Protein Expression Of EGFR,Ras And Gene Mutations Of K-ras In Colorectal Carcinoma

Background and Objective:Studies have shown the association be- tween colorectal carcinogenesis and several signal transduction pathways. One of these pathways, the Ras/Mitogen Activated Protein Kinase- (MAPK) -dependent pathway is a critical signal pathway that transmiting signal from the trsnsmembrane receptor, to the nucleus via a series of intermediate genes. The upstream signal epidermal growth factor receptor (EGFR) is a transmembrane glycoprotein. It has been recognized that EGFR is widely overexpressed in various kinds of tumors, including colorectal carcinoma. K-ras oncogene, downstream signal of EGFR, is a mediator of transmiting extracellular signal to intracellular domain. In colorectal car- cinoma, K-ras gene is one of the key genes which switch on canceration, it is activated by piont mutation and the most common mutation position locate in codons 12 and 13 of 2 exon. Although most studies have demonstrated that EGFR and K-ras gene are two important factors in the genesis and progress of colorectal cancer, the exact relationship remains unclear and co-expression of these two protein has no reports. By analyzing (1)the protein expression of EGFR and Ras in the colorectal carcinoma and their relationship with clinicopathological parameters (2)the status of K-ras mutations in part of the colorectal carcinoma and the possible relationship with Ras protein expression in colorectal carcinoma. This project investigated the role of these two genes in the genesis and progress of the colorectal carcinoma from piont of proteinic and genic view respectively.Methods:115 cases of colorectal carcinoma tissues with clear path- ological diagnosis were obtained by surgical excision and 36 cases of colorectal adenoma were obtained by endoscope biopsy. Immuno- histochemistry was used to detect the protein expressions of EGFR and K-ras in carcinoma group of all the colorectal carcinoma tissues and in adjacentmucosa group of 43 patients, and also in the adenoma tissues; 70 cases colorectal carcinoma were randomly selected for mutation status analysis by PCR Direct Sequencing.These were considered with clinico- pathological parameters. SPSS16.0 statistic software was used to analyze the correlation of their abnormal expressions to colorectal carcinoma.Results:1.In carcinoma group, adenoma group and adjacent mucosa group, the positive expression rates of EGFR were 62.61%(72/115 ) , 30.56%(11/36)and 12.77%(6/47) respectively, the difference was statistic meaning among the three groups(P < 0.05); the positive rate of Ras expressions were 46.09%(53/115), 38.89%(14/36) and 10.63%(5/47) respectively, the two former groups were obviously lower than the last group (P<0.05).2.In carcinoma that infiltrate to submucosa and muscular layers, subserous layer and penetrating subserous layer, the positive expression rates of EGFR were 36.84%(7/19), 67.09%(53/79) and 70.59%(12/17) respectively,the latter two was higher than the former(P < 0.05); the expressions of EGFR had no relationship with sex, age, tumous site, differ- ention degree, lymph node metastasis and distant metastasis(P>0.05).3.In carcinoma,the positive rate of Ras protein expressions in well- moderate differentiation and poor differentiation were 59.52%(25/42) and 38.36%(28/73),there was significant difference between the two groups(P<0.05). No correlation was found expression levers of Ras protein with their clinicopathological features such as gender, age, tumous site, depth of invasion, lymph node metastasis and distant metastasis(P>0.05).4.EGFR protein expression was positive correlation with Ras protein expression in colorectal carcinoma(r=0.354,P<0.05).5.The frequency of K-ras mutations was 30%(21/70),there are 66.67%(14/21)mutations in codons 12 and 33.33%(7/21)in codons 13.The mutation position located in the second base of codons 12(8 were G→T, 4 were G→A, 2 were G→C mutation; G→T,G→A,G→C mutation rates were 38.10%,19.05%,9.52% respectively) and the first/second codons 13 (4 were G→T, 2 were G→C mutation,1 had two mutations with both G→T and G→ A; G→T,G→A,G→C mutation rates were 19.05%,4.76%,9.52% respectively).6.K-ras gene mutation was positive correlation with Ras protein expression in colorectal carcinoma(r=0.237,P<0.05).Conclusions:1.The expressions of EGFR and Ras proteins were up-regulated in colorectal carcinoma.2.The expression of EGFR protein has positive correlation to the depth of invasion.3.The expression of Ras protein has negative correlation to the cell differentiation.4.EGFR and Ras protein expressions have a close relationship, a joint test will help the accurate joint detection evaluation in the diagnosis and prognosis of colorectal carcinoma.5. In colorectal carcinoma, G→T and G→A mutations in codons 12 are the most common mutation types, mutations in codons 12 of K-ras gene may be the reason for the aberrant expression of Ras protein.