| Objective: The carcinoma of gastrointestinal tractthreatens people's health,and colorectal carcinoma is the mostcommon malignant tumor in the world. The tumorigenesis ofcolorectal carcinoma is a complicated process involving inheredity , environment and gene mutation.MSI(microsatellite instability, MSI) plays an importantrole in the tumorigenesis and development of colorectalcarcinoma.MSI means repeated sequence lose or gain in DNAgenome, which is also called copy error. Up to now, there are9 mismatch repair genes: hMLH1, hMLH3, hPMS1, hPMS2,hMSH2, hMSH3, hMSH4, hMSH5 and hMSH6. Among themhMLH1 / hMSH2 are the most important mismatch repairgenes, their principal role is keeping the integrity and stabilityof genetic substance and true of duplication. If these geneswere defective which result in MSI and probably led to theinstability of genome and tumorigenesis of tumor.COX-2(cyclooxygnase-2, COX-2) is an importantisoenzyme of COX (cyclooxygenase, COX). COX –2 proteintakes part in many pathophysiological procedures, especiallyin the tumorigenesis and development of tumor. Some studiesfound that the expression of COX-2 protein was high in mostadenocarcinoma and adenoma of colon, but in some MSIcolorectal carcinoma, the expression was low, which possiblywas resulted from the promoter methylation of COX-2. At themeantime,people found that the promoter methylation ofhMLH1, hMSH2 would result in the low expression, which ledto the presence of MSI and the tumorigenesis and developmentof tumor.Investigating the presence of MSI in colorectal carcinomawith methods of molecular biology and on the basis of this,studying the relationship of COX-2(cyclooxygnase-2),hMLH1(human mut-l homologue 1)and hMSH2(human mut-shomologue 2)protein in cases of MSI with Western Blot,MSScolorectal carcinoma and adjacent normal mucosa, at themeantime,To investigate the methylation of COX-2, hMLH1and hMSH2 in MSI colorectal carcinoma and study therelationship between the paths of the promoter methylation.Methods:1 The presence of MSI in colorectal carcinoma.1.1 Material: Forty-two surgically resected colorectalcarcinoma cases and 42 adjacent normal mucosa (10 cm awayfrom the margin of carcinoma). All cases were fresh andsurgically resected, keeping in liquid nitrogen. All cases werenot treated by any medical therapy and proved by pathology.1.2 To select 5 MSI loci: BAT-25,BAT-26,D2S123,D5S346,D17S250 and detect the presence of MSI in colorectalcarcinoma with PCR comparing with adjacent normal mucosa.2 To investigate the expression of COX-2, hMLH1 and hMSH2with Western Blot in cases of MSI, MSS colorectal carcinomaand adjacent normal mucosa.3 To investigate the methylation of COX-2, hMLH1 andhMSH2 in MSI colorectal cancer and study the relationship ofthree genes in molecular level.Results:1 The presence of MSI in cases of colorectal carcinoma andadjacent normal mucosa.In 42 adjacent normal mucosa,no MSI was found. But in42 colorectal carcinoma cases, 18(42.86%) MSI cases werefound,and MSI-H 28.57% (12/42),MSI-L14.29% (6/42);MSS 57.14% (24/42).In BAT-25,BAT-26,D2S123,D5S346,D17S250 5 loci, MSI were found respectively 19.05%(8/42),16.67%(7/42),11.90% (5/42),4.76%(2/42)and 7.14% (3/42).2 The expression of COX-2, hMLH1 and hMSH2 in adjacentnormal mucosa,MSI and MSS colorectal carcinoma.2.1 In 42 colorectal carcinoma cases, the low expression rate ofCOX-2 was 30.09%(16/42),there was significantly differentfrom that in adjacent normal mucosa(P<0.05). In 18 MSIcolorectal carcinoma, the low expression rate of COX-2 was61.11%(11/18),there was significantly different from that inMSS(P<0.05).2.2 In 42 colorectal carcinoma cases, the low expression rate ofhMLH1, hMSH2 were 40.47%(17/42)and 33.33%(14/ 42 ) respectively, there was significantly differentcomparing with 42 cases of adjacent normal mucosa(P<0.05).But in 18 MSI colorectal carcinoma , the low expression rate ofhMLH1, hMSH2 were 77.78%(14/18),16.67%(3/18)respectively, there was significantly different from that in MSS(P<0.05).2.3 Analysis of the relationship between hMLH1 and COX-2,hMSH2 and COX-2.The results implied that hMLH1 and COX-2, hMSH2 andCOX-2 had completely positive correlation in colorectalcarcinoma( P<0.01).3 The promoter methylation of COX-2,hMLH1 and hMSH2 inMSI colorectal cancer.3.1 In 42 adjacent normal mucosa, no promoter methylation ofCOX-2, hMLH1 and hMSH2 was observed, as in MSScolorectal cancer. But in MSI cancer, methylation rates ofCOX-2 hMLH1 and hMSH2 were respectively 72.22%(13/18), 83.33%(15/18),27.78%(5/18).3.2 Analysis of methylation in gene promoter between hMLH1and COX-2, hMSH2 and COX-2 in MSI colorectal carcinoma.The results implied that hMLH1 and COX-2 had completelypositive correlation in MSI colorectal carcinoma( P<0.05);hMSH2 and COX-2 had no correlation in thispath( P>0.05).Conclusions:1 There were probably two paths in the tumorigenesis ofgenesis of colorectal carcinoma (MSI and MSS) That meansthere would be a type colorectal carcinoma by the path of MSI.2 In MSI colorectal carcinoma, 5 microsatellite loci(BAT-25,BAT-26, D2S123, D5S346,D17S250) were sensitive in theinvestigation of MSI.3 In tumorigenesis and development of MSI colorectalcarcinoma, there were probably low expressions of COX-2 andhMLH1 in the meantime. Suspecting the low expression ofhMLH1 was an important mechanism in MSI colorectalcarcinoma; but COX-2 had no significant effect on MSIcolorectal carcinoma as hMSH2. In MSS colorectal carcinoma,there were the high expression of COX-2, which impliedCOX-2 had important role in MSS colorectal carcinoma, butthe exact mechanism of MSS pathway needed to be studied.4 In MSI colorectal carcinoma, the low expression ofhMLH1 and COX-2 was probably related to the gene promotermethylation, which replied the gene promoter methylation wasan important mechanism; hMLH1,COX-2 had positiverelationship in molecule path and hMLH1, COX-2 probablyhad correlated target in gene pathway. But the specificmechanism was still needed be profound studied. The lowexpression of hMSH2 had no relation with the gene promotermethylation, probably was related with gene mutation.5 Treatment of colorectal carcinoma should take tumor typesinto account. COX-2 inhibitor had effect on colorectal... |
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