DNMT3B expression might contribute to CpG island methylator phenotype in colorectal cancer.
OBJECTIVE
DNA methyltransferase-3B (DNMT3B) plays an important role in de novo CpG island methylation. Dnmt3b can induce colon tumor in mice with methylation in specific CpG islands. We hypothesized that cellular DNMT3B level might influence the occurrence of widespread CpG island methylation (i.e., the CpG island methylator phenotype, CIMP) in colon cancer.


METHODS
Utilizing 765 colorectal cancers in two cohort studies, we detected DNMT3B expression in 116 (15%) tumors by immunohistochemistry. We assessed microsatellite instability, quantified DNA methylation in repetitive long interspersed nucleotide element-1 (LINE-1) by Pyrosequencing, eight CIMP-specific promoters [CACNA1G, CDKN2A (p16), CRABP1, IGF2, MLH1, NEUROG1, RUNX3, and SOCS1], and eight other CpG islands (CHFR, HIC1, IGFBP3, MGMT, MINT1, MINT31, p14, and WRN) by real-time PCR (MethyLight).


RESULTS
Tumoral DNMT3B overexpression was significantly associated with CIMP-high [> or =6/8 methylated CIMP-specific promoters; odds ratio (OR), 3.34; 95% confidence interval, 2.11-5.29; P < 0.0001]. The relations between DNMT3B and methylation in 16 individual CpG islands varied substantially (OR, 0.80-2.96), suggesting variable locus-to-locus specificities of DNMT3B activity. DNMT3B expression was not significantly related with LINE-1 hypomethylation. In multivariate logistic regression, the significant relation between DNMT3B and CIMP-high persisted (OR, 2.39; 95% confidence interval, 1.11-5.14; P = 0.026) after adjusting for clinical and other molecular features, including p53, beta-catenin, LINE-1, microsatellite instability, KRAS, PIK3CA, and BRAF. DNMT3B expression was unrelated with patient outcome, survival, or prognosis.


CONCLUSIONS
Tumoral DNMT3B overexpression is associated with CIMP-high in colorectal cancer. Our data support a possible role of DNMT3B in nonrandom de novo CpG island methylation leading to colorectal cancer.
Nosho
Katsuhiko
K
Department of Medical Oncology, Dana-Farber Cancer Institute and Harvard Medical School, Boston, Massachusetts, USA.
Shima
Kaori
K
Irahara
Natsumi
N
Kure
Shoko
S
Baba
Yoshifumi
Y
Kirkner
Gregory J
GJ
Chen
Li
L
Gokhale
Sumita
S
Hazra
Aditi
A
Spiegelman
Donna
D
Giovannucci
Edward L
EL
Jaenisch
Rudolf
R
Fuchs
Charles S
CS
Ogino
Shuji
S
D000368:Aged; D015331:Cohort Studies; D015179:Colorectal Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D018899:CpG Islands / Q000235:genetics*; D004248:DNA (Cytosine-5-)-Methyltransferases / Q000096:biosynthesis*; D019175:DNA Methylation; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D016015:Logistic Models; D020084:Long Interspersed Nucleotide Elements / Q000235:genetics; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D015999:Multivariate Analysis; D010641:Phenotype; D016133:Polymerase Chain Reaction / Q000379:methods; D011401:Promoter Regions, Genetic / Q000235:genetics; D017422:Sequence Analysis, DNA; D016159:Tumor Suppressor Protein p53 / Q000235:genetics; D051176:beta Catenin / Q000235:genetics; D000097584:DNA Methyltransferase 3B
D004248:DNA (Cytosine-5-)-Methyltransferases; D016159:Tumor Suppressor Protein p53; D051176:beta Catenin; D000097584:DNA Methyltransferase 3B