Study On The DNA Methylation Molecular Markers Of Warning And Early Screening In Human Colorectal Adenocarcinoma

Objective: It’s proved that promoter CpG islands hypermethylationof tumor suppressor genes is one of the mechanisms which leads to theinactivation of tumor suppressor that may contribute to tumourigenesis. Thepresent study was to observe the methylation status of the promoter of P16andRASSF1A genes in colorectal adenocarcinoma, colorectal adenoma and normalperipheral blood and to explore the clinical significance of the methylation ofthe promoter of P16and RASSF1A in order to accumulate reliable statistics forwarning, early screening and predicting prognosis of human colorectaladenocarcinoma. Methods: Phenol-chloroform method was used to extractDNA after the specimens of colorectal adenocarcinoma，colorectal adenomaand normal peripheral blood being collected. Then the methylation status of thepromoter of P16and RASSF1A genes was detected by nested methylationspecific PCR(nMSP) and the results were analyzed later. Results:1.The positiverate of colorectal adenocarcinoma，colorectal adenoma and normal peripheralblood of the promoter methylation of P16was45.45%(15/33)、34.48%(10/29),12.5%(3/24), respectively. The difference was significant (χ~2=6.746，P＜0.05).The positive rate of colorectal adenocarcinoma，colorectal adenomaand normal peripheral blood of the of the promoter methylation of RASSF1Awas27.27%(9/33),24.14%(7/29),0%， respectively. The difference wassignificant(χ~2=7.709，P＜0.05) too. While there were no significant difference between the colorectal adenocarcinoma and colorectal adenoma peripheralblood in both the two genes(χ~2=0.772，P＞0.05；χ~2=0.079，P＞0.05).2、Thepositive rate of colorectal adenocarcinoma peripheral blood of the promotermethylation of P16was27.14%in a well-differentiated tumour grade, and56.25%in a moderately differentiated tumour grade,which were bothsignificantly lower than100%in a poorly differentiated tumour grade(χ~2=7.622，P＜0.05). The positive rate of colorectal adenocarcinoma peripheralblood of the promoter methylation of RASSF1A was14.29%in awell-differentiated tumour grade, and25%in a moderately differentiatedtumour grade,which were both significantly lower than100%in a poorlydifferentiated tumour grade(χ~2=9.232，P＜0.01). It’s found that promotermethylation status of both the two genes the had no significant correlations withgender, age, the depth of invasion, lymph node involvement and staging incolorectal adenocarcinoma peripheral blood. The positive rate of of thepromoter methylation of both the two genes was not associated with gender andage in colorectal adenoma peripheral blood(P＞0.05).3.There was norelationship between the promoter methylation status of p16and RASSF1Agenes(P＞0.05).Conclusions:1.Hypermethylation of P16and RASSF1A genesis present in the colorectal adenocarcinoma and colorectal adenoma peripheralblood and the rate is higher than the normal peripheral blood, suggesting thathypermethylation of P16and RASSF1A genes may participate intumourigenesis and development of colorectal adenocarcinoma.2.There is hypermethylation of P16and RASSF1A genes in colorectal adenoma peripheralblood，which has no previous difference with colorectal adenocarcinomaperipheral blood, therefore, suggests that the promoter methylation of P16andRASSF1A genes may occur at early colorectal adenocarcinoma.3.Thepromoter methylation status of P16and RASSF1A genes may be associatedwith degree of differentiation.4.There was no relationship between thepromoter methylation status of p16and RASSF1A genes, therefore, suggeststhat they may be independent risk factor in tumourigenesis and development ofcolorectal adenocarcinoma.5.The detection of the promoter methylation statusof p16and RASSF1A genes in colorectal tumors could be the basic for furtherresearch, and could accumulate reliable statistics for warning,early screeningand predicting prognosis of human colorectal adenocarcinoma.6.Thereversibility of methylation may become a new target of the therapy ofcolorectal adenocarcinoma.