RUNX3 inactivation in colorectal polyps arising through different pathways of colonic carcinogenesis.
OBJECTIVE
We hypothesized that RUNX3 inactivation by promoter hypermethylation in colorectal polyps is an early molecular event in colorectal carcinogenesis.


METHODS
RUNX3 protein expression was analyzed immunohistochemically in 50 sporadic colorectal polyps comprising 19 hyperplastic polyps (HPs), 14 traditional serrated adenomas (TSAs), and 17 sporadic traditional adenomas (sTAs) as well as in 19 familial adenomatous polyposis (FAP) samples from 10 patients showing aberrant crypt foci (ACF) (n=91), small adenomas (SmAds) (n=40), and large adenomas (LAds) (n=13). In addition, we assessed the frequency of promoter hypermethylation of RUNX3 by methylation-specific PCR (MSP) in all the 50 sporadic polyps as well as 38 microdissected FAP polyps comprising ACF, SmAds, and LAds obtained from 7 FAP samples. A total of 12 normal colon samples were also included for RUNX3 MSP analysis.


RESULTS
Compared to normal colon (2 of 12, 16%) and sTAs (3 of 17, 18%), HPs (15 of 19, 79%) and TSAs (8 of 14, 57%) displayed significant inactivation of RUNX3 (P<0.05). In FAP, RUNX3 inactivation was more frequently seen in ACF (78 of 91, 86%), SmAds (25 of 40, 62%), and LAds (6 of 13, 46%) compared to normal mucosa (0 of 19, 0%) in the same samples (all P<0.05). Promoter hypermethylation of RUNX3 was significantly higher in colorectal polyps (64 of 87, 74%) compared to normal colon (2 of 12, 16%) (P=0.001). Serrated polyps such as HPs (17 of 19, 89%) and TSAs (12 of 14, 86%) were significantly more methylated than sTAs (7 of 17, 44%) (P=0.004). RUNX3 hypermethylation was observed in 28 of the total 38 (74%) FAP polyps. Overall, RUNX3 promoter methylation correlated with inactivation of RUNX3 expression in sporadic (27 of 36, 75%) (P=0.022) and FAP (21 of 28, 75%) (P=0.021) polyps.


CONCLUSIONS
Our data suggest that RUNX3 inactivation due to promoter hypermethylation in colorectal polyps represents an early event in colorectal cancer (CRC) progression. In addition, epigenetic RUNX3 inactivation is a frequent event in the serrated colonic polyps as well as in the ACF of FAP polyps.
Subramaniam
Manish M
MM
Faculty of Medicine, Oncology Research Institute,National University of Singapore, Singapore.
Chan
Jason Y
JY
Soong
Richie
R
Ito
Kosei
K
Yeoh
Khay G
KG
Wong
Reuben
R
Guenther
Thomas
T
Will
Olivia
O
Chen
Chee L
CL
Kumarasinghe
Marian P
MP
Ito
Yoshiaki
Y
Salto-Tellez
Manuel
M
D011125:Adenomatous Polyposis Coli / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D016022:Case-Control Studies; D003110:Colonic Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology*; D003111:Colonic Polyps / Q000235:genetics* / Q000378:metabolism / Q000473:pathology*; D050677:Core Binding Factor Alpha 3 Subunit / Q000235:genetics* / Q000378:metabolism; D019175:DNA Methylation / Q000502:physiology; D044127:Epigenesis, Genetic / Q000502:physiology; D006801:Humans; D006965:Hyperplasia; D011401:Promoter Regions, Genetic
D050677:Core Binding Factor Alpha 3 Subunit; C493729:Runx3 protein, human