Influence of methylated p15 and p16 genes on clinicopathological features in colorectal cancer.
OBJECTIVE
Genetic silencing by promoter methylation has attracted attention in the carcinogenesis of colorectal cancer. Methylation of the p16(INK4a) gene has been found in primary colorectal cancer. Although the p15(INK4b) gene displays high homology to the p16(INK4a) gene in the amino acid sequence, methylation of p15(INK4b) has not been fully studied. We investigated p15(INK4b) methylation status in patients with colorectal cancer to verify the association between the methylation of p15(INK4b) and clinicopathological features compared with p16(INK4a).


METHODS
DNA samples from the tissues of primary colorectal cancer and corresponding adjacent normal colon mucosa were obtained from surgical resections of 88 patients (47 males and 41 females, aged 29-83 years). Methylation-specific polymerase chain reaction was used to analyze p15(INK4b) and p16(INK4a) methylation status after bisulfite modification. Cumulative survival rates (mean follow-up period: 53.2 months) were calculated by the Kaplan-Meier analysis. Methylations of p15(INK4b) and p16(INK4a) genes were detected in 23 (26.1%) and 20 (22.7%) colorectal cancers, respectively.


RESULTS
Methylation of p15(INK4b) was not associated with any clinicopathological features. Compared with normal mucosa, the methylation of p15(INK4b) was more prominent in tumor tissue (P < 0.001). Reverse transcription-polymerase chain reaction (RT-PCR) revealed that p15(INK4b) methylaton decreased mRNA expression. Kaplan-Meier analysis showed that patients with stage I-II had a significant difference in survival rate between those with and without methylated p15(INK4b) (P = 0.018).


CONCLUSIONS
Our results suggest that methylation of the p15(INK4b) gene contributes to the process of carcinogenesis in colorectal cancer as well as p16(INK4a) and is useful as a prognostic factor in the early stage.
Ishiguro
Atsushi
A
First Department of Internal Medicine, Hirosaki University School of Medicine, Hirosaki, Japan.
Takahata
Takenori
T
Saito
Masato
M
Yoshiya
Gen
G
Tamura
Yoshihiro
Y
Sasaki
Mutsuo
M
Munakata
Akihiro
A
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015179:Colorectal Neoplasms / Q000235:genetics* / Q000401:mortality / Q000473:pathology; D050762:Cyclin-Dependent Kinase Inhibitor p15 / Q000235:genetics*; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000235:genetics*; D019175:DNA Methylation; D004273:DNA, Neoplasm / Q000032:analysis; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009367:Neoplasm Staging; D047428:Protein Kinase Inhibitors; D012333:RNA, Messenger / Q000032:analysis; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016019:Survival Analysis; D025521:Tumor Suppressor Proteins / Q000235:genetics
D050762:Cyclin-Dependent Kinase Inhibitor p15; D019941:Cyclin-Dependent Kinase Inhibitor p16; D004273:DNA, Neoplasm; D047428:Protein Kinase Inhibitors; D012333:RNA, Messenger; D025521:Tumor Suppressor Proteins