4a), p14(ARF), COX2, DAPK, MGMT, and the two regions in hMLH1 in 468 CRCs and matched normal mucosa.


RESULTS
BRAF V599E mutations were identified in 21 (9%) of 234 CRCs, and KRAS mutations were identified in 72 (31%) of 234 CRCs. Mutations in BRAF and KRAS were never found in the same tumor. CRCs with BRAF mutations showed high-level promoter methylation in multiple loci, with a mean number of methylated loci of 7.2 (95% CI, 6.6 to 7.9) among 11 loci examined (P < .0001). Tumors with KRAS mutations showed low-level promoter methylation, and CRCs with neither mutation showed a weak association with promoter methylation, with an average number of methylated loci of 1.8 (95% CI, 1.5 to 2.1) and 1.0 (95% CI, 0.79 to 1.3), respectively.


CONCLUSIONS
In CRC, the methylation status of multiple promoters can be predicted through knowledge of BRAF and, to a lesser extent, KRAS activating mutations, indicating that these mutations are closely associated with different patterns of DNA hypermethylation. These changes may be important events in colorectal tumorigenesis.
Nagasaka
Takeshi
T
Department of Gastroenterological Surgery and Surgical Oncology, Okayama University Graduate School of Medicine and Dentistry, Okayama, Japan.
Sasamoto
Hiromi
H
Notohara
Kenji
K
Cullings
Harry M
HM
Takeda
Masanori
M
Kimura
Keigo
K
Kambara
Takeshi
T
MacPhee
Donald G
DG
Young
Joanne
J
Leggett
Barbara A
BA
Jass
Jeremy R
JR
Tanaka
Noriaki
N
Matsubara
Nagahide
N
D000368:Aged; D016022:Case-Control Studies; D015179:Colorectal Neoplasms / Q000235:genetics* / Q000473:pathology; D019175:DNA Methylation; D004252:DNA Mutational Analysis; D004260:DNA Repair; D005260:Female; D011905:Genes, ras / Q000235:genetics*; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D008875:Middle Aged; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic; D048493:Proto-Oncogene Proteins B-raf / Q000235:genetics*
C482119:BRAF protein, human; D048493:Proto-Oncogene Proteins B-raf