Hypermethylation and expression regulation of secreted frizzled-related protein genes in colorectal tumor.
OBJECTIVE
To investigate the functions of promoter hyper-methylation of secreted frizzled-related proteins (sFRPs) genes in colorectal tumorigenesis and progression.


METHODS
The promoter hypermethylation and expression of sFRP genes in 72 sporadic colorectal carcinomas, 33 adenomas, 18 aberrant crypt foci (ACF) and colorectal cancer cell lines RKO, HCT116 and SW480 were detected by methylation-specific PCR and reverse transcription PCR, respectively.


RESULTS
None of the normal colorectal mucosa tissues showed methylated bands of any of four sFRP genes. sFRP1, 2, 4 and 5 were frequently methylated in colorectal carcinoma, adenoma and ACF (sFRP1 > 85%, sFRP2 > 75%, sFRP5 > 50%), and the differences between three colorectal tissues were not significant (P > 0.05). Methylation in colorectal tumors was more frequent than in normal mucosa and adjacent normal mucosa. The mRNA of sFRP1-5 genes was expressed in all normal colorectal mucosa samples. Expression of sFRP1, 2, 4 and 5 and sFRP1, 2 and 5 was downregulated in carcinoma and adenoma, respectively. The downregulation of sFRP2, 4 and 5 was more frequent in carcinoma than in adenoma. Expression of sFRP3 which promoter has no CpG island was downregulated in only a few of colorectal tumor samples (7/105). The downregulation of sFRP1, 2, 4 and 5 expression was significantly associated with promoter hypermethylation in colorectal tumor. After cells were treated by DAC/TSA combination, the silenced sFRP mRNA expression could be effectively re-expressed in colorectal cancer cell lines.


CONCLUSIONS
Hypermethylation of sFRP genes is a common early event in the evolution of colorectal tumor, occurring frequently in ACF, which is regarded as the earliest lesion of multistage colorectal carcinogenesis. It appears to functionally silence sFRP genes expression. Methylation of sFRP1, 2 and 5 genes might serve as indicators for colorectal tumor.
Qi
Jian
J
Department of Gastroenterology, Zhongnan Hospital of Wuhan University, Wuhan, 430071, Hubei Province, China.
Zhu
You-Qing
YQ
Luo
Jun
J
Tao
Wen-Hui
WH
D048868:Adaptor Proteins, Signal Transducing; D000236:Adenoma / Q000235:genetics / Q000378:metabolism*; D000328:Adult; D000368:Aged; D002277:Carcinoma / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D015179:Colorectal Neoplasms / Q000235:genetics / Q000378:metabolism*; D019175:DNA Methylation; D005136:Eye Proteins / Q000235:genetics / Q000378:metabolism; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D020868:Gene Silencing; D045325:HCT116 Cells; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism; D008297:Male; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D008875:Middle Aged; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D000094742:Secreted Frizzled-Related Proteins
D048868:Adaptor Proteins, Signal Transducing; D005136:Eye Proteins; D036341:Intercellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D011518:Proto-Oncogene Proteins; C117636:SFRP1 protein, human; D000094742:Secreted Frizzled-Related Proteins; C109618:SFRP2 protein, human; C118723:SFRP4 protein, human; C118511:SFRP5 protein, human